Abstract:
A flow regulation vent for venting washout gas to atmosphere and for regulating flow from a pressurized gas supply includes a fixed portion adapted to engage a gas supply conduit; a spring force biased movable portion structured for flowing communication with the pressurized gas supply; and a hinge pivotally connecting the movable portion to the fixed portion. The fixed portion has a gas flow orifice and the movable portion is pivotally movable between 1) a relaxed position, wherein below a specified operating pressure, the movable portion is pivoted by the spring force to a position away from the fixed portion to establish a first gas washout flow area between the movable portion and the gas flow orifice, and 2) a fully pressurized position. At or above the specified operating pressure, the pressurized gas offsets the spring force to pivot the movable portion to a position adjacent the fixed portion to cover at least a portion of the gas flow orifice and establish a second gas washout flow area between the movable portion and the gas flow orifice. The second gas washout flow area is less than the first gas washout flow area.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. application Ser. No. 11/322,237, filed Jan. 3, 2006, which is a continuation of U.S. application Ser. No. 10/164,370, filed Jun. 10, 2002, now U.S. Pat. No. 7,207,334, which is a divisional of U.S. application Ser. No. 09/498,705, filed Feb. 7, 2000, now U.S. Pat. No. 6,491,034, and related to the following applications: U.S. application Ser. No. 09/985,457, filed Nov. 2, 2001, now U.S. Pat. No. 7,185,652, and U.S. application Ser. No. 09/985,458, filed Nov. 2, 2001, now U.S. Pat. No. 7,089,939, and U.S. application Ser. No. 11/285,077, now U.S. Pat. No. 7,174,893, each incorporated herein by reference in its entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to improvements in patient gas delivery apparatus of the kind used in the analysis and treatment of respiratory disorders. The invention will be described with particular reference to patient gas delivery apparatus used in the treatment of respiratory disorders such as Obstructive Sleep Apnea (OSA) but it is not intended to be limited thereto. 
         [0003]    The present invention also relates to an anti-asphyxia valve. The valve has been developed primarily for use between a patient and means (e.g., a blower or respirator) to deliver a breathable gas to the patient, such as is used in the Continuous Positive Airway Pressure (CPAP) treatment of Obstructive Sleep Apnea (OSA), and will be described hereinafter with reference to this application. The valve is also suitable for use in other gas delivery systems, such as those used in assisted respiration and Non-Invasive Positive Pressure Ventilation (NIPPV). 
       BACKGROUND OF THE INVENTION 
       [0004]    Patient gas delivery apparatus of the kind having a mask worn by a patient and a gas delivery conduit attached to the mask are commonly used in the analysis and treatment of respiratory disorders. The gas conduit delivers a gas under pressure to the patient. It is necessary that the gas conduit is detachable from the mask to facilitate cleaning. 
         [0005]    Patient gas delivery apparatus typically includes at a minimum, a gas delivery conduit and a nose or full face mask. In some cases it is a clinical requirement that additional components be included, such as means for CO 2  washout, for example, vents, anti-asphyxia valves and the like. In some cases, these additional components must be assembled in between the gas delivery conduit and the mask. Problems with prior art assemblies include: (a) they may be inadvertently assembled without the additional components; (b) they may be incorrectly assembled, for example, incorrectly aligned; (c) during the course of treatment, the patient may inadvertently remove or dismantle the assembly and incorrectly reassemble it. 
         [0006]    Further, known mask cushions are usually molded from a relatively soft, resilient, elastic material and they are shaped during manufacture to match the facial contours of an average intended wearer. However, a problem with the known types of masks is that, because individuals vary so much from the average, the masks must be forced against their inherent resiliency to deform and so adapt to the shapes of the users in order to avoid gas leakage. This requires that the masks be secured firmly by retaining straps or harnesses in order to prevent air leakage. 
         [0007]    Flow generators are typically utilized to deliver a breathable gas (i.e., air) to a patient wearing the mask. In CPAP treatment, gas is delivered to the patient&#39;s airways at about 2-30 cm H 2 O above atmospheric pressure. The flow generator is generally connected to flexible tubing which is secured to the mask worn by the patient. If the flow generator&#39;s operation is interrupted as a result of a power outage or other mechanical or electrical failure, there may be a significant build up of carbon dioxide in the mask as the patient&#39;s exhaled air is not washed out of outlet vents which are usually contained in the mask. This may present a health problem to the patient. 
         [0008]    There have been numerous patents which have addressed some sort of safety valve for gas or air delivery masks. An example of such a patent is U.S. Pat. No. 5,438,981. This patent discloses a counter balanced, rigid valve element which depending on the gas flow, either covers an opening to the ambient air or covers the gas flow airway such that the air or breathing gas is forced out into the ambient air opening. However, this system suffers from being a fairly complicated and expensive system whose correct operation relies on a counter balanced moving part moving relative to its housing. Further, if any condensation from the air gets on or around the balanced valve element, the operation of this valve element can be compromised. This valve is also difficult to clean. 
         [0009]    Applicant&#39;s International Application PCT/AU97/00849 discloses a valve having a single valve element. However, whilst being simpler than preceding valves of this type, the valve shown in PCT/AU97/00849 still relies on the use of a rigid valve element moving relative to its housing and biased by magnets. 
       SUMMARY OF THE INVENTION 
       [0010]    One aspect of the present invention is directed towards solving or ameliorating one or more of these problems. One aspect of the invention will be described with reference to a full face mask and an anti-asphyxia valve, though other forms of mask and additional components may be used, such as the nasal mask shown in  FIG. 4 . 
         [0011]    It is a further aspect of the present invention to provide an improved valve of simpler construction than those prior art valves discussed above. 
         [0012]    Accordingly, in a preferred embodiment, the present invention provides an anti-asphyxia valve adapted to, in use, be disposed between a patient and structure to deliver a breathable gas to the patient. The valve includes a housing having an interior, at least one port to provide fluid communication between the housing interior and atmosphere and at least one flap comprising a first portion adapted for mounting to the housing and a second portion adapted to flex between a first biased open position allowing gas to pass from the housing interior through the at least one port to atmosphere when a difference in gas pressure in the housing interior and atmosphere is below a predetermined operating threshold and a second forced closed position substantially occluding the at least one port when the difference in gas pressure between the housing interior and atmosphere is substantially equal to or above the operating threshold. 
         [0013]    The operating threshold can be altered to suit particular applications. For example, a valve suitable for use in adult ventilatory assist therapy has an operating threshold of about 2 cm H 2 O. 
         [0014]    The second portion preferably completely occludes the at least one port in the closed position. 
         [0015]    Preferably, the housing may include two housing parts that are releasably engageable with one another. In an embodiment, the housing parts engage by way of bayonet style fittings. 
         [0016]    Desirably, the housing may include a gas inlet in the form of a first substantially frusto-conical portion adapted to frictionally engage a flexible conduit in fluid communication with the structure to deliver a breathable gas to the patient and a gas outlet in the form of a second substantially frusto-conical portion adapted to engage a mask or a flexible or rigid conduit in fluid communication with the mask. The frusto-conical portions preferably taper from a smaller distal end to a larger proximal end relative to the housing of the inlet valve. 
         [0017]    Desirably also, one of the gas inlet or outlet may include a snap-engageable and detachable swivel portion adapted to engage the mask or flexible conduit. In a preferred embodiment, the inlet and outlet are respectively provided on one of the two housing parts. 
         [0018]    In an embodiment, the housing may include a plurality of ports spaced about the periphery thereof and the second portion of the flap includes a like plurality of flaps. In one preferred form, the housing includes six ports (three pairs of ports) and the second portion of the flap includes three flaps each adapted to close adjacent pairs of the ports. In another embodiment, the second portion of the flap is a single flap which is adapted to occlude all the ports in the second position. The single flap can also include perforations, ribs, pleats or folds or the like. 
         [0019]    In one form, the first and second portions are integrally formed. In another form, the first and second portions are initially formed from separate components that are later attached to each other. 
         [0020]    The first portion preferably includes a rim adapted to assist in mounting the flap means to the housing. In an embodiment, the rim is an external rim of rectangular cross section which is adapted to engage an internal recess of substantially like cross-section in the housing. 
         [0021]    The first portion may also include a cylindrical portion between the rim and the second portion. 
         [0022]    The rim and/or the cylindrical portion may also be tapered. 
         [0023]    The second portion of the flap preferably terminates in an internal orifice. In a preferred embodiment, the orifice can include a one-way valve adapted to only allow gas flow through the orifice in a direction towards the patient. 
         [0024]    In one preferred form, the flap is substantially round in cross-section. In other forms, the cross-section of the flap is full or part elliptical or rectangular or other non-round shapes. 
         [0025]    The housing is preferably manufactured from plastics material, for example polycarbonate. The flap assembly is preferably manufactured from a flexible elastomeric material such as a silicone rubber. 
         [0026]    In another embodiment, the valve is integral with a mask. 
         [0027]    In a further embodiment, the housing is of unitary construction. 
         [0028]    These and other aspects of the invention will be described in or apparent from the following detailed description of preferred embodiments. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0029]    Further preferred embodiments of the invention will now be described by way of example only with reference to the accompanying drawings in which: 
           [0030]      FIG. 1  is a perspective view showing the mask, anti-asphyxia valve housing and conduit connection assembly; 
           [0031]      FIG. 2  is an exploded view of the anti-asphyxia valve and conduit connection assembly shown in  FIG. 1 ; 
           [0032]      FIG. 3  is an exploded view of the mask assembly shown in  FIG. 1 ; 
           [0033]      FIG. 4  is a general schematic drawing of a system comprising a flow generator being connected to a valve and mask via tubing in which the mask is connected to a patient; 
           [0034]      FIG. 5  is a side view of an embodiment of a valve of the present invention; 
           [0035]      FIG. 6A  is a cross-sectional view of  FIG. 5  in which the flow generator is not operating; 
           [0036]      FIG. 6B  is a cross-sectional view of  FIG. 5  in which the flow generator is operating and generating a pressure differential below the operating threshold; 
           [0037]      FIG. 7  is a cross-sectional view of the valve of  FIG. 5  in which the flow generator is operating and generating a pressure differential above the operating threshold; 
           [0038]      FIG. 8  is a perspective view of an alternative embodiment of the present invention wherein the valve is attached to a mask having a CO 2  gas washout vent; 
           [0039]      FIG. 9  is a cross-sectional view of a further embodiment of the present invention wherein the valve has a unitary housing; 
           [0040]      FIG. 10  is a cross-sectional view of a yet further embodiment of the present invention wherein the valve includes a swivel conduit connector; 
           [0041]      FIG. 11  is a perspective view of another embodiment of the present invention wherein the valve is integral with a mask; 
           [0042]      FIG. 12  is a cross-sectional view of an embodiment of a flap; 
           [0043]      FIG. 13  is a cross-sectional view of another embodiment of a flap; 
           [0044]      FIG. 14  is a cross-sectional view of yet another embodiment of a flap; 
           [0045]      FIG. 15  is a perspective view of a further embodiment of a flap; 
           [0046]      FIG. 16  is a perspective view of a further embodiment of a flap; 
           [0047]      FIG. 17  is a perspective view of a further embodiment of a flap; 
           [0048]      FIG. 18  is a perspective view of a further embodiment of a flap; 
           [0049]      FIG. 19  is a perspective view of the flap shown in  FIG. 14 ; 
           [0050]      FIG. 20  is a perspective view of a further embodiment of a flap; 
           [0051]      FIG. 21  is a half-cutaway view of the flap shown in  FIG. 20 ; 
           [0052]      FIG. 22  is a first sectional view of the flap of  FIG. 20  along the line  22 ,  23 - 22 ,  23 ; 
           [0053]      FIG. 23  is a second sectional view of the flap of  FIG. 20  along the line  22 ,  23 - 22 ,  23 ; 
           [0054]      FIG. 24  is a sectional view of the flap means of  FIG. 20  along the line  24 - 24 ; 
           [0055]      FIG. 25  is a perspective view of a further embodiment of a flap; 
           [0056]      FIG. 26  is a cross-sectional side view of the flap of  FIG. 25  in the open position; and 
           [0057]      FIG. 27  is a cross-sectional side view of the flap of  FIG. 25  in the closed position. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0058]    In  FIG. 1  a mask frame is shown generally at  10 . The mask is designed to be worn on a patient&#39;s face and is secured by means of straps (not shown) received by attachment points  18 . 
         [0059]    A conduit end assembly is shown generally at  20 , including an elbow part  26  having at one end thereof a combined vent/connector piece  28 . The elbow and vent/connector piece together form a housing for an anti-asphyxia valve (as will be further discussed) or other internal components (not shown). At the other end of the elbow is a detachable swivel tube  29  for connection of the gas delivery conduit (not shown). 
         [0060]    The mask  10  includes a circular aperture  12  sized to receive a mating portion  22  of the vent/connector piece  28 . The mating portion  22  has an annular groove  23  formed therein that receives a locking means  30  in the form of a C-shaped clip attached after mating to the mask. The clip  30  has an outside diameter greater than the width of the aperture  12  and an inner diameter adapted to ensure a snug fit within the annular groove  23 . The clip  30  is resilient and can expand sufficiently to allow the clip to be fitted into and removed from the groove  23 . As shown in  FIG. 1 , the clip  30  is located onto the mating portion  22  on the inside of the mask  10 . In this position, the clip  30  is inaccessible while the mask is being worn by a patient. Once the mating portion  22  of the vent/connector piece  28  has been inserted through the aperture  12  and the locking clip placed in the annular groove, the conduit end assembly  20  and the mask  10  cannot be separated without first removing the mask from the patient. 
         [0061]    An exploded view of one embodiment of the anti-asphyxia valve and conduit connector assembly is shown in  FIG. 2 . 
         [0062]    As illustrated in  FIG. 2 , the end of the elbow  26  adjacent the mask  10  is fitted with an anti-asphyxia valve arrangement that provides an air passage to the patient in the event of failure of the gas delivery apparatus, consisting of a valve membrane  27  fitted into the end of elbow  26  and vents  31  in the vent/connector piece  28 . During proper operation of the gas delivery system, the valve membrane remains in the orientation shown in  FIG. 2 , closing off the vents  31 . In the event of a drop in pressure below a predetermined level, the valve membrane  27  flips to a reverse orientation, opening the vents  31 . The construction and operation of the anti-asphyxia valve is described in more detail in the Applicant&#39;s Australian Patent Application No. 65527/99, the contents of which are incorporated herein by reference and described herein. 
         [0063]    Resilient detents  42  on the elbow  26  pass through and engage behind slot-forming formations  44  in the vent/connector piece  28  to provide releasable engagement of the two parts. 
         [0064]    The vent/connector piece has a collar  47  that abuts a corresponding surface of the mask  10  to limit the distance that the vent/connector piece can be inserted into the mask aperture  12  ( FIG. 1 ). The corresponding surface is an annulus  50  having a protruding rim  51  the outer circumference of which preferably engages the inner surface of the detents  42  on insertion of the mating portion  22  into the aperture  12 . This engagement prevents the detents from being pushed radially inwards sufficiently for the detents to disengage from behind the slot-forming formations  44 , thus preventing the elbow  26  and vent/connector piece  28  from separating whilst still attached to the mask frame  11 , for example during patient treatment. The result of this is that the anti-asphyxia valve arrangement cannot be disassembled without first removing the elbow and vent/connector piece assembly from the mask. However, once disconnected from the mask, the assembly may be readily separated for cleaning and then reassembled. 
         [0065]    The other, distal end of elbow  26  has an enlarged diameter portion which receives the swivel tube  29 , onto which a flexible gas conduit (not shown) may be fitted. The swivel tube  29  has a pair of flanges  56  and  57  defining an annular groove  58  therebetween. The end of swivel tube  29  is inserted into the elbow  26  until the end flange  57  abuts an inner surface (not shown) within elbow  26 . In this position the annular groove  58  is at least partially aligned with an annular groove  61  in the exterior of the elbow, which receives a swivel clip  41 . 
         [0066]    The swivel clip  41  has an inner diameter only slightly greater than the diameter of the groove  61 , to ensure a snug fit within the groove. The clip  41  is resilient to permit sufficient expansion for attachment and removal of the clip from the groove. The groove  61  has slots  59  which receive lugs  62  on the clip. These lugs rotatably engage in the groove  58  between flanges  56  and  57  of the swivel tube. The swivel tube arrangement thus acts as a rotatable coupling between the conduit and the elbow whilst allowing quick attachment and removal of the gas conduit from the elbow regardless of whether the assembly is attached to the mask at the time. 
         [0067]    As shown in  FIG. 3 , the mask includes a mask frame  11 , cushion  13  and cushion clip  14 . The cushion is received on a rib  15  extending around the periphery of the mask frame  11 . The cushion is held to the rib by the cushion clip  14 . The mask frame includes attachment points  18  that receive straps (not shown) for attaching the mask to the patient, an aperture  16  for receiving an air vent  17 , and measurement ports  19 . 
         [0068]    The details of construction and of the operation of the anti-asphyxia valve will now be described with reference to  FIGS. 4   27 . As illustrated in  FIG. 4 , a flow generator  100  having a flexible air flow conduit  112  is secured to an embodiment of a valve  114  which is thereafter connected to a nasal mask  116  of a patient  121 . The mask  116  illustrated in  FIG. 4  includes a mask cushion  117  and a CO.sub.2 gas washout vent  119  and is just one example of numerous types of patient interface. As described above, the mask may be designed to cover the patient&#39;s face. 
         [0069]    The location of the valve  114  shown in  FIG. 4  is just one example of numerous possible locations. The valve  114  could be connected to the mask  116  as shown in  FIGS. 4 and 8 , or it could be an integral part of the mask  116 , as shown in  FIG. 11 . There could also be two or more valves located on a single system. It is preferred to put the valve  114  as close to the mask  116  as possible, or to make it part of the mask  116 . 
         [0070]    The flow generator  100  produces a flow of breathable gas, typically air, and can be an electric blower, a controlled bottled gas system, a ventilator, or any other type of device that delivers breathable, therapeutic or anaesthetic gas. 
         [0071]    The valve  114  shown in  FIGS. 4 to 7  is comprised of two housing parts  118  and  120  which may be locked together by way of respective male and female bayonet fittings  122  and  124 . The housing part  118  includes an inlet in the form of frusto-conical portion  126 . The housing part  120  includes an outlet in the form of frusto-conical portion  128 . The portions  126  and  128  allow push-on assembly and frictional engagement with the gas supply conduit  112  and the mask housing  116  respectively. The housing part  120  includes six peripherally arranged ports  130  each separated by one of six connecting members  131 . A flexible flap  132  of generally round cross-section is formed from a silicone rubber and has a central orifice  133 . The flap  132  includes a first portion in the form of outer rim  134 . The flap  132  is glued, clamped or otherwise attached or mounted to the second housing part  120  at the outer rim  134 . The flap  132  includes a second portion in the form of flexible flaps  135 . 
         [0072]    As shown in  FIG. 6A , when the difference in the gas pressure between the housing interior and atmosphere is below a predetermined operating threshold of, for example 2 cm H 2 O, the flaps  135  are in a relaxed state and inherently biased to an “open” position allowing gas flow from the interior of the housing through the ports  130  and to atmosphere. Accordingly, if the supply of breathable gas falls below the threshold or ceases, the patient  121  is still able to inhale air through the open ports  130  and exhale carbon dioxide out through the open ports  130 , as indicated by arrows  129 . 
         [0073]    When the breathable gas supply commences or resumes and the difference in the gas pressure between the housing interior and atmosphere builds up to equal or above 2 cm H 2 O the flaps  135  move to a “closed” position occluding the ports  130  shown in  FIG. 7 . Thereafter the flaps  135  are maintained closed by the gas pressure in the housing interior being above the predetermined operating threshold. In this closed position all the gas supplied from the flow generator  100  can pass through the orifice  133  of the flap  132  to be delivered to the mask  116  of the patient  121 , as indicated by arrows  139 . 
         [0074]    In the embodiment shown in  FIGS. 4 to 7 , the flap  132  has three of the flaps  135  which each subtend an angle of approximately 120°. The three flaps  135  are each separated by slits  136  (only one of three slits  136  shown). The slits  136  allow the flaps  135  to flex between the open and closed positions, as shown in  FIG. 6A  and  FIG. 7  respectively, without crinkling or binding. Every second one of the six connecting members  131  includes a flange  137  which abuts adjacent outer edges (adjacent the slits  136 ) of each of the flaps  135  in the closed position to assist in sealing the ports  130 . 
         [0075]    Each flap  132  is preferably manufactured by moulding of a single silicone rubber component in the shape shown in  FIG. 6A  (i.e. the open position). The flaps  135  are preferably 0.15 mm thick. The thickness of each of the flaps is adjusted to suit their application and, in particular, the pressure of the operating threshold. If too flimsy, the flaps will distend or crumple across the ports  130  and may not move to return from the closed position at the correct pressure. If too stiff, the flaps will not move to the closed position at the correct pressure. 
         [0076]    Testing of a prototype of the valve  114  shown in  FIGS. 4 to 7  was conducted with a flow generator connected to the inlet cylindrical portion  126  via an air flow conduit. A mask was connected to the valve  114  at the outlet cylindrical portion  128 . The mask cushion seals the mask interior relative to the wearer&#39;s face such that the only gas flow from the mask  116  to atmosphere is through the mask gas washout vent. 
         [0077]    With this arrangement the flap assembly  132  closed the ports  130  at an approximately 2 cm H 2 O pressure difference (operating threshold) between the interior of the valve  114  and atmosphere. 
         [0078]    The inherent resilience of the silicone rubber flaps  135  re-opened the ports  130  when the pressure difference (operating threshold) between the interior of the valve  114  and atmosphere fell below approximately 2 cm H 2 O. 
         [0079]      FIG. 6B  shows the flap assembly  132  in the open position when the flow generator is operating but the pressure difference between the valve interior and atmosphere is below the operating threshold. Under these conditions, some of the supplied gas passes through the ports  130  and the remainder passes through the valve outlet  128  to the mask, as indicated by arrows  127  and  139  respectively. 
         [0080]    As the flow through the valve outlet  128  is thus less than the supplied flow through the valve inlet  126 , a pressure differential is created between the downstream side of the flaps  135  (that side adjacent the valve outlet  128 ) and the upstream side of the flaps  135  (that side adjacent the valve inlet  126 ) which forces the flaps  135  to deform against their inherent resilience towards the ports  130  and, ultimately, to the closed position shown in  FIG. 7 . 
         [0081]    When in the closed position shown in  FIG. 7 , there is no gas flow through the ports  130 . Under these conditions, a pressure differential between the valve interior and atmosphere above the operating threshold will maintain the flaps  135  in the closed position. 
         [0082]    The inherent resilience of the flaps  135  moves the flaps  135  away from the ports  130  and towards the open position when the pressure difference between the valve interior and atmosphere falls below the operating threshold. 
         [0083]      FIG. 8  illustrates another embodiment in which the valve  114  is attached to another type of mask  116  that includes a CO 2  gas washout vent  138 . 
         [0084]      FIG. 9  illustrates an embodiment of the valve  114  having a unitary housing  140 . 
         [0085]      FIG. 10  illustrates another embodiment of the valve  114  having a unitary housing  140  and a swivel connector  142  that snap-engages with the cylindrical portion  128  over resilient fingers  144 . This embodiment obviates the need for a separate swivel connector elsewhere in the gas supply circuit. 
         [0086]    In another embodiment (not shown) the swivel connection  142  is used in conjunction with the unitary housing  140 . 
         [0087]      FIG. 11  illustrates a further embodiment of the valve  114  incorporated into a mask  146  having a mask shell  148  and a mask cushion  150 . In this embodiment, the valve  114  is integrally formed with the mask shell  148  thereby obviating the push-on connection between the mask  116  and the valve  114 . 
         [0088]      FIG. 12  shows an embodiment of the flap  132  which includes an external rim  152  of stepped cross section which assists in locating the flap  132  in the housing. The rim  154  is received within a corresponding recess in the housing to facilitate locating and mounting the flap  132  in the housing. 
         [0089]      FIG. 13  shows another embodiment of the flap  132  having an internal rim  154  of rectangular cross section. 
         [0090]      FIGS. 14 and 19  show yet another embodiment of the flap means  132  having a substantially cylindrical formation  156  between the flaps  135  and the rim  152 . The cylindrical formation  156  and the rim  152  facilitate locating the flap  132  with correct orientation in the housing. 
         [0091]      FIG. 15  illustrates a further embodiment of the flap  132  which includes a series of pleats or folds  160  which flex to allow movement of the flap  132  between the open and closed positions. 
         [0092]      FIG. 16  shows another embodiment of the flap  132  similar to that shown in  FIG. 14  but without the slits  136 . This embodiment thus has only a single flap  135  which distorts when moving between the open and closed positions. 
         [0093]      FIG. 17  shows an embodiment similar to that of  FIG. 16  but including three rows of perforations  158  which provide localised flexibility to assist in movement of the flaps  135  between the open and closed positions. 
         [0094]      FIG. 18  shows an embodiment of a flap  132  that has the cylindrical formation  156  of the embodiment of  FIGS. 14 and 19  and the pleats or folds  160  of the embodiment of  FIG. 15 . 
         [0095]      FIGS. 20 and 21  show a further embodiment of a flap  132  with a single flap  135  that includes a number of radial protuberances&#39; or ribs  162  of greater thickness than the flap  135 . In the embodiment shown, the ribs  162  are of equal thickness. In other embodiments (not shown) the ribs are of unequal thickness and, for example, can be thicker on one side for operation in applications where flow is different across the flap such as in a curved or angled conduit or the like. 
         [0096]      FIGS. 22 and 23  show examples of the cross section the flap  135  can assume in the closed position. 
         [0097]      FIG. 24  shows an example of the cross section that the ribs  162  can assume in the open position. 
         [0098]      FIGS. 25 and 27  are schematic views of another embodiment of a flap  132  that includes a one-way valve device  164  adapted to only allow gas flow in the direction of the patient. The one-way valve device  164  is known as a non-rebreathe valve. 
         [0099]      FIGS. 25 and 27  show the flap  132  in the closed position and the one-way valve  164  in the open position, thereby allowing gas flow to the patient, as indicated by arrows  166 .  FIG. 26  shows the flap  132  in the open position and the one-way valve  164  in the closed position, thereby directing all of the gas flow directed through the ports of the valve to atmosphere. 
         [0100]    Another embodiment of the invention (not shown) includes a port or series of ports that function as both the flap assembly ports and the mask CO 2  gas washout port. 
         [0101]    In this embodiment, the ports and the flap assembly are sized so each port is not totally occluded by the flap assembly in the closed position. Accordingly, in the closed position each port is occluded to an extent that it is of a size suitable to function as the mask CO 2  gas washout vent. When the pressure differential between the interior of the valve and atmosphere is below the operational threshold, the flap assembly moves to the open position and each port to atmosphere is enlarged to a size suitable to function as the anti-asphyxia port. 
         [0102]    One advantage is that the valve can be used with nasal, mouth mask and full face (nose and mouth) mask systems for both adults and infants. In the situation of infants, the airflow is generally less, and thus the force needed to flex the flap assembly into the closed position is lowered accordingly. 
         [0103]    The valve according to the present invention can be used for any type of air delivery system, it is preferably used in CPAP applications for the treatment of OSA or NIPPV. 
         [0104]    Preferred embodiments of the valve of the present invention have the advantage of being able to operate independent of orientation. That is, although the valve has to be connected in the right direction between the flow generator and the mask, it can be inverted, held sideways, etc. which often occurs during the time when the patient sleeps. 
         [0105]    Another advantage of the valve of the present invention is it may have only one moving or flexing part providing consistent operation. 
         [0106]    Further, the valve can be disassembled, cleaned and reassembled very easily at home or at a hospital or clinic due to it having less parts. 
         [0107]    The valve of the present invention is also very quiet in operation. 
         [0108]    While particular embodiments of this invention have been described, it will be evident to those skilled in the art that the present invention may be embodied in other specific forms without departing from the essential characteristics thereof. The present embodiments and examples are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.