Abstract:
An apparatus ( 10 ) for supplying breathable gas is disclosed. The apparatus ( 10 ) includes a main housing ( 12 ), a sub-housing ( 14 ), having a gas flow path ( 28 ) between a gas inlet ( 16 ) and a gas outlet ( 18 ), a motive power source ( 22 ) within the main housing ( 12 ) and an impeller ( 30 ) within the sub-housing ( 14 ) in fluid communication between the gas inlet ( 16 ) and the gas outlet ( 18 ). The impeller ( 30 ) is adapted to releaseably engage the motive power source ( 22 ) external the gas flow path ( 28 ) and the sub-housing ( 14 ) is releasably connectable to said main housing.  
     Also disclosed is a method of cleaning, sterilising or disinfecting the gas flow path ( 28 ) of the breathable gas supply apparatus ( 10 ). The method of cleaning comprising the steps of removing the sub-housing ( 14 ) from the main housing ( 12 ) cleaning, sterilising, disinfecting or replacing the sub-housing ( 14 ) and connecting the sub-housing ( 14 ) to the main housing ( 12 ).

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to an apparatus for supplying breathable gas to a human used in, for example, the Continuous Positive Airway Pressure (CPAP) treatment of Obstructive Sleep Apnea (OSA), other respiratory diseases/disorders such as emphysema or the application of assisted ventilation.  
         BACKGROUND OF THE INVENTION  
         [0002]    CPAP treatment of Obstructive Sleep Apnea (OSA) involves the delivery of a breathable gas (generally air) pressurised above atmospheric pressure to a patient&#39;s airways via a conduit and a mask. CPAP pressures of 4 cm H 2 O to 22 cm H 2 O are typically used for treatment of OSA, depending on patient requirements. Treatment pressures for assisted ventilation can range of up to 32 cm H 2 O and beyond, again depending on patient requirements.  
           [0003]    For either the treatment of OSA or the application of assisted ventilation or similar, the pressure of the gas delivered to patients can be constant level, bi-level (in synchronism with patient breathing) or auto setting in level. Throughout this specification reference to CPAP is intended to incorporate a reference to any one of, or combinations of, these forms of pressurised gas supply.  
           [0004]    A disadvantage of existing CPAP gas supply apparatus, especially those used in hospitals and the like, is the danger of biological contamination and disease/virus/bacteria transfer. More particularly, there can be a significant reverse flow during heavy expiration and/or coughing and biological material exhaled by a patient can be deposited in the gas supply apparatus and transferred to another patient who uses the same machine. Further, a patient continually using the same machine can be re-infected by a prior condition.  
           [0005]    Hitherto, CPAP apparatus have basically comprised a closed outer casing surrounding internal components. Components inside, and constituting part of, the gas flow path include the gas inlet, inlet filter, impeller, outlet muffler and gas outlet. Components outside the gas flow path include control electronics, power regulators and motor. As a result, present CPAP apparatus have a gas flow path that is extremely difficult to clean/sterilise without the time consuming dismantling and removal of all the “gas flow path” components. Further, without disassembly, common sterilisation procedures such as autoclaving will damage the circuit boards and other electrical components.  
           [0006]    An attempt to solve the above problem involves incorporating a bacteriological filter into the gas flow path adjacent the gas outlet to prevent biological material being forced back into the machine and any such material leaving the machine and being inhaled by the patient. However, these filters are expensive and add a significant resistance to the air path requiring larger and noisier fans and motors. A more restricted air path also represents a major difficulty to administering bi-level CPAP treatment due to the higher inspiratory air flow requirements of patients with advanced respiratory disease. Moreover, it is difficult to produce a biological filter which can trap very small biological particles such as viruses and spores that is still able to pass the required amount of air with an acceptable pressure drop, as decreasing filter pore size decreases hydraulic permeability.  
           [0007]    It is an object of the present invention to substantially overcome or at least ameliorate one or more of the above prior art deficiencies.  
         SUMMARY OF THE INVENTION  
         [0008]    Accordingly, in a first aspect, the present invention provides an apparatus for supplying breathable gas, the apparatus including:  
           [0009]    a main housing;  
           [0010]    a sub-housing having a gas flow path between a gas inlet and a gas outlet;  
           [0011]    a motive power source within the main housing;  
           [0012]    an impeller within the sub-housing in fluid communication between the gas inlet and the gas outlet, the impeller adapted to releaseably engage the motive power source external the gas flow path,  
           [0013]    wherein the sub-housing is releasably connectable to said main housing.  
           [0014]    Preferably, the sub-housing includes one or more of an inlet filter, outlet muffler, gas flow rate sensing means, gas pressure sensing means or gas supply vent valve assembly.  
           [0015]    Desirably, the motive power source is an electric motor.  
           [0016]    Desirably also, the main housing includes one or more of a power supply and control system for the motor.  
           [0017]    The motor preferably includes an output shaft terminating in an engaging formation adapted to releasably engage a complimentary engaging formation provided on the impeller.  
           [0018]    The main housing preferably also includes a removable or pivotable lid adapted to restrain the sub-housing adjacent the main housing. In a preferred form, the lid includes acoustic shielding to reduce the emission of noise generated by the impeller and motor.  
           [0019]    In a preferred embodiment, the gas flow rate sensing means includes a flexible flap in the gas flow path, the flap disposed between a light source and a linear image sensor respectively disposed either side of the flap and external to the gas flow path, whereby the amount of light incident on the image sensor is proportional to the deflection of the flap which is proportional to the gas flow rate.  
           [0020]    In another preferred embodiment, the gas pressure sensing means includes a flexible membrane having one side in fluid communication with the gas flow path and an opposite side abutting a force probe coupled to a force transducer, whereby the displacement of the probe and transducer is proportional to the displacement of the membrane which is proportional to the gas pressure.  
           [0021]    In yet another preferred embodiment, the gas vent valve assembly includes a gas venting conduit in fluid communication with the gas flow path, the gas venting conduit adapted to be selectively restricted by a cam abutting the gas venting conduit exterior, whereby varying the cam position varies gas passing through the gas venting conduit which varies the flow rate of remaining gas leaving the gas outlet.  
           [0022]    Preferably, the motor power source includes a disk having magnets thereon and the impeller includes magnets mounted thereon, the disk magnets and the impeller magnets being adapted to attract.  
           [0023]    Alternatively, the motive power source includes a disk having magnets thereon and the impeller includes a magnetically attractable plate mounted thereon, the disk magnets and the plate being adapted to attract.  
           [0024]    In another embodiment, the motive power source includes a disk having magnets thereon and the impeller includes a non-ferrous metal plate, or a plate formed from a non magnetically attractable material having non-ferrous metal therein, mounted thereon.  
           [0025]    In a further embodiment, the impeller includes a shaft having ferrite or other magnetic material mounted thereon and the main housing includes electric motor windings adapted to surround the ferrite or other magnetic material.  
           [0026]    In a second aspect, the present invention discloses a method of cleaning, sterilising or disinfecting the gas flow path of the breathable gas supply apparatus of the first aspect, said method comprising the steps of:  
           [0027]    (a) removing the sub-housing from the main housing, and  
           [0028]    (b) cleaning, sterilising, disinfecting or replacing the sub-housing; and  
           [0029]    (c) connecting the sub-housing to the main housing. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0030]    Preferred embodiments of the invention will now be described by way of example only, with reference to the accompanying drawings in which:  
         [0031]    [0031]FIG. 1 is a cross sectional side view of a first embodiment of an apparatus according to the invention in an assembled state;  
         [0032]    [0032]FIG. 2 is a side view of the apparatus shown in FIG. 1 in a disassembled state;  
         [0033]    [0033]FIG. 3 is a sectional side view of a gas flow rate sensing mean which can be incorporated into the apparatus of FIG. 1;  
         [0034]    [0034]FIG. 4 is a side view of a gas pressure sensing means which can be incorporated into the apparatus of FIG. 1;  
         [0035]    [0035]FIG. 5 is a side view of a portion of a gas vent valve assembly which can be incorporated into the apparatus of FIG. 1;  
         [0036]    [0036]FIG. 6 is a top view of another gas vent valve assembly which can be incorporated into the apparatus of FIG. 1;  
         [0037]    [0037]FIG. 7 is a schematic sectional side view of a second embodiment of an apparatus according to an invention in an assembled state;  
         [0038]    [0038]FIG. 8 is a schematic cross sectional side view of an alternative form of sub-housing which can be used with the main housing shown in FIG. 7;  
         [0039]    [0039]FIG. 9 is a top view of an impeller housing and motor assembly adapted for use with an apparatus according to the invention;  
         [0040]    [0040]FIG. 10 is a cross sectional side view of the assembly shown in FIG. 9 along line  10 - 10  of FIG. 9;  
         [0041]    [0041]FIG. 11 is an exploded view of the housing shown in FIG. 10;  
         [0042]    [0042]FIG. 12 is a schematic top view of a first magnet arrangement used in the embodiment shown in FIG. 7;  
         [0043]    [0043]FIG. 13 is a schematic top view of a second magnet arrangement used in the embodiment shown in FIG. 7;  
         [0044]    [0044]FIG. 14 is a schematic top view of a third magnet arrangement used in the embodiment shown in FIG. 7;  
         [0045]    [0045]FIG. 15 is a schematic cross sectional side view of the magnet arrangement shown in FIG. 14; 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0046]    Referring firstly to FIG. 1, there is shown an apparatus  10  for supplying breathable gas in accordance with a first embodiment of the invention. The apparatus  10  includes a main housing  12  and a sub-housing  14 . The sub-housing  14  has a gas inlet  16  and a gas outlet  18  which is connected to a face mask (not shown) by a flexible conduit  20  to supply a breathable gas (eg. air) to a patient.  
         [0047]    The main housing  12  includes a motive power source in the form of an electric motor  22  which receives power from an electrical power source  24 . An electronic control system  26  controls the power source  24  to thus control the speed of the motor  22 .  
         [0048]    The inlet  16  and the outlet  18  represent the beginning and end respectively of a gas flow path through the sub-housing  14 . The passage of gas along the flow path is represented by arrows  28 . The sub-housing  14  also includes an impeller  30  disposed in the flow path in fluid communication between the inlet  16  and outlet  18  and partitions  32  which form a housing around the impeller  30  and an expansion chamber-type outlet muffler  31 .  
         [0049]    The impeller  30  includes a female engagement formation in the form of slotted cylinder  34  which is adapted to releasably engage to the male engagement formation on the end of motor shaft  36  in the form of projections  38  (only one shown). It is important to note that the engagement between the impeller  30  and the motor shaft  36  is external the gas flow path. Other engaging arrangements such as splines, dogs, clips, non contact magnetic couplings or the like can also be used.  
         [0050]    The main housing  12  includes a hinged lid  40  which is adapted to releasably clamp the sub-housing  14  to the main housing  12 . The lid  40  can include acoustic shielding to reduce the emission of noise generated by the impeller  30  and the motor  22 .  
         [0051]    [0051]FIG. 2 shows the lid  40  in an open position in which the motor shaft  36  is disengaged from the impeller  30  allowing the sub-housing  14  to be removed from the main housing  12 .  
         [0052]    The removability of the sub-housing  14  represents a major improvement over prior art devices as the sub-housing  14  contains most of the “gas flow path” components of the breathable gas supply apparatus  10  that can come into contact with airborne particles from atmosphere or from the patient being treated and it can easily be removed, disposed and replaced with a clean, sterile or disinfected sub-housing  14 . Alternatively, the sub-housing  14  can be removed, cleaned, sterilised or disinfected and then reinstalled.  
         [0053]    The protruding portion of the shaft  36  may also contact airborne particles and removing the sub-housing  14  provides easy access to this component for cleaning, sterilising or disinfecting.  
         [0054]    In a preferred form, the sub-housing  14  is moulded from plastics material such as polypropylene, polycarbonate, acrylic, aluminium, polyurethane foam (such as 1SF-1350 type manufactured by URETEC) or other like high temperature resistant biocompatible materials which can be easily cleaned, sterilised or disinfected using common procedures such as autoclaving.  
         [0055]    Depending on the requirements of the breathable gas supply apparatus  10 , the sub-housing  14  can also include an inlet filter  42  (see FIG. 1).  
         [0056]    In some breathable gas supply apparatus, such as those used for bi-level CPAP, it is desirable to measure the flow rate of gas delivered to the patient. An embodiment of a gas flow rate sensing means  44  suitable for use with the removable sub-housing  14  is shown in FIG. 3 and includes a flexible flap  46  disposed in the gas flow path between a light source  48  and a linear image sensor  50 . The greater the gas flow passing the flap  46  causes proportionally greater deflection of the flap  46  and thus a proportionally greater amount of occluding of light from the light source  48  that falls on the linear image sensor  50 . In this way, the output of the sensor  50  can be calibrated to be indicative of flap deflection and thus gas flow rate.  
         [0057]    With this arrangement, only the flexible plastic flap  46  is within the flow path and is therefore cleaned etc or replaced along with the sub-housing  14 . The expensive and delicate light source  48  and sensor  50  are external of gas flow path, free from contamination risk and remain fixed to the main housing  12 .  
         [0058]    In some breathable gas supply apparatus, it is also necessary or desirable to be able to measure the pressure of the gas delivered to the patient. An embodiment of a pressure sensing arrangement suitable for use with the removable sub-housing  14  is shown in FIG. 4 and includes a flexible membrane  60  having one side  62  in fluid communication with the flow path and an opposite side  64  abutting a force probe  66  coupled to a force transducer  68 . Increases and decreases in gas pressure cause the membrane  60  to expand and contract respectively and displace the force probe  66  thereby altering the output of the transducer  68 . Thus, it is possible to calibrate a relationship between gas pressure and transducer output.  
         [0059]    As with the gas flow rate sensing means  44 , this embodiment is suitable for use with the removable sub-housing  14  as the membrane remains fixed to the sub-housing  14  and may be easily cleaned, sterilised or disinfected or replaced along with the sub-housing  14 . The probe  66  and transducer  68  are external the flow path, free from contamination risk and remain fixed to the main housing  12 .  
         [0060]    Bi-level CPAP is usually administered by either altering the impeller motor speed in synchronism with patient breathing or using a vent valve assembly to control the ratio of gas vented to atmosphere to gas delivered to the patient. FIG. 5 shows an embodiment of a gas vent valve assembly  70  suitable for use with the removable sub-housing  14 . The vent valve assembly  70  includes gas venting conduit  72  in fluid communication with the gas outlet  18  shown in FIG. 1 and having a flexible portion  74 . A pivotable cam  76  controlled by a motor  78  is used to selectively restrict the internal cross section of the flexible portion  74  and thereby control the proportion of gas vented to atmosphere from the system to regulate the pressure of remaining gas supplied to the patient. As with the embodiments of FIGS. 3 and 4, the venting conduit  72  and flexible portion  74  can be removed, cleaned and replaced with the sub-housing  14 , whilst the cam  76  and motor  78  remain external the flow path and fixed to main housing  12 .  
         [0061]    [0061]FIG. 6 shows another embodiment of a gas vent valve assembly, suitable for use with the removable sub-housing  14 , which controls the pressure of gas supplied to the patient with two pivotable cams  76 A and  76 B which restrict respective flexible portions  74 A and  74 B. The cams  76 A,  76 B form part of two vent valve assemblies  70 A and  70 B of a similar nature to the assembly  70  shown in FIG. 5. The cams  76 A,  76 B are linked so that upon rotation by motor  78  one flexible portion is progressively restricted while the other is progressively enlarged and vice-versa.  
         [0062]    In the embodiment shown, the cams  76 A,  76 B are installed adjacent a Y shaped conduit  80  which comprises three conduit portions  82 ,  84  and  86  which are in fluid communication with the impeller  30 , outlet  18  and atmosphere respectively. If a low gas supply pressure to the patient is desired, the valve assemblies  70 A,  70 B are used to simultaneously restrict the gas flow in the conduit portion  82  from the flow generator while increasing the gas flow to the atmosphere through conduit portion  86 . If a high gas supply pressure to the patient is desired, the pivotable cams  76 A and  76 B are turned in the opposite direction to simultaneously restrict the venting of gas to the atmosphere through conduit portion  86  and increase the gas supplied to the patient through conduit portion  84 .  
         [0063]    The embodiment of FIG. 6 provides an apparatus for supplying breathable gas that uses relatively less power and causes less wear on the flow generator motor and bearings. The gas flow vented to atmosphere is also reduced which thereby reduces the associated noise of the gas passing through the vent to atmosphere.  
         [0064]    [0064]FIG. 7 shows an apparatus  90  for supplying breathable gas in accordance with a second embodiment of the invention. Similar to the first embodiment, the apparatus  90  includes a main housing  92  and a sub-housing  94 .  
         [0065]    The sub-housing  94  has an inlet chamber  96  and an outlet chamber  98  within which is located an impeller  100 . The impeller  100  is mounted on the bottom end of a shaft  102 . The top end of the shaft  102  is retained in a bearing assembly  103  mounted to the inlet chamber  96 . The impeller  100  also includes a number of magnets  104  mounted near its periphery. Six equiangularly spaced magnets are used in the preferred embodiment.  
         [0066]    The main housing  92  includes a motive power source in the form of an electric motor  106 . A disk  108  is attached to the output shaft  110  of the motor  106 . Magnets  112  are mounted near the periphery of the disk  108  in general alignment with the magnets  104  provided on the impeller  100 . The magnets  104  and  112  are configured to attract each other.  
         [0067]    Energising the motor  106  causes the disk  108  to rotate. The attraction between the magnets  104  and  112  causes the impeller  100  to rotate also. The rotation of the impeller  100  draws air through upper openings  114  in the inlet chamber  96 , through to a lower opening  116  and into the impeller  100 . Pressurised air is then forced through outlet  118  of the outlet chamber  98 , as indicated by arrows  120 . The outlet  118  of the sub-housing  94  is connected to a face mask (not shown) by a flexible conduit (not shown) to supply the air (or other breathable gas) to a patient.  
         [0068]    As with the first embodiment, the sub-housing  94 , which contains all of the components that can come into contact with particles from atmosphere or from the patient being treated, can be easily and quickly removed from the main housing  92  by overcoming the attraction between the magnets  104  and  112 . As with the first embodiment, this allows the sub-housing  94  to be easily removed and disposed and replaced with a new clean, sterile or disinfected sub-housing  94  or removed, cleaned, sterilised or disinfected and then reinstalled.  
         [0069]    [0069]FIGS. 12, 13, and  14  and  15  respectively show three preferred arrangements of the magnets  112  on the disk  108 . In FIG. 12, the magnets  112  have their poles aligned in one direction (North being shown). In FIG. 13, the magnets  112  are arranged with adjacent magnets  112  having alternating poles. In FIGS. 14 and 15, the magnets  104 ,  112  have alternating poles grouped in pairs by magnetic bridges  122 . The magnets  104  on the impeller  100  are arranged with opposite (ie. attracting) polarity to those of the disk  108 .  
         [0070]    [0070]FIG. 8 shows an alternative form of a sub-housing  130  that can also be used with the main housing  92  shown in FIG. 7. The sub-housing  130  is very similar to the sub-housing  94  and like reference numerals have been used to denote like features. However, in the sub-housing  130 , the impeller  100  includes a plate  132  on its underside rather than the magnets  104  shown in the embodiment of FIG. 7.  
         [0071]    In one form, the plate  132  is made from a material that is attracted to magnets, for example steel. As with the embodiment shown in FIG. 7, when the disk  108  rotates the attraction between the magnets  112  and the plate  132  causes rotation in the impeller  100  also.  
         [0072]    In another form, the plate  132  is made of a non-ferrous metal, for example Aluminium. In this form, when the disk  108  rotates the magnets  112  produce a magnetic field which passes through the plate  132  and causes eddy currents in, and rotation of, the plate  132  and thus the impeller  100  also. Alternatively, the plate  132  can be formed from a non magnetically attractive material, for example a polymer, having a non-ferrous metal, such as Aluminium, therein.  
         [0073]    FIGS.  9  to  11  show an impeller housing and motor assembly  140  suitable for use in an apparatus for supplying breathable gas in accordance with another embodiment of the invention. In this embodiment, the assembly  140  includes an upper part  142  which constitutes a sub-housing and a lower part  144  which constitutes a main housing. The upper part  142  includes an inlet  146 , an outlet  147  and an impeller  148  mounted therein.  
         [0074]    As best shown in FIG. 11, the impeller  148  includes a hollow shaft  150  to which is mounted ferrite material  152 . The lower part  144  includes a shaft  154  which is adapted to be received within the interior of the hollow shaft  150  to form a bearing. The lower part  144  also includes motor windings  156  that surround the ferrite material  152 . Energising the motor windings  156  creates a magnetic field which causes the ferrite material  152 , and thus the impeller  148 , to rotate and draw air from the inlet  146  to the outlet  147  for supplying gas to the patient by the means previously described.  
         [0075]    Similar to the earlier embodiments, the upper part  142  and the impeller  148  can be removed for cleaning, sterilising, disinfecting or replacement without dismantling the rest of the apparatus to which the lower part  144  is attached. Removing the upper part  142  and the impeller  148  also provides easy access to external surfaces  158  of the lower part  144  for cleaning, sterilising or disinfecting.  
         [0076]    In a variation (not shown) of the embodiment shown in FIGS.  9  to  11 , gas is bled from the impeller  148  into the interface between the hollow shaft  150  and the shaft  154  to float the impeller  148  (in the manner of an air bearing) and thus reduce noise.  
         [0077]    Although the invention has been described with reference to the preferred embodiments, it would be appreciated by those skilled in the art that the invention may be embodied in many other forms.