US20120279953A1

US20120279953A1 - Heated under-body warming systems

Info

Publication number: US20120279953A1
Application number: US13/422,279
Authority: US
Inventors: Scott D. Augustine; Ryan S. Augustine; Randall C. Arnold; Rudolf A. Deibel; Scott A. Entenman; Thomas F. Neils; Keith J. Leland
Original assignee: Augustine Biomedical and Design LLC
Current assignee: Augustine Temperature Management LLC; Augustine Biomedical and Design LLC
Priority date: 2011-03-16
Filing date: 2012-03-16
Publication date: 2012-11-08
Also published as: EP2685954A4; EP2685954A2; WO2012125916A2; WO2012125916A3

Abstract

A heated underbody supports including heated mattresses, heated mattress overlays and heated pads, and methods of using heated underbody supports, for therapeutic warming. The heated underbody supports include a heater assembly and a layer of compressible support material. The heater assembly includes a flexible heating element , first and second bus bars, and a temperature sensor. The flexible heating element is a conductive fabric which can be adapted to stretch into a 3-dimensional compound curve without wrinkling or folding while maintain electrical conductivity, and wherein the heating element is adapted to return to the planar shape when pressure is removed. The flexible heating element may include a fabric which is coated with a conductive or semi-conductive polymer. The heated underbody support may also include a water resistant shell which may encase the heater assembly and the compressible support material.

Description

PRIORITY

This application claims priority to U.S. Provisional Application No. 61/453,311, Heated Mattress and Heated Mattress Overlay for Therapeutic Under-Body Warming, filed Mar. 16, 2011, the disclosure of which is hereby incorporated by reference in the entirety.

BACKGROUND

There have been many attempts at making heated mattresses and heated mattress overlays for therapeutic patient warming. Therapeutic patient warming is especially important for patients during surgery. It is well known that without therapeutic intra-operative warming, most anesthetized surgical patients will become clinically hypothermic during surgery. Hypothermia has been linked to increased wound infections, increased blood loss, increased cardiac morbidity, prolonged ICU time, prolonged hospital stays, increased cost of surgery and increased death rates.
Since the early 1990s, the standard of care for surgical warming has been forced air warming blankets. Prior to that time, warm water mattresses were commonly used. The warm water mattresses went out of common use because they were relatively stiff and inflexible. The stiff water mattress negated any pressure relief that the under-laying support mattress may have provided. As a result, the combination of pressure applied to the bony prominences and the heat from the warm water mattress both reduced blood flow and accelerated metabolism, causing accelerated ischemic pressure injuries to the skin (“bed sores”). Additionally, the warmed water recirculating in the warming system could become contaminated with bacteria, which was especially important when a leak occurred. As a result, warm water mattresses are rarely used today.
Historically, electrically heated pads and blankets for the consumer market have been made with resistive wire heaters. The safety of wire-based heaters has been questionable in consumer applications. However, in the operating room environment with anesthetized patients, the possibility of hot spots caused by the wires in normal use and the failure mode of broken heater wires resulting in sparking, arcing and fires are unacceptable. Therefore, resistive wire-based heaters are rarely used in the operating room today.
Since the mid 1990s, unsuccessful attempts have been made to make effective and safe heated mattresses for operating room use using flexible, sheet-like electric resistance heaters. Sheet-like heaters have been shown to be more effective in warming patients because of the even heat production and generally they do not cause arcing and sparking when they fail.
Some existing devices employ sheet-like heaters using a polymeric fabric that has been baked at high temperature until it becomes carbonized and is thus conductive of electricity. The carbonization process makes the fabric fragile, and therefore, it must be laminated between two layers of plastic film or fiber-reinforced plastic film for stability and strength. The lamination process results in a relatively stiff, although somewhat flexible, non-stretching, non-conforming heater. In some devices, metal foil bus bars are attached to the heater material with an electrically conductive adhesive or bonding composition and are then encapsulated with polyurethane-coated nylon fabric. The result is a stiff and relatively inflexible bus bar.
In some devices incorporating sheet-like heaters, temperature sensors used for control are located directly below the uppermost surface of the mattress. There is no foam or other thermal insulation between the heater and the upper surface of the mattress or the patient. This design can cause several problems. First, the patient is laying on a relatively stiff heater without padding therebetween. Second, the heater is not stretchable and is relatively inflexible. Third, the bus bars are stiff and inflexible. Finally, the controlling temperature sensor is in thermal contact with the environment through the thin upper surface material. Environmental thermal influences, such as a cold metal pan laying on top of the sensor, can drive the heater into a significant over-temperature and unsafe condition. While having the heater material in close proximity to the patient makes sense from the heat transfer point of view, the inflexibility and non-stretchability of the heater and the potential of an over-temperature condition due to the exposed temperature control sensor make this device uncomfortable and potentially unsafe.
Other sheet-like heaters found in some existing devices use a carbon-filled electrically conductive plastic ink, printed on and laminated between two sheets of polyester film. Copper film bus bars can be “suspended” in the carbon-filled plastic and also laminated between the two sheets of polyester film. The resulting heater and bus bar assembly is relatively stiff, non-conforming and non-stretching. Because the heater is relatively stiff, a layer of foam which may be greater than 1.5 inches thick (0.25-3 inches), may be placed between the heater and the patient. This thick layer of foam may pad the patient from the stiff heater, but it also introduces a significant thermal insulation between the heater and the patient, making the mattress less effective for patient warming. Finally, the heater elements of these devices are similar to flat wires and are not sheet-like. In some of these devices, the polyester film is cut out of the large spaces between the individual heater elements in order to improve flexibility which makes it impossible to produce even heat across the surface of the pad, as it would be with any wire heater for use in a warming pad. It is hot where the wire or heater element is located and cold in between.
In other devices, the heater material is a carbon impregnated plastic film. The film may contain greater than 50% carbon by weight. The carbon-laden plastic film is relatively weak and non-elastic and therefore may be extruded or laminated onto a woven fabric for stability and to prevent tearing. Metal film or woven wire bus bars can be bonded to the conductive plastic with a conductive adhesive and then potted in a thick layer of plastic or laminated between sheets of plastic for durability and strength. Such fabric-reinforced film heaters can be relatively flexible, but are not stretchable or elastic. The bus bars are relatively stiff and inflexible and totally non-stretchable. In addition, the adhesives and laminates can crack or delaminate or otherwise fail with repeated flexing, and bus bar failures are common in flexible heaters. Such devices can additionally include a thick layer of high-loft fibrous thermal insulation placed between the heater and the upper surface of the mattress. This thermal insulation reduces the effectiveness of the mattress for patient warming.
Electrically conductive fabric made of carbon fibers has been used as heater material in therapeutic blankets. However, carbon fiber fabric has not been used for therapeutic mattresses. Carbon fiber fabric used in heating elements are stabilized by laminating it between layers of plastic film in order to keep the “slippery” fiber bundles from shifting randomly and altering the electrical conductivity and heat production. Additionally, the carbon fibers can fracture over time with repeated flexing, which also changes the electrical conductivity. Fiber fracturing can be minimized by laminating the fabric between layers of plastic film. The stiffer the resultant laminate, the more protective it is of the fibers. However, stiff heaters are not optimal when used in therapeutic heating blankets and mattresses because they can contribute to the undesirable combination of localized elevated pressure and temperature. Finally, carbon fiber fabric may heat unevenly, resulting in “hot spots.” To prevent thermal injury, the temperature of the applied heat from these devices must be accurately and tightly controlled, and if the heat production of the heater is not even, accurate control is impossible.
In summary, existing devices that incorporate electrically conductive fabric heaters are of necessity relatively stiff because of the need to laminate them between two layers of plastic film. These laminated heaters are somewhat flexible in that they can be deformed into a simple curve. However, they cannot respond to pressure applied to a point on their surfaces and deform into three dimensional compound curves resembling a half sphere without folding and wrinkling This is because these laminates do not stretch. Stretching is critical to evenly distributed, non-wrinkling 3-dimensional deformation. Finally, these heaters utilize bonding and laminating or potting of the bus bars to the heater material to make an electrical connection and avoid “hot” bus bar failures. The heaters become very inflexible and totally non-stretchable in the areas of the bus bars. Therefore, such laminated fabric heaters have limited utility for use in pressure-reducing therapeutic mattresses.
Conductive and semi-conductive films have been made into heater elements by applying the film to a relatively non-stretchable fabric. The non-stretchable fabric carrier is important because the carbon-laden plastic film is relatively weak and inelastic. The inelasticity is important to note because even if the film did not tear while stretching, it would not return to its original planar shape when the deforming pressure is removed.
Another existing device includes an inflatable air mattress with a single air chamber and a heater incorporating a resistive wire heating element stretched across its upper surface. This device may be suitable for home use, but the single air chamber design provides insufficient accommodation and is relatively mechanically unstable rendering it inappropriate for surgical table use. In addition, the heater assembly is attached to the mattress around its edges and could exhibit hammocking when deformed by the weight of a patient. Hammocking refers to the undesirable effect that occurs when the heater retains a planar form because of its stiffness or is suspended from its edges like a hammock or cot.
Clearly, there is a need for conductive fabric heaters for use in therapeutic heated mattresses that are highly flexible, stretchable in at least one direction and durable without needing lamination to stabilize or protect the heater fabric. There is also a need for bus bar construction that does not result in thick, stiff, inflexible areas along the side edges of the heater. Then, maximally effective and safe therapeutic heated mattresses need to be designed using the stretchable, durable fabric heaters.

SUMMARY

Various embodiments include flexible and conformable heated underbody supports including mattresses, mattress overlays, and pads for providing therapeutic warming to a person, such as to a patient in an operating room setting. In various embodiments, the heated underbody support is maximally flexible and conformable allowing the heated surface to deform and accommodate the person without reducing the accommodation ability of any under-laying mattress, for example.
In some embodiments, the heated underbody support includes a heater assembly and a layer of compressible material. The heater assembly may include a heating element including a sheet of conductive fabric having a top surface, a bottom surface, a first edge and an opposing second edge, a length, and a width. the conductive fabric may include threads separately and individually coated with an electrically conductive or semi-conductive material, with the coated threads of the fabric being able to slide relative to each other such that the sheet is flexible and stretchable. The heater assembly may also include a first bus bar extending along the entire first edge of the heating element and adapted to receive a supply of electrical power, a second bus bar extending along the entire second edge of the heating element, and a temperature sensor. The layer of compressible material may be adapted to conform to a person's body under pressure from a person resting upon the support and to return to an original shape when pressure is removed. It may be located beneath the heater assembly and may have a top surface and an opposing bottom surface, a length, and a width, with the length and width of the layer being approximately the same as the length and width of the heater assembly.
In some embodiments, the conductive or semi-conductive material is polypyrrole.
In some embodiments the compressible material includes a foam material and in some embodiments it includes one or more air filled chambers. In some embodiments, the heated underbody support also includes a water resistant shell encasing the heater assembly, including an upper shell and a lower shell that are sealed together along their edges to form a bonded edge, with the heater assembly attached to the shell only along one or more edges of the heater assembly. In some embodiments, the heating element has a generally planar shape when not under pressure, is adapted to stretch into a 3 dimensional compound curve without wrinkling or folding while maintaining electrical conductivity in response to pressure, and to return to the same generally planar shape when pressure is removed.
In some embodiments, the heated underbody support includes a heater assembly including a flexible heating element comprising a sheet of conductive fabric having a top surface, a bottom surface, a first edge and an opposing second edge, a length, and a width, a first bus bar extending along the first edge of the heating element and adapted to receive a supply of electrical power, a second bus bar extending along the second edge of the heating element, and a temperature sensor. The heating element may have a generally planar shape when not under pressure, and, in response to pressure, may be adapted to stretch into a 3-dimensional compound curve without wrinkling or folding while maintaining electrical conductivity, and then to return to the same generally planar shape when pressure is removed. The underbody support may further include a layer of compressible support material located beneath the heater assembly which conforms to a patient's body under pressure and returns to an original shape when pressure is removed.
In some such embodiments, the heating element includes a fabric coated with a conductive or semi-conductive material, which may be a carbon fiber or metal containing polymer or ink, or may be a polymer such as polypyrrole. In some embodiments, the heated underbody support also includes a shell including two sheets of flexible shell surrounding the heater assembly, the shell being a water resistant plastic film or fiber reinforced plastic film with the two sheets sealed together near the edges of the heater assembly. In some embodiments, the heated underbody support also includes a power supply and controller for regulating the supply of power to the first bus bar.
In some embodiments, the compressible material comprises one or more flexible air filled chambers. In some such embodiments, the compressible material is a foam material. The heater assembly may be attached to the top surface of the layer of compressible material. In some embodiments, the heated underbody support includes a water resistant shell encasing the heater assembly and having an upper shell and a lower shell that are sealed together along their edges to form a bonded edge. In some such embodiments, one or more edges of the heater assembly may be sealed into the bonded edge. In some embodiments, the heater assembly is attached to the upper layer of water resistant shell material. In some embodiments, the heater assembly is attached to the shell only along one or more edges of the heater assembly. In some embodiments, the heated underbody support also includes an electrical inlet, wherein the inlet is bonded to the upper shell and the lower shell and passes between them at the bonded edge.
In some embodiments, the heating element has a first Watt density when in a generally planar shape and a second Watt density when stretched into a 3 dimensional shape such as a compound curve, with the first Watt density being greater than the second Watt density. In some embodiments, the temperature sensor is adapted to monitor a temperature of the heating element and is located in contact with the heating element in a substantially central location upon which a patient would be placed during normal use of the support. In some embodiments, the heated underbody support also includes a power supply and a controller for regulating a supply of power to the first bus bar.
In some embodiments, the heated underbody support is a heated mattress and includes a heater assembly and a layer of compressible material which conforms to a patient's body under pressure and returns to an original shape when pressure is removed located beneath the heater assembly. The layer of compressible material may include one or more inflatable chambers positioned under the heater assembly. A flexible, water resistant cover may encase the heater assembly, the layer of compressible material and the inflatable chambers. The heater assembly may include a flexible heating element including a sheet of conductive fabric having a top surface, a bottom surface, a first edge and an opposing second edge, a length, and a width, a first bus bar extending along the first edge and adapted to receive electrical power from a power supply, a second bus bar extending along the second edge, and at least one temperature sensor. The heating element may have a generally planar shape when not under pressure, may stretch into a 3-dimensional compound curve without wrinkling or folding while maintain electrical conductivity in response to pressure, and may return to the generally planar shape when pressure is removed.
In some embodiments, the heated underbody support may also include one or more additional inflatable chambers positioned under the layer of compressible material, with each of the inflatable chambers being elongated, having a longitudinal axis and being positioned side-by-side one another with their longitudinal axes extending substantially from the first end to the second end of the support. In some embodiments, the inflatable chambers can be inflated and deflated in two groups while the support is in use, with the inflatable chambers being in alternating groups such that each inflatable chamber is in a different group from each inflatable chamber which is beside it.
In some embodiments, the heated underbody support includes a plurality of additional inflatable chambers. In some embodiments, the inflatable chambers can each be inflated and deflated independently while the support is in use. In some embodiments, the inflatable chambers can all be inflated and deflated simultaneously as a group while the support is in use. In some embodiments, the inflatable chambers can be inflated and deflated in two or more groups while the support is in use. In some embodiments, each of the chambers belongs to one of two or more groups, and the support includes separate conduits to each group with each conduit providing independent fluid communication one groups of inflatable chambers for independently introducing or removing air from that group of inflatable chambers.
In some embodiments, the heated underbody support also includes a pressure sensor for measuring an actual internal air pressure of the groups of inflatable chambers, and a controller including a comparator for comparing a desired internal air pressure for each group of inflatable chambers with the actual internal air pressure of each group inflatable chambers. The controller may be operatively connected to each of the conduits and to an air pump and may further including or be operatively associated with a pressure adjusting assembly for adjusting the actual internal pressure. The controller may be adapted to cause inflation or deflation of each group of inflatable chambers to adjust the actual internal air pressure of each of the group of inflatable chambers toward the desired internal air pressure. In some embodiments, each inflatable chamber within each group of inflatable chambers is in fluid connection with every other inflatable chamber of its own group so that air pressure changes in one inflatable chamber redistribute to all of the other inflatable chambers in the same group. In some embodiments, an interface pressure is maintained on a top surface of each group of chambers at a location which supports a patient's body during normal use, the interface pressure being below a capillary occlusion pressure threshold of 32 mm Hg. Some embodiments include methods of warming a person using any of the heated underbody supports described herein. In some embodiments, the method includes positioning the person on the heated underbody support, activating the support, and directing the support to maintain a desired temperature. The heated underbody support may include a heater assembly, a layer of compressible material located beneath the heater assembly, and a flexible water resistant shell encasing the heater assembly. The heater assembly may include a flexible heating element including a sheet of conductive fabric having a top surface, a bottom surface, a first edge and an opposing second edge, a length, and a width, a first bus bar extending along the first edge and adapted to receive a supply of electrical power, a second bus bar extending along a second edge, and a temperature sensor on or near the heating element. The heating element may have a generally planar shape when not under pressure, and may, in response to pressure from the person positioned on the support, stretch into a 3 dimensional compound curve without wrinkling or folding while maintain electrical conductivity.

BRIEF DESCRIPTION OF THE DRAWINGS

The following drawings are illustrative of particular embodiments and therefore do not limit the scope of the invention. The drawings are not to scale (unless so stated) and are intended for use in conjunction with the explanations in the following detailed description. Various embodiments will hereinafter be described in conjunction with the appended drawings, wherein like numerals denote like elements.

FIG. 1 is a cross sectional view of a heater assembly undergoing deformation in accordance with some embodiments.

FIG. 2 is a cross sectional view of a heater assembly in accordance with some embodiments.

FIG. 3 is an illustration of a heater assembly in accordance with some embodiments.

FIG. 4 is an illustration of a power connection portion of a heater assembly in accordance with some embodiments.

FIG. 5 is an illustration of a heater assembly in accordance with some embodiments.

FIG. 6 is a cross sectional view of a heated mattress overlay or pad in accordance with some embodiments.

FIG. 7 is a cross sectional view of a heated mattress overlay or pad in accordance with some embodiments.

FIG. 8 is a cross sectional view of a heated mattress overlay or pad in accordance with some embodiments.

FIG. 9 is an illustration of a heated mattress overlay or pad in accordance with some embodiments.

FIG. 10 is a cross sectional view of a heated mattress overlay or pad in accordance with some embodiments.

FIG. 11 is a cross sectional view of a heated mattress overlay or pad in accordance with some embodiments.

FIG. 12 is a cross sectional view of a heated mattress overlay or pad in accordance with some embodiments.

FIG. 13 is a cross sectional view of a heated mattress overlay or pad with partial thickness cuts or channels in the foam layer in accordance with some embodiments.

FIG. 14 is an illustration of a heated mattress overlay or pad with a segmented foam layer in accordance with some embodiments.

FIG. 15 is a cross sectional view of a heated mattress overlay or pad with a contoured foam layer in accordance with some embodiments.

FIG. 16 is an illustration of a heated mattress overlay or pad with a foam ring by the temperature sensor assembly in accordance with some embodiments.

FIG. 17 is a cross sectional view of a heated mattress overlay or pad with a foam ring surrounding the temperature sensor assembly in accordance with some embodiments.

FIG. 18 is a cross sectional view of a heated mattress overlay or pad with a foam ring surrounding the temperature sensor assembly in accordance with some embodiments.

FIG. 19 is a flow diagram showing the operation of a heater assembly in accordance with some embodiments.

FIG. 20 is a cross sectional view of a heated mattress overlay or pad with a thin foam layer located above the heater element assembly in accordance some embodiments.

FIG. 21 is an illustration of a heated mattress overlay or pad with a thin upper foam layer with a plurality of apertures in accordance some embodiments.

FIG. 22 is a cross sectional view of a heated mattress overlay or pad with a power entry assembly located in the peripheral bond between the shell layers in accordance some embodiments.

FIG. 23 is an illustration of a heated mattress overlay or pad with attachment tabs in accordance with some embodiments.

FIG. 24 is an illustration of a strap and a heated mattress overlay or pad with attachment tabs in accordance some embodiments.

FIG. 25 is a cross sectional view of a heated mattress including a visco-elastic foam layer in accordance with some embodiments.

FIG. 26 is a cross sectional view of a heated mattress including an inflatable chamber in accordance with some embodiments.

FIG. 27 is a cross sectional view of a heated mattress including plurality of inflatable chambers in accordance with some embodiments.

FIG. 28 is a cross sectional view of a heated mattress including a plurality of inflatable chambers in accordance with some embodiments.

FIG. 29 is a schematic diagram of a console in accordance with some embodiments.

DETAILED DESCRIPTION

The following detailed description is exemplary in nature and is not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the following description provides practical illustrations for implementing various exemplary embodiments. Examples of constructions, materials, dimensions, and manufacturing processes are provided for selected elements, and all other elements employ that which is known to those of skill in the field. Those skilled in the art will recognize that many of the examples provided have suitable alternatives that can be utilized.
Embodiments include heated underbody supports which include heated mattresses, heated mattress overlays, and heated pads. The term underbody support may be considered to encompass any surface situated below and in contact with a user in a generally recumbent position, such as a patient who may be undergoing surgery, including heated mattresses, heated mattress overlays and heated pads. Heated mattress overlay embodiments may be identical to heated pad embodiments, with the only difference being whether or not they are used on top of a mattress. Furthermore, the difference between heated pad embodiments and heated mattress embodiments may be the amount of support and accommodation they provide, and some pads may be insufficiently supportive to be used alone like a mattress. As such, the various aspects which are described herein apply to mattresses, mattress overlay and pad embodiments, even if only one type of support is shown in the specific example.
Various embodiments improve patient warming effectiveness by increasing accommodation of the patient into the heated mattress, mattress overlay, or pad, in other words, by increasing the contact area between the patient's skin and the heated surface of the mattress or mattress overlay. The heating element, and the foam or air bladders of the mattress, which may also be included, are easily deformable to allow the patient to sink into the mattress, mattress overlay, or pad. This accommodation increases the area of the patient's skin surface in contact with the heated mattress, mattress overlay, or pad and minimizes the pressure applied to the patient at any given point. It also increases the surface contact area for heat transfer and maximizes blood flow to the skin in contact with the heat for optimal heat transfer. The accommodation of the patient into the mattress, mattress overlay, or pad is not hindered by a stiff, non-conforming, non-stretching, hammocking heater. Additionally, in various embodiments, the heating element is at or near the top surface of the underbody support, in thermally conductive contact with the patient's skin, not located beneath thick layers of foam or fibrous insulation.
Various embodiments further provide improved safety. For example, some embodiments provide a heating element that does not produce or reduces “pressure points” against the patient's body, such as against bony prominences, which can occur when a heater is stiff. In addition, various embodiments can reduce or prevent thermal “grounding” of the temperature control sensor. Various embodiments can provide an automatic reduction in Watt density in areas of maximum loading and deformation that correspond to areas of maximum pressure. In some embodiments, if the heater assembly eventually fails, it fails “cool” (stops heating) rather than failing “hot” and risking an injury or fire.
In certain embodiments, the heater assembly includes a heating element made of a conductive material. The conductive material may be stretchable in at least one direction or, alternatively, in at least two directions. One way to create a stretchable fabric heating element is to coat a conductive material onto individual threads or fibers of a carrier fabric which may be a non-conductive material. The threads or fibers may be woven or knitted, for example, into a stretchable fabric. Other examples of conductive fabrics which may be employed include, without limitation, carbon fiber fabrics, fabrics made from carbonized fibers, and woven or non-woven substrates coated with a conductive material, for example, polypyrrole, carbonized ink, or metalized ink.
The conductive material may be applied to the fibers or threads before they are woven or knit into a fabric. In this way, the coated threads can move and slide relative to each other as the fabric is stretched, and can return to their original orientation when the stretching is stopped such that the fabric can return to its original shape. Alternatively, the conductive materials that coat the individual fibers in the fabric may be applied after the fabric is woven or knit using a dipping, spraying, coating or polymerization process or combinations thereof. A conductive polymer can be selected that coats to the individual threads without bonding them together such that the threads remain able to slide relative to each other.
Types of materials which may be used for the fabric base include natural and synthetic materials such as polyurethane-polyurea copolymer (for example spandex or Lycra made by INVISTA, Wichita, Kans., polyester, polyamide, (for example Nylon) or combinations thereof. The material may be elastic in nature such that the threads or fibers can stretch and then return to their original size or length. Alternatively or additionally, stretch and elasticity may be provided by the manner in which the threads or fibers are knit or woven, such as by forming a twill weave. Alternatively or additionally, stretch and elasticity may be provided by the manner in which fibers or groups of fibers are twisted or combined prior to being knit or woven into fabric. Alternatively, or additionally, the stretch and elasticity may be provided by the structure introduced to the fabric through shaping of the physical structure or shape of the fabric such as by embossing, creping or other mechanical means. Alternatively or additionally stretch and elasticity may be provided by the use of stretchable polymer or fibers in a nonwoven fabric.
The conductive coating may be applied to the individual fibers or threads before or after forming a fabric by spraying, coating or dipping, for example. Various conductive materials may be used. Examples include conductive and semi-conductive polymers include polypyrrole, polyaniline and polyacetylene.
In some embodiments, in contrast to non-stretchable conductive film heaters, where a carbon (or other conductive material) impregnated plastic film is extruded onto or bonded onto a base layer such as a fabric base layer, the heating element material may have a conductive or semi-conductive material coated onto the individual threads or fibers of the carrier fabric. This maintains the natural flexibility and stretch-ability of the fabric rather than turning the fabric into a non-stretchable fiber reinforced film.
The conductive or semi-conductive coating may comprise a polymer that is bound as a layer surrounding the individual threads or fibers by a process of polymerization. Polymerization results in a very secure bond. Embodiments of the flexible coating on each individual thread or fiber may not crack, fracture or delaminate during flexion. Polymerization of these conductive or semi-conductive materials onto individual fibers of the carrier fabric is one example of a process for producing a durable, flexible and stretchable heater assembly according to various embodiments. Semi-conductive polymer coatings such as polypyrrole are useful in various embodiments, however, other coating processes are anticipated and conductive coatings that use carbon or metal as the conductive material are also anticipated.
The electrically conductive or semi-conductive fabric heater materials used in heating elements may be highly flexible and durable such that neither the carrier fiber nor the semi-conductive polymer coating will fracture with repeated flexing, loading and stretching. Additionally, the conductive or semi-conductive fabric heating element does not require lamination between layers of plastic film for protection or stabilization, though it may be laminated if desired.
The conductive fabric heating element material may be highly flexible and conformable, allowing the heated surface to comfortably deform and accommodate the patient. To accomplish this, the heater assembly has a flexible, electrically conductive fabric heating element that may be made of woven or knit fabric that can stretch in at least one direction. The fabric heating element may be durable without requiring lamination between plastic film sheets for stabilization and protection, though in some embodiments the heating element may be laminated. In some embodiments, the flexible and conformable fabric heating element can be included in a mattress overlay and can be positioned directly against the plastic film of the upper surface of a mattress with which it is used without requiring a foam pad there between, or alternatively a foam pad may be included beneath the heating element. Furthermore, with no foam or thermal insulation layer between the heating element and the patient, heat transfer from the heating element to the patient is maximized.
The heating element comprises a flexible flat sheet of the conductive material. In some embodiments, it is rectangular having opposing first and second edges and opposing third and fourth edges extending from the first to second ends, a first planar surface and an opposing bottom planar surface. According to some embodiments, the heating element also includes closely spaced conductive elements such that the heating element has a substantially uniform Watt density output, in some embodiments less than approximately 0.5 watts/sq. inch, such as between approximately 0.1 and approximately 0.4 watts/sq. inch, of one or both surfaces, across a portion of or the entirety of the surface including and extending to the edges of the heating element. The closely spaced elements can be conductive threads woven into the fabric or conductive materials such as conductive ink applied to the fabric.
According to an exemplary embodiment, a conductive fabric comprising the heating element comprises woven polyester fibers individually coated with polypyrrole (available from Eeonyx Inc., Pinole, Calif.). The coated fabric may have an average resistance, for example, determined with a four point probe measurement, of approximately 15-20 ohms per square at about 48 volts, which is suitable to produce a Watt density of approximately 0.1 to approximately 0.4 watts/sq. in. for the surface of the heating element, when the heating element has a width between the bus bars in the neighborhood of about 16-28 inches, though wider and narrower heater element widths are also contemplated. Such widths are suitable for a mattress, mattress overlay, or pad heating assembly, some embodiments of which will be described below. The resistance of such a conductive fabric may be tailored for different widths between bus bars (with wider requiring a lower resistance and narrower requiring a higher resistance) by increasing or decreasing a surface area of the fabric that can receive the conductive coating, for example, by increasing or decreasing the basis weight of the fabric. Resistances over surface areas of conductive fabrics such as these may vary, for example, due to variation in a thickness of a conductive coating, variation within the conductive coating itself, variation in effective surface area of the substrate which is available to receive the conductive coating, or variation in the density of the substrate itself. Local surface resistance across a heating element is directly related to heat generation according to the following relationship: Q (Joules)=I²(Amps)×R(Ohms). Variability in resistance thus translates into variability in heat generation, which is measured as a temperature. Precise temperature control can be maintained in embodiments which are employed to warm patients undergoing surgery, for example.
The stretchable fabric heating element is able to deform in response to a focal pressure applied to the surface of the heater fabric, into a smooth 3-dimensional compound curve without wrinkling or folding. A smooth compound curve cannot be formed out of non-stretchable fabrics or films. The stretchable fabric heating element may also exhibit elastic properties that allow it to revert to its original planar shape when the deforming pressure is relieved. The fabric heating element can be provided with appropriate tensile properties such that the amount of stretch, or strain, required to prevent hammocking and allow accommodation of the patient into the heated mattress or mattress overlay does not result in stresses that exceed the elastic limit of the material. In some embodiments, for example, an increase in the width of a 20 inch wide mattress or mattress overlay of approximately one inch during stretching achieves the desired goals without exceeding the elastic limit of the stretchable fabric heating element or introducing permanent plastic deformation.
An example of a heater assembly 1 including a stretchable fabric heating element 10 is shown in FIG. 1, which depicts a cross section of a portion of the heater assembly 1. This example includes a heating element 10, a compressible material layer 20 beneath the heating element 10 and bonded to the heating element 10 by a layer of adhesive 30. The heater assembly 1 also includes an upper shell 40 and a lower shell 42. The heater assembly 1 curves smoothly under pressure from a patient's body (not shown) to stretch into an area of compound curve deformation 22.
In the embodiment shown in FIG. 1 and in several other embodiments, a foam layer 20 is included beneath the heating elements 10. However, the compressible material layer 20 may alternatively be described as a layer of foam in each of these embodiments but is not limited to foam. For example, the layer of compressible material may comprise gel, stuffing material such as polyester, polyester pellets, bean bag material such as polystyrene beads, air filled compartment, or any material that provides a flexible layer for patient accommodation.
Heat transfer is maximized when the heating element 10 is in conductive thermal contact with the patient. However, in some embodiments, at least one layer of plastic film is interposed between the heating element 10 and the patient to protect the heating element 10. One or more layers of thin plastic film may form an upper shell 40 between the heating element 10 and the patient to introduce minimal thermal resistance to heat flow. In certain embodiments the fabric heating element 10 may be laminated between two layers of thin (such as less than 0.003 inches) plastic films (e.g. urethane or polyvinyl chloride) that may also be stretchy. Laminating a thin layer of plastic film directly onto each side of the heating element 10 protects the heating element fabric from damage by liquids and oxidation. Thin layers of plastic film are sufficient to protect the heating element 10 from liquid and gases, add minimal if any stiffness to the construction, and still allow the heating element 10 to stretch and return to its original shape. This is in contrast to some other conductive fabrics which require lamination between two thick layers of plastic film in order to provide structural strength and durability, resulting in a stiff and non-stretchable heater.
The heating element 10 can stretch in at least one dimension and in some embodiments in two dimensions, such that it can easily deform from a flat planar surface to a half sphere type of formation when loaded with the weight of a patient, particularly of a bony prominence. Since the heat output of the heating element 10 is constant, the heat output per area (Watt density) will decrease as an area of the heating element material is stretched, for example, from a planar shape such as a circle into a three dimensional shape such as a half sphere, by the weight of the patient's body or body part. For example, the area of a circle is πr², while the area of a half sphere is 2πr²and is therefore double. Therefore, in some embodiments the Watt density of the heater is naturally and automatically reduced by up to approximately half in the load-bearing areas as the heater material stretches from the two dimensional shape such as a circle into a three dimensional shape such as substantially a half sphere. This reduction in Watt density due to the increase in surface area caused by stretching results in an automatic, inherent decrease in temperature of the heating element under the points of increased pressure.
The pressure relief provided by the underbody support is maintained by allowing maximal accommodation (allowing the patient to sink into the support) without the heater creating a “hammocking” force. By allowing maximal accommodation and avoiding hammocking, cutaneous blood flow is maximized at the pressure points which minimizes the risk of pressure ulcers. The pressure needed to collapse capillaries is said to be 32 mm Hg. By allowing maximal accommodation and avoiding hammocking, cutaneous blood flow is generally maximized. By maximizing blood flow, the ability of the skin and tissue to absorb heat from the heating element and transfer it to the rest of the body is also maximized. Further, by allowing the patient to sink into the underbody support (accommodation), the surface area of the heating element 10 in contact with the patient is maximized and thus heat transfer is maximized.
Mattresses used in the operating room typically have a useful life span of 5-15 years. Flexible, conductive fabric heaters may be expected to fail in less than 10 years. In prior art heaters, the failure is usually at the bus bar/fabric heater connection, and will usually result in a “hot spot” which can cause burning of the patient. For example, carbon and metal based conductive fabrics and films retain relative stability of their conductivity over time and it is therefore hot failure may occur.
Some materials such as semi-conductive materials used to create conductive fabric heating elements in certain embodiments, such as polypyrrole, slowly lose their electrical conductivity over time. Oxidation of the semi-conductive material can cause the electrical resistance of the heating element to increase in some instances, such as by approximately 10% per year during normal use. Therefore, in some embodiments, the controller is electrically connected to the heating element and bus bars such that it can measure resistance. In some embodiments, the controller a regulates the power supply to the heating element and can be programmed to check the total resistance of the heating element 10 periodically, such as before each use. If the resistance of the heating element 10 eventually increases over time to a predetermined level set as a cut off point, an alarm may be triggered and the controller may cease to energize the heating element 10. This safety feature allows the heated underbody support to fail safely, or “cold,” without hot spots, and therefore without risking burning the patient, before a mechanical failure. Such a safe failure is in contrast to a bus bar delamination, for example, which can cause an unsafe, or “hot,” failure.
Other types of failures may occur over time in heater assemblies including flexible, conductive fabric heating elements 10 and some embodiments can plan for such failures to mitigate or eliminate any associated risk. For example, failures may occur at the bus bar/heating element 10 connection, or alternatively may result from a failure of the heating element material itself, such as a tear or fractured fibers or threads or thread coating. In any of these examples, the failure could result in a “hot spot,” or localized area running at a temperature greater than intended. Therefore, a heated mattress or mattress overlay that utilizes a heating element 10 comprising a conductive material that is electrically stable and does not loose electrical conductivity over time may be kept in service until it experiences a mechanical failure that results in a “hot spot” that could injure a patient. This eventual failure can be prevented through planned obsolescence. To prevent hot failures, certain embodiments include planned obsolescence, achieved by the gradual degradation of the electrical conductivity of the heater element and monitoring of resistance as described above. This safety feature results in a cold failure with no potential for patient injury, before any hot failures are likely to occur. This planned obsolescence is therefore a safety feature in that the mattress fails cold, before a mechanical failure, such as a bus bar delamination, could cause a hot failure. The resistance cut off point may be set by the manufacturer, for example, as being a resistance level that the conductive fabric is expected to reach prior to mechanical failure during normal use. For example, the resistance cut off may be between about 125 percent and about 300 percent of the original resistance value, such as when the support was new or when the support was first used. Alternatively, the resistance cut off value may be the resistance at which the support will produce less than a certain number of Watts per square inch of heated space, such as less than between about 0.04 and about 0.15 Watts per square inch. Planned obsolescence is therefore a useful safety feature because it results in cold failure and no patient injury.
In certain embodiments, the conductive or semi-conductive fabric heating element 10 is made into a heater assembly 1 by attaching two electrical conductors, or bus bars, along opposing ends of the fabric heating element 10. The bus bars of some embodiments may be attached to the heating element material by sewing with electrically conductive thread. This construction maintains flexibility and durability with repeated flexing. The sewn connection between the bus bar and the heating element fabric according to embodiments results in a connection that is very robust, flexible and tolerant of extreme flexing and resistant to degradation.
According to some embodiments, the bus bars are coupled to the heater by a stitched coupling, for example, formed with electrically conductive thread such as silver-coated polyester or nylon thread (Marktek Inc., Chesterfield, Mo.), extending through the conductive fabric material and through the bus bars. Alternative threads or yarns employed by some embodiments may be made of other polymeric or natural fibers coated with other electrically conductive materials. In addition, nickel, gold, platinum and various conductive polymers can be used to make conductive threads. Metal threads such as stainless steel, copper or nickel could also be used for this application. According to an exemplary embodiment, the bus bars are comprised of flattened tubes of braided wires; for example, a flat braided silver coated copper wire, and may thus accommodate the attaching thread extending there through, passing through openings between the braided wires thereof. In addition, such bus bars are flexible, thereby enhancing the flexibility of the mattress heater assembly. According to alternate embodiments, the bus bars can be a conductive foil or wire, flattened braided wires not formed in tubes, an embroidery of conductive thread, a printing of conductive ink, or other suitable bus bar construction. The bus bars may comprise a flat braided silver-coated copper wire material, since a silver coating has shown superior durability with repeated flexion, and is less susceptible to oxidative interaction with a polypyrrole coating of the heating element 10. Additionally, an oxidative potential due to dissimilar metals in contact with one another is reduced if a silver-coated thread is used for the stitched coupling of a silver-coated bus bar.
According to some embodiments, two or more rows of stitches are applied to each bus bar for added safety and stability of the bus bar/heating element 10 interface. Two rows of stitches may be used and may be oriented in a pattern such as a “zigzag” pattern so that each row of stitches captures or extends back and forth across each longitudinal edge of the bus bar and onto the heating element, along the length of the bus bar where it abuts the heating element. A zigzag pattern of relatively closely positioned stitches stabilizes the flexible fabric heating element 10 and holds it in close opposition to the bus bar so that the fabric heating element cannot physically pull away from the bus bar during flexing. According to some additional embodiments, a ribbon of highly conductive material is interposed between the bus bar and the fabric heater element. For example, a ribbon or strip of cloth that has been coated with a conductive metal such as silver may be used. The cloth ribbon may be soft, flexible and fibrous or bristly and, therefore, the fibers or bristles may integrate themselves into the spaces within the materials of the bus bars and/or of the fabric heater element. Other embodiments comprising options for improving the electrical connection between the bus bar and the fabric heating element 10 include a layer of highly conductive paint or ink, selectively applied to the conductive fabric of the heating element 10 and to which the bus bar is attached rather than the bus bar being attached directly to the conductive fabric of the heating element 10.
FIG. 2 depicts a side view of a heater assembly 1 and a stitched bus bar construction according to some embodiments. It includes a heating element 10, a first bus bar 62 at a first end 12 of the heating element 10 and a second bus bar 64 at a second end 14 of the heating element 10. A first insulating member 72 is located between first end 12 and first bus bar 62 and a second insulating member 74 is located between second end 14 and second bus bar 64. Conductive thread 80 connects the heating element 10 to the bus bars 62, 64 through the insulating members 72, 74. In this way, the electrical contact points between the bus bars 62, 64 and the heating element 10 may be solely defined by the conductive thread 80 of the stitched couplings.
Insulating members 72, 74 may be fiberglass material strips having an optional polytetrafluoroethylene (PTFE) coating and a thickness of approximately 0.003 inch, for example. Alternatively, electrically insulating members 72, 74 could be comprised of a polymeric film, a polymeric film reinforced with a fibrous material, a cellulose material, a glass fibrous material, rubber sheeting, polymeric or rubber-coated fabric or woven materials or any other suitable electrically insulating material.
The use of conductive thread stitches 80 of the coupling maintains a stable and constant contact with the bus bar 62, 64 on one side and the heating element 10 on the other side of the insulator 72, 74. Specifically, the stitches can produce a stable contact in the face of any degree of flexion, so that the potential problem of intermittent contact between the bus bar 62, 64 and the heating element 10 (that could arise in embodiments where the bus bar relies upon direct physical contact between the surface of the bus bar with the surface of the heating element) can be avoided. The stitching 80 comprises the electrical connection between the bus bar 62, 64 and the heating element 10, and by using a conductive thread that has a lower electrical resistance than the conductive fabric of the heating element 10, the thread does not generate significant heat under normal conditions. In addition to the heated mattress, mattress overlay, and pad applications described herein, such a design for providing for a uniform and stable conductive interface between a bus bar and a conductive fabric material can be used to improve the conductive interface between a bus bar or an electrode and a conductive fabric in non-flexible heaters, in electronic shielding, in radar shielding, in mats for pressure measuring and mapping and in other applications of conductive fabrics.
Due to the flexible nature of the heating element 10 in certain embodiments of the heater assembly 1, the thread of a stitched coupling between the heating element 10 and the bus bar may 62, 64 undergo stresses that, over time and with multiple uses of an underbody support containing the heater assembly 1, could lead to one or more fractures along the length of the stitching 80. Such a fracture could also result in intermittent contact at points between the bus bar 62, 64 and the heating element 10, which could lead to a thermal melt down of the element 10 along the bus bar 62, 64. But, if such a fracture were to occur with an insulating member 72, 74 positioned between the bus bar 62, 64 and the heating element 10, the insulating member 72, 74 may prevent a meltdown of the heating element 10, so that only the very small area of the heating element material directly in contact with the conductive thread of the stitching 80 melts along the bus bar 62, 64 with a very small spot of excessive heat insufficient to cause an injury to a patient. The “hot area” is limited to an area approximately 2-4 mm in diameter at any time. The “hot area” may move down the bus bar 62, 64 as the heating element fails but at any given time the “hot area” is limited to a very small area.
In some embodiments, the stitched coupling between the bus bar 62, 64 and the heating element 10 comprises two or more rows of stitches 80 for redundancy and stability. In other embodiments, a single row may be used. The stitching 80 may extend along substantially the entire end 12, 14 of the heating element 10.
An aerial view of an embodiment of a heater assembly 1 is shown in FIG. 3, in which the bus bars 62, 64 extend past the ends 16, 18 of the heating element 10. If the ends of bus bars 62, 64 do not extend at least to the ends 16, 18 of the heating element 10, increased current can flow from the ends of the bus bars and into the heating element. In rectangular heater assemblies 1, the current flows approximately perpendicularly between the bus bars 62, 64, therefore, each point on one of the bus bars 62, 64 in effect supplies a narrow line of current to the other of the bus bars 62, 64. If either bus bar terminates before reaching the end of the heating element, excessive current can flow out the end of that bus bar. The excess current flow at that point can result in excessive heating of the heating element adjacent the end of that bus bar, which can cause a hot spot and degradation of the fabric leading to a failure of the heating element. To avoid such a failure and to improve manufacturing reliability, by avoiding the inadvertent manufacturing error of the bus bar not extending to the ends of the heating element 10, both ends of the bus bars 62, 64 are extended beyond the ends 16, 18 of the heating element 10, such as by a length of at least approximately 0.060″. In certain embodiments, the conductive thread stitches 80, previously described, also extend past the ends 16, 18 of the heating element 10, being terminated on the bus bar extensions 66. This design advantageously creates an easy manufacturing process, which assures a dependable and repeatedly manufacturable bus bar termination that avoids the creation of hot spots at the ends of the bus bars 62, 64.
In some embodiments, the power connection between the power source and the heater is located at a portion of the bus bar 62, 64 that is not touching the fabric heating element 10. For example, in some embodiments, the bus bars 62, 64 extend beyond the end of the heating element 10, such as by about 1 to 2 inches, and the power lead is soldered to the bus bar extension 66 such that it is spaced away from and is not physically touching the heating element 10. Such a location of the solder joint of this power connection may make the connection less susceptible to stress and breaking Other ways of connecting the power lead to the bus bar extension 66 include, but are not limited to, crimping, weaving, or riveting.
Power lead electrical connections according to some embodiments are made a short distance off of the heating element 10 in order to improve bus bar 62, 64 durability and avoid creating uncomfortable lumps. Also, the use of solder connections and rivets are avoided in some embodiments. A close-up view of a power connection portion of a heater assembly is shown in FIG. 4. A short length of conductive material, such as a short power connection “tail” 90 of woven wire bus bar material, is partially inserted inside an inner lumen of the flattened tube of a woven wire bus bar 60 and sewn to the bus bar 60 and the heating element 10 when the bus bar 60 is stitched (not shown) to the heating element 10. This stitched mechanical connection between the tail 90 and the bus bar 60 retains full flexibility of the woven bus bar 60 because there is no solder. The power connection to the bus bar 60 can then be made by soldering the power lead 100 to the other end of the tail 90 that is not physically touching the heating element 10. Other means of connecting the power lead to the bus bar extension include, but are not limited to, crimping, weaving, or riveting. A layer of electrical insulation 92 may be placed over the soldered connection in case the bus bar or connected power wire fails at the edge of the solder joint with repeated flexing. The insulation may be tubular in order to surround the wires and connection. The insulation prevents the broken wire end from contacting the heating element, causing a short and localized melting of the heating element.
In embodiments that do not include a laminated or otherwise dimensionally stabilized fabric heating element 10, sewing the bus bars 62, 64 to the heating element 10 can be difficult. For example, the fabric heating element 10 may stretch or shift on the bias during sewing. Because of this, some embodiments include bonding a ribbon, or strip of woven or non-woven fabric, such as a strip about 0.5-2.0 inches wide, or other dimensionally stabilizing woven fabric, film, or fiber reinforced plastic film, to the fabric heating element 10 where the bus bars 62, 64 are to be attached. The strip may be bound to the heating element 10 along ends 12, 14 using an adhesive, for example. These strips of less stretchable or non-stretchable fabric or film provide dimensional stability to the heating element material and prevent stretching during the attachment of the bus bars 62, 64. In certain embodiments where the bus bars 62, 64 are located at or near the edges of the fabric heating element 10, the dimensionally stabilizing ribbons or strips are bonded to the heating element 10 at or near its ends 12, 14. In embodiments where electrically conductive stitching is used to electrically couple the bus bar 62, 64 and the heating element 10, the stabilizing material may be electrically insulating and serve the dual purpose of stabilizing the heating element 10 during assembly and acting as an electrically insulating member 72, 74 between the bus bar 62, 64 and the heating element 10.
A uniform Watt density output across the surfaces of some embodiments of the heating element 10 translates into generally uniform heating of the surfaces, but not necessarily a uniform temperature. At locations of a heating element 10 that are in conductive contact with a mass acting as a heat sink, for example a body, the heat is efficiently drawn away from the heating element and into the body. At those locations where a heating element 10 does not come into conductive contact with the body, for example the peripheral portions, an insulating air gap exists between the body and those portions, so that the heat is not drawn off those portions as rapidly. Therefore, those portions of the heating element 10 not in conductive contact with the body will rise in temperature, since heat is not transferred as efficiently from these non-contacting portions as from those in conductive contact with the body. The non-contacting portions of the heating element will reach a higher equilibrium temperature than that of the contacting portions of the heating element. This new equilibrium temperature will be reached when the radiant and convective heat losses equal the constant heat production of the heating element. Under the laws of thermodynamics it can be understood that as long as there is uniform heat production, even at the higher temperature, the radiant and convective heat transfer from non-contact areas of an underbody support of this construction will result in an equivalent or lower heat flux to the skin than the conductive heat flux at the contacting portions operating at the lower temperature. Even though the temperature at non-contacting portions is higher, the Watt density is uniform and, since the radiant and convective heat transfer is less efficient than conductive heat transfer, the non-contacting portions have an equivalent or lower heat flux to the skin. Therefore, by controlling the contacting portions of the heated underbody support to maintain a safe temperature, for example, via a temperature sensor proximate the heating element 10 in a location where the element will be in conductive contact with the body, the non-contacting portions, for example the lateral portions, will also be operating at a safe (although higher) temperature because of the less efficient radiant and convective heat transfer. The higher temperatures in the non-contacting portions also result in more effective radiant and convective heat transfer compared to a lower temperature. According to some embodiments, the heating element 10 comprises a conductive fabric having a relatively small thermal mass such that when a portion of the heating element 10 that is operating at a first higher temperature is touched, suddenly converting a non-contacting portion into a contacting portion, that portion will cool almost instantly to a second lower operating temperature.
Various embodiments include heated mattresses, mattress overlays, and pads that automatically optimize both the safety and efficacy of the warming in multiple zones across the surface of the mattress, mattress overlay, or pad. The zones are differentiated by whether the mattress or mattress overlay is directly contacting the patient or is substantially not contacting the patient. In general, the central portion of the mattress or mattress overlay will be contacting the patient and the lateral edge portions will predominately not be contacting the patient. Therefore, the central region will transfer heat to the patient conductively and the lateral regions will transfer heat to the patient via radiation and natural convection. The location of the central contact zone is predictable because the patient is anesthetized and therefore, is not spontaneously moving or rolling in bed.
FIG. 5 is an aerial view of a heater assembly 1 for use in a heated underbody support according to some embodiments. As shown in FIG. 5, the heating element 10 may have a substantially uniform Watt density across its surface. This may be accomplished with a conductive fabric heater material. The central zone and the adjacent peripheral zones of the heating element 10 are powered by the same controller. The temperature sensor assembly 110 which inputs to the controller is attached to the heating element 10 in a location which is predicted to be in direct conductive contact with the patient's body when the patient is positioned on the support—the central zone. Once the patient is in position on the support, the area of contact between the patient defines a contact portion while the remaining area is the non-contact portion of the support. The central zone is therefore the portion of the heating element upon which a patient is positioned during normal use and is an estimate of where at least the contact portion is most likely to be. Locating the temperature sensor assembly in the central zone can be used to optimize the safety and efficacy of the warming mattress or mattress overlay. During use, in the central zone 10 where the temperature sensor assembly 110 is attached to the heating element 10, the top surface of the heated underbody support is in contact with the patient for effective conductive heat transfer. For safety reasons, the temperature of the heating element 10 in the conductive zone or contact portion may be controlled to temperatures no greater than between about 38 and about 41° C., for example. In the areas of contact between the patient and the mattress or mattress overlay, the patient's body can act as a heat sink and draw heat from the heating element 10. If the temperature sensor assembly 110 in that region senses the temperature of the support decreasing, it provides an input to the controller, and the controller responds by increasing the electrical power to the entire heating element 10. The temperature of the central zone of the heating element 10 may eventually reach—but not exceed—the set point. This assures optimal heat transfer as well as optimal safety in the contact portion which is the conductive heat transfer region.
In the adjacent peripheral zones, where the heated underbody support is typically substantially not contacting the patient, the added electrical power to the whole heating element 10 results in an increased heating element 10 temperature, which may be greater than the set point or desired temperature as directed by a user. This occurs because there is no heat sink in contact with the heating element 10 to remove the heat. The non-contact portion will be warmer than the contacting portion. The increased temperature in the non-contact portion results in more effective radiant heat transfer in the non-contact portion than if this phenomenon had not occurred. However, since radiant heat transfer is less efficient than conductive heat transfer, despite the higher temperature, the radiant heat is still safe.
For example, the central zone is located substantially in the central area of the support, extending along the longitudinal midline of the support and measuring about 12 inches wide and about 36 inches long. The peripheral zone is in general, the 4-6 inch wide strip of heater running longitudinally along each side edge of the support.
Additionally, the conductive fabric heating elements 10 may have a low thermal mass. Therefore, if the peripheral portion of the heated underbody support that is operating at the higher temperature is touched, suddenly converting a non-contact zone into a contact zone, that part of the heating element 10 quickly cools to the safe operating temperature of the conductive central zone. The non-contact peripheral zones 14 of a heated underbody support may momentarily feel warm when contacted, but will quickly cool to the lower temperature of the contact zone without transferring sufficient thermal energy to injure the patient. Thermal mass, or heat storing capacity, is commonly defined as the product of the mass and the specific heat of a material. Materials with a low specific heat, a low density, or a combination thereof, will exhibit a low thermal mass. For example, a polymer such as polyurethane, with a density of 1100 kg/m³and a specific heat of 1.7 kiloJoules (kJ) per kilogram-degree Kelvin has a volumetric heat capacity of 1870 kJ/m³−° K, and foam can have a heat capacity of 20-200 kJ/m³−° K. A thin layer of polyurethane film covering a fabric heating element and a foam layer has significantly lower thermal mass than a water mattress, for example, given the volumetric heat of water of 4180 kJ/m³−° K. The thermal mass of a heated underbody support can therefore be reduced by using components that exhibit a low density and/or specific heat. In addition, reducing the thickness, or total volume of materials used in the shell, for example, will reduce the thermal mass of the heated underbody support. Various embodiments may be made with materials with a low thermal mass such as films, fabrics and foams. Some embodiments do not incorporate materials such as thick pieces of metal, liquid water or water-based materials such as gels that have relatively high thermal masses.
In these embodiments, when the temperature sensor assembly 110 is attached to an area of the heating element 10 that is typically in conductive contact with the patient during normal use, any other area of the heating element 10 that is also in conductive contact with the patient will also be at or near the set point or desired temperature. The temperature differentiation and location of the zones is automatic and depends on whether or not there is conductive contact between the heating element 10 and the patient.
Various embodiments therefore optimize both heat transfer and safety by automatically creating multiple zones in the heated underbody support. The non-contact, radiant heat zones which are typically peripheral, operate at a higher temperature than the patient contact, conductive heat zones which are typically central.
When not stretched, fabric heating elements 10 as described herein provide an even heat output or Watt density across their surface, unless they are folded or wrinkled which can double or triple the heating element 10 layers in the folded or wrinkled portion. The entire heating element 10 may have a relatively low Watt density, such as less than 0.5 watts per square inch, for example. Therefore, some embodiments prevent local wrinkling of the heating element 10. An embodiment of a heated mattress overlay 2 including a heater assembly 1 and a compressible material layer 20 and having reduced wrinkling or folding is shown in FIG. 6. It should be noted, however, that whether a unit is described as a heated mattress, heated mattress overlay, or heated pad is largely unimportant, and most embodiments could be used variously as heated underbody supports. While a heated mattress overlay may have a thin layer of padding, a heated pad typically has padding that may be thin or thick, a heated mattress may have an even thicker layer of padding. As such, various embodiments may be used alone, in the manner of a mattress, or on top of a mattress, in the manner of a mattress overlay. Descriptions relating to heated mattress overlays therefore also apply to descriptions of heated mattresses and heated pads, and vice versa.
The mattress overlay 2 as shown in FIG. 6 includes a fabric heating element 10 with bus bars 62, 64 attached that is additionally attached to a layer of compressible material 20 by a layer of adhesive 30 beneath the heating element 10. To prevent wrinkling, the compressible material layer 20 may be comprised of a simple urethane upholstery foam or its equivalent or one of the many “high tech” foams such as visco-elastic foams. Many foams are suitable for the compressible material layer 20 but should be durable and able to prevent wrinkling of the heater during use, yet should also be flexible, stretchable and accommodating. In the embodiment shown, the mattress overlay 2 also includes an upper shell 40 and a lower shell 42 forming an outer shell that encases the heater assembly 1 and compressible material layer.
The compressible material layer 20 may be a single layer of foam or may be a stack of materials that includes a layer of foam. This stack could include foam layers of different densities, different accommodation properties, different stiffness or different polymers. Additionally, the compressible material layer can include other materials such as woven or non-woven fabrics or films, to achieve other characteristics such as lateral stiffness or durability and strength. The term compressible material layer 20 therefore refers generally to single layers of compressible material such as foam as well as multilayered stacks that may include one or more layers of foam and may include other materials. Also, the layer of compressible material may alternatively be a layer of foam as described above.
Attachment of the heating element 10 to the compressible material layer 20 may be achieved by adhesive bonding across the entire interface between the two. Alternately, the heating element 10 may be bonded to the compressible material layer 20, intermittently across its surface, for example in dot, matrix, lines, boxes or other patterns or in a random pattern. The bond may be made with an adhesive comprising a pressure-sensitive adhesive without a reinforcing fiber or film carrier. Since the compressible material layer 20 may be flexible, stretchable and compressible, such a bonding made with such an adhesive does not alter the flexibility and stretch-ability of the heating element 10 or heated mattress overlay 2. Alternately, the heating element 10 may be attached to the compressible material layer 20 only along one or more of the edges 12, 14, 16, 18 such as along two opposing edges such as edges 12, 14, or in an intermittent pattern.
FIG. 7 depicts a cross section of a portion of an alternative embodiment of a heated mattress overlay 2, in which the fabric heating element 10 is bonded to an overlaying plastic film layer comprising an upper shell 40 by a layer of adhesive 35. In such embodiments, the upper shell 40 can be stretched and held in position by the compressible material layer 20 or by anchoring the mattress overlay 2 laterally, with or without bonding the shell 40 to the heating element. When the stretched layer of upper shell material is bonded to the heating element 10, this may reduce or prevent wrinkling or folding of the heater element 10 and yet maintain flexibility and stretchability (depending on the stretchability of the shell material). In the embodiment shown, the heated mattress overlay 2 further includes a lower shell 42 beneath the compressible material layer 20.
An alternative embodiment is shown in the heated mattress overlay 2 of FIG. 9, a cross section of which is shown in FIG. 8. In this embodiment, the fabric heating element 10 is anchored to a shell including an upper shell 40 and a lower shell 42 along its edges 12, 14, 16, 18 and thus held in an extended and wrinkle-free condition. Anchoring strips 46 comprised of plastic film or a suitable alternative are attached along the edges 12, 14, 16, 18 of the heating element 10, such as by sewing to form a sewn connection 85, though other forms of attachment may be used such as adhesive bonding. The anchoring strips 46 may extend along all four edges 12, 14, 16, 18 of the heating element 10 to form a peripheral bond 48. Alternatively, the anchoring strips 46 may extend along only one pair of opposing edges such as edges 12 and 14 or edges 16 and 18. The anchoring strips 46 may be made of the same material as the shells 40, 42, such as plastic film, and therefore can be bonded around the periphery of the mattress overlay 2, being sandwiched between and incorporated into the bond between the upper shell 40 and lower shell 42.
Since some embodiments maintain the heating element 10 in an extended and unwrinkled condition in order to avoid hot spots, more than one of these heating element 10 anchoring embodiments may be used simultaneously. To maintain flexibility, conformability and stretchability, the upper and/or lower shell 42, 44 may be adhered to the heating element 10 or the compressible material layer 20, across their broad surfaces as shown, for example, in FIG. 7, or may not be so adhered. However, in an alternate embodiment the heating element 10 can be bonded to the upper shell 40, for example. This may be advantageous for minimizing wrinkling of the heating element 10 or plastic film layer of the shell 40, 42.
Stretching the heating element 10 from the edges 12, 14 could result in hammocking of the heating element 10, such as if the mattress overlay 2 or pad is anchored tightly to the operating room table along the lateral edges. Various embodiments therefore include a beveled edge 24 on the compressible material layer 20, as shown in FIG. 10, for example, to help prevent hammocking by creating a slight excess of heating element 10 material as the heating element 10 transitions across the angle between the upper surface 21 of the compressible material layer 20 and the beveled edges 22,24. Additionally, the angle also creates an area of compressible foam that can compress in response to the heating element 10 being deformed by a weight resulting in the heating element 10 pulling toward the center from the edges 12, 14. Rather than being stretched tight out to the edge as would occur with a non-beveled compressible material layer 20, thereby potentially forming a hammock, the heating element 10 moves toward the center by compressing the compressible material layer 20 at the angle between the upper surface 21 and the beveled edge 24 of the compressible material layer 20, in response to deformation by a weight applied to the central area of the heated mattress or mattress overlay 2. In this way, the risk of hammocking is further reduced or eliminated.
The compressible material layer 20 (or layer of compressible material) supporting the heater assembly 1 in certain embodiments could be almost any thickness that is advantageous for the given application (for example, 0.5-6.0 inches). The compressible material layer 20 may be uniform in thickness and density or it may be contoured in thickness, shaped, scored or segmented according to areas of different densities.
FIG. 10 depicts a cross section of a heated mattress overlay 2 including a shaped compressible material layer 20 according to various embodiments. In this embodiment, the compressible material layer 20 is beveled or tapered along one or more edges, such as the edges that abut and support the bus bars 62, 64 which are attached to the compressible material layer 20 along the beveled edges 22, 24. The compressible material layer 20 is generally planar with an upper surface 21 and an opposing and parallel lower surface 23. The beveled ends 22, 24 of the compressible material layer 20 are not perpendicular to the surfaces 21, 23 but rather angle inwardly, toward the upper surface 21. On cross section, the compressible material layer 20 is trapezoidal in shape rather than rectangular, with the lower surface 23 forming the larger trapezoid base and the upper surface 21 forming the smaller trapezoid top. Alternatively, the lower portion of the edge could be perpendicular to the bottom surface while only the upper portion of the edge may be angled inwardly to form a bevel. Other embodiments including beveled edges are also anticipated.
The portions of the heating element 10 attached to the bus bars 62, 64 may be bonded to the compressible material layer 20 along the beveled ends 22, 24. Locating the bus bars 62, 64 on the beveled ends 22, 24 of the compressible material layer 20 provides some protection of the bus bars 62, 64 from mechanical stress when patients are sitting or lying on the underbody support. Alternatively, to provide additional protection to the bus bars 62, 64, the heating element 10 may be wrapped around the compressible material layer 20 and onto the bottom surface 23 so that the bus bars 62, 64 are located under the compressible material layer beveled ends 22, 24 and attached to the bottom surface 23 as shown in the cross section shown in FIG. 11, for example. In a further alternative shown in FIG. 12, the beveled piece of foam that is removed from the compressible material layer 20 or any other triangular or wedge shaped piece of foam of complementary size and shape to fit the space may be bonded over the heater assembly's bus bars 62, 64, along the beveled edges 22, 24 of the compressible material layer 20 to form a filler 25, to fill in the beveled space and protect the bus bars 62, 64. The foam filler 25 may be sized such that, when in place above the bus bars, the horizontal upper surface of the heated mattress overlay 2 (or other underbody support) above the central, non-beveled portion of the foam, is level with the horizontal upper surface of the overlay 2 above the beveled end 24. In these embodiments the heating element 10 extends across the upper surface 21 of the compressible material layer 20, and the bus bars 62, 64 are away from and lower than the upper surface 21. In this way, the bus bars 62, 64 may be physically protected from damage by bonding them onto or beneath the beveled edges 22, 24 of the compressible material layer 20, where they are effectively recessed from the upper surface 21 of the compressible material layer 20. The beveled edges 22, 24 of the compressible material layer 20 allow the bus bars 62, 64 to be optionally covered with a foam filler 25 to act as a protective barrier in this location for added protection, without adversely affecting the look of the smooth top surface of the underbody support, thereby basically filling the bevel space with a foam filler 25 to create an overall rectangular cross sectional shape.
In other embodiments, a portion of the compressible material layer 20 is thinned or scored in an area, from one lateral edge to the other of the area, with the area located to overlie the area of transition from one cushion of an operating table to the adjacent cushion under normal conditions of use. The thinning or scoring may be on the bottom surface 23 of the compressible material layer 20 and therefore away from the patient contact top surface 21. Since operating room tables are designed to flex at the area between the operating table cushions, a thinned compressible material layer 20 at the area of transition between cushions will aid in flexion of the heating element 10 and reduce the chances of the heating element 10 wrinkling during flexion. Alternatively, the compressible material layer 20 could be scored or cut or otherwise have one or more gaps or channels completely through or partially through its thickness on the bottom surface 23 at the flexion locations or other areas where added flexibility is important, as shown in FIG. 13, for example. In the embodiment shown, multiple small channels 27 are present in a portion of the compressible material layer 20 where the compressible material layer 20 is thinner. These channels 27 may extend across the compressible material layer 20, from one end to the opposing end, such as across the width or the length of the compressible material layer 20, such as in a direction parallel to and aligned with the transition between operating table cushions. In use, the underbody support may be positioned over a table or bed with which it is designed to be used such that the channels are located over the flexion locations of the table or bed. The table or bed may then be adjusted by bending at a flexion point (such as to raise or lower a patient's upper body or legs by bending or extending the patient at his or her hips) and the compressible material layer 20 of the underbody support can bend easily at this location due to thinness or scoring at the location of flexion, while the heating element 10 can likewise bend without wrinkling or folding due to its flexibility and elasticity.
In some embodiments, the compressible material layer 20 may be thinned or scored or have gaps or channels longitudinally in order to increase flexibility for bending the heated underbody support around a longitudinal axis such as a long axis of a body. This may be advantageous to aid in wrapping the heated underbody support around a patient being in the lateral position while laying within a “bean bag” or “peg board” positioner. The longitudinal thinning or scoring or presence of gaps or channels allows the heated underbody support to be wrapped around the dependent portion of the patient, increasing the area of surface contact between the heating element 10 and the skin while avoiding wrinkling of the heating element 10 due to the bending of the compressible material layer 20. In these embodiments, the bending of the compressible material layer 20 can be facilitated by corrugations in the lower shell 42, which may be created by , at a location corresponding to or adjacent to the location of the gaps or channels in the compressible material layer 20. The corrugations of the shell material may be longitudinal or from side to side. The excess lower shell material created by the corrugations may allow the support to be bent forward at the edges or ends, without causing the upper shell 40 and heating element 10 to wrinkle The redundant lower shell material 42 of the corrugations, in conjunction with gaps or channels in the compressible material layer 20, allow the lower shell to stretch when the support is bent forward, rather than the upper shell 40 and heater element 10 compressing and wrinkling
In some embodiments, the compressible material layer 20 is segmented into portions having different thicknesses or different material composition or characteristics. For example, the compressible material layer 20 may include a central portion that may be a rectangular, round or oval section portion within a surrounding portion. Other sectional shapes are anticipated. The surrounding portion may resemble a picture frame or may only surround a portion of the central portion. The central section or sections may be filled with a plug of less dense foam, for example, to increase the accommodation of lightweight pediatric patients or patients' extremities. The surrounding portion of the compressible material layer 20 which may surround the plug may be a denser foam that is more suitable for stabilizing the heating element 10, for example to prevent wrinkling of the heating element 10. An example of such an embodiment is shown in FIG. 14, which is an aerial view of a heated mattress overlay 2 with a compressible material layer 20 with a centrally located plug 27 of less dense foam.
In still other embodiments, such as the heated mattress overlay 2 embodiment shown in the cross section in FIG. 15 or other heated underbody supports, the compressible material layer 20 includes a depression 29 in a given location to encourage the proper location of the patient on the mattress overlay 2 by contouring the compressible material layer 20, for example. The depression 29 may also stabilize small pediatric patients on the mattress overlay 2. The depression 29 may be a longitudinal, semicircular half-pipe shape gap or cut out that creates a trough-like depression for the pediatric patient to lay in. A depression 29 in the compressible material layer 20 for small pediatric patients may also increase the amount of skin surface in contact with the heating element 10 by extending the heating element 10 up the sides of the patient's body. The increased surface area of the support contacting the sides of the pediatric patient increases the heat transfer between the support and the patient. The depression 29 also assures accurate positioning so that the patient is contacting the temperature sensor assembly 110 if it is located substantially in the middle or at or near the bottom of the depression 29. For all of these reasons, a pediatric heated mattress or mattress overlay 2 with a longitudinal depression 29 cut into the compressible material layer 20, may be more effective at warming pediatric patients than a simple flat underbody support. Such heated underbody supports may also be more effective for heating adult patients. Other examples of contouring, shaping or segmenting the compressible material layer 20 are anticipated.
In some embodiments, the temperature sensor assembly 110 includes a substrate, for example, of polyimide (Kapton), on which the temperature sensor, for example, a surface mount chip thermistor (such as a Panasonic ERT-J1VG103FA: 10K, 1% chip thermistor), is mounted. A heat spreader, for example, a copper or aluminum foil, is mounted to an opposite side of the substrate, for example, being bonded with a pressure-sensitive adhesive. The substrate is relatively thin, for example about 0.0005 inch thick, so that heat transfer between the heat spreader and sensor 110 is not significantly impeded. The temperature sensor assembly 110 may be bonded to the fabric heating element 10 with an adhesive layer, for example, hotmelt ethyl vinyl acetate. The temperature sensor assembly 110 may be potted with a flexible electrically insulating material, such as silicon or polyurethane. A heat spreader is a desirable component of a temperature sensor assembly 110, according to some embodiments, since conductive fabrics employed by the heating element 10, such as those previously described, may not exhibit perfectly uniform resistance across surface areas thereof. In some embodiments, a secondary over-temperature sensor assembly 115 of similar construction to the temperature sensor assembly 110 may be located within one inch of the primary control sensor, so that both the temperature sensor assembly 110 and the secondary over-temperature sensor assembly 115 may respond to the same inputs. In some embodiments, both assemblies 110, 115 are mounted to the same heat spreader.
In embodiments where the temperature sensor assembly 110 and secondary over-temperature temperature sensor assembly 115 are attached to the heating element 10 and the heating element 10 is separated from the environment by an upper film 40, there is a risk that the assemblies 110, 115 may be influenced by environmental factors. Under certain conditions, the sensors may measure the “cool” ambient temperature from the environment, or from an object such as a wet towel or a metal pan inadvertently positioned over the temperature sensor 115, and provide that input to the controller which will then drive the heating element 10 into an over-temperature condition in areas contacting the patient. Various embodiments of the heated underbody supports may reduce or eliminate this risk as described below.
FIG. 16 is an aerial view of a heated mattress overlay 2 in which a thin layer (such as less than about 0.5 inches) of compressible material such as foam is located around the temperature sensor assembly 110 and the over-temperature sensors assembly 115 to limit the effect of environmental or ambient temperatures in instances where the patient is not properly positioned over the temperature sensor assembly 110. Alternatively, a thin layer of compressible material such as foam may cover some or all of the upper surface of the heater assembly 1. In some alternative embodiments, the material layer may be in the form of a ring 120 surrounding the temperature sensor assembly 110, as shown in FIG. 17. When the patient is not positioned over the temperature sensor assembly 110 and over temperature sensor assembly 115, the ring 120 will remain expanded (uncompressed) and lift the upper shell 40 away from the temperature sensor assembly 110 and the over temperature sensor assembly 115, creating an air space 122 within the ring of foam 120 and between the temperature sensor assembly 110 and the upper shell 40. In this instance, the air space 122 will act as a thermal insulator, minimizing the influence of the environmental temperature on the temperature sensor assembly 110 and the over temperature sensor assembly 115. The space within the ring 120 should be large enough (for example about 0.5 to about 2.0 inches) and the ring material should be compressible enough to allow the over-laying layer of plastic film of the upper shell 40 to be compressed directly against the temperature sensor assembly 110 and the over temperature sensor assembly 115 when a patient is laying on the assemblies 110, 115, as shown in the cross-sectional view of FIG. 18, in which the downward force of the patient (not shown) is indicated by downward printing arrows. In this condition, the temperature sensor assembly 110 and the over temperature sensor assembly 115 will respond to the temperature of the heating element 10 that is in direct thermal contact with the patient. This affords the correct information to the controller to allow for accurate temperature control of the heated underbody support. The weight of the patient laying on the ring 120 surrounding the assemblies 110, 115 or on a material layer over the assemblies 110, 115 will compress the material and the patient will end up in thermal contact with the temperature sensor assembly 110 and the over-temperature sensor assembly 115. If the patient is not positioned over the temperature sensor assembly 110 and the over-temperature sensor assembly 115, the non-compressed ring 120 or layer will thermally insulate the assemblies 110, 115 from the cool environmental temperatures which could otherwise cause the heating element temperature to rise to an over-temperature condition.
To prevent overheating, certain embodiments include one or more temperature sensor assemblies 110 in the heated underbody support that can sense the temperature in a desired area and then provide feedback to a controller. The temperature sensor assembly 110 can be placed in an area that would be in contact with a patient as described above or in an area that would reflect an average temperature of the heated underbody support. The controller may shut off the power supply to the heating element and/or triggers an alarm, such as an audible or visible alarm, if the sensed temperature is too high, such as if the temperature is at or above a maximum or threshold temperature. Thus, the temperature sensor assembly 110 therefore acts as a safety feature to help protect patients from overheating.
Yet other embodiments include additional safety features in case the temperature sensor assembly 110 does not reliably report an accurate average temperature of the heated underbody support. This could happen in a number of situations. In some cases, the temperature sensor assembly 110 itself may simply be damaged and may provide false information to the controller. In other cases, the temperature sensed may be cooler than the temperatures of other areas of the heated underbody support. This could occur, for example, if a “thermal grounding” condition should occur, for example if a cool object such as a metal pan or a bag of IV fluids were placed on the temperature sensor assembly 110. The cool object could act as a heat sink and absorb heat from the heated underbody support, causing the area around the assembly 110 to feel cooler. In another example, the area of the heated underbody support near the temperature sensor assembly 110 may become wet or damaged. In each of these examples, the temperature of the heated underbody support in the temperature sensor assembly 110 area may be cooler than the temperature of other areas of the heated underbody support. Alternately, if the portion of the heating element 10 in contact with the temperature sensor assembly 110 fails, the assembly 110 may not detect that the heating element 10 is being adequately energized and may cause the controller to supply more power to the heating element 10. Finally, the temperature sensor assembly 110 itself could fail. Any of these fault conditions could result in significant over-temperatures (temperatures above a desired temperature) of the heating element 10 when the inaccurately cool sensed temperature results in the controller continuing to supply power to the heating element 10, even though the temperatures in some or all areas are too high. If undetected, the temperature would continue rising to excessive levels and body parts in contact with these areas of the heated underbody support may suffer thermal burn injury if in contact with the heated underbody support for a prolonged period of time. To prevent this, various embodiments include safety features which allow the controller to detect these fault conditions and then turn off and/or signal an alarm, as described further below. The additional safety feature may be somewhat or entirely independent of the temperature sensor assemblies 110, 115. This independence can provide an additional safety feature that can detect or prevent injury in the event of a failure or inaccurate reading of the temperature sensor assemblies 110, 115.
For example, some embodiments provide a safety feature that cuts power to a heater assembly 1 after a certain period of time has elapsed (a cut off time), irrespective of the feedback provided by a temperature sensor 110 concerning the heated underbody support temperature. That period of time may be longer than it takes for the mattress or mattress overlay 2 to reach its threshold or desired or maximum cut-off temperature under normal operating conditions, but shorter than it normally takes to cause thermal burn injury and may be determined by the manufacturer and set into the controller. This safety feature, referred to as a shut-off timer, may be controlled by the controller as described below, for example.
The operation of some embodiments of the heated underbody support systems will now be described. In operation, the controller is first turned on or activated, prompting the power source to begin supplying power to the heating element 10. The heating element 10 continues to receive this power until the temperature sensor assembly 110 senses a threshold or desired temperature. Any type of duty cycle and voltage level can be used, so long as a desired threshold temperature is achieved in a reasonable amount of time. The threshold temperature can be any desired temperature that medical personnel wish to supply to a patient. In some embodiments, the threshold temperature is 37° C., 39° C., 41° C., or other temperatures and may be preset or may be set by a user. Some patients (e.g., those with poor blood perfusion) should not have prolonged contact with conductive heat in excess of approximately 39° C. Thus, according to certain embodiments, the threshold temperature is set by the user to a maximum of approximately 40° C. in order to achieve a temperature of about 39-40° C. on a surface of the heated underbody support. The skin temperature may or may not reach this threshold temperature of the heated underbody support. In many cases, the skin temperature is slightly lower than the threshold temperature.
Once the temperature sensor assembly 110 senses the threshold temperature, the controller prompts the power source to stop supplying power to the heating element 10. At some point after the power supply is stopped, the temperature of the heated mattress or mattress overlay 2 cools to below the threshold temperature. Once the temperature sensor assembly 110 senses a temperature below the threshold temperature, the controller prompts the power source to again supply power to the heating element 10. This process operates much like common thermostats and continues to oscillate on and off around the threshold temperature until the controller is shut off by the user.
In embodiments including a shut-off timer, the shut-off timer operates simultaneously during the process just described. Regardless of the temperature sensed by the temperature sensor assembly 110, the shut-off timer limits the amount of time that power is supplied to heating element 10. This way, in case the temperature sensor assembly 110 never reaches the threshold temperature (even though other areas of the heated underbody support may be above the threshold temperature), the shut-off timer only allows the power to be supplied for a limited time. The shut-off timer responds to an indication that the prescribed threshold temperature has been reached in less than the prescribed shut-off timer time limit. The indicators of reaching the threshold temperature can be a direct temperature reading from the temperature sensor assembly 110 or the controller or detection of at least a momentary interruption of power to the heating element 10. If the timer function does not detect an indicator of the threshold temperature having been reached within the prescribed time, the controller will discontinue power to the heating element 10 and/or signal an alarm. This is an additional safety feature that helps to prevent patients from being exposed to temperatures at or above the threshold temperatures for a prolonged period of time.
According to some embodiments, once the controller is turned on, it prompts the shut-off timer to start. The shut-off timer runs for a desired period of time and upon expiration of this period of time, the controller prompts the power source to stop supplying power to the heating element 10. In addition, the controller may signal an audible and/or visible alarm and/or display a visible cue to let the user, such as medical personnel, know that the desired time period has expired. The expiration of the time period tells the user that the temperature sensor assembly may not be working, the heating element in the area of the temperature sensor may be damaged, or the resistance of the heating element may have increased to the point where the resulting Watt density is too low to allow the heating element to reach the threshold temperature within the time period, or the temperature sensor may be experiencing thermal grounding, for example. Any of these conditions constitute failure modes. None of these failure conditions could have been detected by the control temperature sensor.
If the temperature sensor assembly 110 is functioning properly, the time period for power supply allowed by the shut-off timer should not run out before the threshold temperature has been reached and therefore would have no effect on the power. Each time the temperature sensor assembly 110 reaches the threshold temperature, the controller prompts the power source to stop supplying power and also stops and resets the shut-off timer. Once the sensed temperature cools to less than the threshold temperature, the controller prompts the power source to again supply power and also starts the shut-off timer. This process continues throughout normal operation of the heated underbody support. Should the temperature sensor assembly 110 ever malfunction and fail to sense a threshold temperature within the shut-off timer time period or if the shut-off timer fails to detect at least a momentary discontinuation of power to the heater indicating that the threshold temperature has been reached, the controller will prompt the power source to stop supplying power and/or may trigger an alarm. The user would then fix the offending condition, e.g., by removing a metal pan or other object that may be influencing the temperature sensor, or by disposing of the heated underbody support and replacing it with a new one. Thus, embodiments of the heated underbody support may have an additional safety feature to protect patients.
The period of time selected for the shut-off timer is a time period that is less than a time it takes for thermal burn injury to occur with a particular heated underbody support (“thermal burn injury time”). The thermal burn injury time may vary depending on the type of mattress, the Watt density of the mattress and/or the type of power supplied to such mattress. The shut-off timer may be preset by the manufacturer to a single time or to a time that varies depending upon the threshold temperature, or may be set by the user.
Accordingly, the time limit imposed by the shut-off timer may be the same regardless of whether the heating element 10 is just beginning operation or is in the middle of operation. In other embodiments, the controller may make a determination that the heating element 10 has been operating for a period of time at a steady state (e.g., as evidenced by continued cycling of the power supply over a period of time) and may adjust the shut off time lower than its setting for initial start up time.
The shut-off time period may depend upon the Watt density of the heated underbody support. For heated underbody supports operating at a Watt density of less than approximately 0.25 watts/square inch, programming the timer for a shut-off time period of about 20 minutes may be desirable. To provide an additional margin of safety, programming the timer for a shut-off time period between about 5 and about 15 minutes may be desirable. This time period is well below the predicted thermal burn injury time, regardless of whether the heated underbody support is just beginning operation or is in the middle of operation. Thus, in certain embodiments, the shut-off timer is set to expire after a time period which is between about 5 and about 15 minutes. In some embodiments, the shut-off timer is set for a shut-off period of about 10 minutes. The time period may need a minimum of about 5 minutes in these embodiments because it could take up to 5 minutes for a room temperature heating element 10 to reach the threshold temperature. The time period may be greater than what is required to reach the threshold or desired temperature under normal operating conditions in order to avoid being a nuisance to the user of the heated underbody support.
Heated underbody supports having a Watt density higher than 0.25 watts/square inch might have a shut-off time period that is shorter, perhaps about 10 minutes or less. Supports operating at a higher Watt density (e.g., 0.5 watts/square inch) may have even shorter shut-off times. In contrast, heated underbody supports having a Watt density much lower than 0.25 watts/square inch might have a time period that is longer, perhaps more than about 10 minutes, as discussed above.
The operation of the heated underbody support may be described with reference to a temperature sensor assembly 110 having a single temperature sensor. Of course, temperature sensor assemblies 110 can be used that have multiple temperature sensors. For example, the temperature sensors can be provided in the form of conventional temperature sensors, over-temperature sensors, and super-over temperature sensors, as described in U.S. application Ser. No. 11/537,189, the contents of which are incorporated herein by reference. Each temperature sensor can provide input to the controller. The temperature sensors can all have the same threshold temperature or some can have different threshold temperatures. For example, sensors located in an outer or peripheral area 116 of the heating element 10 that would not normally be in contact with a patient may have a higher threshold temperature than sensors located in an area that would normally be in contact with a patient during normal use.
In embodiments having multiple temperature sensors, the controller can be configured in any manner so that when a specific temperature scenario is reached, it prompts the power source to stop the supply of power and resets the shut-off timer. For example, in one embodiment, the threshold temperature can be the same for each sensor, and the controller system can determine an average of the overall sensed temperature. When a desired average temperature is reached, the controller can shut off power and the shut-off timer can be reset. In other embodiments, the controller can be configured to shut off power and the shut-off timer can be reset each time a threshold temperature for any sensor is reached. Varieties of scenarios are possible and are within the scope of this disclosure. In any event, no matter how many sensors are provided and no matter what the threshold temperatures are, the shut-off timer can operate the same way. The shut-off timer begins to track time when the controller is turned on and continues until either the shut-off time period expires or until the controller resets the shut-off timer or it senses an interruption of power to the heating element 10 when a programmed temperature threshold is reached.
A flow chart depicting the operation or programming of a controller according to various embodiments is shown in FIG. 19. At step 300, the controller is activated to supply power to the heating element 10. This immediately starts the timer at step 305 and also starts receiving measured temperatures from temperature sensors at step 310. At step 315, the controller determines whether the measured temperature is less than the set point or threshold temperature. If the answer at step 315 is NO, the controller prompts the power source to shut off the power supply at step 320. This in turn stops and resets the timer at step 325. The timer delays at step 330 and then repeats this process starting at step 305. If the answer at step 315 is YES, the controller prompts the power supply to turn the heat on if it is not already on at step 335. The controller then determines whether the timer has reached the maximum time period at step 340. If the answer in step 340 is YES, the controller shuts off the power and/or signals an alarm at step 345. If the answer in step 340 is NO, the controller delays at step 350 and repeats this process starting at step 310.
In many of the embodiments described above, the shut-off timer is correlated to a threshold temperature in an on/off power control system. That is, the controller resets the timer and stops a supply of power each time the threshold temperature is sensed. However, the shut-off timer can be correlated to operating parameters other than the temperature sensor measurement. In addition, the controller may be more sophisticated than an on/off power supply system. For instance, in some embodiments, the controller modulates the amount of power supplied (rather than simply turning a single power type on and off). Here, the controller monitors temperature of the heated underbody support based on input received from one or more temperature sensors and modulates the power levels accordingly. For example, as the sensed temperature approaches a threshold temperature, the controller can gradually or incrementally reduce the power level. As the sensed temperature falls below the threshold temperature, the controller can increase the power level to increase the temperature. If the sensed temperature is far below a threshold temperature, the controller can increase the power level even higher than that for a temperature just below the threshold temperature.
Under a modulated power control system, the controller and shut-off timer can be programmed so that if the power level does not fall below a threshold level within a desired period of time, the timer expires and the controller shuts off the power supply and/or signals an alarm. Likewise, each time the power level does fall below the threshold level, the timer is reset. Accordingly, in such embodiments, the shut-off timer reset may be based on the power supply level and not directly on temperature or power supply interruption.
One known power modulating controller which may be used in some embodiments is a PID (proportional/integral/derivative) based control system. In embodiments including a PID control system, the controller can monitor one or more process control parameters, such as an integral control term. The controller and timer can be programmed so that if the integral control term does not reach a desired level within a desired period of time, the shut-off timer time limit expires and the controller shuts off the power supply. Likewise, each time the integral control term reaches the desired level, the timer is reset.
In some embodiments, the temperature control comprises a thermostatic switch, such as a bi-metallic thermostat, thermally coupled to the heating element 10 and in-line with the power supply for the heating element 10. In such embodiments, the switch opens, thereby cutting off current to the heating element 10 when the heating element 10 and its thermally coupled switch reach a set point temperature. The shut-off timer can sense the discontinuation of power to the heater and reset its timer.
In some embodiments, the flexible heating element 10 itself may comprise a temperature sensor. In such embodiments, the flexible heating element 10 is formed of a material having a resistance that varies with temperature. The controller may determine the temperature of the flexible heating element by measuring the resistance or change in resistance in the power supply circuit. The resistance of the heating element 10 may also be used to determine the Watt density output of the heating element 10. Thus, the heating element resistance measurement may be used as a control parameter by the controller to control or adjust the Watt density output of the heated underbody support as desired.
The shut-off timer may comprise a safety device that may operate independently of the temperature measured by the temperature sensor and control circuit, based on the assumption that the heating element 10 will normally reach operating temperature in less than a prescribed amount of time, for example, ten minutes. Normally, the electric current to the heating element 10 may be on continuously until the threshold temperature is reached. Then the controller maintains the desired set temperature by either turning the current on and off or the controller proportionally reduces and increases the current flow. If the shut-off timer does not sense that the current has been at least momentarily turned off or reduced prior to the shut-off time elapsing, or does not sense that a prescribed temperature has been reached, the controller will recognize this as a fault condition.
In some embodiments, such as the embodiment as shown in FIG. 20, there may be an upper insulating layer 125 which may be made of foam or high loft fibrous material, for example, between the heating element 10 and the upper shell 40. If the material of the upper insulating layer 125 is easily compressible, it may extend in a thin layer (for example about 0.25 inches or less, such as about 0.01 to about 0.025 inches) over the entire surface of the heating element 10 with minimal detrimental effect on heat transfer. This upper insulating layer 125 may reduce the impact of environmental temperature on the temperature sensor assembly 110 in instances where a patient is not positioned on the temperature sensor 110. To improve heat transfer and retain a thin, distributed insulating layer over the heating element 10, an array of holes 127 (for example 0.5-2.0 inches in diameter) can extend through the upper insulating layer 125 as shown in FIG. 21, for example. Hole shapes other than round may also be used. The holes 127 may spread over the entire layer 125 or only a portion of layer 125. When the upper insulating layer 125 is compressed by the weight of the patient, the upper shell 40 of the heated mattress or mattress overlay 2 directly contacts the heating element 10 within each of the holes 127. The holes 127 may be absent (the material may be continuous and uninterrupted) in certain locations such as along the edges of the upper insulating layer 125 above the bus bars 62, 64 where the uncompromised material may provide added protection to the bus bars 62, 64. This construction gives improved heat transfer by placing the heating element 10 very close to the patient while still protecting the heating element 10 and temperature sensor assemblies 110 from unwanted environmental thermal influences.
The combination of conductive fabric heating elements 10 made from flexible and stretchable material, bus bars 62, 64 attached near opposing edges 12, 14 of the heating element 10, one or more temperature sensors 110 and a controller, comprises a heater assembly 1 according to some embodiments. The heater assembly 1 may be secured to a compressible material layer 20 or other compressible layer and may be covered with a water- resistant shell 40, 42 that may be made of a stretchable plastic film such as urethane or PVC, however, other film materials and fiber-reinforced films are anticipated.
The shell 40, 42 protects and isolates the heater assembly 1 from an external environment of the heater assembly 1 or heated underbody support and may further protect a patient disposed on the heated underbody support from electrical shock hazards. According to some embodiments, the shell 40, 42 is waterproof to prevent fluids, for example, bodily fluids, IV fluids, or cleaning fluids, from contacting the heater assembly 1, and may further include an anti-microbial element, such as SILVERion™ antimicrobial available from Domestic Fabrics Corporation (Kinston, N.C.), which is extruded in the plastic film of the shell material.
In some embodiments, a layer of plastic film is placed over each broad surface of the heater assembly 1, as an upper shell 40 and a lower shell 42 but is not bonded to the heater assembly. The two layers of plastic film are bonded to each other around the periphery of the heater assembly 1 to form a water-resistant shell. The bond may be from heat, radio frequency (RF), ultrasound, solvent or adhesive, for example. The heater assembly 1 may be “free floating” within the shell with no attachment to the shell, or can be attached to the shell, such as only at the edges 12, 14, 16, 18 of the heater assembly 1 as described above, for example. This bond construction around the periphery of the heated underbody support creates a durable shell without folds, creases, crevasses or sewing needle holes that can collect infectious debris and be difficult to clean. The heater assembly 1 covered by a shell of plastic film and optionally including a foam or other compressible material layer comprises a heated mattress, mattress overlay, or pad according to some embodiments.
In certain embodiments, such as the embodiments shown in FIGS. 22 and 23, the shell construction allows the power entry module 130 to be located and bonded between the shell, such as the layers of plastic film, at the edge of the shell within the bonded layers 48. The power entry module 130 can be bonded with adhesive, solvent, heat, RF or ultrasound for example, between the adjacent layers of upper and lower shell 40, 42 at the periphery of the shell. Sewn shell constructions known in the art prevent the power entry from being more peripherally located because the periphery includes a stitch line and as a result the power entry must be located on the flat surface of the shell rather than the edge. Locating the power entry on the flat surface of the support may result in the patient laying on the hard lump created by the power entry module and could contribute to the formation of a pressure injury. In some embodiments, the power entry module 130 is a piece of molded plastic, for example in a shield-shape, that can be sealed between the sheets 42 and 44 in the peripheral bond 48 edge seal of the shells 42, 44. The pointed ends of the shield-shaped power entry module 130 allow the shells 42, 44 to transition smoothly from the area where the upper and lower shells 42, 44 are sealed to each other, to the adjacent area where the shells 42, 44 are sealed to the power entry module 130 module and then back to the shells 42, 44 being sealed to each other. In some embodiments, the power entry module 130 includes a tubular channel traversing from the outer side to the inner side of the shell. The tubular channel may be sized to accommodate the wire cable that contains the power and sensor wires. The wire cable can pass through the tubular channel from outside to inside the heated underbody support and can be adhesive, solvent or heat bonded to the power entry module in this position, creating a water-tight seal. In another embodiment, the power entry module 130 may be shaped and sized to house a plug-in connector.
The heater assembly 1 can be encased in a shell of plastic film as described, or may have no shell. With or without a shell or compressible material layer 20, it can be used as a mattress overlay on top of, or can be inserted into, a pressure reducing mattress. For example, since pressure reducing mattresses typically have water resistant covers, the heater assembly 1 may be inserted directly into the mattress, inside the mattress cover, without a shell on the heater assembly 1. In either case, the heated underbody support is designed to have little or no negative impact on the pressure reducing capabilities of the mattress on which it is laying or into which it is inserted.
When used as a mattress overlay, the shell of the heater assembly 1 may be water resistant, flexible, and durable enough to withstand the wear and tear of operating room use. Examples of materials which may be used for the shell include but are not limited to urethane and PVC. Many other suitable plastic film or fiber-reinforced plastic film shell materials are anticipated. In some embodiments, the shell material is between about 0.010 and about 0.015 inch thick. In this thickness range, both urethane and PVC, for example, are strong but retain an adequate stretchability. The heated underbody support may cover approximately the entire surface of the surgical table or any other bed. Alternately, the heated underbody support may be sized to fit some or all of the cushion that forms the support surface of a surgical table. For example, if the cushion has multiple separate sections, such as three, the heated underbody support may be sized to fit over one or two or all three of the cushion sections.
The heated underbody support may have two or more attachment points such as tabs 140 for securing the support over the top of a surgical mattress or table such as is shown in FIG. 23. These attachment points may be tabs 140 or flaps made from shell material that extend outward from the peripheral bond 48 of the shell. These attachment points may be fiber-reinforced and yet flexible and somewhat loose, so that they do not cause hammocking of the shell. The attachment points can be secured to the table with many different means including straps, ties, loops, hooks, snaps, barbs, Velcro or other attachment means.
In an example of an attachment method shown in FIG. 24, there are a series of barbs 142 extending radially outward from a longitudinally extending body 144 in the form of a strap, made of rubber or other flexible material, for example. A loop or aperture 146 extending through the strap can engage the side rail of the table and the barbs 142 can engage an aperture 148 in the tab 140 of the heated mattress overlay 2.
In some embodiments, a high tech foam may be included in the compressible material layer 20 or may be in addition to the layer of compressible material 20, to reduce the pressure exerted against the patient's skin during surgery. High tech foams include but are not limited to visco-elastic foams that are designed to maximize accommodation of the patient into the mattress. As previously noted, accommodation refers to the sinking of the user, such as the patient, into the underbody support until a maximal amount of support surface area is in contact with a maximal amount of skin surface, and the pressure exerted across the skin surface is as uniform as possible. These high tech foam materials may accommodate the patient more effectively than simple urethane upholstery foam. Unlike prior art mattress heaters or heating materials, the unique stretchable, flexible, free floating design of the heater assemblies 1 described herein allow them to overlay a layer of visco-elastic foam and maintain the accommodation properties of the foam. Further, the heater assembly 1 may be soft, flexible and stretchable enough to be the separated from the patient by only a single layer of plastic film and still be comfortable. The avoidance of multiple layers of materials interposed between the patient and the mattress foam maximizes accommodation and heat transfer.
In embodiments comprising heated mattresses 3 including foam layers 150, a water-resistant shell or cover 160 may encase the foam 150 as shown, for example, in FIG. 25. The foam 150 may be simple urethane foam or high-tech foam such as visco-elastic foam, for example. The cover 160 may be made of plastic film that has been extruded onto a woven fabric (e.g., Naugahyde), for example. In one embodiment, the heater assembly 1 may be located within or may be removably inserted directly into the mattress cover 160, with or without a shell 40 on the heater assembly 1. The heater assembly 1 may be placed directly on top of the mattress foam 150 inside the cover 160 or a heater assembly 1 (with its own shell) may be placed on top of a mattress outside of the mattress cover 160. If a foam mattress has its own shell, the thickness of the shell 40 of the heater assembly 1 can be reduced to, for example, about 0.003 and about 0.010 inch, or even omitted, because the heater assembly 1 is protected from mechanical damage by the cover 160 of the mattress 150. The thinner shell material improves the stretch-ability of the shell. Alternately, the heating element 10 may be bonded directly to the mattress foam 150.
The thermal effectiveness of this heated underbody support can be optimized when the heating element 10 is overlaying a layer that can provide maximal accommodation of the patient positioned on the support. In this condition, the heating element 10 is in contact with a maximal amount of the patient's skin surface which maximizes heat transfer. Heated underbody supports made with inflatable air chambers forming or included in the compressible material layer 20 or in addition to the compressible material layer 20, can provide excellent accommodation. Further, a heated underbody support with excellent accommodation properties having a heating element 10 as described herein avoids degrading the accommodation properties of the mattress when a heater assembly 1 is added. Therefore, the combination of the heater assembly 1 design with an accommodating mattress such as a mattress made with one or more inflatable air chambers 170 as shown in FIG. 26, for example, is advantageous and synergistic for the effectiveness of both technologies.
An embodiment of a heated mattress 3 comprising one or more air chambers 170, 172 and a heater assembly 1 overlaying the one or more air chambers 170, 172 is shown in FIGS. 26, 27 and 28. In some embodiments, a single air chamber 170 or a plurality of elongated inflatable chambers 172 are positioned under the heater assembly 1. The plurality of elongated inflatable chambers 172 may be cylindrical in shape and may be oriented in parallel and positioned side-by-side one another, with their long axes extending substantially from one side of the mattress to the other side. However, other inflatable chamber shapes and orientations are anticipated. The inflatable chambers 172 may be round or ovoid in cross section. They may or may not be physically secured to the adjacent air chamber. Alternately, they could be secured to a base sheet or simply positioned and contained within the mattress cover 160 without being secured. The chambers 170, 172 may be made of a fiber-reinforced plastic film or a plastic film that has been bonded, laminated or extruded onto a woven or non-woven fabric reinforcing layer. Urethane may be used as the plastic film, but other plastic film materials are anticipated. Woven nylon may be used as the reinforcing layer, but other fabric materials are anticipated.
The inflatable chamber 170 or chambers 172 can be sealed and static, or connected together in fluid connection to allow redistribution of air between the chambers 172. In some embodiments, the chamber 170 or chambers 172 can be actively inflated and deflated while the heated mattress 3 is in use. The inflatable chambers 172 may be inflated and deflated each independently, all simultaneously, or in separate groups, while the heated mattress 3 is in use. In some embodiments, the chambers 172 are each a part of two separate groups and may be segregated for example by every other chamber 172 (alternating chambers 172) according to their relative side-by-side positions. A conduit or conduits may be in separate independent fluid communication with each chamber 172 of the group of inflatable chambers for independently introducing or removing air from that group of inflatable chambers.
Alternately, there may be only a single group of chambers 172 or there may be more than two groups of chambers 172 which can be separately inflated or deflated. If multiple groups of chambers 172 are used, they may or may not be evenly or symmetrically arranged. For example, chamber groups may be separated according to the amount of weight-bearing associated with that area. For example, chambers 172 in greater weight bearing areas, such as the torso and hips, may be in a first group, while chambers 172 in areas bearing less weight, such as those supporting the head and legs, may be a separate group of chambers 172. In this way, the lighter portions of the patient's body may be supported by chambers 172 that are inflated to a lower air pressure than chambers 172 that support more weight/heavier body portions.
Chambers 172 may be secured to the adjacent chamber or to a base sheet or may be secured by the ends to an element running along each side of the mattress 3, and in some embodiments the chambers 172 and their connectors for fluid connection may be individually detachable. In this instance, if a single chamber 172 or connector fails or is damaged, it can be replaced without requiring the replacement of the entire inflatable heated mattress 3.
The material forming the chamber 170 or chambers 172, such as a plastic film, may be bondable with RF, ultrasound, heat, solvent, or other bonding techniques. The film or film layer of the laminate may be folded back on itself and a single longitudinal and two end bonds may cooperate to form an inflatable chamber 170, 172. More complex chamber construction and bonding embodiments are anticipated.
The conduit fluid connection for air flow to and from and between the inflatable chambers 172 may be plastic tubing, for example. The inlet into the inflatable chamber 172 can be through one of the bonded seams or may be through a surface of the chamber 172. To prevent occlusion of the tubing at the inlet, the tubing may extend one or more inches into the chamber. Other conduits are anticipated, such as a molded or inflatable plenum that may run the length of the heated mattress 3.
In some embodiments, a heater assembly 1 (such as a heater assembly 1 encased within a water resistant shell) is placed on top of the inflatable chambers 170, 172 so that the conductive fabric heating element 10 is at or near the top surface of the heated mattress 3. Alternately, a heater assembly 1 (without a shell) could be placed on top of the inflatable chambers 170, 172 so that the heating element 10 is at or near the top surface of the mattress. The heated mattress 3 may include a flexible, water resistant cover 160 that encases the heater assembly 1 and the inflatable chambers 170, 172.
In some embodiments, the water resistant mattress cover 160 is a plastic film laminated or extruded onto a woven or knit fabric such as “Naugahyde.” This construction is soft and durable. Alternately, the cover 160 can be made of plastic film, fiber-reinforced plastic film or a plastic film laminated or bonded to a woven, non-woven, or knit fabric.
The heater assembly 1 of the heated mattress 3 may be “free floating” within the water resistant cover 160 of the heated mattress 3. Alternately, the heater assembly 1 may be attached to the chamber 170 or chambers 172 or foam 150 or attached to the cover 160, either at the edges of the heater assembly 1 or on or across the top or bottom surface of the heating element 10.
One or more edges of the heater assembly 1, such as two or four edges, may be attached to the ends of the elongated inflatable chambers 172 by snaps, Velcro or any other suitable forms of attachment. Such embodiments maximally stabilize the heater assembly 1 within the heated mattress 3. A series of independent securing tabs or flaps may extend laterally from the bonds 48 of the heating unit shell 40. Where 2 to 4 tabs 140 may be sufficient to secure the heater assembly 1 to a surgical table as a mattress overlay, a series of tabs 40 that correspond with some or all of the inflatable chambers 172 may be desirable for anchoring the heater assembly 1 inside the inflatable heated mattress 3. As the inflatable chambers 170, 172 inflate and become turgid, they simultaneously stretch the heater assembly 1 laterally, assuring that the heating element 10 cannot wrinkle and fold on itself or become displaced.
The inflatable heated mattress 3 may include pressure sensor assemblies capable of detecting in real time the actual internal air pressure of the inflatable chambers 170, 172 and may also include a comparator which may be in operational communication with the controller for comparing a desired internal air pressure value of the inflatable chambers 170, 172 with the actual internal air pressure, and a pressure adjusting assembly, also in operational communication with the controller, for adjusting the actual internal pressure. The controller may be activated by active feedback data derived from the comparator for maintaining a desired internal pressure value in the inflatable chambers 170, 172 by adjusting the amount of inflation of the inflatable chamber 170 or of the groups of inflatable chambers, such as first and second groups of inflatable chambers 172.
The controller may be operationally connected to a first conduit and a second (or multiple) conduit and a pump for inflating the air chamber 170 or plurality of inflatable chambers 172. Each chamber 172 or plurality of chambers 172 may be independent of each other chamber 172 so that each chamber 172 may react to air pressure changes independently, or may be connected as a group and may react in concert with the air pressure changes in the other chambers 172 of the group. The air may be redistributed within the chambers 172 and the interface pressure may be maintained at any point on the top surface of each of the plurality of chambers 172 which is engaged with an anatomical portion of the user's body, at an average pressure below a capillary occlusion pressure threshold of 32 mm Hg, for example.
The optimal air pressure in the chambers may be predetermined, for example, at a pressure between about 0.4 and about 0.6 psi. The controller may add to or release air from the chambers, in order to maintain a stable and constant pressure in the chambers when the mattress is loaded with a patient. The predetermined pressure may be programmed into the controller or it may be selected by the operator.
Alternately, the controller may include an algorithm for determining the optimal air pressure in the chambers 170, 172, for each patient size, shape, weight and position, to achieve the maximal accommodation of the patient into the air chambers. Maximal accommodation occurs when the chambers 170, 172 are collapsed to a point where a maximal surface area is in contact with the patient and yet the protruding areas such as the patient's butt in the supine position or the hip and shoulder in the lateral position, are not “bottoming out” against the table below or other surface beneath the mattress. If the chambers 170, 172 are inflated more than is needed to support the patient, the patient effectively would be laying on the uppermost part of each over-inflated tubular chamber and is supported by a relatively small surface area. If the chambers 170, 172 are deflated too much, protruding parts of the patient would “bottom out” and be resting on the table or other surface. Both of these conditions result in significant and potentially dangerous pressure being applied to the patient's skin. The optimal air pressure is somewhere in between these two extremes, where the patient in the given position is maximally accommodated into the chamber without “bottoming out,” effectively floating.
One way to determine the amount of air pressure that is optimal for maximum accommodation is to inflate the chambers to a pressure that is expected to be greater than the optimal pressure, for example 1.0-1.5 psi. Then the air is released slowly, such as in increments, allowing time between each release for equilibration of the air in the chamber 170 or groups of chambers 172 if necessary, and an accurate measurement of the static air pressure in the chambers 170, 172 is then taken. The air release increment may be determined by the duration of time that air is released, for example 2-5 seconds. Alternately the air release increment may be determined by a measured volume of air released. The air release increment may be determined by a combination of time and pressure used to calculate and standardize the volume of air released with each increment. In some embodiments, the duration of air release lengthens as the air pressure decreases resulting in relatively similar volumes of air being released with each increment.
An algorithm which may be used by the controller to determine optimal air pressure, plots the curve of pressures for each sequential air release. The resulting plot has two phases: a first phase wherein the measured pressures decrease relatively rapidly and a second phase wherein the measured pressures decrease relatively slowly. The part of the curve represented by the first phase has a steeper downward slope and the part of the curve represented by the second phase has a more gradual downward slope. The first phase generally represents the over-inflated chambers with the patient supported by a relatively small upper surface area of the chamber. The second phase generally represents the patient sinking into the gradually collapsing chambers, wherein little additional surface area is enlisted with each additional incremental deflation. In the second phase, the patient is effectively “floating” to the maximal extent of the mattresses ability to accommodate the patient.
The controller can identify the pressure at which the pressure change transitions from the steep downward slope of the first phase, to the gradual downward slope of the second phase. The second phase may be identified by identifying a decreased or minimal pressure drop between two sequential air releases. For example, if a decrease of less than about 10% is detected between two sequential air releases, the controller may then stop the air releases and maintain that pressure as the optimal pressure. Depending on the design and sizes of the chambers and the amount of air released in each increment, the pressure drop indicating that the pressure is at the optional pressure may be less than from about 2 to 15% between increments, and may be identified by the air pressure drop between increments being significantly less than the air pressure drop in the first phase. When the second phase is first identified by recording a reduced or minimal pressure drop between sequential air release increments, the air pressure is near the optimal pressure and the controller may be programmed to maintain that air pressure. Alternately, when the first minimal difference in air pressures are detected with a subsequent air release, the controller may be programmed to release an additional predetermined amount of air or to re-inflate the air chamber with a predetermined amount of air.
A controller which may be used in various embodiments is shown in FIG. 29. The controller 182 may be included in a console 180. A shut off timer 184 and a power supply 186 may each be operatively coupled to the controller 182, meaning that the shut-off timer 184 can be a separate component, or the shut-of timer 184 and the controller 182 can have any other suitable functional relationship. The temperature sensor assembly 110 and over-temperature sensor assembly 115 can be configured to provide temperature information to the controller 182, which may act as a temperature controller. The controller may function to interrupt such power supply (e.g., in an over-temperature condition) or to modify the duty cycle to control the heating element 10 temperature. In embodiments including an inflatable support, an air pressure comparator (not shown) may be in operatively coupled to the controller 182, meaning, like the shut-off timer 184, the air pressure controller can be a separate component, or the air pressure controller and the controller 182 can have any other suitable functional relationship. The air pressure sensor assemblies can be configured to provide air pressure information to the controller 182, which may act as an air pressure controller.
In the foregoing detailed description, the invention has been described with reference to specific embodiments. However, it may be appreciated that various modifications and changes can be made without departing from the scope of the invention as set forth in the appended claims.

Claims

1. A heated underbody support comprising a heated mattress, heated mattress overlay, or heated pad, the heated underbody support comprising:

a heater assembly comprising:

a flexible heating element comprising a sheet of conductive fabric having a top surface, a bottom surface, a first edge and an opposing second edge, a length, and a width, wherein the sheet is comprised of threads separately and individually coated with an electrically conductive or semi-conductive material, and wherein the coated threads of the fabric are able to slide relative to each other such that the sheet is flexible and stretchable;

a first bus bar extending along the entire first edge of the heating element, the first bus bar adapted to receive a supply of electrical power;

a second bus bar extending along the entire second edge of the heating element; and

a temperature sensor; and

a layer of compressible material adapted to conform to a person's body under pressure from a person resting upon the support and to return to an original shape when pressure is removed, the layer located beneath the heater assembly and having a top surface and an opposing bottom surface, a length, and a width, wherein the length and width of the layer are approximately the same as the length and width of the heater assembly.

2. The heated underbody support of claim 1 wherein the conductive or semi-conductive material comprises polypyrrole.

3. The heated underbody support of claim 1 wherein the compressible material comprises a foam material.

4. The heated underbody support of claim 1 further comprising a water resistant shell encasing the heater assembly, the shell comprising an upper shell and a lower shell that are sealed together along their edges to form a bonded edge, wherein the heater assembly is attached to the shell only along one or more edges of the heater assembly.

5. The heated underbody support of claim 1 wherein the compressible material comprises one or more flexible air filled chambers.

6. The heated underbody support of claim 1 wherein the heating element has a planar shape when not under pressure, wherein, in response to pressure, the heating element is adapted to stretch into a 3 dimensional compound curve without wrinkling or folding while maintaining electrical conductivity, and wherein the heating element is adapted to return to the planar shape when pressure is removed.

7. A heated underbody support comprising a heated mattress, heated mattress overlay, or heated pad, the heated underbody support comprising:

a heater assembly comprising:

a flexible heating element comprising a sheet of conductive fabric having a top surface, a bottom surface, a first edge and an opposing second edge, a length, and a width;

a first bus bar extending along the first edge of the heating element, the first bus bar adapted to receive a supply of electrical power;

a second bus bar extending along the second edge of the heating element; and

a temperature sensor;

wherein the heating element has a planar shape when not under pressure,

wherein, in response to pressure, the heating element is adapted to stretch into a 3-dimensional compound curve without wrinkling or folding while maintaining electrical conductivity, and wherein the heating element is adapted to return to the planar shape when pressure is removed; and

a layer of compressible material which conforms to a patient's body under pressure and returns to an original shape when pressure is removed, wherein the layer of compressible material is located beneath the heater assembly.

8. The heated underbody support of claim 7 wherein the flexible heating element comprises a fabric coated with a conductive or semi-conductive material, the conductive or semi-conductive material comprising a carbon fiber or metal containing polymer or ink.

9. The heated underbody support of claim 7 wherein the flexible heating element comprises a fabric coated with a conductive or semi-conductive material, the conductive or semi-conductive material comprising a polymer.

10. The heated underbody support of claim 7 wherein the compressible material comprises a foam material.

11. The heated underbody support of claim 7 wherein the heater assembly is attached to the top surface of the layer of compressible material.

12. The heated underbody support of claim 7 further comprising a water resistant shell encasing the heater assembly, the shell comprising an upper shell and a lower shell that are sealed together along their edges to form a bonded edge.

13. The heated underbody support of claim 12 wherein one or more edges of the heater assembly are sealed into the bonded edge.

14. The heated underbody support of claim 12 wherein the heater assembly is attached to the upper layer of water resistant shell material.

15. The heated underbody support of claim 12 wherein the heater assembly is attached to the shell only along one or more edges of the heater assembly.

16. The heated underbody support of claim 12 further comprising an electrical inlet, wherein the inlet is bonded to the upper shell and the lower shell and passes between them at the bonded edge.

17. The heated underbody support of claim 7 wherein the compressible material comprises one or more flexible air filled chambers.

18. The heated underbody support of claim 7 wherein the heating element has a first Watt density when in a planar shape and a second Watt density when stretched into a 3 dimensional compound curve, and wherein the first Watt density is greater than the second Watt density.

19. The heated underbody support of claim 7 wherein the temperature sensor for monitoring a temperature of the heating element in located in contact with the heating element in a substantially central location upon which a patient would be placed during normal use of the support.

20. The heated underbody support of claim 7 further comprising a power supply and a controller for regulating a supply of power to the first bus bar.

21. A heated underbody support comprising a heated mattress having a first end and a second end, the heated underbody support comprising:

a heater assembly comprising:

a first bus bar extending along the first edge of the heating element;

a second bus bar extending along the second edge of the heating element;

at least one temperature sensor;

the first bus bar is adapted to receive electrical power from a power supply;

wherein the heating element has a planar shape when not under pressure,

wherein, in response to pressure, the heating element is adapted to stretch into a 3-dimensional compound curve without wrinkling or folding while maintain electrical conductivity, and wherein the heating element is adapted to return to the planar shape when pressure is removed;

a layer of compressible material which conforms to a patient's body under pressure and returns to an original shape when pressure is removed, wherein the layer of compressible material is located beneath the heater assembly;

an inflatable chamber positioned under the layer of compressible material; and

a flexible, water resistant cover that encases the heater assembly, the layer of compressible support material and the inflatable chamber.

22. The heated underbody support of claim 21 further comprising one or more additional inflatable chambers positioned under the layer of compressible material, wherein each of the inflatable chambers are elongated and have a longitudinal axis and are positioned side-by-side one another with their longitudinal axes extending substantially from the first end to the second end of the support.

23. The heated underbody support of claim 21 further comprising one or more additional inflatable chambers, wherein the inflatable chambers can each be inflated and deflated independently while the support is in use.

24. The heated underbody support of claim 21 further comprising one or more additional inflatable chambers, wherein the inflatable chambers can all be inflated and deflated simultaneously as a group while the support is in use.

25. The heated underbody support of claim 21 further comprising one or more additional inflatable chambers, wherein the inflatable chambers can be inflated and deflated in two or more groups while the support is in use.

26. The heated underbody support of claim 25 wherein the inflatable chambers can be inflated and deflated in two groups while the support is in use, and wherein the inflatable chambers are in alternating groups such that each inflatable chamber is in a different group from each inflatable chamber which is beside it.

27. The heated underbody support of claim 21 further comprising one or more additional inflatable chambers, each of the inflatable chambers belonging to one of two or more groups, and further comprising separate conduits to each group, each conduit providing independent fluid communication one groups of inflatable chambers for independently introducing or removing air from that group of inflatable chambers.

28. The heated underbody support of claim 27 further comprising:

a pressure sensor for measuring an actual internal air pressure of the groups of inflatable chambers; and

a controller including a comparator for comparing a desired internal air pressure for each group of inflatable chambers with the actual internal air pressure of each group inflatable chambers, the controller operatively connected to each of the conduits and to an air pump, the controller further including a pressure adjusting assembly for adjusting the actual internal pressure;

wherein the controller is adapted to cause inflation or deflation of each group of inflatable chambers to adjust the actual internal air pressure of each of the group of inflatable chambers toward the desired internal air pressure.

29. The heated underbody support of claim 27 wherein each inflatable chamber within each inflatable chamber is in fluid connection with every other inflatable chamber of its own group so that each air pressure changes in one inflatable chamber redistribute to all of the other inflatable chambers in the same group; and

wherein the an interface pressure is maintained on a top surface of each group of chambers at a location which supports a patient's body during normal use, the interface pressure being below a capillary occlusion pressure threshold of 32 mm Hg.

30. The heated underbody support of claim 21 further comprising a shell comprising two sheets of flexible surrounding the heater assembly, the shell comprising a water resistant plastic film or fiber reinforced plastic film, wherein the two sheets are sealed together near the edges of the heater assembly.

31. The heated underbody support of claim 21 including a power supply and controller for regulating the supply of power to the first bus bar.

32. A method of warming a person comprising:

positioning the person on a heated underbody support comprising a heated mattress, heated mattress overlay, or heated pad, the heated underbody support comprising:

a heater assembly comprising:

a first bus bar extending along the first edge, the first bus bar adapted to receive a supply of electrical power;

a second bus bar extending along a second edge;

a temperature sensor near the heating element;

wherein the heating element has a planar shape when not under pressure, and

wherein, in response to pressure from the person positioned on the support, the heating element stretches into a 3 dimensional compound curve without wrinkling or folding while maintain electrical conductivity;

a layer of compressible material located beneath the heater assembly; and

a flexible water resistant shell encasing the heater assembly;

activating the support; and

directing the support to maintain a desired temperature.