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 , fig1 - 4 depict a ventilation mask 10 ( e . g ., a nasal pillows mask ) constructed in accordance with the present invention . though the mask 10 is depicted as a nasal pillows mask , those skilled in the art will recognize that other ventilation masks are contemplated herein , such as nasal prongs masks , nasal masks , fill face masks and oronasal masks . as such , for purposes of this application , the term mask and / or ventilation mask is intended to encompass all such mask structures . the mask 10 includes an integrated , diaphragm - implemented , piloted exhalation valve 12 , the structural and functional attributes of which will be described in more detail below . as shown in fig1 - 5 , the mask 10 comprises a housing or cushion 14 . the cushion 14 , 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 fig6 . the cushion 14 includes a main body portion 16 which defines a first outer end surface 18 and an opposed second outer end surface 20 . the main body portion 16 further defines an interior fluid chamber 22 which is of a prescribed volume . in addition to the main body portion 16 , the cushion 14 includes an identically configured pair of hollow pillow portions 24 which protrude from the main body portion 16 in a common direction and in a prescribed spatial relationship relative to each other . more particularly , in the cushion 14 , the spacing between the pillow portions 24 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 fig3 and 4 , each of the pillow portions 24 fluidly communicates with the fluid chamber 22 . as shown in fig2 , the main body portion 16 of the cushion 14 includes an enlarged , circularly configured valve opening 26 which is in direct fluid communication with the fluid chamber 22 . the valve opening 26 is positioned in generally opposed relation to the pillow portions 24 of the cushion 14 , and is circumscribed by an annular valve seat 27 also defined by the main body portion 16 . as also shown in fig2 , the main body portion 16 further defines opposed first and second inner end surfaces 28 , 30 which protrude outwardly from the periphery of the valve opening 26 , and are diametrically opposed relative thereto so as to be spaced by an interval of approximately 180 °. the valve opening 26 , valve seat 27 , and first and second inner end surfaces 28 , 30 are adapted to accommodate the exhalation valve 12 of the mask 10 in a manner which will be described in more detail below . as shown fig3 - 6 , the main body portion 16 of the cushion 14 further defines first and second gas delivery lumens 32 , 34 which extend from respective ones of the first and second outer end surfaces 18 , 20 into fluid communication with the fluid chamber 22 . additionally , a pressure sensing lumen 36 defined by the main body portion extends from the first outer end surface 18 into fluid communication with the fluid chamber 22 . the main body portion 16 further defines a valve pilot lumen 38 which extends between the second outer end surface 20 and the second inner end surface 30 . the use of the first and second gas delivery lumens 32 , 34 , the pressure sensing lumen 36 , and the valve pilot lumen 38 will also be discussed in more detail below . those of ordinary skill in the art will recognize that the gas delivery lumens 32 , 34 , may be substituted with a single gas delivery lumen and / or positioned within the cushion 14 in orientations other than those depicted in fig6 . for example , the gas delivery lumen ( s ) of the cushion 14 may be positioned frontally , pointing upwardly , pointing downwardly , etc . rather than extending laterally as shown in fig6 . referring now to fig2 - 5 and 7 - 9 , the exhalation valve 12 of the mask 10 is made of three ( 3 ) parts or components , and more particularly a seat member 40 , a cap member 42 , and a diaphragm 44 which is operatively captured between the seat and cap members 40 , 42 . the seat and cap members 40 , 42 are each preferably fabricated from a plastic material , with the diaphragm 44 preferably being fabricated from an elastomer having a shore a hardness in the range of from about 20 - 40 . as is most easily seen in fig2 , 7 and 9 , the seat member 40 includes a tubular , generally cylindrical wall portion 46 which defines a distal , annular outer rim 48 and an opposed annular inner seating surface 49 . as shown in fig9 , the diameter of the outer rim 48 exceeds that of the seating surface 49 . along these lines , the inner surface of the wall portion 46 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 51 . in addition to the wall portion 46 , the seat member 40 includes an annular flange portion 50 which protrudes radially from that end of the wall portion 46 opposite the outer rim 48 . as shown in fig2 and 7 , the flange portion 50 includes a plurality of exhaust vents 52 which are located about the periphery thereof in a prescribed arrangement and spacing relative to each other . additionally , as is apparent from fig9 , the seat member 40 is formed such that each of the exhaust vents 52 normally fluidly communicates with the bore or fluid conduit defined by the wall portion 46 . the cap member 42 of the exhaust valve 12 comprises a circularly configured base portion 54 which defines an inner surface 56 and an opposed outer surface 58 . in addition to the base portion 54 , the cap member 42 includes an annular flange portion 60 which circumvents and protrudes generally perpendicularly relative to the inner surface 56 of the base portion 60 . the flange portion 60 defines a distal annular shoulder 62 . as shown in fig9 , the shoulder 62 and inner surface 56 extend along respective ones of a spaced , generally parallel pair of planes . further , as shown in fig8 , formed in the outer surface 58 of the base portion 54 is an elongate groove 64 which extends diametrically across the outer surface 58 . the use of the groove 64 will be described in more detail below . the seat and cap members 40 , 42 , when attached to each other in the fully assembled exhalation valve 12 , collectively define an interior valve chamber 59 of the exhalation valve 12 . more particularly , such valve chamber 59 is generally located between the inner surface 56 defined by the base portion 54 of the cap member 42 and the seating surface 49 defined by the wall portion 46 of the seat member 40 . the diaphragm 44 of the exhalation valve 12 , which resides within the valve chamber 59 , has a circularly configured , central body portion 66 , and a peripheral flange portion 68 which is integrally connected to and circumvents the body portion 66 . the body portion 66 includes an annular lip 72 which circumvents and protrudes upwardly from one side or face thereof . the flange portion 68 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 68 extends between the distal region thereof and the body portion 66 , and defines a continuous , generally concave channel 70 . in the exhalation valve 12 , the flange portion 68 of the diaphragm 44 is operatively captured between the flange portions 50 , 60 of the seat and cap members 40 , 42 . more particularly , the annular distal region of the flange portion 68 is compressed ( and thus captured ) between the shoulder 62 defined by the flange portion 60 of the cap member 42 , and a complimentary annular shoulder 53 which is defined by the flange portion 50 of the seat member 40 proximate the exhaust vents 52 . the orientation of the diaphragm 44 within the valve chamber 59 when captured between the seat and cap members 40 , 42 is such that the channel 70 defined by the arcuately contoured primary region of the flange portion 68 is directed toward or faces the seating surface 49 defined by the wall portion 46 of the seat member 40 . the diaphragm 44 ( and hence the exhalation valve 12 ) is selectively moveable between an open position ( shown in fig3 - 5 and 9 ) and a closed position . when in its normal , open position , the diaphragm 44 is in a relaxed , unbiased state . importantly , in either of its open or closed positions , the diaphragm 44 is not normally seated directly against the inner surface 56 defined by the base portion 54 of the cap member 42 . rather , a gap is normally maintained between the body portion 66 of the diaphragm 44 and the inner surface 56 of the base portion 54 . the width of such gap when the diaphragm 44 is in its open position is generally equal to the fixed distance separating the inner surface 56 of the base portion 54 from the shoulder 62 of the flange portion 60 . further , when the diaphragm 44 is in its open position , the body portion 66 , and in particular the lip 72 protruding therefrom , is itself disposed in spaced relation to the seating surface 49 defined by the wall portion 46 of the seat member 40 . as such , when the diaphragm 44 is in its open position , fluid is able to freely pass through the fluid conduit defined by the wall portion 46 , between the seating surface 49 and diaphragm 44 , and through the exhaust vents 52 to ambient air . as shown in fig3 , 8 and 9 , the flange portion 60 of the cap member 42 is further provided with a pilot port 74 which extends therethrough and , in the fully assembled exhalation valve 12 , fluidly communicates with that portion of the valve chamber 59 disposed between the body portion 66 of the diaphragm 44 and the inner surface 56 of the base portion 54 . the use of the pilot port 74 will also be described in more detail below . as will be discussed in more detail below , in the exhalation valve 12 , the diaphragm 44 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 44 is normally biased to its open position which provides a failsafe to allow a patient to inhale ambient air through the exhalation valve 12 and exhale ambient air therethrough ( via the exhaust vents 52 ) during any ventilator malfunction or when the mask is worn without the therapy being delivered by the ventilator . when the diaphragm 44 is moved or actuated to its closed position , the lip 72 of the body portion 66 is firmly seated against the seating surface 49 defined by the wall portion 46 of the seat member 40 . the seating of the lip 72 against the seating surface 49 effectively blocks fluid communication between the fluid conduit defined by the wall portion 46 and the valve chamber 59 ( and hence the exhaust vents 52 which fluidly communicate with the valve chamber 59 ). in the mask 10 , the cooperative engagement between the exhalation valve 12 and the cushion 14 is facilitated by the advancement of the wall portion 46 of the seat member 40 into the valve opening 26 defined by the cushion 14 . as best seen in fig5 , such advancement is limited by the ultimate abutment or engagement of a beveled seating surface 76 defined by the flange portion 50 of the seat member 40 against the complimentary valve seat 27 of the cushion 14 circumventing the valve opening 26 . upon the engagement of the seating surface 76 to the valve seat 27 , the fluid chamber 22 of the cushion 14 fluidly communicates with the fluid conduit defined by the wall portion 46 of the seat member 40 . as will be recognized , if the diaphragm 44 resides in its normal , open position , the fluid chamber 22 is further placed into fluid communication with the valve chamber 59 via the fluid conduit defined by the wall portion 46 , neither end of which is blocked or obstructed by virtue of the gap defined between the lip 72 of the diaphragm 44 and the seating surface 49 of the wall portion 46 . when the exhalation valve 12 is operatively coupled to the cushion 14 , in addition to the valve seat 27 being seated against the seating surface 76 , the first and second inner end surfaces 28 , 30 of the cushion 14 are seated against respective , diametrically opposed sections of the flange portion 68 defined by the cap member 42 . as best seen in fig3 and 4 , the orientation of the exhalation valve 12 relative to the cushion 14 is such that the end of the valve pilot lumen 38 extending to the second inner end surface 30 is aligned and fluidly communicates with the pilot port 74 within the flange portion 60 . as such , in the mask 10 , the valve pilot lumen 38 is in continuous , fluid communication with that portion of the valve chamber 59 defined between the inner surface 56 of the base portion 54 and the body portion 66 of the diaphragm 44 . to assist in maintaining the cooperative engagement between the exhalation valve 12 and the cushion 14 , 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 64 formed in the outer surface 58 defined by the base portion 54 of the cap member 42 . as shown in fig3 and 4 , the opposed end portions of the frame members 78 are cooperatively engaged to respective ones of the first and second outer end surfaces 18 , 20 of the cushion 14 . more particularly , as shown in fig2 , 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 . an inner portion of the first connector 80 is advanced into and frictionally retained within the first gas delivery lumen 32 of the cushion 14 . similarly , an inner portion of the second connector 82 is advanced into and frictionally retained within the second gas delivery lumen 34 of the cushion 14 . in addition to the inner portions advanced into respective ones of the first and second gas delivery lumens 32 , 34 , the first and second connectors 80 , 82 of the frame member 78 each further include an outer portion which , as will be described in more detail below , 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 10 . as shown in fig3 and 4 , the frame member 78 further includes a tubular , cylindrically configured pressure port 84 which is disposed adjacent the first connector 80 . the pressure port 84 is aligned and fluidly communicates with the pressure sensing lumen 36 of the cushion 14 . similarly , the frame member 78 is also provided with a tubular , cylindrically configured pilot port 86 which is disposed adjacent the second connector 82 . the pilot port 86 is aligned and fluidly communicates with the valve pilot lumen 38 of the cushion 14 . as will also be discussed in more detail below , 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 64 of the cap member 42 ensures that the cushion 14 , the exhalation valve 12 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 14 may be formed so as not to include the valve pilot lumen 38 . 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 74 of the exhalation valve 12 . in the mask 10 , the exhalation valve 12 is piloted , with the movement of the diaphragm 44 to the closed position described above being facilitated by the introduction of positive fluid pressure into the valve chamber 59 . 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 38 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 59 normally defined between the body portion 66 of the diaphragm 44 and the inner surface 56 defined by the base portion 54 of the cap member 42 via the pilot port 74 extending through the flange portion 60 of the cap member 42 . the fluid pressure level introduced into the aforementioned region of the valve chamber 59 via the pilot port 74 will be sufficient to facilitate the movement of the diaphragm 44 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 38 and hence into the aforementioned region of the valve chamber 59 via the pilot port 74 , coupled with the resiliency of the diaphragm 44 and / or positive pressure applied to the body portion 66 thereof , will facilitate the movement of the diaphragm 44 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 44 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 66 via the pillows portions 24 of the cushion 14 , the fluid chamber 22 , and the fluid conduit defined by the wall portion of the seat member 40 . as will be recognized , the movement of the diaphragm 44 to the open position allows the air exhaled from the patient to be vented to ambient air after entering the valve chamber 59 via the exhaust vents 52 within the flange portion 50 of the seat member 40 which , as indicated above , fluidly communicate with the valve chamber 59 . as will be recognized , based on the application of pilot pressure thereto , the diaphragm 44 travels from a fully open position through a partially open position to a fully closed position . in this regard , the diaphragm 44 will be partially open or partially closed during exhalation to maintain desired ventilation therapy . further , when pilot pressure is discontinued to the diaphragm 44 , 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 is an important feature of the present invention which 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 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 10 , during patient inhalation , the valve pilot lumen 38 is pressurized , which causes the diaphragm 44 to close against the seating surface 49 , thus effectively isolating the fluid chamber 22 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 14 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 38 is controlled so that the exhaled flow from the patient can be exhausted to ambient air through the exhalation valve 12 in the aforementioned manner . in this regard , the pilot pressure is “ servoed ” so that the position of the diaphragm 44 relative to the seating surface 49 is modulated , hence modulating the resistance of the exhalation valve 12 to the exhaled flow and effectively ensuring that the pressure in the fluid chamber 22 of the mask 10 is maintained at a prescribed therapeutic level throughout the entire length of the exhalation phase . when the valve pilot lumen 38 is not pressurized , the exhalation valve 12 is in a normally open state , with the diaphragm 44 being spaced from the seating surface 49 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 h2o at 601 / min . as a result , the patient can comfortably breathe while wearing the mask 10 and while therapy is not being administered to the patient . referring now to fig1 a , 11 b and 11 c , during use of the mask 10 by a patient , the functionality of the exhalation valve 12 can be characterized with three parameters . these are pt which is the treatment pressure ( i . e ., the pressure in the mask 10 used to treat the patient ; pp which is the pilot pressure ( i . e ., the pressure used to pilot the diaphragm 44 in the exhalation valve 12 ); and qv which is vented flow ( i . e ., flow that is exhausted from inside the exhalation valve 12 to ambient . these three particular parameters are labeled as pt , pp and qv in fig9 . when the patient is ventilated , pt is greater than zero , with the functionality of the exhalation valve 12 being described by the family of curves in the first and second quadrants of fig1 a . in this regard , as apparent from fig1 a , for any given pt , it is evident that by increasing the pilot pressure pp , the exhalation valve 12 will close and the vented flow will decrease . a decrease in the pilot pressure pp will facilitate the opening of the valve 12 , thereby increasing vented flow . the vented flow will increase until the diaphragm 44 touches or contacts the inner surface 56 of the base portion 54 of the cap member 42 , and is thus not able to open further . conversely , when the patient is not ventilated , the inspiratory phase can be described by the third and fourth quadrants . more particularly , qv is negative and air enters the mask 10 through the valve 12 , with the pressure pt in the mask 10 being less than or equal to zero . pilot pressure pp less than zero is not a configuration normally used during ventilation of the patient , but is depicted for a complete description of the functionality of the valve 12 . the family of curves shown in fig1 a can be described by a parametric equation . further , the slope and asymptotes of the curves shown in fig1 a can be modified by , for example and not by way of limitation , changing the material used to fabricate the diaphragm 44 , changing the thickness of the diaphragm 44 , changing the area ratio between the pilot side and patient side of the diaphragm 44 , changing the clearance between the diaphragm 44 and the seating surface 49 , and / or changing the geometry of the exhaust vents 52 . an alternative representation of the functional characteristics of the valve 12 can be described by graphs in which δp = pt − pp is shown . for example , the graph of fig1 b shows that for any given pt , the vented flow can be modulated by changing δp . in this regard , δp can be interpreted as the physical position of the diaphragm 44 . since the diaphragm 44 acts like a spring , the equation describing the relative position d of the diaphragm 44 from the seating surface 49 of the seat member 40 is k · d + pt · at = pp · ap , where at is the area of the diaphragm 44 exposed to treatment pressure pt and ap is the area of the diaphragm 44 exposed to the pilot pressure pp . a similar , alternative representation is provided in the graph of fig1 c which shows pt on the x - axis and δp as the parameter . in this regard , for any given δp , the position d of the diaphragm 44 is determined , with the valve 12 thus being considered as a fixed opening valve . in this scenario pt can be considered the driving pressure pushing air out of the valve 12 , with fig1 c further illustrating the highly non - linear behavior of the valve 12 . fig1 provides a schematic representation of an exemplary ventilation system 88 wherein a tri - lumen tube 90 is used to facilitate the fluid communication between the mask 10 and a blower or flow generator 92 of the system 88 . as represented in fig1 , one end of the tri - lumen tube 90 is fluidly connected to the flow generator 92 , with the opposite end thereof being fluidly connected to a y - connector 94 . the three lumens defined by the tri - lumen tube 90 include a gas delivery lumen , a pressure sensing lumen , and a valve pilot lumen . the gas delivery lumen is provided with an inner diameter or id in the range of from about 2 mm to 15 mm , and preferably about 4 mm to 10 mm . the pressure sensing and valve pilot lumens of the tri - lumen tube 90 are each preferably provided with an id in the range of from about 0 . 5 mm to 2 mm . the outer diameter or od of the tri - lumen tube 90 is preferably less than 17 mm , with the length thereof in the system 88 being about 2 m . the y - connector 94 effectively bifurcates the tri - lumen tube 90 into the first and second bi - lumen tubes 96 , 98 , each of which has a length of about 6 inches . the first bi - lumen tube 96 includes a gas delivery lumen having an id in the same ranges described above in relation to the gas delivery lumen of the tri - lumen tube 90 . the gas delivery lumen of the first bi - lumen tube 96 is fluidly coupled to the outer portion of the first connector 80 of the frame member 78 . the remaining lumen of the first bi - lumen tube 96 is a pressure sensing lumen which has an id in the same range described above in relation to the pressure sensing lumen of the tri - lumen tube 90 , and is fluidly coupled to the pressure port 84 of the frame member 78 . similarly , the second bi - lumen tube 98 includes a gas delivery lumen having an id in the same ranges described above in relation to the gas delivery lumen of the tri - lumen tube 90 . the gas delivery lumen of the second bi - lumen tube 98 is fluidly coupled to the outer portion of the second connector 82 of the frame member 78 . the remaining lumen of the second bi - lumen tube 98 is a valve pilot lumen which has an id in the same range described above in relation to the valve pilot lumen of the tri - lumen tube 90 , and is fluidly coupled to the pilot port 86 of the frame member 78 . in the system 88 shown in fig1 , the pilot pressure is generated at the flow generator 92 . in the prior art , a secondary blower or proportional valve that modulates the pressure from a main blower is used to generate a pressure to drive an expiratory valve . however , in the system 88 shown in fig1 , the outlet pressure of the flow generator 92 is used , with the flow generator 92 further being controlled during patient exhalation in order to have the correct pilot pressure for the exhalation valve 12 . this allows the system 88 to be inexpensive , not needing additional expensive components such as proportional valves or secondary blowers . fig1 provides a schematic representation of another exemplary ventilation system 100 wherein a bi - lumen tube 102 is used to facilitate the fluid communication between the mask 10 and the blower or flow generator 92 of the system 100 . as represented in fig1 , one end of the bi - lumen tube 102 is fluidly connected to the flow generator 92 , with the opposite end thereof being fluidly connected to the y - connector 94 . the two lumens defined by the bi - lumen tube 102 include a gas delivery lumen and a pressure sensing lumen . the gas delivery lumen is provided with an inner diameter or id in the range of from about 2 mm to 10 mm , and preferably about 4 mm to 7 mm . the pressure sensing lumen of the bi - lumen tube 102 is preferably provided with an id in the range of from about 0 . 5 mm to 2 mm . the outer diameter or od of the bi - lumen tube 90 is preferably less than 11 mm , with the length thereof being about 2 m . the y - connector 94 effectively bifurcates the bi - lumen tube 102 into the first and second bi - lumen tubes 96 , 98 , each of which has a length of about 6 inches . the first bi - lumen tube 96 includes a gas delivery lumen having an id in the same ranges described above in relation to the gas delivery lumen of the bi - lumen tube 102 . the gas delivery lumen of the first bi - lumen tube 96 is fluidly coupled to the outer portion of the first connector 80 of the frame member 78 . the remaining lumen of the first bi - lumen tube 96 is a pressure sensing lumen which has an id in the same range described above in relation to the pressure sensing lumen of the bi - lumen tube 102 , and is fluidly coupled to the pressure port 84 of the frame member 78 . similarly , the second bi - lumen tube 98 includes a gas delivery lumen having an id in the same ranges described above in relation to the gas delivery lumen of the bi - lumen tube 102 . the gas delivery lumen of the second bi - lumen tube 98 is fluidly coupled to the outer portion of the second connector 82 of the frame member 78 . the remaining lumen of the second bi - lumen tube 98 is a valve pilot lumen which has an id in the same range described above in relation to the pressure sensing lumen of the bi - lumen tube 102 , and is fluidly coupled to the pilot port 86 of the frame member 78 . in the system 100 shown in fig1 , the valve pilot lumen 38 is connected to the gas delivery air path at the y - connector 94 . more particularly , the gas delivery lumen of the bi - lumen tube 102 is transitioned at the y - connector 94 to the valve pilot lumen of the second bi - lumen tube 98 . as such , the pilot pressure will be proportional to the outlet pressure of the flow generator 92 minus the pressure drop along the bi - lumen tube 102 , which is proportional to delivered flow . this solution is useful when small diameter tubes are used in the system 100 , since such small diameter tubes require higher outlet pressure from the flow generator 92 for the same flow . in this regard , since the pressure at the outlet of the flow generator 92 would be excessive for piloting the exhalation valve 12 , a lower pressure along the circuit within the system 100 is used . in the system 100 , though it is easier to tap in at the y - connector 94 , anywhere along the tube network is acceptable , depending on the pressure level of the flow generator 92 which is the pressure required by the patient circuit in order to deliver the therapeutic pressure and flow at the patient . in each of the systems 88 , 100 , it is contemplated that the control of the flow generator 92 , and hence the control of therapeutic pressure delivered to the patient wearing the mask 10 , may be governed by the data gathered from dual pressure sensors which take measurements at the mask 10 and the output of the flow generator 92 . as will be recognized , pressure sensing at the mask 10 is facilitated by the pressure sensing lumen 36 which , as indicated above , is formed within the cushion 14 and fluidly communicates with the fluid chamber 22 thereof . as also previously explained , one of the lumens of the first bi - lumen tube 96 in each of the systems 88 , 100 is coupled to the pressure port 84 ( and hence the pressure sensing lumen 36 ). as a result , the first bi - lumen tube 96 , y - connector 94 and one of the tri - lumen or bi - lumen tubes 90 , 102 collectively define a continuous pressure sensing fluid path between the mask 10 and a suitable pressure sensing modality located remotely therefrom . a more detailed discussion regarding the use of the dual pressure sensors to govern the delivery of therapeutic pressure to the patient is found in applicant &# 39 ; s co - pending u . s . application ser . no . 13 / 411 , 257 entitled dual pressure sensor continuous positive airway pressure ( cpap ) therapy filed mar . 2 , 2012 , the entire disclosure of which is incorporated herein by reference . referring now to fig1 , there is shown a mask 10 a which comprises a variant of the mask 10 . the sole distinction between the masks 10 , 10 a lies in the mask 10 a including a heat and moisture exchanger or hme 104 which is positioned within the fluid chamber 22 of the cushion 14 . the hme 104 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 a . this is possible because the average flow through the system envisioned to be used in conjunction with the mask 10 a is about half of a prior art cpap mask , due to the absence of any intentional leak in such system . the hme 104 as a result of its positioning within the fluid chamber 22 , is able to intercept the flow delivered from the flow generator to the patient in order to humidify it , and is further able to capture humidity and heat from exhaled flow for the next breath . the pressure drop created by the hme 104 during exhalation ( back - pressure ) must be limited , in the order of less than 5 cmh2o at 601 / min , and preferably lower than 2 cmh2o at 601 / min . these parameters allow for a low back - pressure when the patient is wearing the mask 10 a and no therapy is delivered to the patient . it is contemplated that the hme 104 can be permanently assembled to the cushion 14 , or may alternatively be removable therefrom and thus washable and / or disposable . in this regard , the hme 104 , if removable from within the cushion 14 , could be replaced on a prescribed replacement cycle . additionally , it is contemplated that the hme 104 can be used as an elastic member that adds elasticity to the cushion 14 . in this regard , part of the elasticity of the cushion 14 may be attributable to its silicone construction , and further be partly attributable to the compression and deflection of the hme 104 inside the cushion 14 . the integration of the exhalation valve 12 into the cushion 14 and in accordance with the present invention allows lower average flow compared to prior art cpap masks . as indicated above , normal masks have a set of apertures called “ vents ” that create a continuous intentional leak during therapy . this intentional leak or vented flow is used to flush out the exhaled carbon dioxide that in conventional cpap machines , with a standard iso taper tube connecting the mask to the flow generator or blower , fills the tubing up almost completely with carbon dioxide during exhalation . the carbon dioxide accumulated in the tubing , if not flushed out through the vent flow , would be inhaled by the patient in the next breath , progressively increasing the carbon dioxide content in the inhaled gas at every breath . the structural / functional features of the exhalation valve 12 , in conjunction with the use of small inner diameter , high pneumatic resistance tubes in the system in which the mask 10 , 10 a is used , ensures that all the exhaled gas 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 12 can close , and the flow generator 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 can be kept comparable to those of traditional cpap machines , though the pressure delivered by the flow generator will be higher and the flow lower . the reduced average flow through the system in which the mask 10 , 10 a is used means that less humidity will be removed from the system , 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 envisioned system of the prent invention , as not having any intentional leak flow , does not need to introduce additional humidity into the system . as indicated above , the hme 104 can be introduced into the cushion 14 of the mask 10 a so that exhaled humidity can be trapped and used to humidify the air for the following breath . in addition , a big portion of the noise of conventional cpap systems is noise conducted from the flow generator through the tubing up to the mask and then radiated in the ambient through the vent openings . as previously explained , the system described above is closed to the ambient during inhalation which is the noisiest part of the therapy . the exhaled flow is also lower than the prior art so it can be diffused more efficiently , thus effectively decreasing the average exit speed and minimizing impingement noise of the exhaled flow on bed sheets , pillows , etc . as also explained above , a patient can breathe spontaneously when the mask is worn and not connected to the flow generator tubing , or when therapy is not administered . in this regard , there will be little back pressure and virtually no carbon dioxide re - breathing , due to the presence of the exhalation valve 12 that is normally open and the inner diameters of the tubes integrated into the system . this enables a zero pressure start wherein the patient falls asleep wearing the mask 10 , 10 a wherein the flow generator does not deliver any therapy . prior art systems can only ramp from about 4 mh2o up to therapy pressure . a zero pressure start is more comfortable to patients that do not tolerate pressure . as seen in fig1 , due to the reduced diameter of the various tubes ( i . e ., the tri - lumen tube 90 and bi - lumen tubes 96 , 98 , 102 ) integrated into the system 88 , 100 , such tubes can be routed around the patient &# 39 ; s ears similar to conventional o2 cannulas . more particularly , the tubing can go around the patient &# 39 ; s ears to hold the mask 10 , 10 a to the patient &# 39 ; s face . this removes the “ tube drag ” problem described above since the tubes will not pull the mask 10 , 10 a away from the face of the patient when he or she moves . as previously explained , “ tube drag ” typically decreases mask stability on the patient and increases unintentional leak that annoys the patient . in the prior art , head gear tension is used to counter balance the tube drag , which leads to comfort issues . the tube routing of the present invention allows for lower head gear tension and a more comfortable therapy , especially for compliant patients that wear the mask 10 approximately eight hours every night . the reduction in tube drag in accordance with the present invention also allows for minimal headgear design ( virtually none ), reduced headgear tension for better patient comfort as indicated above , and reduced cushion compliance that results in a smaller , more discrete cushion 14 . the tube dangling in front of the patient , also commonly referred to as the “ elephant trunk ” by patients , is a substantial psychological barrier to getting used to therapy . the tube routing shown in fig1 , in addition to making the mask 10 , 10 a more stable upon the patient , avoids this barrier as well . another benefit to the smaller tubing is that the mask 10 , 10 a can become smaller because it does not need to interface with large tubing . indeed , large masks are another significant factor leading to the high non - compliance rate for cpap therapy since , in addition to being non - discrete , they often cause claustrophobia . 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 .
a mask for achieving positive pressure mechanical ventilation , and a method for a operating a ventilation system including such mask . the mask 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 pilot may also be a preset pressure derived in the mask , a separate pneumatic line from the ventilator , or an electro - mechanical control . the mask of the present invention may further include a heat and moisture exchanger which is integrated therein .