WO2003082175A1

WO2003082175A1 - Patient support structures

Info

Publication number: WO2003082175A1
Application number: PCT/EP2003/003441
Authority: WO
Inventors: Patrick Noel Daly
Original assignee: Rbf Industries Ltd
Priority date: 2002-04-02
Filing date: 2003-04-02
Publication date: 2003-10-09
Also published as: GB0207595D0; AU2003224026A1; GB2387113A

Abstract

A patient support structure such as a cushion or mattress comprises a body of supporting foam material (20) encapsulated by sheet material such as polyurethane to form a closed chamber. Pressure sensors (26) are disposed with the body of supporting foam material and a valve is provided to allow passage of air into and out of the chamber. An output device is connectable to the sensors and provides an audible or visual warning when the pressure sensors experience a predetermined pressure. When a patient is supported by the structure, the valve is opened gradually to allow the expulsion of air from the chamber until the predetermined pressure is reached and the warning signal is provided, at which point the valve is closed. The pressure is set to be the optimum for reducing the risk or occurrence of pressure sores in the patient.

Description

PATIENT SUPPORT STRUCTURES

The present invention relates to structures, in particular cushions and mattresses, for supporting patients, and especially for supporting patients who remain in substantially the same position for long periods of time. Such patients are vulnerable to the formation of pressure sores and ulcers. For example, in the case of a person confined to a sitting position, as in a wheelchair, much of the person's weight is concentrated in the regions of the ischia (or ischial tuberosities) and if the person has limited movement, the blood flow to the tissues in these regions becomes restricted. This limits the supply of nutrients to these regions and equally limits the transport of waste products away from these regions. Necrosis of the tissues can thereby result.

Conventional therapy for the avoidance of pressure sores and pressure ulcers (or the treatment of such sores and ulcers if formed), has relied on reducing the pressure on the patient by increasing the area of the sitting (or lying) surface underneath the patient, applying the equation Pressure = Force/ Area. This reduction is commonly achieved by means of a so-called floatation cushion which comprises a cushion in the form of a flexible closed chamber. The chamber is normally filled with air through a suitable valve. Before use, the chamber is inflated with air to a pressure which is greater than that thought to be required for the particular patient, and the patient is then seated on the cushion. Air is then released from the chamber through the valve so that the cushion achieves a greater conformity, and hence greater area of contact, with the patient. The valve is closed when the desired degree of deflation is achieved. Typically a cushion might be deflated until the ischia are within about 1 to 2cm or so of the base of the cushion.

Cushions of this type have certain disadvantages. For example, the cushion provides a highly displaceable surface which tends to "roll" or "float" the patient and so reduce the patient's stability. This is a particular problem if the patient lacks adequate strength or has certain deformities in the pelvis or thighs. In order to address this problem, cellular cushions have been developed which may, for example, include individual cells of different heights (see US 4 698 864) or in which the cells are divided into zones between which there is, in use, no fluid communication (see WO 92/07492), each zone nevertheless being at the same internal pressure as each other zone.

A further and more significant disadvantage lies in the fact that it is virtually impossible for a patient using the cushion, or for a therapist working with the patient, to know whether the cushion has been deflated to the extent necessary to achieve optimum pressure reduction and comfort. The present applicant believes that in the majority of cases, the cushions are not correctly adjusted, such that they are either over inflated or over deflated. If the cushion is over inflated, an excess pressure is exerted on the skin tissues which causes occlusion of the blood supply to the tissues with the consequences being pressure sore and ulcer formation as discussed above. If the cushion is deflated too far, the patient will "bottom out" and effectively be in contact with the underlying supporting surface (such as the wheelchair seat), again causing excess pressure on the tissues with occlusion of the blood supply leading to ulcer formation. Correct adjustment of the deflation of the cushion is therefore vital. It is this problem in particular which the present invention seeks to address.

According to a first aspect of the present invention, there is provided a support structure for a patient comprising:

(i) at least one closed chamber defined by a lower surface and a flexible upper surface; (ii) a valve for operably allowing passage of air into or out of the chamber; (iii) at least one body of supporting foam material disposed within the chamber; and (iv) at least one pressure sensor disposed within the body of supporting foam material and operative to provide an output in accordance with the pressure exerted by the foam material on the sensor.

In one preferred variation of the invention, the support structure is a cushion. In another preferred variation of the invention, the support structure is a mattress. In one preferred embodiment, the support structure comprises a plurality of closed chambers, each chamber including a valve, a body of supporting foam material and a pressure sensor disposed within the body of supporting foam material.

In another preferred embodiment, the support structure comprises a plurality of pressure sensors disposed in a body of supporting foam material.

Preferred pressure sensors include those which act as a variable resistor whose resistance decreases (or increases) as the sensor experiences greater applied force (in effect, pressure).

Preferably, the body of foam material comprises an open-celled foam, and in particular, a foam having a hardness in the range of 80 to 120 Newtons and a density in the range of from 15 to 30 kgm^' .

Most preferably, the body of foam material comprises a polyether polyurethane foam.

In a preferred construction according to the invention, the sensor is disposed in a pre- sliced cut in the body of foam material, said cut being nominally horizontal in the normal use position of the structure. Preferably, the sensors are disposed not more than about 15mm from the base of the structure.

Preferably, the support structure further comprises a base layer which is external to the closed chamber and most preferably comprises a moulded closed cell foam. The closed chamber and the base layer are preferably contained within a suitable cover.

In a particularly preferred construction, the closed chamber is defined by opposing polyurethane sheet layers, which sheet layers are heat welded together towards their edges to form the closed chamber. Preferably, the structure of the invention includes a housing for holding the valve, said housing communicating with the exterior and with the interior of the chamber. In a preferred construction, the housing is heat sealed between the margins of the polyurethane sheet layers.

According to a second aspect of the invention, there is provided an assembly comprising a support structure as defined in the first aspect of the invention and an output device removably connectable to a sensor of said support structure and responsive to the sensor output to provide a signal when a desired pressure is reached on deflation of the structure. Most preferably, the output device is adjustable by a user to vary the value of the desired pressure at which said signal is provided.

For a better understanding of the invention and to show how the same may be carried into effect, reference will now be made by way of example only, to the following drawings in which:

Figure 1 is a schematic plan view of a cushion according to the present invention; Figure 2 is a schematic end view of the cushion of Figure 1; Figure 3 is a section along the line A-A of Figure 1; Figure 4 is similar to Figure 3 showing the deformation of the cushion in use. Figures 5 and 6 show variations of the cushion according to the invention; and Figure 7 is a schematic illustration of a method of manufacture of a cushion according to the present invention.

Referring now in particular to Figures 1 to 4, the structure of the invention, illustrated in the form of a cushion 10, comprises a flexible upper surface 12 which is preferably of a polyurethane material and a lower surface 14 which is preferably also of the polyurethane material. The surfaces 12, 14 are heat sealed or heat welded together around their edges as at 16, forming a seam of about 8mm diameter, or as appropriate to the construction. The joined upper and lower layers or surfaces 12, 14 together define a closed chamber 18 which is substantially filled by a body of supporting foam material 20. The closed chamber communicates with the exterior by way of a valve 22 which in use is openable and closeable by the user. The valve 22 may be biased towards a closed position in which the chamber 18 cannot communicate with the exterior and from which a positive action is required by the user to open the valve 22.

Beneath the lower surface 14 a base layer 24 is provided. The base layer 24 is preferably formed from a durable material which assists in preventing puncturing of the lower layer 14 from below. A moulded closed cell polyethylene foam is suitable in this respect. (The base layer is omitted in Figures 3 and 4).

One or more pressure sensors 26 are provided in the body of supporting foam material 20. These sensors are shown in the illustrations substantially in the middle of the foam (with respect to its thickness), but this need not be so and the actual position can be chosen depending on, for example, the type of sensor 26, the nature of the foam material 20 and the particular intended end use of the cushion 10. In one preferred arrangement, two or more sensors 26 may be provided in one body of supporting foam material 20. In this way, the sensors 26 can be strategically placed in the body of supporting foam material 20 in order to provide maximum benefit for patients with particular medical conditions or disabilities. In another variation, a range of cushions may be produced each with only one sensor, but with the sensor placed in a different location in each cushion. For example, if the patient has a pelvic obliquity, the sensor or sensors can be positioned or adjusted to accommodate this. Sensors of different sizes and shapes may also be used in different locations to accommodate different patient needs.

In further variations as illustrated in Figures 5 and 6, the structure of the invention may comprise a number of distinct closed chambers(18a,18b, 18e,18f,18g) each with a body of supporting foam material 20, a valve 22 and preferably at least one sensor 26 (the sensors in chambers 18a and 18e are not shown). The individual chambers (18a,b,e,f,g) are formed by providing a weld (42a,42b.42c) between upper and lower layers (12,14). In this way, each particular zone of the structure (cushion 10) can be independently adjusted to suit particular patient needs and requirements. An output device 28 is provided for use with the structures (cushions 10) of the invention. The output device 28 is preferably small enough to be hand held and portable and is connectable to the pressure sensors 26 by suitable connecting leads 30, 32 by way of suitable connectors 34 (such as jack plugs and sockets 34a, b). In this way, the output 28 device may be connected to the sensors 26 only as and when required and a user may use a single output device 28 at different times with a number of different cushions 10. For example, the user may be a therapist working with a number of patients. The output device 28 processes the pressure-dependent signals produced by the pressure sensor or sensors 26 and may, for example, provide a numerical reading of the pressure experienced by the, or each, sensor. Alternatively, and preferably, the output device may simply produce an audible and/or visual signal when the pressure experienced by the sensor or by one of the sensors reaches a predetermined level. Preferably, the output device is adjustable so that the pre-determined level at which the signal is produced may be set by the user. This variability in the pressure experienced by the sensor (and therefore in the pressure experienced by the patient) is beneficial in selecting an appropriate treatment regime taking account of, for example, the patient's weight and particular medical condition. The output device 28 (and sensors 26) are preferably battery powered (e.g. from a 12N DC battery supply) but may be mains powered (via a suitable transformer, if necessary).

In use of the support structure (cushion 10) of the present invention, the user may first open the valve 22 to ensure that the cushion 10 is in its most expanded state. The cushion 10 may, for example, initially be in a partly compressed state from a previous use. With the valve 22 open, if the body of supporting foam material 20 was in a compressed state, the foam material 20 expands to its maximum configuration by virtue of its natural resilience, at the same time drawing air into the closed chamber 18 through the valve 22, by virtue of the open-celled nature of the foam material 20. When the foam material 20 reaches its most expanded state, the valve 22 is closed so that the chamber 18 is no longer in communication with the exterior. The cushion 10 is then placed in its position of use and the patient is seated on the cushion. The output device 28 is connected to the sensor or sensors 26 at an appropriate point prior to this stage. When the patient is appropriately seated, the valve 22 is opened to slowly release air from the cushion 10 (i.e. from chamber 18). The body of supporting foam material 20 is gradually compressed by the action of the patient's weight and, as illustrated in Figure 4, and the cushion 10 conforms to the shape of the patient 36. This increases the area of contact of the cushion 10 and so reduces the pressure experienced by the patient 36. During this time, the output device 28 monitors the signals from the pressure sensor or sensors 26.

As more air is released, the body of supporting foam material 20 is compressed to a greater extent so that the pressure sensor or sensors 26 experience an increasing pressure and send appropriate pressure related signals to the output device 28. When the pressure experienced by the sensor or sensors 26 reaches a pre-determined desired level, this is detected by the output device 28 on the basis of the signals from the sensor or sensors 26 and the output device emits an audible and/or visual warning signal. At this point the user closes the valve 22 so that the chamber 18 is again closed with respect to the exterior. The output device 28 may then be disconnected from the cushion 10 so that the cushion 10 can be used independently of the output device 28 until such time as any further adjustment of the cushion 10 might be required.

The pre-determined pressure at which the output device 28 should emit its warning signal may be determined by the therapist in accordance with the particular clinical needs of the patient, and the settings of the output device adjusted accordingly. In this way, the pressure reduction experienced by the patient is much more accurately determined with much reduced scope (or no scope) for over inflation or under inflation of the cushion 10. It also becomes much easier to consistently set the inflation level correctly for any particular patient each time the cushion 10 is used. Another benefit of the structure according to the present invention is its ease of manufacture. The method of manufacture is illustrated schematically with reference to Figure 7 which shows a body of supporting foam material 20 incorporating a sensor or sensors 26. First and second sheets of heat sealable material (12a, 14a), preferably of a polyurethane, which form the upper and lower surfaces (12, 14) of the cushion 10 are disposed respectively above and below the body of supporting material 20. A valve housing 38 is disposed at a convenient point at an edge of the lower sheet of heat sealable material 14a, as are connectors 34b, the leads 30, 32 of which run through the body of supporting foam material to the sensor(s) 26. Heated press platens 40a, b are disposed respectively above and below the above described components (20, 26, 12a, 14a) and are moveable in a substantially vertical direction (in the plane of the paper as illustrated) from the open configuration shown in Figure 7 to a closed configuration in which the sheets of heat sealable material 12a, 14a are held by formations 40c on the platen 40a together with platen 40b and are thereby heat sealed, encapsulating the body of supporting foam material 20, the valve housing 38 and the connectors 34b. The base layer 24 may be applied subsequently, and a valve 22 is seated in the valve housing 38.

The choice of material used for the body of supporting foam material 20 is important. If the foam material 20 is too dense, the sensors 26 may reach their predetermined pressure too early so that the output device 28 would then give its warning signal too early, that is, before the cushion 10 was sufficiently deflated to achieve the desired pressure reduction for the patient. Conversely, if the foam material 20 is too open- celled or insufficiently dense, the sensor(s) 26 may reach their predetermined output pressure too late so that the output device 28 would give its warning signal too late, that is, when the cushion 10 has been deflated too far. The choice of foam to meet these criteria is, on the basis of the present specification, a matter of simple testing by a person skilled in the art. However, the applicant believes that it is preferable to use an open celled foam such as a polyether polyurethane foam having a density of about 15 to 30 kgm^"3 (more preferably 22 to 25 kg^"3) and having a hardness of about 80 to 120 Newtons (more preferably about 100 Newtons). The sensors 26 used in the present invention are well known and widely available, so that the skilled person can select a suitable sensor from those on the market. A typical sensor might have a size in the range of from about 2.5 cm square to about 20 cm square. In another variation, the sensors may have a rectangular shape having the longer side of the rectangle arrange generally parallel to the lateral direction of the cushion in use. Preferably the sensor or sensors 26 is/are placed towards the base of the body of supporting foam material 20, for example not more than about 1.5 cm from the base, more preferably about 1 cm from the base.

As indicated above, preferred sensors act as variable resistors and in a particularly preferred construction the sensor essentially comprises first and second sheets of printed substrates laminated together. A double sided adhesive die cut spacer is disposed between the first (conductor) substrate and the second (polymer link) substrate and serves two purposes, that is, holding the two active faces of the substrates slightly spaced apart and also bonding the whole sensor construction together. Sensors of this type are known as Force sensor array systems (FSR) or linear potentiometers (linpots) and are ideal for sensing seat occupancy using both pressure and position. These devices can be sensitive to 0.05mm. Typically, for a pressure sensor used in the structure according to the invention, a human sitting on the cushion with the sensor therein will apply a force anywhere between 0.1N to 10 N. This will cause the sensor to alter resistance continuously over a range of from 1 MegaOhm (MΩ) to around 2kiloOhm (kΩ). This type of sensor is an ideal sensor to semi-quantitatively assess pressure and position within the cushion. The sensors are also inexpensive, thin (0.15mm), durable (10 million actuations), insensitive to vibration and environmentally resistant. The output device 28 may for example measure the voltage across the sensor 26 which, for a given current will vary in accordance with the variation of the resistance of the sensor 26.

The choice of a polyurethane material for the upper (and lower) surfaces 12, 14 is important in that this material can imitate the natural tension in the skin, thereby reducing shear forces on the skin. Such shear forces also contribute to the formation of pressure sores and ulcers. The patient support structure (cushion, mattress or the like) according to the present invention provides effective therapy for the prevention and treatment of pressure sores and ulcers which is extremely simple, reliable and accurate in use. The invention avoids the complexity of prior art systems which rely on pneumatic inflation of the cushion and therefore require additional pumps, air lines and switching systems, so adding complexity and cost and reducing reliability. Such pneumatic systems require the air pump to be supplied with (but detachable from) the cushion so that the cushion may be periodically manually inflated and re- adjusted, or the air pump may be permanently attached in order for the pump to supply and alternate the pressure in order to provide continuously moving pressure points. This is often uncomfortable for the patient.

By dispensing with the complexity of manual pumping and electrically driven pneumatic systems, the patient is provided with a simple and convenient cushion which, when the correct pressure has been set, does not require any ancillary equipment to maintain that pressure. The output device can be disconnected after the correct pressure has been set so that, for example, a therapist such as a district nurse can carry a single output device for use with each patient who is visited by the therapist. For wheelchair use, the absence of air tubes or wires connected to the cushion, which could become entangled in the wheelchair is a clear advantage.

Although the present invention has principally been described in connection with a cushion 10, such as for wheelchair use, the structure of the invention is equally applicable to a mattress or the like, or for forming specific parts of a mattress where, in relation to a patient lying on the mattress, the occurrence of pressure sores and ulcers is most likely.

Claims

1. A support structure for a patient comprising:

(i) at least one closed chamber defined by a lower surface and a flexible upper surface

(ii) a valve for operably allowing passage of air into or out of the chamber; (iii) at least one body of supporting foam material disposed within the chamber; and (iv) at least one pressure sensor disposed within the body of supporting foam material and operative to provide an output in accordance with the pressure exerted by the foam material on the sensor.

A structure as claimed in Claim 1 comprising a cushion.

A structure as claimed in Claim 1 comprising a mattress.

4. A structure as claimed in any preceding claim comprising a plurality of closed chambers, each chamber including a valve, a body of supporting foam material and a pressure sensor disposed within the body of supporting foam material.

5. A structure as claimed in any of Claims 1 to 3 comprising a plurality of pressure sensors disposed in a body of supporting foam material.

6. A structure as claimed in any preceding claim wherein the body of foam material comprises an open celled foam.

7. A structure as claimed in any preceding claim wherein the body of foam material comprises a foam having a hardness in the range of 80 to 150N.

8. A structure as claimed in any preceding claim wherein the body of foam material comprises a foam having a density in the range of from 15 to 30 kgm^"3.

9. A structure as claimed in any preceding claim wherein the body of foam material comprises a polyether polyurethane foam.

10. A structure as claimed in any preceding claim wherein the sensor is disposed in a pre-sliced cut in the body of foam material, said cut being nominally horizontal in the normal use position of the structure.

11. A structure as claimed in Claim 10 wherein the sensors are disposed not more than 15 mm from the base of the structure.

12. A structure as claimed in any preceding claim further comprising a base layer which is external to the closed chamber.

13. A structure as claimed in claim 12 wherein the base layer comprises a moulded closed cell foam.

14. A structure as claimed in any preceding claim wherein the closed chamber is defined by opposing polyurethane sheet layers, which sheet layers are heat welded together forwards their edges to form the closed chamber.

15. A structure as claimed in any preceding claim including a housing for holding the valve, said housing communicating with the exterior and with the interior of the chamber.

16. A structure as claimed in Claim 15 when dependent on Claim 14 wherein the housing is heat sealed between the margins of the polyurethane sheet layers.

17. An assembly comprising a support structure as claimed in any of Claims 1 to 16 and an output device removably connectable to a sensor of said support structure and responsive to the sensor output to provide a signal when a desired pressure is reached on deflation of the structure.

18. An assembly as claimed in Claim 17 wherein the output device is adjustable by a user to vary the value of the desired pressure at which said signal is provided.

19. A support structure as hereinbefore defined with reference to any of Figures 1 to 6.

20. A method of treating a patient having, or at risk of having, pressure sores or ulcers, the method comprising (i) providing a support structure as claimed in any of Claims 1 to 15;

(ii) connecting an output device to the sensor or sensors of the support structure, said output device being operative to provide a warning signal when said sensor or sensors experience a predetermined pressure; (iii) supporting the patient on the support structure;

(iv) opening the valve to release air from the closed chamber of the support structure until the output device provides the warning signal; (v) closing the valve; and (vi) optionally disconnecting the output device from the support structure.