Patent Publication Number: US-2017361046-A1

Title: Patient interface and non-invasive positive pressure ventilating method

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. application Ser. No. 12/134,801, filed Jun. 6, 2008, now allowed, which claims priority to U.S. Provisional Application 60/949,692, filed Jul. 13, 2007, each of which is incorporated herein by reference in their entirety. 
    
    
     FIELD OF THE INVENTION 
     Sample embodiments of the present invention relate to a patient interface for use in delivering a flow of breathable gas to an airway of a patient. Sample embodiments of the present invention also relate to a non-invasive positive pressure ventilating method. 
     BACKGROUND OF THE INVENTION 
     Non-invasive positive pressure ventilation (NIPPV) techniques, such as, for example, the application of continuous positive airway pressure (CPAP) have been used to treat sleep disorder breathing (SDB) such as obstructive sleep apnea (OSA) and other disorders such as chronic obstructive pulmonary disease (COPD) and congestive heart failure (CHF). Apparatuses for applying NIPPV techniques typically include a flow generator, including a blower, and a patient interface. A delivery conduit or hose is connected between the flow generator and the patient interface to deliver breathable gas at a positive pressure to the patient. A number of different patient interfaces are known and include, for example, nasal masks, nose and mouth masks, full-face masks, and nasal prongs and pillows. A headgear is typically utilized to position the patient interface on the patient&#39;s face and counterbalance the force of gravity and the force which results from the application of pressurized air which seeks to push the mask off the face. 
     NIPPV therapies are typically administered at night while the patient sleeps. In order for the therapy to be effective, the patient interface must be comfortable enough for the patient to remain sleeping, while maintaining a seal that is sufficient to deliver the breathable air at the required pressure. 
     Air leakage from between the patient&#39;s skin and the patient interface reduces the effectiveness of the therapy. Even very small leaks can be perceived by the patient and/or bed partner. The air leakage may cause the patient to increase the pressure of the mask against the patient&#39;s face. The air leakage may also cause the flow generator to increase the pressure of the delivered air, thus increasing the speed and noise of the flow generator. Increasing the pressure of the delivered air results in an increase in the flow of air, including the vent flow and leak flow. If a humidifier is used, the increase in the leak flow results in a waste of water from the humidifier. If supplemental oxygen is being provided to the flow of air, the increase in the leak flow causes a waste of some of the supplemental oxygen. Moreover, the air leakage may act as an irritant to the patient&#39;s eyes and disturb the patient&#39;s sleep. 
     Various masks have been proposed for minimizing leakage between the mask cushion and the face of the patient. Examples of these respiratory masks are disclosed in U.S. Patent Application Publication 2003/0029455, U.S. Pat. No. 6,418,928 and WO Patent Application Publication 2006/113321. Other approaches to minimizing leakage include attempting to provide a perfect seal between the patient&#39;s face and the patient interface. U.S. Pat. No. 6,834,650 is an example of such an attempt. WO Patent Application Publication 2006/102707 discloses a patient interface having a vacuum line as a return path from the patient interface. Leakage is prevented, but requires the use of non-vented patient interfaces. 
     There still exists a need for a patient interface that controls leakage and improves therapy for the patient by reducing, or eliminating, the main discomfiture associated with leakage. 
     SUMMARY OF THE INVENTION 
     One aspect of the invention relates to a patient interface that improves therapy to a patient by reducing, or eliminating, problems caused by leakage from the patient interface. 
     Another aspect of the invention relates to a patient interface that improves therapy to a patient by reducing, or eliminating, patient discomfort caused by leakage from the patient interface. 
     Yet another aspect of the invention relates to a patient interface that reduces, or eliminates, the occurrence of explosive, or bursting, leakage. 
     Still another aspect of the invention relates to a patient interface that can catch or collect leakage from a first seal with a second seal to prevent leakage from the patient interface. 
     An even further aspect of the invention relates to a patient interface that increases the resistance to leakage. 
     A still further aspect of the invention relates to a patient interface that diffuses leakage to reduce irritation to the patient. 
     Another aspect of the invention relates to a patient interface that vents or deflects leakage to reduce or prevent disturbance to the patient. 
     According to one embodiment of the invention a patient interface for use in delivering a flow of breathable gas to an airway of a patient is provided. The patient interface comprises a first seal adapted to contact the patient&#39;s face and seal a first space between the patient interface and the patient&#39;s face at a first positive pressure; and a second seal adapted to contact the patient&#39;s face and seal a second space between the patient interface and the patient&#39;s face at a second positive pressure. The first seal is configured to seal the first space from the second space. 
     According to another embodiment of the invention, a patient interface for use in delivering a flow of breathable gas to an airway of a patient comprises a seal adapted to contact the patient&#39;s face and seal a space between the patient interface and the patient&#39;s face at a positive pressure; and a leak reducing means provided on the seal for reducing leakage of gas from the space. 
     According to a further embodiment of the invention, a patient interface for use in delivering a flow of breathable gas to an airway of a patient comprises a first seal adapted to contact the patient&#39;s face and seal a first space between the patient interface and the patient&#39;s face at a first positive pressure; and a second seal adapted to contact the patient&#39;s face and seal a second space between the patient interface and the patient&#39;s face. A vacuum line is configured to create a negative pressure in the second space and remove any gas leaking from the first space to the second space. The negative pressure is sufficient to deform the first and second seals and a portion of the patient&#39;s face covered by the second space. 
     According to yet another embodiment of the invention, a patient interface for use in delivering a flow of breathable gas to an airway of a patient comprises a frame; and a conduit for delivering the flow of breathable gas. The conduit is incorporated with the frame. A seal is connected to the conduit. The seal is inflatable by the flow of breathable gas to pressurize the seal against the patient&#39;s face and includes a vent to direct the flow of breathable gas to a space between the patient interface and the patient&#39;s face. 
     According to still another embodiment of the invention, a patient interface for use in delivering a flow of breathable gas to an airway of a patient comprises a seal adapted to contact the patient&#39;s face and seal a space between the patient interface and the patient&#39;s face. The sealed space includes a nasal bridge region of the patient&#39;s face. A cuff is provided over the seal in the nasal bridge region to direct any leakage of the gas flow from the seal in the nasal bridge region in a direction away from the patient&#39;s eyes. 
     According to another embodiment of the invention, a non-invasive positive pressure ventilating method comprises delivering a flow of breathable gas to a patient interface; sealing a first space between the patient interface and the patient&#39;s face at a first positive pressure; and sealing a second space between the patient interface and the patient&#39;s face at a second positive pressure. The first space is sealed from the second space. 
     According to still another embodiment of the invention, a non-invasive positive pressure ventilating method comprises delivering a flow of breathable gas to a patient interface; sealing a first space between the patient interface and the patient&#39;s face at a first positive pressure; and diffusing any leakage from the sealed first space. 
     According to a further embodiment, a non-invasive positive pressure ventilating method comprises delivering a flow of breathable gas to a patient interface; sealing a first space between the patient interface and the patient&#39;s face at a first positive pressure; and deflecting any leakage of air from the first space in a nasal bridge region away from the patient&#39;s eyes. 
     Other aspects, features, and advantages of this invention will become apparent from the following detailed description when taken in conjunction with the accompanying drawings, which are a part of this disclosure and which illustrate, by way of example, principles of this invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings facilitate an understanding of the various embodiments of this invention. In such drawings: 
         FIG. 1  is a model according to an example of the present invention that illustrates leakage from a patient interface having two seals in series; 
         FIG. 2  is a model according to an example of the present invention that illustrates different possible conditions and resulting statuses that may evolve for a patient interface having two seals provided in series; 
         FIG. 3 a    illustrates a patient interface; 
         FIGS. 3 b , 3 c , 3 d , and 3 e    illustrate different foam shapes that may be used with the patient interface of  FIG. 3   a;    
         FIG. 4  illustrates a patient interface according to another embodiment of the present invention; 
         FIG. 5  illustrates a patient interface according to another embodiment of the invention; 
         FIG. 6  illustrates a patient interface according to another embodiment of the invention; 
         FIGS. 7 a  and 7 b    illustrate a patient interface according to another embodiment of the invention; 
         FIG. 8  illustrates a patient interface according to another embodiment of the invention; 
         FIG. 9  illustrates a sectioned patient interface according to another embodiment of the invention; 
         FIG. 10  is a diagram illustrating the operation of a patient interface having a primary seal and a secondary seal in accordance with another embodiment of the invention; and 
         FIG. 11  illustrates a patient interface and an air delivery hose in accordance with another embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS 
     The following description is provided in relation to several embodiments which may share common characteristics and features. It is to be understood that one or more features of any one embodiment may be combinable with one or more features of the other embodiments. In addition, any single feature or combination of features in any of the embodiments may constitute additional embodiments. 
     In this specification, the word “comprising” is to be understood in its “open” sense, that is, in the sense of “including”, and thus not limited to its “closed” sense, that is the sense of “consisting only of”. A corresponding meaning is to be attributed to the corresponding words “comprise”, “comprised” and “comprises” where they appear. 
     The term “air” will be taken to include breathable gases, for example air with supplemental oxygen. It is also acknowledged that the blowers described herein may be designed to pump fluids and/or gases other than air. 
     Patient Interface Models 
     Referring to  FIG. 1 , a patient interface may include two seals S 1 , S 2  that are provided in series. Each seal S 1 , S 2  has a resistance R 1 , R 2 , respectively, to leakage. A pressure P 1  is delivered at the patient interface by a flow generator. A pressure P 2  exists between the two seals S 1 , S 2 . Ambient pressure P amb  is provided outside the patient interface. 
     When the pressure P 1  delivered at the patient interface by the flow generator is greater than the maximum pressure P 1max  that the first seal can withstand, then the seal S 1  breaks and a leak flow Q occurs against the resistance R 1 . Initially, a leak flow Q 1  flows across the first seal S 1 . In the space between the first seal S 1  and the second seal S 2 , a pressure P 2  develops as a result of the leak flow Q 1 . The pressure P 2  is a positive pressure, i.e., greater than ambient pressure P amb . If the pressure P 2  is greater than the maximum pressure P 2max  that the seal S 2  can withstand, a second leak flow Q 2  flows across the second seal S 2  and out of the patient interface into the ambient air. 
     The space between the first and second seals S 1 , S 2  has a volume V 2  that contains a volumetric mass ρ 2  of breathable gas (e.g. air). 
     Various conditions may be present at the patient interface. In designing a seal arrangement for a patient interface, the various conditions may be considered in addition to the desired status of the patient interface. For example, the seal arrangement of the patient interface may be designed to collect and/or control any possible leakage, including any leakage between the first and second seals, and/or any leakage from the second seal, i.e., leakage out of the patient interface. As another example, seal arrangement may be designed to avoid leakage by sealing properly under any condition. The seal arrangement should thus be designed to avoid leakage that causes annoyance and/or discomfort to the patient, and to improve the quality of the therapy by reducing, or eliminating, problems associated with leakage, e.g., disruption of bi-level algorithms for control of the flow generator. 
     Although a seal arrangement that prevents all leakage, i.e., a perfect seal, would be the most desired arrangement, such an arrangement is very difficult to achieve. Such a seal arrangement may have a desired effect in a relatively small number of cases, for example in high pressure bi-level devices. A more practical seal arrangement may be provided to control leakage when it occurs. Such an arrangement would have a desired effect in a larger number of cases. Controlling leakage allows the flow generator to react properly to leakage, and thus improves the delivery of the therapy. Controlling leakage may also prevent the leakage from causing patient discomfort. Preventing disturbance of the patient&#39;s sleep is one way to ensure proper treatment. 
     A seal arrangement for a patient interface according to the invention may be designed to prevent explosive leak from the patient interface. The seal arrangement according to examples of the invention may also be designed to reduce or eliminate noise disturbance to the patient, and to reduce or eliminate eye irritation by reducing or eliminating leakage. Other design objectives than those specifically discussed herein may also be considered. 
     Referring to  FIG. 2 , a model which may be used in designing patient interfaces according to examples of the invention is illustrated. As shown in condition C 1 , when the maximum sealing pressure P 1max  of the first seal S 1  is larger than the pressure P 1  delivered at the mask by the flow generator, and greater than the pressure P 2  between the first and second seals S 1 , S 2 , there is no leak flow across the first and second seals S 1 , S 2 , i.e., Q=Q 1 =Q 2 =0. 
     If the condition C 1  is changed by another condition C 2  that increases the pressure P 1  delivered at the patient interface by the flow generator so that the pressure P 1  exceeds the maximum sealing pressure P 1max  of the first seal P 1 , another set of conditions C 3  occurs at the patient interface. Under the conditions C 3 , the pressure P 1  delivered by the flow generator exceeds the maximum sealing pressure P 1max  of the first seal S 1 , and also exceeds the pressure P 2  between the first and second seals S 1 , S 2  and the ambient pressure P amb . Under these conditions C 3 , a leak flow Q 1  occurs across the first seal S 1 . However, there is no leak flow across the second seal S 2 , i.e., Q 2 =0. Accordingly, there is no leakage from the patient interface to the ambient. 
     The leak flow Q 1  across the first seal S 1  may cause the pressure P 2  between the first seal S 1  and the second seal S 2  to increase (condition C 4 ). As the pressure P 2  between the first and second seals S 1 , S 2  increases, additional design conditions C 5 , C 9  may effect the performance of the patient interface. Under a first design condition C 5 , the maximum sealing pressure P 1max  of the first seal S 1  is less than the maximum sealing pressure P 2max  of the second seal S 2 . Under this design condition C 5 , if the pressure P 1  delivered by the flow generator at the patient interface is less than or equal to the maximum sealing pressure P 2max  of the second seal S 2  (condition C 6 ), then the pressure P 2  between the first and second seals S 1 , S 2  equals the pressure P 1  delivered by the flow generator (condition C 7 ) As delivered pressure P 1  is less than the maximum sealing pressure P 2max  of the second seal S 2 , the leak flow Q, including the leak flow Q 1  across the first seal and the leak flow Q 2  across the second seal S 2 =0. 
     When the conditions C 1 -C 7  discussed above are satisfied, the patient interface assumes a first status S 1 . In this status S 1 , the second seal S 2  is in sealing engagement with the patient&#39;s face to prevent leakage. The first seal S 1  does not seal against the patient&#39;s face, but may return to a sealing engagement upon a change of condition(s). When the patient interface is in the first status S 1 , and the cushion is moved, such as during the patient&#39;s sleep session, the second seal S 2  may open and allow an explosive leak of air from the patient interface. If the first seal S 1  is not in sealing condition, a short circuit may occur when the cushion moves so that a leak flow occurs across both the first and second seals S 1  and S 2 . 
     Referring back to the condition C 5  (P 1max &lt;P 2max ), if the pressure P 1  at the patient interface delivered by the flow generator exceeds the maximum sealing pressure P 2max  of the second seal (condition C 8 ), another condition C 10  develops. It is also possible for the condition C 10  to develop when the pressure P 2  between the first and second seals is increasing (condition C 4 ) and the maximum sealing pressure P 1max  of the first seal S 1  is greater than the maximum sealing pressure P 2max  of the second seal S 2  (condition C 9 ). 
     In condition C 10 , the pressure P 2  between the first and second seals exceeds the maximum sealing pressure P 2max  of the second seal S 2 . The pressure P 1  delivered by the flow generator also is greater than the pressure P 2  between the seals, which is greater than the ambient pressure P amb . Under this condition C 10 , a leak flow Q includes a leak flow Q 1  across the first seal S 1  and a leak flow Q 2  across the second seal S 2 . 
     If the flow Q 1  across the first seal S 1  is less than the flow Q 2  across the second seal S 2  (C 11 ) and the pressure P 2  between the first and second seals is decreasing such that the pressure P 2  is less than or equal to the maximum sealing pressure P 2max  of the second seal S 2  (C 12 ), the patient interface returns to condition C 3 . In condition C 3 , there is a flow Q 1  across the first seal S 1 , but no flow across the second seal S 2  (i.e. Q 2 =0). This can cause cyclic explosive leaks. 
     If the leak flow Q 1  across the first seal S 1  is greater than the leak flow Q 2  across the second seal S 2  (condition C 13 ) and the pressure P 2  between the first and second seals is increasing such that the pressure P 2  is greater than the maximum sealing pressure P 2max  of the second seal S 2  (condition C 14 ), the leak flows Q 1 , Q 2  across the first and second seals S 1 , S 2  will equalize to a value greater than 0 (condition C 15 ) This condition C 15  may also result directly from condition C 10  if the leak flows Q 1 , Q 2  across the first and second seals S 1 , S 2  are both greater than zero and equal to each other. 
     In condition C 15 , the pressure P 1  at the patient interface delivered by the flow generator is greater than the pressure P 2  between the first and second seals, which is greater than ambient pressure. If this condition C 15  is present, the patient interface is in a second status S 2  in which there is a continuous leak, or short circuit, through both the first and second seals. As discussed below, various seal arrangements may be designed to reduce or eliminate the problems associated with a continuous leak as occurs in the second status S 2 . 
     The model discussed above with respect to  FIG. 2  may rely on certain assumptions. For example, it may be assumed that there are no relative movements between the patient&#39;s face and the patient interface. It may also be assumed that a leak flow occurs when the pressure across the seal exceeds the maximum sealing pressure of the seal, i.e., when P&gt;P max . Another assumption that may be made is that the pressure P 1  that is supplied by the flow generator is constant. Furthermore, it may be assumed that the volume V 2  between the first and second seals is constant. 
     Although certain assumptions, such as those discussed above, may be relied upon in modeling the behavior of the patient interface, the model may also take into account variations to those assumptions. For example, relative movements between the frame of the patient interface and the patient&#39;s face may be interpreted as variations of the maximum sealing pressure P 1max , P 2max  of the first and second seals S 1 , S 2 . 
     First Embodiment 
     Referring to  FIGS. 3 a  and 3 b   , a patient interface  10  according to one embodiment of the invention includes a cushion  12  having a filler layer  14  provided on the cushion  12 . The filler layer  14  is adapted to be in contact with the patient&#39;s skin. The cushion  12  may be formed of, for example, silicone and the filler layer  14  may be formed of, for example, foam. The filler layer  14  may be, for example, adhesively attached to the cushion  12 , for example by glue. The filler layer  14  may also be mechanically connected to the frame of the mask as a skin that envelops the cushion. In that case, the filler layer  14  may be replaced, for example in a manner similar to replacing the foam over earphones. The filler layer  14  may be connected at the same location as the cushion, on the cushion itself, or at another point on the frame. The filler layer  14  may also be silicone foam injected over the silicone cushion  12  so that the cushion and the filler layer are a single object. The filler layer  14  serves to fill gaps between the cushion  12  and the patient&#39;s skin. The filler layer  14  also reduces, or eliminates, vibrations of the cushion  12  and reduces any leak flow by increasing the resistance of the seal formed by the cushion  12 . The filler layer  14  also diffuses any leak flow that may occur. Moreover, any leak flow passing through the filler layer  14  may inflate the filler layer  14  and permit the patient&#39;s skin to breathe. The filler layer  14  may be uniform in cross sectional shape and material, or the filler layer  14  may be made of differing materials in different areas  14   a - 14   d  and also differing shapes (as shown in  FIG. 3 b   ). The filler layer may be a closed loop or selected areas may be left empty. 
     Second Embodiment 
     As shown in  FIG. 4 , an interface  22  may include a seal  24  in contact with the patient&#39;s skin  20 . A diffuser  26  (e.g., of foam material) is provided outside the seal  24  of the interface  22  to increase the resistance to leak flow Q and diffuse any leak flow that may actually occur. The diffuser  26  may be connected to the seal  24  in a manner similar to the connection of the filler layer  14  to the cushion  12  of the first embodiment. However, unlike the first embodiment, in which only the filler layer  14  contact the patient&#39;s face, according to the second embodiment the seal  24  of the interface  22  and the diffuser  26  are provided in series and both contact the patient&#39;s face. Accordingly, in the second embodiment the “sealing” provided by the seal  24  and diffuser  26  is broader than the “sealing” provided by the first embodiment as the seal  24  and the diffuser increase the resistance to leak flow. It should be appreciated that the seal may provide very little, or no resistance, to leak flow while the diffuser  26  may be configured to limit the leak flow to small values. The diffuser  26  may be a porous material, for example a porous material that provides a high resistance to leak flow while providing compliance with the patient&#39;s face. The diffuser  26  may be mechanically connected to the interface  22  in a manner similar to the mechanical connection of the filler layer  14  to the cushion  12  discussed above with respect to the first embodiment. The diffuser  26  may also be silicone foam injected on the interface so that they are a single object. The diffuser  26  may also be attached to the interface  22  adhesively. Although the diffuser  26  is shown in  FIG. 4  as being provided on the exterior of the interface  22 , it should be appreciated that the diffuser may be provided in the interior of the interface  22  and diffuse any leak flow before it passes the seal  24 . Such a configuration may also prevent explosive leakage from the interface  22 . 
     Third Embodiment 
     Referring to  FIG. 5 , an interface  22  includes a primary seal  24  adapted to contact the patient&#39;s skin  20 . The primary seal  24  may be, for example, silicone. A secondary seal  32  is placed inside the interface  22  and may also be in contact with the patient&#39;s face. The secondary seal  32  may be, for example, foam. The space between the primary seal  24  and a secondary seal  32  includes secondary vents  30  which are provided in addition to primary vents  28 . A vent flow VF is vented through the primary vents  28 . The volume between the primary seal  24  and the secondary seal  32  is vented through secondary vents  30  to create a local low-pressure area near the primary seal  24 , i.e. P 2 &lt;P 1 . Any leak flow across the secondary seal  32  will be vented through the secondary vents  30 . The secondary vents  30  may be placed in an area of the patient interface where the vented leak flow Q will not disturb the patient. 
     Fourth Embodiment 
     Referring to  FIG. 6 , an air delivery hose or conduit  34  may be incorporated into a frame of the patient interface. The conduit  34  is connected to an inflatable cushion  36 . The inflatable cushion  36  may comprise a hollow gel seal. The inflatable cushion  36  is pressurized against the patient&#39;s skin  20  by pressure force and the force caused by the deflection of the air flow through vents  38  formed in the inflatable cushion  36  that deliver the breathable gas to the patient. The flow generator of the breathing apparatus supplies breathable gas via the hose or conduit  34  to the patient interface. The hose or conduit  34  may be connected to the patient interface by an elbow, for example a swivel elbow. The flow generator delivers the flow to the elbow at a pressure P 1 . Due to the resistance of the hose or conduit, and the elbow if provided, the pressure P 1  drops to a pressure P 2  which inflates the inflatable cushion  36 . The drop in pressure is in the hose or conduit, and optional elbow, is ΔP 1 =P 1 −P 2 . The pressure of the flow of breathable gas is further reduced by the resistance of the vents  38 , and the pressure drops to the therapy pressure P T . The pressure drop from the vents is ΔP 2 =P 2 −P T . Therefore, in order for the correct therapy pressure P T  to be delivered to the patient, the pressure P 1  supplied by the flow generator is P 1 =P T +ΔP 2 +ΔP 1 . 
     Fifth Embodiment 
     A patient interface according to another embodiment of the invention is shown in  FIGS. 7 a  and 7 b   . The patient interface  22  includes first and second seals  40 ,  42  which form a seal against the patient&#39;s skin  20 . A vacuum line  44  sucks any leak flow that may occur between the first and second seals  40  and  42  and deforms the seals  40  and  42 , and the skin between them, into the position shown in  FIG. 7 b   . The seals  40  and  42  may be formed, for example, as gel cushions. The vacuum may only be switched on, for example, when the second space is at a pressure higher than ambient. 
     Sixth Embodiment 
     According to another embodiment of the invention shown in  FIG. 8 , a leak cuff  46  may be provided over a seal  44  of a patient interface in the nasal bridge area of the patient&#39;s face. Any leak flow passing the seal  44  is directed by the leak cuff  46  around the nose bridge  45  of the patient and away from the patient&#39;s eyes  47  as shown by the arrows in  FIG. 8 , effectively redirecting the leak flow. It should be appreciated that the leak cuff  46  may be provided around the perimeter of the entire patient interface, or may be provided only in the nasal bridge region. It should also be appreciated that the leak cuff  46  may be configured to seal against the patient&#39; face. It should further be appreciated that the leak cuff  46  may be provided to a dual wall cushion, in which case the leak cuff  46  may take the form of a third wall. 
     Seventh Embodiment 
     A patient interface  10   a  according to another embodiment of the invention shown in  FIG. 9  includes a first seal  50  and a second seal  52 . The patient interface  10   a  also includes a convergent-divergent nozzle  54  in an elbow  64  attached to the patient interface  10   a  creating a Bernoulli effect. Any leak flow  58  that occurs between the first seal  50  and the second seal  52  is effectively re-circulated by the nozzle  54 . The re-circulated leak flow  60  is added to the flow  62  delivered by the flow generator to provide a supply  66  of breathable gas to the patient. 
     The pressure between the first seal  50  and the second seal  52  should be lower than the pressure in the patient interface  10   a,  but slightly higher than the ambient pressure in order to avoid loss of the leak flow  58  to the ambient. 
     Eighth Embodiment 
     Referring to  FIG. 10 , a patient interface may include a primary seal and secondary seal. The primary seal has a higher maximum sealing pressure P max  at a lower displacement of the patient interface with respect to the patient&#39;s face than the secondary seal. When the patient interface is displaced, the maximum sealing pressure of P max  of the primary seal decreases while the maximum sealing pressure P max  of the secondary seal increases. Such an arrangement may include a deformable patient interface frame, such as a mask frame, that automatically adjusts according to the load condition placed on the frame. After a certain amount of displacement, the secondary seal has a maximum sealing pressure P max  that is higher than the maximum sealing pressure P max  of the primary seal. As shown in  FIG. 10 , the maximum overall sealing pressure P max  of the combination of the primary seal and the secondary seal is higher than either the maximum sealing pressure of the primary seal or the secondary seal alone. 
     Ninth Embodiment 
     It is also possible to reduce the leak flow from the patient interface by considering other components of the breathing apparatus. As shown in  FIG. 11 , the patient interface  10   b  is connected to an air delivery conduit or hose  70 . The conduit  70  includes a localized area  72  having a high axial deformability that can compensate for the pull of the conduit  70  on the patient interface  10   b  (i.e. tube drag). The conduit  70  may also be a retractable tube, for example as disclosed in U.S. Applications 60/973,902, filed Sep. 20, 2007, 60/987,825, filed Nov. 14, 2007, and 61/031,407, filed Feb. 26, 2008, the entire contents of all three being incorporated herein by reference. 
     It should be appreciated that the sample embodiments disclosed herein may be used in various NIPPV therapies, including Continuous Positive Airway Pressure (CPAP), Variable Positive Airway Pressure (VPAP), and Bi-level Positive Airway Pressure (BiPAP). In these therapies, a pressurized flow of breathable gas, e.g. air, may be supplied to a patient&#39;s airways at a pressure of, for example, between 4 cm H 2 0 to 20 cm H 2 0. 
     While the invention has been described in connection with what are presently considered to be the most practical embodiments, it is to be understood that the invention is not to be limited to the disclosed embodiments, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the invention. Also, the various embodiments described above may be implemented in conjunction with other embodiments, e.g., aspects of one embodiment may be combined with aspects of another embodiment to realize yet other embodiments. Further, each independent feature or component of any given assembly may constitute an additional embodiment. Furthermore, each individual component of any given assembly, one or more portions of an individual component of any given assembly, and various combinations of components from one or more embodiments may include one or more ornamental design features. In addition, while the invention has particular application to patients who suffer from OSA, it is to be appreciated that patients who suffer from other illnesses (e.g., congestive heart failure, diabetes, morbid obesity, stroke, barriatric surgery, etc.) can derive benefit from the above teachings. Moreover, the above teachings have applicability with patients and non-patients alike in non-medical applications.