Patent Publication Number: US-9884160-B2

Title: Breathing assistance apparatus

Description:
INCORPORATION BY REFERENCE TO ANY PRIORITY APPLICATIONS 
     Any and all applications for which a foreign or domestic priority claim is identified in the Application Data Sheet as filed with the present application are hereby incorporated by reference and made a part of the present disclosure. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     This invention relates to patient interfaces particularly though not solely for use in delivering CPAP therapy to patients suffering from obstructive sleep apnoea (OSA). 
     Description of the Related Art 
     In the art of respiration devices, there are well known variety of respiratory masks which cover the nose and/or mouth of a human user in order to provide a continuous seal around the nasal and/or oral areas of the face such that gas may be provided at positive pressure within the mask for consumption by the user. The uses for such masks range from high altitude breathing (i.e. aviation applications) to mining and fire fighting applications, to various medical diagnostic and therapeutic applications. 
     One requisite of such respiratory masks has been that they provide an effective seal against the user&#39;s face to prevent leakage of the gas being supplied. Commonly, in prior mask configurations, a good mask-to-face seal has been attained in many instances only with considerable discomfort for the user. This problem is most crucial in those applications, especially medical applications, which require the user to wear such a mask continuously for hours or perhaps even days. In such situations, the user will not tolerate the mask for long durations and optimum therapeutic or diagnostic objectives thus will not be achieved, or will be achieved with great difficulty and considerable user discomfort. 
     U.S. Pat. Nos. 5,243,971 and 6,112,746 are examples of prior art attempts to improve the mask system. U.S. Pat. No. 5,570,689 and PCT publication No. WO 00/78384 are examples of attempts to improve the forehead rest. 
     Where such masks are used in respiratory therapy, in particular treatment of obstructive sleep apnea (OSA) using continuous positive airway pressure (CPAP) therapy, there is generally provided in the art a vent for washout of the bias flow or expired gases to the atmosphere. Such a vent may be provided for example, as part of the mask, or in the case of some respirators where a further conduit carries the expiratory gases, at the respirator. A further requisite of such masks is the washout of gas from the mask to ensure that carbon dioxide build up does not occur over the range of flow rates. In the typical flow rates in CPAP treatment, usually between 4 cm H 2 O to 20 cm H 2 O, prior art attempts at such vents have resulted in excessive noise causing irritation to the user and any bed partners. 
     In common with all attempts to improve the fit, sealing and user comfort is the need to avoid a concentrated flow of air at any portion of the respiratory tracts. In particular with oral masks or mouthpieces it is a disadvantage of prior art devices that the oral cavity may become overly dehydrated by use of the device, causing irritation and possible later complications. 
     Furthermore, a common complaint of a user of CPA therapy is pressure sores caused by the mask about the nose and face and in particular in the nasal bridge region of the user. 
     In this specification where reference has been made to patent specifications, other external documents, or other sources of information, this is generally for the purpose of providing a context for discussing the features of the invention. Unless specifically stated otherwise, reference to such external documents is not to be construed as an admission that such documents, or such sources of information, in any jurisdiction, are prior art, or form part of the common general knowledge in the art. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to attempt to provide a patient interface which goes some way to overcoming the abovementioned disadvantages in the prior art or which will at least provide the industry with a useful choice. 
     Accordingly in a first aspect the present invention consists in a mask assembly for use as part of an apparatus for supplying a flow of respiratory gases to a user comprising: 
     a mask body, said mask body including an inlet through which said flow of respiratory gases are provided to the interior of said mask body, the inlet adapted to in use be connected, to a gases conduit, 
     a mask seal assembly comprising a flexible seal and a rigid clip, 
     said seal having a first side and a second side, the first side of said seal being shaped to approximately match the contours of a user&#39;s face and in use substantially seal against a user&#39;s face, said second side adapted for attachment to said clip, 
     said clip being shaped to generally follow the contours of a user&#39;s face, and a rear periphery of said mask body also being correspondingly shaped to generally follow the contours of a user&#39;s face, 
     said clip providing a rigid interface extending substantially the full perimeter or periphery of the mask seal assembly for releasably attaching the mask seal assembly to the mask body, and 
     one of the clip or the mask body having at least one recess and the other one of the mask body or the clip having a series of bumps, interference between the bumps and the clip or the mask body during attachment of the clip to the mask body providing a positive snap type engagement of the clip to the mask body as the bumps locate in the at least one recess, and 
     one of the clip or the mask body having a lead in section providing a gradual deflection of the clip, or the mask body, or both, when attaching the clip to the mask body, the lead-in section extending substantially the full perimeter of the clip or the mask body. 
     Preferably the seal has a wall portion extending around the periphery of the seal assembly between the first and second sides, the wall being approximately or substantially constant in depth. 
     Preferably wherein the recesses are located immediately behind the lead-in section. 
     Preferably a cross section of the mask seal assembly at the clip has a width to height ratio of 1.5 to 2. 
     Preferably the clip is adapted to disengage the seal assembly from the mask body when squeezed at opposite perimeter portions at positions absent of a said bump. 
     Preferably the corresponding shape of the clip and the mask body provides for automatic correction of angular misalignment between the seal assembly and the mask body when fitting the seal assembly to the mask body. 
     Preferably the seal assembly attaches to the mask body in a sealed engagement, a first bearing surface of the seal bearing against: a corresponding second bearing surface of the mask body in a butting engagement. 
     Preferably the first bearing surface comprising a raised rim, in use the raised rim being compressed against the second bearing surface. 
     Preferably the clip has at least one wing portion, the wing portion providing a gripping flange to assist with removing the seal assembly from the mask body. 
     Preferably the lead-in section extends at least 50% of the full perimeter of the seal assembly clip or the mask body. 
     Preferably the mask assembly further comprises headgear for securing the mask assembly to the head of a user. 
     Preferably the mask assembly further comprises an inner cushion around the outer periphery of the mask body between the mask body and the first side of the sea). 
     The term “comprising” as used in this specification means “consisting at least in part of”. Related terms such as “comprise” and “comprised” are to be interpreted in the same manner. 
     To those skilled in the art to which the invention relates, many changes in construction and widely differing embodiments and applications of the invention will suggest themselves without departing from the scope of the invention as defined, in the appended claims. The disclosures and the descriptions herein are purely illustrative and are not intended to be in any sense limiting 
     The invention consists in the foregoing and also envisages constructions of which the following gives examples. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Preferred forms of the present invention will now be described with reference to the accompanying drawings. 
         FIG. 1  is a block diagram of a humidified continuous positive airway pressure (system) as might be used in conjunction with the sealing interface of the present invention. 
         FIG. 2  is an illustration of the nasal mask including a sealing interface in use according to the preferred embodiment of the present invention. 
         FIG. 3  shows a perspective view of a mask with a sealing interface that is a cushion. 
         FIG. 4  is a cutaway view of the mask showing the sealing interface cushion that has an inner sealing member and an outer sealing member. 
         FIG. 5  is a cutaway view of the periphery of the outer sealing member or membrane. 
         FIG. 6  is a cutaway view of the periphery of the mask body portion. 
         FIG. 7  shows a mask and sealing interface as used with a forehead rest on a patient. 
         FIG. 8  shows a cross section of a second preferred embodiment of the sealing interface. 
         FIG. 9  shows perspective view of an inner sealing member of the second preferred embodiment of the sealing interface. 
         FIG. 10  shows a cross section of a third preferred embodiment of the inner and outer sealing members of the present invention. 
         FIG. 11  shows a perspective view of the inner sealing member of the third preferred embodiment of the sealing interface. 
         FIG. 12  shows a plan view of the inner sealing member of the third preferred embodiment of the mask cushion. 
         FIG. 13  shows a cross section of a fourth preferred embodiment of the sealing interface of the present invention. 
         FIG. 14  shows a perspective view of the inner sealing member according to a fifth preferred embodiment of the sealing interface of the present invention. 
         FIG. 15  shows a cross section of a sixth preferred embodiment of the sealing interface of the present invention. 
         FIG. 16  shows a perspective view of the inner sealing member according to a seventh preferred embodiment of the sealing interface of the present invention. 
         FIG. 17  shows a perspective view of the inner sealing member according to an eighth preferred embodiment of the sealing interface of the present invention. 
         FIG. 18  shows a perspective view of the inner sealing member according to a ninth preferred embodiment of the sealing interface of the present invention. 
         FIG. 19  shows a perspective view of the inner sealing member according to a tenth preferred embodiment of the sealing interface of the present invention. 
         FIG. 20  shows a cross section of a further embodiment of the sealing interface of die present invention where the inner sealing foam member touches the outer sealing member at all times. 
         FIG. 21  is a side view of a nasal mask of the present invention where the outer sealing member is substantially thinner in width in the nasal bridge region than the rest of the outer sealing member. 
         FIG. 22  is a close-up view of detail A in  FIG. 21 . 
         FIG. 23  is a perspective view of the nasal mask of  FIG. 21 . 
         FIG. 24  is a cross-section of the outer sealing member of  FIG. 21 . 
         FIG. 25  is a front perspective view of a full face mask of the present invention, where the outer sealing member is substantially thinner in width in the nasal bridge region than the rest of the outer sealing member. 
         FIG. 26  is a back perspective view of a full face mask of  FIG. 25 . 
         FIG. 27  is a cross-section through BB of the full face mask of  FIG. 25 . 
         FIG. 28  is a perspective view of the outer sealing member of the full face mask of  FIG. 25  in isolation, where the thin nasal bridge region is particularly shown. 
         FIG. 29  is a cross-section through CC of the outer sealing member of  FIG. 28 . 
         FIG. 30  is a front view of the outer sealing member of  FIG. 28 . 
         FIG. 31  is a front view of a first alternative outer sealing member. 
         FIG. 32  is a front view of a second alternative outer sealing member. 
         FIG. 33  is a front view of a third alternative outer sealing member. 
         FIG. 34  is a perspective view of a preferred embodiment of a patient interface. 
         FIG. 35  is an exploded view of the patient interface of  FIG. 34 , the patient interface comprising headgear, a mask seal assembly, a mask cushion and a mask body. 
         FIG. 36 a    is a perspective view of the mask seal assembly of the patient interface of  FIG. 34  and  FIG. 35 , the mask seal assembly comprising a seal and a seal clip. 
         FIG. 36 b    is a perspective view of the seal clip of the mask seal assembly of  FIG. 36   a.    
         FIG. 37  is a perspective view showing the mask body and the mask seal assembly, with the mask seal assembly removed from the mask body. 
         FIG. 38  is a sectional view on line X-X of the patient interface of  FIG. 34 . 
         FIG. 39 a    is a part sectional view on line X-X showing a preferred form of the interface arrangement between the mask body and the mask seal assembly of the patient interface of  FIG. 34 . 
         FIG. 39 b    is a part sectional view showing a first alternative form of the interface arrangement between the mask body and the mask seal assembly. 
         FIG. 39 c    is a part sectional view showing a second alternative form of the interface arrangement between the mask body and the mask seal assembly. 
         FIG. 39 d    is a part sectional view showing a third alternative form of the interface arrangement between the mask body and the mask seal assembly. 
         FIG. 39 e    is a part sectional view showing a forth alternative form of the interface arrangement between the mask body and the mask seal assembly. 
         FIGS. 40 a  and 40 b    are perspective views of the mask cushion of the patient interface of  FIG. 34 . 
         FIGS. 41 a  to 41 c    illustrate alternative arrangements for providing vent paths between the mask seal assembly and the mask body. 
         FIG. 42  is a side view of the mask body and the mask seal assembly of  FIG. 34 . 
         FIG. 43  is a part sectional view from the side showing tire clip and seal arrangement of the mask seal assembly of  FIG. 34 . 
         FIG. 44 a    and  FIG. 44 b    are pail sectional views from tire side of preferred forms of connector for connecting a conduit, to the mask assembly. 
         FIGS. 45 a    and  45   aa  show a perspective view and a rear view of a first alternative form of connector for connecting a conduit to the mask assembly of  FIG. 34 , the connector incorporating radial baffles extending from the circumferential edge of the connector partway towards the centre. 
         FIGS. 45 b    and  45   bb  show a perspective view and a rear view of a second alternative form of connector for connecting a conduit to the mask assembly, the connector incorporating a single wave like baffle. 
         FIGS. 45 c    and  45   cc  show a perspective view and a rear view of a third alternative form of connector for connecting a conduit to the mask assembly, the connector incorporating a single circular baffle centrally located within the connector. 
         FIGS. 45 d    and  45   dd  show a cutaway side view and a rear view of a fourth alternative embodiment of connector for connecting a conduit to the mask assembly, the connector incorporating two radially aligned baffles. 
         FIG. 46  is a part sectional view of the mask seal assembly showing the seal in an un-pressurised state and a pressurised elastically stretched state. 
         FIGS. 47A to 47F  show a side view of various mask seal assemblies each comprising a circumferential thin portion. 
         FIG. 48  is a cross sectional view of a seal assembly comprising a circumferential thin portion. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The sealing interface of the present invention provides improvements in the delivery of CPAP therapy. In particular a patient interface is described which reduces the pressure of the mask on the patient&#39;s face and may be quieter for the patient to wear and reduces the side leakage as compared with the prior art. It will be appreciated that the patient interface as described in the preferred embodiment of the present invention can be used in respiratory care generally or with a ventilator, but will now be described below with reference to use in a humidified CPAP system. It will also be appreciated that the present invention can be applied to any form of patient interface including, but not limited to, nasal masks, oral masks and mouthpieces. 
     With reference to  FIG. 1  a humidified Continuous Positive Airway Pressure (CPAP) system is shown in which a patient  1  is receiving humidified and pressurised gases through a patient interface  2  connected to a humidified gases transportation pathway or inspiratory conduit  3 . It should be understood that delivery systems could also be VPAP (Variable Positive Airway Pressure) and BiPAP (Bi-level Positive Airway Pressure) or numerous other forms of respiratory therapy. Inspiratory conduit  3  is connected to the outlet  4  of a humidification chamber  5  that contains a volume of water  6 . Inspiratory conduit  3  may contain heating means or heater wires (not shown) which heat the walls of the conduit to reduce condensation of humidified gases within the conduit. Humidification chamber  6  is preferably formed from a plastics material and may have a highly heat conductive base (for example an aluminium base) which is in direct contact with a heater plate  7  of humidifier  8 . Humidifier  8  is provided with control means or electronic controller  9  which may comprise a microprocessor based controller executing computer software commands stored in associated memory. 
     Controller  9  receives input from sources such as user input means or dial  10  through which a user of the device may, for example, set a predetermined required value (preset value) of humidity or temperature of the gases supplied to patient  1 . The controller may also receive input from other sources: for example temperature and/or flow velocity sensors  11  and  12  through connector  13  and heater plate temperature sensor  14 . In response to the user set humidity or temperature value input via dial  10  and the other inputs, controller  9  determines when (or to what level) to energise heater plate  7  to heat the water  6  within humidification chamber  5 . As the volume of water  6  within humidification chamber  5  is heated, water vapour begins to fill the volume of the chamber above the water&#39;s surface and is passed out of the humidification chamber  5  outlet  4  with the flow of gases (for example air) provided from a gases supply means or blower  15  which enters the chamber through inlet  16 . Exhaled gases from the patient&#39;s mouth are passed directly to ambient surroundings in  FIG. 1 . 
     Blower  15  is provided with variable pressure regulating means or variable speed fan  21  which draws air or other gases through blower inlet  17 . The speed of variable speed fan  21  is controlled by electronic controller  18  (or alternatively the function of controller  18  could be carried out by controller  9 ) in response to inputs from controller  9  and a user set predetermined required value (preset value) of pressure or fan speed via dial  19 . 
     According to a first embodiment of the present invention the patient interface is shown in  FIG. 2  as a nasal mask. The mask includes a hollow body  102  with an inlet  103  connected to the inspiratory conduit  3 . The mask  2  is positioned around the nose of the patient  1  with the headgear  108  secured around the back of the head of the patient  1 . The restraining force from the headgear  108  on the hollow body  102  and the forehead rest  106  ensures enough compressive force on the mask cushion  104 , to provide an effective seal against the patient&#39;s face. Straps  120  may connect to the headgear  108  via connectors  122  to provide compressive force. 
     The hollow body  102  is constructed of a relatively inflexible material for example, polycarbonate plastic. Such a material would provide the requisite rigidity as well as being transparent and a relatively good insulator. The expiratory gases can be expelled through a valve (not shown) in the mask, a further expiratory conduit (not shown), or any other such method as is known in the art. 
     Mask Cushion 
     Referring now to  FIGS. 3 and 4  in particular, the mask cushion  1104  is provided around the periphery of the hollow body  1102  of the nasal mask to provide an effective seal onto the face of the patient to prevent leakage. The hollow body  1102  of the nasal mask has an inspiratory conduit  1103 . The mask cushion  1104  has an opening  1115 . The mask cushion  1104  is shaped to approximately follow the contours of a patient&#39;s face. The mask cushion  1104  will deform when pressure is applied by the headgear  2108  (see  FIG. 7 ) to adapt to the individual contours of any particular patient, in particular, there is an indented section  1150  intended to fit over the bridge of the patient&#39;s nose as well as an indented section  1152  to seal around the section beneath the nose and above the upper lip. As shown in  FIG. 7 , according to an embodiment the patient interface is shown as a nasal mask  1999 . The mask  1999  includes a hollow body  2102  with an inlet  2103  connected to the inspiratory conduit  2003 . The mask  1999  is positioned around the nose of the patient  2001  with the headgear  2108  secured around the back of the head of the patient  2001 . The restraining force from the headgear  2108  on the hollow body  2102  and the forehead rest  2106  ensures enough compressive force on the mask cushion  2104 , to provide an effective seal against the patient&#39;s face. Straps  2120  may connect to the headgear  2108  via connectors  2122  to provide compressive force. The hollow body  2102  is constructed of a relatively inflexible material for example, polycarbonate plastic. Such a material would provide the requisite rigidity as well as being transparent and a relatively good insulator. The expiratory gases can be expelled through a valve (not shown) in the mask, a further expiratory conduit (not shown), or any other such method as is known in the art. 
     In  FIG. 4  we see that the mask cushion  1104  is composed of an inner sealing member that is an inner cushion  1110  covered by an outer sealing sheath or member  1112 . The inner cushion  1110  is constructed of a resilient material for example polyurethane foam, to distribute the pressure evenly along the sea) around the patient&#39;s face. In other forms the inner cushion  1110  may be formed of other appropriate material, such as silicone or other composite materials. The inner cushion  1110  is located around the outer periphery  1114  of the open face  1116  of the hollow body  1102 . Similarly the outer sheath  1112  may be commonly attached at its base  1113  to the periphery  1114  and loosely covers over the top of the inner cushion  1110 . The hollow body  1102  may have a series of holes  1160 . 
     In the preferred embodiment of the present invention as shown in  FIGS. 4 to 6  the bottom of the inner cushion  1110  fits into a generally triangular cavity  1154  in the hollow body  1102 . The cavity  1154  is formed from a flange  1156  running mid-way around the interior of the hollow body. 
     The outer sheath  1112  fits in place over the cushion  1110 , holding it in place. The sheath  1112  is secured by a snap-fit to the periphery  1114  of the hollow body. In  FIGS. 5 to 6  the periphery  1114  is shown including an outer bead  1158 . The sheath  1112  includes a matching bead  1159 , whereby once stretched around the periphery; the two beads engage to hold the sheath in place. 
     A second preferred embodiment to the mask cushion is depicted in  FIGS. 9 and 10 . In the second embodiment the inner cushion  2000  includes a raised bridge  2002  in the nasal bridge region. The raised bridge  2002  can also be described as a cut out section made in the cushion. Also, the notch in the contacting portion (between the inner cushion and outer sheath) is less pronounced than, proceeding embodiments. However, as the raised bridge  2002  is unsupported it is much more flexible and results in less pressure on the nasal bridge of the patient. The outer sheath  2004  contacts the inner cushion  2000  throughout the raised bridge  2002 . The peaks  2005 ,  2007 ,  2009 ,  2011  in the inner cushion  2000  between each of the indented sections  2006 ,  2008  and the raised bridge  2002  contact the outer sheath  2004  and when in use the sheath  2004  contacts the facial contours of the patient in the regions of these peaks. 
     Referring particularly to  FIG. 10  the inner cushion  2000  includes a cheek contour  2006  to follow the cartilage extending from the middle of the nose, and a contoured lip scaling portion  2008  to seal between the base of the nose and the upper lip. 
     Referring now to  FIGS. 11 and 12  a third preferred embodiment of the mask cushion is depicted, in this case, the inner cushion  2010  tapers down  2012  towards the nasal bridge region  2014 . For a short portion either side of the nasal bridge region  2014  the inner cushion  2010  is absent, forming a semi annular form in plan view as seen in  FIG. 12 . 
     Referring to  FIG. 13 , a fourth preferred embodiment of the mask cushion is depicted. The outer sheath  2020  is adapted to contact the inner cushion  2022  completely about the inner cushion, including in the nasal bridge region  2024  and the check contour  2026 .  FIG. 18  shows the inner cushion  2022  where the upper edge  2050  of the cushion docs not have any contours and thus will contact the outer sheath all around the edge of the inner cushion.  FIG. 20  shows a sealing interface similar to that of  FIG. 13  where the inner cushion also follows and touches the outer sheath all around its edge. 
       FIG. 14  illustrates a fifth preferred embodiment of the inner cushion  2030 . In the nasal bridge region  2032  the inner cushion includes a lower bridge  2034  and upper bridge  2036 . Due to the gap the upper bridge  2036  is unsupported to reduce pressure on the patient&#39;s nasal bridge, but the lower rim  2034  of the inner cushion  2030  is continuous, which aids installation. The inner cushion  2030  may include the portion  2038  connecting ends of the nasal bridge region  2032 . 
     In yet other forms of the sealing interface of the present invention the inner cushion may be provided with other contours on the front side of the inner cushion or cut outs on the back side of the inner cushion, so that in the areas where there are regions cutout of die back side of the cushion the cushion is more flexible. In particular, cut outs in the nasal bridge, cheek and upper lip regions provide the patient with a mask cushion that is more flexible and thus more comfortable.  FIG. 15  shows an embodiment of an inner cushion  2024  that has a curved cut out or dead space  2044  in the cheek region.  FIGS. 16 and 17  show embodiments of an inner cushion  2000  that has a cut out or dead space  2046  in the area where the patient&#39;s upper lip rests in the foam. 
     A final form of a sealing interface is shown in  FIG. 19 , here the inner foam member has an annular shape but has a thin bridge or membrane  2048  that, extends across and provides flexibility to the nasal bridge region. 
     Referring now to  FIG. 21 , to improve the comfort to the patient the nasal mask  200  includes a thin bridge section  203  in the nasal bridge region of the outer sealing member  201 , that is, that part extending over the bridge of a patient&#39;s nose. 
     Similar to that described above the outer sealing member or outer sheath  201  fits in place over the inner sealing member (inner cushion)  202 , holding it in place. The outer sheath  201  is secured by a snap-fit to the periphery  205  of the mask hollow body  204 . The periphery  205  is shown including an outer bead  206 . The outer sheath  201  includes a matching bead  207 , whereby once stretched around the periphery  205 ; the two beads engage to hold the outer sheath  201  in place. 
     The outer sealing member or sheath  201  is shown in more detail in  FIGS. 22 to 24 . The outer sheath  201  has formed in it a region  203  that is thinner than the remainder of the cross-sectional thickness  210  of the sheath. In particular, the side walls  211 , 212  (see  FIG. 23 ) must be thicker than in the region  203  so as to provide structural support for the sheath and ensure the sheath does not collapse in use, or when being assembled with the mask body. As an example only, for a nasal mask, if the thin bridge region was 0.2 mm thick, the side walls may be 0.3 to 0.6 mm thick. Therefore, the thin bridge region  203  is approximately half the thickness of the rest of the sheath  201  and so can provide a significant effect, such that the pressure to the patient&#39;s nose in the nasal bridge region is reduced compared to when a sheath does not have any reduced thickness section. Furthermore, a thin bridge region  203  in the outer sheath  201  allows for different sized patient&#39;s to comfortably use the mask and outer sheath of the present invention. 
     In use, when a force is placed against the outer sheath  201  the thin bridge region  203  will collapse more than the rest of the outer sheath  201 . Therefore, this section  203  is more flexible and allows for added patient comfort. 
     Referring particularly to  FIG. 22 , the thin bridge region  203  on the outer sheath  201  preferably does not extend completely to the outer edge  214  of the outer sheath  201 , but grows thicker in thickness. This is because the outer edges of the outer sheath  201  when thicker are less prone to tearing. 
     In particular, in  FIG. 23 , that outer sheath  201  is substantially heart shaped and the thin bridge region  203  is shown to extend more than halfway down the sides of the sheath from the apex  213 . As shown in  FIG. 23 , the thin bridge region  203  does not extend fully down the edges  214  and  212  of the outer sheath  201 . This is because support is required in the edges of the sheath  201 , to provide structural stability of the sheath. 
     In other forms of the nasal mask of the present invention, the thin bridge region may not extend as far as that shown in  FIG. 23 , but be restricted merely to the nasal bridge region (similar in manner to the mask cushion shown in  FIG. 30 , in relation to a full face mask). 
     Full Face Mask 
     A further embodiment of the present invention is shown in  FIGS. 25 to 31  where the patient interface is a full face mask similar to that described in co-pending New Zealand patent application number 528029. The full face mask  300  includes a hollow body  302  and outer sealing member or mask cushion  301 . The cushion  301  is attached to the body  302  in a similar manner as described with reference to the nasal mask, but here no inner cushion is provided. Thus, the cushion  303  periphery extends over a flange on the mask body. 
     The hollow body  302  has an integrally formed recess (not shown) in which an insert  304  is fitted into. The recess and insert  304  each have complimentary circular apertures (generally indicated as  305 ) that form an inspiratory inlet when the insert  304  is placed in the recess. The inlet  304  is capable of being connected to the tubing that forms the inspiratory conduit  3  (as shown on  FIG. 1 ). Gases, supplied to the inspiratory conduit  3  from the CPAP device and humidifier, enter the mask through the apertures  305  and the patient is able to breathe these gases. The mask  300  is positioned around the nose and mouth of the patient and headgear (not shown) may be secured around the back of the head of the patient to assist in the maintaining of the mask on tire patient&#39;s face. The restraining force from the headgear on the hollow body  302  ensures enough compressive force on the mask cushion  301  to provide an effective seal against the patient&#39;s face. 
     The hollow body  302  and insert  304  are injection moulded in a relatively inflexible material, for example, polycarbonate plastic. Such a material would provide the requisite rigidity for the mask as well as being transparent and a relatively good insulator. The mask cushion  301  is preferably made of a soft plastics material, such as silicone, KRATON™ or similar materials. 
     The cushion  301  of the mask  300  includes a thin bridge section  305  in the nasal bridge region of the cushion  301  that is, that part extending over the bridge of a patient&#39;s nose. As an example, in the region of the thin bridge section  305  the walls of the cushion may be 0.2 to 0.3 mm thick and the rest of die cushion may have a thickness of 1 mm. In particular, the side walls need to be thicker to provide support in the cushion, so that it does not collapse during use or assembly with the mask body. In  FIG. 29 , this is particularly illustrated, as the section  305  in the nasal bridge region is shown as being much thinner than the rest of the cushion (in particular the bottom side wall region  306 , which are much thicker in cross-section). 
     Note must be made that the inner flange  307  of the cushion  301  that rests against the patient&#39;s face is also thinner in section than the side walls of the cushion  301  to provide flexibility to the cushion and thus comfort to the patient. In use the inner flange  307  is the area of the cushion that seals against the patient&#39;s face and the side walls of the cushion provide stability to the cushion  301 . 
     In use, when a force is placed against the cushion  301  the thin bridge section  305  will collapse more than the rest of the cushion  301 . Therefore, this section  305  is more flexible and allows for added patient comfort. 
     Other forms of the cushion that may be used with the full face mask of the present invention are shown in  FIGS. 31 to 33  and each show alternative thin sections that may be provided for patient comfort, and to allow for fitting to different sized patients. 
     Referring first to  FIG. 31 , cushion  310  may have a thin bridge section  311  that is narrower than that shown in  FIG. 30 . 
     In  FIG. 32  the cushion  312  has a thin bridge section  313  only near the outer edge  317  of the cushion  312 . This cushion  312  also has a thin section  314  in the region of the cushion that would rest against the patient&#39;s chin. 
     Finally, in  FIG. 33 , the thin section  316  of the cushion  315  may extend down the sides  318 ,  319  of the cushion. 
     Forehead Rest 
     The nasal mask and/or full face mask of the present invention is preferably provided with a fixed forehead rest ( 208 , as shown in relation to the nasal mask in  FIG. 21 and 23 or 303 , as shown in relation to the full face mask in  FIG. 25 ). The forehead rest is not required to be adjustable as the cut out in the nasal bridge region of the inner foam (for the nasal mask) and the thin section in the outer sheath (for both the nasal and full face masks) provides enough flexibility of the mask cushion to provide fitting to a number of different patients. 
     Improved Patient Interface 
     A further preferred embodiment of the present invention is patient interface  50  described with reference to  FIG. 34  and  FIG. 35 . The patient interface  50  includes a mask assembly  402  and headgear  421 . 
     Headgear 
     Headgear  421  is worn by the user in use, and holds the mask assembly  402  in the required position on the user&#39;s face. The headgear  421  in the preferred form is comprised of headgear straps  435 ,  436 ,  437 ,  438 , and an elongate glider member  434 . The elongate glider member extends across the front of the mask assembly  402  and attaches to the mask body  430  of the mask assembly  402  via at least one clip type fitting  433 . The elongate member  434  may slide, or glide, within the clip type fitting  433  so that the mask assembly  402  may move laterally with respect to the head gear. This arrangement for attaching the headgear to the mask assembly is the preferred arrangement. Other arrangements may also be used, such as a fixed or static arrangement. 
     Each end of the elongate glider member may include a hook  432  to which each end of headgear strap  435  may releasably attach. Alternatively, headgear strap  435  may attach directly to the mask body  430 . 
     In the preferred form, the mask assembly  402  includes a forehead support  431 . The forehead support, is attached to the mask body  430  by a vertical support member  429 , the forehead, support and vertical support member together forming a T shape. The forehead support  431 , vertical support member  429  and mask body  430  may be integrally formed as a single piece. 
     Alternatively, the forehead support may be adjustable in a vertical direction, or may be pivotably attached to the mask body  430 . 
     One end of headgear strap  436  may attach to a first end of the forehead support, and the opposite end of headgear strap  436  may attach to a second end of the forehead support  431 . The forehead support may include at least one support pad or cushion  428 . In use, the forehead support locates against the user&#39;s forehead and provides stability to the nasal interface  50  when fitted, to the user. 
     Headgear straps  437  and  438  extend substantially vertically between headgear straps  435  and  436 . Headgear straps  437  and  438  provide support to straps  435  and  436 , positioning straps  435  and  436  a set distance apart around the user&#39;s head. 
     The headgear straps are preferably made from a laminated sheet of open cell foam sandwiched between two sheets of textile fabric. 
     It should be noted that many equivalent forms of head gear known in the art may be suitable for use with the mask assembly  402 . What has been described above is the preferred farm. 
     Mask Body 
     The mask assembly  402  of  FIGS. 34 and 35  comprises a mask body  430  and a mask seal assembly  440 . 
     The mask body  430  provides the overall structural support for the mask assembly, and provides at least one clip type fitting for attaching the mask assembly  402  to the headgear  421 . 
     A rear side of the mask body  30  interfaces to the seal assembly  440 , the seal assembly  440  providing a sealing interface against a user&#39;s face in use. The rear side of the mask body  430  is the side that faces towards a user, when the user has the mask assembly  402  in place on their face. The mask body  430  has an inlet for receiving a flow of respiratory gases. The mask body forms an internal cavity to which respiratory gases are supplied via the inlet from the CPAP system. The inlet comprises a tubular projection  422  extending from a front side  471  of the mask body  430 . The front side  471  of the mask body  430  is the side that faces away from a user, when the user has the mask assembly  402  in place on their face. 
     Connector 
     A first end of connector  423  connects to the mask body tubular projection  422 . The interface between the tubular projection  422  and the connector  423  preferably allows the connector  423  to swivel with respect to the mask body  430 . 
     Alternatively, as shown in  FIGS. 44 a  and 44 b   , the inlet may comprise a semi-tubular projection  480  extending from the front side  471  of the mask body. The semi-tubular projection forms a socket for receiving a correspondingly shaped first end of the connector  423 . In use, the first end of the connector and the semi-tubular projection form a ball joint allowing the connector  423  to swivel and pivot within the socket, relative to the mask body  430 . In alternative embodiments the mask body  430  may not include a projection, and the inner surface of the mask body  430  may be curved to form a socket for receiving the connector. In other alternative forms, other types of connection may be utilised between the mask body and the connector, such as a flexible piece of silicone, or other appropriate connection mechanism. 
     The connector  423  is preferably an elbow connector having a first leg, a bend and a second leg. The bend is preferably a substantially 90 degree bend. 
     A second end of the connector connects to the inspiratory conduit  3 , either directly to the conduit  3 , or via a second connector  424 . The interface between the elbow connector  423  and the conduit  3  or the second connector  424  preferably allows the conduit  3  to swivel with respect to the connector  423 . 
     Alternatively, the interface between the second end of the connector and the conduit  3  may comprise a ball joint that allows the second end of the connector to swivel and pivot relative to the conduit, as shown in  FIG. 44A . 
     Preferably the connection between the mask body  430  and the conduit  3  can be flexed or rotated to allow for the conduit to be moved without causing the dislodgement of the mask assembly  402  from the user&#39;s face. This is a preferred feature, but is not essential. 
     As best shown in  FIG. 35 , the preferred form of elbow connector  423  is a substantially right angle connector with the tubular inlet projection  422  aligned substantially perpendicular to the front of the mask body  430 . Other alternative arrangements may be incorporated in the mask assembly of the present invention. For example, the connector may be a straight connector, with any necessary bend accommodated by the conduit  3 . Alternatively, the tubular inlet projection may extend from the front of the mask body at an angle, for example angling downwards, with the connector having a corresponding obtuse angle. 
     Preferably the connector  423  may be easily removed from the mask body by pulling the connector  423  away from the mask body  430 . 
     Reducing Diameter Connector 
     As shown in  FIG. 35 , in the preferred form, the first end  4100  of the elbow connector  423 , interfacing with the mask body  430 , is smaller in diameter than the second end  4101  of the elbow connector. Preferably the diameter of the connector  423  reduces around the length of the bend in the connector  423 , from the full diameter at the second or outer end, to the reduced diameter at the first or inner end. As an example, the diameter of the inspiratory conduit commonly used in the art is approximately 25 mm. Prior art masks continue this full diameter through to the mask body interface. In the preferred form, the diameter of the connector  423  at the mask body interface is reduced to approximately 20 mm. 
     It is desirable to have a mask assembly that is as small and lightweight as possible, while at the same time providing an effective seal against a user&#39;s face. The reducing diameter of the connector  423  helps to make the mask assembly lightweight and small. The reducing diameter of the connector  423  helps to visually give the mask assembly a small, compact look. 
     One problem with a connector  423  having a reducing diameter connector is that air flow through the connector can become unacceptably noisy. Noise is created as the air flow passes through the reducing cross section of the connector. It is thought that this noise is created by an increase in the speed and turbulence of the flow of inspiratory gases through the reduced cross section portion  4102  of the connector  423 . The additional noise level is clearly undesirable as it can disturb the user&#39;s sleep, or the sleep of a user&#39;s partner. 
     To overcome the problem of increased noise levels, the connector  423  of the preferred embodiment includes at least one baffle  4103  located in the reduced cross section portion of connector  423 . 
       FIGS. 45 a    and  45   aa  show a first alternative form of the connector  423 , including six equally spaced baffles  4103 , each baffle extending from a first end  4100  of the reduced cross section portion  4102  of connector  423  to a second end  4104  of the reduced cross section portion of connector  423 . The introduction of the baffles significantly reduces the noise create by the reduced cross section portion. 
     A downside to introducing the baffles is a higher pressure drop through the connector  423 . It has been determined by the inventors following extensive research that a significant reduction in noise level is achieved by incorporating two baffles only, the baffles located at the third and fifth positions when considering six equally spaced positions spaced from top-dead-centre around the circumference of the reduced cross section portion of connector  423 , top-dead-centre being position  1 , with the second leg of the elbow at the downwards fourth, or 6 o&#39;clock, position. This arrangement is shown as a fourth alternative embodiment in  FIGS. 45 d    and  45   dd.    
     The noise reduction achieved by incorporation of two baffles only in the positions described is similar to the noise reduction achieved with incorporation of all six baffles. The introduction of two baffles in the third and fifth positions results in a significant reduction in noise levels, a similar result to the introduction of six baffles as shown in  FIGS. 45 a    and  45   aa . However, the pressure drop in the flow of gases through the connector  423  due to the incorporation of two baffles is lower than the pressure drop with six baffles. The most preferred form of baffle arrangement is therefore to include two baffles, located at the positions described, resulting in an acceptable compromise between acceptable noise levels and acceptable resistance to flow through the connector  423 . The fourth alternative embodiment, which shows the most preferred form of baffle arrangement, is shown in  FIGS. 45 d    and  45   dd . The baffles are preferably aligned radially within the reduced cross section portion of connector  423 . 
     In the preferred embodiment the baffles connect to the circumferential wall  4105  of connector  423 . The baffles extend along the wall  4105  substantially parallel to a longitudinal axis of the reduced portion  4102 . Preferably the baffles extend from the second end  4104  of the reduced diameter portion to the first end  4100  of the reduced portion. Alternatively, the baffles may extend part way along the reduced diameter portion. Preferably the baffles extend along the full length of the reduced diameter portion  4102  and connect along the wall  4105 , along the full length of the baffle except for an end portion  4107  near the first end  4100  of the connector  423 , the end portion  4107  of each baffle  4103  being detached from the side wall  4105 . The end portion  4307  of each baffle  4103  is not connected to the wall  4105  of the connector  423  so that additional strength provided by the baffles is not applied to the connector wall at the first end  4100 . This allows the wall  4105  at the first, end  4100  to deflect more easily when connecting connector  423  to the mask body  430 . 
     The baffles are around 1.5 mm thick and around 3 mm in radial height from the side wall  4105 . The thickness of the baffle is not overly important for achieving a reduction in noise level. The thickness dimension is chosen to allow ease of manufacturing. The connector  423  is typically manufactured by plastic injection moulding. Other injection moulding techniques may be incorporated for ease of manufacture, such as (halting the internal bore of the connector and drafting the baffles. Preferably the sides  4106  of the baffles  4103  have a draft of around 0.5″. The edge  4107  of the baffles  4103  have the same draft as the internal diameter of the reduced diameter portion  4102 , that is, a draft of around 1° to 1.5°. 
     Further research found that the radial height of the baffles had a significant effect on the reduction in noise levels. A significant reduction in noise level was obtained with a baffle radial height of 3 mm. There was a large improvement in noise reduction by increasing the radial height from 2 mm to 3 mm. However, the improvement achieved by increasing the radial height from 3 mm to 4 mm was not as significant. 
     In an alternative embodiment the baffles  4103  may be connected to form a continuous bridge across the cross section of the reduced diameter portion  4102 . However, for performance and ease of manufacture this is not a preferred embodiment. 
     Alternative baffle arrangements have also been found to be useful in reducing noise levels of gases flow through connector  423 .  FIGS. 45 b    and  45   bb  show a single baffle that extends across the reduced cross sectional area of the connector, the baffle being curved to extend towards the side nearest the elbow bend of connector  423 , that is, the side opposite top-dead-centre with the second leg in the downward 6 o&#39;clock position.  FIGS. 45 c    and  45   cc  show a single circular baffle located centrally within the reduced cross section portion of connector  423 , the circular baffle being supported by extensions at the six and three o′clock positions connecting between the outer wall of the single circular baffle and the inner wall of the connector. However, based on testing carried out by the inventors, these alternative embodiments are not the most preferred forms. 
     The use of baffles may also be helpful in reducing noise levels in an elbow connector with equal diameter legs, as turbulence in the gases flow is caused by flow around the bend of the elbow. 
     Alternatively, the use of baffles may also be helpful in reducing noise levels caused by a gases flow through a reducing diameter connector that has a straight through bore. 
     Mask Seal Assembly and Mask Seat Assembly to Mask Body Interface 
     Preferred and alternative forms of the mask body  430  and a mask seal assembly  440  shall now be described with reference to  FIG. 36-43 . 
     In the preferred form, the seal assembly  440  comprises a flexible seal  443  attached to a relatively rigid plastic clip  442 , as shown in  FIG. 36 a   . Preferably the flexible seal  443  is permanently attached to the plastic clip  442  so that the seal assembly  440  forms a single, item of the mask assembly  402 . 
     In the preferred form, the seal  443  is over-moulded to the plastic clip  442 . The plastic clip has a series of holes  446  around its perimeter. During manufacture, over moulding of the seal to the clip causes the seal material to flow through the series of holes  446 . During manufacture, the seal material is cured. Once cured, the seal  443  is mechanically linked to the plastic clip  442  via holes  446 , providing a mechanical joint between the clip and the seal. In the preferred embodiment, the holes  446  are located through a raised ridge  445  running around the inside perimeter of the clip. Preferably the raised ridge  445  and holes  446  are located on a inside surface of the clip, so that the mechanical bond is located on the inside of the clip, with the joint between the clip  442  and the seal  443  visible as a simple butt joint on the outside surface of the seal assembly  440 . 
     In alternative embodiments, the raised ridge  445  may be located on the outside perimeter of the clip, as shown in  FIGS. 39 c    and  39   d.    
     Alternatively, the seal  443  may be chemically bonded to the plastic clip. Chemical bonding may be used in combination with the mechanical bond described above. 
     Alternatively, the seal  443  could be glued to the plastic clip  442  with an appropriate adhesive, or the seal could be mechanically fixed to the clip. For example the seal could be sandwiched between the clip and a flange, with screws or other mechanical fixings securing clip and the flange together, with the seal sandwiched in between. This type of mechanical fixing could be permanent, or the fixings, such as screws, may allow the seal to be dismantled from the plastic clip. 
     Alternatively, the seal  443  could be assembled to the clip  442  in a press fit arrangement. The press fit may allow the seal  443  to be attached to and detached from the seal clip  442  many times. Alternatively, the press fit may be a permanent connection of the seal  443  to the clip  442 . 
     The clip  442  forms a rigid perimeter for the seal assembly  440 , the clip  442  being rigid relative to the seal  443 . The clip provides a rigid interface extending the full perimeter of the seal assembly or at least substantially the full perimeter of the seal assembly. 
     The interface between the rigid clip  442  and the rigid mask body  430  provides a positive engagement between the seal assembly  440  and the mask body  430 . This positive engagement provides an improvement over prior art masks that have a flexible seal interfacing directly to a mask body. The face seal assembly of the present invention may be easily and quickly assembled and disassembled to and from the mask body in a single engagement action. A flexible seal to mask body interface requires a comparatively more difficult seal to body engagement, as discrete portions of the seal must be fitted one at a time to the mask. 
     Preferably the seal assembly clip  442  and mask body  430  are made from polycarbonate, nylon, acetyl or other similar rigid plastic. 
     Alternatively, the seal assembly clip  442  and mask body  430  could be made from a semi-rigid material such as a thermoplastic elastomer, silicone rubber or urethane, or other similar semi-rigid material. Preferably the semi-rigid material has a Shore-A hardness of 60 or higher. 
     The clip  442  is shaped to match the shape of the back perimeter region  452  of the mask body  430 . The clip  442  may only be attached to the mask body in a single orientation. It is therefore not possible to attach the seal assembly  440  to the mask body  430  incorrectly. 
     The clip  442  attaches to the mask body in a ‘clip’ or ‘snap’ type engagement. A series of bumps  448 , or raised portions, on the mask body  430  interact with corresponding recesses  447  on the clip  442 , to hold the clip  442  in place on the body  430 . For example, for a mask that has a substantially equilateral perimeter with three sides, three recesses  447  may be located on the inside surface of the clip, the recesses being spaced apart, one recess being located on each side of the equilateral perimeter. The mask body, being correspondingly shaped to match the seal assembly clip, has three corresponding bumps  448 . As the clip  442  attaches to the mask body, interference between the clip and each mask body bump  448  causes the clip or the mask body, or both, to deflect to a deflected condition until each bump  448  reaches a corresponding recess  447 , Once the clip has been fully engaged with the body, each bump  448  locates within a corresponding recess  447 . And the clip or body, or both un-deflect from the deflected condition to an un-deflected or partially deflected condition, the parts being clipped or snapped together in a fully engaged position. Preferably the clip or the mask body or both remain in a slightly deflected condition when fully engaged together. 
     The recesses  447  may be formed by having a second series of bumps on the clip, each recess effectively created, by a rear shoulder of a bump. In this arrangement, interference between bumps on the clip and bumps on the mask body occurs until the clip bumps and the mask body bumps pass to sit adjacent one other in an engaged position 
     As best shown in  FIGS. 39 a  and 39 d   , the clip  442  preferably has a relatively long lead in, or ramped profile  449 , leading to the clip recess  447 . This lead in section preferably extends the full inside perimeter length or substantially the full inside perimeter length of the clip  442 . Preferably the lead-in section extends at least 50% of the full perimeter length of the clip. 
     Preferably each recess  447  is located immediately behind the lead-in section. The lead-in section assists with the attachment of the clip to the mask body. The clip  442  or mask body  430 , or both, are gradually deflected over the length of the lead-in section until the apex  475  of the lead-in section and each mask body bump  448  pass each other. Once the bumps  448  have passed over the lead-in section, the bumps  448  locate within each corresponding recess  447 , such that there is little or no interference between the two parts  430  and  442 . The two parts un-deflect in a relatively sudden snap action compared to the gradual deflection caused by the lead, in section  449  during engagement. This arrangement provides a positive, single engagement action. The positive single engagement action provides the user with assurance that the seal assembly has been correctly fitted to the mask body. The clipping arrangement preferably generates a clipping sound as the bumps  448  located into the recesses  447 . The clipping sound provides reassurance to the user that the clip has been correctly fitted to the mask body. The seal assembly  440  may be attached to and detached from the mask body  430  many times. 
     Alternatively, the lead in section, or ramp, described above may be provided on the mask body, as shown in the alternative embodiments of  FIGS. 39 b    and  39   c.    
     The lead in or ramped section  449  has a length to height ratio of approximately 3 to 7. In the preferred embodiment the lead in section has a length to height ratio of around 5. That is, for a ramp length of around 5 mm, the ramp height is around 1 mm. The lead in section ratio is best identified in  FIG. 43 , where the ramp length B is around five times the ramp height A. 
     The ramp section results in a seal clip cross section with a relatively high width to height ratio. The cross section of the preferred form of the seal clip has a width to height ratio of around 2. Once the seat  443  is attached to the clip  442 , the cross section of the seal assembly  440  at the seal clip has a width to height ratio of around 1.5-2, with the shorter dimension transverse to the direction in which the clip is engaged to the mask body. Preferably this ratio is around 1.8. 
     In the preferred embodiment of  FIG. 39 , and in die alternative embodiments of  FIGS. 39 b  and 39 d   , the clip  442  interfaces with the mask body such that the clip engages to an outwardly facing surface of the mask body. However, in the alternative embodiment of  FIG. 39 c   , the clip  442  interfaces to an internal or inwardly facing surface of the mask body. 
     A series of bumps  448  and recesses  447  around the perimeter of the mask body and clip have been described above. The bumps and recesses are located so that the seal assembly may be disengaged from the mask body by squeezing the sides or opposite perimeter portions of the clip, to deflect the clip and disengage the bumps  448  from the recesses  447 . To disengage the clip from the mask body, opposite perimeter portions of the clip are squeezed at positions where bumps  448  are absent, allowing the clip to deflect, to ‘pop’ the bumps out of the corresponding recesses. Given the ratio of the seal assembly cross section at the clip, as described above, the clip is relatively thin transverse to the direction in which the clip is engaged to the mask body. The thin clip is relatively easy to deflect by squeezing the opposite perimeter portions in a direction transverse to the direction in which the clip engages to the mask body, to easily deflect the clip from the mask body. 
     Alternatively, a continuous bump extending fully around the mask perimeter may be utilised to provide the snap interface between the seal assembly  440  and the mask body  430 . In this configuration, the bump may not have a constant height all the way around the mask perimeter. Having a continuous bump with different heights may allow the clip to be disengaged front the mask body by squeezing the sides or opposite perimeter portions of the clip, to deflect the apex  475  of the lead in section  449  of the clip  442  past a corresponding higher portion of the continuous bump. 
     Alternatively the clip  442  may have a continuous recess passing around the full perimeter or substantially the full perimeter of the clip, the recess being located immediately behind the lead-in section  449 , the mask body bump  448  passing over the lead in section before clipping into a portion of the continuous recess. 
     In alternative embodiments such as the embodiments shown in  FIGS. 39 b  and 39 c   , the recesses  447  may be provided in the mask body  430 , and the corresponding bumps may be formed on the mask clip  442 . 
     The face seal assembly  440  may include at least one wing portion  444  to assist a user to disengage the face seal assembly from the mask body. The wing portions  444  provide a gripping flange to pull the clip  442  away from the mask body  430 . 
     In a further alternative embodiment, the clip may be clipped to the mask body in a permanent engagement. With reference to  FIG. 39 e   , the mask body  430  has a series of protrusions  481 . Each protrusion has a ramped surface  482  and an abutment surface  483 . For each body protrusion  481 , the mask clip  442  has a corresponding protrusion  484 , each mask clip protrusion having a ramp surface  485  and an abutment surface  486 . Alternatively, a single continuous protrusion  481  may pass around the perimeter of the mask, with a corresponding continuous protrusion  484  passing around the perimeter of the clip. During an assembly process, the seal assembly clip  442  is interfaced to the mask body in a pressing operation, the mask body and mask clip are pressed together. The mask body, or the mask clip, or both deflect as the ramp surfaces  482  and  485  contact, and slide past one another. Once each mask body protrusion  481  and mask clip protrusion  484  pass each other, mask body  430  or clip  442 , or both, return to an un-deflected or partially deflected condition, and mask body protrusion abutment face  483  abuts against clip protrusion abutment face  486 , retaining mask, body  430  and clip  442  together. The abutment faces  483  and  486  are aligned substantially laterally relative to the direction in which the clip and body are pressed together. With the abutment faces arranged laterally, or substantially perpendicular to the pressing direction, the clip  442  may not be removed from the mask body easily, creating a substantially permanent joint between the clip and the body. 
     This alternative embodiment is useful for disposable masks that are disposed of after a single use. Such an embodiment is useful in simplifying the manufacturing process. During manufacture, moulding the seal  443  to the seal clip  442  may be easier than moulding the seal  443  directly to the mask body  430 . Once the seal is moulded or attached to the seal clip as in any of the embodiments described above, the subsequent operation of pressing the clip  442  and mask body  443  together is a relatively simple assembly operation. 
     As best shown, in  FIG. 37  and  FIG. 39 a   , the seal preferably has a bearing surface  451  extending around the perimeter of the clip. The seal bearing surface  451  faces a corresponding bearing surface  452  on the mask body. The seal bearing surface and the mask bearing surface are in contact when the seal assembly is attached to the mask body in a butting engagement. When the seal assembly  440  is attached to the mask body  430 , the seal  443  at the bearing interface is compressed so that a sealing interface is formed between the seal assembly and the mask body. Preferably, the clip has a raised ridge  445  running around the inside perimeter of the clip. The seal  443  is compressed by being squashed between the raised ridge  445  and the mask body bearing surface  452  when the seal assembly  440  is attached to the mask body  430 . 
     To assist with creating a good seal between the seal assembly and the mask body, a continuous rim  453  may be provided on the seal bearing surface  451 . The rim provides a small contact area in contact with the mask, body bearing surface  452 . The small contact area allows a relatively high compression of the rim, and therefore effective seal, for a relatively small seal assembly to mask body engagement force. 
     Profiled Seal Clip 
     The seal  443  is shaped to approximately match the facial contours of a user&#39;s face. For the preferred form of the nasal mask shown in  FIGS. 34 to 38 , the face seal is contoured to approximately match the facial contours of a user around the user&#39;s nose, from the bridge of the nose, continuing down the cheek regions adjacent each side of the user&#39;s nose and across the user&#39;s philtrum area. In particular, there is an indented section  454  intended to fit over the bridge of the patient&#39;s nose, a cheek contour  455  on each side to follow the cartilage extending from the middle of the user&#39;s nose, and an indented section  456  to seal around the philtrum area of the user. 
     The present shape of the seal is chosen to ‘approximately match’ the facial contours of a range of users. To approximately match tire contours of a user&#39;s face, the seal is contoured in three dimensions, that is, shaped to fit around a user&#39;s nose, and contoured in a direction substantially normal to a user&#39;s face, as described above and shown in the accompanying figures. 
     Similarly, if the invention was applied to a full face mask covering a user&#39;s nose and mouth, the face seal would be shaped to approximate the facial contours of the user&#39;s chin and wider check regions. 
     As best shown in  FIG. 42 , the seal, assembly clip  442  and the rear portion, or back edge  452  of the mask body are shaped to generally follow the contours of the user&#39;s face. Shaped to ‘generally follow’, means that the contoured shape of the portion of the seal in contact with a user&#39;s face is generally replicated in the shape of the clip. The profile of the clip and the profile of the seal in contact with the user&#39;s face are therefore similar. The main difference in the shape of the clip and the shape of the portion of the seal in contact with the user&#39;s face is that the shape of the clip does not include the indent  455  in the cheek contour portion of the seal, the shape of the clip being flatter in this region. The profiled clip allows the walls  457  of seal assembly  440  to have a generally constant depth around the circumference of the seal  443 . Preferably the wall depth varies by less than around one third of the deepest wall depth. A generally constant wall depth helps the seal to apply even pressure to the face around the circumference of the seal. The profiled seal clip  442  and mask body  430  also helps to minimise the size of the mask assembly. Minimising the size of the mask is an important feature for a comfortably fitting mask. A small size provides a lightweight mask that is more comfortable to wear and less obstructive to the user. 
     A profiled seal assembly clip  442  and a corresponding profiled mask body  430  provides the additional benefit that a small amount of misalignment may be corrected when fitting the seal assembly to the mask body due to the shape of the parts. For example, the inventors have found that the profiled shape of the clip and mask body, combined with the ramp section  449  that extends the full perimeter length or substantially the full perimeter length of the clip, automatically corrects an angular misalignment of approximately 5 degrees when engaging the clip to the mask body. When pushing the clip and body together, misalignment is corrected as a portion of the mask body contacts the lead in section  449  of clip  442 . For example, given a small amount of angular misalignment between the clip and mask body, the initial contact between the clip and lire mask body occurs at a first position on one side of the nasal bridge region of the mask body and at a second position on the mask body diametrically opposite the first position. The two positions of the mask body in contact with the clip are angled partially in line with the direction in which the clip is engaged to the mask body. As engagement force is applied to the clip and mask body, the angled shape of the clip and mask body causes the clip and the mask body to slide into alignment until the clip and mask body snap together. In prior art masks with a planar interface between the mask body and seal clip, the interface between the clip and the mask body is transverse to the direction in which the clip engages to the mask body; the seal clip and the mask body must be accurately aligned in order to correctly fit the clip to the body. 
     Inflatable Seal 
     Preferably the seal  443  includes a thin region  426 . The thin region  426  is a region formed in the seal  443  which is thinner than the remainder of the cross-sectional thickness of the seal  443 . In the preferred embodiment the thin region is in the nose bridge region, the extent of which is indicated by line  427  in  FIG. 36 a   . The thin bridge region  426  is shown to extend approximately halfway down the sides of the seal from the apex  458 . Alternatively, the thin region  426  may extend around the perimeter of the seal  442 , as indicated by line  27   a  in  FIG. 36   a.    
     In particular, the edge portion  490  must be thicker than region  426  so as to provide strength to prevent the seal losing its shape under typical CPAP pressures. The seal thickness is also thicker al the interface between the seal  443  and the clip  442 , to provide strength in the joint between the seal  442  and the clip  442 . 
     For example, the thick portions of the seal may have a thickness of around 0.3 to 0.6 mm. The thin region has a thickness that is in the range of around 20-80% of the thickness of the rest of the seal, that is, a thickness of around 0.05 mm-0.5 mm. Preferably the thin section is ultra thin with a thickness of around 0.05 mm-0.2 mm. In the preferred embodiment, the ultra thin region reduces the pressure on a patient&#39;s nose in the nasal bridge region, compared to when a seal does not have any reduced thickness section. Furthermore, a thin region  426  in the seal  443  allows for different sized patient&#39;s to comfortably use the mask and seal of the present invention. 
     In use, when a force is placed against the seal  443  the thin region  426  will yield more than tire rest of the seal  443 . Therefore, this region  426  is more flexible and allows for added patient comfort. 
     In addition to being more flexible, due to the thin region being so thin, in the preferred embodiment the thin region  426  inflates as the CPAP pressure is applied to the mask. 
     Prior art masks include seals that inflate under typical CPAP pressures. However, prior art nasal masks inflate to a preformed shape or a displaced preformed shape. The preformed shape is loose when not in use. In use, the loose shape fills with air or gases and is supported in die preformed shape or a displaced preformed shape by the air or gases at positive pressure being supplied by the CPAP system. The prior art mask seal does not inflate to an elastically stretched state significantly larger than the molded or formed shape of the un-pressurized seal. For example, prior art mask seals include a bellows section which is loose when not in use. When in use, the bellows section fills up with air. The seal material of the bellows section is not significantly stretched, as the material thickness of the bellows section does not allow for significant elastic stretch under normal CPAP pressures, the material of the bellows section being too thick. 
     In the preferred embodiment of the present invention, the ultra thin section  26  inflates under CPAP pressure to an elastically stretched state significantly larger than the molded or formed shape of the seal. The ultra thin region provides a seal that remains tight, with no loose sections that may crimp or fold, when un-deflated. Inflation by typical CPAP pressures to a significantly stretched state helps the sealing performance of the mask, as the seal elastically inflates to the facial contours of the user&#39;s face and allows for more movement of the mask on the user&#39;s face. The ultra thin region  426  inflates to an elastic stretch condition under typical CPAP pressures of 4 cm-25 cm H2O head. The seal of the present invention includes a thin region that inflates under typical CPAP pressures to an elastically stretched condition with strain in the thin region greater than 0.1. That is, the length E of the thin region as shown in  FIG. 46  increases by at least 10% when pressurized under normal CPAP pressures. In  FIG. 46 , seal  443  drawn in continuous line type shows the thin region  426  un-pressurized. The dashed lines show the seal  443  pressurized, with the thin region  426  pressurized to a significantly stretched condition, with an elastic stretch of approximately 10%. Preferably the thin region inflates under typical CPAP pressures to an elastically stretched condition with strain in the thin region greater than 0.2. 
     The seal is typically formed during manufacture by injection molding. Such a thin region has been achieved in manufacture by injecting the seal material into a closed seal mold via the thin region  426 . Having the injection point within the thin region allows better control of the seal forming process and allows the ultra thin region to be formed successfully. Injection via the thin section is preferred. 
     The thickness figures provided above are preferable for silicone with a shore A hardness of approximately 40. If an alternative silicone or other rubber material with similar properties to silicone is used, the thickness figures should be adjusted. The thickness figures may be adjusted inversely proportionally with respect to the hardness or elasticity of the material. For example, for a material with a Shore A hardness of 20, the seal thickness may be twice as thick as the figures provided above. 
     As best shown in  FIG. 36 a   , the thin region  426  on the seal  443  preferably does not extend completely to the outer edge  459  of the seal  443 , but grows in thickness in region  490 . This is because the outer edges of the seal  459  when thicker are less prone to tearing. Also thicker region  490  provides structural support to the seal  443  so that seal  443  maintains its perimeter length in contact with the user&#39;s face when inflated, the perimeter length extending around the seal opening  491 . 
     In additional, as shown in  FIG. 39 a   , the seal preferably has a bead  460  on the perimeter edge of the seal surrounding the seal opening  491 . Preferably this bead is formed at the inside surface  461  of the seal. The diametrical cross-section of the bead will typically be in the range 0.4 mm-1.0 mm. Preferably the bead diameter will be about 0.5 mm. The bead provides additional strength to the edge of the seal, to add additional strength and support at the perimeter of the seal opening  491  and reduce the likelihood of the seal being torn if the seal is inadvertently caught or snagged by a foreign object. 
     Alternatively, the seal  443  may be molded without an opening. Opening  491  is then cut out of the molded seal in a cutting operation, following the molding process. The opening  491  may be cut with a knife or press in the cutting operation. The cutting operation results in a clean edge which is less susceptible to tearing compared to a molded edge. For a seal manufactured in this way, a bead  460  is less important. 
     An inflatable seal may also be incorporated into the mask embodiment of  FIG. 23 . For example, thin region  203  could have a thickness of around 0.05 mm to 0.2 mm, so that this region inflates under typical CPAP pressures to an elastically stretched state, as described above in relation to the embodiment of  FIG. 36   a.    
     As shown in  FIG. 24 , the length  217  of the thin region increases by at least 10% when pressurised under normal CPAP pressure. The stretched pressured seal is indicated by the dashed fines  216 . The edge portion  209  of seal  201  is thicker than region  203  so as to provide strength to prevent the seal losing its shape under typical CPAP pressures. The seal thickness is also thicker at the outer edge  214  as described earlier to provide strength in this area of the seal. 
     Mask Cushion 
     The mask assembly of  FIG. 34  preferably includes a mask cushion  441 , as described in the similar earlier embodiment of  FIGS. 21 to 23 . 
     In the interface  402  of  FIG. 34 , the cushion  441  is provided around the periphery of the mask, and is surrounded by the seal assembly  440 . When using a thin seal, the cushion  441  provides support to the seal assembly  440  to achieve an effective seal onto the face of the user to prevent leakage. 
     One end  462  of the mask cushion is shaped to match the shape of the seal in contact with the user&#39;s face, and an opposite end  463  is shaped to match the mask body. 
     As described above, the seal assembly clip  442  and mask body  430  generally follow the contours of the user&#39;s face, and therefore provide a generally constant seal depth between the mask body  430  and seal surface in contact with the user&#39;s face. The cushion in the preferred embodiment therefore has a wall  464  with a generally constant depth. The constant depth cushion helps to provide an even pressure to the face around the periphery of the mask. 
     The cushion is constructed of a resilient material, for example polyurethane foam, to distribute the pressure evenly along the seal around the patient&#39;s face. In other forms the cushion  441  may be formed of other appropriate material, such as gel, silicone, or other composite materials. 
     In the preferred embodiment, tire mask cushion includes a raised bridge  465  in the nasal bridge region. The raised bridge  465  can also be described as a cut out section made in the cushion, the cut out being on the mask body end  463  of the cushion. As the raised bridge  465  is unsupported by the mask body  430 , it is much more flexible and results in less pressure on the nasal bridge of the patient. 
     In other forms, the cushion may be provided with other contours or cut outs on the mask body end  463  of the cushion, so that in the areas where there are regions cut out, the cushion is more flexible. 
     Preferably, the extent of the raised bridge portion  465  of the cushion substantially aligns with the extent  427  of the thin bridge section  426  of the seal described above. 
     The cushion  441  is located around the outer periphery of the mask body, contacting the mask body except for in the raised bridge portion  465  of the cushion. As best shown in  FIG. 37 , the cushion is located in a generally triangular cavity  466 , the cavity continuing around the periphery of tire body, terminating at each side of the nose bridge region  467  of the mask, where the raised bridge portion  465  of the cushion does not contact the mask body  430 . The cavity  466  is generally formed by two spaced apart walls  476  and  477 . 
     The cushion  441  in the preferred embodiment is a separate item, the seal assembly  440  lining in place over the cushion to hold it in place within the mask assembly  402 . Alternatively, the cushion may be permanently or releasable attached to the seal assembly  440  so that the seal, seal clip and cushion may be provided as a single assembly. The cushion may be permanently or releasable attached to the seal  443  or to the seal clip  442 . Alternatively, the cushion may be permanently or releasable attached to the mask body  430 . 
     Exhaust Holes 
     In use the user exhales his or her breath either via an expiratory conduit, (not shown in the Figures) or directly to the atmosphere. In use, the user may exhale a portion or his or her breath via the mask assembly, that is, back into the inspiratory side of the mask assembly. In prior art masks, exhaust holes are provided in the connector  423 , to assist with flushing exhaled air from the mask assembly. In the preferred form of the patient interface, the mask body  430  has exhaust flow holes  425 . The exhaust holes  425  in the mask body  430  improves the flushing of exhaled air from the assembly. The exhaust holes  425  consist of 5-50 holes, each hole with a diameter of 0.3 mm-1.5 mm. 
     In a preferred form the exhaust holes  425  are provided through the front of the mask body substantially perpendicular to the front of the mask body  430 . Alternatively, the exhaust holes may pass through the front of the mask body at an angle, for example, angled approximately 445 degrees upwards, the outlet of the exhaust holes at the outside surface of the mask body being higher than the inlet of the exhaust holes at the inside of the mask body. 
     The holes may be provided directly through the mask body  430 . Alternatively, the holes may be formed in a separate rubber or plastic insert, the insert being fitted to a corresponding aperture (not shown) in the mask body  430 . 
     The exhaust holes  425  may be provided through the front of the mask body in an upper portion of tire mask body. Alternatively, the holes  425  may be provided through a side or sides of the mask body  430 , in an upper portion of the mask body. Alternatively, the holes may be provided in a lower portion of the mask body, for example, adjacent a bottom edge of die mask body. 
     As described above, the mask body  430  preferably includes exhaust holes  425  to allow exhaled breath to be vented from the mask assembly. Alternatively, or in addition to the vent holes, the mask assembly may provide additional vent paths between the seal assembly  440  and the mask body  430 , as shown in  FIGS. 41 a  to 41 c   . The bearing surface  452  of the mask body in contact with the rim  453  or seal assembly bearing surface  451  may not extend continuously around the perimeter of the mask body. Discrete portions  468  of the rear edge of the mask body may be removed, providing a flow path from the mask assembly to the atmosphere. Alternatively, discrete portions  469  may be removed from the rim  453 , or the seal assembly bearing surface  451 , or both. 
     For clarity, discrete portions  468  and  469  have been shown enlarged in  FIGS. 41 a  and 41 b   . In practice, the flow path via either discrete portions  468  or discrete portions  469  should be similar to the flow path via holes  25 , discrete portions  468  or discrete portions  469 , or both, being provided in place of holes  425 . 
     Vent paths provided by discrete portions  468  or  469  or both are visually hidden from the exterior of the mask. This arrangement provides a desirable look to the mask assembly. 
     Alternatively, holes  470  through the mask body  430  adjacent to the mask bearing surface  452  may be provided to vent exhaled air. Space  478  is a part annular channel space passing around the mask, the channel being formed between the mask body  430 , the mask cushion  441  and the seal assembly  440 . Exhaled air passes into the channel space  478  via the raised nasal bridge region of the mask. Such holes  470  provide flow paths from the mask to the atmosphere via channel space  478 . Holes  470  are provided through a side of the mask body which is partially concealed by a portion of clip  442 . The holes  470  are therefore partially visually hidden from the exterior of the mask assembly in use. 
     In order to improve venting of exhaled air from the mask, a flow path  479  may be provided directly from the interior of the mask to the vent holes  470 . In this embodiment, exhaled air does not need to pass via the raised nasal bridge region and channel space  478 , but may pass directly from the interior of the mask, via flow path  479  and through holes  470 . Flow path  479  is provided by a cut-out region in the mask cushion  441 , indicated by the dashed line in  FIG. 40 a   . Similar cut out portions are provided in the spaced apart wails  476  and  477  which form cavity  466 . The venting of exhaled air is assisted by the downwards flow path  479 , with holes  470  preferably being located in a bottom side portion of the mask, body  430 . When a user uses the nasal interface of the present invention, air exhaled from the user&#39;s nostrils is exhaled substantially in line with the flow path  479  and holes  470 , improving the vent flow path. 
     Circumferential Thin Portion 
     The seal  201 ,  443  may comprise a thin portion approximately circumferentially aligned with the circumferential perimeter of the seal. The circumferential thin portion  4200 , as shown in  FIGS. 47A to 47D , may extend continuously around the full circumference or perimeter of the sea). Alternatively, the circumferential thin portion  4200  may extend around only a portion of the circumference of the seal  201 ,  443 . 
     The circumferential thin portion  4200  provides flexibility in the wall  457  of the seal. This flexibility can assist with allowing the seal area in contact with the users face to move laterally with respect to the mask body and head gear. Allowing lateral movement can assist with maintaining an effect seal against the user&#39;s face. The circumferential thin portion can provide a decoupling between the mask body and the area of tire seal in contact with the user&#39;s face. 
     Typical CPAP pressures applied to the interior of the mask assist with providing support to the seal so that the seal  201 ,  443  does not collapse in the region of the circumferential thin portion when pressure is applied between the seal and the users face by the head gear. The seal  201 ,  443  may be used with or without an inner cushion  202 ,  441 . 
     As shown in the partial cross section of  FIG. 48 , the thin section  4200  may be formed at an interior surface of the seal wail. Alternatively, the thin portion may be formed at an exterior surface of the seal wall, or may be formed centrally with respect to the cross section of the seal wail. 
     As shown in  FIG. 47A , the circumferential thin portion  4200  may have approximately constant width around the circumference of the seal. Alternatively, as shown in  FIG. 47B , the circumferential thin portion may comprise wide portions and narrow portions. For example, the circumferential thin portion may be wider in the nasal bridge region, or the chin region or both compared to other circumferential positions around the seal. 
     The width of the circumferential thin portion may vary at a repeating pitch around the circumference or a portion of the circumference of the seal. For example, the width may vary at a pitch between wide and narrow sections of between approximately 10 mm to 20 mm. As shown in  FIGS. 47C and 47D , the width varies at a repeating pitch in the chin and lower check regions of the seal. 
     Alternatively, as shown in  FIGS. 47E and 47F , the circumferential thin portion may comprise one or more thin portions  4200 A,  4200 B extending in a circumferential direction around the seal; thin portions  4200 A,  4200 B may be in the nasal bridge region or chin region or both. 
     A varying width circumferential thin portion may provide different facial sealing forces at different positions around the seal perimeter. For example, it is desirable to reduce the sealing force in the nasal bridge region. By widening the circumferential thin portion in the nasal bridge region, the seal  201 ,  443  will provide less resistance in this area against the face of a user. 
     The circumferential thin portion may have a thickness of approximately 0.2 mm to 0.3 mm, the other sections of the seal wall having a thickness of approximately 1 mm. 
     The foregoing description of the invention includes preferred forms thereof. Modifications may be made (hereto without departing from the scope of the invention as claimed.