Humidifier module for use in a gas humidification assembly
BACKGROUND OF THE INVENTION 
     1. Related Applications 
     This application is a continuation-in-part of copending Ser. No. 07/139,962, filed Dec. 31, 1987. 
     2. Field of the Invention 
     This invention is directed generally to gas humidifiers, and relates more particularly to a replaceable module for use in a gas humidification assembly, and the combination of the humidifier module with the gas humidification assembly. The humidifier module may be made to be suitable for sterilization and therefore reusable, or disposable. 
     3. Description of Related Art 
     In the treatment of patients with ventilators for inhalation therapy, air may be supplied directly to the trachea, bypassing normal moistening of the air in the nose and mouth. Air for such patients is therefore generally humidified, and various technologies have been used for this purpose. In bubble humidifiers, air is bubbled through a volume of heated water, in order to add water vapor to the air. With wick humidification, air is passed over a wick which is saturated by capillary action with water, and the wick may also be heated. Steam may be created by direction of water to a heating element, or water may be nebulized or atomized with the air to be breathed by the patient, or with a supplemental gas, such as oxygen. A more modern development in materials technology takes advantage of a hydrophobic membrane which will permit the passage of water vapor. Water is vaporized and passed through the hydrophobic membrane into a humidification chamber, through which a breathable gas for the patient is circulated. The membrane has the advantage of filtering materials which might pass from the water into the air to be breathed by the patient. 
     A typical utilization of a hydrophobic membrane in a humidifier is described in U.S. Pat. Nos. 4,532,088 and 4,657,713, in which a supply of water is passed to a heating unit for direct heating for vaporization of the water in a vaporization chamber. The vaporization chamber is covered with a hydrophobic filter membrane which allows the water vapor, but not liquid water, to pass into an outer humidification chamber, through which breathing gas is circulated. The cover of the humidifier unit may be removed for access to the hydrophobic membrane for purposes of replacement of the humidification chamber or the membrane. 
     It would be desirable for a humidifier to utilize a replaceable humidifier module which does not require direct contact between the water and the surface of the heater element. The present invention satisfies this need. 
     SUMMARY OF THE INVENTION 
     The present invention provides a gas humidification assembly having a heater, an enclosure for receiving a humidifier module, a water supply source and a controller for coordinating the supply of heat and water. The humidifier module is replaceable, and may either be made to be sterilizable and reusable, or disposable. The humidifier module has a humidification chamber and a water storage and heating chamber which are separated by a water-vapor-permeable membrane. The water storage and heating chamber is heated in the humidification assembly by indirect heat exchange, and the humidifier module is quickly and easily replaceable when necessary. 
     Briefly and in general terms, a humidifier module for use in a gas humidification assembly having a heat source, and an enclosure for receiving the module, comprises a housing forming a hollow shell adapted to be received in the heater enclosure; a water-vapor-permeable, liquid-water impermeable membrane disposed within the housing dividing the hollow shell into a first chamber and a second chamber and forming a common wall between the first and second chambers; the first chamber comprising a humidification chamber with a gas inlet port and gas outlet port; and the second chamber comprising a water heating chamber having an inlet port and a heat exchange member formed of material capable of high heat transfer, with the heat exchange member being adapted to receive heat from the heat source within the gas humidifier assembly. 
     In a preferred embodiment, the humidification assembly and the humidifier module have means to detect when water or other fluid within the humidification chamber exceeds a predetermined level and to generate an alarm signal when this level is exceeded. This prevents aspiration of such fluids by the patient. The humidification assembly and humidifier module also preferably have a combination of a sensor for detecting and a means for controlling the water level in the water storage and heating chamber. 
     The heat exchange member of the humidifier module is designed to be exposed to a heat source in the humidification assembly, to receive heat and to provide for a high heat transfer to water within the water heating or vaporization chamber. In order to provide a high rate of heat transfer, the heat exchange member may be composed of a metal, such as aluminum, or stainless steel. 
     The membrane separating the vaporization chamber from the humidification chamber may be composed of a conventional hydrophobic material having pores dimensioned to permit water vapor to pass through the material, but not liquid water, at operational pressures. One such material commonly used is polytetrafluoroethylene. In the embodiment in which the humidifier module may be disassembled, the housing of the humidifier module comprises a base portion including the heat exchange member and the water inlet, and a separable vapor chamber portion which includes the gas inlet and outlet. The membrane is placed between the base portion and the vapor chamber portion and sealed to prevent liquid water from passing to the humidification chamber. The base portion and vapor chamber portion of the housing are releasably secured together, preferably with a locking ring. In an alternative embodiment in which the humidifier module is not reusable, but is rather disposable, the housing is permanently sealed with the membrane separating the water heating chamber and the humidification chamber. In either embodiment, the humidifier module is also preferably transparent to permit viewing of the humidification chamber of the humidifier module, for monitoring the liquid water level in the humidification chamber, due to condensation or leaks in the membrane, and for verification that water vapor is being produced in the humidification chamber. 
     The invention further generally provides for the combination of the gas humidification assembly with the humidifier module. Thus, invention further contemplates at least a portion of one or more of the snap fit connectors on the gas humidification assembly, in the enclosure, and sensors for detecting the water level in the water storage and heating chamber, and within the humidification chamber. The humidification assembly also preferably has a portion of the heater enclosure open so that the operation of the humidifier module may be viewed through the transparent housing while the humidifier is being used. 
     The humidification assembly also preferably contains controller circuitry for monitoring and controlling the temperature of the gas being supplied through the humidifier module, monitoring and controlling the supply of water to the water heating and storage chamber of the humidifier module, in response to the level of water in the humidifier module water storage and heating chamber. Thus, ideally, when the water level is sensed to be too low in the water heating and storage chamber, water would be supplied to the water heating chamber. Other aspects and advantages of the invention will become apparent from the following detailed description, and the accompanying drawings, illustrating by way of example the features of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a humidifier module cartridge in a humidifier unit; 
     FIG. 2 is a front view of a humidifier cartridge; 
     FIG. 3 is an exploded view of one embodiment of the humidifier module; 
     FIG. 4 is an elevational sectional view taken along line 4--4 of FIG. 2; 
     FIG. 5 is an elevational sectional view taken along line 5--5 of FIG. 2; 
     FIG. 6 is a schematic diagram of the gas humidification assembly and humidifier module; and 
     FIG. 7 is an elevational sectional view of an alternative embodiment of a humidifier module. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     As is shown in the drawings for purposes of illustration, the invention is embodied in a humidifier module for use in a gas humidification unit having a heat source, a water supply source, an enclosure for the humidifier module, with the module comprising a housing forming a hollow shell adapted to be received in the heater enclosure; a water vapor permeable, liquid water impermeable membrane disposed within the housing dividing the hollow shell into a first chamber and a second chamber and forming a common wall between the first and second chambers; the first chamber comprising a humidification chamber having a gas inlet port and a gas outlet port; and the second chamber comprising a water heating chamber having a water inlet port and a heat exchange member formed of a material capable of high heat transfer, the heat exchange member being adapted to receive heat from the heat source of the gas humidification unit. The humidifier module is designed to be quickly replaceable, and may be either reusable or disposable. There is a need for such a humidifier module for a humidification assembly in which heat is supplied indirectly, by way of a heat exchange member with the capability for high heat transfer, and in which a hydrophobic membrane permits only water vapor to pass therethrough. 
     As is shown by way of example in the drawings, the present invention includes a gas humidification assembly or unit 10 having an enclosure 12 with a heater therein. The assembly also has a water supply storage 14, with a water supply tube 16 extending from the water supply storage to a pump (not shown), and generally extending toward the heater enclosure area. Within the gas humidification assembly there is provided a heater or heat source 18 generally adjacent the heater enclosure. A humidifier module or cartridge 20 fits into the heater enclosure, for receiving heat from the heat source of the humidification unit, and for receiving a supply of water through the water supply tube. 
     The humidifier module generally comprises a housing 22, and a membrane 24 formed of hydrophobic material permeable to water vapor but not to liquid water, placed in the housing to separate the humidifier module into a first, humidification or vapor chamber 26, and a second, water heating or vaporization chamber 28. A suitable membrane is a polytetrafluoroethylene filter material, such as Goretex, available from W. L. Gore Associates, although other hydrophobic, microporous materials may also be suitable for such a membrane. The humidifier module also includes a gas inlet port 30, and a gas outlet port 32, allowing the gas to enter the humidification chamber, mix with the vapor, and exit as a warmed, humidified gas for breathing by a patient, or for further treatment of the gas before reaching the patient. 
     Provided on the top of the humidifier module is a water inlet port 34, to which a water supply tube may be connected, for receiving water from the water supply of the gas humidification unit. On one side of the humidifier module there is also provided a heat exchange member or wall 36, which may be a metal plate, to provide for the capability of high heat transfer from the heat source of the humidification unit into the water heating chamber of the humidifier module. The heat exchange wall is preferably made of aluminum, but other materials which provide high heat transfer, such as stainless steel, may be suitable as well. 
     Proper placement of the humidifier module in the humidification assembly is important for all of the components to cooperate together. To ensure the proper positioning of the module within the unit a snap fit connection is provided, so that when the module snaps into place, the operator can be sure that the module is in proper position with the light sources and sensors for detecting fluid level in the water storage and humidification chambers. An example of the preferred method of seating the module in the humidification unit is the provision of a spring plate or clip 38 on one side of the heater enclosure, made of spring metal and extending outward to engage an opposing indentation 40 for receiving the spring clip. One or more of these indentations may be arranged around the outside of the housing of the humidifier module, to correspond with spring plates arranged around the inside of the enclosure of the humidification unit. 
     There is also preferably provided a means for sensing the liquid level within the humidification chamber. Such a sensor can be an optical sensor providing a beam of light such as infrared light, to be emitted into a reflector site, which will be reflected back to a photodetector giving a logic level change when an emitted beam is either refracted or reflected, depending upon the presence of fluid in the humidification chamber. For example, as shown in the drawings, there is provided a reflector site 42 on the housing of the humidification chamber for reflecting a light beam provided by an optical sensor 44 back to the optical sensor, which also contains a photodetector for receiving the reflected light beam. As will be further described later, the light is reflected back to the photodetector when fluid in the humidification chamber is not above the level of the reflection site, and light is refracted into the fluid when the fluid rises to a level so as to surround the reflector site. The optical sensor provides a signal indicating whether fluid in the humidification chamber has risen to a predetermined level, which signal can be utilized for controlling the heat source and water supply module. It will also be appreciated that a light beam may be directed to pass through a target area of the transparent module, instead of being reflected by a reflector site, to be detected by a photodetector on the other side of the module, to provide a signal indicating the fluid level in the humidification chamber. 
     With reference to FIG. 3, in a preferred embodiment of the humidifier module, the housing forms a hollow shell containing the humidification chamber and the water heating chamber, and is comprised of a base portion 46 carrying the heat exchange wall and the water inlet port. The filter membrane is received over a shoulder portion 47 of the base portion of the housing to define the water heating chamber within the base portion between the membrane and the heat exchange wall. A sealing means, such as an O-ring 48 fits over the outer margin of the membrane, sealing the water heater chamber to prevent leakage of water into the humidification chamber. A vapor chamber portion 50 of the housing is also provided to fit over the O-ring and membrane onto the base portion of the housing, to define the humidification chamber of the module. 
     In the embodiment in which the humidifier module is sterilizable and reusable, the vapor chamber and base portions of the humidifier module may be releasably secured together by a locking ring 52 having locking tabs 53 or other means for receiving corresponding locking tabs 54 on the base portion of the housing. Rotation of the locking ring in one direction while the other components of the humidifier module are assembled will secure the vapor chamber portion to the base portion, and rotation of the locking ring in the opposite direction will release the vapor chamber portion of the housing from the base portion for disassembly. Alternatively, conventional types of spring clips bolts or screws may be utilized for releasably securing the vapor chamber portion of the housing in a sealed relationship to base portion of the housing. In the embodiment in which the humidifier module is disposable, the means for releasably securing the two portions of the housing together may be dispensed with, and the vapor chamber portion of the housing may be permanently bonded to the base portion of the housing by heat sealing, welding, conventional adhesives, or other methods commonly known to those skilled in the art. 
     Detection of the liquid level within the water heating chamber of the humidifier module is preferably accomplished by means of a reflector site 56 provided in the upper portion of the water heating chamber having a conical surface 57 or any other surface which provides an angled surface for reflection of light. The reflector site operates in combination with a water level optical sensor 58 positioned appropriately in the heater enclosure of the humidification unit to provide a beam of light such as infrared light, to be emitted into the reflector site, which will be reflected back to a photodetector in the optical sensor when water within the water heating chamber does not surround the reflector site. When water in the water heating chamber rises to a level so as to surround the reflector site, ideally all emitted light from the optical sensor refracts into the water, so that little or no reflected light would be detected by the photodetector of the optical sensor. As in the fluid level detection in the humidification chamber, it will be apparent that a light beam may be directed through a target area of the transparent module instead of to a reflector site, to be detected by a photodetector on the other side of the module. As will be further described later, in this manner, the optical sensor will produce a signal indicating whether water in the water heating chamber is up to the level of the reflector site, which can be utilized to control the pumping of liquid to the humidifier module by the gas humidification unit. 
     Referring to FIG. 6, showing a schematic diagram of the humidification assembly unit with the humidifier module or humidification chamber installed, an operator&#39;s panel 60 permits the programming of a control module 62, functioning to control the operation of the humidification unit. The control module or controller is operatively connected with a heater module 64 adjacent the heater enclosure, a power module 66, a thermistor 68, a pump module 70, and the water level optical sensor 58, or opto sensor, and the vapor chamber optical sensor 44 or chamber detector. Also shown schematically is the water supply storage or reservoir, from which the pump module supplies water to the water heating chamber of the humidifier module. Thermistor 68 monitors the temperature of the humidified gas passing from the humidifier module to the patient, producing a temperature signal received by the controller, which functions to regulate the heat source in the heater module. The signal produced by the optical sensor indicating water is not up to the level of the reflector site in the water heating chamber will be received by the controller, which functions to activate the pump module to supply water from the reservoir to the water heating chamber. When the level of water reaches the reflector site, the signal from the optical sensor is received by the controller which operates to inactivate the pump to prevent overflow of the water heating chamber and potential rupturing of the filter membrane. The vapor chamber optical sensor, indicated as the chamber detector, produces a signal indicating whether fluid has risen to a predetermined level within the humidification chamber. When the fluid is to the level of the reflector site, the light beam produced by the optical sensor is refracted into the fluid so that it is not fully reflected back by the reflector site to the photodetector of the chamber detector, altering the signal from the sensor to indicate the presence of fluid at the predetermined level in the humidification chamber, and the controller acts to activate an alarm 72. 
     Also, the operator may set a high temperature alarm limit via the operator panel, such that in the event of the temperature monitored by the thermistor reaching or exceeding that limit, the heater power will be shut off, and audible or visual alarms may be engaged. A thermal fuse operatively connected to the power module may also be placed in the vicinity of the heater module, to cut off the power in the event of a heater runaway, in order to prevent a fire hazard. 
     Referring to FIG. 7, in an alternative embodiment of the humidifier module, shown for illustrative purposes in a horizontal position, the heat exchange wall includes a portion 74 extending into the water heating chamber. The portion is in a currently preferred form of the invention formed with a frustoconical shape, for ease of manufacture but may also take a cylindrical shape, a spherical shape, or other appropriate shapes. The portion is preferably approximately symmetrically formed about the heater source 76, and most preferably the heater source is approximately equidistant from all areas of the outwardly bulging portion, for even, and more efficient heating than is generally possible with a flat plate. 
     From the foregoing description, it will be appreciated that the heat exchange wall of the humidifier module will provide an indirect heating of the water heating chamber, and that the humidifier module itself may be quickly and easily replaced, to permit a substantially continuous functioning of the gas humidification unit, as may be required by a patient. Further, the humidifier module itself may be made to be either sterilizable and reusable, in its most economic form, or completely disposable for convenience. 
     It will also be apparent that the gas humidification assembly operates in combination with and in cooperation with the humidifier module to provide the humidified gas to a patient, monitor the temperature of the gas being supplied to the patient, monitor the water level in the humidifier module and ensure minimum fluid levels in the humidification chamber. Thus, the combination of the humidifier module in the gas humidification assembly provides for automatic functioning of the unit. In addition, the transparency of the humidifier module humidification chamber allows for independent verification of the proper functioning of the unit by an operator by visual inspection. 
     From the foregoing, it will be appreciated that the humidifier module and combination of the humidifier module with the gas humidification assembly according to the invention provides a safe and effective humidification device which may operate automatically to provide properly humidified and temperature controlled gas to a patient, on a substantially continuous basis. 
     While a particular preferred form of the invention has been illustrated and described, it will be apparent that the invention is susceptible to numerous modifications and embodiments within the ability of those skilled in the art and without the exercise of the inventive faculty. Thus, it should be understood that the various changes in form, detail and application of the present invention may be made without departing from the spirit and scope of this invention.