Abstract:
A breathable gas supply apparatus has a flow generator configured to pressurize a flow of breathable gas and a humidifier base unit configured to be coupled to the flow generator. A water container is configured to be removably coupled to the humidifier base unit and includes an air inlet and an air inlet passage extending into an interior of the water container from the air inlet. The air inlet passage is configured to direct the pressurized flow of breathable gas in a direction that is substantially parallel to a base of the water container. A barrier wall is provided across an outlet end of the air inlet passage and extends downward from the air inlet passage toward the water container base. In addition, a curved wall opposes both the outlet end of the air inlet passage and the barrier wall and extends downward toward the water container base. The breathable gas supply apparatus also includes a connector defining an airflow passage between an outlet of the flow generator and the air inlet of the water container.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 14/445,190, filed Jul. 29, 2014, now allowed, which is a continuation of U.S. application Ser. No. 12/659,963 filed Mar. 26, 2010, now pending, which is a continuation of U.S. application Ser. No. 10/533,940, filed May 4, 2005, now U.S. Pat. No. 8,006,691, which is a national stage application of PCT/AU04/00810, filed Jun. 21, 2004 in English, which claims the benefit of Australian Application No. 2003903139, filed Jun. 20, 2003, Australian Application No. 2003905136, filed Sep. 22, 2003, and Australian Application No. 2004901008, filed Feb. 27, 2004, each incorporated herein by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to breathable gas supply apparatus, and particularly but not exclusively to such apparatus for use in Continuous Positive Airways Pressure (CPAP) treatment of conditions such as Obstructive Sleep Apnea. It will be described herein in its application to CPAP treatment apparatus, but it is to be understood that the features of the invention will have application to other fields of application, such as mechanical ventilation and assisted respiration. 
     BRIEF SUMMARY OF THE INVENTION 
     The advantages of incorporating humidification of the air supply to a patient are known, and CPAP machines are known which incorporate humidifying devices. One of the objects of the invention is to provide a simple and compact breathable gas supply apparatus incorporating a humidifier which is simple and economic in its construction, compact, and easy to use. Other objects and advantages of the invention will be described throughout the specification. 
     It is to be understood that apparatus described herein contains a number of advances on the prior art, many of which independent inventions, although they contribute together to the realisation of the general object expressed above. 
     The apparatus described herein incorporates novel aspects of architecture which contribute to a reduction in size compared with known units having similar performance. Techniques for noise reduction and damping are described which enable such a smaller machine to have noise performance which is at least as good as known larger machines. 
     The apparatus described achieves full integration of the humidifier with the flow generator, in the sense that air flow, electrical and, if required, data connection between the flow generator and the humidifier are provided automatically upon the physical engagement of the two devices, without the need for any other process of interconnection. 
     In such an integrated device, provisions to guard against flowback of water from the humidifier tank to the flow generator are important, and novel sealing arrangements, and novel arrangements for minimising the occurrence of flowback while at the same time improving the uptake of water vapour in the humidifier are also described. The humidifier is readily detached and replaced on the machine, and has very few parts to be disassembled during cleaning. 
     Also described herein are improved, modular, devices for enabling data connection with the apparatus, including the connection of data storage devices such as memory cards, smart cards, communication ports and the like to be selectively attached by the user or by medical personnel. 
     The various aspects of the invention will now be described with reference to the accompanying illustrations, which show a presently proposed embodiment. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a general view of breathable gas apparatus embodying the various features of the invention; 
         FIG. 2  shows the flow generator of the apparatus; 
         FIG. 3  shows the humidifier unit; 
         FIG. 4  is a cutaway view of the flow generator; 
         FIG. 5  is a rear view of the humidifier; 
         FIG. 6  is an exploded view of components of the flow generator; 
         FIG. 7  is an underneath view of a chassis forming part of the flow generator; 
         FIG. 8  is a rear view of the chassis; 
         FIG. 9  is a general view of a fan forming part of the flow generator; 
         FIG. 10  is an underneath view of the fan; 
         FIG. 11  is a cross-sectional view of the fan; 
         FIG. 12  shows the humidifier in partly disassembled state; 
         FIG. 13  is an underneath view of the tank of the humidifier; 
         FIG. 14  is an underneath view of the tank showing an alternative valve; 
         FIG. 15  is a view of the tank cover; 
         FIG. 16  is an underneath view of the tank cover; 
         FIG. 17  is an underneath view of a modified tank cover; 
         FIG. 18  shows an exemplary modular connector arrangement; 
         FIG. 19  shows an exemplary cover for an exemplary modular connector arrangement; 
         FIG. 19A  shows an exemplary modular connector arrangement with the exemplary cover of  FIG. 19 ; 
         FIG. 20  shows an exemplary modular connector arrangement; 
         FIG. 21  shows an exemplary modular connector arrangement; 
         FIG. 22  is a rear view of a first cradle component of a humidifier according to another embodiment; 
         FIG. 23  is a perspective view from the front and above, of the cradle component of  FIG. 22 ; 
         FIG. 24 . is a perspective view from the front and above of a second cradle component of the humidifier of  FIG. 22 ; 
         FIG. 25  is a perspective view from the rear and below of the cradle component of  FIG. 24 ; 
         FIG. 26  is a perspective view from the front and above, of a water receptacle of the humidifier of  FIG. 22 ; 
         FIG. 27  is an underneath view of the receptacle of  FIG. 26 ; 
         FIG. 28  is a perspective view from the front and above, of a lid of the humidifier of  FIG. 22 ; 
         FIG. 29  is a perspective view from the rear, of the lid of  FIG. 28 ; 
         FIG. 30  is an underneath view of the lid of  FIG. 28 ; 
         FIG. 31  is a perspective view from the front and above, of a lid seal of the humidifier of  FIG. 22 ; 
         FIG. 32  is an underneath view of the lid seal of  FIG. 31 ; 
         FIG. 33  is a schematic side elevation, shown partly cut away, and partly in hidden detail, of the humidifier of  FIG. 22 ; 
         FIG. 34  is a perspective view from the rear, of an airway seal of the humidifier of  FIG. 22 ; 
         FIG. 35  is a perspective view from the front and below of the airway seal of  FIG. 34 ; 
         FIG. 36  is a perspective view from the front and below, of a lid catch of the humidifier of  FIG. 22 ; 
         FIG. 37  is a perspective view of an interengagement catch of the humidifier of  FIG. 22 ; 
         FIG. 38  is a schematic section view through parts of the humidifier of  FIG. 22 ; 
         FIG. 39  is a perspective view from behind and below of a first cradle component of a humidifier according to yet a further embodiment; 
         FIG. 40  is a perspective view from the front and above of the component of  FIG. 39 ; 
         FIG. 41  is a perspective view from the front and above of a second cradle component of the humidifier of  FIG. 39 ; 
         FIG. 42  is a perspective view from the rear and below of the component of  FIG. 41 ; 
         FIG. 43  is a plan view of a lid of the humidifier of  FIG. 39 ; 
         FIG. 44  is an underneath view of the lid of  FIG. 43 ; 
         FIG. 45  is a perspective view from the front and below of a seal forming part of the humidifier of  FIG. 39 ; 
         FIG. 46  is a perspective view from the front and above of the seal of  FIG. 45 ; 
         FIG. 46A  is a schematic section view through the seal of  FIG. 46 ; 
         FIG. 47  is a perspective view from the front and below of a lower component of a water receptacle of the humidifier of  FIG. 39 ; 
         FIG. 48  is a perspective view from the front and above of the component of  FIG. 47 ; 
         FIG. 49  is a perspective view from the front and above of an upper component of the water receptacle of  FIG. 47 ; 
         FIG. 49A  is a perspective view from the front, of an air connector component of the humidifier of  FIG. 39 ; and 
         FIG. 49B  is a perspective view from the rear, of the air connector component of  FIG. 49A .; 
         FIG. 50  is an exploded view of a further embodiment of the flow generator; 
         FIG. 51  is a more detailed illustration of the bottom case and power supply of  FIG. 50 ; 
         FIG. 52  is a more detailed illustration of the chassis, chassis lid and fan housing of  FIG. 50 ; 
         FIG. 53  is a more detailed illustration of the PCB, top case and exterior fittings of  FIG. 50 ; 
         FIG. 54  is an exploded view of a humidifier adapted for use with the flow generator of  FIG. 50 ; 
         FIG. 55  is a perspective of a seal for the air flow path; 
         FIG. 56  is an underside perspective of the humidifier lid of  FIG. 54 ; 
         FIG. 57A  is a perspective view of the humidifier lid seal of  FIG. 54 ; 
         FIG. 57B  is a detail cross section of the humidifier lid seal of  FIG. 54   
         FIG. 58A  is a perspective view of the humidifier tub lid of  FIG. 54 ; and 
         FIG. 58B  is a longitudinal cross section of the humidifier tub lid of  FIG. 54 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The illustrated apparatus comprises a flow generator  50  and a humidifier  150 , shown in their assembled condition in  FIG. 1 . As shown in  FIG. 2 , the flow generator engages with the separable humidifier at an engagement face  52 , from which protrudes an air connector  53  for the delivery of air from the fan to the humidifier container, and electrical connectors  54  for the delivery of power to the humidifier heater described below. 
     The face  52  also carries a pair of slots  55  which are engaged by corresponding tongues  156  provided on the humidifier engagement face  157  ( FIG. 5 ) by which the flow generator  50  and humidifier  150  are connected together, as will be described in more detail below. 
     Externally, the flow generator  50  is also provided with an LCD screen  58  and associated keys  59  by which the user can set the operating parameters of the unit. 
     The flow generator  50  has an external case of rigid plastics material moulded in two parts, a top case  60  and a bottom case  61 . The lower edge of the top case  60  is stepped and flanged at  62  to mate with the periphery of the bottom case  61 . Overmoulded with the rigid plastics body of the bottom case  61  is a rubber sealing flange  63 , which locates between and seals against the cases  60  and  61  on the one hand, and the outer surface of a chassis  64  described further below. 
     Formed in the bottom case  61  by walls which join the outer wall of the case are the lower portions  65  and  67  of, respectively, a power supply cavity and a resonator cavity. The upper portions  66  and  68  of these cavities are formed in the chassis  64 , described below. 
     The chassis  64  is formed with a peripheral wall  69  flanged around its lower edge to engage with the inner periphery of the overmoulded sealing flange  63 . The chassis  64  includes a downwardly extending fan cavity  70  in which is mounted the fan  90  described below. This cavity  70  is formed by moulded side walls  71  and base  72 , which are formed by moulding thermoplastic around an inserted stainless steel liner  73 . The fan cavity  70  opens to the upper surface of the chassis  64  to enable insertion of the fan  90 , this opening being closed by a lid  74 . Like the cavity  70 , the lid  74  has an imbedded stainless steel plate insert moulded within a thermoplastics material, and at its edges the lid is provided with co-molded elastomer sealing edges. The formation of the cavity  70  by insert moulding from differing materials provides very effective acoustic damping, as does the combination by co-moulding of the hard and soft plastics described already and further described below. In this aspect of the present invention, the use of co-moulding or overmoulding in the combination of materials of different, preferably widely different, stiffness and different, preferably widely different, density has been found to be particularly advantageous in providing acoustic damping. 
     The upper portion  66  of the power supply cavity is formed by a side wall  75  extending downwardly from the roof of the chassis  64 , which sealingly engages the opposed wall of the lower portion  65  of this cavity. Preferably, the lower wall is provided for this purpose with a co-moulded or overmoulded rubber sealing flange  63  similar to the flange. The power supply compartment is thus sealed against the ingress of moisture from the interior of the unit in the case of backflow from the humidifier. Similarly, the air path is sealed from the power supply compartment. The interior is at the same time acoustically sealed from the power supply cavity, which may not be completely sealed from the exterior, due to the necessity of providing mains power input and low voltage power output to the humidifier, via connectors  54  mounted in apertures  78  and  80  respectively in the rear and front walls of the cavity, and if necessary the venting of the compartment to outside air for cooling. 
     Supported on the top of the chassis  64 , in the space formed between the chassis and the top of the top case  60  is a printed circuit board  81  carrying the electronic control components of the unit. At the rear of the board  81  an edge connector  82  and a sliding connector are accessible from a connector aperture  83  in the rear of the top case  60 , providing for modular connector arrangements to be described in more detail below. 
     Also provided in the rear wall of the top case is an air inlet  84 , and this communicates with an air inlet passage  85  formed in the roof of the upper portion  66  of the power supply cavity, this passage in turn opening through the inner side wall of that cavity at  87  to the air space surrounding the fan cavity  70  in the interior of the unit. Air drawn into the unit by the fan will thus pass over the roof of the power supply and thereby assist in the dissipation of heat generated by the power supply. 
     A removable air filter body  85 A containing a replaceable filter element attaches to the inlet  84 , as shown in  FIGS. 2 and 6 . 
     From the air space surrounding the fan cavity  70 , inlet air passes to the fan cavity via an inlet tube  88  depending from a horizontal extension of the side wall  71  of the fan cavity. 
     The fan cavity and the space surrounding it and enclosed by the upper and lower cases form a pair of serially connected volume mufflers, and the dimensions of the inlet tube  88  and the air inlet passage  85  are chosen to optimise the noise attenuation produced by these mufflers, within the constraint of avoiding unacceptable air flow restriction. 
     It will now be convenient to describe the features of the fan, which are shown in  FIGS. 9 to 11 . 
     The fan  90  comprises a motor  91 , preferably brushless DC motor, provided with a coaxial impeller  92 , mounted vertically within a fan housing consisting of a cover  93  and a base  94 . An air inlet  95  is provided in the floor of the base  94  on the impeller axis, and cavities in the cover and base form a volute  96  which leads from the impeller to an air outlet  97 . The cover and base  93  and  94  are joined by means of slotted tabs  98  which extend upwardly from the base to snap over stepped ribs  99 , the tabs  98  being further located by fitting between parallel ribs on the cover  93 . The joint between the cover  93  and the base  94  is sealed by an elastomeric sealing ring  101 . 
     The bottom surface of the fan housing base  94  is provided with radial stiffening ribs  102 , and overmoulded to the base  94  is an elastomer damping member  103  which covers that bottom surface between the ribs  102 , and extends around the edge of the base by a flange portion  104  and peripherally spaced tabs  105 . By overmoulding to the rigid plastic base  94  an elastomer of much lower stiffness and much lower density substantial acoustical damping is provided to the fan housing. 
     Moulded integrally with the rigid plastics portion of the fan housing base are feet  106  which extend through the overmoulded elastomer damping member  103  to receive helical mounting springs (not shown) by which the fan is mounted on the base  72  of the fan cavity. 
     The degree of size reduction which is an objective of the present invention requires great care to be taken to minimise the transmission of noise and vibration, particularly from the motor and the impeller of the fan  90 . The mounting springs are therefore chosen to ensure minimal transmission of the vibration frequencies encountered during operation. This is achieved by choosing the springs with reference to the mass of the fan  90 , such that the natural frequency of the system comprising the springs and the fan is at least approximately one tenth of the vibration frequency encountered when the motor is running at its lowest operating speed. 
     The air outlet  97 , upon the introduction of the fan into the fan cavity, is connected by means of a thermoplastic elastomer coupling member with an air outlet passage  109  which extends from the side wall of the fan cavity to a connecting nozzle  110  extending through an aperture  111  provided for this purpose in the front face of the flow generator. 
     The fan  90  therefore floats within its cavity  70  in the chassis  64  with minimum acoustic coupling to the remainder of the flow generator. The characteristics of the mounting springs and the coupling member are chosen to minimise the transmission of characteristic vibration frequencies of the fan. 
     The air outlet passage  109  is formed in the roof of the upper portion  68  of the resonator cavity. Holes  112  communicating with the resonator cavity are provided in the floor of the passage  109  where it crosses this cavity, which acts in the manner of a Helmholtz resonator. By adjusting the dimensions and number of the holes  112 , the frequency response of the resonator can be adjusted for optimum noise cancellation. If desired, a second Helmholtz resonator cavity can be provided opposite the upper portion  68  of the resonator cavity, if the dimensions of the top case  60  allow this. 
     The novel use of Helmholtz resonators for noise attenuation contributes to the success in achieving significant size reduction in the flow generator of the present invention. 
     As shown in  FIG. 12 , the humidifier  150  comprises a base unit  151  designed for simple attachment to and detachment from the flow generator  50 , and a tank  152  which is similarly attachable to and detachable from the base unit. 
     The rear face of the base unit  151  has a peripheral flange  153  which seats in a corresponding peripheral recess  113  surrounding the front face of the flow generator  50  when the two units are brought together by linear movement towards each other. The tongues  156  are moveable vertically and resiliently urged downwardly, so that these tongues engage in the slots  55  and snap home to engage the two units by means of the downwardly extending fingers  158  at the ends of the tongues. 
     An air flow passage  160  passes through the humidifier engagement face  157  and opens to the front wall of the base unit. This passage is surrounded at the rear wall with a cylindrical connecting portion  161  which receives the nozzle  110  of the flow generator upon engagement of the two units. The inner surface of the portion  161  is provided with a sealing device such as a layer of elastomer or other soft resilient material. 
     The rear face of the base unit also carries a connector  162 , in this embodiment a pair of flat male blade connectors, for engagement with a mating connector on the front face of the flow generator, to provide power to the humidifier heater from the power supply in the power supply cavity. Although not shown in the illustrated embodiment, the respective faces may also carry further interconnecting devices, where other electrical or data connections are required to be established between the flow generator and the humidifier or downstream devices including the air conduit or the mask. Such devices may take the form of optically coupled devices, or connectors of other suitable kinds. 
     The use of such an opto-coupling connector enables the implementation of a simple protocol for communications between the flow generator and the humidifier. For example, the current flow levels of the flow generator can be sent to the humidifier controller which then adjusts the operation of the humidifier according to a predetermined algorithm. 
     Within the humidifier base unit  151  but not shown here is provided a variable power supply for a heating element which heats a circular metal pad  163 . A control knob  164  is provided on the upper surface of the unit for adjustment of the heat supplied to the pad  163 . A semicircular wall  165  surrounds the rear part of the pad  163 , and carries at its upper edge an inwardly directed flange  166 . The pad  163  stands proud of the surrounding base surface  168 . 
     It will be observed that the air flow passage  160  opens to the front face of the base unit at the foot of a circular recess  167  of larger diameter, corresponding to the diameter of the tank air inlet  175  described below. The effect of this is to provide a vertical offset between the air flow passage  160  and the inlet  175 , with the former lower than the latter in the normal orientation of the unit. This configuration assists in the prevention of backflow as will be described below. It is to be observed that the axial offset in question could be achieved in other ways. 
     The recess  167  is provided with a sealing layer of elastomer or other sealing material. 
     The tank  152  comprises a cover  170  which is preferably of a transparent plastics material, a metal tank base  171  preferably of stainless steel, a base flange  172  which functions to couple the cover and the base, and a sealing gasket  173  which locates between the base of the cover and the metal tank base  171 . 
     The periphery of the base flange  172  is dimensioned to slide into engagement with the wall  165  of the base unit and beneath the flange  166  to engage the tank with the base unit, and the tank cover  170  is provided with a cylindrical air inlet  175  extending from its side wall. The inlet  175  is dimensioned to fit sealingly within the recess  167  when the tank is engaged with the base unit as described above and as shown in  FIG. 3 . An air outlet  176  extends upwardly from the roof of the cover  170  for connection with an air hose for the delivery of humidified air to the patient. 
     The metal tank base  171  seats within the base flange  172  which is provided with a central aperture, so that the bottom of the metal tank base  171  is exposed to contact the pad  163  when the tank is engaged with the base unit. The metal tank base  171  is thus heated by the heating element of the base unit. To assist in achieving good heat transfer between the pad  163  and the metal tank base  171 , the former is resiliently biased upwardly, for example by means of a spring or springs (not shown). This has the further advantage of providing for positive retention of the tank in the base unit, by providing around the central aperture in the base flange, a downwardly directed rim (not shown) which will initially depress the heating plate as the tank is moved into position on the base unit, and which forms a central space into which the heating plate moves under its spring pressure, upon full engagement of the tank with the base unit. 
     In alternative embodiments not illustrated here, the tank may be provided with locking detents for retention on the base unit. 
     The lower edge of the cover  170  and the inner edge of the base flange  172  are provided with bayonet type engagement formations  177  and  178  respectively, so the tank components can be assembled and disassembled simply by relative rotation of the cover and the base flange. To assist in this operation, a peripheral groove  179  is provided in the base of the base flange  172 , and this groove is interrupted at intervals by finger-engaging bridges  180 . The inner wall of the groove  179  protects the user&#39;s fingers against accidental contact with the metal tank base  171 , in case removal of the cover is carried out while the base is still hot. 
     The tank is intended to be filled via the air outlet  176 , and the apparatus may be provided with a filling bottle with a spout dimensioned for a convenient fit with that outlet. Such a bottle may be provided with a spout of the kind incorporating an air bleed passage which will allow the tank to fill to the correct predetermined height. 
     In alternative embodiments, other filling arrangements may be employed. The correct filling height is also indicated by filling level graduations  184  scribed or otherwise marked on the wall of the cover  170 . 
     As will be seen in  FIG. 16 , the air inlet  175  of the cover  170  extends within the cover in the form of an arcuate passage  181 , to open to the interior of the cover at a point beyond, in the direction of air flow, the outlet  176 . The outlet  183  of the passage  181  is directed obliquely towards the inner wall of the cover. The outlet  176  is, furthermore, between the convexly curved side of the passage  181 . This configuration has several important consequences. 
     Firstly the curvature of the passage  181  and the oblique orientation of its outlet  183  will induce a swirling action on the air mass within the tank, as the air moves around the tank to escape from the outlet  176 . This swirling action will enhance the uptake of water vapour from the water contained in the tank. 
     Secondly the configuration minimises the risk of water from the tank flowing back into the air inlet passage should the tank be tilted while containing water. Whenever the orientation of the tank is such that the air outlet  176  is below the outlet  183 , water will flow into the air outlet  176  before it will flow into the inlet passage, and whenever the air outlet is above the outlet  183 , then except in the case of inversion of the tank, water will not escape via the arcuate passage  181  unless the tank has been filled with a volume of water which is greater than that which is contained within the sector of the tank below a tangent to the convex surface of the passage  181 . This can be avoided by appropriate setting of the heights of the filling level graduations  184 . 
     Should water escape into the passage  181  due to inversion of the humidifier while it is engaged with the flow generator, its path to the air flow passage  160  will be blocked by the dam formed by the face of the recess  167 , which will then be below the passage  160 . 
       FIG. 17  shows a modified form of tank cover in which a downwardly extending wall  187  is provided across the end of the arcuate passage  181 , this wall extending in a curved wall  188  beyond the outlet  183 . The curved wall  188  assists in the formation of a swirling air flow within the tank, while both walls  187  and  188  tend to protect the outlet  183  against wave action within the tank during transport. 
     If desired, further security against backflow can be provided by locating a non-return valve at an appropriate point. An example of this is shown in  FIG. 14 , where a valve comprising a flexible membrane  185  supported on a spider  186  is placed in the mouth of the tank air inlet  175 . 
     In the illustrated embodiment the arcuate passage  181  is shown as a low profile passage of substantially rectangular cross-section. An alternative approach is to continue this passage as a cylindrical passage having a diameter similar to that of the air passage leading from the flow generator to the humidifier. The advantage of this will be to avoid the introduction of impedance to the flow of air through the humidifier. Generally speaking it is desirable to minimise pressure drop through the humidifier, to avoid interfering with diagnostic or monitoring functions in the flow generator, for example the detection of snoring, which require the detection of sound transmitted back through the system from the patient. 
     The enhanced uptake of water vapour achieved by inducing the swirling of air as it passes through the tank enables, in an alternative embodiment of the invention, the elimination of the heating of the water in the tank  152 . In such an embodiment the heating element and its controls, and the heat transfer components including the pad  163  and the metal tank base  171  are eliminated, and the humidifier becomes a simpler, passive, device. 
       FIGS. 18 to 21  show various forms of modular data connections foreshadowed earlier, utilizing the connector aperture  83  in the rear of the flow generator housing. 
     The connector aperture  83  is provided in the wall of a rectangular recess  115 . An arcuate depression  123  is provided in the upper surface of the unit above the recess  115  to facilitate removal of closure elements from the depression, as described below. 
     Where the flow generator in question is not intended to be employed with any data connection, the connector aperture  83  is closed off by a blank closure element  117 , shaped to fit into the recess  115 . This element snaps into the recess by means of lower tabs  118  and an upper tab  119  which fit corresponding depressions such as  122  in the walls of the recess  115 , to close the connector aperture  83  and conform to the contours of the surrounding surface of the unit. 
     Complementarily shaped closure elements can be provided for the reception of different kinds of data devices. Shown in  FIG. 20  is an element  116   a  provided with a slot for the reception of a smart card  120 . The element  116   a  or the printed circuit board itself may carry the necessary smart card socket. Shown in  FIG. 21  is an element  116   b  provided with a DB type data socket. In this case the element  116   b  is contoured to provide a lower front recess  121  to facilitate gripping of the associated plug. 
     Other forms of element  116  can be provided to enable the connection of devices such as memory cards and pre-programmed devices as required. This facility furthermore enables a wide range of devices to be integrated with the apparatus in modular fashion, for example a clock display which may utilise the system clock contained in the flow generator controller, a voice activation unit, oximetry, ECG and other diagnostic aids, a sound recorder, a light. 
     First Further Embodiment of the Humidifier 
     With references to  FIGS. 22 to 38 , a humidifier according to another embodiment of the invention, is described. The humidifier is adapted for attachment to the flow generator in generally similar fashion to the humidifier described above with reference to  FIGS. 12 to 17 . 
     The humidifier according to the present embodiment includes a first cradle component  202  (see  FIGS. 22 and 23 ) and a second cradle component  204  (see  FIGS. 24 and 25 ), each being generally L-shaped in side view. 
     The first cradle component  202  includes a horizontally extending portion  206  and a vertically extending portion  208 . The horizontally extending portion  206  has an outer wall  210  and a floor  212 , the outer wall and floor defining a recess  214 . An aperture  216  is provided in the front extremity of the outer wall  210 . 
     The outer sides  218  of the vertically extending portion  208  are slightly recessed relative to the outer surface of the outer wall  210 , so as to define side recesses  220  with forward projecting walls  222 . 
     The vertically extending portion  208  extends upwardly from the upper surface of the outer wall  210 , and, about midway up, at  224 , is angled rearwardly. A rectangular aperture  226  opens through the vertically extending portion  208 , the front of the aperture being defined by a rim  228  which forms a continuation of the rearwardly angled portion at  224 . 
     At the upper end of the vertically extending portion  208  there is provided a rearwardly projecting flange  230 , which has a step  232  at its forward extremity. 
     Defined between the flange  230  and the outer sides  218 , at each side of the vertically extending portion  208 , is a recess  234 . 
     Referring to  FIG. 22 , at the rear of the first cradle component  202 , there is provided a rearwardly projecting wall  236  which is curved so as to define a closed path, and which extends around the rear of the aperture  226 , where the aperture opens through the rear of the vertically extending portion  208 . The wall  236  is adapted for fitting of a seal  280  (see  FIGS. 34 and 35 ), and defines a lower, substantially circular region  238  and a narrowed pathway  240  extending from the circular region to the aperture  226 . 
     Between the lowermost edge of the vertically extending portion  208  and the floor  212 , there is defined an opening  242 . 
     Reference is now made to the second cradle component  204  in  FIGS. 24 and 25 . The second cradle component  204  also includes a horizontally extending portion  244  and a vertically extending portion  246 . 
     The horizontally extending portion  244  includes an outer wall  248  and a floor  250 . The floor  250  defines a circular opening for retaining a circular heater pad (not shown), generally similar to the circular metal pad  163  shown in  FIG. 12 . At the rear of the floor  250  is a hole  254  passing through the floor. Beneath the floor  250 , there is provided an extension tube  255 , the passage of which forms a continuation of the hole  254 . 
     At the front extremity of the outer wall  248  are a pair of brackets  256  which are spaced apart from each other, each bracket having an upwardly extending slot  258  which is opened at its upper end, and closed at its lower end. 
     The vertically extending portion  246  of the second cradle component  204  has a circular aperture  260  with a rearwardly extending spigot  261 , as well as a pair of narrow vertical slots  262 , opening through it. 
     There is also provided a rectangular shaped aperture  264 , for electrical connections between the humidifier and the flow generator, or for electrical and signal connections to the humidifier. 
     The upper and side extremities of the vertically extending portion  246  project rearwardly, beyond a rear face  266  of the vertically extending portion, to form a flange  268 . At each of the outer two upper corners of the vertically extending portion, there is provided a dog-legged gap  270 , each gap separating, from a remainder of the flange  268 , a support formation  272 . Each support formation  272  has a cylindrically shaped hub  274  extending sideways from it. It will be appreciated that each support formation  272 , as a result of the respective gap  270 , is only joined to the remainder of the flange  268  at a lower end of the support formation. Accordingly, the gaps  270  allow for a degree of movement of each support formation  272 , and hence its respective hub  274 , relative to the remainder of the vertically extending portion  246 , for a reason that will be described below. 
     After attachment of the seal  280  to the wall  236  at the back of the first cradle component, as described below, the first cradle component  202  and second cradle component  204  are assembled together by inserting the horizontally extending portion  244  of the second cradle component through the opening  242  in the first cradle component, so that the horizontally extending portion  244  is disposed above the floor  212  of the first cradle component, within the recess  214 . In this configuration, a front face  276  of the vertically extending portion  246  of the second cradle component  204  abuts a rear face  278  of the vertically extending portion  208  of the first cradle component  202 . 
     In this configuration, the vertically extending portion  246  of the second cradle component  204  is accommodated below the flange  230 , and between the outer sides  218  of the vertically extending portion  208  of the first cradle component  202 , with the hubs  274  being accommodated in the recesses  234 . 
     The configuration of the assembled first and second cradle components  202  and  204 , respectively, may be better understood with reference to  FIG. 33 . 
     Prior to assembly of the first and second cradle components  202  and  204 , respectively, as described above, an airway seal  280  (see  FIGS. 34 and 35 ) is engaged with the rearwardly projecting wall  236 . The airway seal  280  has a side wall  282  defining a perimeter of the airway seal, the side wall having a shape which is complimentary to that of the rearwardly projecting wall  236 . This permits the rearwardly projecting wall  236  to be attached to the side wall  282  as a press-fit. 
     The airway seal  280  defines a circular aperture  284  which opens through the front face  286  of a rear wall  288  of the airway seal  280 , and through a tubular portion  290 , which projects rearwardly from a rear face  292  of the rear wall  288 . It will be appreciated that the circular aperture  284  is aligned with the circular region  238  defined by the rearwardly projecting wall  236 . Accordingly, with the airway seal  280  engaged with the rearwardly projecting wall  236 , when the second cradle component  204  is engaged with the first cradle component  202  as described above, the tubular portion  290  of the airway seal  280  is received as a close fit in the circular aperture  260  of the vertically extending portion  246  of the second cradle component. As a result, the airway seal  280  defines a closed passage from the circular aperture  260  to the rectangular aperture  226  in the vertically extending portion  208  of the first cradle component  202 . 
     Referring to  FIGS. 26 and 27 , there is shown a water receptacle  294 . The water receptacle  294  has a front wall  296  and a rear wall  298 . The front wall  296  extends forwards from the rear wall  298  to a curved front at  300 . The water receptacle  294  has a floor  302 , the floor having a rim  304  defining a circular opening  306 . 
     At the top of the front and rear walls  296  and  298 , respectively, there is provided an outwardly extending flange  310 . Although the flange is present along the full extent of the upper edges of the front wall  296  and rear wall  298 , it is of a greater dimension at the front of the water receptacle  294  (above the position  300 ) as shown in  FIG. 26 . 
     At each side of the circular opening  306 , there is a hook-shaped formation  308 , which extends from the rim  304 , inwards relative to the opening  306 , and then downwards. The formation  308  is used to engage with a heat-transferable bottom (not shown) which extends over the opening  306  and which forms a seal with the rim  304  so that the water receptacle  294  is suitable for retaining a supply of water therein. 
     The water receptacle  294  is shaped complementarily relative to the space defined by the outer wall  248  and floor  250  of the horizontally extending portion  244  of the second cradle component  204 . Thus, once the second cradle component  204  has been assembled with the first cradle component  202  as described above, the water receptacle  294  can be placed on the floor  250  of the second cradle component as illustrated in  FIG. 33  (in which the water receptacle is shown in phantom lines). 
     Referring now to  FIGS. 28 to 30 , there is shown a lid  318  of the humidifier according to the present embodiment. The lid  318  has an upper wall  320  and a downwardly extending wall  322 , extending from the upper wall. 
     The lid  318  includes a pair of sockets  324  positioned at the rear extremities of the downwardly extending wall  322 , immediately below the upper wall  320 , for hinged connection to the hubs  274  of the second cradle. 
     A double wall  326  depends from the upper wall  320  and includes an inner wall portion  326 . 1  and an outer wall portion  326 . 2 . The wall portions  326 . 1  and  326 . 2  define, between them, a channel  327 . At the rear of the double wall  326  is a tubular structure  328  of substantially rectangular cross-section. The lower end of the tubular structure is constituted by a rim  330  which is angled upwardly in a rearward direction. The tubular structure  328  defines an internal passage  332  which passes through the double wall  326 , to create an air passage from the aperture  226  in the first cradle to an internal region  334  of the lid defined by the inner portion  326 . 1  of the double wall. 
     Extending at an acute angle to the horizontal, from the upper surface of the upper wall  320 , is a pipe  336 . This is for attachment of a hose to supply humidified air to a patient. The pipe  336  passes through the upper wall  320 , with the lower end of the pipe projecting beyond the lower surface of the upper wall, to terminate at a rim  338 . The passage  340  of the pipe  336  opens into the internal region  334 . 
     The upper wall  320  defines, at its rear edge, a recess  342 . At the front of the downwardly extending wall  322 , there is an outwardly-curved finger-grip formation  344 . 
     Attached to the lid  318 , as shown in  FIG. 33 , is a lid seal  350 , which is illustrated in  FIGS. 31 and 32 . The position of the lid seal  350  relative to the lid  318  is illustrated in  FIG. 33 . The lid seal  350  has a centre wall  352 , and, projecting upwards from the centre wall, an outer wall  354  and an inner wall  356 . The outer wall  354  and inner wall  356  define, between them, a channel  358 . In addition, the upper surface of the centre wall  352  has an upwardly projecting curvature  362  which terminates, at its rear edge, at a position spaced from the inner wall  356 , such that a recess  364  is defined immediately adjacent the inner wall, positioned inwards relative to the lid seal  350 . 
     At the rear of the lid seal  350  is a frame formation  366  having an outer wall  368  and an inner wall  370 , the outer and inner wall defining, between them, a channel  372 . The inner wall  370  defines a substantially rectangular centre aperture  374 . The outer and inner walls,  368  and  370 , respectively, each terminate, at their forwardmost edges at  375 , in line with the inner surface of the outer wall  354 , so as not to interrupt the channel  358  defined between the outer wall  354  and inner wall  356 . 
     The lid seal  350  has a roughly elliptical inlet opening  376 , and an elliptical outlet opening  378 . Extending upwardly from the upper surface of the centre wall  352  is an outlet formation  380  which consists of an inner wall  382  and an outer wall  384 , the inner and outer walls defining, between them, a channel  386 . 
     The lower surface of the centre wall  352  of the lid seal  350  is concave as shown in  FIG. 32 , to define a rear, forwardly projecting face  387 . 
     The lid seal  350  is attached to the lid  318 . This is achieved by way of the inner wall  356  of the lid seal being received as a press-fit in the channel  327  defined by the double wall  326  of the lid. The outer portion  326 . 2  is accommodated in the recess  364  of the lid seal  350 . In addition, the rim  338  of the humidified air outlet pipe  336  passing through the lid  318  is received as a press-fit in the channel  386  of the outlet formation  380  of the lid seal  350 . Furthermore, the rim  330  of the rectangular tubular structure  328  of the lid  318  is received as a press-fit in the channel  372  of the frame formation  366 . Accordingly, the manner of attachment of the lid seal  350  effects proper sealing with the lid  318  to define an internal region  334  of the lid. 
     The rectangular centre aperture  374  defined by the frame formation  366  of the lid seal  350  is aligned with the passage  332  in the tubular structure  328  of the lid  318 , so as to open into the internal region  334 . However, as a result of the press-fit between the rim  338  of the pipe  336  and the outlet formation  380  of the lid seal  350 , the passage  340  of the pipe does not open into the internal region  334 , but effectively extends, from the upper edge of the pipe as shown in  FIG. 29 , through the lid to a position below the lid seal. 
     The lid seal  350  may be provided with a downwardly extending, and inwardly curved, sealing flange  388  as shown in  FIG. 38 . 
     When the lid  318  is in its closed position, the lid seal  350  seals against the flange  310  of the water receptacle  294 .  FIG. 38  shows the embodiment of the lid seal  350  which includes a sealing flange  388 , this sealing flange being the part of the lid seal which engages the flange  310 . 
     The lid  318  is engaged with the second cradle component  204  by way of the hubs  274  of the second cradle component being received in the sockets  324  of the lid, so that the hubs and sockets together constitute hinges. This allows the lid  318  to be opened and closed relative to the first and second cradle components  202  and  204 , respectively, as indicated by the arrows  389  and  390  in  FIG. 33 . 
     During opening of the lid  318 , it may be freely rotated about the hubs  274  through greater than 90° until it reaches a maximum extent of normal travel. The lid  318  and second cradle component  204  are configured such that, if the lid  318  is then rotated further, the hubs  274  pop out of the sockets  324 . This may be achieved, as would be understood by a person skilled in the art, by providing suitable chamfers on the hubs  274  and/or sockets  324 , or other suitable formations on the lid  318  or second cradle component  204 , so that the support formations  272  flex relative to the remainder of the vertically extending portion  246  of the second cradle component, to allow the hubs to be displaced from the sockets. 
     Referring to  FIG. 36 , there is shown a lid catch  392 . The catch  392  has a pair of laterally projecting axles  394  and a catch formation  396 . An upper front part  398  of the catch formation  396  is chamfered. A centre portion  400  of the lid catch  392  is recessed and constitutes a thumb actuation pad. 
     The lid catch  392  is mounted on the brackets  256  at the front of the horizontally extending portion  244  of the second cradle component  204 . This is achieved by the axles  394  being accommodated in the slots  258 . When the second cradle component  204  is assembled to the first cradle component  202  as described above, the centre portion  400  of the lid catch  392  is slid into place in the aperture  216  at the front of the horizontally extending portion  206  of the first cradle component  202 . It will be appreciated that the aperture  216  is shaped complementarily to the centre portion  400 , so that the centre portion is surrounded by that part of the horizontally extending portion  206  which defines the aperture  216 . The catch formation  396  then projects above the upper edge of the outer wall  210  of the horizontally extending portion  206 . 
     A suitable biasing means, which may be in the form of a coil spring or other type of spring (not shown), may be provided to urge the catch formation  396  in a forward direction. The lid  318  is provided, at its front extremity, with a suitable recess, indentation, ledge or the like (not shown) which is configured to snap-engage with the catch formation  396  when the lid is closed in the direction of the arrow  390  in  FIG. 33 , to secure the lid in a closed position. The chamfer  398  causes the catch formation  396  to move backwards against the force of the biasing means, to allow the lid  318  to close before the catch formation snaps back to its locking position. To open the lid  318 , the centre portion  400  must be depressed to release the catch formation  396  from the lid  318 . The finger-grip formation  344  facilitates opening of the lid. 
     The humidifier according to the present embodiment may be used in conjunction with a flow generator similar to the flow generator  50  described above. The humidifier is releasably fixed to the flow generator by means of a catch  404  (see  FIG. 37 ). The catch  404  includes an actuation portion  406 , a central bar  408  extending from the actuation portion, and a pair of catch formations  410  and  412  which are supported on support bars  414  which extend laterally from the central bar. It will be noted that each of the catch formations  410  and  412  is provided with a chamfer  416 . 
     The way that the catch  404  is configured to be mounted will depend on the particular embodiment. For example, the catch  404  may be mounted on either the first cradle component  202  or the second cradle component  204 , with the catch formations  410  and  412  extending through the slots  262  in the vertically extending portion  246  of the second cradle component. Suitable biasing means such as a spring (not shown) may be provided to urge the catch  404  in a downward direction. As the humidifier is engaged with the flow generator, suitable slots or other formations on the flow generator engage with the catch formations  410  and  412 . The chamfers  416  allow the catch formations  410  and  412 , and hence the catch  404  as a whole, to ride over the relevant formation on the flow generator so as to move upwards against the urging of the biasing means, so that the catch formations can snap-engage with the flow generator. To release the humidifier from the flow generator, the actuation portion  406  can be depressed from a position below the humidifier, in an upward direction, to release the catch formations  410  and  412 . 
     When the humidifier according to the present embodiment is to be used, the lid  318  can be opened as described above, and the water receptacle  294  removed to allow filling thereof with water. Suitable markings (not shown) can be provided on the water receptacle  294  to indicate a maximum level to which the it is to be filled with water. 
     A microswitch (not shown) or other sensing means may be provided to turn off power to the heater pad when the lid is opened, and/or when the water receptacle is removed. 
     The water receptacle  294  can then be replaced, so that it rests upon the heater pad (not shown) of the horizontally extending portion  244  of the second cradle component  204 . The lid  318  is then closed and the humidifier can be allowed to operate in conjunction with the flow generator. 
     A suitable flow generator is one having an air outlet pipe which is aligned for engagement with the circular aperture  260  in the vertically extending portion  246  of the second cradle component  204 . Thus, air from the flow generator is forced through the circular aperture  260 , via the circular aperture  284  of the airway seal  280  and along the passage defined by the airway seal and the rearwardly projecting wall  236  of the first cradle component  202 , through the rectangular aperture  226 . 
     The lid  318  and frame formation  366  of the lid seal  350  are configured such that when the lid  318  is in its closed position as described above, the frame formation presses and seals against the rim  228  defining the aperture. It will be appreciated that the angle at which the rim  228  slopes corresponds to the angle of the rim  330  of the rectangular tubular structure  328  of the lid  318 , and also the angle at which the frame formation  366  extends, to facilitate this sealing engagement. Thus, air passing from the flow generator via the rectangular aperture  226  passes through the aperture  374  of the seal frame formation  366 , and though the passage  332  in the tubular structure  328  of the lid  318 , into the space defined by the internal region  334  of the lid and the lid seal  350 . This air then travels over the upper surface of the centre wall  352  of the lid seal  350  and then passes downwardly, through the inlet opening  376  and into the headspace of the water receptacle  294 . 
     Where the lid seal  350  includes an inwardly curved sealing flange  388  as described above, the pressure of the air within the headspace of water receptacle from the flow generator serves to force the extension portion outwards, and hence downwards, so as to increase the sealing effect against the flange  310  of the water receptacle  294 . The flexibility of the lid seal  350 , especially where it includes the sealing flange  388 , provides for a certain amount of play of the lid  318  while maintaining the sealing effect. 
     Once the air from the flow generator passes via the inlet opening  376  of the lid seal  350  into the water receptacle, the air then travels across the surface of the water in the water receptacle so that the air becomes humidified. The heating of the water by the heating element enhances this humidification. The air then exits the water receptacle  294  by passing through the outlet opening  378  in the lid seal  350 , and then through the passage  340  of the pipe  336  in the lid  318 . As indicated, the pipe  336  is attached to a suitable hose (not shown) for supplying the humidified air to a patient. 
     In addition to those features and advantages already described, the components and features of the humidifier according to the present embodiment have various advantages. 
     By providing the top seal to the water receptacle as part of the humidifier lid, improved simplicity of use is achieved while minimising the risk of spillage of water. Furthermore, like the first-described embodiment of the humidifier, the humidifier of  FIGS. 22-38  is configured to reduce the risk of water backflow into the flow generator, for example by the relative positioning of the opening  376  and the aperture  226  and the height differential between the aperture  226  and the air outlet of the flow generator. Also, the shape of the air path defined by the seal  280 —including an upper portion which is above the aperture  226  in the first cradle component—reduces the possibility of backflow from splashing of water if the user uses a jug or similar to fill the water receptacle in situ, as the water will flow back out of the aperture  226  rather than back through to the circular aperture  260  in the second cradle component. 
     In addition, the recess  364  and the forwardly projecting face  387  in the lid seal  350  are adapted to collect condensation which may form in the lid cavity and the headspace of the water receptacle, preventing backflow of this condensation to the flow generator when the lid is opened. 
     Furthermore, the configuration of the first and second cradle components  202  and  204  and is adapted to allow fitting together in a vertical orientation, to minimise the need for reorientation during assembly of the humidifier unit on the production line. 
     In addition, the resilience of the connection between the lid and the water receptacle, provided by the lid seal, is adapted to maintain downwards pressure on the water receptacle when the lid is closed, to maintain good heat-transfer contact between the base of the water receptacle and the heater pad without the added complexity and expense of spring-loaded mounting of the heater pad. 
     Second Further Embodiment of the Humidifier 
       FIGS. 39 to 49B  relate to a humidifier according to yet a further embodiment of the invention. The humidifier according to this embodiment has components generally corresponding to those of the previous embodiment, although the specifics of the components differ, as will be apparent from the description below. 
     The humidifier according to the present embodiment includes a first cradle component  602  which has a horizontally extending portion  604  and a vertically extending portion  606 . The horizontally extending portion  604  has an outer wall  608 , and the vertically extending portion  606  has a front wall  610 . 
     The front wall  610  and outer wall  608  together define an opening  612  at the bottom of the first cradle component  602 , and the front wall has a recess  614  at its lower edge. 
     At each side of the first cradle component  602 , the upper edge of the outer wall  608  continues rearwardly of the front wall  610  and curves upwards to define a forward projecting, face  616 . The outer wall  608  continues rearwardly of each face  616  to form rear side-walls  608 . 1 . The first cradle component  602  also has an upper wall  618  which extends from the front wall  610  and side-walls  608 . 1 . The upper wall  618  has a rear recess  620 . 
     Immediately in front of the face  616  at each side of the first cradle component  602 , adjacent the upper wall  618 , there is a socket  622 . Adjacent each socket  622  there is a further, smaller socket, referred to below as a stud socket  623 . The inside of each socket  622  and stud socket  623  is closed by a formation  624  as seen in  FIG. 39 . 
     The front wall  610  defines a circular aperture  626  and has a pair of tubular protrusions  628  extending rearwardly from the rear surface of the front wall. Each protrusion  628  has a central passage  630 . 
     Referring to  FIGS. 41 and 42 , there is shown a second cradle component  632 . The second cradle component  632  has an upper wall  634  and a downwardly extending wall  636  extending from the upper wall. At the rear of the upper wall  634  is a flange  638 . The flange  638  defines two semi-circular notches  640  with two pairs of semi-circular arches  642  being attached, at each side of the second cradle component  632 , to the flange  638 . Thus, each pair of arches  642  and their corresponding notches  640  define a circular passage  644 . 
     At the front extremity of the wall  636  there is provided a forward extending tab  646 . The tab  646  is of dog-legged shaped, having a first tab portion  646 . 1  extending from the wall  636 , a second tab portion  646 . 2  sloping upwards from the first portion, and a third tab portion  646 . 3  extending forwards from the second tab portion. 
     The second cradle component  632  is configured to accommodate, below the upper wall  634  and within bounds of the wall  636 , a heater pad or other heating means such as an induction heater, for causing heating of the water in the humidifier water container. 
     Referring to  FIGS. 43 and 44 , there is shown a lid  648  of the humidifier according to the present embodiment. The lid  648  has an upper wall  650  and a front wall  652  which extends downwards, and outwardly, from the upper wall. The upper wall  650  has a recess  654  at its rear side, such that the part of the upper wall and front wall  652  on each side of the recess constitutes a rearwardly projecting arm  656 . At the rearmost extremity of each arm  656  there is an inwardly projecting hub  658 . The hubs  658  are configured to be received in the sockets  622  of the first cradle component  602  such that each hub and its corresponding socket constitute a hinge connection, for attaching the lid  648  to the first cradle component. 
     The lower edge of each arm  656  is shaped complementarily to the shape of the upper portion of the face  616  to accommodate that part of the arm when the lid  648  is in a closed position, as will be described further below. 
     Immediately adjacent each hub  658  there is provided an inwardly projecting stud  660 , each stud being configured to snap-engage into a respective stud socket  623 . This is to restrain the lid  648  against opening too easily. 
     The lid  648  includes a humidified air outlet pipe  662  which passes through the upper wall  650  and extends upwards and forwards from the top of the upper wall. The pipe  662  continues below the lower surface of the upper wall  650  to define a spigot  664 . 
     Extending downwards from the lower surface of the upper wall  650  is a wall  666  which is configured to define a closed path and hence a U-shaped enclosed region  668  within the confines of the wall. Strengthening webs  670  are provided to brace the wall  666  and spigot  664  relative to the upper wall  650 , to provide added strength. 
     There is provided a pipe  672  which passes through a rear part of the wall  666  at one end of the U-shaped enclosed region  668 . 
     At the front extremity of the front wall  652 , that is, adjacent the lower edge of that wall, there is provided a recessed notch  674  on the rear (inner) surface of that wall. 
     A resilient sealing member  676  of elastomeric or other suitable resilient material (see  FIGS. 45 and 46 ) is mounted on the lower extremities of the wall  666  and spigot  664 . The sealing member  676  has a first U-shaped portion  678  of a shape corresponding to that of the wall  666 , and a second portion  680  of elliptical shape, corresponding to the downwardly projecting shape of the lower extremity of the spigot  664 . The first and second portions  678  and  680 , respectively, are joined to each other by a web  682 . 
     As can be seen in  FIG. 46 , the first portion  678  has an inner wall  683  and an outer wall  684 , the inner and outer walls defining a channel  686  between them. Similarly, the second portion  680  has an inner wall  688  and an outer wall  690 , these inner and outer wall defining a channel  692  between them. The sealing member  676  is engaged with the lid  648  by way of the wall  666  being received as a press-fit in the channel  686 , and the spigot  664  being received as a press-fit in the channel  692 . 
     The sealing member  676 , at the bottom of each of the first and second portions  678  and  680 , has a sealing flange  694  and  696 , respectively. The sealing flange  694  (which is similar to the sealing flange  696 ) is shown schematically in cross-section in  FIG. 46A . 
     Referring to  FIGS. 47 to 49 , there are shown a lower component  698  and an upper component  700  of a water receptacle forming part of the humidifier according to the present embodiment. The lower component  698  has a lower wall  702  and side walls  704  extending upwardly from the lower wall. A U-shaped recess  706  is provided in the lower wall  702 , to assist positioning of the receptacle on the heater pad upper wall  634 . At the upper edge of the side walls  704  there are provided rebates  708  on the outer edges of the walls. It will be appreciated that the side walls  704  together form a continuous wall. 
     The upper component  700  has an upper wall  710  and front wall  712  extending downwardly from the edges at the sides and front of the upper wall, and a rear wall (not shown). The front wall  712  extends beyond the rearmost extremity of the upper wall  710  to form a pair of side wings  714 . 
     A roughly elliptical aperture  716  opens through the upper wall  710 . In addition, there is provided an arc-shaped recess  718  which extends around the aperture  716 , and which increases in depth from one end  718 . 1  to an opposite end  718 . 2 . At the end  718 . 2  there is provided a further aperture  720  which opens out below the upper wall  710  to the headspace of the water receptacle. 
     The humidifier according to the present embodiment is assembled by sliding the second cradle component  632  through the recess  614  in the front wall  610  of the first cradle component  602  until the tab  646  engages with the forwardmost part of the outer wall  608 . In this position, the third tab portion  646 . 3  extends over the upper edge of the outer wall  608 . As the second cradle component  632  is slid into place as described, the protrusions  628  projecting from the rear of the front wall  610  protrude through the passages  644  defined by the flange  638  and arches  642  of the second cradle component  632 . Fasteners (not shown) such as screws or bolts can be used to secure the second cradle component  632  to the first cradle component  602 . This is achieved by screwing the fasteners into the passages  630  of the protrusions  628  so that the heads of the fasteners hold the second cradle component  632  captive. 
     The lid  648  is engaged with the first cradle component  602  by manipulating the arms  656  so that the hubs  658  snap-engage into the sockets  622 , so that each hub and the corresponding socket constitute a hinge. The lid  648  is thus capable of rotating relative to the first cradle component  602 . 
     Also forming part of the humidifier according to the present embodiment is a flexible air connector component  722  as shown in  FIGS. 49A and 49B . The air connector component  722  includes a first bellows-like flexible hose  724  having an end rim  726 , and a second tube  728  extending in an opposite direction to the flexible pipe, the flexible pipe and second tube being interconnected by a connection chamber  730  which serves a generally similar function to seal  280  of  FIGS. 34 and 35 . 
     It will be noted that the configuration of the air connector component  722  is such that the flexible hose  724  and second tube  728  are arranged in a dog-leg configuration so as not to be in alignment with each other. 
     During assembly of the humidifier according to the present embodiment as was partly described above, the flexible hose  724  is passed through the circular aperture  626  in the front wall  610  until the front face of the connection chamber  730  abuts the rear face of the front wall. The air connector component  722  may then be fixed in place relative to the front wall  610  by suitable means (not shown). The end rim  726  is then engaged with the pipe  672  of the lid, by receiving this pipe as a press-fit, to create a flexible connection which can withstand opening and closing of the lid. The second tube  728  connects to the air outlet of the flow generator. 
     To form the water receptacle, the lower component  698  and upper component  700  thereof are fitted together, so that a lower edge of the front wall  712  of the upper component is accommodated in the rebate  708  of the lower component, which ensures that these components are sealed in a substantially watertight manner to each other. The assembled water receptacle can then be lowered onto the upper wall  634  of the second cradle component  632 , this upper wall being disposed within the bounds of the outer wall  608  of the first cradle component  602 . The shape of the front wall  712  of the upper component  700  of the water receptacle, and in particular the wings  714 , is such that the water receptacle is accurately located in position by the outer wall  608  and front wall  610  of the first cradle component  602 . 
     When the lid  648  (which was attached to the first cradle component  602  as described above) is rotated downwards about the hinges formed by the hubs  658  and sockets  622 , the front tip of the third portion  646 . 3  of the tab  646  of the second cradle component  632  is received as a snap-fit in the notch  674  at the front of the lid to hold the lid closed. 
     Furthermore, the first portion  678  of the sealing member  676  forms a substantially watertight seal around the recess  718  in the top of the upper component  700  of the water receptacle. Similarly, the second portion  680  of the sealing member  676  forms a substantially water tight seal around the aperture  716  in the upper component  700  of the water receptacle. The watertightness of the seals is enhanced by the sealing flanges  694  and  696  of the first and second portions  678  and  680 , respectively, of the sealing member  676 . 
     In use, the water receptacle may be filled by first opening the lid  648  by disengaging the notch  674  from the third tab portion  646 . 3  and rotating the lid upwards relative to the first cradle component  602 . Water can then be poured into the water receptacle via the aperture  716  in the upper component  700 , whereafter the lid  648  can be closed again. 
     The humidifier according to the present embodiment can be used in conjunction with a flow generator similar to the flow generator  50  described above, and may be attached to the flow generator using a catch, and catch arrangement, similar to that described in relation to the catch  404  of the previous embodiment. 
     The humidifier according to the present embodiment is configured such that, when it is mounted on the flow generator, the second tube  728  of the air connector component  722  is engaged with an air outlet pipe of the flow generator. In use, air travels from the flow generator through the second tube  728 , via the connection chamber  730  and then through the flexible hose  724  which, as described above, extends through the circular aperture  626  in the front wall  610  of the first cradle component  602 . The air then travels through the pipe  672  of the lid  648  and into one end of the U-shaped enclosed region  668  defined by the wall  666  which depends from the lid. The flexibility of the flexible hose  724  allows the rim  726  to remain engaged with the pipe  672  while the lid  648  is opened or closed. 
     It will be appreciated that when the lid  648  is in its closed position, the sealing member  676 , which is attached to the wall  666  and spigot  664 , presses down on top of the upper component  700  of the water receptacle, as described above, so that the enclosed region  668  is not only enclosed by the wall  666  and the lower surface of the upper wall  650  of the lid, but also by the floor of the arc-shaped recess  718  defined in the upper component  700  of the water receptacle. Accordingly, the air from the flow generator which passes through the pipe  672  flows through the U-shaped path defined in the enclosed region  668  before passing through the further aperture  720  at the other end  718 . 2  of the recess  718 , into the headspace of the water receptacle. The U-shape of the enclosed region  668  and recess  718  results in the air entering the water receptacle with a swirling motion which facilitates the humidifying of the air as it passes over the water in the receptacle. 
     The air then exits the water receptacle via the elliptical aperture  716 . As described above, the second portion  680  of the sealing member  676  is sealed around the aperture  716  so that the humidified air exiting the water receptacle via the aperture  716  passes through the second portion of the sealing member, via the spigot  664  and out through the humidified air outlet pipe  662  at the top of the lid  648 . A suitable hose (not shown) delivers the humidified air as required to a patient. 
     As the air supplied from the flow generator is under pressure, this pressure assists the sealing flange  694  of the sealing member  676  to create a firm seal around the recess  718  by forcing the extension portion outwards and downwards. A similar effect is created on the sealing flange  696  of the second portion  680  surrounding the elliptical aperture  716  due to the pressure of the air exiting the water receptacle. 
     New Flow Generator Embodiment 
       FIG. 50  is an exploded view of a flow generator  1050  according to a further embodiment, which is an alternative version of the flow generator  50  of the first embodiment.  FIGS. 51-53  are more detailed views of components of the flow generator of  FIG. 50 . 
     The components and functioning of the flow generator  1050  are similar in many respects to that of  FIGS. 1 to 21 , and reference may be made to those figures and their description for more detailed description of the flow generator and its components. 
     The bottom case  1061  of flow generator  1050  has a shell  1120  of rigid plastics material, such polycarbonate/ABS blend, forming the structure of the case, integrally overmoulded with a lining  1121  of an elastomer such as a synthetic rubber which forms the seal  1063  between the top and bottom cases and the chassis  1064  and forms the external feet of the case (not shown). The lining  1121  also covers the internal surface of the chassis-receiving cavity  1122  of the bottom case and the dividing wall  1123  between the power supply cavity  1065  and chassis-receiving cavity, to reduce radiated noise levels from the flow generator by damping acoustic resonance of the walls. 
     A power supply unit  1124  is received in the power supply cavity  1065 , for providing electrical power for operation of the fan, control functions and the humidifier heater pad. 
     The chassis  1064  forms the fan cavity  1070 , inlet and outlet air flow paths and the top of the power supply cavity  1065 . The fan cavity  1070  includes a metal liner tub  1073  insert moulded into the chassis as described above in relation to  FIGS. 1 to 21 . Preferred materials for the chassis and liner tub are polypropylene thermoplastic for the chassis and metal, preferably steel, for the liner tub. The applicant has found that by forming the fan cavity as a composite of metal and polymer—having a differential in density of greater than 5 times, preferably about 7-8 times, and also significantly different stiffness and damping properties—the resonance peaks of the composite structure are well damped so that noise generated by the fan is well-suppressed by the fan cavity construction. 
     The top of the fan cavity is formed by the chassis lid  1074 , which is formed of a steel insert overmoulded with elastomer to provide acoustic damping. 
     The fan  1090  and fan housing  1093 ,  1094 , substantially similar to the fan  90  shown in  FIGS. 9 and 10 , fit into the fan cavity  1070  of the chassis and connect to electrical connector  1126  on the chassis at the top of the fan cavity. Elastomer overmoulding of the base  1094  of the fan housing seals the housing, provides acoustic damping of the fan housing base and forms feet on the bottom of base to act as bump stops protecting the fan in case the unit is bumped or dropped. 
     An elastomeric outlet seal  1108  connects the volute outlet  1097  to the connecting nozzle  1110  of the flow generator chassis  1064 . A Helmholtz resonator, as previously described, or a volume muffler cavity (not shown), may be incorporated in the chassis moulding to communicate with the air between the fan volute outlet  1097  and the nozzle  1110 . 
     The printed circuit board  1081 , which controls operation of the machine, sits on top of the chassis lid  1074  under the top case  1060  of the flow generator, and includes an LCD display  1058 . 
     A keypad  1059 , facia  1127 , transport handle  1128  and slots  1155  attach to the top case  1060 . 
     The top case further defines an air inlet to the flow generator, and a replaceable foam filter  1129  and filter cover  1130  fit to the top case  1060 , held in place by an inlet wedge  1131 . A blank cover  1132  clips in place over apertures in the case which align with ports on the PCB for communications, etc. 
     The illustrated flow generator construction and materials combinations are adapted to result in a compact CPAP flow generator unit of similar performance and noise characteristics to larger units—eg. capable of generating from 4-20 cm H2O pressure and a flow rate of 120 L/min and a total noise volume (radiated plus conducted) of less than 33 dbA, more preferably less than about 30 dbA, when operating at 10 cm H2O—in a flow generator unit having a total volume of about 2 liters or less. 
     New Humidifier 
       FIGS. 54 to 58B  illustrate a modified version of the humidifier arrangement of  FIGS. 39 to 49B , adapted to mate with the flow generator unit of  FIGS. 50-53 . The general arrangement of the humidifier components is similar to that of  FIGS. 39 to 49B , including a front cover  1602  onto which is fitted a heater pad  1799  comprising and an upper part  1806  and a heater pad cover  1632  which supports a water tub (tub base  1698 , seal  1699  and tub lid  1700 ) and a hinged humidifier lid  1648  which seals against the tub lid  1700  to form an air path into the tub through the tub lid. 
     The heater pad cover  1632  has an upper surface  1634 , a downwardly extending peripheral wall  1636  and a rear flange with a pair of attachment portions  1640  for attachment of the heater pad  1799  to tubular protrusions  1628  on the rear of the front cover  1602 . The front of the heater pad cover  1632  has a forwardly extending tab  1646  of dog-legged shape, which extends to the front of the humidifier cradle front cover  1602  to support the heater pad  1799  and also provide a catch for the humidifier lid  1648 . 
     The floor of the tub base  1698  is of complementary shape to the heater pad  1799 . The floor has a generally horizontal portion  1900  corresponding to the upper surface  1634  of the heater pad cover  1632  and a U-shaped portion below the level of the upper surface  1634 , including a generally vertical heat transfer portion  1902  below the horizontal portion  1900  corresponding to the downwardly extending peripheral wall  1636  of the heater pad cover  1632 . When the water tub is placed in the humidifier cradle and the hinged lid  1648  is closed, the water tub base  1698  is held in close contact with the heater pad  1799 . 
     The lid  1648  has an upper wall  1650  and a front wall  1652  which extends downwards, and outwardly, from the upper wall  1650 . The upper wall  1650  has a recess at its rear side, such that the part of the upper wall  1650  and front wall  1652  on each side of the recess constitutes a rearwardly projecting arm  1656 . At the rearmost extremity of each arm  1656  there is an inwardly projecting hub  1658 . The hubs  1658  are configured to be received in the sockets  1622  of the humidifier front cover  1602  such that each hub  1658  and its corresponding socket  1622  constitute a hinge connection, for attaching the lid  1648  to the front cover  1602 . 
     The lid  1648  includes a humidified air outlet pipe  1662  which passes through the upper wall  1650  and extends upwards and forwards at an acute angle from the top of the upper wall  1650 . The pipe  1662  continues below the lower surface of the upper wall  1650  to define an elliptical rim  1664 . 
     Extending downwards from the lower surface of the upper wall  1650  is a wall  1666  which is configured to define a closed path and hence a U-shaped enclosed region  1668  within the confines of the wall  1666 . 
     At the front extremity of the front wall  1652 , that is, adjacent the lower edge of that wall, there is provided a recessed notch  1674  on the rear (inner) surface of that wall, for snap-fit engagement with the tab  1646  of the heater pad cover  1632  to act as the catch for the lid  1648 . The lid  1648  may be opened by flexing the assembly to release the tab  1646  from the notch  1674 . 
     The humidifier of  FIG. 54  differs substantially from that of  FIGS. 39-49B  by a modified sealing arrangement for the air path from the flow generator outlet into the humidifier tub, without the flexible connector component  722  of  FIGS. 49A and 49B . 
     The humidifier front cover  1602  and tub lid  1700  of  FIG. 54  are similar in many respects, including their attachment, to their correspondingly numbered components  602 ,  700  described and shown with reference to  FIGS. 39, 40 and 49 . The aperture  1626  of the modified front cover is enlarged, and receives an elastomer seal  1722  ( FIG. 55 ) having an inlet connector portion  1722   a  which connects to the flow generator outlet and a peripheral seal portion  1722   b  which extends about the aperture  1626  periphery at the front face of the cover  1602 . A wall portion  1722   c  of the seal closes off a lower part of the aperture  1626 , leaving a smaller aperture  1722   d  defined by the seal. 
     As shown in  FIG. 58A , the rear surface of the tub lid has an inlet aperture  1801  leading to an inlet end of the U-shaped air passage  1718 . When the humidifier lid  1648  is closed, the tub  1698  and tub lid  1700  are pressed rearwards so that the peripheral seal  1722   b  abuts the rear surface of the tub lid in a locus surrounding the rear opening of the inlet aperture  1801 , creating a sealed air path from the flow generator to air passage  1718  and into the headspace of the humidifier tub. This allows the humidifier tub to be removed for refilling and replaced without the need for a separate operation to connect the air flow. 
     With reference to  FIG. 58B , the inside wall of the tub lid  1700  has projections  1802  which serve to limit the press fitting of the tub lid onto the tub base  1698 . One projection  1802   a  is provided at the front of the tub, and further projections  1802   b , or sets of projections, are provided on opposed side walls of the tub lid, forward of the rear of the tub. This positioning of the projections  1802   b  allows one-handed disengagement of the tub base and tub lid by squeezing together of the base and lid at their rear end, causing the connection to pivot about the side projections  1802   b  and the tub and lid to separate at the front. The ability to separate these components one-handed is a feature of considerable utility, especially for stroke patients or other users with limited dexterity. 
       FIGS. 56 to 57B  show the underside of the humidifier lid  1648  and the seal  1676  which provides a seal to the tub lid  1700  about the U-shaped passage  1718  and the humidified air exit aperture  1716 . The seal  1676  comprises an edge seal portion  1676   a  and membrane portion  1676   b.    
     The humidifier construction of  FIG. 54  further includes back cover  1803  which fits to the rear of the front cover  1602  to cover the underside of the heater plate and provide support for a control PCB  1804  and a catch assembly. The catch assembly includes a latch  1404  held in place by latch retainer  1404   a  to be moveable vertically and resiliently urged downwardly by spring  1404   b , so that the tongues  1156  engage in the slots  1155  and snap home to engage the two units by means of the downwardly extending fingers  1158  at the ends of the tongues. In other words, the catch assembly operates to attach the humidifier to the flow generator generally as described for the earlier embodiments. A control knob  1805  on the top of the front cover  1602  is connected to the PCB  1804  to allow patient control over the degree of humidification. 
     The illustrated humidifier construction provides a compact humidifier adapted for ease of manufacture and use, and further provides protection against backflow of water into the flow generator when the humidifier and flow generator units are assembled together. Backflow protection is provided by the sloping floor of the air passage and the location of the air inlet aperture  1801  and the aperture  1722   d  in the seal  1722  relative to the air inlet  1720  from the air passage  1718  into the headspace of the humidifier tub  1698 . In particular, if the tub is overfilled while in its horizontal position, the water will flow back along the U-shaped air passage  1718  only as far as its forwardmost portion, which has a front wall  1717  lower than the air inlet aperture  1801 , and will drain towards the front of the machine. If the machine is tipped up onto its rear, the water will be prevented from flowing back along the air passage from the tub to the air inlet  1801  as the intermediate portion of the air passage  1718  will be above the level of the air inlet  1720 . The water will then flow back into the tub once the machine is righted. 
     It is emphasised that the forgoing disclosure has sought to describe many innovations in flow generator and humidifier design, and it is foreshadowed that these will be the subject of separate claims to protection in applications claiming the priority of this document. 
     While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.