US3806102A

US3806102A - Medical humidifier

Info

Publication number: US3806102A
Application number: US00264694A
Authority: US
Inventors: J Valenta; A Cibulka; S Drabkin
Original assignee: ARIRCO Inc
Current assignee: ARIRCO Inc
Priority date: 1972-06-20
Filing date: 1972-06-20
Publication date: 1974-04-23
Anticipated expiration: 1991-04-23
Also published as: GB1401399A; CA1003325A; JPS4957692A; IT994884B; FR2189085B1; FR2189085A1

Abstract

A humidifier for use with a medical respirator having a hot plate type of heating unit entirely separable from a water reservoir which heats the water within the reservoir. The reservoir is provided with an inlet for receiving gas from the respirator and an outlet for delivering heated humidified gas to a patient and a bubble chamber partially submersed in the heated water intermediate the inlet and the outlet and which forms tiny discrete bubbles to be expelled through the water to humidify the gas. A valve means is provided to prevent water in the humidifier from being forced upstream into the respirator yet the valve means introduces relatively minor back resistance to the patient in the event of a cough.

Description

United States Patent 1191 Valenta et a1.

1451 Apr. 23, 1974 MEDICAL HUMIDIFIER [75] Inventors: James D. Valenta, Madison;

Anthony B. Cibul ka, Poynette, both of Wis.; Stephen H. Drabkin, Woodbridge, Conn. [73] Assignee: Airco jlhc, New York, NY.

[22] Filed: June 20, 1972 [21] Appl. No.: 264,694

[52] US. Cl 261/142, 128/193, 261/122 [51] Int. Cl. ..F02m 15/04 [58] Field of Search 261/142, 122, 126, 78 A; 128/186, 188, 194, 198, 192; 219/280, 432, 283, 310, 311, 312, 362, 401; 239/338 [56] References Cited UNlTED STATES PATENTS 3,744,771 7/1973 Deaton 261/78 A 3,724,454 4/1973 Brown 128/194 3,638,926 2/1972 Melville et al.... 128/192 X 3,434,471 31 9 9 Liston 128/192 x 2,709,577 5/1955 Pohndorf et al. 239/338 x 2,522,718 9/1950 2,166,574 7/1939 Adolphsen 261/122 X FOREIGN PATENTS-OR APPLICATIONS 1,092,612 11/1960 Germany ..128/194 Primary ExaminerAndrew R. Juhasz Assistant ExaminerW. R. Briggs Attorney, Agent, or Fir mRoger M. Rathbun; H. Hume Mathews; Edmund W. Bopp [57] ABSTRACT A humidifier for use with a medical respirator having a hot plate type of heating unit entirely separable from a water reservoir which heats the water within the reservoir. The reservoir is provided with an inlet for receiving gas from the respirator and an outlet for delivering heated humidified gas to a patient and a bubble chamber partially submersed in the heated water intermediate the inlet and the outlet and which forms tiny discrete bubbles to be expelled through the water to humidify the gas. A valve means is provided to prevent water in the humidifier from being forced upstream into the respirator yet the valve means introduces relatively minor back resistance to the patient in the event of a cough.

17 Claims, Drawing Figures 111' 1 j 76 v l s 9 111 A I 4 54 Q 44 66 a0 1: 82 l L5 84 60 e S M PATENTEBAPR 23 1574' 3.8061102 SHEET 1 BF 2 FIG.1

PATENTED APR 2 3 I974 SHEET 2 [IF 2 FIG.3.,

FIGA

MEDICAL HUMIDIFIER BACKGROUND OF THE INVENTION This invention relates to a medical respirator apparatus and, more particularly, to a humidifier for receiving gas from a respirator and heating and humidifyin'g that gas in order to deliver a warm, saturated gas to the patient.

Humidifying devices are often associated with medical respirators in order to introduce a predetermined amount of liquid to the gas supplied to the patient as well as to heat the gas to or near the patients body tem perature. It is particularly important to heat and humidify the gas to the patient when a tracheotomy tube is employed for any considerable period of time. In such case, the gas from the respirator is introduced directly into the patients trachea, thereby bypassing the patients nasal passages which normally both heat and humidify air during inhalation.

Various types of humidifiers have been used in the past and some included a hot plate type of heating unit which underlies and provides heat to a water reservoir compartment yet is removable therefrom without draining the water from the reservoir.

In addition, various types of bubble chambers have been used which, in effect, receive the gas from the respirator and cause it to bubble up through heated water to humidify and heat the gas for introduction to a patient.

As a further feature in humidifiers it is advantageous to provide a valve means to prevent water within the humidifier reservoir from inadvertently being forced backward into the respirator itself, where, in such instance a loss of functioning of the respirator could occur temporarily, or even permanently, cutting off the source of life sustaining oxygen to the patient. To this end, check valves have been located in the humidifier to prevent the backflow of water, such as could commonly occur by the patient coughing to force air back into the reservoir. The normal location of such a check valve in prior art devices has, however, generally cut off all return flow of gas from the patient so that extreme discomfort would occur to the patient in his coughing into a closed system.

The precise location of this check valve is further critical in the event that the humidifier is inadvertently placed into the respiration system in an incorrect manner, that is, the humidifier inlet is connected to the patient circuit while the humidifier outlet is joined to the respirator. In this event, the check valve may well prevent any flow at all through the humidifier, thus the patient, until the error is discovered and corrected, may not be receiving any oxygen enriched gas from the respirator.

Also, a further desired feature in humidifiers utilized with some respirators, is a through passage which, in effect, allows some direct communication between the humidifier inlet and its outlet. The purpose of this passage is to allow a patient triggered respirator upstream of the humidifier to instantaneously and positively sense any attempt by the patient to inhale, whereupon the respirator can be triggered to switch into its inhala tion phase.

SUMMARY OF THE INVENTION The present invention provides a combination of desirable features, including economical construction and convenient assembly and disassembly. The humidifier is quickly and easily disassembled for cleaning, yet is efficient in use and adequately humidifies and heats the gas from a respirator to be introduced to the patient. A separable hot plate type of heater is used to underlie and support a water reservoir in good heat transfer relationship therewith. The heater is adjustable to maintain the water at a desired elevated temperature to control the amount of heat and humidification. Further, inasmuch as the heater is completely isolated from the patient circuit, it does not require special cleansing or sterilization after use with each patient. In addition, because the heater completely underlies the water reservoir, a relatively large surface area heater us utilized and overall heater temperatures may be maintained at relatively low values and still adequately humidify and heat the gas to body temperature.

A bubble chamber lies partially submerged within the level of water normally occupying the water reservoir. The bubble chamber receives the gas from the respirator and channels the gas through a plurality of small apertures to form finely dispersed bubbles, which rise through the heated water to the surface. The gas, thus heated and humidified leaves the humidifier through an outlet in the water reservoir to the patient. A valve means is located within the gas 'flow passages of the humidifier such that water within the humidifier reservoir cannot be forced back into the respirator. At the same time, the valve means does not prevent the reverse flow of gas from the patient, that is, if the patient coughs, the return flow of gas does not meet a blocked passage in the humidifier to cause discomfort in the patient. Instead, the valve means allows this gas from the patient to continue through the humidifier to be eventually dissipated in the upstream passages.

As a safety feature, the valve means allows gas to pass through the humidifier in the event the humidifier is inadvertently connected into the respirator circuit in reverse position, i.e., the humidifier inlet in connected to the patient circuit and, correspondingly, the humidifier outlet is connected to the respirator. In this incorrect circuit connection, the present humidifier does not block flow to the patient which could result in immediate harm, but allows the free flow of gas from the respirator to the patient, however, the gas will not be heated or humidified. The connection error can safely be recognized by observing the temperature of gas entering the patient and necessary steps to alleviate the situation taken without great harm to the patient.

The present humidifier also includes a bleed passageway which allows direct communication between the humidifier inlet and its outlet. This passageway allows a patient triggered respirator to be utilized wherein the patient inhalation sensing device may be upstream of the humidifier. As the patient attempts to inhale, the slight vacuum which is drawn is immediately communicated through the humidifier to the respirator sensing means whereby the respirator can react by switching to its inhalation phase.

The assembly and disassembly of the humidifier is accomplished with relative ease. The water reservoir and hot plate heater are separable and are held in good heat conductivity by a single securing means which is easily removable to separate the units. The bubble chamber is secured in place by fairly simple means and its complete disassembly for servicing or cleaning can be accomplished with ease.

BRIEF DESCRIPTION OF THE DRAWINGS.

FIG. 1 is a side elevational view of-the humidifier constructed in accordance with the present invention.

FIG. 2 is a plan view from above FIG. 1. FIG. 3 is a vertical cross-sectional view of the water reservoir removed from the completed assembly 'of FIG. 1.

FIG. 4 is a vertical cross-sectional view of the plate heater utilized with the present invention.

SPECIFICATION Referring to FIGS. 1 and 2, there is shown a humidifier having a heater 12 and a reservoir 14. As shown, the heater 12 is of the electrical hot plate type which is adapted to underlie and support the reservoir 14 when the humidifier 10 is assembled. The heater 12 is adapted to be connected to a conventional electrical source, not shown, such as 110 volt AC potential through the power cord 16. A control means may be conveniently located in the base of the heater 12 to vary the temperature of the heater l2 and preferably includes a projecting knob 18 having printed indicia thereupon to indicate the precise location of the control and direction of rotation to increase or decrease the heat output of the heater 12.

An inlet 20 introduces gas from the respirator to the reservoir 14 and is shaped in a circular upstanding projection to be connected to conventional tubing, not shown, conveying the gas from the respirator. An outlet 22 is provided, similarly shaped as inlet 20, and serves to be easily connectible to conventional tubing for conveying the heated humidified gas from the humidifier 10 to the patient circuit.

The reservoir 14 is firmly attached to the heater 12 by a tie bolt 24 which extends through the interior of reservoir 14 and is screwed to the heater 12 such that the reservoir 14 may be easily and conveniently removed for cleaning and the like. When the humidifier 10 is assembled, the tie bolt 24 assures that some force holds the reservoir 14 firmly against the heater 12 to insure that good thermal conductivity exists, as will be later explained. I

Turning now to FIG. 4, there is shown, in crosssection, the heater 12 utilized with the present invention. Basically the heater 12 is of conventional design comprising a hot plate 26 in which there is embedded a resistance heating element 28 providing an overall generally constant temperature of the heating surface 30. A bottom cover plate 32 is affixed to the hot plate 26 by means such as a screw 34 and covers the internal wiring, not shown. A high temperature cut-out 36 abuts the undersurface of the hot plate 26 and serves as a safety device to terminate electrical power to the resistance element 28 in the event its temperature exceeds a predetermined maximum value. An adjustable thermostat 38 also abuts the undersurface of the hot plate 26 and controls the temperature of the hot plate 26 within a predetermined range. External control of the thermostat 38 is afforded by means of shaft 40 which extends through the bottom cover plate 32 to be controlled by the projecting knob 18. A threaded hole 42 is provided in the heating surface and is generally located at or near the center of the surface 30, the purpose of which will be later explained.

With reference to FIG. 3, the reservoir 14 utilized with this invention comprises a housing 44 preferably of a molded transparent plastic such as polypropylene. The inlet 20 and outlet 22 may be formed into housing 44, each of which communicate with the interior thereof. A water chamber 46 is formed within housing 44 when the bottom plate 48 is operatively positioned as shown. The bottom plate 48 is formed of a good heat conducting material such as brass and has joined thereto an upwardly extending hollow tubing 50 which extends through the top of the housing 44 through a hole 52 formed therein. The tubing 50 is firmy affixed to bottom plate 48 such as by a threaded connection which is further soldered to insure a watertight joint around the external circumference of the tubing 50. An O-ring 54 seals the tubing 50 within hole 52. The upper end of tubing 50 is provided with screw threads which are adapted to receive a nut 56 which, when tightened onto the tubing 50, secures the bottom plate 48 firmly to the housing 44 containing therein the water chamber 46. A sealing gasket 56 surrounds the outer periphery of the bottom plate 48 to seal against a downwardly directed circular projection 58 of the housing 44.

Within the water reservoir 14 there is positioned a bubble chamber assembly 60. The bubble chamber assembly 60 includes a bubble chamber housing 62 having external threads 64 which are adapted to be screwedinto'internal threads 66 formed in the housing 44. By this means the bubble chamber housing 62 is suspended firmly from housing 44 within the overall reservoir 14. A bottom cover 67 is affixed to the bubble chamber housing 62, preferably by being screwed into the bubble chamber housing 62 by mating threads at 68.

-Within the bubble chamber housing 62 there is formed a diffuser inlet passage 69 which receives gas from the inlet 20. The diffuser inlet passage 69 extends downwardly and terminates at a distance above the bottom cover 67. A diffuser 70 extends from the periphery of the diffuser inlet passage69 at the bottom end thereof to the lateral inner peripheral surface of the bubble chamber housing 62, forming a lower chamber 72 within the bubble chamber housing 62. The diffuser may be of plastic construction having a large plurality of small closely-spaced holes therein. A plurality of apertures 74 are formed in the bubble chamber housing 62 generally toward the upper portion thereof.

A valve means is provided in the bubble chamber housing 62 and, as shown, comprises a plurality of valve apertures 76 radially oriented about the top of the housing 62. A resilient disc 78 covers each of the valve apertures 76 and is affixed to housing 62 at its internal circumference. In practice the disc 78 may be easily assembled by being snapped into a circular recess 80 in the bubble chamber housing 62. A bleed orifice 82 extends from inlet passage 69 to allow direct communication between the inlet passage 69 to the outlet 22 through apertures 74.

In the operation of the humidifier, the reservoir 14 is filled to within a predetermined level range with water, generally to a level as indicated by the dashed line 84. The heater 12 is turned on and its temperature adjusted by knob 18 to a predetermined value in order to bring the temperature of the water up to its desired temperature. After attaining this temperature, the heater thermostat 38 maintains that temperature relatively constant or stable. Gas, such as oxygen or oxygen enriched air, is caused to enter the inlet 20 at a positive pressure from a respirator. The gas continues downwardly through the diffuser inlet passage 69 and is forced through the water into the lower chamber 72 and bubbles upwardly through the diffuser 70 which causes a plurality of minute bubbles to be formed which bubble up through the warm water, causing the bubbles of gas to be warmed as well as humidified. The gas is thus heated and humidified as it reaches the surface of the water within the bubble chamber housing 62 where it is caused to pass through the apertures 74 into the upper interior of the reservoir 14 and leaves the humidifier through outlet 22 to the patient circuit. Thus, the gas from the respirator is both heated and humidified as it passes through the humidifier to the patient.

In the event the humidifier is inadvertently connected within the circuit in a manner opposite of that intended, that is, humidifier outlet 22 is connected to the respirator and the inlet is connected to the patient circuit, the humidifier valve means provides a safety feature by allowing the free flow of gas from outlet 22 through apertures 74 and out through the inlet 20 via the valve apertures 76. The resilient disc 78 acts as a check valve which freely allows the flow of gas in the direction from outlet 22 to inlet 20. This is not only a safety feature to allow reverse flow if the humidifier is incorrectly installed, but the resilient disc 78 also allows a reverse flow of gas during normal operation which may occur by the patient coughing. The resilient disc 78 freely allows backflow of gas through the valve apertures 76 so that the patient does not feel discomfort by coughing into a dead ended space.

Since the reservoir 10 may be used with a respirator having a patient triggering control, an open passageway is provided between the outlet 22 and the inlet 20 by a small bleed orifice 82. An attempt by the patient to inhale is thereby signaled directly through the reservoir 10 through the outlet 22, apertures 74 and then to the inlet through orifice 82 to a sensing means upstream of the reservoir 10. Thus, a patient triggering means, responsive to a minute vacuum drawn as the patient com mences inhalation, can be located at the respirator and yet the patient vacuum drawn is rapidly transmitted directly through the reservoir.

Thus, there is provided a unique, easily disassembled reservoir having a reservoir which is separable from the heating unit for ease of cleaning. The reservoir protects the reverse flow of water upstream into the respirator or other apparatus, yet allows a backflow of gas from the patient for comfort in the event of coughing. As a safety feature, the reservoir may be incorporated into the respirator patient circuit in the reverse of its intended flow position, yet the flow of gas to the patient is not interrupted so that the patient still receives lifesustaining oxygen.

Further, the reservoir, when in operation, allows free use of patient triggering devices to control the respirator.

We claim:

1. A humidifier for heating and humidifying gas received from a medical respirator and delivering the gas to a patient circuit, comprising in combination:

a reservoir adapted to contain a quantity of water; heating means underlying and supporting said reservoir, said means being adapted to maintain the water in said reservoir at a predetermined elevated temperature;

an inlet in said reservoir for normally receiving gas from said respirator and an outlet in said reservoir for normally delivering gas to said patient circuit;

bubble chamber means within said reservoir connected to said inlet and defining a normal first gas flow path between said inlet and outlet which at least partially passes through the water in said reservoir, whereby to heat and humidify said gas;

said bubble chamber means including normally closed check valve means positioned in said chamber means to define a second gas flow path in the direction between said outlet and inlet, said second flow path bypassing said water, and said check valve being opened to establish said second flow path by gas pressure at said outlet exceeding the gas pressure at said inlet.

2. Apparatus in accordance with claim 1 further including bleed orifice means providing direct communication between said reservoir inlet and outlet, whereby patient triggering of devices at said respirator is enabled.

3. Apparatus in accordance with claim 1 wherein said bubble chamber means includes a diffuser inlet passage connected to said reservoir inlet and passing downwardly to a point beneath the water level of said reservoir, a lower chamber for receiving the gas flow from said passage and a chamber housing concentric with said passage and connected thereto through a diffuser plate, said housing being provided with a plurality of first openings permitting gas flow toward said reservoir outlet.

4. Apparatus in accordance with claim 3 further including a bleed orifice in the wall defining said diffuser inlet passage at a point above the water level of said reservoir, said orifice connecting into the space between said passage and concentric housing thereby providing a direct flow path between said reservoir inlet and said plural openings of said bubble chamber housing, whereby pressure changes at said patient circuit may be directly communicated to said reservoir inlet to provide triggering of devices thereat.

5. Apparatus in accordance with claim 3 wherein said check valve means comprises a plurality of second openings at the upper portion of said bubble chamber means, said openings communicating with said reservoir inlet; and flexible flapper valve means biased against said openings from the sides adjacent said reservoir inlet, normally maintaining said openings in their closed condition; said second openings communicating directly with said first openings to enable a backflow path between said reservoir outlet and inlet.

6. Apparatus in accordance with claim 5 wherein said biasing force is sufficiently small as to enable said backflow path upon coughing or similar disturbance at said patient circuit.

7. A humidifier for use with a heating plate in the heating and humidifying of gas received from a medical respirator, for delivery of said gas to a patient circuit, comprising in combination:

a reservoir adapted to contain a quantity of water,

and including a liquid-tight chamber and a bottom plate adapted for thermal engagement with said heating plate;

8. Apparatus in accordance with claim 7 further including bleed orifice means providing direct communication between said reservoir inlet and outlet, whereby patient triggering of devices at said respirator is enabled.

9. Apparatus in accordance with claim 7 wherein said bubble chamber means includes a diffuser inlet passage connected to said reservoir inlet and passing downwardly to a point beneath the water level of said reservoir, a lower chamber for receiving the gas flow from said passage and a chamber housing concentric with said passage and connected thereto through a diffuser plate, said housing being provided with a plurality of first openings permitting gas flow toward said reservoir outlet.

10. Apparatus in accordance with claim 9 further including a bleed orifice in the wall defining said diffuser inlet passage at a point above the water level of said reservoir, said orifice connecting into the space between said passage and concentric housing thereby providing a direct flow path between said reservoir inlet and said plural openings of said bubble chamber housing, whereby pressure changes at said patient circuit may be directly communicated to said reservoir inlet to provide triggering of devices thereat.

11. Apparatus in accordance with claim 9 wherein said check valve means comprises a plurality of second openings at the upper portion of said bubble chamber means, said openings communicating with said reservoir inlet; and flexible flapper valve means biased against said openings from the sides adjacent said reservoir inlet, normally maintaining said openings in their closed condition; said second openings communicating directly with said first openings to enable a backflow path between said reservoir outlet and inlet. I

12. Apparatus in accordance with claim 11 wherein said biasing force is sufficiently small as to enable said backflow path upon coughing or similar disturbance at said patient circuit.

13. A humidifier for heating and humidifying fluid received from a medical respirator and delivering the fluid to a patient circuit, said humidifier comprisinga reservoir adapted to contain a quantity of water, heating means underlying and supporting said reservoir,

said heating mean adapted to maintain the water in said reservoir at a predetermined elevated temperature, an inlet in said reservoir for receiving fluid from the respirator and an outlet in said reservoir for delivering-fluid to the patient circuit, a bubble chamber within said reservoir intermediate said inlet and said outlet adapted to heat and humidify fluid flowing between said inlet and siad outlet, said bubble chamber including normally closed check valve means positioned in said chamber to define a second gas flow path in the direction between said outlet and inlet, said second flow path bypassing said water, and said check valve being opened to establish said second flow path by gas pressure at said outlet exceeding the gas pressure at said inlet, and securing means passing vertically centrally through said reservoir and secured to said heating means whereby said reservoir is securely affixed to said heating means.

14. A humidifier as defined in claim 13 werein said securing means comprises a tie bolt extending through the interior of said reservoir, said tie bolt being threadedly engaged to said heating means whereby said reservoir is easily completely disconnectable from said heater means.

15. A reservoir comprising a housing bottom plate, secured to housing containing therein a liquid-tight chamber, a tubing means upwardly extending through said housing affixed to said bottom plate, a bubble chamber suspended from cover plate within reservoir,

inlet means for introducing fluid to bubble chamber, outlet means in cover plate for receiving fluid within reservoir, check valve means adjacent the inlet located in parallel with the flow of fluid through said bubble chamber and adapted to pass fluid uni-directionally from said outlet to said inlet, bypassing said bubble chamber, bleed orifice providing direct communicatio between said inlet and said outlet.

16. A humidifier for heating and humidifying fluid received from a medical respirator, said humidifier comprising a reservoir adapted to contain a quantity of water, heating means associated with said reservoir adapted to maintain the water at a predetermined temperature, inlet means in said reservoir for receiving fluid from the respirator, a bubble chamber in said reservoir adapted to receive fluid from said inlet and cause the fluid to bubble through the water thereby heating and humidifying the fluid, outlet means in said reservoir for receiving the heated and humidified fluid for delivery to a patient circuit, check valve means located in parallel with the flow of fluid through said bubble chamber and adapted to pass fluid uni-directionally from said outlet to said inlet when the pressure in said outlet is greater than the pressure in said inlet whereby fluid may freely flow from said outlet to said inlet, bypassing said bubble chamber.

17. A humidifier as described in claim 16 wherein said check valve comprises a resilient ring normally covering a plurality of radially oriented apertures, said ring adapted to be displaced by a positive flow of fluid from said outlet, whereby the flow of fluid passes through said apertures.

Claims

1. A humidifier for heating and humidifying gas received from a medical respirator and delivering the gas to a patient circuit, comprising in combination: a reservoir adapted to contain a quantity of water; heating means underlying and supporting said reservoir, said means being adapted to maintain the water in said reservoir at a predetermined elevated temperature; an inlet in said reservoir for normally receiving gas from said respirator and an outlet in said reservoir for normally delivering gas to said patient circuit; bubble chamber means within said reservoir connected to said inlet and defining a normal first gas flow path between said inlet and outlet which at least partially passes through the water in said reservoir, whereby to heat and humidify said gas; said bubble chamber means including normally closed check valve means positioned in said chamber means to define a second gas flow path in the direction between said outlet and inlet, said second flow path bypassing said water, and said check valve being opened to establish said second flow path by gas pressure at said outlet exceeding the gas pressure at said inlet.

7. A humidifier for use with a heating plate in the heating and humidifying of gas received from a medical respirator, for delivery of said gas to a patient circuit, comprising in combination: a reservoir adapted to contain a quantity of water, and including a liquid-tight chamber and a bottom plate adapted for thermal engagement with said heating plate; an inlet in said reservoir for normally receiving gas from said respirator and an outlet in said reservoir for normally delivering gas to said patient circuit; bubble chamber means within said reservoir connected to said inlet and defining a normal first gas flow path between said inlet and outlet which at least partially passes through the water in said reservoir, whereby to heat and humidify said gas; said bubble chamber means including normally closed check valve means positioned in said chamber means to define a second gas flow path in the direction between said outlet and inlet, said second flow path bypassing said water, and said check valve being opened to establish said second flow path by gas pressure at said outlet exceeding the gas pressure at said inlet.

11. Apparatus in accordance with claim 9 wherein said check valve means comprises a plurality of second openings at the upper portion of said bubble chamber means, said openings communicating with said reservoir inlet; and flexible flapper valve means biased against said openings from the sides adjacent said reservoir inlet, normally maintaining said openings in their closed condition; said second openings communicating directly with said first openings to enable a backflow path between said reservoir outlet and inlet.

13. A humidifier for heating and humidifying fluid received from a medical respirator and delivering the fluid to a patient circuit, said humidifier comprising a reservoir adapted to contain a quantity of water, heating means underlying and supporting said reservoir, said heating mean adapted to maintain the water in said reservoir at a predetermined elevated temperature, an inlet in said reservoir for receiving fluid from the respirator and an outlet in said reservoir for delivering fluid to the patient circuit, a bubble chamber within said reservoir intermediate said inlet and said outlet adapted to heat and humidify fluid flowing between said inlet and siad outlet, said bubble chamber including normally closed check valve means positioned in said chamber to define a second gas flow path in the direction between said outlet and inlet, said second flow path bypassing said water, and said check valve being opened to establish said second flow path by gas pressure at said outlet exceeding the gas pressure at said inlet, and securing means passing vertically centrally through said reservoir and secured to said heating means whereby said reservoir is securely affixed to said heating means.

15. A reservoir comprising a housing bottom plate, secured to housing containing therein a liquid-tight chamber, a tubing means upwardly extending through said housing affixed to said bottom plate, a bubble chamber suspended from cover plate within reservoir, inlet means for introducing fluid to bubble chamber, outlet means in cover plate for receiving fluid within reservoir, check valve means adjacent the inlet located in parallel with the flow of fluid through said bubble chamber and adapted to pass fluid uni-directionally from said outlet to said inlet, bypassing said bubble chamber, bleed orifice providing direct communication between said inlet and said outlet.