Abstract:
A respiratory mask for treatment of obstructive sleep apnea using gas pressurized in the range of about 4 to 20 cm H 2 O, the mask comprising a mask body, a flexible inlet tube having a first end coupled to the mask body and second end adapted to extend upwardly over a patient&#39;s head in use for connection to an air delivery tube. a cushion supported by the mask body, a harness to support the mask body and cushion on the patient&#39;s head, an elongated clip extending from each lateral side of the mask body, each said clip having a slot to receive an engaging strap of the harness, a ball and socket joint including a ball portion and a socket, wherein the ball portion comprises a part-spherical hollow profile, and wherein the ball portion and the socket are selectively attachable to and detachable from one another.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a divisional of U.S. application Ser. No. 11/987,616, filed Dec. 3, 2007, now allowed, which is a divisional of U.S. application Ser. No. 10/961,091, filed Oct. 12, 2004, now U.S. Pat. No. 7,318,439, which is a continuation of U.S. application Ser. No. 10/235,846, filed Sep. 6, 2002, now U.S. Pat. No. 6,823,869, which claims the benefit of U.S. Provisional Application Nos. 60/342,854, filed Dec. 28, 2001, and 60/317,486, filed Sep. 7, 2001, each incorporated herein by reference in its entirety. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The invention relates to a mask assembly for use in the delivery of Non-invasive Positive Airway Pressure (NPPV) for therapy of Sleep Disordered Breathing (SDB). 
         [0004]    2. Background Information 
         [0005]    The application of Continuous Positive Airway Pressure (CPAP) for therapy of Obstructive Sleep Apnea (OSA) was first taught by Sullivan in U.S. Pat. No. 4,944,310 (Sullivan). In CPAP treatment for OSA, pressurized air or other breathable gas is provided to the entrance of a patient&#39;s airways at a pressure elevated above atmospheric pressure, typically in the range 4 to 20 cm H 2 O to “splint” open the patient&#39;s airways and prevent obstructive apneas. Apparatus to deliver NPPV therapy typically comprises a blower, an air delivery conduit and a patient interface. The blower may be programmed to deliver a range of different forms of therapy. 
         [0006]    In one form, a constant pressure of air or breathable gas is provided to the patient. It is also known for the level of treatment pressure to vary from breath to breath in accordance with patient need, that form of CPAP being known as automatically adjusting nasal CPAP treatment as described in U.S. Pat. No. 5,245,995 (Sullivan and Lynch). In another form, a relatively higher pressure of gas may be provided in the patient mask during the inspiratory phase of respiration and a relatively lower pressure or atmospheric pressure being provided in the patient mask during the expiratory phase of respiration. In other modes, the pressure can be made to vary in a complex manner throughout the respiratory cycle. For example, the pressure at the mask during inspiration or expiration can be varied through the period of treatment. See, for example, U.S. Pat. No. 5,704,345 and International Publication Nos. WO98/12965 and WO99/61088, all of which are incorporated by reference herein. In this specification, the term NPPV therapy will be used to embrace all these forms of therapy. 
         [0007]    The patient interface may take many forms, such as a nasal mask assembly, a nose and mouth mask assembly or nasal prongs assembly. A mask assembly typically, but not always, includes a rigid shell, a soft face-contacting cushion, a forehead support and headgear for securing the mask to the head. 
         [0008]    In one known mask assembly, the headgear includes a cap portion with four straps. In use, the cap portion engages the occiput of the patient. Furthermore, in use, the two lower straps extend between the cap portion and a nasal mask while the two upper straps extend between the cap portion and a forehead support. 
         [0009]    Some patient interfaces include quick release mechanisms. Since the patient must be able to sleep while wearing the patient interface, it must be comfortable. In addition, the patient interface must provide a good seal so any unintentional leak that occurs is minimized and any intentional leak is controlled. Since the shape of people&#39;s noses, faces and heads vary widely, from a commercial perspective, it is important to be able to manufacture patient interfaces which can accommodate this range of facial shapes without carrying excessive inventory. A number of patient interfaces have been designed with the goals in mind of patient comfort, ease of use, adjustability and the ability to accommodate a wide range of patient face and head shapes. 
         [0010]    U.S. Pat. No. 5,243,971 (Sullivan and Bruderer) provides a nasal mask which is suitable for use in CPAP or NPPV therapy. The mask has a face-contacting portion mounted to a shell which is sized and shaped to overfit the nose region of an intended wearer, and the face contacting portion is in the form of a distendable membrane which is molded from an elastomeric material. The distendable membrane and the shell together define a chamber, and pressurized gas admitted to the chamber causes the membrane to distend outwardly from the shell. When placed in contact with the face of the wearer, the distendable membrane is caused to overlay the covered facial regions and, under the influence of the pressurized gas, to conform three-dimensionally with the contours of the overlayed regions. An orifice is formed within the membrane and is shaped and positioned to admit gas from the chamber to the nasal passages of the wearer. The contents of this patent are hereby incorporated by cross-reference. 
         [0011]    U.S. Pat. No. 6,112,746 (Kwok and Styles) describes a nasal cushion which comprises a substantially triangularly shaped frame from which extends a membrane. The frame has a scalloped edge by which the cushion is affixed to a mask body. The membrane has an aperture into which the wearer&#39;s nose is received. The membrane is spaced away from the rim of the frame and its outer surface is of substantially the same shape as the rim. Respective notches receive the bridge of the wearer&#39;s nose. The wearer&#39;s nose is received through the aperture into the chamber within the mask body. The seal forming portion thus contacts both the surface of the wearer&#39;s nose and a portion of the wearer&#39;s face in the region between the base of the nose and the upper lip, and around the sides and over the bridge of the nose. The shape of the seal forming portion is particularly suited to effectively seal the difficult region of the facial contour that is the crease between the sides of the nose and the face. The contents of this patent are hereby incorporated by cross reference. 
         [0012]    U.S. Pat. No. 6,119,693 (Kwok, Matchett and Grant) describes an adjustable forehead support for a nasal mask. An adjustable forehead support for a nasal or full-face mask is described wherein the forehead support may be adjusted for the different shapes and sizes of a facial profile. The forehead support utilizes a dual-arm system which adjusts the position of the forehead support vis-a-vis the mask and/or air flow tube. The angle of the mask to the face may be adjusted with the invention of the &#39;693 patent. The contents of that patent are hereby incorporated by cross-reference. 
         [0013]    In international patent application PCT/AU00/00097 (WO 00/78384), a forehead support is disclosed that is adapted to be secured to a respiratory mask. The forehead support includes a joining member for securing to the mask and a cushion frame pivotally mounted to the joining member. The cushion frame is adapted to locate one or more forehead cushions. The cushion frame is also adapted to pivot relative to the joining member. In one form the cushion frame is also selectively lockable at two or more predetermined angular positions relative to the joining member. A respiratory mask assembly comprising a respiratory mask and a forehead support adapted to be secured to the mask is also disclosed. The contents of this specification are hereby incorporated by cross-reference. 
         [0014]    Pending U.S. application Ser. No. 09/482,718 (Lithgow), now U.S. Pat. No. 6,422,238 describes headgear for securing a respiratory mask to a patient that incorporates a quick release arrangement. The headgear has at least one strap extending from each side of the mask, the straps being releasably fastened rearwards of the patient&#39;s face to secure the mask. The headgear further includes release means in the form of a pull cord attached to an overlying strap at its region of fastening to the underlying strap and guided forward to be gripped at the front of patient. The contents of this specification are hereby incorporated by cross-reference. 
         [0015]    A mask cushion for use with a mask assembly in NPPV therapy is disclosed in U.S. patent application Ser. No. 09/885,445, “Mask with Gusset” to Frater et al. filed on Jun. 21, 2001, now U.S. Pat. No. 6,986,352 and assigned to the assignee of the present application, which application is incorporated by reference herein. The mask system disclosed therein includes a suspension mechanism to allow relative movement between a face-contacting cushion and a mask shell. The suspension mechanism also provides a predetermined force to the cushion that is a function of mask pressure, displacement of the cushion or both. In one embodiment of that invention, the mask cushion assembly includes an inflatable gusset acting as the suspension mechanism. 
       SUMMARY OF THE INVENTION 
       [0016]    It has been a problem in the art to stabilize a mask frame (or shell) in a position over the user&#39;s face so that the face-contacting side of the cushion is free to move relative to the frame-contacting side of the cushion while maintaining a seal. It is desirable to correct this problem in such a way that is comfortable for the patient and does not create excessive forces on the face of the user because of over-tightened straps. 
         [0017]    In one aspect, the present invention discloses a head mount arrangement which is adapted to floatingly stabilize a mask frame in position without the use of a forehead support. 
         [0018]    In another aspect, the present invention discloses a head mount arrangement which applies very small forces on the face through the mask frame until the mask is pressurized. In another aspect, the present invention discloses a force-passive or force-neutral mounting arrangement for a mask. In another aspect, a head mount arrangement is disclosed which allows adjustment of the angle and/or distance between the head mount and mask frame (or shell). In another aspect a method of stabilizing on a face a mask assembly comprising flexible straps and a semi-rigid head mount is provided, the method comprising positioning the head mount on a patients head, loosely adjusting the straps length and then applying pressure to the mask assembly. 
         [0019]    An additional problem in the art has been that the cushion of a mask assembly is not easily attachable, removable and/or re-attachable to/from the shell. It is desirable for a user to be able to easily assemble, disassemble and/or reassemble the cushion and shell assembly for periodic cleaning and other miscellaneous purposes. 
         [0020]    In one aspect, the present invention discloses a retaining ring which provides a secure, sealed connection between the cushion and the shell and is further easily disassembled from the shell for cleaning or other purposes. 
         [0021]    An additional problem in the art occurs for a user of a respiratory mask to maintain a previously set strap adjustment position on the mask especially given the fact that it can be quite time consuming to correctly adjust strap positions on the mask. More particularly, in some respiratory mask assemblies, once the user had properly adjusted the mask and needed to remove the mask, there was no way to maintain the previously set positions. 
         [0022]    In another aspect, the present invention discloses latching mechanisms which provide for a low-profile attachment between the shell of the mask and the harness and permit the mask to be to quickly, accurately and easily released and latched for use. Thus, the latching mechanisms allow the user to remove and reinstall the mask assembly and maintain the same preset strap adjustment. 
         [0023]    The swivel and elbow arrangements of the prior art present problems for the air connections between a pressurized air source and the mask such as leakage around the elbow. The arrangements also suffer from tube drag which can cause the seal between the mask and user&#39;s face to break. Some prior art swivel and elbow arrangements use and tight tolerances, which result in heavy friction in the movement of the ball and thus reduced mobility and flexibility of the elbow swivel joint. In another aspect, the mask assembly of the present invention includes a ball and socket joint for breathable air connection to the mask that reduces the effects of tube drag and provides increased flexibility between the air supply tube and the mask. In particular, the ball and socket joint of the present invention allows an air supply tube to be moved on an increased area of movement in comparison to the conventional elbow swivel joint. 
         [0024]    In an embodiment of the present invention, the mask assembly includes a rigid shell, a cushion for attachment to the shell and a harness or headgear for attaching the cushion and shell to the patient (or user). The shell includes one or more latching mechanisms for attachment between the shell and the harness and for allowing the harness to be quickly, accurately and repeatedly tightened and untightened with respect to the user&#39;s head while maintaining a preset harness length and fit. The latching mechanisms operate on an over center principle to quickly and easily be manipulated by the user (or a care-giver) from an open (or unlatched) position to a closed (or latched) position, and vice-versa. 
         [0025]    The shell assembly further includes several features for improving the flow of gases (including air) through the mask and reducing noise levels associated with such gas flow. One such feature is the provision of exhalation ducts that direct the exhalation gas flow from an interior of the mask assembly to an exterior of the mask assembly in a flow direction alongside an air inlet tube to the mask. Another such feature is the provision of one or more baffles in an interior of the shell to direct and help keep separated the intake and exhalation gas flows. 
         [0026]    The mask assembly also includes several features for quickly adjusting the fit of the mask assembly to the particular user to improve the sealing of the mask and the comfort of the user. Several different embodiments of adjustment mechanisms are disclosed, including mechanisms that can quickly and easily change the height and/or angle of a head mount with respect to the shell either simultaneously or independently of one another and mechanisms that can alter the fit of the connection between the shell assembly and the harness or headgear. In one embodiment of the present invention, the structure used for securing the shell/cushion assembly to the user&#39;s head does not include a forehead support and does not contact the user&#39;s forehead and also has the advantage of not leaving unsightly (though usually temporary) pressure marks on the user&#39;s forehead as can other known masks. 
         [0027]    In another embodiment, a ball and socket joint is provided that permits freedom of movement of a pressurized gas supply tube with respect to the mask assembly, thus preventing the movement of the gas supply tube from affecting the stability of the cushion and shell assembly and the integrity of the mask/face seal. The ball and socket joint may be positioned at some point in the air supply line to provide a highly flexible joint in the line for patient comfort. 
         [0028]    Of course, portions of the aspects may form sub-aspects of the present invention. Also, various ones of the sub-aspects and/or aspects may be combined in various manners and also constitute additional aspects or sub-aspects of the present invention. These and other features and aspects of the present invention will be described in or be apparent from the detailed description below read in conjunction with the attached Figures, where like reference numerals indicate like components. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0029]    The above and other features and advantages of the present invention are further described in the detailed description which follows, with reference to the drawings, and by way of non-limiting exemplary embodiments of the present invention wherein: 
           [0030]      FIG. 1  shows a perspective view of a mask assembly of the present invention; 
           [0031]      FIG. 2  shows a front perspective view of a shell of the mask assembly of  FIG. 1 ; 
           [0032]      FIG. 3  shows a plan view of a portion of a latching mechanism of the mask assembly of  FIG. 1 ; 
           [0033]      FIG. 4  shows a perspective view of the portion of the latching mechanism of  FIG. 3 ; 
           [0034]      FIG. 5  shows a perspective view of a clip link of the latching mechanism of  FIG. 3 ; 
           [0035]      FIG. 6  shows a perspective view of a clip pin of the latching mechanism of  FIG. 3 ; 
           [0036]      FIG. 7  shows a perspective view of a clip portion of a latching mechanism of the mask assembly of  FIG. 1 ; 
           [0037]      FIGS. 8A-8C  are force diagrams showing the forces acting on the latching mechanism of the mask assembly of  FIG. 1 ; 
           [0038]      FIG. 9A  shows a rear perspective view of the shell of  FIG. 2 ; 
           [0039]      FIG. 9B  shows a sectional view of an alternative embodiment of the shell of  FIG. 2 ; 
           [0040]      FIG. 10  shows a partial cut away side elevational view of a mask assembly of the present invention; 
           [0041]      FIG. 11  shows a bottom rear perspective view of a portion of a head mount of the mask assembly of  FIG. 10 ; 
           [0042]      FIGS. 12-16  show a ball and socket joint of the present invention with  FIG. 15  being a detail of  FIG. 14 ; 
           [0043]      FIG. 17  shows a rear perspective view of an alternative embodiment of the shell of the present invention; 
           [0044]      FIG. 18  shows a front perspective view of an alternative embodiment of the shell of  FIG. 17  and an alternative embodiment of the latching mechanism of the present invention; 
           [0045]      FIG. 19  shows a perspective view of a clip of the latching mechanism of  FIG. 18 ; 
           [0046]      FIG. 20  shows a front perspective view of an alternative embodiment of the shell of the present invention; 
           [0047]      FIG. 21  shows a top perspective view of an alternative embodiment of the shell of the present invention; 
           [0048]      FIG. 22  shows a perspective view of an alternative embodiment of a mask assembly of the present invention installed on a user; 
           [0049]      FIG. 23  shows a side elevational view of the mask assembly of  FIG. 22 ; 
           [0050]      FIG. 24  shows a front perspective view of the mask assembly of  FIG. 22 ; 
           [0051]      FIG. 25  shows a perspective view of a head strap of the mask assembly of  FIG. 22 ; 
           [0052]      FIG. 26  shows a rear perspective view of a shell of the mask assembly of  FIG. 22 ; 
           [0053]      FIG. 27  shows a front perspective view of the shell of  FIG. 26 ; 
           [0054]      FIG. 28  shows a perspective view of a clip portion of a latching mechanism of the mask assembly of  FIG. 22 ; 
           [0055]      FIG. 29  shows a perspective view of a unitary clip link of the latching mechanism of the mask assembly of  FIG. 22 ; 
           [0056]      FIGS. 30A and 30B  show, respectively, a perspective view of the socket and a side elevational view of the ball of the mask assembly of  FIG. 22 ; 
           [0057]      FIG. 31  shows a perspective view of an alternative embodiment of a head mount adjustment mechanism of the mask assembly of the present invention; 
           [0058]      FIG. 32  shows a side elevational view of the head mount adjustment mechanism of  FIG. 31 ; 
           [0059]      FIG. 33  shows a front elevational view of the operation of the head mount adjustment mechanism of  FIG. 31 ; 
           [0060]      FIG. 34  shows a perspective view of an alternative embodiment of a head mount adjustment mechanism of the mask assembly of the present invention; 
           [0061]      FIG. 35  shows an enlarged perspective detail view of the head mount adjustment mechanism of  FIG. 34 ; 
           [0062]      FIG. 36  shows a rear perspective view of the head mount adjustment mechanism of  FIG. 34  mounted to an alternative embodiment shell of the mask assembly of the present invention; 
           [0063]      FIG. 37  shows a side perspective view of the head mount adjustment mechanism and shell of  FIG. 36 ; 
           [0064]      FIG. 38  shows a front elevational view of the head mount adjustment mechanism and shell of  FIG. 36 ; 
           [0065]      FIG. 39  shows a side elevational view of the head mount adjustment mechanism and shell of  FIG. 36 ; 
           [0066]      FIG. 40  shows a front perspective view of an alternative embodiment of a head mount adjustment mechanism mounted to an alternative embodiment shell of the mask assembly of the present invention; 
           [0067]      FIG. 41  shows a perspective detail view of the head mount adjustment mechanism and shell of  FIG. 40 ; 
           [0068]      FIG. 42  shows a rear exploded view of the head mount adjustment mechanism and shell of  FIG. 40 ; 
           [0069]      FIG. 43  shows a front exploded view of the head mount adjustment mechanism and shell of  FIG. 40 ; 
           [0070]      FIG. 44  shows a side elevational view of a portion of the head mount adjustment mechanism of  FIG. 40 ; 
           [0071]      FIG. 45  shows a front perspective view of a portion of the head mount adjustment mechanism of  FIG. 40 ; 
           [0072]      FIG. 46  shows a front elevational view of a connecting bracket of the head mount adjustment mechanism of  FIG. 40 ; 
           [0073]      FIG. 47  shows a side elevational view of the connecting bracket of  FIG. 46 ; 
           [0074]      FIG. 48  shows a rear perspective view of the connecting bracket of  FIG. 46 ; 
           [0075]      FIG. 49  shows a front perspective view of a locking bracket of the head mount adjustment mechanism of  FIG. 40 ; 
           [0076]      FIG. 50  shows a front elevational view of the locking bracket of  FIG. 49 ; 
           [0077]      FIG. 51  shows a side elevational view of the locking bracket of  FIG. 49 ; 
           [0078]      FIG. 52  shows a perspective view of an alternative embodiment of the mask assembly of the present invention; 
           [0079]      FIG. 53  shows a side elevational view of the mask assembly of  FIG. 52 ; 
           [0080]      FIG. 54  shows a front elevational view of an alternative embodiment of a latching mechanism of the present invention; 
           [0081]      FIG. 55  shows a bottom elevational view of the latching mechanism of  FIG. 54  with the latching mechanism in a closed position; 
           [0082]      FIG. 56  shows a bottom elevational view of the latching mechanism of  FIG. 54  with the latching mechanism in an open position; 
           [0083]      FIG. 57  shows a front elevational view of an alternative embodiment of a latching mechanism of the present invention; 
           [0084]      FIG. 58  shows a bottom elevational view of the latching mechanism of  FIG. 57  with the latching mechanism in closed and open positions; 
           [0085]      FIG. 59  shows a perspective view of an alternative embodiment of the mask assembly of the present invention; 
           [0086]      FIG. 60  shows a side elevational view of the mask assembly of  FIG. 59 ; 
           [0087]      FIG. 61  shows a front elevational view of the mask assembly of  FIG. 59 ; 
           [0088]      FIG. 62  shows a front perspective view of an alternative embodiment of a latching mechanism in a partially open position; 
           [0089]      FIG. 63  shows a front perspective view of the latching mechanism of  FIG. 62  in a closed position; 
           [0090]      FIG. 64  shows a rear perspective view of the latching mechanism of  FIG. 62  in a partially open position; 
           [0091]      FIG. 65  shows a sectional view of the mechanism used to secure the cushion to the shell; 
           [0092]      FIG. 66  shows a front view of the mask assembly of  FIG. 59  installed on a user; 
           [0093]      FIG. 67  shows a side view of the mask assembly of  FIG. 59  installed on a user; 
           [0094]      FIG. 68  shows a perspective view of an alternative embodiment of the mask assembly of the present invention; 
           [0095]      FIG. 69  shows a front elevational view of the embodiment of  FIG. 68 ; 
           [0096]      FIG. 70  shows a side elevational view of the embodiment of  FIG. 68 ; 
           [0097]      FIG. 71  shows a bottom perspective view of the embodiment of  FIG. 68 ; 
           [0098]      FIG. 72  shows a front perspective view of a mask shell of the embodiment of  FIG. 68 ; 
           [0099]      FIG. 73  shows a rear perspective view of the mask shell of the embodiment of  FIG. 68 ; 
           [0100]      FIG. 74  shows a front perspective view of a clip of a latching mechanism of the embodiment of  FIG. 68 ; 
           [0101]      FIG. 75  shows a rear perspective view of the clip of  FIG. 74 ; 
           [0102]      FIG. 76  shows a rear perspective view of a clip link of a latching mechanism of the embodiment of  FIG. 68 ; 
           [0103]      FIG. 77  shows a rear perspective view of a harness engaging clip of a latching mechanism of the embodiment of  FIG. 68 ; 
           [0104]      FIG. 78  shows a front perspective view of a harness engaging clip of a latching mechanism of the embodiment of  FIG. 68 ; 
           [0105]      FIG. 79  shows a sectional view of the latching mechanism and mask shell of the embodiment of  FIG. 68 ; 
           [0106]      FIG. 80  shows a perspective view of the embodiment of  FIG. 68 ; 
           [0107]      FIG. 81  shows a perspective view of a head support of the embodiment of  FIG. 68 ; 
           [0108]      FIG. 82  shows a perspective view of an adjustment clip of a head support adjustment mechanism of the embodiment of  FIG. 68 ; 
           [0109]      FIG. 83  shows a perspective view of a portion of a head support adjustment mechanism of the embodiment of  FIG. 68 ; 
           [0110]      FIG. 84  shows a bottom perspective view of a portion of a head support adjustment mechanism of the embodiment of  FIG. 68 ; 
           [0111]      FIG. 85  shows a sectional view of a portion of a head support adjustment mechanism of the embodiment of  FIG. 68 ; 
           [0112]      FIG. 86  shows a bottom perspective view of a vent of the embodiment of  FIG. 68 ; 
           [0113]      FIG. 87  shows a top perspective view of the vent of  FIG. 86 ; 
           [0114]      FIG. 88  shows a perspective view of a retaining ring of a cushion/shell connection mechanism of the embodiment of  FIG. 68 ; 
           [0115]      FIG. 89  shows a partial sectional view of a cushion/shell connection mechanism of the embodiment of  FIG. 68 ; 
           [0116]      FIGS. 90A-90D  shows multiple views of the retaining ring in an alternate embodiment of the present invention; 
           [0117]      FIGS. 91A-91C  shows isometric views of the retaining ring of  FIGS. 90A-90D ; 
           [0118]      FIG. 92  shows a detailed view of the clip portion of the retaining ring of  FIGS. 90A-90D ; 
           [0119]      FIG. 93  shows on underside view of the retaining ring and clip of  FIGS. 90A-90D ; 
           [0120]      FIGS. 94A-94B  show top and back view of the retaining ring of  FIGS. 90A-90D ; 
           [0121]      FIG. 95  shows a perspective view of a cushion in an alternate embodiment of the present invention; 
           [0122]      FIG. 96  shows a side view of the cushion of  FIG. 95 ; 
           [0123]      FIGS. 97A-97B  show side elevational views of the cushion of  FIG. 95 ; 
           [0124]      FIGS. 98A-98B  show front and perspective views of the cushion of  FIG. 95 ; 
           [0125]      FIGS. 99A-99B  show further front and perspective views of the cushion of  FIG. 95 ; 
           [0126]      FIG. 100  shows a sectional view of the cushion of  FIG. 95 ; 
           [0127]      FIG. 101  shows an exploded side view of an alternate embodiment of the present invention; 
           [0128]      FIG. 102  shows a front view of the cushion and ring assembly of the embodiment in  FIG. 101 ; 
           [0129]      FIG. 103  shows a exploded view of the cushion and ring assembly of  FIG. 102 ; 
           [0130]      FIG. 104  shows a side cross-sectional view of the mask in the alternate embodiment of  FIG. 101 ; 
           [0131]      FIG. 105  shows a rear view of the mask of  FIG. 104 ; 
           [0132]      FIG. 106  shows a front view of the mask of  FIG. 104 ; 
           [0133]      FIG. 107  shows the mask and ring assembly along a reference point  107 - 107  of  FIG. 106 ; 
           [0134]      FIG. 108  shows a side view of alternate embodiment of  FIG. 101 ; 
           [0135]      FIG. 109  shows a cross-section view of an upper detent of the embodiment of  FIG. 101 ; 
           [0136]      FIG. 110  shows a cross-section view of a lower detent of the embodiment of  FIG. 101 . 
           [0137]      FIG. 111  shows a cross-sectional view of the alternate embodiment of the mask assembly shown in  FIG. 101 ; 
           [0138]      FIG. 112  shows a cross-sectional view of the alternate embodiment of the mask assembly shown in  FIG. 101 ; and 
           [0139]      FIG. 113  shows a cross-sectional view of the alternate embodiment of the mask assembly shown in  FIG. 101 ; 
       
    
    
     DETAILED DESCRIPTION 
       [0140]      FIG. 1  shows a perspective view of the mask assembly  10  of the present invention. The mask assembly  10  includes a shell assembly  20  and a cushion  30 . One example of the type of cushion with a gusset that can be used with the present invention is disclosed in U.S. patent application Ser. No. 09/885,445, “Mask with Gusset” to Frater et al. filed on Jun. 21, 2001, now U.S. Pat. No. 6,986,352 and assigned to the assignee of the present application, which application is incorporated by reference herein. In the Frater application, a good seal with the face may be obtained under a variety of pressures without the need to over tighten the straps of the mask. The gusset of the cushion disconnects the frame contacting side of the cushion from the patient contacting side of the cushion and allows 6 degrees of freedom between the two sides. However, the present invention is not restricted to use with such a cushion with a gusset and can be used with any NPPV therapy cushion. It should be understood that even where a Figure described herein does not show a cushion, only shows a portion of a cushion or only a gusset portion of a cushion, it is understood that such embodiment is intended to be used with a complete cushion and the use of the term cushion in describing a Figure that only shows a portion of a cushion is not intended to be limiting. 
         [0141]    The shell assembly  20  includes a generally rigid shell  40  to which the cushion  30  can be attached. The shell  40  includes a base  42  and a pair of flange assemblies  44  and  46  extending upward from the base  42 . In the preferred embodiment, the flange assemblies  44  and  46  are generally mirror images of one another, although they need not be. Each of the flange assemblies  44 ,  46  includes an upper flange and a lower flange with a bore  50  passing therethrough, the bore preferably having an axis parallel to a major planar surface  52  of the shell  40 . See also  FIG. 2 . 
       Quick Release Latching Mechanism 
       [0142]    Each of the flange assemblies  44  and  46  support a quick-release latching mechanism  60 . Each latch mechanism  60  preferably uses identical components to minimize the number of parts required to manufacture the mask assembly, although the components can be different where desirable. Each latching mechanism  60  includes an upper clip link  62  and a lower clip link  64 , which are preferably identical but are reversed upon installation in the shell  40 . See also  FIGS. 3-6 . Each clip link  62 ,  64  includes an axially extended body  66  with a first end  68  having a pivot pin  70  extending outward from the axially extended body  66  and having an axis perpendicular to an axis of the body  66 . The pivot pins  70  are sized and adapted to pivotally engage the respective bores  50  in the flange assemblies  44 ,  46 . As illustrated in  FIG. 4 , each clip link  62 ,  64  also includes a second end  72  having a bore  74  therethrough, the bore  74  having an axis parallel to the axis of the pivot pin  70 . 
         [0143]    In  FIG. 6 , each latching mechanism  60  also includes a clip pin  80  having an axially extending shaft  82  and an enlarged head  84 . The axially extending shaft  82  is sized and adapted to pivotally engage the bores  74  of the respective upper and lower clip links  62  and  64 , respectively, of each assembly. The enlarged head  84  provides a more easily graspable surface to assemble and disassemble the pin with respect to the latching mechanism and also provides an alignment surface to prevent the pin from passing too far through the bores  74 . 
         [0144]    As shown in  FIG. 7 , each latching mechanism  60  also includes a clip  88 . Each clip  88  includes a first end  90  having a bore  92  therethrough sized and adapted to pivotally mount over the axially extending shaft  82  of the clip pin  80  between the upper and lower clip links  62  and  64 . Each clip  88  also includes a second end  94  that includes a mask harness-engaging portion  96 . The harness-engaging portion  96  preferably extends away from a central portion of the clip  88  at an angle toward a face side of the mask  10  generally in alignment with an angle of the harness portion extending from the user&#39;s head toward the harness-engaging portion  96 . See  FIG. 8A . Thus, the harness will exert a pulling force F H  on the harness-engaging portion  96  of the clip  88  that is generally aligned with the angle of the harness-engaging portion  96 . In an embodiment, the harness-engaging portion  96  may be a slot through which a portion of the harness can pass to be secured to the clip  88 . In one embodiment, the harness may include an engaging strap that can pass through the harness-engaging portion  96  and then be connected to itself by use of Velcro®, snap connections, buckles or other known connections. Each clip  88  includes a flip arm  98  extending away from a body of the clip  88  that is easily graspable by the mask user to manipulate the clip  88  with respect to the mask  10 . Each clip  88  may optionally be provided with a stop surface  95  that may be adapted to engage the shell  40  or other fixed portion of the shell assembly  20  to provide a positive stop to movement of the clip  88  in a direction toward the shell  40 . 
         [0145]    Each latching mechanism  60  may be assembled to the shell  40  as follows. The upper and lower clip links  62  and  64  are first pivotally mounted to the respective upper and lower flanges of the flange assemblies  44 ,  46  by engaging the respective pivot pins  70  with the respective portion of the bores  50  passing through the upper and lower flanges. The clip  88  is then inserted between the upper and lower clip links  62  and  64 . The width of the clip  88  is established so that once the clip  88  is inserted between the upper and lower clip links  62 ,  64 , the clip  88  will prevent the clip links  62 ,  64  from disengaging from the respective flanges  44 ,  46 . The bore  92  of the clip  88  is then aligned with the respective bores  74  of the upper and lower clip links and the clip pin  80  is inserted through each of the bores to pivotally mount the clip  88  with respect to the clip links  62 ,  64  and the flange assemblies  44 ,  46 . 
         [0146]    The operation of the latching mechanism  60  will now be described. The latching mechanism  60  works on an over-center principle. That is, when a pulling force F H  from the harness is applied to the harness-engaging portion  96  of the clip  88 , the clip  88  will have a tendency to move in a direction away from a force equilibrium or force center position of the latching mechanism. In the embodiment shown in  FIGS. 8A-8C , the force equilibrium or force center is on a line intersecting the axes of the shaft  82  and the pins  70 . If the summation of forces acting on the clip  88  result in a summed force component acting on the shaft  82  that extends at an angle below the axis of pins  70 , such as F L , seen in  FIG. 8A , the clip  88  will be maintained in a bottomed or latched position against the shell  40 . However, if the summation of forces acting on the clip  88  result in a summed force component acting on the shaft  82  that extends at an angle above the axis of pins  70 , such as F U  seen in  FIG. 8A , the clip  88  will move toward an open or unlatched position, as shown in  FIG. 8B . 
         [0147]    Thus, where the pulling force of the harness F H  results in a summation force F L  acting on the clip  88 , the clip  88  will remain in the latched position. Where a release force F R  is exerted on the clip by the user or other person such that the summation of forces F R  and F H  result in a summation force F U , the clip  88  will move to the unlatched position. Of course, if the angle of the force F H  is altered such that the summation force acting on the clip  88  changes from F L  to F U , the clip  88  will also move from the latched to the unlatched position. For this reason, it is important to design the positioning of the harness with respect to the mask such that the force F H  under normal wearing conditions will not result in a summation force that will unintentionally unlatch the latching mechanism  60 . Rather, in a preferred embodiment, under normal conditions, it is intended that the mechanism  60  will unlatch only when an additional release force is applied to the clip  88  by the user or other person. In the unlatched position, each latching mechanism provides  60  slack in the harness of approximately two times the distance between the axes of pins  70  and shaft  82 . 
         [0148]    In an alternative embodiment shown in  FIG. 8C , the shell  40  includes an extension  41  over which the strap of the harness must pass to prevent the strap from pulling directly downward on the clip  88  and thereby possibly unintentionally providing the necessary force to unlatch the latching mechanism  60 . The extensions prevents the strap from applying a pulling force F H  on the clip in an undesired direction. 
         [0149]    The use of the quick-release latching mechanism  60  as described above provides for a low-profile attachment mechanism between the shell  40  and the harness, while also allowing the attachment to be quickly, accurately, repeatedly and easily released and latched. The latching mechanism  60  assures that the preset strap adjustment is maintained over repeated latchings and unlatchings. That is, once the strap is adjusted properly for the user, the latching mechanism  60  allows the user to remove and reinstall the mask assembly  10  and maintain the same preset strap adjustment, unlike known mask systems. Further, the slack provided in the harness when each latching mechanism  60  is unlatched also makes it easier for the user to place the mask assembly  10  on the head and to remove it from the head. Such a quick-release is not only convenient for the user, but also provides a level of comfort to the user that the mask can be quickly and readily removed should the user experience any discomfort or sensation of suffocation while wearing the mask. If desired, the design of the latching mechanisms may also be configured to permit the latching mechanisms  60 , and thus the straps, to be quickly removed from the shell by placing the latching mechanism  60  in the unlatched position and removing the pins  70  from the bore  50 . 
       Shell 
       [0150]    The shell  40  may also includes a number of other features. For example, the shell  40  may include an air inlet tube  100  connected to an upper central portion of the shell  40  and having a port  102  opening to an interior of the mask assembly  10  at an upper central position on the shell  40  to supply breathable gas from a pressurized supply to an interior of the mask assembly  10 . See  FIGS. 1 ,  2  and  9 . The air inlet tube  100  may include an external thread  101  for connecting the air inlet tube  100  to further components of the air supply path. The shell  40  may also include a pair of exhalation ducts  104  positioned on respective sides of the air inlet tube  100  for exhausting gases from the mask assembly  10 . Each exhalation duct  104  includes a port  106  opening to an interior of the mask assembly  10  at a position toward the respective side of the shell  40 . As is best seen in  FIG. 9A , the air inlet tube opening port  102  is separated from the exhalation duct opening ports  106  by a pair of raised walls  108  extending from an interior surface  110  of the shell  40 . The raised walls  108  extend from a position adjacent the air inlet tube opening port  102  downward along the shell  40  while angled outward as they extend downward to provide clearance for the user&#39;s nose. The raised walls  108  stop before reaching a bottom edge  116  of the shell  40 . The raised walls  108  define a central gas intake channel  112  in the mask through which the pressurized gas can flow to the user&#39;s nostrils. The raised walls  108  also define a pair of lateral gas exhaust channels  114  within the mask but outside of the central gas intake channel through which exhalation gases can flow to the exhalation ducts  104 . 
         [0151]    The raised walls  108  improve air flow in the mask by separating the intake gas from the exhalation gas in the mask to help reduce the short-circuiting of oxygen-rich intake gas to the exterior of the mask through the exhalation ducts. The positioning of the exhalation duct opening ports  106  to the outside of the central air inlet tube opening port  102  with the raised walls  108  positioned therebetween utilizes the natural flow of gas in the mask. That is, when the user is inhaling, the gas can flow through the central channel to the user&#39;s nostrils. However, when the user exhales, the exhaled gas will flow from the nostrils downward, hitting the bottom edge of the shell and moving outward along the bottom edge of the shell and into the pair of lateral gas exhaust channels. Thus, the flow management provided by the raised walls  108  not only reduces short-circuiting of the intake air to the exhalation ducts  104 , it reduces carbon dioxide levels in the mask and also assists in moving the exhalation gas from the user&#39;s nostrils to the exhalation ducts  104  while minimizing exhalation backwash into the intake charge. 
         [0152]    Alternatively, as shown in  FIG. 9B , the shell  40  may be provided with a single centrally positioned exhalation duct  104  having a port  106  positioned beneath the air inlet tube opening port  102  and separated by a central baffle  109 . 
         [0153]    The exhalation ducts  104  may be curved upward and have exhaust ports  120  facing upward with respect to the shell  40  alongside the air inlet tube  100 . In this way, the exhalation ducts  104  receive the exhalation gas from the interior of the mask and channel such gas out of the exhaust ports  120 , upward alongside the air inlet tube  100 . The channeling of the exhalation gases to the exterior of the mask in this manner provides an exhaust flow that follows the air inlet tube upward. This minimizes exhaust flow either toward the mask user&#39;s face or toward a bed partner of the user, as can happen with conventional masks that exhaust gas from the front of the mask and which can be disturbing to bed partners when the user is facing the bed partner. Also, locating the exhaust ports farther from the user&#39;s nostrils helps reduce breathing noise that escapes from the mask. 
         [0154]    The curving of the exhalation ducts  104  upward such that the exhaust ports are remote from the base of the shell can allow greater ease in configuring the cross-section of the exhaust ports for enhanced sound reduction and the accommodation of exhalation diffusers within the mask. 
         [0155]    The shell  40  may also include a pair of access ports  118  located at a bottom of the mask  10 . The access ports  118  are connectable to one or more supply tubes through which medication or oxygen can be supplied to an interior of the mask. The access ports  118  may also be used to access an interior of the mask  10  for control or measurement purposes, such as to measure a mask interior pressure, CO 2  levels, etc. While two such ports are shown, the number of access ports can be altered as is desired. When not in use, the access ports  118  can be capped to prevent leaks from the interior of the mask. The access ports  118  may also be positioned at an upper portion of the shell so that the supply tubes can run alongside the air inlet tube  100  and minimize tangling of the tubes or can be positioned elsewhere on the mask assembly  10  as desired. 
       Overall Assembly 
       [0156]      FIG. 10  shows a partial cutaway side elevational view of an overall mask assembly  10 . In addition to the shell assembly  20  and the cushion  30  (of which only a portion is shown), the mask assembly  10  also includes a head mount  130  and head mount height adjuster  146 . The head mount  130  and adjuster  146  provide a connection between an air supply tube  100  and the mask assembly  10 . As shown in  FIG. 11 , the head mount  130  includes a base portion  132  for contacting the user&#39;s forehead. The base portion  132  is curved to conform generally to the shape of a user&#39;s forehead. A foam or other soft layer may be provided on an underside surface of the base portion  132  to increase the comfort of the user when wearing the mask assembly  10 . The base portion  132  also includes three slots  134  and  136  for connecting the head mount  130  to the harness to secure the head mount  130  to the user&#39;s head. The two laterally positioned slots  134  mount to portions of the harness extending from around the sides of the user&#39;s head, while the centrally positioned slot  136  mounts to a portion of the harness extending from the top of the user&#39;s head. Other types of connectors may also be used to connect the head mount  130  to the harness, such as snap connections, hook connections, Velcro®. connections or other connections. 
         [0157]    The head mount  130  further includes a pedestal  138  mounted to the base portion  132 . The pedestal  138  supports a ball and socket joint socket joint  200  flowingly connected to an air connector tube  142 . The ball and socket joint will be described in detail below. The air connector tube  142  includes a thread  144  for connecting to the height adjuster  146 . The head mount height adjuster  146  is generally configured as a hollow tube to permit air flow from the head mount  130  to the air inlet tube  100 . Head mount adjuster  146  includes a first threaded portion  148  for connecting to the threaded portion  101  of air inlet tube  100  and a second threaded portion  150  for connecting to the threaded portion  144  of air connector tube  142 . The height adjuster  146  also includes a centrally mounted finger wheel  152  for rotating the adjuster  146  to adjust the spacing between the head mount  130  and the shell assembly  20 . 
         [0158]    In a preferred embodiment, one of threaded portions  148  and  150  is right-hand threaded and the other is left-hand threaded, as are the respective corresponding threaded portions of the air inlet tube  100  and the air connector tube  142 , so that the distance between the head mount  130  and the shell assembly  20  can be altered by rotating the adjuster  146  only, and without rotating either the head mount  130  or the shell assembly. See  FIG. 10 . This feature makes it easy for the user to adjust the spacing between the head mount  130  and the shell assembly  20  for the best fit and comfort once the mask assembly  10  has been placed on the user&#39;s head without the need for removing the mask assembly to rotate either the head mount  130  or the shell assembly  20  with respect to one another as would be necessary if all of the threaded portions were right-handed or left-handed. 
         [0159]    Although not preferred, the threaded portions may be made all right-handed or left-handed. Further, the internal and external threaded portions of the respective mating components may be reversed. It is preferred that the threaded connections between the air inlet tube  100 , the height adjuster  146  and the air connector tube  142  be of a sufficiently close tolerance such that any substantive air leaks at the joints may be prevented. Further, adjustment will remain as set under normal wearing conditions, and the tolerances are not so tight as to prevent ready rotation of the adjuster  146  with only the user&#39;s fingers when the user desires to alter the adjustment. 
         [0160]    In the preferred embodiment of the present invention, the shell  40  is made of polycarbonate, the latching mechanism  60  components may be made of a semi-rigid plastics material such as acetal or nylon, and the head mount  130  may be made of acetal or polypropylene. The various components can also be made of other known materials. 
       Ball and Socket 
       [0161]    Existing swivel and elbow arrangements for the air connections between a pressurized air source and the mask can have detractions such as leakage and squeaks around the elbow. In another embodiment of the present invention,  200  these shortcomings may be overcome with a mask assembly  10  having a novel ball and socket joint  200  for the breathable air inlet connection to the mask  10 . The ball and socket joint  20  may also augment the advantages of an embodiment of the present invention incorporating a gusset portion by providing additional flexibility between the air supply tube and the mask. The ball and socket joint  200  is shown in detail in  FIGS. 12-16 . In the embodiment shown in  FIGS. 12-16 , the ball and socket joint  200  is mounted closer to a base plate  202  and includes a curved air connector tube  214 . The details of the joint  200  are applicable to the embodiment of  FIGS. 10 and 11 .  FIG. 12  shows a ball and socket joint  200  attached to a base plate  202  that can be attached to the patient&#39;s forehead with the harness/headgear. Alternatively, the ball and socket joint  200  may be mounted directly to the mask shell  40  or can be attached only to an air supply tube connected to the air inlet tube  100  of the shell  40 . In this latter embodiment, shown for instance, in  FIGS. 59-60 , the ball and socket joint  200  can freely move, as it is not rigidly attached to the shell  40  or some other stationary structure. The joint  200  includes a ball  204  mounted on the end of flexible air tube  206 . The air tube  206  maybe adapted for connection with a pressurized air source. The ball  204  is adapted for mounting in a socket  208 . Pressurized air from the air tube  206  flows through an orifice  210  in the ball  204  into the socket  208  and through an orifice  212  in the socket  208  to the mask  10  through tube  214 . The socket  208  includes an inner circumferential seat  216  and a lip  218  at an outer edge of the socket  208 . The ball  204  can be relatively easily inserted into the socket  208  and removed, if necessary. Once the ball  204  is inserted into the socket  208 , it rests between the seat  216  and the lip  218  with a small clearance provided between the ball  204  and the seat  216  and lip  218  of the socket. 
         [0162]    Conventional ball and socket joints typically have very tight tolerances to avoid air leaks but this can cause heavy friction in the movement of the ball and thus negate any mobility and flexibility advantage that might be desired. However, the small clearance provided between the ball  204  and the seat  216  and lip  218  of the socket  208  allows the ball  204  to move or rotate freely with respect to the socket  208 . While the ball  204  is in motion, the clearance allows a small amount of the pressurized air to escape between the ball  204  and socket  208  to the atmosphere. However, once the ball  204  is in a static position, the air pressure forces the ball  204  against the lip  218  and seals the connection between the ball  204  and socket  208  until the ball  204  is again placed in motion. See  FIG. 16 . The ball and socket joint  200  allows the air supply tube to be moved about the socket  208  anywhere in a range of movement in the form of a cone projecting from the socket and provides increased movement of the air tube over a conventional elbow swivel joint. 
         [0163]    In testing, the ball and socket joint of the present invention was found to leak at a rate of less than 1 ltr/min at pressures between 2 and 20 cm of water. The ball and socket joint  200  may be formed by methods and materials well known in the art, such as, for example, polypropylene. This material has the advantage of having a soft wax-like surface texture, which helps reduce noise between the part s during movement. The ball can also preferably be made of polycarbonate. The ball and socket joint  200  may, like the remainder of the invention, be manufactured of any of the materials known to be used for the production of such joints or mask parts, although it is preferred that one of the ball and socket be made from a relatively rigid material and the other made from a relatively flexible material for best operation. 
         [0164]    An alternative embodiment of the shell  40  is shown in  FIGS. 17 and 18 . In this embodiment, an internal wall  160  of the shell  20  has been given an increased height such that this internal wall  160  will project into the cushion  30 . This embodiment is especially designed for use with a gusseted cushion, as discussed above and shown in  FIGS. 1 and 10 . The internal wall  160  is configured so as to project into the gusset portion  32  of the cushion without actually contacting the interior of the gusset portion  32  so as not to interfere with pressurization and movement of the gusset portion  32  of the cushion  30 . This projection into the gusset portion  32  helps maintain alignment of the cushion  30  with the shell  40  when the gusset is in a deflated or closed state. The projection need not be continuous around the periphery to provide effective alignment and can include separate independent projecting portions to achieve the same result. 
         [0165]    The embodiment of  FIGS. 17 and 18  also includes a flange  162  extending around a periphery of the shell  40 . This flange  162  contacts a front side of the gusset portion  32  of cushion  30  when the mask is in use and effectively stiffens the gusset portion  32  of the cushion  30  to provide more force on the face from the cushion. This feature is further described in U.S. patent application Ser. No. 09/885,445, “Mask with Gusset” to Frater et al. filed on Jun. 21, 2001, now U.S. Pat. No. 6,986,352 discussed above. The shell  40  in this embodiment is also provided with exhalation ducts  104  of an increased size. The air inlet tube  100  is also shortened in this embodiment as compared to the embodiment of  FIG. 2 . 
       Alternative Embodiments 
       [0166]    In addition, an alternative embodiment of the clip  88  is shown in  FIGS. 18 and 19 . In this embodiment, the flip arm  98  is positioned generally directly over the bore  92 , instead of intermediate bore  92  and end  94  as in the embodiment shown in  FIG. 7 . With such a placement of the flip arms  98 , when the latching mechanisms  60  are in the closed state, the flips arms  98  are closely adjacent one another. This allows both flip arms  98  to be grasped simultaneously between the thumbs and forefingers of the user when in the closed position and moved to a position where the latching mechanisms  60  will both unlatch and open. Each flip arm  98  also has a lower height to reduce the chance that the flip arm  98  will become entangled in the bed linens and unintentionally unlatch the latching mechanism upon movement of the user or bed linens. In this embodiment, the flip arm is provided with grasping extensions  99  on both sides. The grasping extensions  99  are preferably dished to allow secure grasping of the flip arm  98  between the user&#39;s thumb and forefinger. This embodiment clip  88  does not include a stop surface  95  in order to better conform to the flatter upper surface of the shell  40  shown in  FIG. 18 . 
         [0167]    An alternative embodiment of the shell  40  is shown in  FIGS. 20-21 . In this embodiment, the exhalation ducts are further increased in size to increase a cross-sectional area of the exhaust ports  120 , reducing exhalation gas velocity and/or providing additional space for an exhalation gas diffuser. 
       Alternative Mask Assembly 
       [0168]      FIGS. 22-29  show an alternative embodiment of the mask assembly  10 . In this embodiment, the mask assembly does not use a separate head mount as the embodiment discussed above. Rather, the shell  40  includes an extension bracket  220  extending from an upper portion of the shell  40 . The extension bracket  220  is generally rectangular but may have other configurations as well. The extension bracket  220  is configured to engage a retaining channel  222  of a head strap  224 . Because the sides of the extension bracket  220  and the retaining channel  222  are generally parallel, the head strap  224  can be moved up and down the extension bracket  220  to adjust the distance between the head strap  224  and the main body of the shell  40 /cushion  30 . This allows the head strap  224  to be adjusted to properly fit the user. Compare  FIG. 23  and  FIG. 24  depict different adjustments that may be made to the head strap  224  along the extension bracket  220 . 
         [0169]    In  FIGS. 25 and 26 , the head strap  224  also includes a pair of raised projections  232  positioned in the retaining channel  222  adapted to engage any one of a plurality of detent slots  234  positioned along an under side of the extension bracket  220 . When the head strap  224  is adjusted along the extension bracket  220  until the projections  232  engage one of the slots  234 , the head strap  224  will be maintained in this adjusted position, under normal wearing conditions, until the user re-adjusts the head strap  224  with respect to the extension bracket  220 . The height of the projections  232  is established in connection with the flexibility of the head strap  224  such that the projections  232  may be moved from one detent slot  234  to another without requiring undue force to make such an adjustment. In a preferred embodiment, one or both of the edges of the projections  232  and the detention slots  234  may be rounded to ease movement of the projections  232  out of the respective slots  234 . Although two generally round projections  232  are shown in  FIG. 25 , other numbers and configurations of projections may also be used. The head strap  224  also includes a retaining loop  226  mounted above the retaining channel  222 . In  FIG. 24 , the retaining loop  226  is sized to engage and retain a connector tube  228  connecting the air inlet tube  100  with a ball and socket joint  200 . In this embodiment, the positioning of the ball and socket joint  200 , with respect to the shell  40 , is reversed as compared to the embodiments shown above. If desired, the positioning can be as discussed above. The retaining loop  226  thus supports both the connecting tube  228  and the ball and socket joint  200 . 
         [0170]    In  FIG. 25 , the head strap  224  includes a plurality of adjustment slots  230  and adjustment slots  231  on both free ends. The adjustment slots  230  are for connecting to side portions of a harness or retaining strap extending between the free ends of the head strap  224  and the adjustment slots  231  are for connecting to top portions of a harness or retaining strap extending between the free ends of the head strap  224  to secure the head strap  224  to the user&#39;s head. While the head strap  224  includes the retaining channel  222  on an outside surface thereof, the inner surface of the head strap  224  may be kept generally smooth. 
         [0171]    In this embodiment, the head strap  224  does not actually contact the user&#39;s forehead but floats in front of the user&#39;s forehead. When the gusset portion of the cushion  30  is inflated, the shell  40  is pushed away from the user&#39;s face, placing tension on the head strap  224  being held in place by the harness extending between free ends of the head strap  224 . This tension pulls the head strap  224  away from the user&#39;s forehead. This results in increased comfort for the user, since there is less contact with the user&#39;s face and also prevents unsightly pressure marks from occurring on the user&#39;s forehead due to contact with the mask assembly  10 , as can occur with known mask assemblies. 
         [0172]    In  FIG. 26 , the access ports  118  are positioned closer together and more centrally on the shell  40  than in the previous embodiments. In  FIG. 27 , the access ports  118  also extend from a front of the shell  40 , as opposed to a bottom of the shell  40 . As with the embodiment shown in  FIG. 17 , the shell  40  in this embodiment also includes a flange  162  extending around its periphery to contact and support the gusset portion of the cushion  30  and stiffen the action of the gusset portion. 
         [0173]    In  FIG. 29 , each latching mechanism  60  in this embodiment replaces the two clip links  62 ,  64  and pin  80  of the embodiment shown in  FIGS. 1-7  with a unitary clip link  240 . Each latching mechanism  60  also includes a clip  88 , similar to the clip shown in  FIGS. 1-7  except as described below. See  FIG. 28 . 
         [0174]    The unitary clip link  240 , depicted in  FIG. 29 , includes two pins  70  for engaging bore  50  of the respective flange assembly. The two pins  70  are mounted on pin arms  71  extending freely away from a central portion of the link  240  to provide a spring action so that they can be squeezed toward one another to allow clearance for inserting the pins  70  in the bore  50 . Likewise, unitary clip link  240  includes two inwardly facing pins  83  for engaging bore  92  in clip  88 . The pins  83  are mounted on pin arms  85  extending away from a central portion of the link  240  to provide a spring action so that they can be flexed outward to provide clearance for inserting the pins in the bore  92 . The unitary clip link  240  also includes a pair of centrally positioned side extensions  242 . These side extensions  242  engage inner surfaces of the flange assemblies when the latching mechanism  60  is latched to provide lateral stability to the latching mechanism  60 . 
         [0175]    The unitary clip link  240  also includes a third extension  244  extending between pin arms  85  toward pins  83  and a fourth extension  216  extending between pin arms  71 . The third extension  244  includes an extending tab  245  that is adapted to engage a slot  89  on clip  88 . The slot  89  is configured such that an end surface of the slot  89  contacts the tab  245  when the latching mechanism  60  has reached full extension in the open position to provide a positive stop to further movement of the latching mechanism  60 . The slot  89  can also be configured to provide a positive stop to the tab  245  when the latching mechanism  60  is in the closed position. Extensions  242 ,  244  and  246  all act to limit excessive movement of adjacent pin arms  71  and  85  and provide underlying support to the clip  88  when the latching mechanism  60  is in the closed position. Clip  88  can also be optionally provided with a protrusion  91  on an underside surface to contact extension  246  and provide a further stop mechanism when the latching mechanism  60  is in the closed position. 
         [0176]      FIG. 30  shows the ball  204  and socket  208  of the embodiment of the ball and socket joint  200  shown in  FIGS. 22-24 . 
       Alternative Mask Assembly 
       [0177]      FIGS. 59-61  and  FIGS. 66-77  show an alternative embodiment of the mask assembly  10  of the present invention. In this embodiment, the shell  40  includes an extended air inlet tube  100 . A head strap  450  includes a connecting member  460  to which are connected a front harness mount  452  for connecting to a harness, an upper harness mount  456  for connecting to the harness and an upper head mount  454  for contacting an upper portion of the user&#39;s head to position and stabilize the head strap  450 . Each of the harness mounts  452  and  456  include slots  458  for connecting to the harness  461  (see  FIGS. 66 and 67 ), although other attachment mechanisms may also be used. Similarly to the embodiment shown in  FIGS. 22-29 , none of the front harness mount  452 , the upper harness mount  456  or the shell  40  contact the user&#39;s head. Rather, when the gusset portion of the cushion is inflated, the shell  40  is pushed away from the user&#39;s face, placing tension on the front harness mount  452  and harness  461 , and thus, pulling the front harness mount  452  and upper harness mount  456  away from the user&#39;s head. In the embodiment shown in  FIGS. 66-67 , the harness  461  is shown as only connecting to the front harness mount  452 . However, in other embodiments, the harness  461  can be configured to connect to both harness mounts  452  and  456 . 
         [0178]    The front harness mount  452  includes a split retaining loop  462  that is adapted to slidingly connect to the extended air inlet tube  100 . In this manner, the shell assembly  20  and cushion  30  are connected to the head strap  450  and can be adjusted vertically with respect to the head strap  450  to fit the mask assembly  10  to the particular user. The latching mechanisms  60  are similar to the latching mechanisms  60  discussed above with respect to  FIGS. 22-29 . However, in this embodiment of  FIG. 59 , each flip arm  98  of each clip  88  is configured so that when both latching mechanisms  60  are in the closed position, the flip arms  98  are positioned closely adjacent one another and upper and lower edges of each flip arm  98  are raised sufficiently to be readily grasped between the user&#39;s thumb and forefinger. Thus, both flip arms  98  can be grasped between the thumb and forefinger of the user and simultaneously manipulated with one hand to unlatch each latching mechanism  60  and quickly allow each latching mechanism  60  to move to the open position using only the one hand. 
         [0179]    In an alternative embodiment, any of the latching mechanisms  60  described herein may be modified to include a positive latch that will hold the latching mechanism in the latched position. In one such embodiment, the positive latch can be a detent mechanism between the latching mechanism and the shell that positively holds the latching mechanism in the latched position until unlatched by the user. Such a positive latch mechanism may be configured to provide an audible indicator, such as a click, or other sensory indicator, that indicates that the latching mechanism is in the fully latched position. 
         [0180]    The head strap  450  and air inlet tube  100  may be provided with a detent mechanism similar to the detent mechanism discussed above with respect to the embodiment shown in  FIGS. 22-29  to maintain an adjusted position between the head strap  450  and the air inlet tube  100 . Alternatively, the air inlet tube  100  and the retaining loop  462  may be threaded to provide an adjustable connection between the two components capable of maintaining the adjusted position. 
       Alternative Latching Mechanism 
       [0181]      FIGS. 62-64  show an alternative embodiment of the latching mechanism  60  and shell assembly  20 . In this embodiment, only one latching mechanism  60  is used. As above, the clip  88  is pivotally mounted to a clip link  240 , which is pivotally mounted to the shell  40 . The clip  88  includes a second end  94  having a mask harness-engaging portion  96 . To provide the same amount of harness slack take-up as do the two latching mechanism embodiments disclosed above, the single latching mechanism  60  of the present embodiment is approximately twice as long as each latching mechanism discussed above. Thus, the clip  88  and the clip link  240  of this embodiment are approximately twice as long as each clip  88  and clip link  240  shown in the embodiment of  FIGS. 22-29 . The clip  88  can optionally include a flip arm  98  for manipulating the clip  88 , similarly to the previous embodiments. However, since the first end  90  of the clip  88  extends generally to the other side of the shell  40  when in the closed position because of the increased length of the clip  88  and clip link  240 , the latching mechanism  60  can also be unlatched by manipulating the exposed first end  90  of the clip  88 . 
         [0182]    In  FIG. 63  since only one latching mechanism  60  is used, a harness-engaging clip  470  is provided in this embodiment to engage the second side of the harness. As depicted in  FIG. 64 , the harness engaging clip  470  includes a pair of inwardly extending pins  472  to pivotally engage the bore  50  of the shell  40 , as does the left latching mechanism of the embodiments discussed above, and a mask harness engaging portion  474  for engaging the harness. Since the pins  472  engage the bore  50  from the outside of the flange assembly  44 , the harness engaging clip  470  does not interfere with the latching mechanism  60  when in the closed position, even though the width of the clip link  240  is preferably set so as to engage the inner sides of the flange assembly  44  in the closed position to provide stability to the latching mechanism  60 . Alternatively, a fixed harness-engaging portion can be provided on the shell itself, but with the present embodiment, the same shell  40  can be used in either a double or a single latching mechanism mode. Also, with the embodiment shown, the latching mechanism  60  can be attached to the shell  40  on either side of the shell  40 , as can the harness engaging clip  470 , to provide left and right handed mask versions, using the identical components. 
         [0183]    In a modification of this embodiment, two latching mechanisms  60  of the increased length can be provided on the shell  40  with one latching mechanism positioned by an extended flange assembly to be further out from the shell  40  than the other latching mechanism such that the more outwardly positioned latching mechanism can overlay the inner latching mechanism. In a latching mode, the inner latching mechanism would first be manipulated to the closed position and then the outer latching mechanism. In an unlatching mode, the process would be reversed. Such an embodiment would provide approximately double the harness slack take-up ability, as compared to the embodiments described above. Alternatively, the inner latching mechanism can be provided with a grasping member that does not interfere with movement of the outer latching mechanism such that manipulation of the grasping member by the user opens the inner latching mechanism, which in turn, simultaneously opens the outer latching mechanism. 
         [0184]    Each of the latching mechanisms described herein operate on the same over center principal as described with respect to  FIGS. 8A and 8B . 
       Alternative Head Mount Adjustment Mechanism 
       [0185]      FIGS. 31-32  show an alternative embodiment of a head mount adjustment mechanism  250 . The mechanism includes a pair of generally parallel extending spring tabs  252  extending from the shell  40  (only a portion of which is shown) on opposite sides of the air inlet tube  100 . A generally round locking gear  254  is fixedly mounted to a distal end of each spring tab  252  and, in the preferred embodiment, is integrally cast with the spring tab  252 . A plurality of teeth  256  are evenly spaced around a periphery of each locking gear  254 . In a referred embodiment, the locking gears  254  are coaxial with one another and each locking gear  254  has a raised projection  258  for manipulation of the locking gear/spring tab assembly by the user. 
         [0186]    Head mount  260  includes a base  262  for engaging a user&#39;s forehead and slots  264  or other attachment mechanisms for attaching the head mount  260  to a head strap or harness. The head mount  260  also includes a pair of generally parallel extending brackets  266 . Each extending bracket  266  includes an elongated slot  268  passing therethrough with longitudinal axes of the elongated slots  268  being generally parallel to one another. Each elongated slot  268  includes a pair of generally straight, parallel opposing rows of locking teeth  270 . The locking teeth  270  and locking gear teeth  256  are each configured so that they can readily and stably engage each other. Likewise, the pitch of the locking teeth  270  is set to correspond to the pitch of the locking gear teeth  256  and the distance between the rows of teeth  270  is set to correspond to a diameter of the locking gear  254  to provide proper engagement between the teeth  270  and the gear  254 . In the embodiment shown in  FIGS. 31-32 , the locking teeth  270  have generally rounded crowns  275  and more pointed roots  277  while the teeth  256  correspondingly have more pointed crowns  276  and generally rounded roots  278 . Other gear shapes and configurations can also be used. 
         [0187]    Since the opposing rows of teeth  270  are generally parallel and space apart a distance to readily mesh with the generally round locking gear  254 , the locking gear  254  can be engaged with the rows of teeth  270  at a plurality of discrete points along substantially all of the length of the slot  268 , thereby altering a distance between the head mount  260  and a main body of the shell  40 . This configuration also allows the angle of the head mount  260  with respect to the shell  40  to be altered (again within the limitations imposed by the pitch of the teeth) by engaging the teeth  270  with different teeth  256  around the locking gear  254 . This angle does not extend entirely around the locking gear  254  since, at some point, some portion of the head mount  260  will contact and be stopped by some portion of the shell  40  or cushion  30 . However, this is of little concern because in most instances for most users, the desired angle of the head mount  260  with respect to the shell  40  will fall within a limited range of substantially less than 90°. 
         [0188]    Thus, by selecting which teeth  270  engage which teeth  256 , both the distance and the angle between the head mount  260  and the shell  40  can either be altered simultaneously or altered independently of one another to provide the desired fit for the user. To this end, the spring tabs  252 , while fairly rigid, are flexible enough such that when the user squeezes the opposing projections  258  extending above the slots  268 , the spring tabs will move toward one another, thereby disengaging the locking gear  254  from the locking teeth  270 . See  FIG. 33 . The desired distance and angle between the head mount  260  and shell  40  can then be set as desired and the spring tabs  252  released to engage the locking gear  254  with the locking teeth  270  and lock the head mount  260  in the desired position. The degree of flexibility of the spring tabs  252  can be altered by altering a thickness, material and/or shape thereof. 
         [0189]    To facilitate engagement between the teeth  256  and teeth  270 , an outer edge of the teeth  256  and/or an inner edge of the teeth  270  can be rounded. The thickness of the teeth  256  and  270 , and thus the amount of engagement between the respective teeth, will be set based on the magnitude of forces that the adjustment mechanism is expected to encounter in use, with higher expected forces suggesting thicker teeth and greater engagement between the respective teeth. To increase the strength and stability of the head mount  260 , one or more support members  272  can interconnect the extending brackets  266 . In addition, the head mount includes a passageway  274  positioned between the extending brackets  266  so that an air supply tube can be routed therethrough for connection to the air inlet tube  100 . Further, ends of the slots  268  can be radiused, as shown at  276 , to provide increased clearance for the locking gear  254 , thereby allowing an increased length of engagement between the locking gear  254  and the rows of teeth  270 . Alternatively, the interacting structures on the head mount  260  and the shell  40  can be reversed. 
         [0190]    In an alternative embodiment of the adjustment mechanism  250  shown in  FIGS. 34-35 , each locking gear  254  is provided with a generally cylindrical projection  278 . The projection  278  has an outer diameter approximately the same or slightly less than the distance between the crowns of opposing rows of teeth  270  and a height that extends beyond the slot  268 , preferably by a sufficient distance such that when the spring tabs  252  are squeezed together for adjustment of the mechanism  250 , the projections  278  remain engaged with the teeth of their respective slots  268 . In this way, increased stability is provided between the head mount  260  and the shell  40  during adjustment of the mechanism  250  since the projections  278  remain movably engaged with the rows of teeth  270  even though the locking gear  254  is disengaged from the rows of teeth  270 . 
         [0191]    In this embodiment depicted in  FIGS. 34-35 , a distal end  280  of each slot  268  is curved and provided with teeth  270  such that when the distance between the head mount  260  and the shell  40  is adjusted to its maximum, there is engagement between the teeth  270  and the teeth  256  around 180° of the locking gear  254 . This increased engagement provides additional stability to the adjustment mechanism  250  at a time when the increased distance between the head mount  260  and the shell  40  is acting to decrease stability of the adjustment mechanism  250 . The curved, toothed distal end  280  of the slot  268  also continues to provide angular adjustment ability to the mechanism  250  at the maximum adjustment distance of the mechanism  250 . In this embodiment, further raised projections  258  are not needed for manipulation by the user and the projections  278  can optionally be dished or hollow for material savings. In this embodiment, the teeth  256  and  270  have a slightly different configuration than in the previous embodiment and the outer diameter of each projection is approximately the same as the root diameter of the locking gear  254 . 
         [0192]      FIGS. 36-39  show perspective views of the adjustment mechanism  250  with an alternative embodiment of the shell  40 . In this embodiment, one exhalation duct port  106  is provided below air inlet tube port  102  with a laterally extending baffle  282  extending therebetween to separate the two gas flows through these ports. In this embodiment, the duct port  106  connects to a single exhalation duct  104  that extends upward and partially surrounds the air inlet tube  100  with exhalation gases exiting through a single exhaust port  120 . 
       Alternative Head Mount Adjustment Mechanism 
       [0193]      FIGS. 40-51  show an alternative embodiment of a head mount adjustment mechanism  300 . A shell portion  302  of the adjustment mechanism may be the same as any of the shell embodiments shown in  FIGS. 31-39  and includes spring tabs  252 , locking gears  254  and a plurality of locking teeth  256  positioned around a periphery of the locking gear  254 . The shell  40  may be changed if desired. 
         [0194]    In  FIG. 41 , a head mount portion  304  of the adjustment mechanism  300  is different from the previous embodiments. The head mount portion  304  includes a locking bracket  306  having a pair of generally parallel extending brackets  266 . Each extending bracket  266  includes a generally round slot  268  passing therethrough with the two slots  268  being generally coaxial to one another. Each slot  268  includes plurality of locking teeth  270  positioned around an inner circumference of the slot positioned and configured to engage the teeth  256  in a locking manner. Since each slot  268  is round, the engagement between the teeth  270  and the teeth  256  of this embodiment only allow for changes of an angle between the locking bracket  306  and the shell  40  and does not allow for a height adjustment between the two components. This angle can be adjusted by depressing the spring tabs  252  and rotating the locking bracket  306  in the same manner as was described above with respect to the previous embodiments. 
         [0195]    In  FIG. 43 , the locking bracket  306  includes a retaining channel  308  sized and configured to slidingly receive a first extending tab  310  of a connecting bracket  312 . The connecting bracket  312  includes a second extending tab  315  extending at an angel with respect to the first extending tab  310 . The connecting bracket  312  is generally L-shaped, although the angle between the first and second extending tabs need not be 90°, and in the preferred embodiment, is closer to 100°. However, any angle can be chosen that provides the best fit for the intended user. In the embodiment shown, the first extending tab  310  is relieved for much of its distal extent to provide clearance for an air tube although such clearance can also be provided by an enclosed slot on the tab  310 . Each side of the tab  310  includes a plurality of spaced apart detent slots  314 . Correspondingly, locking bracket  306  includes a pair of detent spring arms  316 , each having a raised detent projection  318  projecting into the retaining channel  308  from opposing sides and adapted to engage respective pairs of the detent slots  314  to lock the connecting bracket  312  in a desired adjusted position with respect to the locking bracket  306 . While the locking bracket preferably uses two detent spring arms  316 , one or more spring arms can optionally be used. Further, while it is preferred that the raised detent projections  318  be positioned at the end of spring arms to ease movement, adjustment and longevity of the components, the raised detents need not be on spring arms and can be merely positioned on opposing interior walls of the retaining channel  308 . 
         [0196]    With this construction, the position of the connecting bracket  312  can be adjusted fore and aft with respect to the locking bracket/shell/cushion, which in turn, adjusts the fore and aft position of a head mount  320  attached to the connecting bracket  312  with respect to the locking bracket/shell/cushion, by sliding the tab  310  within the retaining channel  308  until the raised projections  318  engage the detent slots  314  in the desired position and lock the connecting bracket  312  with respect to the locking bracket  306 . The raised detent projections  318  and/or the detent slots  314  can be chamfered to lessen the amount of force required to move the connecting bracket  312  with respect to the locking bracket  306 . Likewise, the size, shape and configuration of the spring arms  316  can be altered to vary a spring force imparted by the spring arms  316  on the raised projections  318  to adjust the force required to move the connecting bracket  312  within a desired range. The distal end of tab  310  can be chamfered for ease of insertion into retaining channel  308 . 
         [0197]    The second extending tab  315  of connecting bracket  312  includes a centrally positioned row of spaced apart detent slots  322  that are adapted to engage a detent projection  324  positioned in a first retaining channel  326  of head mount  320 . Although the detent projection  324  is not shown positioned on a spring tab, it can be where desired. Similarly to the engagement between first extending tab  310  and retaining channel  308  of connecting bracket  312 , second extending tab  315  is adapted to engage retaining channel  326  of head mount  320  to provide a generally vertical adjustability to the head mount  320  with respect to the connecting bracket/shell/cushion. The engagement of the detent projection  324  with one of the plurality of detent slots  322  maintains the head mount  320  in the adjusted position until readjusted. 
         [0198]    Head mount  320  may also includes a second retaining channel  328  in which a detent projection  330  is positioned. The second retaining channel  328  is positioned adjacent the first retaining channel but on an opposite side of the head mount  320 . The second retaining channel  328  is adapted to engage an extending tab  332  on a head strap  334 . The extending tab  332  includes a row of detent slots  336  adapted to selectively engage the detent projection  330  and maintain and adjusted position of the head strap  334  with respect to the head mount  320 , similarly to manner in which the detent slots  322  and the detent projection  324  maintain the adjusted position of the head mount  320  with respect to the connecting bracket.  312 . In this way, the head strap  334  can be adjusted with respect to the head mount  320 , shell  40  and cushion  30 . Head strap  334  is adapted to engage further straps or a harness to secure the mask to the head. The head mount  320  can also include a foam or other soft liner on its underside for comfortable engagement with the user&#39;s head. The head mount  320  includes slots  336  or other attachment devices for connection to other head straps or a harness. 
         [0199]    In  FIG. 44 , a socket portion  208  of a ball and socket joint  200  described above is connected to the second extending tab  315  of the connecting bracket  312  by a connecting flange  340  and is interconnected between the first extending tab  310  and the second extending tab  315  with a support flange  338  to provide stability to the socket  208 . 
         [0200]    The embodiments shown in  FIGS. 31-51  may also be configured such that no portion of the mask assembly contacts the user&#39;s forehead, similarly to the embodiments of  FIGS. 22-29  and  FIGS. 59-67  described above. 
       Alternative Mask Assembly 
       [0201]      FIGS. 52 and 53  show an alternative embodiment of the mask assembly  10 . This embodiment uses a shell  40  similar to the shell  40 —shown in  FIGS. 22-27 . In  FIG. 52 , a head strap assembly  360  includes a front head strap  350  which includes a retaining channel  352  adapted to slidingly engage the extension bracket  220  of the shell  40  in the same manner as does the head strap  224  discussed above with respect to  FIGS. 22-27 . The head strap assembly  360  further includes a rear head strap  362  and a crown mount  364  that interconnects the front and rear head straps. The rear head strap  362  includes a distal portion  366  having a plurality of spaced apart detent slots  368  positioned on an upper surface thereof and a strengthening groove  376  extending along a length thereof. The rear head strap also includes a rear mounting plate  378  for engaging a rear portion of the user&#39;s head and attaching to a retaining harness. The front head strap  350  similarly includes a distal portion  354  having a plurality of spaced apart detent slots  356  positioned on a lower surface thereof and a strengthening groove  358  extending along a length thereof. 
         [0202]    The crown mount  364  includes a retaining channel  370  adapted to simultaneously receive and engage the distal portions of both the front head strap  350  and the rear head strap  362 . The lower surface of rear head strap  362  and upper surface of front head strap  350  are smooth so as to be readily movable over one another when both head straps are inserted in the retaining channel  370 . The retaining channel  370  includes a first detent projection  372  projecting downward to selectively engage the detent slots  368  of the rear head strap  362 . The retaining channel  370  also includes a second detent projection  374  projecting upward to selectively engage the detent slots  356  of the front head strap  350 . The crown mount  364  further includes a mounting plate  380  for engaging a top portion of a user&#39;s head and attaching to the retaining harness. 
         [0203]    With the structure depicted in  FIGS. 52 and 53 , the front head strap  350 , rear head strap  362  and the crown mount  364  are all adjustable with respect to one another to adjust the extending lengths of both head straps as well as the positioning of the crown mount atop the user&#39;s head. 
       Alternative Latching Mechanism 
       [0204]      FIGS. 54-58  disclose alternative embodiments of the latching mechanism discussed above. The latching mechanism  400  shown in  FIGS. 54-56  is a simplified version of the latching mechanism  60  discussed above. In  FIGS. 54-58 , each latching mechanism  400  includes a unitary link  402  having a pair of link arms  404  interconnected by a transverse shaft  406 . Each link arm  404  includes a pivot pin  408  adapted for pivotal engagement in bores in the shell, as with the latching mechanism  60 . A harness strap  410  is connected to each shaft  406 . The link  402  can be pivoted about the pins  404  between a latched position as depicted in  FIGS. 54 and 55  where slack in the harness is taken up by the latching mechanism and an unlatched position as depicted in  FIG. 56  where the harness strap  410  is loosened. This embodiment does not include the clip  88  of latching mechanism  60  but otherwise operates in the same manner as the latching mechanism  60 . Positive stops  412  may be provided on the shell  40  to stop movement of the latching mechanism in the latched position. In the preferred embodiment, the stops  412  are positioned inward from the shaft  406  so that the shaft end of the link  402  hangs free and can be manipulated by a finger to unlatch the mechanism. In an alternative embodiment, a lever mechanism can be installed on the mask to unlatch both latching mechanisms  400  simultaneously. A latching mechanism may also be used on any other straps connecting to the shell  40 . 
         [0205]    In  FIG. 57 , the latching mechanism  420  is similar to the latching mechanism  400  but includes an extension link  422  that interconnects the link  402  with the shell  40 . The extension link  422  includes a pair of hooks  424  for connecting to the shell  40  and while the extension link can pivot somewhat with respect to the shell  40 , it does not pivot between a latched position and an unlatched position as does the link  402 . This latching mechanism  420  otherwise operates in the same manner as latching mechanism  400  discussed above. 
       Cushion Connecting Mechanism 
       [0206]    A further aspect of the mask assembly of the present invention is a connecting mechanism for connecting the cushion  30  to the shell  40 . In many known masks, the cushion is provided with a lip around its shell side periphery which engages a flange running around a cushion side periphery of the shell. The cushion lip can be either single sided, wherein it engages an outer edge or an inner edge of the shell flange, or it can be double sided, wherein it engages both sides of the shell flange. While such a mechanism is effective in retaining the cushion to the shell, it can require finger strength and dexterity to assemble and disassemble the cushion/shell assembly. Since the shell and cushion should preferably be disassembled periodically for cleaning, it is desirable to provide a connection mechanism between the cushion and the mask that is easier to assemble and disassemble. This is especially important where the user may lack finger strength and/or dexterity due to injury, impairment or advanced age. 
         [0207]    An improved cushion/shell connection mechanism is shown in  FIG. 65 , with reference to  FIGS. 1 and 9A . The shell  40  of the present invention includes a channel  500  running around a cushion side periphery. The channel  500  is surrounded by an inner wall  502 , an outer wall  504  and a channel floor  506  formed by the surface  52  of shell  40 . The channel  500  is configured in the generally triangular shape of the shell  40  or any other suitable shape and is preferably wide enough that the cushion can be inserted in the channel without rubbing against the side walls of the channel. See  FIG. 9A . The channel  500  includes two slots  508  that pass through the channel floor  506  to allow access to the surface  52  of the shell  40 . 
         [0208]    The mechanism includes a retaining ring  510  configured to have a similar general shape as the channel  500 . The retaining ring  510  has two clips  512  positioned on two respective spring arms  513 . The clips  512  are positioned and configured to pass through the respective slots  508  such that an underside lip  514  of each clip engages the surface  52  or a suitable section on shell  40  when the retaining ring  510  is positioned in the channel  500 . An upper surface  515  of each clip  512  is beveled to provide easier passage through the slot  508  upon assembly. While only two slots  508  and clips  512  are shown, the mechanism may have a different number of such components. The retaining ring  510  has a cushion retaining lip  516  that runs around a periphery of the retaining ring  510  and extends outward from a bottom portion of the retaining ring  510 . 
         [0209]    The cushion  30  includes a retaining channel  520  and a retaining lip  522  extending outward from the channel  520 . The retaining channel  520  and retaining lip  522  are configured to snugly engage the cushion retaining lip  516  of the retaining ring  510  when the cushion  30  is installed on the retaining ring  510 . The cushion  30  also includes a sealing lip  524  that extends from the cushion  30  to engage the channel  500  or other portion of the shell  40  around an entire periphery of the cushion  30  to provide a continuous airtight seal between the cushion  30  and the shell  40 . In the embodiment shown in  FIG. 65 , the sealing lip  524  engages an outer surface of the inner wall  502 , i.e., the surface forming a portion of the channel  500 . In alternative embodiments, the sealing lip  524  may also be configured to sealingly engage a top surface of the inner wall  502  and/or an inner surface of the wall  502 . 
         [0210]    To assemble the cushion  30  to the shell  40 , the cushion is first mounted on the retaining ring  510  by engaging the channel  520  and lip  522  with the retaining lip  526  around the periphery of the lip  526 . This procedure requires some finger strength and dexterity, but it has been found that the required strength and dexterity is less than for assembling the known cushions and shells together. Alternatively, this assembly step can be performed at the factory prior to shipment of the cushion or the cushion  30  can be integrally molded to the retaining ring  510 . Next, the assembled retaining ring/cushion assembly is placed in the channel  500  such that the retaining clips  512  align with their respective slots  508  and the retaining ring/cushion assembly is pressed toward the shell  40  such that the spring arms  513  bend back slightly to allow the clips  512  to pass through the slots  508 . Once the clips  512  clear the slots  508 , the spring arms  513  will spring back, engaging the surfaces  514  of the clips  512  with the surface  52  of the shell  40  and retaining the cushion  30  to the shell  40 . This clamps the lip  522  of the cushion  30  to the channel floor  506  and engages the sealing lip  524  with the inner wall to provide a secure, sealed connection between the cushion  30  and the shell  40 . 
         [0211]    To disassemble the cushion  30  from the shell  40 , the user need only press the two clips  512  toward one another until they are no longer engaging the surface  52  such that the clips  512  can pass back through the slots  508 . In this regard, it is preferable to have only two clips  512  positioned across from one another with a sufficiently small distance therebetween such that the user can grasp both clips  512  between the thumb and forefinger of one hand so that disassembly is a one-handed procedure. In this manner, the cushion/retaining ring assembly can easily be disassembled from the shell  40  for cleaning or other purposes. Although not necessary, the cushion  30  can also be disassembled from the retaining ring  510  for cleaning. 
         [0212]    In a preferred embodiment, the retaining ring is made of acetal, although other materials can be used. Further, the channel  500  and/or retaining ring  510  may be provided with a keyway feature for assisting in the alignment of the retaining ring  510  with the shell  40  upon assembly. 
         [0213]    While subassembly between cushion  30  and retaining ring  510  that engages two parts internally through retaining channel  520  and retaining lip  522  is shown, in alternative embodiments, the retaining ring  510  can be subassembled to cushion  30  externally through outer or top walls of the cushion with suitable channel and lip arrangements. 
         [0214]      FIGS. 68-89  illustrate an alternative embodiment of the mask assembly  10  of the present invention utilizing a single latching mechanism  60  similar to the latching mechanism shown in  FIGS. 62-64 . The mask assembly includes a shell  40  and a cushion  30 . In  FIGS. 72 and 73 , the shell  40  includes a pair of flanges assemblies  44  and  46 . Each flange assembly  44  and  46  includes an integrally molded pivot pin  45 , with the two pivot pins  45  being generally parallel to one another in a preferred embodiment. 
         [0215]    In  FIGS. 79 and 76 , the latching mechanism  60  further includes a clip  88  and a clip link  240 . The clip link  240  includes a first end  500  having a gripping mechanism  502  adapted for fitting over and grasping one of the selected pins  45  to pivotally attach the clip link  240  to the shell  40 . The clip link  240  further includes a second end  504  having a pair of pins  83  for engaging bores  92  in a first end  90  of clip  88  to pivotally attach the clip  88  to the clip link  240 . The pins  83  are mounted on pin arms  85  extending away from a central portion of the clip link  240  to provide a spring action so that they can be flexed toward each other for inserting the pins  83  into the bores  92  of the clip  88 . A spring member  506  interconnects the two pin arms  85  to provide additional spring force to the pin arms  85 , as well as to provide lateral stability to the pin arms  85  to resist twisting of the clip link  240 . The effective spring force on the pin arms  85  can be varied as desired by altering the size and length of the pin arms  85  and/or the size and positioning of the spring member  506 . 
         [0216]    The clip  88  also includes a second end  94  having a mask harness-engaging portion  96  in the form of a transverse slot. The first end  90  includes a locking slot  508 , discussed below, and a lifting member  510  for engagement and lifting by the user to unlatch the latching mechanism  60 . Since the clip link  240  can be mounted on either of the pins  45 , the latching mechanism  60  is reversible on the mask assembly  10  for easy manipulation by either right or left handed users. The latching mechanism  60  operates in the same manner as the embodiment shown in  FIGS. 62-64 , pivoting about the pin  45  when unlatched to an open position that releases tension on the harness. In  FIGS. 68 and 69 , the clip  88  includes can include a pair of opposing ornamental raised portions  512  for providing a smooth, aesthetic transition between the clip  88  and the shell  40 , regardless of whether the latching mechanism  60  is mounted on the left or right side of the shell  40 . 
         [0217]    In  FIGS. 77 and 78 , the latching mechanism  60  also includes a harness engaging clip  470 . The harness engaging portion  470  includes a gripping mechanism  514  adapted for fitting over and grasping the other of the pins  45  to attach the harness engaging clip  470  to the shell  40 . The harness engaging clip  470  also includes a mask harness engaging portion  474  in the form of a transverse slot, a locking tab  516  and a stop tab  518 . In this embodiment, the harness engaging clip  470  is not intended to pivot about the pin  45 . This is accomplished by engagement of the locking tab  516  and stop tab  518  with adjacent surfaces  520  and  522 , respectively, of shell  40  when the clip  470  is mounted over the desired pin  45 . In  FIG. 79 , the harness engaging clip  470  cannot pivot about the pin  45  and must be installed over the pin  45  by use of a generally vertical movement of the clip  470  downward over the pin  45 . The locking tab  516  is adapted to engage and disengage the locking slot  508  of the clip  88 . 
         [0218]    In a preferred embodiment, the locking tab  516  only partially engages the locking slot  508  in the locked position. In this manner, the clip  88  is inhibited from lifting during use, but due to the natural elasticity of the clip  88  and the harness engaging clip  470 , the locking engagement can be overcome without pivoting the harness engaging clip to the up position by applying a direct lifting force to the lifting member  510 . The amount of lifting force needed to overcome the locking engagement can be varied by altering the extent of engagement between the locking tab  516  and the locking slot  508  and/or the rigidity of the clip  88  and/or the clip  470 . The locking tab  516  and a locking engagement surface  524  of the locking slot  508  are angled away from horizontal to allow easier engagement and disengagement of the locking mechanism. 
         [0219]    In an alternative embodiment, the stop tab  518  can be removed and the locking tab  516  reconfigured so as not to engage the shell  40  so that the clip  470  can pivot about pin  45 . With this alternative configuration, the mechanism can also be locked and unlocked by pivoting locking tab  516  and harness engaging clip  470  about the pin  45  between an unlocked up position (away from the user&#39;s face) where the locking tab  516  does not engage the locking slot  508 , and a locked down position (toward the user&#39;s face) where the locking tab  516  does engage the locking slot  508  and inhibits lifting of the clip  88 . In such an embodiment, the harness engaging clip  470  is naturally pulled into the locked down position when the mask assembly  10  is being worn by the tension in the mask harness. In such an embodiment, the locking tab  516  and locking slot  508  can be configured such that the locking engagement cannot be readily overcome unless the harness engaging clip  470  is pivoted to the unlocked up position. In the preferred embodiment, the harness engaging clip  470 , clip  88  and clip link  240  are each unitarily molded from a suitable plastic. 
       Head Support Adjustment Mechanism 
       [0220]    In  FIG. 80 , the mask assembly  10  of this embodiment also includes a head support adjustment mechanism  550  that vertically adjustably mounts a head support  552  to air tube  100  of the shell  40 . The head support adjustment mechanism  550  includes a pair of detent portions  554  connected to opposite exterior sides of the air tube  100  and running axially along the air tube  100 . The detent portions  554  each include a plurality of slots  556  spaced along the detent portions  554  to define locating positions along the air tube  100  with corresponding pairs of slots  556  of the two detent portions  554  being generally positioned at the same height along the air tube  100 . 
         [0221]    The head support adjustment mechanism  550  also includes a loop portion  558  connected to the head support  552  that is adapted to slideably fit over the air tube  100  and detent portions  554 . The fit between the loop portion  558  and the air tube  100  is preferably such that the loop portion  558  can readily slide over the air tube  100  without allowing so much clearance that there is excessive movement and play between the head support  552  and the shell  40  once the head support  552  is adjusted. In  FIG. 83 , to provide the desired fit without too much clearance, the loop portion  558  includes a pair of slot portions  560  to receive the corresponding detent portions  554 . This engagement between the detent portions  554  and the slot portions  560  prevents undesired rotational movement between the loop portion  558 /head support  552  and the air tube  100 /shell  40 . Further, the loop portion  558  includes a plurality of raised ridges  562  running axially along an interior surface  564  of the loop portion  558 . These raised ridges  562  contact the air tube  100  and assist in providing the desired fit between the loop portion  558  and the air tube  100  while reducing the amount of friction causing contact area between the loop portion  558  and the air tube  100  that can prevent easy movement of the loop portion  558  along the air tube  100  during adjustment of the adjustment mechanism  550 . 
         [0222]    In  FIG. 82 , the loop portion  558  includes a transverse slot  566  adapted to receive an adjustment clip  568 . The adjustment clip  568  includes a semi-circular body  570  interconnecting a pair of spring tabs  572 . A split flange projection  574  is mounted to a back side of the semi-circular body  570  for insertion into a bore  576  on a back portion  579  of the loop portion  558  and engagement with an exterior surface  580  of the loop portion  558  to removably mount the adjustment clip  568  to the loop portion  558 . In  FIG. 84 , the transverse slot  566  includes a pair of forward facing shoulders  578  for engaging corresponding outboard rear surfaces  579  of the semi-circular body  570  to stabilize the adjustment clip  568  when it is mounted to the loop portion  558  by means of the projection  574 . Upper and lower surfaces of the transverse slot  566  engage upper and lower surfaces of the adjustment clip  568  to provide vertical stability to the adjustment clip  568 . The clip  568  and loop portion  558  can alternatively be molded as a single unitary component but the two piece construction described is easier to manufacture. In  FIG. 85 , a front side  582  of the semi-circular body  570  is adapted to engage a back side of the air tube  100  to provide stability between the air tube  100  and the adjustment clip  568 /loop portion  558 . 
         [0223]    In  FIG. 82 , each of the spring tabs  572  includes a grasping portion  586  positioned rearward of the body  570  and a detent engagement portion  584  positioned forward of the body  570 . In this manner, the body  570  acts as a fulcrum to each spring tab  572  such that when the grasping portions  586  are grasped by the user and pressed together, the detent engagement portions  584  move apart. When the grasping portions  586  are released, the natural spring action of the clip  568  moves the detent engagement portions  584  closer together. The body  570  can be thinned at its outboard edges  581  to increase the flexibility of the spring tabs  572  with respect to the body  570 . When the adjustment clip  568  is mounted to the loop portion  558 , the grasping portions  586  are positioned outside of the loop portion  558  for manipulation by the user while the detent engagements portions are positioned in the transverse slot  566 . 
         [0224]    Each grasping portion  586  includes a spring arm  588  mounted thereto for engaging an exterior surface of the loop portion  558  to assist in spring biasing the grasping portions  586  away from each other and the detent engagement portions  584  toward each other. Each detent engagement portion  584  includes an engagement tab  590  sized and adapted to engage corresponding slots  556  of the detent portions  554  to vertically lock the loop portion  558 /head support  552  with respect to the air tube  100 /shell  40 . The positioning of the loop portion  558 /head support  552  can be adjusted with respect to the air tube  100 /shell  40  by squeezing together the grasping portions  586  to release the engagement tabs  590  from the slot  556 , moving the loop portion  558  to the desired position on the air tube  100  and releasing the grasping portions  586  so that the engagement tabs engage the corresponding slots  556  of the detent portions  554 . In the embodiment shown, there are four sets of slots  556 , and thus, four vertical positions to which the loop portion  558  can be adjusted with respect to the air tube  100 . The number of slots can be altered to provide an alternative number of adjustment positions. 
         [0225]    In  FIG. 81 , the head support  552  includes a plurality of slots  592  or other engagement mechanisms for attaching the head support  552  to a corresponding mask harness and a loop portion  553  for engaging the patient&#39;s head and stabilizing the head support  552 . Although not shown, the head support  552 , especially the loop portion  553 , and other components of the mask  10  may be covered in foam, fabric or other soft material to provide a cushioned and more comfortable fit for the patient. 
         [0226]    Although the air tube  100  is shown as being aligned generally parallel with a plane of the shell  40 , the air tube  100  can be angled backward somewhat toward the user to provide a better alignment for connection to an air supply conduit. It has been found with this embodiment, angling the air tube  100  back by up to 18°, and preferably by about 10°, provides a desired alignment with the air supply conduit and a comfortable fit for the user. Other angles can also be used as the situation warrants. 
       Exhalation Port 
       [0227]    In  FIG. 73 , the shell  40  includes a single exhalation port  106  positioned centrally outboard of the intake port  102 . Unlike the embodiment shown in  FIG. 9B , in this embodiment, there is no exhalation duct, as the exhalation passage in the shell  40  is only as long as the thickness of the shell. An exterior of the exhalation port  106  is directed upwardly and partially surrounding the air tube  100 . See  FIG. 68 . Although the exhalation port  106  can be used alone if sized properly for a desired flow rate, it is preferred that it be used in conjunction with an additional exhalation vent  600  as depicted in  FIGS. 86 and 87  or in  FIG. 80  showing the vent  600  installed on the shell  40 . The vent  600  is generally flexible and preferably molded of silicone, although other materials can be used. 
         [0228]    The vent  600  includes a body  602  having an upper surface  604  and a lower surface  606 . The body  602  includes a generally semi-circular cutaway  608  configured and sized to receive and grip the air tube  100  to secure the vent  600  to the shell  40 . The semi-circular cutaway  608  includes a pair of axially extending slots  610  configured to receive the two detent portion  554  and provide additional gripping force between the vent  600  and the air tube  100 . The body  602  also includes a pair of tapered raised wings  612  positioned at outboard ends of the semi-circular cutaway  608  to contact the air tube  100  to provide additional gripping force and an aesthetic transition between the air tube  100  and the shell  40 . When installed on the shell  40 , the lower surface  606  is adapted to sit on an upwardly facing vent platform  614  of the shell  40 . 
         [0229]    A baffle  620  is connected to and extends downwardly from the lower surface  606  of the vent  600 . The baffle  620  extends into the exhalation port  106  and the interior of the shell  40  to assist in keeping intake and exhaust flows in the mask separate. This reduces cyclic noise and improves the removal of exhaust gas from the mask. The baffle  620  includes an axially extending rib  622  that adds rigidity and strength to the baffle  620 . The baffle  620  is shown as having a generally semi-circular cross-section with flat outboard portions but the configuration can be altered as desired for different flow characteristics. In  FIG. 86 , a flange  624 , spaced apart from the baffle  620 , also is connected to and extends downwardly from the lower surface  606  of the vent  600 . The flange  624  and baffle  620  are configured to contact the interior sides of the exhalation port  106  to correctly position the vent  600  with respect to the shell  40  and exhalation port  106 , as well as to help secure the vent  600  to the shell  40 . 
         [0230]    A plurality of vent apertures  626  are positioned between the baffle  620  and the flange  624  for venting the exhalation gases to the atmosphere. The number of vent apertures  626 , and their size and configuration can be altered as desired to achieve different flow properties. However, in a preferred embodiment shown, there are six apertures  626  that each taper along at least a portion of their length from an interior side to an exterior side of the vent  600 . That is, the interior side of the vent apertures  626  is larger than the exterior side of the apertures  626 . Such a configuration helps reduce noise generated by the exhalation flow. 
         [0231]    The length of each vent aperture  626  can affect the flow characteristics of the aperture and is determined by the thickness of the vent body  602  in the region of the vent apertures  626 . In order to reduce the length of the vent apertures  626  to a preferred 3.6 mm, the vent body  602  includes a recess  628  on the upper surface  604  of the vent body  602  surrounding the vent apertures  626  that reduces the thickness of the vent body  602  in the region of the vent apertures  626 . The recess  628  can have other configurations and be positioned on the lower surface  606  of the vent body  602  or even be positioned on both upper and lower surfaces of the vent body  602 . The length of the vent apertures  626  can be altered as desired by using one or more recesses on either side of the vent body  602  to vary the thickness of the vent body  602  in the region of the vent apertures  626 . The overall thickness of the vent body  602  can also be altered as desired to affect the length of the vent apertures, but a certain minimum thickness is generally preferred to provide the necessary rigidity to the vent  600  to remain in the desired position on the shell  40 . Thus, the use of a recess allows the overall vent thickness to meet the desired minimum thickness while still providing a desired vent aperture length. The configuration of the recess can also be altered to operate in conjunction with the vent apertures  626  to provide different flow characteristics to the vent  600 . Other recesses  630  can also be positioned elsewhere on the vent body  602  where the rigidity of the vent  600  is less critical to reduce the amount of material needed to mold the vent  600 . 
       Cushion/Shell Connection Mechanism 
       [0232]    The mask assembly of this embodiment uses a cushion/shell connection mechanism similar to the mechanism shown in  FIG. 65 . See especially,  FIGS. 68 ,  73 ,  88  and  89 . In  FIG. 73 , the shell  40  includes a channel  500  running around a cushion side periphery. The channel  500  is surrounded by an inner wall  502 , an outer wall  504  and a channel floor  506  formed by the surface  52  of shell  40 . The channel  500  is configured in the generally triangular shape of the shell  40 . The channel  500  includes two slots  508  that pass through the channel floor  506  to allow access to the surface  52  of the shell  40  and a third slot  509  in the outer wall  504  at the bottom of the triangle. The third slot  509  extends through the outer wall  504  of the channel  500  generally at an angle of 90° to the slots  508 . 
         [0233]    In  FIGS. 74 and 69 , the mechanism includes a retaining ring  510  configured to have a similar general shape as the channel  500 . The retaining ring  510  has two clips  512  positioned on two respective spring arms  513 . The clips  512  are positioned and configured to pass through the respective slots  508  such that an underside lip  514  of each clip  512  engages the surface  52  when the retaining ring  510  is positioned in the channel  500 . In  FIG. 88 , an upper surface  515  of each clip  512  is beveled to provide easier passage through the slot  508 . The retaining ring  510  also includes a retaining tab  511  positioned on the remaining third side of the retaining ring  510  that does not include a clip  512 . The retaining tab  511  extends outward from the retaining ring  510 , generally in a plane at 90° to the planes in which the clips  512  generally extend. The retaining tab  511  is adapted to engage the retaining slot  508 . 
         [0234]    In  FIG. 88 , the retaining ring  510  includes a lower retaining lip  640 , an upper retaining lip  642  and a channel  644  positioned therebetween, all generally running around a periphery of the retaining ring  510 . Notches  646  on the sides of each clip  512  cut through the upper lip  642  and into the channel  644  to increase the flexibility of the clips  512 . 
         [0235]    In  FIG. 89 , the cushion  30  includes a retaining channel  520  and a retaining lip  522  extending outward from the channel  520 . The retaining channel  520  is configured to snugly engage the lower retaining lip  640  of the retaining ring  510  and the retaining lip  522  is configured to snugly engage the retaining ring channel  644  between the lower lip  640  and the upper lip  642  when the cushion  30  is installed on the retaining ring  510 . The cushion  30  also includes a pair of sealing lips  524  that extend from the cushion  30  to engage the inner wall  502  of the channel  500  around an entire inner periphery of the cushion  30  to provide a continuous airtight seal between the cushion  30  and the shell  40 . The sealing lips  524  are flexible to assure a sealing contact with the shell  40 . The sealing lips  524  are shown in the position they would assume when the cushion  30  is mounted to the shell but would return to a relaxed state when the cushion  30  is disassembled from the shell  40 . This deformation of the flexible sealing lips  524  also applies a tension to the cushion/retaining ring/retaining clips when installed to help maintain a secure connection between the connection mechanism and the shell  40 . One or more sealing lips  524  may be employed. 
         [0236]    This embodiment does not clamp a portion of the cushion  30  between the retaining ring  510  and the channel floor  506 , as does the embodiment shown in  FIG. 65 , but relies only on the contact between the sealing lips  524  and the shell  40  to provide an airtight seal between the cushion  30  and the shell  40 . In this embodiment, the retaining ring/cushion assembly is positioned at an angle in the channel  500  with the bottom side of the triangle in the channel  500  and the top two sides of the triangle pivoted slightly out of the channel  500  so that the retaining tab  511  can engage the retaining slot  508 . Then, the retaining ring/cushion assembly  510  is pivoted upward toward the shell  40  so that the remaining portions of the retaining ring move into the channel  500  and the clips  512  engage the slots  508  to lock the retaining ring  510  into place with respect to the shell  40 . In this manner, the retaining tab  511  and retaining slot  508  provide additional clamping force between the retaining ring  510  and shell  40  at the bottom side of the retaining ring  510 , as compared to the embodiment shown in  FIG. 65 . Disassembly is performed by squeezing the clips  512  together, as in the embodiment shown in  FIG. 65 , and pivoting the retaining ring  510  out of the channel  500  until the retaining tab  511  can be disengaged from the retaining slot  509  and the retaining ring/cushion assembly can be completely disengaged from the shell  40 . 
         [0237]    In  FIG. 92 , the shell  40  also includes a pair of spaced apart, downwardly projecting access ports  118 , as described above, positioned in a recess  592  located at a bottom portion of the shell  40 . 
         [0238]      FIGS. 90A-90D  illustrate multiple views of retaining ring  6010  in an alternate embodiment of the present invention. As shown in the front view of  FIG. 90C , the retaining ring  6010  is of a generally triangular shape and includes two (2) clip portions  6012  and a retaining tab  6013 . The retaining ring  6010  has a base  6014  and two sides  6016 . Shapes other than the generally triangular shape depicted in  FIG. 90C  may be used, as well as a number of sides  6016  other than two. 
         [0239]    As illustrated in  FIGS. 90B and 90D , clip portion  6012  extends out from the retaining ring  6010 . The clip portions  6012  may be adapted to resiliently flex outwardly or inwardly in the direction of arrows  6020  or  6022  respectively.  FIG. 90B  shows the retaining ring  6010  along the reference line  90 A- 90 B of  FIG. 90C .  FIG. 90D  shows a right side view of the retaining ring  6010 .  FIG. 90A  shows the retaining ring  6010  along the reference line  90 A- 90 A of  FIG. 90C . 
         [0240]      FIGS. 91A-90C  illustrate multiple isometric view of the retaining ring  6010 . In  FIG. 91A , retaining ring  6010  has a frontwardly projecting wall  7004  with an outer surface  7006  and an inner surface  7008 . In the underside, isometric view of  FIG. 91B , the clip portion  6012  includes a ribbed surface to provide a gripping surface for the finger of the user.  FIG. 91C  shows an enlarged detail view of the ribbed surface of clip portion  6012 . 
         [0241]      FIG. 92  shows a detailed view of the clip portion  6012 . Clip portion  6012  may protrude from the retaining ring at an angle in a range between 77°-97°, preferably 87°. 
         [0242]      FIG. 93  shows the underside view of the retaining ring  6010  having two clip portions  6012 , a retaining tab  6013  and a radius of curvature in a range of 94.00 mm-114.00 mm, preferably 104.00 mm. 
         [0243]      FIGS. 94A and 94B  show the top and back views, respectively, of the retaining ring  6010  having clip portions  6012  and retaining tab  6013 . 
         [0244]      FIG. 95  shows a perspective view of a cushion  7402  along the reference line  95 - 95  of  FIG. 98A  and having a radius of curvature in a range between 88°-108°, preferably 98°. 
         [0245]      FIG. 96  shows a side perspective view of the cushion  7402  along the reference line  96 - 96  of  FIG. 98A . 
         [0246]      FIGS. 97A and 97B  show a side and underside view, respectively of the cushion  7402 . 
         [0247]      FIG. 98A  shows the cushion  7402  having gusset portions  7404 .  FIG. 98B  shows a detailed view of the gusset portions  7404  along the reference line  98 B- 98 B of  FIG. 98A . 
         [0248]      FIGS. 99A and 99B  show front and side views of the cushion  7402  having a thickness in the range 42.0 mm-62.0 mm, preferably 52.0 mm. 
         [0249]      FIG. 100  shows a sectional view of the cushion  7402  and clip portion  6012 . 
         [0250]      FIG. 101  shows an exploded side view of an alternate embodiment of the mask assembly of the present invention. The mask assembly  8001  has a cushion  8000 , a retaining ring  8002  and shell  8004 . The cushion  8000 , having a seal-forming membrane  8006  and gusset portion  8008  is assembled around the retaining ring  8002  by engaging the flange portions  8016  and  8032  of the retaining ring  8022  into a shoulder portion  8010  of the cushion  8000 . The cushion and retaining ring assembly is inserted into the shell  8004  by inserting the clip portions  8012  into the slot portions  8020  of the shell  8004  to engage an underside of the shell  8004 . The slot portions  8020  are located in the inner wall of the shell  8004 . There is one slot portion  8020  and clip portion  8012  depicted in  FIG. 101 ; however more than one clip portion and slot portion may be used. 
         [0251]      FIG. 102  shows a front view of the cushion and ring assembly  8100  of the embodiment of  FIG. 101  having two clip portions  8012  and retaining tab  8013 .  FIG. 103  shows an exploded sectional view of the cushion and ring assembly  8100  of  FIG. 102  along the reference line  103 - 103 . 
         [0252]      FIG. 104  shows a side cross-sectional view of the shell  8004  of  FIG. 101 . In  FIG. 104 , shell  8004  has an inner wall  8022  and outer wall  8034  such that a clip portion  8012  of the cushion and retaining ring assembly may be received through the slot  8020  between the inner wall  8022  and the outer wall  8034 . 
         [0253]      FIG. 105  shows a rear view of the shell  8004  of  FIGS. 101 and 104  in which a channel  8036  is located between the outer wall  8034  and the inner wall  8022  of the shell  8004 . The shell  8004  has three slot portions  8020  to receive the clip portions and retaining tab from the cushion and retaining ring assembly. 
         [0254]      FIG. 106  shows a front view of the shell  8004  having three slots  8022  and a reference line  107 - 107 .  FIG. 107  shows a sectional view of the cushion and retaining ring assembly and shell along the reference line  107 - 107  of  FIG. 106 . 
         [0255]      FIG. 108  shows a side view of the mask assembly  8001  of  FIG. 101 .  FIGS. 109 and 110  show cross sections of the upper and lower clip portions  8012  having a flange portion  8040 . In  FIG. 108 , the mask assembly  8001  includes the fully assembled cushion and retaining ring assembly inserted into the shell, as well as the head mount portion  8701  and air inlet section  8705 . The head mount portion  8701  includes a mechanism  8703  to stabilize the mask assembly on the user. 
         [0256]      FIGS. 100-103  show cross-sectional views of the cushion and ring assembly inserted in the inner wall of the shell. The clip portion  8012  of the cushion and retaining ring are secured to the shell by the seal forming portion  8006 .  FIG. 111  shows the cushion and retaining ring assembly inserted in the shell along the reference line  111 - 111  in  FIG. 102 .  FIG. 112  shows the cushion and ring assembly inserted in the shell along the reference line  112 - 112  in  FIG. 102 . FIG.  113  shows the cushion and ring assembly inserted in the shell along the reference line  113 - 113  in  FIG. 102 . 
         [0257]    In  FIGS. 109 and 112 , the flange portion  8040  of the upper clips  8012  has an undercut to improve retention in the frame or shell. In contrast, the flange portion of the lower clip  8012  of  FIGS. 110 and 113  has an angled profile to permit easy disassembly. 
         [0258]    It is intended that the components, elements and features of the various above-described embodiments can be used together in any desired combination or permutation to create new mask embodiments. For example, while the invention has been described in relation to a nasal mask, the teachings are also applicable to nasal/oral masks as well.