Abstract:
In accordance with the present invention, there is provided a mask, such as a nasal pillows mask, for achieving positive pressure mechanical ventilation (inclusive of CPAP, ventilator support, critical care ventilation, emergency applications). The mask of the present invention includes a piloted exhalation valve that is used to achieve the target pressures/flows to the patient. The pilot for the valve may be pneumatic and driven from the gas supply tubing from the ventilator. The mask of the present invention further includes a heat and moisture exchange (HME) device which is directly integrated into the housing or cushion thereof (thus residing in extremely close proximity to the patient&#39;s nostrils), and is further uniquely configured to induce a flow pattern between it and the cushion which maximizes the transmission of heat and moisture to air which is inhaled by and exhaled from the patient through the mask.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     Not Applicable 
     STATEMENT RE: FEDERALLY SPONSORED RESEARCH/DEVELOPMENT 
     Not Applicable 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to systems and methods for controlling delivery of a pressurized flow of breathable gas to a patient and, more particularly, to a ventilation mask such as nasal mask, nasal prongs mask or nasal pillows mask for use in critical care ventilation, respiratory insufficiency or OSA (obstructive sleep apnea) with CPAP (Continuous Positive Airway Pressure) therapy and incorporating a heat and moisture exchange device which is uniquely configured to maximize the transmission of heat and moisture to and from air flowing through the ventilation mask. 
     2. Description of the Related Art 
     The use of ventilator and breathing circuits to provide respiratory assistance to a patient is well known in the medical arts. The ventilator and breathing circuit provides mechanical assistance to patients who are having difficulty breathing on their own. In certain types of breathing circuits, a ventilator unit or flow generator is fluidly connected to a ventilation mask worn by the patient. Such fluid connection is typically achieved through the use of ventilation tubing or a tubing circuit which is operative to deliver the ventilation gas from the flow generator to the patient via the mask worn by the patient. 
     In normal, unassisted respiration, heat and moisture are absorbed from the exhaled air by the inner walls of the oral and nasal cavities of the patient as the air travels from the patient&#39;s lungs to the outside environment. This heat and moisture is then transferred to the inhaled air in the next breath, helping to keep the mucus membranes of the patient&#39;s lungs humidified and at the proper temperature. Mechanical ventilation bypasses this natural system, often resulting in dry air of incorrect temperature being introduced into the oral and nasal cavities, and hence the lungs of the patient. After a period of time, the respiratory tract of the ventilated patient becomes dried, often causing discomfort. Thus, one of the known disadvantages of conventional breathing circuits is that the air delivered to the patient&#39;s lungs is not at the appropriate humidity and/or temperature level. 
     In order to provide for proper humidity and temperature of the air in ventilator and breathing circuits, it is known to integrate a heat and moisture exchange (HME) device into the breathing circuit. Typically, HME devices are placed into the breathing circuit somewhere within the flow path of the warm, moist air which is exhaled by the patient. The exhaled air enters the HME device, where the moisture and heat are absorbed by those materials used to fabricate the same. These materials then impart the absorbed heat and moisture to the inhaled air in the next breath. The retention of warmth and high humidity helps to prevent the patient&#39;s lungs and mucus layers from drying out. Currently known HME devices generally consist of a housing that contains a layer of flexible, fibrous, gas-permeable media or material. As indicated above, this media has the capacity to retain moisture and heat from the air that is exhaled from the patient&#39;s lungs, and then transfer the captured moisture and heat to the inhaled air when the patient is inhaling with the assistance of the flow generator. The fibrous material or media in the HME device may be made of foam or paper or other suitable materials that are untreated or treated with hygroscopic material. 
     However, currently known HME devices possess certain deficiencies which detract from their overall utility. More particularly, the structural attributes of currently known HME devices does not make them particularly well suited for integration into ventilation masks such as nasal prongs or nasal pillows masks. In this regard, nasal pillows masks typically comprise a housing or cushion, the size of which is adapted to allow it to be positioned below the patient&#39;s nostrils and above the patient&#39;s mouth. The resultant relatively small size or profile of the cushion does not lend itself to the easy integration of conventional HME devices directly therein. Rather, such HME devices must typically be located within the tubing circuit proximate, but not directly within, the cushion. As will be recognized, the integration of the HME device within the cushion immediately adjacent the patient&#39;s nostrils would optimize the ability of such HME device to facilitate the desired heat and moisture exchange operation with air inhaled and exhaled by a patient wearing the corresponding nasal pillows mask. The present invention addresses this issue by providing a ventilation mask such as a nasal pillows mask wherein an HME device is directly integrated into the housing or cushion thereof (thus residing in extremely close proximity to the patient&#39;s nostrils), and is further uniquely configured to induce a flow pattern between it and the cushion which maximizes the transmission of heat and moisture to air which is inhaled by and exhaled from the patient through the nasal pillows mask. These, as well as other features and advantages of the present invention will be described in more detail below. 
     BRIEF SUMMARY OF THE INVENTION 
     In accordance with the present invention, there is provided a ventilation mask (e.g., a nasal pillows mask) for achieving positive pressure mechanical ventilation (inclusive of CPAP, ventilatory support, critical care ventilation, emergency applications). The mask preferably includes a pressure sensing modality proximal to the patient connection. Such pressure sensing modality may be a pneumatic port with tubing that allows transmission of the patient pressure back to the ventilator for measurement, or may include a transducer within the mask. The pressure sensing port is used in the system to allow pressure sensing for achieving and/or monitoring the therapeutic pressures. Alternately or additionally, the mask may include a flow sensing modality located therewithin for achieving and/or monitoring the therapeutic flows. 
     The mask of the present invention also includes a piloted exhalation valve that is used to achieve the target pressures/flows to the patient. In the preferred embodiment, the pilot for the valve is pneumatic and driven from the gas supply tubing from the ventilator. The pilot can also be a preset pressure derived in the mask, a separate pneumatic line from the ventilator, or an electro-mechanical control. In accordance with the present invention, the valve is preferably implemented with a diaphragm. 
     The mask of the present invention further includes a heat and moisture exchange (HME) device which is integrated therein. The HME device can fully or at least partially replace a humidifier (cold or heated pass-over; active or passive) which may otherwise be included in the ventilation system employing the use of the mask. The HME device is positioned within the mask so as to be able to intercept the flow delivered from a flow generator to the patient in order to humidify it, and further to intercept the exhaled flow of the patient in order to capture humidity and heat for the next breath. The HME device can also be used as a structural member of the mask, adding a cushioning effect and simplifying the design of the cushion thereof. 
     The present invention is best understood by reference to the following detailed description when read in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These, as well as other features of the present invention, will become more apparent upon reference to the drawings wherein: 
         FIG. 1  is top perspective view of a nasal pillows mask constructed in accordance with a first embodiment of the present invention and including a heat and moisture exchange device integrated into the cushion thereof; 
         FIG. 2  is an exploded view of the nasal pillows mask shown in  FIG. 1 ; 
         FIG. 3  is a partial cross-sectional view of the nasal pillows mask shown in  FIG. 1 , further depicting the flow pattern through the cushion of the mask and the heat and moisture exchange device disposed therein during an inhalation phase of a patient wearing the mask; 
         FIG. 4  is a partial cross-sectional view of the nasal pillows mask shown in  FIG. 1 , further depicting the flow pattern through the cushion of the mask and the heat and moisture exchange device disposed therein during an exhalation phase of a patient wearing the mask; 
         FIG. 5  is an exploded view of a nasal pillows mask constructed in accordance with a second embodiment of the present invention and including a sub-assembly comprising a heat and moisture exchange device and a piloted exhalation valve; 
         FIG. 6  is a partial cross-sectional view of the nasal pillows mask shown in  FIG. 5 , further depicting the flow pattern through the cushion of the mask and the heat and moisture exchange device of the sub-assembly disposed therein during an inhalation phase of a patient wearing the mask; 
         FIG. 7  is a side-elevational view of the sub-assembly comprising the heat and moisture exchange device and piloted exhalation valve as shown in  FIG. 5 ; 
         FIG. 8  is top perspective view of a nasal pillows mask constructed in accordance with a third embodiment of the present invention and including a heat and moisture exchange device integrated into the cushion thereof; 
         FIG. 9  is an exploded view of the nasal pillows mask shown in  FIG. 8 ; 
         FIG. 10  is a partial cross-sectional view of the nasal pillows mask shown in  FIG. 8 , further depicting the flow pattern through the cushion of the mask and the heat and moisture exchange device disposed therein during an exhalation phase of a patient wearing the mask; and 
         FIG. 11  is a front-elevational view of the nasal pillows mask constructed in accordance with either the first, second or third embodiments of the present invention, and further depicting an exemplary tri-lumen tube, Y-connector, and pair of bi-lumen tubes which are used to collectively facilitate the operative interface between the nasal pillows mask and a flow generating device. 
     
    
    
     Common reference numerals are used throughout the drawings and detailed description to indicate like elements. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings wherein the showings are for purposes of illustrating various embodiments of the present invention only, and not for purposes of limiting the same,  FIGS. 1-4  depict a ventilation mask  10  (e.g., a nasal pillows mask) which is constructed in accordance with a first embodiment of the present invention and has a heat and moisture exchange (HME) device  12  integrated therein. Though the mask  10  is depicted as a nasal pillows mask, it is contemplated that that the HME device  12 , as will be described in more detail below, may be integrated into other types ventilation masks, such as nasal prongs masks, nasal masks, full face masks and oronasal masks. The mask  10  includes an integrated, diaphragm-implemented, piloted exhalation valve  14 , the structural and functional attributes of which will be described in more detail below as well. 
     The mask  10  comprises a housing or cushion  16 . The cushion  16 , which is preferably fabricated from a silicone elastomer having a Shore A hardness in the range of from about 20 to 60 and preferably about 40, is formed as a single, unitary component, and is shown individually in  FIG. 2 . The cushion  16  includes a main body portion  18  which defines a first outer end surface  20  and an opposed second outer end surface  22 . The main body portion  18  further defines an interior fluid chamber  24  which is of a prescribed shape and volume. In addition to the main body portion  18 , the cushion  16  includes an identically configured pair of hollow pillow portions  26  which protrude from the main body portion  18  in a common direction and in a prescribed spatial relationship relative to each other. More particularly, in the cushion  16 , the spacing between the pillow portions  26  is selected to facilitate the general alignment thereof with the nostrils of an adult patient when the mask  10  is worn by such patient. As seen in  FIGS. 3 and 4 , each of the pillow portions  26  fluidly communicates with the fluid chamber  24 . 
     As shown in  FIG. 2 , the main body portion  18  of the cushion  16  includes an enlarged, circularly configured valve opening  28  which is in direct fluid communication with the fluid chamber  24 . The valve opening  28  is positioned in generally opposed relation to the pillow portions  26  of the cushion  16 , and is circumscribed by an annular valve seat  30  also defined by the main body portion  18 . As also shown in  FIG. 2 , the main body portion  18  further defines opposed first and second inner end surfaces  32 ,  34  which protrude outwardly from the periphery of the valve opening  28 , and are diametrically opposed relative thereto so as to be spaced by an interval of approximately 180°. The valve opening  28 , valve seat  30 , and first and second inner end surfaces  32 ,  34  are adapted to accommodate the exhalation valve  14  of the mask  10  in a manner which will be described in more detail below. 
     The main body portion  18  of the cushion  16  further defines first and second gas delivery lumens  36 ,  38  which extend from respective ones of the first and second outer end surfaces  20 ,  22  into fluid communication with the fluid chamber  24 . Additionally, a pressure sensing lumen  40  defined by the main body portion  18  extends from the first outer end surface  20  into fluid communication with the fluid chamber  24 . The main body portion  18  further defines a valve pilot lumen  42  which extends between the second outer end surface  22  and the second inner end surface  34 . The use of the first and second gas delivery lumens  36 ,  38 , the pressure sensing lumen  40 , and the valve pilot lumen  42  will also be discussed in more detail below. Those of ordinary skill in the art will recognize that the gas delivery lumens  36 ,  38  may be substituted with a single gas delivery lumen and/or positioned within the cushion  16  in orientations other than those depicted in  FIGS. 4 and 5 . For example, the gas delivery lumen(s) of the cushion  16  may be positioned frontally, pointing upwardly, pointing downwardly, etc. rather than extending laterally as shown in  FIGS. 4 and 5 . 
     The exhalation valve  14  of the mask  10  is made of three (3) primary parts or components, and more particularly a seat member  44 , a cap member  46 , and a diaphragm  48  which is operatively captured between the seat and cap members  44 ,  46 . The seat and cap members  44 ,  46  are each preferably fabricated from a plastic material, with the diaphragm  48  preferably being fabricated from an elastomer having a Shore A hardness in the range of from about 20-40. The detailed structural and functional attributes of the exhalation valve  14  are described with particularity in Applicant&#39;s co-pending U.S. patent application Ser. No. 13/411,348 entitled VENTILATION MASK WITH INTEGRATED PILOTED EXHALATION VALVE filed Mar. 2, 2012, now issued as U.S. Pat. No. 8,844,533, the disclosure of which is incorporated herein by reference. 
     The seat member  44  includes a tubular, generally cylindrical wall portion  50  which defines a distal, annular outer rim  52  and an opposed annular inner seating surface  54 . As shown in  FIG. 4 , the diameter of the outer rim  52  exceeds that of the seating surface  54 . Along these lines, the inner surface of the wall portion  50  is not of a uniform inner diameter, but rather is segregated into first and second inner surface sections which are of differing inner diameters, and separated by an annular shoulder  56 . In addition to the wall portion  50 , the seat member  44  includes an annular flange portion  58  which protrudes radially from that end of the wall portion  50  opposite the outer rim  52 . The flange portion  58  includes a plurality of exhaust vents  60  which are located about the periphery thereof in a prescribed arrangement and spacing relative to each other. The seat member  44  is formed such that each of the exhaust vents  60  normally fluidly communicates with the bore or fluid conduit defined by the wall portion  50 . 
     The cap member  46  of the exhaust valve  14  comprises a circularly configured base portion  62  which defines an inner surface and an opposed outer surface. In addition to the base portion  62 , the cap member  46  includes an annular flange portion  64  which circumvents and protrudes generally perpendicularly relative to the inner surface of the base portion  62 . The flange portion  64  defines a distal annular shoulder. The distal shoulder of the flange portion  64  and the inner surface of the base portion  62  extend along respective ones of a spaced, generally parallel pair of planes. Formed in the outer surface of the base portion  62  is an elongate groove  66  which extends diametrically across such outer surface. The use of the groove  66  will be described in more detail below. The seat and cap members  44 ,  46 , when attached to each other in the fully assembled exhalation valve  14 , collectively define an interior valve chamber  68  of the exhalation valve  14 . More particularly, such valve chamber  68  is generally located between the inner surface defined by the base portion  62  of the cap member  46  and the seating surface  54  defined by the wall portion  50  of the seat member  44 . 
     The diaphragm  48  of the exhalation valve  14 , which resides within the valve chamber  68 , has a circularly configured, central body portion  70 , and a peripheral flange portion  72  which is integrally connected to and circumvents the body portion  70 . The body portion  70  includes an annular lip  74  which circumvents and protrudes upwardly from one side or face thereof. The flange portion  72  includes an arcuately contoured primary region and a distal region which protrudes radially from the primary region. As such, the primary region of the flange portion  72  extends between the distal region thereof and the body portion  70 , and defines a continuous, generally concave channel. 
     In the exhalation valve  14 , the flange portion  72  of the diaphragm  48  is operatively captured between the flange portions  58 ,  64  of the seat and cap members  44 ,  46 . More particularly, the annular distal region of the flange portion  72  is compressed (and thus captured) between the shoulder defined by the flange portion  64  of the cap member  46 , and a complimentary annular shoulder which is defined by the flange portion  58  of the seat member  44  proximate the exhaust vents  60 . The orientation of the diaphragm  48  within the valve chamber  68  when captured between the seat and cap members  44 ,  46  is such that the channel defined by the arcuately contoured primary region of the flange portion  72  is directed toward or faces the seating surface  54  defined by the wall portion  50  of the seat member  44 . 
     The diaphragm  48  (and hence the exhalation valve  14 ) is selectively moveable between an open position (shown in  FIG. 4 ) and a closed position (shown in  FIG. 3 ). When in its normal, open position, the diaphragm  48  is in a relaxed, unbiased state. Importantly, in either of its open or closed positions, the diaphragm  48  is not normally seated directly against the inner surface defined by the base portion  62  of the cap member  46 . Rather, a gap is normally maintained between the body portion  70  of the diaphragm  48  and the inner surface of the base portion  62 . The width of such gap when the diaphragm  48  is in its open position is generally equal to the fixed distance separating the inner surface of the base portion  62  from the distal shoulder of the flange portion  64 . Further, when the diaphragm  48  is in its open position, the body portion  70 , and in particular the lip  74  protruding therefrom, is itself disposed in spaced relation to the seating surface  54  defined by the wall portion  50  of the seat member  44 . As such, when the diaphragm  48  is in its open position, fluid is able to freely pass through the fluid conduit defined by the wall portion  50 , between the seating surface  54  and diaphragm  48 , and through the exhaust vents  60  to ambient air. The flange portion  64  of the cap member  46  is further provided with a pilot port  76  which extends therethrough and, in the fully assembled exhalation valve  14 , fluidly communicates with that portion of the valve chamber  68  disposed between the body portion  70  of the diaphragm  48  and the inner surface of the base portion  62  of the cap member  46 . The use of the pilot port  76  will also be described in more detail below. 
     In the exhalation valve  14 , the diaphragm  48  is resiliently deformable from its open position (to which it may be normally biased) to its closed position. Since the diaphragm  48  is normally biased to its open position, it provides a failsafe to allow a patient to inhale ambient air through the exhalation valve  14  and exhale ambient air therethrough (via the exhaust vents  60 ) during any ventilator malfunction or when the mask  10  is worn without the therapy being delivered by the ventilator. When the diaphragm  48  is moved or actuated to its closed position, the lip  74  of the body portion  70  is firmly seated against the seating surface  54  defined by the wall portion  50  of the seat member  44 . The seating of the lip  74  against the seating surface  54  effectively blocks fluid communication between the fluid conduit defined by the wall portion  50  and the valve chamber  68  (and hence the exhaust vents  60  which fluidly communicate with the valve chamber  68 ). 
     In the mask  10 , the cooperative engagement between the exhalation valve  14  and the cushion  16  is facilitated by the advancement of the wall portion  50  of the seat member  44  into the valve opening  28  defined by the cushion  16 . Such advancement is limited by the ultimate abutment or engagement of a beveled seating surface defined by the flange portion  58  of the seat member  44  against the complimentary valve seat  30  of the cushion  16  circumventing the valve opening  28 . Upon the engagement of such seating surface of the flange portion  58  to the valve seat  30 , the fluid chamber  24  of the cushion  16  fluidly communicates with the fluid conduit defined by the wall portion  50  of the seat member  44 . As will be recognized, if the diaphragm  48  resides in its normal, open position, the fluid chamber  24  is further placed into fluid communication with the valve chamber  68  via the fluid conduit defined by the wall portion  50 , neither end of which is blocked or obstructed by virtue of the gap defined between the lip  74  of the diaphragm  48  and the seating surface  54  of the wall portion  50 . 
     When the exhalation valve  14  is operatively coupled to the cushion  16 , in addition to the valve seat  30  being seated against the beveled seating surface  59  of the flange portion  58  of the seat member  44 , the first and second inner end surfaces  32 ,  34  of the cushion  16  are seated against respective, diametrically opposed sections of the flange portion  64  defined by the cap member  46 . The orientation of the exhalation valve  14  relative to the cushion  16  is such that the end of the valve pilot lumen  42  extending to the second inner end surface  34  is aligned and fluidly communicates with the pilot port  76  within the flange portion  64  of the cap member  46 . As such, in the mask  10 , the valve pilot lumen  42  is in continuous, fluid communication with that portion of the valve chamber  68  defined between the inner surface of the base portion  62  of the cap member  46 , and the body portion  70  of the diaphragm  48 . 
     To assist in maintaining the cooperative engagement between the exhalation valve  14  and the cushion  16 , the mask  10  is further preferably provided with an elongate frame member  78 . The frame member  78  has a generally V-shaped configuration, with a central portion thereof being accommodated by and secured within the complimentary groove  66  formed in the outer surface defined by the base portion  62  of the cap member  46 . The opposed end portions of the frame member  78  are cooperatively engaged to respective ones of the first and second outer end surfaces  20 ,  22  of the cushion  16 . More particularly, as shown in  FIG. 2 , the frame member  78  includes an identically configured pair of first and second connectors  80 ,  82  which extend from respective ones of the opposed end portions thereof. The first and second connectors  80 ,  82  each define opposed inner and outer portions which have generally cylindrical, tubular configurations. The inner portion  80 ′ of the first connector  80  is advanced into and frictionally retained within the first gas delivery lumen  36  of the cushion  16 . Similarly, the inner portion  82 ′ of the second connector  82  is advanced into and frictionally retained within the second gas delivery lumen  38  of the cushion  16 . As will be described in more detail below, the outer portions of the first and second connectors  80 ,  82  of the frame member  78  are each adapted to be advanced into and frictionally retained within a corresponding lumen of a respective one of a pair of bi-lumen tubes fluidly coupled to the mask  10 . 
     The frame member  78  further includes a pressure port  84  which is disposed adjacent the first connector  80 . Like each of the first and second connectors  80 ,  82 , the pressure port  84  defines opposed inner and outer portions which each have a generally cylindrical, tubular configuration. The inner portion  84 ′ of the pressure port  84  is aligned and fluidly communicates with the pressure sensing lumen  40  of the cushion  16  subsequent to being advanced and frictionally maintained therein. The frame member  78  is also provided with a pilot port  86  which is disposed adjacent the second connector  82  and also defines opposed inner and outer portions which each have a generally cylindrical, tubular configuration. The inner portion  86 ′ of the pilot port  86  is aligned and fluidly communicates with the valve pilot lumen  42  of the cushion  16  subsequent to being advanced and frictionally maintained therein. The outer portions of the pressure and pilot ports  84 ,  86  of the frame member  78  are adapted to be advanced into and frictionally maintained within corresponding lumens of respective ones of the aforementioned pair of bi-lumen tubes which are fluidly connected to the mask  10  within a ventilation system incorporating the same. The receipt of the frame member  78  within the groove  66  of the cap member  46  ensures that the cushion  16 , the exhalation valve  14  and the frame member  78  are properly aligned, and prevents relative movement therebetween. Though not shown, it is contemplated that in one potential variation of the mask  10 , the cushion  16  may be formed so as not to include the valve pilot lumen  42 . Rather, a suitable valve pilot lumen would be formed directly within the frame member  78  so as to extend therein between the pilot port  86  thereof and the pilot port  76  of the exhalation valve  14 . 
     In the mask  10 , the exhalation valve  14  is piloted, with the movement of the diaphragm  48  to the closed position described above being facilitated by the introduction of positive fluid pressure into the valve chamber  68 . More particularly, it is contemplated that during the inspiratory phase of the breathing cycle of a patient wearing the mask  10 , the valve pilot lumen  42  will be pressurized by a pilot line fluidly coupled to the pilot port  86 , with pilot pressure being introduced into that portion of the valve chamber  68  normally defined between the body portion  70  of the diaphragm  48  and the inner surface defined by the base portion  62  of the cap member  46  via the pilot port  76  extending through the flange portion  64  of the cap member  46 . The fluid pressure level introduced into the aforementioned region of the valve chamber  68  via the pilot port  76  will be sufficient to facilitate the movement of the diaphragm  48  to its closed position described above. 
     Conversely, during the expiratory phase of the breathing cycle of the patient wearing the mask  10 , it is contemplated that the discontinuation or modulation of the fluid pressure through the valve pilot lumen  42  and hence into the aforementioned region of the valve chamber  68  via the pilot port  76 , coupled with the resiliency of the diaphragm  48  and/or positive pressure applied to the body portion  70  thereof, will facilitate the movement of the diaphragm  48  back to the open position or to a partially open position. In this regard, positive pressure as may be used to facilitate the movement of the diaphragm  48  to its open position may be provided by air which is exhaled from the patient during the expiratory phase of the breathing circuit and is applied to the body portion  70  via the pillows portions  26  of the cushion  16 , the fluid chamber  24 , and the fluid conduit defined by the wall portion  50  of the seat member  44 . As will be recognized, the movement of the diaphragm  48  to the open position allows the air exhaled from the patient and entering the valve chamber  68  to be vented to ambient air after via the exhaust vents  60  within the flange portion  58  of the seat member  44  which, as indicated above, fluidly communicate with the valve chamber  68 . 
     As will be recognized, based on the application of pilot pressure thereto, the diaphragm  48  travels from a fully open position through a partially open position to a fully closed position. In this regard, the diaphragm  48  will be partially open or partially closed during exhalation to maintain desired ventilation therapy. Further, when pilot pressure is discontinued to the diaphragm  48 , it moves to an open position wherein the patient can inhale and exhale through the mask  10  with minimal restriction and with minimal carbon dioxide retention therein. This allows a patient to wear the mask  10  without ventilation therapy being applied to the mask  10 . The aforementioned structural and functional features of the mask  10  also make it more comfortable to wear, and further allow it to be worn without carbon dioxide buildup, thus making it highly advantageous for the treatment of obstructive sleep apnea wherein patients complain of discomfort with ventilation therapy due to mask and pressure discomfort. When it is detected that a patient requires sleep apnea therapy, the ventilation therapy can be started (i.e., in an obstructive sleep apnea situation). 
     To succinctly summarize the foregoing description of the structural and functional features of the mask  10 , during patient inhalation, the valve pilot lumen  42  is pressurized, which causes the diaphragm  48  to close against the seating surface  54 , thus effectively isolating the fluid chamber  24  of the mask  10  from the outside ambient air. The entire flow delivered from a flow generator fluidly coupled to the mask  10  is inhaled by the patient, assuming that unintentional leaks at the interface between the cushion  16  and the patient are discarded. This functionality differs from what typically occurs in a conventional CPAP mask, where venting to ambient air is constantly open, and an intentional leak flow is continuously expelled to ambient air. During patient exhalation, the pilot pressure introduced into the valve pilot lumen  42  is controlled so that the exhaled flow from the patient can be exhausted to ambient air through the exhalation valve  14  in the aforementioned manner. In this regard, the pilot pressure is “servoed” so that the position of the diaphragm  48  relative to the seating surface  54  is modulated, hence modulating the resistance of the exhalation valve  14  to the exhaled flow and effectively ensuring that the pressure in the fluid chamber  24  of the mask  10  is maintained at a prescribed therapeutic level throughout the entire length of the exhalation phase. When the valve pilot lumen  42  is not pressurized, the exhalation valve  14  is in a normally open state, with the diaphragm  48  being spaced from the seating surface  54  in the aforementioned manner, thus allowing the patient to spontaneously breathe in and out with minimal pressure drop (also referred to as back-pressure) in the order of less than about 2 cm H 2  O at 60 l/min. As a result, the patient can comfortably breathe while wearing the mask  10  and while therapy is not being administered to the patient. 
     As indicated above, the mask  10  includes an HME device  12  which is integrated therein. More particularly, the HME device  12  is positioned within the fluid chamber  24  of the cushion  16 . The HME device  12  is operative to partially or completely replace a humidifier (cold or heated pass-over; active or passive) which would otherwise be fluidly coupled to the mask  10 . This is possible because the average flow through the system envisioned to be used in conjunction with the mask  10  is about half of a prior art CPAP mask, due to the absence of any intentional leak in such system. 
     The HME device  12  is preferably formed to have a generally hour-glass shape defining an opposed pair of enlarged end portions  88  having a reduced width, integral central portion  90  extending between the end portions  88 . Prior to its advancement into the fluid chamber  24  of the cushion  16 , the HME device  12  has the generally flat or planar profile shown in  FIG. 2 . As shown in  FIGS. 3 and 4  and as will be described in more detail below, the size and shape of the HME device  12  relative to that of the fluid chamber  24  and the exhalation valve  14  partially advanced therein causes the HME device  12  to assume a generally arcuate profile when operatively positioned within the fluid chamber  24 . 
     The HME device  12  preferably has a layered construction. More particularly, the HME device  12  is preferably fabricated to include three layers including a low density layer  92 , a medium density layer  94  and a high density layer  96 . The medium density layer  94  is interposed between the low and high density layers  92 ,  96 . Those of ordinary skill in the art will recognize that the use of the three layers  92 ,  94 ,  96  to construct the HME device  12  is exemplary only, and that it may alternatively be fabricated from a single layer of material, two layers, or more than three layers without departing from the spirit and scope of the present invention. 
     As indicated above, the size and shape of the HME device  12  relative to the shape and internal volume of the fluid chamber  24  is selected such that the HME device  12  assumes a prescribed contour or profile when operatively positioned within the fluid chamber  24 . In the mask  10 , the advancement of the HME device  12  into the fluid chamber  24  occurs prior to the operative engagement of the exhalation valve  14  to the cushion  16  in the above-described manner. In this regard, prior to the cooperative engagement of the exhalation valve  14  to the cushion  16 , the HME device  12  is advanced into the fluid chamber  24  via the valve opening  28  defined by the cushion  16 . Though, as is apparent from  FIG. 2 , the size of the HME device  12  exceeds that of the valve opening  28 , the pliable nature of the material(s) preferably used for the layers  92 ,  94 ,  96  of the HME device  12  allows the same to be compressed and/or folded in a manner which facilitates the advancement through the valve opening  28  and into the fluid chamber  24 . 
     When the HME device  12  is operatively positioned within the fluid chamber  24 , at least portions of the continuous peripheral side surface of the HME device  12  are abutted against corresponding regions of the interior surface of the main body portion  18  of the cushion  16  which defines the fluid chamber  24 . For instance, as seen in  FIGS. 3 and 4 , portions of the peripheral side surface of the HME device  12  defined by each of the opposed end portions  88  thereof are abutted against corresponding interior surface regions of the main body portion  18  which are located between the inlet ends of respective ones of the first and second gas delivery lumens  36 ,  38 , and corresponding ones of the pillow portions  26 . In this regard, the size and shape of the HME device  12  is preferably such that when fully deployed within the fluid chamber  24 , the HME device  12  will form a complete or substantially complete barrier between the open interiors of the pillow portions  26  and the fluid chamber  24 , yet will not obstruct the inlet ends of either of the first and second gas delivery lumens  36 ,  38 . Though not apparent from  FIGS. 3 and 4 , it is contemplated that the pressure sensing lumen  40  may be formed within the main body portion  18  of the cushion  16  such that the inlet end thereof which extends to the fluid chamber  24  is not covered or otherwise obstructed by the fully deployed HME device  12 . 
     In addition to at least portions of the peripheral side surface of the HME device  12  being abutted against corresponding regions of that interior surface of the main body portion  18  defining the fluid chamber  24 , it is also contemplated that a portion of the bottom surface of the HME device  12  (as viewed from the perspective shown in  FIGS. 3 and 4 ) as defined by the low density layer  92  thereof will be abutted against the distal rim defined by the wall portion  50  of the seat member  44  upon the cooperative engagement of the exhalation valve  14  to the cushion  16 . Further, as also viewed from the perspective shown in  FIGS. 3 and 4 , a portion of the top surface of the HME device  12  as defined by the high density layer  96  thereof is abutted against a portion of the interior surface of the main body portion  18  which is defined by that segment thereof extending between the pillow portions  26 . The abutment of the opposed top and bottom surfaces of the HME device  12  against the main body portion  18  of the cushion  16  and seat member  44  of the exhalation valve  14  in the aforementioned manner, coupled with the abutment of the peripheral side surface of the HME device  12  against the main body portion  18 , results in the HME device  12  assuming and being maintained in the arcuately shaped profile shown in  FIGS. 3 and 4 . As indicated above, when it assumes the position shown in  FIGS. 3 and 4 , the HME device  12  effectively segregates or separates the open interiors of the pillow portions  26  of the cushion  16  from the fluid chamber  24 . 
     Referring again to  FIG. 3 , during an inhalation phase of a patient using the mask  10 , air enters the fluid chamber  24  via the first and second gas delivery lumens  36 ,  38  which, as indicated above, are preferably unobstructed by the HME device  12 . Due to the permeability of the HME device  12 , the air is able to pass through the HME device  12  and into the nostrils of the patient via the pillow portions  26  of the cushion  16 . This flow path is identified by the arrows shown in  FIG. 3 . Moisture and heat retained by the HME device  12  is transferred into the air passing therethrough prior to the air reaching the nostrils of the patient. Though air delivered into the fluid chamber  24  via the first and second gas delivery lumens  36 ,  38  is also capable of flowing through the HME device  12  into the exhalation valve  14 , during the inhalation phase of the patient, the exhalation valve  14  is normally maintained in its closed position as described above. As a result, any gas entering the exhalation valve  14  via the HME device  12  during the inhalation phase is prevented from being vented via the exhaust vents  60  as a result of the diaphragm  48  being sealed against the seat member  44  in the aforementioned manner. 
     In the mask  10  having the HME device  12  positioned in the cushion  16  in the aforementioned manner, the size and shape of the HME device  12  relative to the shape and internal volume of the fluid chamber  24  is also selected such that the resultant shape of that portion of the fluid chamber  24  which is separated from the pillow portions  26  by the HME device  12  is operative to maximize flow over the exposed portions of the bottom surface of the HME device  12  defined by the low density layer  92  thereof. Such shape is also selected to impart a prescribed measure of turbulence to the air flowing into the fluid chamber  24  via the inlet ends of the first and second gas delivery lumens  36 ,  38 . This turbulence, and the vortices resulting therefrom, assists in maximizing flow over the exposed portions of the bottom surface of the HME device  12 . This in turn optimizes the level of moisture and heat transferred into the air passing through the HME device  12  and to the patient via the pillows portions  26  during the inhalation phase of the patient. An exemplary airflow pattern during the inhalation phase of the patient is shown by the arrows included in  FIG. 3 . 
     Referring again to  FIG. 4 , during the exhalation phase of the patient wearing the mask  10 , exhaled air travels through the open interiors of the pillow portions  26  and into the exhalation valve  14  through the HME device  12 . Along these lines, the material(s) preferably used to facilitate the fabrication of the HME device  12  provide for the easy passage of exhaled air through the HME device  12  and into the exhalation valve  14  without causing the patient to exert any greater exhalation force, i.e., the patient does not sense that there is an obstruction within the mask  10  during the exhalation phase. As explained above, during the exhalation phase, the diaphragm  48  of the exhalation valve  14  is actuated to its open position, thus allowing air passing through the HME device  12  and into the exhalation valve  14  to be vented to ambient via the vent ports  60  within the seat member  44  of the exhalation valve  14 . As will be recognized, the HME device  12  is operative to retain moisture and heat from the air exhaled by the patient and passing therethrough during the exhalation phase, and to transfer such moisture and heat to the patient in the aforementioned manner during the inhalation phase. 
     It is contemplated that the HME device  12  can be permanently assembled to the cushion  16 , or may alternatively be removable therefrom and thus washable and/or disposable. In this regard, the HME device  12 , if removable from within the cushion  16 , could be replaced on a prescribed replacement cycle. Along these lines, it is further contemplated that the HME device  12  may be impregnated with a chemical agent which facilitates a color change therein when certain conditions are satisfied indicative of a need for the replacement thereof. Additionally, it is contemplated that the HME device  12  can be used as an elastic member that adds elasticity to the cushion  16 . In this regard, part of the elasticity of the cushion  16  may be attributable to its silicone construction, and further be partly attributable to the compression and deflection of the HME device  12  inside the cushion  16 . Still further, it is contemplated that the HME device  12  may be infused with any one of a number of different scents which may be chosen by the patient according to preference. 
     Referring now to  FIGS. 5 and 6 , there is shown a nasal pillows mask  10   a  constructed in accordance with a second embodiment of the present invention. The mask  10   a  is substantially similar in construction to the above-described mask  10 , with only the distinctions between the masks  10 ,  10   a  being highlighted below. The primary distinction between the masks  10 ,  10   a  lies in the substitution of the above-described HME device  12  of the mask  10  with an HME device  12   a  in the mask  10   a . In the mask  10   a , the HME device  12   a  is permanently attached to the exhalation valve  14 , with the HME device  12   a  and the exhalation valve  14  thus collectively defining a HME subassembly  98  of the mask  10   a.    
     The HME device  12   a  is preferably formed to have a generally frusto-conical shape, and preferably has a layered construction. More particularly, the HME device  12   a  is preferably fabricated to include three layers including a low density layer  92   a , a medium density layer  94   a  and a high density layer  96   a . The medium density layer  94   a  is interposed between the low and high density layers  92   a ,  96   a . Those of ordinary skill in the art will recognize that the use of the three layers  92   a ,  94   a ,  96   a  to construct the HME device  12   a  is exemplary only, and that it may alternatively be fabricated from a single layer of material, two layers, or more than three layers without departing from the spirit and scope of the present invention. In the HME subassembly  98 , a portion of the bottom surface of the HME device  12   a  (as viewed from the perspective shown in  FIGS. 6 and 7 ) as defined by the low density layer  92   a  thereof is abutted against and permanently attached to the distal rim defined by the wall portion  50  of the seat member  44 . 
     The size and shape of the HME device  12   a  relative to the shape and internal volume of the fluid chamber  24  is selected such that the HME device  12   a  assumes a prescribed orientation within the fluid chamber  24  when operatively positioned therein. Since the HME device  12   a  is part of the HME subassembly  98  in the mask  10   a  (i.e., is attached to the exhalation valve  14 ), the advancement of the HME device  12   a  into the fluid chamber  24  occurs concurrently with the process of attaching the exhalation valve  14  to the cushion  16  in the above-described manner. In this regard, the HME device  12   a  is initially advanced into the fluid chamber  24  via the valve opening  28  defined by the cushion  16 , with the exhalation valve  14  thereafter being cooperatively engaged to the cushion  16 . Though, as is apparent from  FIG. 5 , the size of the HME device  12   a  exceeds that of the valve opening  28 , the pliable nature of the material(s) preferably used for the layers  92   a ,  94   a ,  96   a  of the HME device  12   a  allows the same to be compressed and/or folded in a manner which facilitates the advancement through the valve opening  28  and into the fluid chamber  24 . 
     When viewed from the perspective shown in  FIG. 6 , when the HME device  12   a  is operatively positioned within the fluid chamber  24 , at least a peripheral portion of the top surface of the HME device  12   a  defined by the high density layer  96   a  thereof is abutted against corresponding regions of the interior surface of the main body portion  18  of the cushion  16  which defines the fluid chamber  24 . More particularly, the peripheral portion of the top surface of the HME device  12   a  is abutted against a corresponding interior surface region of the main body portion  18  which is located between the inlet ends of the first and second gas delivery lumens  36 ,  38  and the pillow portions  26 . Further, as also viewed from the perspective shown in  FIG. 6 , a central portion of the top surface of the HME device  12   a  as defined by the high density layer  96   a  thereof is abutted against a portion of the interior surface of the main body portion  18  which is defined by that segment thereof extending between the pillow portions  26 . In this regard, the size and shape of the HME device  12   a  is preferably such that when fully deployed within the fluid chamber  24 , the HME device  12   a  will form a complete or substantially complete barrier between the open interiors of the pillow portions  26  and the fluid chamber  24 , yet will not obstruct the inlet ends of either of the first and second gas delivery lumens  36 ,  38 . As is further shown in  FIG. 6 , the inlet end of the pressure sensing lumen  40  which extends to the fluid chamber  24  is not covered or otherwise obstructed by the fully deployed HME device  12   a.    
     As shown in  FIG. 6 , during an inhalation phase of a patient using the mask  10   a , air enters the fluid chamber  24  via the first and second gas delivery lumens  36 ,  38  which, as indicated above, are preferably unobstructed by the HME device  12   a . Due to the permeability of the HME device  12   a , the air is able to pass through the HME device  12   a  and into the nostrils of the patient via the pillow portions  26  of the cushion  16 . This flow path is identified by the arrows shown in  FIG. 6 . Moisture and heat retained by the HME device  12   a  is transferred into the air passing there through prior to the air reaching the nostrils of the patient. Though air delivered into the fluid chamber  24  via the first and second gas delivery lumens  36 ,  38  is also capable of flowing through the HME device  12   a  into the exhalation valve  14 , during the inhalation phase of the patient, the exhalation valve  14  is normally maintained in its closed position as described above. As a result, any gas entering the exhalation valve  14  via the HME device  12   a  during the inhalation phase is prevented from being vented via the exhaust vents  60  as a result of the diaphragm  48  being sealed against the seat member  44  in the aforementioned manner. 
     In the mask  10   a  having the HME device  12   a  positioned in the cushion  16  in the aforementioned manner, the size and shape of the HME device  12   a  relative to the shape and internal volume of the fluid chamber  24  is also selected such that the resultant shape of that portion of the fluid chamber  24  which is separated from the pillow portions  26  by the HME device  12   a  is operative to maximize flow over the exposed portions of the bottom surface of the HME device  12   a  defined by the low density layer  92   a  thereof. Such shape is also selected to impart a prescribed measure of turbulence to the air flowing into the fluid chamber  24  via the inlet ends of the first and second gas delivery lumens  36 ,  38 . This turbulence, and the vortices resulting therefrom, assists in maximizing flow over the exposed portions of the bottom surface of the HME device  12   a . This in turn optimizes the level of moisture and heat transferred into the air passing through the HME device  12   a  and to the patient via the pillows portions  26  during the inhalation phase of the patient. An exemplary airflow pattern during the inhalation phase of the patient is shown by the arrows included in  FIG. 6 . 
     During the exhalation phase of the patient wearing the mask  10   a , exhaled air travels through the open interiors of the pillow portions  26  and into the exhalation valve  14  through the HME device  12   a . Along these lines, the material(s) preferably used to facilitate the fabrication of the HME device  12   a  provide for the easy passage of exhaled air through the HME device  12   a  and into the exhalation valve  14  without causing the patient to exert any greater exhalation force, i.e., the patient does not sense that there is an obstruction within the mask  10   a  during the exhalation phase. As explained above, during the exhalation phase, the diaphragm  48  of the exhalation valve  14  is actuated to its open position, thus allowing air passing through the HME device  12   a  and into the exhalation valve  14  to be vented to ambient via the vent ports  60  within the seat member  44  of the exhalation valve  14 . As will be recognized, the HME device  12   a  is operative to retain moisture and heat from the air exhaled by the patient and passing therethrough during the exhalation phase, and to transfer such moisture and heat to the patient in the aforementioned manner during the inhalation phase. 
     Since the HME device  12   a  is permanently assembled to the exhalation valve  14  in the HME subassembly  98 , is may be easily removed from within the fluid chamber  24  upon the detachment of the exhalation valve  14  therefrom, thus making it washable and/or replaceable. In this regard, the HME device  12   a  could be replaced on a prescribed replacement cycle. Along these lines, it is contemplated that the HME device  12   a  may be impregnated with a chemical agent which facilitates a color change therein when certain conditions are satisfied indicative of a need for the replacement thereof. It is also contemplated that the HME device  12   a  may be infused with any one of a number of different scents which may be chosen by the patient according to preference. 
     Referring now to  FIGS. 8-10 , there is shown a ventilation mask  110  (e.g., a nasal pillows mask) constructed in accordance with a third embodiment of the present invention. The mask  110  includes an integrated, diaphragm-implemented, piloted exhalation valve  112 , the structural and functional attributes of which will be described in more detail below. 
     As shown in  FIGS. 8-10 , the mask  110  comprises a housing or cushion  114 . The cushion  114 , which is preferably fabricated from a silicone elastomer having a Shore A hardness in the range of from about 20 to 60 and preferably about 40, is formed as a single, unitary component, and is shown individually in  FIG. 9 . The cushion  114  includes a main body portion  116  which defines a first outer end surface  118  and an opposed second outer end surface  120 . The main body portion  116  further defines an interior fluid chamber  122  which is of a prescribed volume. In addition to the main body portion  116 , the cushion  114  includes an identically configured pair of hollow pillow portions  124  which protrude from the main body portion  116  in a common direction and in a prescribed spatial relationship relative to each other. More particularly, in the cushion  114 , the spacing between the pillow portions  124  is selected to facilitate the general alignment thereof with the nostrils of an adult patient when the mask  110  is worn by such patient. Each of the pillow portions  124  fluidly communicates with the fluid chamber  122 . 
     As shown in  FIG. 9 , the main body portion  116  of the cushion  114  includes an enlarged, circularly configured valve opening  126  which is in direct fluid communication with the fluid chamber  122 . The valve opening  126  is positioned in generally opposed relation to the pillow portions  124  of the cushion  114 . The valve opening  126  is adapted to accommodate an exhalation valve subassembly  111  of the mask  110  in a manner which will be described in more detail below. 
     The main body portion  116  of the cushion  114  further defines first and second gas delivery lumens  132 ,  134  which extend from respective ones of the first and second outer end surfaces  118 ,  120  into fluid communication with the fluid chamber  122 . Additionally, a pressure sensing lumen  136  defined by the main body portion  116  extends from the first outer end surface  118  into fluid communication with the fluid chamber  122 . The main body portion  116  further defines a valve pilot lumen  138  which extends from the second outer end surface  120  into fluid communication with the fluid chamber. Those of ordinary skill in the art will recognize that the gas delivery lumens  132 ,  134  may be substituted with a single gas delivery lumen and/or positioned within the cushion  114  in orientations other than those depicted in  FIG. 10 . For example, the gas delivery lumen(s) of the cushion  114  may be positioned frontally, pointing upwardly, pointing downwardly, etc. rather than extending laterally as shown in  FIG. 10 . The main body portion  116  of the cushion  114  further includes a mounting aperture  139  formed therein. As seen in  FIG. 10 , one end of the mounting aperture  139  communicates with the fluid chamber  122 , with the opposite simply terminating blindly within the main body portion  116 . The use of the first and second gas delivery lumens  132 ,  134 , the pressure sensing lumen  136 , the valve pilot lumen  138  and the mounting aperture  139  will be discussed in more detail below. 
     The exhalation valve subassembly  111  of the mask  110  comprises the aforementioned exhalation valve  112  in combination with a shield plate  113 . The exhalation valve  112  of the mask  110  is itself made of three (3) parts or components, and more particularly a seat member  140 , a cap member  142 , and a diaphragm  144  which is operatively captured between the seat and cap members  140 ,  142 . The seat and cap members  140 ,  142  are each preferably fabricated from a plastic material, with the diaphragm  144  preferably being fabricated from an elastomer having a Shore A hardness in the range of from about 20-40. 
     The seat member  140  includes a tubular, generally cylindrical wall portion  146  which defines a distal, annular outer rim  148  and an opposed annular inner seating surface  149 . The wall portion further defines an outlet conduit  147  which extends between the outer rim  148  and seating surface  149 . In addition to the wall portion  146 , the seat member  140  includes an annular flange portion  150  which is integrally connected to the wall portion  146  by a series of spoke portions  151 . The spoke portions  151  extend to locations on the wall portion  146  proximate the seating surface  149 , with the flange portion  150  being positioned radially outward relative to the wall portion  146 . In the seat member  140 , the wall, flange and spoke portions  146 ,  150 ,  151  collectively define a plurality of exhaust vents  152  which are located about the periphery of the wall portion  146  in a prescribed arrangement and spacing relative to each other. The seat member  140  is formed such that each of the exhaust vents  152  normally fluidly communicates with the outlet conduit  147  defined by the wall portion  146 . 
     The cap member  142  of the exhalation valve  112  comprises a circularly configured base portion  154  which defines an inner surface  156 . In addition to the base portion  154 , the cap member  142  includes an annular flange portion  160  which circumvents and protrudes generally perpendicularly relative to the inner surface  156  of the base portion  154 . The cap member  142  further includes an identically configured pair of tube portions  162  which are integrally connected to the flange portion  160  in diametrically opposed relation to each other (i.e., approximately 180° apart). Each of the tube portions defines a lumen  164  extending therethrough and is used for reasons which will be discussed in more detail below. The seat and cap members  140 ,  142 , when attached to each other in the fully assembled exhalation valve  112 , collectively define an interior valve chamber of the exhalation valve  112 , such valve chamber generally being located between the inner surface  156  defined by the base portion  154  of the cap member  142  and the seating surface  149  defined by the wall portion  146  of the seat member  140 . 
     The diaphragm  144  of the exhalation valve  112 , which resides within the valve chamber, has a circularly configured, central body portion  166 , and a peripheral flange portion  168  which is integrally connected to and circumvents the body portion  166 . The flange portion  168  includes an arcuately contoured primary region and a distal region which protrudes radially from the primary region. As such, the primary region of the flange portion  168  extends between the distal region thereof and the body portion  166 , and defines a continuous, generally concave channel  170 . The body portion  166  of the diaphragm  144  may optionally be perforated, i.e., be provided with an array of small apertures which extend therethrough. 
     In the exhalation valve  112 , the flange portion  168  of the diaphragm  144  is operatively captured between complementary engagement surfaces defined by the flange portions  150 ,  160  of the seat and cap members  140 ,  142 . More particularly, the annular distal region of the flange portion  168  is compressed (and thus captured) between an annular shoulder defined by the flange portion  160  of the cap member  142 , and a complimentary annular shoulder which is defined by the flange portion  150  of the seat member  140  proximate the exhaust vents  152 . The orientation of the diaphragm  144  within the valve chamber when captured between the seat and cap members  140 ,  142  is such that the channel  170  defined by the arcuately contoured primary region of the flange portion  168  is directed toward or faces the seating surface  149  defined by the wall portion  146  of the seat member  140 . 
     The capture of the diaphragm  144  between the seat and cap members  140 ,  142  in the aforementioned manner results in the diaphragm  144  effectively segregating the valve chamber collectively defined by the seat and cap members  140 ,  142  into a pilot section  172  and an exhaust section  174 . The pilot section  172  of the valve chamber is located between the diaphragm  144  and the inner surface  156  of the base portion  154  of the cap member  142 . The exhaust section  174  of the valve chamber is located between the diaphragm  144  and both the exhaust vents  152  and the seating surface  149  of the wall portion  146  of the seat member  140 . In this regard, the outlet conduit  147  defined by the wall portion  146  fluidly communicates with the exhaust section  174  of the valve chamber. In addition, the lumens  164  of the tube portions  162  of the cap member  142  each fluidly communicate with the pilot section  172  of the valve chamber. 
     The diaphragm  144  (and hence the exhalation valve  112 ) is selectively moveable between an open position and a closed position. When in its normal, open position, the diaphragm  144  is in a relaxed, unbiased state. Importantly, in either of its open or closed positions, the diaphragm  144  is not normally seated directly against the inner surface  156  defined by the base portion  154  of the cap member  142 . Rather, a gap is normally maintained between the body portion  166  of the diaphragm  144  and the inner surface  156  of the base portion  154 . The width of such gap when the diaphragm  144  is in its open position is generally equal to the fixed distance separating the inner surface  156  of the base portion  154  from the shoulder of the flange portion  160  which engages the distal region of the flange portion  168  of the diaphragm  144 . Further, when the diaphragm  144  is in its open position, the body portion  166  is itself disposed in spaced relation to the seating surface  149  defined by the wall portion  146  of the seat member  140 . As such, when the diaphragm  144  is in its open position, fluid is able to freely pass through the through the exhaust vents  152 , between the seating surface  149  and diaphragm  144 , and through the outlet conduit  147  defined by the wall portion  146  to ambient air. 
     In the exhalation valve  112 , the diaphragm  144  is resiliently deformable from its open position (to which it may be normally biased) to its closed position. An important feature of the present invention is that the diaphragm  144  is normally biased to its open position which provides a failsafe to allow a patient to inhale ambient air through the exhalation valve  112  and exhale ambient air therethrough (via the exhaust vents  152 ) during any ventilator malfunction or when the mask  110  is worn without the therapy being delivered by the ventilator. When the diaphragm  144  is moved or actuated to its closed position, the periphery of the body portion  166  is firmly seated against the seating surface  149  defined by the wall portion  146  of the seat member  140 . The seating of the body portion  166  of the diaphragm  144  against the seating surface  149  effectively blocks fluid communication between the outlet conduit  147  defined by the wall portion  146  and the exhaust section  174  of the valve chamber (and hence the exhaust vents  152  which fluidly communicate with the exhaust section  174 ). 
     In the mask  110 , the cooperative engagement between the exhalation valve  112  and the cushion  114  is facilitated by the advancement of the cap member  142  into the valve opening  126  defined by the cushion  114 . Subsequent to such advancement, one of the two tube portions  162  of the cap member  142  is partially advanced into and frictionally retained within the pilot lumen  138  of the cushion  114  in the manner shown in  FIG. 10 . The advancement of one tube portion  162  of the cap member  142  into the pilot lumen  138  facilitates the placement of the pilot lumen  138  into fluid communication with the pilot section  172  of the valve chamber via the lumen  164  of the corresponding tube portion  162 . The remaining tube portion  162  of the cap member  142  (i.e., that tube portion  162  not advanced into the pilot lumen  138 ) is advanced into and frictionally retained within the above-described mounting aperture  139  in the manner shown in  FIG. 10 . Importantly, the resilient construction of the cushion  114 , and in particular the main body portion  116  thereof, allows for the cushion  114  to be bent, twisted or otherwise manipulated as is needed to facilitate the advancement of the tube portions  162  of the cap member  142  into respective ones of the pilot lumen  138  and mounting aperture  139  in the aforementioned manner. The advancement of the tube portions  162  into respective ones of the pilot lumen  138  and mounting aperture  139  causes the exhalation valve  112  to assume a position within the fluid chamber  122  of the cushion  114  as is best shown in  FIG. 10 . In this regard, the majority of the exhalation valve  112  resides within the fluid chamber  122 , with the exception of a small distal section of the wall portion  146  of the seat member  140  which protrudes from the valve opening  126  of the cushion  114 . 
     Due to the positioning of the majority of the exhalation valve  112  within the fluid chamber  122 , the exhaust section  174  of the valve chamber is placed into direct fluid communication with the fluid chamber  122  via the exhaust vents  152 . Thus, irrespective of whether the diaphragm  144  of the exhalation valve  112  is in its open or closed positions, the pilot lumen  138  of the cushion  114  is maintained in a constant state of fluid communication with the pilot section  172  of the valve chamber. Additionally, irrespective of whether the diaphragm  144  is in its open or closed positions, the fluid chamber  122  is maintained in a constant state of fluid communication with the exhaust section  174  of the valve chamber via the exhaust vents  152 . When the diaphragm  144  is in its open position, the fluid chamber  122  is further placed into fluid communication with both the outlet conduit  147  (and hence ambient air) via the open flow path defined between the body portion  166  of the diaphragm  144  and the seating surface  149  of the wall portion  146  of the seat member  140 . However, when the diaphragm  144  is moved to its closed position, the fluid communication between the fluid chamber  122  and outlet conduit  147  is effectively blocked by the sealed engagement of the body portion  166  of the diaphragm  144  against the seating surface  149  of the wall portion  146 . 
     As indicated above, in addition to the exhalation valve  112 , the exhalation valve subassembly  111  includes the shield plate  113 . The shield plate  113  has a generally oval, slightly arcuate profile, and includes a circularly configured opening  175  within the approximate center thereof. Additionally, formed within the peripheral side surface of the shield plate  113  is an elongate groove or channel  176 . In the mask  110 , the shield plate  113  is adapted to be advanced into the valve opening  126  subsequent to the cooperative engagement of the exhalation valve  112  to the cushion  114  in the aforementioned manner. More particularly, the advancement of the shield plate  113  into the valve opening  126  is facilitated in a manner wherein the wall portion  146  of the seat member  140  is advanced into and through the opening  175  of the shield plate  113 . In this regard, the wall portion  146  and the opening  175  have complimentary configurations, with the diameter of the opening  175  only slightly exceeding that of the outer diameter of the wall portion  146 . 
     Subsequent to the advancement of the wall portion  146  into the opening  175 , that peripheral edge or lip of the main body portion  116  of the cushion  114  defining the valve opening  126  is advanced into and firmly seated within the complimentary channel  176  formed in the peripheral side surface of the shield plate  113 . The receipt of such edge or lip of the cushion  114  into the channel  176  maintains the shield plate  113  in firm, frictional engagement to the cushion  114 . The spatial relationship between the exhalation valve  112  and shield plate  113  when each is cooperatively engaged to the cushion  114  in the aforementioned manner is such that the distal section of the wall portion  146  which defines the outer rim  148  thereof protrudes slightly from the exterior surface of the shield plate  113 . 
     As will be recognized, the shield plate  113 , when cooperatively engaged to the cushion  114 , effectively encloses that portion of the fluid chamber  122  which would otherwise be directly accessible via the valve opening  126 . Importantly, by virtue of the attachment of the shield plate  113  to the main body portion  116  of the cushion  114 , virtually the entirety of the exhalation valve  112  is completely enclosed or contained within the fluid chamber  122  of the cushion  114 . As indicated above, only a small distal section of the wall portion  146  of the seat member  140  protrudes from the shield plate  113 , and in particular the opening  175  defined thereby. As a result, the exhaust vents  152  which facilitate the fluid communication between the fluid chamber  122  and the exhaust section  174  of the valve chamber, and between the fluid chamber  122  and the outlet conduit  147  (and hence ambient air) when the diaphragm  144  is in the open position, are effectively enclosed within the fluid chamber  122  as provides noise attenuation advantages which will be discussed in more detail below. 
     To assist in maintaining the cooperative engagement between the exhalation valve subassembly  111  and the cushion  114 , the mask  110  is further preferably provided with an elongate reinforcement frame member  178  which is attached to the cushion  114 . The frame member  178  has a generally U-shaped configuration, with a central portion thereof including a circularly configured opening  179  formed therein which is adapted to accommodate that aforementioned distal section of the wall portion  146  of the seat member  140  which protrudes from the shield plate  113 . In this regard, the diameter of the opening  179  is sized so as to only slightly exceed the outer diameter of the wall portion  146 . The thickness of the central portion of the frame member  178  is such that when attached to cushion  114  subsequent to the advancement of the wall portion  146  into the complementary opening  179 , the outer rim  148  defined by the wall portion  146  is substantially flush or continuous with the exterior surface of the frame member  178 . 
     As shown in  FIG. 10 , the opposed end portions of the frame member  178  are cooperatively engaged to respective ones of the first and second outer end surfaces  118 ,  120  of the cushion  114 . More particularly, the frame member  178  includes an identically configured pair of first and second connectors  180 ,  182  which are formed on respective ones of the opposed end portions thereof. An inner portion of the first connector  180  is advanced into and frictionally retained within the first gas delivery lumen  132  of the cushion  114 . Similarly, an inner portion of the second connector  182  is advanced into and frictionally retained within the second gas delivery lumen  134  of the cushion  114 . In addition to the inner portions advanced into respective ones of the first and second gas delivery lumens  132 ,  134 , the first and second connectors  180 ,  182  of the frame member  178  each further include an outer portion which is adapted to be advanced into and frictionally retained within a corresponding lumen of a respective one of a pair of bi-lumen tubes fluidly coupled to the mask  110 , in the same manner as described in detail above in relation to the mask  10 . 
     The frame member  178  further includes a tubular, cylindrically configured pressure port  184  which is disposed adjacent the first connector  180 . The pressure port  184  is aligned and fluidly communicates with the pressure sensing lumen  136  of the cushion  114 . Similarly, the frame member  178  is also provided with a tubular, cylindrically configured pilot port  186  which is disposed adjacent the second connector  182 . The pilot port  186  is aligned and fluidly communicates with the valve pilot lumen  138  of the cushion  114 . The pressure and pilot ports  184 ,  186  of the frame member  78  are adapted to be placed into fluid communication with corresponding lumens of respective ones of the aforementioned pair of bi-lumen tubes which are fluidly connected to the mask  110  within a ventilation system incorporating the same, also in the same manner as described in detail above in relation to the mask  10 . The receipt of the wall portion  146  of the seat member  140  into the opening  179  of the frame member  178  ensures that the cushion  114 , the exhalation valve subassembly  111  and the frame member  178  are properly aligned, and prevents relative movement therebetween. 
     In the mask  110 , the exhalation valve  112  is piloted, with the movement of the diaphragm  144  to the closed position described above being facilitated by the introduction of positive fluid pressure into the pilot section  172  of the valve chamber. More particularly, it is contemplated that during the inspiratory phase of the breathing cycle of a patient wearing the mask  110 , the valve pilot lumen  138  will be pressurized by a pilot line fluidly coupled to the pilot port  186 , with pilot pressure being introduced into that portion of the pilot section  172  of the valve chamber via the pilot lumen  138  and the lumen  164  of that tube portion  162  of the cap member  142  advanced into the pilot lumen  138 . The fluid pressure level introduced into the pilot section  172  of the valve chamber will be sufficient to facilitate the movement of the diaphragm  144  to its closed position described above. When the diaphragm  144  is in its closed position, fluid pressure introduced into the fluid chamber  122  via the gas delivery lumens  132 ,  134  is prevented from being exhausted to ambient air. In this regard, though such fluid may flow from the fluid chamber  122  into the exhaust section  174  of the valve chamber via the exhaust vents  152 , the engagement of the diaphragm  144  to the seating surface  149  defined by the wall portion  146  of the seat member  140  effectively blocks the flow of such fluid into the outlet conduit  147  defined by the wall portion  146  and hence to ambient air. 
     Conversely, during the expiratory phase of the breathing cycle of the patient wearing the mask  110 , it is contemplated that the discontinuation or modulation of the fluid pressure through the valve pilot lumen  138  and hence into the pilot section  172  of the valve chamber, coupled with the resiliency of the diaphragm  144  and/or positive pressure applied to the body portion  166  thereof, will facilitate the movement of the diaphragm  144  back to the open position or to a partially open position. In this regard, positive pressure as may be used to facilitate the movement of the diaphragm  144  to its open position may be provided by air which is exhaled from the patient during the expiratory phase of the breathing circuit and is applied to the body portion  166  of the diaphragm  144  via the pillows portions  124  of the cushion  114 , the fluid chamber  122 , the exhaust vents  152 , and the exhaust section  174  of the valve chamber. As will be recognized, the movement of the diaphragm  144  to the open position allows the air exhaled from the patient into the fluid chamber  122  via the pillow portions  124  to be vented to ambient air after flowing from the fluid chamber  122  into the exhaust section  174  of the valve chamber via the exhaust vents  152 , and thereafter flowing from the exhaust section  174  between the diaphragm  144  and seating surface  149  of the wall portion  146  into the outlet conduit  147  also defined by the wall portion  146 . 
     As will be recognized, based on the application of pilot pressure thereto, the diaphragm  144  travels from a fully open position through a partially open position to a fully closed position. In this regard, the diaphragm  144  will be partially open or partially closed during exhalation to maintain desired ventilation therapy. Further, when pilot pressure is discontinued to the diaphragm  144 , it moves to an open position wherein the patient can inhale and exhale through the mask  110  with minimal restriction and with minimal carbon dioxide retention therein. This is an important feature of the present invention which allows a patient to wear the mask  110  without ventilation therapy being applied to the mask  110 , the aforementioned structural and functional features of the mask  110  making it more comfortable to wear, and further allowing it to be worn without carbon dioxide buildup. This feature is highly advantageous for the treatment of obstructive sleep apnea wherein patients complain of discomfort with ventilation therapy due to mask and pressure discomfort. When it is detected that a patient requires sleep apnea therapy, the ventilation therapy can be started (i.e., in an obstructive sleep apnea situation). 
     To succinctly summarize the foregoing description of the structural and functional features of the mask  110 , during patient inhalation, the valve pilot lumen  138  is pressurized, which causes the diaphragm  144  to close against the seating surface  149 , thus effectively isolating the fluid chamber  122  of the mask  110  from the outside ambient air. The entire flow delivered from a flow generator fluidly coupled to the mask  110  is inhaled by the patient, assuming that unintentional leaks at the interface between the cushion  114  and the patient are discarded. This functionality differs from what typically occurs in a conventional CPAP mask, where venting to ambient air is constantly open, and an intentional leak flow is continuously expelled to ambient air. During patient exhalation, the pilot pressure introduced into the valve pilot lumen  138  is controlled so that the exhaled flow from the patient can be exhausted to ambient air through the exhalation valve  112  in the aforementioned manner. In this regard, the pilot pressure is “servoed” so that the position of the diaphragm  144  relative to the seating surface  149  is modulated, hence modulating the resistance of the exhalation valve  112  to the exhaled flow and effectively ensuring that the pressure in the fluid chamber  122  of the mask  110  is maintained at a prescribed therapeutic level throughout the entire length of the exhalation phase. When the valve pilot lumen  138  is not pressurized, the exhalation valve  112  is in a normally open state, with the diaphragm  144  being spaced from the seating surface  149  in the aforementioned manner, thus allowing the patient to spontaneously breathe in and out with minimal pressure drop (also referred to as back-pressure) in the order of less than about 2 cm H 2 O at 60 l/min. As a result, the patient can comfortably breathe while wearing the mask  110  and while therapy is not being administered to the patient. Importantly, the effective containment of the exhaust vents  152  within the fluid chamber  122  substantially mitigates or suppresses the noise generated by the mask  110  attributable to the flow of fluid into the exhaust section  174  of the valve chamber via the exhaust vents  152 . 
     In the mask  110 , it is contemplated that exhalation valve subassembly  111 , and in particular the exhalation valve  112 , may be detached from the cushion  114  and removed from within the fluid chamber  122  as needed for periodic cleaning or replacement thereof. As will be recognized, such removal is facilitated by first detaching the shield plate  113  from the cushion  114  by removing the lip of the cushion  114  defining the valve opening  126  from within the channel  176  of the shield plate  113 . Thereafter, the exhalation valve  112  is simply grasped and pulled from within the fluid chamber  122 , the flexibility/resiliency of the cushion  114  allowing for the easy removal of the tube portions  162  of the cap member  142  from within respective ones of the pilot lumen  138  and mounting aperture  139 . The re-attachment of the exhalation valve subassembly  111  to the cushion  114  occurs in the reverse sequence, the exhalation valve  112  being advanced into the fluid chamber  122  and attached to the cushion  114  in the aforementioned manner prior to the attachment of the shield plate  113  to the cushion  114  in the aforementioned manner. 
     As further shown in  FIGS. 9 and 10 , the mask  110  also includes the above-described HME device  12  integrated therein. More particularly, the HME device  12  is positioned within the fluid chamber  122  of the cushion  114 , and has both the shape and layered construction described with particularly above in relation to the mask  10 . Prior to its advancement into the fluid chamber  122  of the cushion  114 , the HME device  12  has the generally flat or planar profile shown in  FIG. 9 . The HME device  12  is operative to partially or completely replace a humidifier (cold or heated pass-over; active or passive) which would otherwise be fluidly coupled to the mask  110 . This is possible because the average flow through the system envisioned to be used in conjunction with the mask  110  is about half of a prior art CPAP mask, due to the absence of any intentional leak in such system. 
     The size and shape of the HME device  12  relative to the shape and internal volume of the fluid chamber  122  is selected such that the HME device  12  assumes a prescribed contour or profile when operatively positioned within the fluid chamber  122 . In the mask  110 , the advancement of the HME device  12  into the fluid chamber  122  occurs prior to the operative engagement of the exhalation valve subassembly  111  to the cushion  114  in the above-described manner. In this regard, prior to the cooperative engagement of the exhalation valve subassembly  111  to the cushion  114 , the HME device  12  is advanced into the fluid chamber  122  via the valve opening  126  defined by the cushion  114 . Though, as is apparent from  FIG. 9 , the size of the HME device  12  exceeds that of the valve opening  126 , the pliable nature of the material(s) preferably used for the layers  92 ,  94 ,  96  of the HME device  12  allows the same to be compressed and/or folded in a manner which facilitates the advancement through the valve opening  126  and into the fluid chamber  122 . 
     When the HME device  12  is operatively positioned within the fluid chamber  122 , at least portions of the continuous peripheral side surface of the HME device  12  are abutted against corresponding regions of the interior surface of the main body portion  116  of the cushion  114  which defines the fluid chamber  122 . For instance, as seen in  FIG. 10 , portions of the peripheral side surface of the HME device  12  defined by each of the opposed end portions  88  thereof are abutted against corresponding interior surface regions of the main body portion  116  which are located between the inlet ends of respective ones of the first and second gas delivery lumens  132 ,  134 , and corresponding ones of the pillow portions  124 . In this regard, the size and shape of the HME device  12  is preferably such that when fully deployed within the fluid chamber  122 , the HME device  12  will form a complete or substantially complete barrier between the open interiors of the pillow portions  124  and the fluid chamber  122 , yet will not obstruct the inlet ends of either of the first and second gas delivery lumens  132 ,  134 . 
     In addition to at least portions of the peripheral side surface of the HME device  12  being abutted against corresponding regions of that interior surface of the main body portion  116  defining the fluid chamber  122 , it is also contemplated that a portion of the bottom surface of the HME device  12  (as viewed from the perspective shown in  FIG. 10 ) as defined by the low density layer  92  thereof will be abutted against the base portion  154  of the cap member  142  of the exhalation valve  112  upon the cooperative engagement of the exhalation valve subassembly  111  to the cushion  114 . Further, as also viewed from the perspective shown in  FIG. 10 , a portion of the top surface of the HME device  12  as defined by the high density layer  96  thereof is abutted against a portion of the interior surface of the main body portion  116  which is defined by that segment thereof extending between the pillow portions  124 . The abutment of the opposed top and bottom surfaces of the HME device  12  against the main body portion  116  of the cushion  114  and cap member  142  of the exhalation valve  112  in the aforementioned manner, coupled with the abutment of the peripheral side surface of the HME device  12  against the main body portion  116 , results in the HME device  12  assuming and being maintained in the arcuately shaped profile shown in  FIG. 10 . As indicated above, when it assumes the position shown in  FIG. 10 , the HME device  12  effectively segregates or separates the open interiors of the pillow portions  124  of the cushion  114  from the fluid chamber  122 . 
     During an inhalation phase of a patient using the mask  110 , air enters the fluid chamber  122  via the first and second gas delivery lumens  132 ,  134  which, as indicated above, are preferably unobstructed by the HME device  12 . Due to the permeability of the HME device  12 , the air is able to pass through the HME device  12  and into the nostrils of the patient via the pillow portions  124  of the cushion  114  similar to the flow path identified by the arrows shown in  FIG. 3 . Moisture and heat retained by the HME device  12  is transferred into the air passing there through prior to the air reaching the nostrils of the patient. Though air delivered into the fluid chamber  122  via the first and second gas delivery lumens  132 ,  134  is also capable of flowing into the exhalation valve  112 , during the inhalation phase of the patient, the exhalation valve  112  is normally maintained in its closed position as described above. As a result, any gas entering the exhalation valve  112  during the inhalation phase is prevented from being vented via the exhaust vents  152  as a result of the diaphragm  144  being sealed against the seat member  140  in the aforementioned manner. 
     In the mask  110  having the HME device  12  positioned in the cushion  114  in the aforementioned manner, the size and shape of the HME device  12  relative to the shape and internal volume of the fluid chamber  122  is also selected such that the resultant shape of that portion of the fluid chamber  122  which is separated from the pillow portions  124  by the HME device  12  is operative to maximize flow over the exposed portions of the bottom surface of the HME device  12  defined by the low density layer  92  thereof. Such shape is also selected to impart a prescribed measure of turbulence to the air flowing into the fluid chamber  122  via the inlet ends of the first and second gas delivery lumens  132 ,  134 . This turbulence, and the vortices resulting therefrom, assists in maximizing flow over the exposed portions of the bottom surface of the HME device  12 . This in turn optimizes the level of moisture and heat transferred into the air passing through the HME device  12  and to the patient via the pillows portions  124  during the inhalation phase of the patient. An exemplary airflow pattern during the inhalation phase of the patient is also similar to that shown by the arrows included in  FIG. 3 . 
     During the exhalation phase of the patient wearing the mask  110 , exhaled air travels through the open interiors of the pillow portions  124  and into the exhalation valve  112  through the HME device  12 . Along these lines, the material(s) preferably used to facilitate the fabrication of the HME device  12  provide for the easy passage of exhaled air through the HME device  12  and into the exhalation valve  112  without causing the patient to exert any greater exhalation force, i.e., the patient does not sense that there is an obstruction within the mask  110  during the exhalation phase. As explained above, during the exhalation phase, the diaphragm  144  of the exhalation valve  112  is actuated to its open position, thus allowing air passing through the HME device  12  to be vented to ambient via the vent ports  152 , the exhaust section  174 , and the outlet conduit  147  of the exhalation valve  112 . As will be recognized, the HME device  12  is operative to retain moisture and heat from the air exhaled by the patient and passing therethrough during the exhalation phase, and to transfer such moisture and heat to the patient in the aforementioned manner during the inhalation phase. 
     It is contemplated that the HME device  12  can be permanently assembled to the cushion  114 , or may alternatively be removable therefrom and thus washable and/or disposable. In this regard, the HME device  12 , if removable from within the cushion  114 , could be replaced on a prescribed replacement cycle. Along these lines, it is further contemplated that the HME device  12  may be impregnated with a chemical agent which facilitates a color change therein when certain conditions are satisfied indicative of a need for the replacement thereof. Additionally, it is contemplated that the HME device  12  can be used as an elastic member that adds elasticity to the cushion  114 . In this regard, part of the elasticity of the cushion  114  may be attributable to its silicone construction, and further be partly attributable to the compression and deflection of the HME device  12  inside the cushion  114 . Still further, it is contemplated that the HME device  12  may be infused with any one of a number of different scents which may be chosen by the patient according to preference. 
     Referring now to  FIG. 11 , there is shown a front-elevational view of the nasal pillows mask  10 ,  10   a ,  110  of the present invention as integrated into an exemplary ventilation system  100  wherein a tri-lumen tube  102 , Y-connector  104 , and pair of bi-lumen tubes  106 ,  108  are used to collectively facilitate the operative interface between the nasal pillows mask  10 ,  10   a ,  110  and a flow generating device or flow generator  120 . In the ventilation system  100 , the tri-lumen tube  102  is used to facilitate the fluid communication between the Y-connector  104  and the flow generator  120 , with one end of the tri-lumen tube  102  being fluidly connected to the flow generator  120 , and the opposite end thereof being fluidly connected to the Y-connector  104 . The bi-lumen tubes  106 ,  108  are used to facilitate the fluid communication between the Y-connector  104  and the mask  10 ,  10   a ,  110  with one end of each of the bi-lumen tubes  106 ,  108  being fluidly connected to the Y-connector  104 , and the opposite end thereof being fluidly connected to the mask  10 ,  10   a ,  110 . A detailed description of the structural and functional attributes of the tri-lumen tube  102 , Y-connector  104  and bi-lumen tubes  106 ,  108 , as well as the manner in which the bi-lumen tubes  106 ,  108  are operatively connected to the mask  10 ,  10   a , is described with particularity in Applicant&#39;s co-pending U.S. patent application Ser. No. 13/572,368 entitled VENTILATION MASK WITH INTEGRATED PILOTED EXHALATION VALVE filed Aug. 10, 2012, the disclosure of which is also incorporated herein by reference. 
     In each of the masks  10 ,  10   a ,  100  the integration of the exhalation valve  14 ,  112  into the cushion  16 ,  114  allows lower average flow compared to prior art CPAP masks. In this regard, the structural/functional features of the exhalation valve  14 ,  112  ensure that all the exhaled gas of the patient goes to ambient. As a result, a vent flow is not needed for flushing any trapped carbon dioxide out of the system. Further, during inspiration the exhalation valve  14 ,  112  can close, and the flow generator  120  of the system needs to deliver only the patient flow, without the additional overhead of the intentional leak flow. In turn, the need for lower flow rates allows for the use of smaller tubes that have higher pneumatic resistance, without the need for the use of extremely powerful flow generators. The pneumatic power through the system  100  can be kept comparable to those of traditional CPAP machines, though the pressure delivered by the flow generator  120  will be higher and the flow lower. 
     In addition, the reduced average flow through the system  100  in which the mask  10 ,  10   a ,  110  is used means that less humidity will be removed from the system  100 , as well as the patient. Conventional CPAP systems have to reintegrate the humidity vented by the intentional leak using a humidifier, with heated humidifiers being the industry standard. Active humidification introduces additional problems such as rain-out in the system tubing, which in turn requires heated tubes, and thus introducing more complexity and cost into the system. The system  100  of the present invention, as not having any intentional leak flow, does not need to introduce additional humidity into the system. As indicated above, the HME device  12 ,  12   a  can be introduced directly into the cushion  16 ,  114  of the mask  10 ,  10   a ,  110  so that exhaled humidity can be trapped and used to humidify the air for the following breath. Because of its integration directly into the cushion  16 ,  114  of the mask  10 ,  10   a ,  110  in extremely close proximity to the patient&#39;s nostrils, the HME device  12 ,  12   a  optimizes the desired heat and moisture exchange operation with air inhaled and exhaled by a patient wearing the mask  10 ,  10   a ,  110 . 
     This disclosure provides exemplary embodiments of the present invention. The scope of the present invention is not limited by these exemplary embodiments. Numerous variations, whether explicitly provided for by the specification or implied by the specification, such as variations in structure, dimension, type of material and manufacturing process may be implemented by one of skill in the art in view of this disclosure.