Patent Publication Number: US-2020282169-A1

Title: Frame and headgear for respiratory mask system

Description:
BACKGROUND 
     Technical Field 
     The present disclosure generally relates to a respiratory mask system for the delivery of respiratory therapy to a patient. More particularly, the present disclosure relates to various components of a respiratory mask system. 
     Description of the Related Art 
     Respiratory masks are used to provide respiratory therapy to the airways of a person suffering from any of a number of respiratory illnesses or conditions. Such therapies may include but are not limited to continuous positive airway pressure (CPAP) therapy and non-invasive ventilation (NIV) therapy. 
     CPAP therapy can be used to treat obstructive sleep apnea (OSA), which is a condition in which a patient&#39;s airway intermittently collapses, during sleep, preventing the patient from breathing for a period of time. The cessation of breathing, or apnea, results in the patient awakening. Repetitive and frequent apneas may result in the patient rarely achieving a full and restorative night&#39;s sleep. 
     CPAP therapy involves the delivery of a supply of continuous positive air pressure to the airway of the patient via a respiratory mask. The continuous positive pressure acts as a splint within the patient&#39;s airway, which secures the airway in an open position such that the patient&#39;s breathing and sleep are not interrupted. 
     Respiratory masks typically comprise a patient interface and a headgear, wherein the patient interface is configured to deliver the supply of continuous positive air pressure to the patient&#39;s airway via a seal or cushion that forms a substantially airtight seal in or around the patient&#39;s nose and/or mouth. Respiratory masks are available in a range of styles including full-face, nasal, direct nasal and oral masks, which create a substantially airtight seal with the nose and/or mouth. The seal or cushion is held in place on the patient&#39;s face by the headgear. In order to maintain a substantially airtight seal the headgear should provide support to the patient interface such that it is held in a stable position relative to the patient&#39;s face during use. Such respiratory masks may also be used to deliver NIV and other therapies. 
     BRIEF SUMMARY 
     In a first aspect, an embodiment of the invention may broadly be said to comprise a headgear for a respiratory mask comprising an integrally formed closed loop. The closed loop comprises a yoke, a pair of side arms, and a top strap. The yoke is configured to connect to a patient interface. The pair of side arms are each configured to extend from a lateral rearward portion of the yoke, and in use, across a cheek and above an ear of a user. The top strap is configured to extend between the pair of side arms, and in use, across the top of the user&#39;s head. 
     Preferably the top strap comprises separate left and right portions, each having a free end and a fixed end. The fixed end of the left portion is integrally formed with one of the side arms and the fixed end of the right portion is integrally formed with the other side arm. The free ends of the left and right portions are adjustably connected to each other. 
     Preferably the closed loop is made of a semi-rigid material. 
     Preferably comprises a plastic material. 
     Preferably the side arms comprise an integrally formed buckle at a free end. 
     Preferably the headgear further comprising a rear strap configured to extend between the buckles of the side arms and, in use, around the rear of the user&#39;s head. 
     Preferably the rear strap comprises a pair of lateral ends that are each adjustably connected to the buckles of the side arms. 
     Preferably the rear strap is removably connected to the buckles. 
     Preferably the rear strap and top strap are configured, in use, to encircle a rear portion of a user&#39;s head. 
     In a second aspect, an embodiment of the invention may broadly be said to comprise a respiratory mask comprising a patient interface and a headgear as described above. 
     In a third aspect, an embodiment of the invention may broadly be said to comprise headgear for a respiratory mask comprising an integrally formed closed loop and a rear strap. The closed loop comprises a yoke, a pair of side arms and a top strap. The yoke is configured to connect to a patient interface. The side arms are each configured to extend from a lateral rearward portion of the yoke, and in use, across a cheek and above an ear of a user. In use, the top strap is configured to extend across the top of the user&#39;s head joining the pair of side arms. The rear strap is configured to extend between the pair of side arms around the rear of the user&#39;s head. 
     In a fourth aspect, an embodiment of the invention may broadly be said to comprise a headgear for a respiratory mask comprising a yoke, a pair of opposing side arms and a top strap. The yoke is configured to connect to a frame of the respiratory mask. The pair of opposing side arms is configured in use to extend from a pair of lateral rearward portions of the yoke, and in use, across the user&#39;s cheeks and above the top of the user&#39;s ears. The top strap is configured, in use, to extend between the side arms above the user&#39;s ears, over the top of the user&#39;s head. The yoke, side arms and top strap are integrally formed to provide a closed loop, which remains intact when the yoke is separated from the frame. 
     In some embodiments, a frame for a respiratory mask includes a body having an exterior surface and an interior surface. The exterior surface includes a yoke receiving structure configured to receive a yoke and an inlet collar defining and inlet. The yoke receiving structure can span the longitudinal distance of the body. The interior surface includes an outlet collar defining an outlet. A gas pathway is formed between the inlet and the outlet. The perimeter of the gas pathway at the inlet is less than the perimeter of the gas pathway at the outlet. 
     The inlet collar can include a portion of increasing perimeter. The inlet can have an oval shape. The outlet can have an oval shape. The outlet collar can include a truncated portion. A portion of the outlet collar can be longer than another portion of the outlet collar. The outlet collar can include a recessed portion extending partially around the outlet collar. 
     In some embodiments, a frame for a respiratory mask includes a body having an exterior surface and an interior surface. The exterior surface includes a yoke receiving structure configured to receive a yoke and an inlet collar defining an inlet. The yoke receiving structure can span the longitudinal distance of the body. The inlet collar includes a transition portion of increasing perimeter. The interior surface includes an outlet collar defining an outlet. A gas pathway is formed between the inlet and the outlet. The inlet collar includes a vent that allows the passage of gas from the gas pathway to an exterior of the frame. 
     The inlet collar can include a first portion of a first perimeter, and a second portion of a second perimeter coaxially offset from said first portion. The first portion and second portion can be separated by the transition portion of increasing perimeter, and the transition portion can link the first and second portions. The second perimeter can be greater than the first perimeter. The second portion can be located adjacent to the exterior surface of the frame. The transition portion can include the vent. The vent can include a plurality of holes. 
     In some embodiments, a frame for a respiratory mask includes a body having an exterior surface and an interior surface. The exterior surface includes a yoke receiving structure configured to receive a yoke and an inlet collar defining an inlet. The yoke receiving structure can be defined between a first retaining ridge and a second retaining ridge vertically displaced from the first retaining ridge forming a recessed channel configured to receive a yoke. The interior surface can include an outlet collar defining an outlet. A gas pathway can be formed between the inlet and the outlet. 
     In some embodiments, a frame for a respiratory mask includes a body, an inlet collar, and an outlet collar. The body has an exterior surface and an interior surface and extends from a first lateral edge to a second lateral edge. The inlet collar extends from the exterior surface, defines an aperture, and is configured to be coupled to a gas conduit in use. The outlet collar extends from the interior surface. The body comprises a first headgear retaining feature positioned laterally at least partially between the inlet collar and the first lateral edge and a second headgear retaining feature positioned laterally at least partially between the inlet collar and the second lateral edge. 
     The frame and headgear retaining features can be configured such that the first headgear retaining feature can be engaged with a corresponding first frame retaining feature on a headgear and then the frame and headgear can be rotated relative to each other about the headgear retaining feature to align the second headgear retaining feature with a corresponding second frame retaining feature on the headgear. The centers of the first and second headgear retaining features can be vertically displaced relative to a central axis extending through the aperture of the inlet collar. The first and second headgear retaining features can be circular holes. 
     In some embodiments, a frame for a respiratory mask includes a body having an exterior surface and an interior surface and extending from a first lateral edge to a second lateral edge; an aperture configured to receive gases from a gas delivery conduit in use; and a plurality of bias flow holes disposed about a portion of the frame surrounding the aperture and forming an arc extending approximately 240°. 
     The bias flow holes can extend from approximately 4:00 to approximately 8:00 (as on a clock). The frame can further include an inlet collar extending from the exterior surface, the inlet collar comprising a wall defining the aperture and configured to be coupled to a gas conduit in use, the inlet collar comprising the plurality of bias flow holes extending through the wall. The inlet collar can have an oval cross-section. The wall of the inlet collar can angle inwardly at an inlet collar surface angle relative to an axis extending through the aperture as the wall extends away from the frame body. The inlet collar surface angle can vary about a periphery of the inlet collar. 
     In some embodiments, a frame for a respiratory mask includes a body having an exterior distal-facing surface and an interior proximal-facing surface; and an inlet collar extending distally from the exterior surface to a distal rim, the inlet collar comprising a wall defining an aperture and configured to be coupled to a gas conduit in use, wherein a top and bottom of the distal rim project distally relative to lateral sides of the distal rim. The inlet collar can have an oval cross-sectional shape. 
     In some embodiments, a headgear for a respiratory mask includes a yoke configured to connect to a patient interface, first and second side arms, a top strap, and at least one connector configured to connect to a frame in use. Each of the first and second side arms extends from a lateral rearward portion of the yoke and is configured to extend across a cheek and above an ear of a user in use. The top strap is coupled to and extends between the first and second side arms and is configured to extend across the top of the user&#39;s head in use. At least one of the yoke, first and second side arms, and top strap comprises a plastic core and a textile outer casing at least partially surrounding the plastic core, wherein the at least one of the yoke, first and second side arms, and top strap is formed by intramolding, and wherein the at least one connector is formed by a burst-through process such that the at least one connector is integrally formed with the plastic core and extends outside of the outer casing. 
     The connector can include a channel separating two retaining portions. The connector can be generally circular. The headgear can include two connectors, each configured to engage a corresponding headgear retaining feature on a frame, wherein the headgear and connectors are configured such that a first of the two connectors can be engaged with a corresponding first headgear retaining feature on the frame and then the frame and headgear can be rotated relative to each other about the connector to align a second of the two connectors with a corresponding second headgear retaining feature on the frame. 
     In some embodiments, a headgear for a respiratory mask includes a yoke configured to connect to a patient interface, first and second side arms, and a top strap. Each of the first and second side arms extends from a lateral rearward portion of the yoke and is configured to extend across a cheek and above an ear of a user in use. The top strap is coupled to and extends between the first and second side arms and is configured to extend across the top of the user&#39;s head in use. The top strap includes a first portion coupled to the first side arm, a second portion coupled to the second side arm, and an adjustment mechanism configured to couple and allow for adjustment between the first and second portions. The adjustment mechanism includes a guide loop at a free end of the second portion; a plurality of holes along a length of the second portion proximate the free end; a projection extending from an inner surface of the first portion, the inner surface configured to face and at least partially overlie the second portion when the first and second portions are coupled in use, wherein the projection is configured to engage any one of the plurality of holes to secure the first and second portions together; and a plurality of location guides extending along a length of the first portion proximate the projection, the location guides comprising a series of protruding edges having a width greater than a diameter of an aperture defined by the guide loop. In use, the first portion is configured to be advanced and/or withdrawn through the guide loop, and contact between the protruding edges and guide loop provides a resistive force to movement of the first portion through the guide loop. 
     The top strap can include a plastic core and a textile outer casing at least partially surrounding the plastic core, wherein the second portion comprises a surrounding channel extending around at least one of the plurality of holes and wherein the outer casing does not surround the surrounding channel. The projection can include a post extending from and adjacent the inner surface of the first portion and an enlarged head at an end of the post, the enlarged head having a larger diameter than a diameter of the post. 
     In some embodiments, a headgear for a respiratory mask includes a strap including a yoke portion and first and second side arms, and a top strap. The yoke portion is configured to connect to a patient interface. Each of the first and second side arms extends from a lateral rearward portion of the yoke portion and is configured to extend across a cheek and above an ear of a user in use. The yoke portion and the first and second side arms can be integrally formed. The top strap is coupled to and extends between the first and second side arms and is configured to extend across the top of the user&#39;s head in use. A first edge of the strap comprises a soft edge and a second, opposite edge of the strap comprises a soft edge portion and a rigid edge portion. 
     A thickness of the soft edge of the first edge can vary between a maximum thickness at a lateral end of the side arms and a minimum thickness proximate a central point of the yoke portion. A thickness of the soft edge portion of the second edge can vary between a maximum thickness at a lateral end of the side arms and a minimum thickness at a point laterally spaced from a center of the yoke portion. 
     In some embodiments, a headgear for a respiratory mask includes a front strap and a top strap. The front strap includes a yoke configured to connect to a patient interface and first and second side arm portions, each of the first and second side arm portions extending from a lateral end of the yoke and configured to extend across a cheek and above an ear of a user in use. The top strap is coupled to and extends between the first and second side arm portions and is configured to extend across the top of the user&#39;s head in use. The top strap includes a first portion coupled to the first side arm portion, a second portion coupled to the second side arm portion, and an adjustment mechanism configured to couple and allow for adjustment between the first and second portions. At least one of the yoke, first and second side arm portions, and top strap includes a plastic core and a textile outer casing at least partially surrounding the plastic core, wherein the at least one of the yoke, first and second side arm portions, and top strap is formed by intramolding. 
     The adjustment mechanism can include a female connector at a free end of the second portion and a male connector at a free end of the first portion, the female connector comprising a guide loop and a plurality of holes along a length of the female connector, and the male connector comprising a projection extending from an inner surface of the male connector, the inner surface configured to face and at least partially overlie the female connector when the first and second portions are coupled in use, wherein the projection is configured to engage any one of the plurality of holes to secure the first and second portions together. In use, the first portion is configured to be advanced and/or withdrawn through the guide loop. 
     The female connector can be over-molded onto the second portion. The male connector can be over-molded onto the first portion. The male connector can include a grip on or in an outer surface of the male connector. The male connector can include a grip on or in the inner surface of the male connector. The first portion of the top strap can be coupled to the first side arm portion via an over-molded joint. The second portion of the top strap can be coupled to the second side arm portion via an over-molded joint. The headgear can further include a buckle at a lateral end of each of the first and second side arm portions, each of the buckles configured to receive an end of a rear strap. The buckles can be over-molded onto lateral ends of the first and second side arm portions. The yoke can include two frame retaining features, each configured to engage a corresponding headgear retaining feature on a frame. The frame retaining features can be horse-shoe shaped. The front strap can include a pad surrounding and extending laterally outward from each of the frame retaining features, the pads having a greater thickness than a remainder of the front strap. 
     In some embodiments, a respiratory mask assembly includes a headgear, a frame, and a headgear connector. The headgear is configured to secure the mask assembly to a user&#39;s face in use. The frame has a body extending along a longitudinal axis, a top, a bottom, and two sides. The headgear connector is coupled to the headgear and configured to be coupled to the frame by approaching the frame from one of the top or the bottom. 
     The headgear connector can be permanently coupled to the headgear. The headgear connector can include at least one locking protrusion, the frame can include at least one recessed portion, and the at least one locking protrusion can be configured to be received in the at least one recessed portion when the headgear connector is coupled to the frame. The frame can also include at least one scalloped portion positioned proximate the at least one recessed portion. The scalloped portion can be positioned above the corresponding recessed portion. The at least one scalloped portion can be configured to act as a lead-in for the at least one locking protrusion into the at least one recessed portion. The at least one scalloped portion can be separated from the at least one recessed portion by a ridge. A barrier can be configured to inhibit or prevent coupling of the headgear connector when approaching the frame from the other (incorrect one) of the top or the bottom. 
     In some embodiments, the headgear includes a yoke, first and second side arms, and a top strap. Each of the first and second side arms extends from a lateral portion of the yoke and is configured to extend across a cheek and above an ear of the user in use. The top strap is coupled to and extends between the first and second side arms and is configured to extend across the top of the user&#39;s head in use. The headgear connector is coupled to the yoke. The yoke can extend across a front surface of the headgear connector from a first lateral end of the headgear connector to a second, opposite lateral end of the headgear connector. 
     In some embodiments, a respiratory mask assembly includes a headgear, a frame, and a connector. The headgear is configured to secure the mask assembly to a user&#39;s face in use. The frame extends in a first direction from an inlet to an outlet. A longitudinal axis of the frame and a flow path through the frame extend from the inlet to the outlet. The frame extends in a second direction perpendicular to the first direction from a first lateral edge to a second lateral edge. The frame extends in a third direction perpendicular to the first and second directions from a top to a bottom. The connector is coupled to the headgear and configured to be coupled to the frame by approaching the frame along the third direction from the top or bottom. 
     In some embodiments, a respiratory mask assembly includes a headgear, a frame, and a connector. The headgear is configured to secure the mask assembly to a user&#39;s face in use. The frame has an inlet at a front end of the frame, an outlet at a rear end of the frame, a flow path extending through the frame from the inlet to the outlet, a top surface, a bottom surface, and side surfaces. The connector is coupled to the headgear and configured to be coupled to the frame. The connector has lateral portions configured to extend along the side surfaces of the frame and a cross portion extending between the lateral portions and configured to extend along one of the top or bottom surface of the frame when the connector is coupled to the frame. 
     The connector can be permanently coupled to the headgear. The connector can include at least one locking protrusion, the frame can include at least one recessed portion, and the at least one locking protrusion can be configured to be received in the at least one recessed portion when the connector is coupled to the frame. The frame can include at least one scalloped portion positioned proximate and above the at least one recessed portion. The scalloped portion can act as a lead-in for the at least one locking protrusion into the at least one recessed portion. The at least one scalloped portion can be separated from the at least one recessed portion by a ridge. A barrier can be configured to inhibit or prevent coupling of the connector when a user attempts to have the connector extend along the other (incorrect one) of the top or the bottom surface of the frame. 
     In some embodiments, the headgear includes a yoke, first and second side arms, and a top strap. Each of the first and second side arms extends from a lateral portion of the yoke and is configured to extend across a cheek and above an ear of the user in use. The top strap is coupled to and extending between the first and second side arms and configured to extend across the top of the user&#39;s head in use. The connector is coupled to the yoke. The yoke can extend across a front surface of the connector from a first lateral end of the connector to a second, opposite lateral end of the connector. 
     In some embodiments, a frame for a respiratory mask assembly includes a body and a compliant engagement portion. The body includes an inlet end defining an inlet aperture, an outlet end defining an outlet aperture, and a flow path extending through the body from the inlet aperture to the outlet aperture. The compliant engagement portion is disposed on the body and configured to be engaged by a cushion module configured to be coupled to the body. The compliant engagement portion can be configured to compress as the cushion module is coupled to the body. Compression of the compliant engagement portion creates an interference fit between the patient interface and the frame. In the illustrated configuration, the interference fit is a friction fit that frictionally connects the compressed compliant portion and the patient interface. 
     In some embodiments, the cushion module includes a coupling structure configured to be coupled to the body such that the coupling structure engages the compliant engagement portion. The coupling structure can include a first portion having a first inner dimension and a second portion having a second inner dimension that is different from the first inner dimension. The first inner dimension can be an inner perimeter of the first portion. The second inner dimension can be an inner perimeter of the second portion. The coupling structure can include a transition portion between the first portion and the second portion. The second inner dimension can be greater than the first inner dimension. When the coupling structure is coupled to the body, the compliant engagement member can engage the second portion and/or the transition portion of the coupling structure. An interference between the compliant engagement member and the coupling structure can be lower when the coupling structure is in a final connected position on the body than during connection of the coupling structure to the body. The coupling structure can be in the form of a clip. 
     In some embodiments, a frame for a respiratory mask assembly includes a body and a flange. The body includes an inlet end defining an inlet aperture, an outlet end defining an outlet aperture, and a flow path extending through the body from the inlet aperture to the outlet aperture. The flange extends outwardly from a mid-section of the body and extends at least partially circumferentially around the body. In some embodiments, a respiratory mask assembly includes the frame and a headgear configured to secure the mask assembly to a user&#39;s face in use. The headgear is configured to be coupled to the frame such that the headgear contacts a front surface of the flange. In some embodiments, a respiratory mask assembly includes the frame and a cushion module including a seal configured to seal on the user&#39;s face in use. The cushion module is configured to be coupled to the frame such that the cushion module contacts a rear surface of the flange. 
     In some embodiments, a headgear for a respiratory mask assembly includes a body portion and one or more connecting portions. The body portion defines a surface and includes a plastic core portion and an outer surface layer portion. Each connecting portion is unitarily formed with the core portion and extends through the outer surface layer portion. Each connecting portion can be formed by melted plastic material that creates an opening in the outer surface layer portion or passes through an existing opening in the outer surface layer portion during a molding process for creating the core portion. 
     In some embodiments, a respiratory mask assembly includes a headgear and a connector that is over-molded to the headgear and configured to couple the headgear to a frame of the respiratory mask assembly. The headgear can include a yoke, first and second side arms, and a top strap. Each of the first and second side arms extends from a lateral portion of the yoke and extends across a cheek and above an ear of a user in use. The top strap is coupled to and extends between the first and second side arms and is configured to extend across the top of the user&#39;s head in use. The connector can be over-molded to the yoke. 
     In some embodiments, a respiratory mask assembly includes a frame and a cushion module. The frame includes a body and a compliant engagement portion disposed on the body. The body includes an inlet end defining an inlet aperture and an outlet end defining an outlet aperture, a flow path extending through the body from the inlet aperture to the outlet aperture. The body can be harder than the compliant engagement portion. The cushion module is configured to be coupled to the frame. The cushion module includes a seal and a coupling structure coupled to the seal. A surface of the coupling structure is configured to engage the compliant engagement portion of the frame when the cushion module is coupled to the frame. 
     The compliant engagement portion can be configured to compress as the cushion module is coupled to the body, and compression of the compliant engagement portion can create a friction fit between the cushion module and the frame. 
     The coupling structure can include an inner clip and an outer clip. A portion of the seal can be sandwiched between the outer clip and the inner clip. The inner clip can include the surface configured to engage the compliant engagement portion. The surface of the coupling structure configured to engage the compliant engagement portion can include a first portion and a second portion, with a dimension of the first portion being less than a dimension of the second portion. The first portion can be adjacent and extend from a leading edge of the inner clip in an assembly direction as the inner clip is coupled to the frame. The first portion of the surface of the inner clip can contact the compliant engagement portion in an intermediate position of the inner clip relative to the frame as the inner clip is being coupled to the frame. The second portion of the surface of the inner clip can contact the compliant engagement portion in a final connected position of the inner clip on the frame. The surface of the inner clip can further include a transition portion between the first portion and the second portion, and the transition portion can contact the compliant engagement portion in a final connected position of the inner clip on the frame. 
     Further aspects of the invention, which should be considered in all its novel aspects, will become apparent from the following description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A number of embodiments will now be described by way of example with reference to the drawings in which: 
         FIG. 1  is a perspective view of a first non-limiting exemplary embodiment of a respiratory mask according to the present disclosure. 
         FIG. 2  is a front perspective view of a frame of the respiratory mask of  FIG. 1 . 
         FIG. 3  is a rear perspective view of the frame of  FIG. 2 . 
         FIG. 4  is a front view of the frame of  FIG. 2 . 
         FIG. 4A  is a front view of the frame of  FIG. 2 . 
         FIG. 5  is a left side view of the frame of  FIG. 2 . 
         FIG. 5A  is a left side view of the frame of  FIG. 2 . 
         FIG. 5B  is a left side view of an alternate embodiment of the frame of  FIG. 2 . 
         FIG. 6  is a rear view of the frame of  FIG. 2 . 
         FIG. 6A  is a rear view of the frame of  FIG. 2 . 
         FIG. 7  is a top view of the frame of  FIG. 2 . 
         FIG. 7A  is a top view of an alternate embodiment of the frame of  FIG. 2 . 
         FIG. 8  is a bottom view of the frame of  FIG. 2 . 
         FIG. 9  is a front view of the frame of  FIG. 2  with a central cross section taken. 
         FIG. 10  is a central cross sectional view of the frame of  FIG. 2 . 
         FIG. 10A  is a 2D view of the central cross section of the frame of  FIG. 2   
         FIG. 11  is a perspective view of a second non-limiting exemplary embodiment of a respiratory mask according to the present disclosure. 
         FIG. 12  is a side view of the respiratory mask of  FIG. 11 , in use. 
         FIG. 13  is front view of part of a headgear of the respiratory mask of  FIGS. 11 and 12 , in a disengaged arrangement. 
         FIG. 14  is a close-up side view of a top strap of the headgear of  FIG. 13 , in a disengaged arrangement. 
         FIG. 15  is a perspective view of the top of the respiratory mask of  FIG. 11 . 
         FIG. 16  is a close-up front view of a yoke of the headgear of  FIG. 13  in a disengaged arrangement. 
         FIG. 17  is a close-up plan view of the yoke of the headgear of  FIG. 13  in a disengaged arrangement. 
         FIG. 18  is a perspective view of a second non-limiting exemplary embodiment of a headgear for use in combination with the respiratory mask of  FIG. 1 . 
         FIG. 19  is a perspective front view of the yoke of the headgear  FIG. 18 . 
         FIG. 20  is a perspective view of a non-limiting exemplary embodiment of a respiratory mask according to the present disclosure. 
         FIG. 21  is a front perspective view of a frame of the respiratory mask of  FIG. 20 . 
         FIG. 22  is a rear perspective view of the frame of  FIG. 21 . 
         FIG. 23A  is a front view of the frame of  FIG. 21  showing axes of the frame. 
         FIG. 23B  is a front view of the frame of  FIG. 21  showing various axes and dimensions. 
         FIGS. 24A-24B  show a method of coupling a headgear of the respiratory mask of  FIG. 20  to the frame of  FIG. 21 . 
         FIG. 24C  is a front view of an alternative embodiment of the frame of  FIG. 21 . 
         FIG. 24D  is a front perspective view of an alternative embodiment of the frame of  FIG. 21 . 
         FIG. 25  is a perspective partially exploded view of the respiratory mask of  FIG. 20 . 
         FIG. 26A  is a side view of the frame of  FIG. 21 . 
         FIG. 26B  is a side view of the frame of  FIG. 21  showing various axes and dimensions. 
         FIG. 26C  is a partial section view of an inlet collar of the frame of  FIG. 21 . 
         FIG. 26D  is a front view of the frame of  FIG. 21 . 
         FIG. 27A  is a rear view of the frame of  FIG. 21  showing various axes. 
         FIG. 27B  is a rear view of the frame of  FIG. 21  showing various axes and dimensions. 
         FIG. 28  is a side view of the frame of  FIG. 21 . 
         FIG. 29A  is a top view of the frame of  FIG. 21 . 
         FIG. 29B  is a top view of an alternative embodiment of the frame of  FIG. 29A . 
         FIG. 29C  is a top view of the frame of  FIG. 21 . 
         FIG. 30  is a bottom view of the frame of  FIG. 21 . 
         FIG. 31  is a partial front view of the frame of  FIG. 21  showing a section plane. 
         FIG. 32A  is a section view of the frame of  FIG. 21  taken along line  32 A- 32 A in  FIG. 31 . 
         FIG. 32B  is a  2 D view of the section of  FIG. 32A . 
         FIG. 33  is a perspective view of a non-limiting exemplary embodiment of a respiratory mask according to the present disclosure. 
         FIG. 34  is a side view of the respiratory mask of  FIG. 33  as worn by a user. 
         FIG. 35A  is a rear view of a yoke of a headgear of the mask of  FIG. 33 . 
         FIG. 35B  is a rear view of the yoke of the headgear of the mask of  FIG. 33  showing a gate used in molding. 
         FIG. 36A  is a side view of a frame retaining feature of the headgear of the mask of  FIG. 33 . 
         FIG. 36B  is a side view of the frame retaining feature of  FIG. 36A  showing an outline of a casing of the headgear. 
         FIG. 36C  is a side view of a mold used to create the frame retaining feature of  FIG. 36A . 
         FIG. 37  is a front view of the yoke and portions of side arms of the headgear of the mask of  FIG. 33 . 
         FIG. 38A  is a close-up view of a portion of the headgear of the mask of  FIG. 33 . 
         FIG. 38B  is a close-up view of a portion of the headgear of the mask of  FIG. 33 . 
         FIG. 39  is a top view of the top strap of the headgear of the mask of  FIG. 33 . 
         FIG. 40  is a top perspective view of the top strap of the headgear of the mask of  FIG. 33  in a disengaged position or configuration. 
         FIG. 41  is a close-up view of a portion of a second portion of the top strap of  FIG. 40 . 
         FIG. 42  is a close-up view of a portion of the headgear of the mask of  FIG. 33  showing an embodiment of a connection between the side arm and the top strap of the headgear. 
         FIG. 43A  is a bottom view of an example embodiment of a location guide of a first portion of the top strap of the headgear. 
         FIG. 43B  is a bottom view of an example embodiment of a location guide of a first portion of the top strap of the headgear. 
         FIG. 43C  is a side view of a portion of the first portion of the top strap. 
         FIG. 44  is a top perspective view of a non-limiting exemplary embodiment of a respiratory mask assembly according to the present disclosure. 
         FIG. 45  is a front view of the respiratory mask assembly of  FIG. 44 . 
         FIG. 46  is a rear view of a headgear of the respiratory mask assembly of  FIG. 44 . 
         FIG. 47A  is a rear or internal view of a disconnected and expanded portion of the headgear of  FIG. 46 . 
         FIG. 47B  is a front or external view of the portion of the headgear of  FIG. 47A . 
         FIG. 48A  is a front or external view of the right side of the headgear of  FIG. 47A . 
         FIG. 48B  is a rear or internal view of  FIG. 48A . 
         FIG. 49A  is a front or external view of the left side of the headgear of  FIG. 47A . 
         FIG. 49B  is a rear or internal view of  FIG. 49A . 
         FIG. 50A  is a front or external view of a male connector of the headgear of  FIGS. 46 and 47A . 
         FIG. 50B  is a rear or internal view of the male connector of  FIG. 50A . 
         FIG. 50C  is a perspective section view of a variation of the male connector of  FIG. 50A . 
         FIG. 51A and 51B  show different methods of connecting and/or disconnecting the male connector of  FIG. 50A  and a female connector of the headgear of  FIGS. 46 and 47A . 
         FIG. 52A  is a partial perspective external view of a top strap of the headgear of  FIG. 46 . 
         FIG. 52B  is a partial internal view of the top strap of  FIG. 52A . 
         FIG. 53A  is a partial external view of a bottom strap of the headgear of  FIG. 46 . 
         FIG. 53B  is a partial internal view of the bottom strap of  FIG. 53A . 
         FIG. 54A  is a partial external view of a joint between the top strap of  FIG. 52A  and the bottom strap of  FIG. 53A . 
         FIG. 54B  is a perspective view of the joint of  FIG. 54A . 
         FIG. 55A  is a partial internal view of the joint of  FIG. 54A  and an end of the bottom strap. 
         FIG. 55B  is a section view of the joint of  FIG. 54A . 
         FIG. 56A  is a partial internal view of an over-molded joint between the top strap and the bottom strap and a buckle over-molded onto the end of the bottom strap. 
         FIG. 56B  is an external view of  FIG. 56A . 
         FIG. 57  is a section view of the over-molded joint of  FIG. 56A . 
         FIG. 58  is a section view of the male connector of  FIG. 50A  over-molded onto the top strap. 
         FIG. 59  is a perspective view of an alternative embodiment of an end of the top strap. 
         FIG. 60A  is a rear view of the bottom strap and a yoke of the headgear of  FIG. 46 . 
         FIG. 60B  is a bottom view of the yoke of  FIG. 60A . 
         FIG. 61  is a front top perspective view of a frame and gas delivery conduit of the respiratory mask assembly of  FIG. 44 . 
         FIG. 62A  is a rear view of the bottom strap of  FIG. 60A  coupled to the frame of  FIG. 61 . 
         FIG. 62B  is a front view of the bottom strap and frame of  FIG. 62A . 
         FIG. 63  is a rear view of an alternative embodiment of a bottom strap and yoke. 
         FIG. 64  shows relative dimensions of the buckle and bottom strap. 
         FIG. 65  is a top perspective view of a non-limiting exemplary embodiment of a respiratory mask assembly according to the present disclosure. 
         FIG. 66  is a front view of a yoke and clip of the respiratory mask assembly of  FIG. 65 . 
         FIG. 67  is a rear view of the yoke and clip of  FIG. 66 . 
         FIG. 67B  is a rear cross sectional view of the yoke and clip of  FIG. 66 . 
         FIG. 68  is a bottom perspective view of the yoke and clip of  FIG. 66 . 
         FIGS. 69A and 69B  show a method of mounting the clip of  FIG. 66  to the yoke of  FIG. 66 . 
         FIG. 70  is a side perspective view of a frame of the respiratory mask assembly of  FIG. 65 . 
         FIG. 71  is a side view of the frame of  FIG. 70 . 
         FIG. 72  is a front view of the frame of  FIG. 70 . 
         FIG. 73  is a top view of the frame of  FIG. 70 . 
         FIG. 74  is a top perspective view of the yoke and clip of  FIG. 66  coupled to the frame of  FIG. 70 . 
         FIG. 75  is a top view of the assembly of  FIG. 74 . 
         FIG. 76  is a bottom view of the assembly of  FIG. 74 . 
         FIG. 77  is a rear view of the assembly of  FIG. 74 . 
         FIG. 78A  is a front view of a seal and coupling structure coupled to the yoke, clip, and frame of  FIG. 74 . 
         FIG. 78B  is a partial close-up view of the assembly of  FIG. 78A . 
         FIG. 79  is a top view of a seal and coupling structure of the respiratory mask assembly of  FIG. 65 , showing lateral ends of the seal deflected away from the coupling structure. 
         FIG. 80  is a front perspective view of the seal and coupling structure of  FIG. 79 . 
         FIGS. 81A, 81B, 81C, and 81D  show various embodiments of coupling structure connectors for the frame of  FIG. 70 . 
         FIG. 82A  is a side view of a frame including an embodiment of a coupling structure connector having dual protrusions. 
         FIG. 82B  is a perspective view of the frame of  FIG. 82A . 
         FIG. 83  is a front-side perspective view of another example embodiment of a frame. 
         FIG. 84  is a side view of the frame of  FIG. 83 . 
         FIG. 85  is a front view of the frame of  FIG. 83 . 
         FIG. 86  is a top view of the frame of  FIG. 83 . 
         FIG. 87  is a side view of a clip coupled to the frame of  FIG. 83 . 
         FIG. 88  is a front view of the clip and frame of  FIG. 87 . 
         FIG. 89  is an exploded front perspective view of another example embodiment of a clip and frame. 
         FIG. 90  is a front perspective view of the frame of  FIG. 89 . 
         FIG. 91  is a front view of the clip of  FIG. 89 . 
         FIGS. 92A, 92B, and 92C  are side cross-sectional views of other example embodiments of a frame and clip. 
         FIG. 93  is a front view of a non-limiting exemplary embodiment of a respiratory mask assembly according to the present disclosure. 
         FIG. 94  is a side view of the respiratory mask assembly of  FIG. 93 . 
         FIG. 95  is a front view of a portion of the respiratory mask assembly of  FIG. 93 . 
         FIG. 96  is a front perspective view of a portion of the respiratory mask assembly of  FIG. 93 . 
         FIG. 97  is a bottom-side perspective view of a portion of the respiratory mask assembly of  FIG. 93 . 
         FIG. 98  is a bottom perspective view of a portion of the respiratory mask assembly of  FIG. 93 . 
         FIG. 99  is a front view of a frame of the respiratory mask assembly of  FIG. 93 . 
         FIG. 100  is a side view of the frame of  FIG. 99 . 
         FIG. 101  is a bottom view of the frame of  FIG. 99 . 
         FIG. 102  is a bottom-front perspective view of the frame of  FIG. 99 . 
         FIG. 103  is a front perspective view of a non-limiting exemplary embodiment of a frame, seal, and coupling structure assembly. 
         FIG. 104  is a front perspective view of the frame of  FIG. 103 . 
         FIG. 105  is a rear perspective view of the frame of  FIG. 103 . 
         FIG. 106  is a front view of the frame of  FIG. 103 . 
         FIG. 107  is a rear view of the frame of  FIG. 103 . 
         FIG. 108  is a top view of the frame of  FIG. 103 . 
         FIG. 109  is a bottom view of the frame of  FIG. 103 . 
         FIG. 110  is a side view of the frame of  FIG. 103 . 
         FIG. 111  is a section view of the frame of  FIG. 103  taken along line  111 - 111  in  FIG. 106  with a connector of the frame omitted. 
         FIG. 112  is the section view of  FIG. 111  including the connector. 
         FIG. 113  is a front view of the frame, seal, and coupling structure assembly of  FIG. 103 . 
         FIG. 114  is a section view of the assembly of  FIGS. 103 and 113  taken along line  114 - 114  in  FIG. 113 . 
         FIG. 115  is a close-up section view of region  115  of the frame as indicated in  FIG. 114 . 
         FIG. 116  is a front perspective view of the frame and an inner clip of  FIG. 103 . 
         FIG. 117  is a front view of the frame and inner clip of  FIG. 116 . 
         FIG. 118  is a side view of the frame and inner clip of  FIG. 116 . 
         FIG. 119  is a rear view of the frame and inner clip of  FIG. 116 . 
         FIG. 120  is a top view of the frame and inner clip of  FIG. 116 . 
         FIG. 121  is a bottom view of the frame and inner clip of  FIG. 116 . 
         FIG. 122  is a section view of the frame and inner clip of  FIG. 116  taken along line  122 - 122  in  FIG. 117 , showing the inner clip in an intermediate position during coupling of the inner clip to the frame. 
         FIG. 123  is the section view of  FIG. 122 , showing the inner clip in a final connected position on the frame. 
         FIG. 124  is a close-up section view of region  124  as indicated in  FIG. 122 , showing the inner clip in the intermediate position. 
         FIG. 125  is a close-up section view of region  125  indicated in  FIG. 123 , showing the inner clip in the final connected position. 
     
    
    
     DETAILED DESCRIPTION 
     The present disclosure relates to a frame and headgear for a respiratory mask system configured to deliver a respiratory therapy to a patient/user.  FIG. 1  shows a non-limiting exemplary embodiment of a respiratory mask system  1  of the present disclosure. The respiratory mask system  1  comprises a patient interface  2 , a headgear  3 , and a gas delivery conduit  6 . The patient interface  2  comprises a cushion module and a frame  5 . The cushion module includes a seal  4 . The cushion module can also include a coupling structure configured to couple to the frame  5  as described in greater detail herein. 
     The patient interface  2  is configured to provide an air path through which a supply of pressurized air can be provided to the airway of a user. In the embodiments shown and detailed below the patient interface  2  is a nasal mask, in particular an under-nose or sub-nasal mask, having a seal  4  that is configured to seal on the lower surfaces of a patient&#39;s/user&#39;s nose. The seal  4  is configured to form an airtight seal under the nose of the patient/user, along a portion of the face extending lateral to the nose, as well as along the upper lip of the user. 
     In some embodiments the seal  4  may be adapted to extend around and seal over the wing or alar of the nose, which flares out to form a rounded eminence around the nostril. The illustrated mask  1  is adapted to seal around the surfaces that define the opening to the nostril, which may include a portion or entirety of the fleshy external end of the nasal septum, sometimes called the columella. In some configurations, the seal  4  is adapted to extend upwardly to seal along at least a portion of the left and right dorsal side walls of the nose of the user. In some configurations, the seal  4  is adapted to extend upwardly along at least a portion of the left and right dorsal side walls without extending upwardly to the region of the bridge of the nose of the user. In some configurations, a primary sealing surface of the seal  4  contacts the underside of the nose of the user, the upper lip and/or a transition region between the underside of the nose and the upper lip. A secondary sealing surface of the mask can contact the side surfaces of the nose of the user, possibly along with the cheeks at a location near the nose. Such primary and secondary sealing surfaces may not make contact with the face of all users; however, such an arrangement can provide a suitable seal with a relatively large range of facial geometries. 
     In the illustrated configuration, the seal  4  does not extend over the bridge of the nose of the user. More particularly, the illustrated seal  4  does not contact the bridge of the nose of the user. This is advantageous as contact and thus pressure applied to the nasal bridge can result in pressure sores and discomfort for the user. If the seal causes pain or discomfort to the user they may not be compliant with the therapy. 
     An under-nose or sub-nasal mask with a seal  4 , as described above, may be less stable on the user&#39;s face than more traditional masks that contact the nasal bridge as a result of having a reduced contact area with the users face. The reduced contact area provides fewer constraints as to how the seal  4  can move relative to a user&#39;s face, and therefore the seal  4  may be able to roll or rotate relative to the user&#39;s face. Any rolling or rotation of the seal  4  may result in a substantially airtight seal between the seal  4  and the user&#39;s face being broken and the delivery of the respiratory therapy compromised. In some embodiments instability of the seal  4  may be lessened by providing a headgear  3  capable of transferring forces away from the seal  4  to other parts of the users&#39; head. 
     The frame  5  is configured to provide a manifold that connects the components of the patient interface  2  together and secures them to the headgear  3 . The frame  5  can comprise features that are configured to fluidly connect the gas delivery conduit  6  to the seal  4 , such that a continuous air path is provided. 
     The headgear  3  is configured, in use, to secure the patient interface  2  to a user&#39;s face. The headgear  3  comprises a top strap  7 , pair of side arms  8  and a yoke  9 , which are permanently joined to form a closed loop. In use, the top strap  7  is configured to pass over the top of a user&#39;s head, the side arms are configured to extend across the cheeks of the user and the yoke  9  is configured to connect to the frame  5 . The headgear  3  further comprises a rear strap  10  that is adjustably connected to the side arms  8  and is configured, in use to pass around the rear of the user&#39;s head. 
     It is to be understood that while the headgear  3  and frame  5  of the present disclosure is described as being used in combination with a sub-nasal mask, it could be used in combination with any other type of mask, including but not limited to nasal prong or pillow masks, full-face masks that seal above and/or below the nasal bridge, or nasal masks. 
     Frame 
       FIGS. 2 and 3  show perspective views of a first non-limiting exemplary embodiment of a frame  100  that is substantially similar to the frame  5  of  FIG. 1 , and forms part of a respiratory mask system. A vertical axis  105  and a lateral axis  107  (shown in  FIG. 4 ) are defined with an origin at the central point of an inlet collar  114  of the frame  100 . The frame  100  is symmetric about the vertical axis  105 . The frame  100  has an exterior surface  102  and an interior surface  103 . The exterior surface  102  acts as an interface between the frame  100 , a headgear  3  and a gas delivery conduit  6 . The exterior surface  102  includes a recessed channel  106 . The recessed channel is defined by and lies between a first retaining ridge  104  and a second retaining ridge  108 . The first retaining ridge  104  is vertically displaced from the second retaining ridge  108 , the space between the first retaining ridge  104  and the second retaining ridge  108  defining the recessed channel  106 . A recessed surface  110  is located adjacent to the second retaining ridge  108 . A yoke  9  is inserted into the recessed channel  106 , in use. The headgear  3  is connected to the frame  100  by inserting the yoke  9  into the recessed channel. 
     The exterior surface  102  additionally includes an inlet collar  114 . The inlet collar  114  includes a centrally located inlet collar aperture  115 . The inlet collar  114  also includes a collar interior surface  116  and an inlet collar surface  118 . The inlet collar  114  can further include a conduit retaining projection  122 , a number of seal retaining recesses  130 , and/or a number of vent holes  127 . The first retaining ridge  104  extends from a first lateral edge  126  to a second lateral edge  128  of the frame  100 . The second retaining ridge  108  extends from the first lateral edge  126  to meet the inlet collar surface  118  of the inlet collar  114  at a laterally displaced junction  112 a. The second retaining ridge  108  diverges from the inlet collar  114  at a second laterally displaced junction  112 b and extends to the second lateral edge  128 . 
     The interior surface  103  may contact the seal  206  or a coupling structure connected to the seal  206  and spans from the first lateral edge  126  to the second lateral edge  128  of the frame  100 . The interior surface  103  includes an outlet collar  137  that extends proximally from the frame  100  with respect to a user, establishing an outlet collar aperture  117 . In the illustrated embodiment, a number of seal retaining recesses  130  are located on an outlet collar surface  124  to enable interaction between the frame  100  and a seal  206 . 
       FIGS. 4 and 4A  show a front view of the frame  100  aligned with the inlet collar aperture  115 , i.e. a front view of the frame  100 . The frame  100  acts as a manifold that connects multiple components of the respiratory mask system together. The inlet collar aperture  115  is an oval with a major axis  113  and a minor axis  111 . In alternate embodiments, the inlet collar  114  may be circular, triangular or follow the profile of any other polygon desired. 
     The frame  100  is symmetric about the minor axis  111  of the inlet collar  114 . In the illustrated configuration, the minor axis  111  is aligned with the vertical axis  105 . In the illustrated configuration the inlet collar aperture  115  is positioned substantially in the center of the frame  100 . The inlet collar aperture  115  has a major dimension  145  (e.g., length along its major axis  113 ) and a minor dimension  143  (e.g., length along its minor axis  111 ). Additionally, in the illustrated configuration, the major dimension  145  of the inlet collar aperture  115  is 20.7 mm and the minor dimension  143  of the inlet collar aperture  115  is 17.2 mm Another way of expressing this is the ratio between the major dimension  145  and the minor dimension  143  of the inlet collar aperture  115  is approximately 1.2:1. 
     This ratio is, at least to an extent, dictated by the physical characteristics or shape of the gas delivery conduit used in the respiratory mask system. Furthermore, the desire to minimize the pressure drop that exists between a pressure generating device and the user also influences the possible range of ratios between the major dimension  145  and minor dimension  143 . Pressure drop is a phenomenon known to occur in respiratory mask systems where a reduction in pressure occurs between the pressure generating device and the outlet of the respiratory mask system. The pressure drop is largely due to flow resistances and inefficiencies within the system. Minimizing the pressure drop observed in a respiratory mask system improves the efficacy of the therapy delivered to the user. 
     The pressure drop that one may measure across the respiratory mask system is increased with an increasing ratio between the major dimension  145  and the minor dimension  143  of the inlet collar aperture  115 . Increasing the ratio of the major dimension  145  to the minor dimension  143  however, is beneficial as it enables the physical profile of the frame  100  to be reduced. This in turn enables a reduction in the overall profile of the respiratory mask system. Therefore, in other embodiments of frame  100 , the ratio between the major dimension  145  and the minor dimension  143  of the inlet collar aperture  115  may vary from approximately 1:1 to approximately 2:1. 
     Referring again to  FIG. 4 , the recessed channel  106  spans from the first lateral edge  126  to the second lateral edge  128  of the frame  100 . Like the recessed channel  106 , the first retaining ridge  104  spans from the first lateral edge  126  to the second lateral edge  128  of the frame  100 . 
     The lateral portions of the second retaining ridge  108  are substantially concave with respect to the lateral axis  107 . The lateral portions of the second retaining ridge  108  are defined by an inflection region near junction  112  where the relative concavity deviates from concave to convex as the second retaining ridge  108  meets the inlet collar surface  118 . 
     In the illustrated embodiment, the recessed channel  106  passes over the inlet collar  114 . The recessed channel  116  is arcuate in shape and passing over the inlet collar  114 . This is beneficial because the arcuate shape of the recessed channel  116  allows for effective force resolution of forces generated by the seal and headgear. 
     The first retaining ridge  104  and the second retaining ridge  108  project outwardly from the outer surface  102  of the frame in a direction toward the inlet collar  114 . The inlet collar  114  includes a wall that extends from the outer surface  102 . A vertical thickness or height or outward extension of the recessed channel  106  may be defined to be the displacement between a point on the first retaining ridge  104  that is adjacent to the recessed channel  106 , and a corresponding point on the second retaining ridge  104  that is adjacent to the recessed channel  106 , with each of the two points aligned on a common vertical axis. The points of maximum vertical thickness of the recessed channel  106  when defined in this way are at the first lateral edge  126  and second lateral edge  128  of the frame  100 . The point of minimum vertical thickness of the recessed channel  106  is located on the vertical axis  105 . 
     The vertical thickness or height of the recessed channel  106  decreases in magnitude when translating laterally from the first lateral edge  126  and the second lateral edge  128  inwards towards the vertical axis  105  of the frame  100 . In the illustrated configuration, the minimum vertical thickness of the recessed channel  106  is approximately 5.8 mm and the maximum vertical thickness of the recessed channel  106  is approximately 12.7 mm The ratio between the minimum vertical thickness and the maximum vertical thickness of the recessed channel  106  is therefore approximately 1:2.25. The vertical thickness of the recessed channel  106  corresponds with the thickness of the yoke  9  of the headgear  3  being used with the frame  100 . In some configurations, the ratio between the minimum vertical thickness and the maximum vertical thickness of the recessed channel  106  may be between approximately 1:1 and 1:4. 
     Reducing the vertical thickness of the recessed channel  106 , along a portion of the length or at least within a central location of the frame  100 , enables the vertical profile of the frame  100  to be reduced or minimized. Reducing or minimizing the vertical profile of the frame  100  reduces both its real and perceived obtrusiveness and reduces or minimizes its mass, which is desirable for user comfort and may improve user compliance with the therapy. The reduced vertical thickness of the recessed channel  106  near the lateral center of the frame  100  may also provide an alignment feature between the yoke  9  and the recessed channel  106 . The alignment feature may allow the yoke  9  to be connected to the frame  100  in only one orientation and thus prevent incorrect assembly of the headgear  3  to the frame  100 . 
     The yoke  9  may be connected to the frame  100  via the recessed channel  106  through the use of any relevant means of connection. The yoke  9  may be bound to the recessed surface  106  through the use of an adhesive. In some configurations, the yoke  100  may be connected to the frame  100  using a snap fit mechanism, friction fit mechanism or a hook and loop fastening mechanism. In other configurations, the recessed surface may include one or more projections, designed to fit in a recess or hole in the yoke such that the combination of the projection and corresponding recess or hole mates the yoke to the frame. Alternately, the recessed surface  106  may include one or more recesses or holes such that one or more corresponding projections on the yoke mate the yoke to the frame. 
     Alternate configurations of the frame  100  may utilize a number of alternate recessed channel profiles. For instance, a recessed channel may extend either over the top of (as illustrated in  FIGS. 4 and 4A ), or underneath the inlet collar. In another alternative configuration the frame includes two or more recessed channels may extend laterally across the exterior surface of the frame. In some configurations, these recessed channels may include portions where the relevant retaining ridges are adjacent to each other, or where two recessed channels share a common retaining ridge. In some configurations, these recessed channels may not include adjacent portions. In some configurations, one or more recessed channels may both pass over the inlet collar. In some configurations, one or more recessed channels may both pass underneath the inlet collar. 
     In some configurations, two or more recessed channels may first diverge from a common recessed channel near one lateral edge, deviate around the inlet collar and then converge to a common recessed channel near the opposite lateral edge of the frame. In some configurations, multiple recessed channels may be entirely independent on the exterior surface of the frame. In other words, each of the independent recessed channels may have their own independent retaining ridges, or may share a common retaining ridge with another independent recessed channel, while maintaining completely separate channels themselves. In each of the aforementioned variations, one or more of the recessed channels may be used as an interface to connect the respiratory mask system&#39;s headgear  3  to the frame  100 . 
     Referring again to  FIG. 4 , the recessed surface  110  spans from the first lateral edge  126 , below the inlet collar  114 , to the second lateral edge  128  of the frame  100 . The recessed surface  110  is adjacent to the second retaining ridge  108  and the inlet collar  114  on the exterior surface  102  of the frame  100 . In the illustrated configuration, the recessed surface  110  assists in providing support for the seal  206  and maintaining the structural integrity of the frame  100  both during the manufacturing process and during use. In alternative embodiments however, the frame  100  may be completely void of this recessed surface  110 . 
     The lateral length  125  of the frame  100  according to the illustrated embodiment of  FIG. 4A  is approximately 56.00 mm Accordingly, the ratio between the major dimension  145  of the inlet collar aperture  115  and the lateral length  125  of the frame  100  is approximately 1:2.70. The specified lateral length  125  of the frame  100  has been utilized to optimize the behavior of the frame  100  when combined with the seal  206  and headgear  3 . The headgear  3  is desired to flex about the user&#39;s face to a relatively large extent. This behavior is desired to maximize the variance of facial profiles the respiratory mask system may accommodate. The frame  100  has a sufficient lateral length  125  that enables at least some headgear flex and reduces seal  206  displacement. 
     In alternative embodiments of the frame  100 , the lateral length  125  may vary from approximately 45.00 mm to approximately 75.00 mm The variation may be used to accommodate different seal  206  sizes, different profiles of headgear  3  or different headgear connection methods. 
     The vertical length  129  of the frame  100  has a vertical length that to provide adequate structure to enable the headgear  3  to connect effectively to the frame  100 , and to provide the required structural and rotational integrity required by the seal  206 . 
     In alternative embodiments of the frame, the vertical length of the frame may vary from approximately 25.00 mm to approximately 50.00 mm The variation may be used to accommodate different seal sizes, different profiles of headgear  3  or different headgear connection methods. 
       FIGS. 5 and 5A  show a left side view (with respect to the user) of the frame  100  illustrated in  FIG. 1 . The frame  100  is shown from one side of the frame. There is illustrated a vertical axis  105 , an inlet proximal axis  131  and an outlet proximal axis  133 . In the illustrated configuration, the inlet proximal axis  131  intersects the vertical axis  105  at a right angle, and is centrally located with respect to the inlet collar aperture  115 . In other words, the inlet proximal axis  131 , lateral axis  107  (see  FIG. 4 ) and vertical axis  105  form a 3 dimensional space sharing a common origin. The inlet proximal axis  131  is approximately parallel to the flow of gas through the inlet collar aperture  115 . The outlet proximal axis  133  intersects the vertical axis  105  at a right angle. In other words, the outlet proximal axis  133 , secondary lateral axis  109  (shown in  FIG. 6 ) and the vertical axis  105  share a common intersection point. The outlet proximal axis  133  is parallel to the flow of gas through the outlet collar aperture  117  of the frame  100 . The inlet proximal axis  131  is vertically displaced with respect to the outlet proximal axis  133 . In the illustrated configuration, the inlet proximal axis  131  is parallel to the outlet proximal axis  133 . In alternate configurations, the outlet proximal axis  133  and the inlet proximal axis  131  may be aligned on the vertical axis  105 . 
     The distal (with respect to the user) edge of the inlet collar  114  as viewed in  FIG. 5A  aligns with the vertical axis  105 . In alternate configurations, the edge of the inlet collar may be angled with respect to the vertical axis  105 . 
     In the illustrated configuration, the inlet collar surface  118  includes a first portion that is of a first external perimeter, a second portion of a second external perimeter coaxially offset from the first portion, and a transition portion that is integral with, and links the first portion to the second portion. In the illustrated configuration, the external perimeter of the second portion is greater than that of the first portion and the second portion is proximally (when worn by a user) displaced with respect to the first. The difference in perimeter between the first portion and second portion of the inlet collar  114  produces the transition portion that forms an angled surface  135  that is angled with respect to the inlet proximal axis  131 . This angled surface  135  facilitates the increase in perimeter. In some configurations, the inlet collar surface  118  will include only an angled surface. In other configurations, the inlet collar surface  118  may include a combination of angled surfaces and surfaces that aren&#39;t angled with respect to the inlet proximal axis  131 . 
     As seen in the Figures the inlet collar  114  has a perimeter that is less than the perimeter of the outlet collar  137 . The inlet collar  114  is of a different shape to the outlet collar  137 . 
     The angled surface  135  spans the periphery of the inlet collar surface  118 . A projection of the angled surface  135  on the inlet proximal axis  131  is of an approximately constant length at all points along the periphery of the inlet collar surface  118 . The angled surface  135  is angled at approximately 10° with respect to the inlet proximal axis  131 . The displacement between the angled surface  135  and the distal edge (with respect to the user) of the inlet collar surface  118  varies about the perimeter of the inlet collar surface  118 . In the illustrated embodiment, the angled surface  135  includes a number of bias flow holes  127 . In the configuration shown in  FIGS. 4, 5A and 7 , bias flow holes  127  are located on the angled surface  135 , extending substantially around the angled surface  135 . The bias flow holes expel bias flow substantially vertically with respect to the inlet proximal axis  131 . 
     The inclusion of the angled surface  135  on the inlet collar surface  118  is intended to influence the orientation of the bias flow holes  127  in a beneficial manner. An issue encountered with perpendicularly oriented holes however (holes oriented at 90° to the inlet proximal axis  131 ) is the perception of an uncomfortable draft of air by the user when the respiratory mask system is in use. The bias flow holes  127  of the frame  100 , when located on the angled surface  135 , are therefore angled away from the user. As a result, when the frame  100  is in use, the flow of gas through the bias flow holes  127  is directed away from the user. This prevents the user from feeling an uncomfortable draft of air while the respiratory mask system is in use. Alternate embodiments of the frame  100  may include the angled surface  135  with a modified angle with respect to the inlet proximal axis  131 . In some configurations, this angle may be between 0° and 20° or between 5° and 15°. In other configurations, this angle may be greater than 2°. 
     In other configurations, the bias flow holes may span around the entire angled surface. Alternately, a configuration of bias flow holes may be arranged on the inlet collar surface. This configuration may include one or more rows of bias flow holes, and rows may be aligned or offset with respect to each other. In other configurations, bias flow holes may be located anywhere else on the frame  100  in any desired configuration. Some configurations of the frame may include a single vent. Other configurations may include a single vent with a diffusor. The diffusor may be integral with the vent, or may connect to the frame  100  over the vent. The diffusor in such a configuration may act to diffuse the noise emanating from the vent when the respiratory mask system is operational. 
     Referring again to  FIGS. 5 and 5A , the side profile of the recessed channel  106  is shown. The recessed channel  106  is seen to be concave in the lateral direction with respect to the user. The degree of concavity of the recessed channel  106  may vary along the lateral length of the frame  100 . This is a result of the recessed channel  106  twisting along its length. The curvatures of the recessed channel  106  identified are such that the profile of the frame  100  may provide adequate structural support for the seal  206  of the respiratory mask system. 
     Referring to  FIGS. 6 and 6A ,  FIG. 6  shows a rear view of the frame  100  with respect to the vertical axis  105  and the lateral axis  107 . The outlet collar aperture  117  is centrally located on the frame  100  with respect to the vertical axis  105 . The origin of the outlet collar aperture  117  is aligned with the secondary lateral axis  109 . The secondary lateral axis is vertically displaced from the lateral axis  107 . In some configurations of the frame  100 , the secondary lateral axis  109  may align with the lateral axis  107 . 
       FIG. 6A  shows a rear view of the frame  100  and shows that the outlet collar  137  is shaped like a truncated circle or partially D shaped and includes an outlet major axis  119 , an outlet minor axis  121  and a truncated portion  123 . The truncated portion  123  of the outlet collar  137  enables the profile of the frame  100  to be reduced relative to a frame without a truncated portion. Additionally, the truncated portion  123  provides an orientation feature to ensure correct orientation of the seal connection with the frame. The truncated portion  123  also reduces the chances of incorrect orientation when the seal  206  should be connected to the frame  100 . The truncated portion also prevents rotation of the seal  206  relative to the frame  100 . 
     In the illustrated configuration, the outlet collar aperture  117  includes both a larger lateral profile and vertical profile than the inlet collar aperture  115 . The perimeter of the outlet collar aperture  117  is therefore greater than the perimeter of the inlet collar aperture  115 . This larger profile is beneficial from both functional and manufacturability perspectives. From a functional perspective, when the frame  100  has an outlet collar  137  that is larger than the inlet collar  114 , airflow to the user is less restricted. This results in reducing the pressure drop through the respiratory mask system in addition to at least in some way reducing the inspiration noise that is a result of the user breathing through the respiratory mask system. From a manufacturability perspective, having an outlet collar  137  that is larger than the inlet collar  114  allows a tool core to be more easily removed from the molded part. 
     Following the profile of the first retaining ridge  104 , the interior surface  103  that is adjacent to the first retaining ridge  104  is also substantially concave with respect to the lateral axis  107 . In alternate configurations, the interior surface  103  may be substantially convex with respect to the lateral axis  107 . Furthermore, the interior surface  103  may be both substantially concave in regions and substantially convex in other regions with respect to the lateral axis  107 . 
       FIG. 7  shows a top view (with respect to the user) of the frame  100 . Both the exterior surface  102  and the interior surface  103  are concave with respect to the user. This is exemplified by the first retaining ridge  104  being concave with respect to the user, as the first retaining ridge  104  of the exterior surface  102  is also adjacent to the interior surface  103 . This configuration is beneficial as it permits a reduction in the proximal profile of the respiratory mask system. In alternate configurations, the outlet collar  137  may be convex or flat in at least one plane. Additionally, the outlet collar  137  may include both regions of concavity and convexity in at least one plane. 
     The outlet collar surface  124  includes a number of seal retaining recesses  130 . In the illustrated configuration, the outlet collar surface  124  includes two seal retaining recesses  130 . The seal retaining recesses  130  are located near each lateral extrema of the outlet collar  137 . The seal retaining recesses  130  allow a seal  206  to be connected to the frame  100 . In the illustrated configuration, the seal  206  connects to the frame  100  through the use of a coupling structure, such as a clip, that connects to the frame  100 . The coupling structure or clip includes elevated surfaces that correspond with the seal retaining recesses  130  allowing a connection between the components to be made. Some configurations of the outlet collar  137  may include mechanisms of connecting to the seal  206  through the use of a snap fit mechanism; or friction fit mechanism. Alternate embodiments of the frame  100  may include one or more recesses on the outlet collar surface  124  to interface with the seal. Furthermore, as opposed the use of one or more recesses, one or more projections may be included on the outlet collar surface  124 . These projections may interact with corresponding recesses or retaining portions on the seal  206  or coupling structure to connect the components together. 
       FIG. 7A  shows a top view (with respect to the user) of an alternate configuration of the frame  100 . In this configuration, the bias flow holes  127  are disposed on the angled surface  135  over the inlet collar  114 , for example, as also shown in  FIG. 5B . 
       FIG. 8  shows a bottom view (with respect to the user) of the frame  100  illustrated in  FIG. 1 . The outlet collar  137  may be concave in at least one plane. At least one portion of the outlet collar  137  may be proximally displaced with respect to a second portion of the outlet collar  137 . 
     In alternate configurations, the outlet collar  137  may be aligned on a common plane such that it is not concave in form. In some configurations, this plane is perpendicular to the outlet proximal axis  133 . In other words, the vertical and lateral extrema would all share a common proximal displacement from the origin of the outlet proximal axis  133 . 
       FIG. 9  shows a front view of the frame  100  illustrated in  FIG. 1 , and identifies a cross section plane  132  that may be taken. This cross section plane is centrally located with respect to the frame  100  and aligns with the vertical axis  105 . 
       FIG. 10  shows cross-section  10 - 10  formed when viewing the frame  100  perpendicularly to the cross section plane  132 . A central cross section  134  shows the cross sectional profile of the frame  100  as viewed from the cross section plane  132 . 
       FIG. 10A  shows a central cross section  134  of the frame  100 . The conduit retaining projection  122  projects inwardly from the periphery of the inlet collar  114 . In other words, both the lateral and vertical dimensions of the inlet collar aperture  115  are less than those of the collar interior surface  116 . This dimensional variation is a result of the conduit retaining projection  122 . In other words, the conduit retaining projection  122  may form a lip around the interior of the distal end of the inlet collar  114 . This lip may be continuous around the periphery of the inlet collar aperture  115 , or may include sections of the periphery that project, and others that do not. A gas delivery conduit  6  may be connected to the frame  100  through the use of an adhesive, or the use of a coupling structure or clip that engages with the conduit retaining projection  122 . The gas delivery conduit may be positioned adjacent to the conduit retaining projection  122  and then adhesively bonded to the frame  100 . Alternately, the gas delivery conduit  6  may be removably fixed to the frame  100  through the coupling structure or clip. In some embodiments of the frame  100 , the gas delivery conduit  6  may be permanently connected to the frame  100  through the use of a coupling structure or clip, or other permanent boding methods including but not limited to ultrasonic welding or over-moulding. Additionally, a conduit retaining projection  122  may not be included in some embodiments. 
     The conduit retaining projection  122  may alternately be on the inlet collar surface  118 , projecting radially outwards from the center of the inlet collar  114 . In other words, the conduit retaining projection  122  may form a lip around the exterior of the inlet collar  114 . In this configuration, the gas delivery conduit  6  may connect adjacent to the inlet collar surface as opposed to the collar interior surface  116 . The lip may be continuous or intermittent around the periphery of the inlet collar  114 . 
     In the illustrated configuration, the frame  100  is constructed of a hard polymer. In some configurations, the frame  100  may be configured of any of a number of polymeric or non-polymeric materials, for example Nylon  12  or polycarbonate. 
       FIGS. 11 and 12  show a non-limiting exemplary embodiment of a respiratory mask system  200 , which is substantially similar to the respiratory mask system  1  of  FIG. 1 . The respiratory mask system  200  comprises a patient interface  202  and a headgear  204 . The patient interface  202  comprises a seal  206  configured to connect to the frame  100 , previously described, and a gas delivery conduit  208 . The headgear  204  and frame  100  are configured to secure the seal  206  in a stable position below the nose of a user. 
     The seal  206 , is substantially similar to the seal  6  described above, and has a reduced contact area with the user&#39;s face in comparison to more traditional nasal masks that seal around the user&#39;s nose, crossing the nose near or on the nasal bridge. The reduced contact area may result in reduced seal stability, which requires counteraction from the headgear  204 , in order to prevent leaks and loss of therapy. The headgear  204  is configured to provide support that counteracts any forces that may act to break a seal between the seal  206  and the user&#39;s face. Forces that may interrupt the seal may include but are not limited to blow-off forces induced by the pressure of the CPAP therapy provided, hose drag forces and/or contact between the patient interface  202  and bedding caused by movement of the user. 
     The frame  100  provides a connection between the seal  206 , and the headgear  204 .  FIGS. 11-12  show that the frame  100  comprises a gas delivery inlet or inlet collar  114  through which a supply of pressurized air can be provided to the seal  206 , and patient&#39;s airways. The pressurized air is typically provided to the gas delivery inlet  114  via a conduit or hose, such as gas delivery conduit  208 , that connects to a CPAP machine or ventilator (not shown). 
     Headgear 
       FIGS. 11 to 17  show a non-limiting exemplary embodiment of the headgear  204 , of comprising a bifurcated headgear arrangement. The bifurcated headgear  204  comprises a plurality of connected straps including a top strap  212 , a pair of opposing side arms  214 , a yoke  216  and a rear strap  218 . The top strap  212  and rear strap  218  form the bifurcated arrangement. 
     In use, the top strap  212  is configured to pass over the top of the user&#39;s head from one side to the other. In the illustrated configuration, the top strap  212  can comprise a forehead strap that lies over the frontal bone of the user. In this configuration the top strap  212  is angled forward of a coronal plane  11  that passes through the user&#39;s head, as shown in  FIG. 12 . An angle θ of between 5° and 45° is formed between the top strap  212  and the coronal plane  11 . In the illustrated embodiment the top strap  212  forms an angle of 15° with the coronal plane  11 . This angle directs the top strap  212  towards the forehead of the patient, which may improve the stability of the headgear  204 . In other configurations, the top strap  212  is a crown strap that lies over the parietal bone or at or near a junction between the parietal bone and the frontal bone. 
     The rear strap  218  passes around the back of the user&#39;s head and, in some configurations, lies over the occipital bone of the user. However, in other configurations, the rear strap  218  could be positioned higher or lower on the head and/or neck of the user. 
     The top strap  212  and rear strap  218  are joined at the ends by one of the side arms  214  to form the bifurcated structure. In use, the top strap  212  and the rear strap  218  encircle a rear portion of the user&#39;s head. The rear portion of the user&#39;s head that is encircled may include at least part of the parietal and/or occipital regions. 
     In the illustrated arrangement, the top strap  212  joins the side arms  214  on each side of the headgear  204  at a junction  224 . Each one of the pair of side arms  214  extends forwardly, in use, from the junction  224  towards the nose of the user and transitions into the yoke  216 . In use, the headgear  204  is configured such that the junction  224  is positioned above the user&#39;s ear. It may sit forward of or rearward of the ear depending on the size of the user&#39;s head. 
     Integrally Formed Closed Loop 
     In the embodiment shown, at least some portions of the headgear  204  are rigid, semi-rigid, inelastic or substantially inextensible in response to normal or expected forces acting on the headgear  204 . Other portions of the headgear  204  are elastic or extensible in response to normal or expected forces, or are at least substantially flexible in comparison to other portions. 
     In the illustrated configuration, the top strap  212 , junctions  224 , side arms  214  and yoke  216  are rigid, semi-rigid, inelastic or substantially inextensible. The top strap  212 , side arms  214  and yoke  216  are formed as a single integrally formed component, which is flat or substantially two-dimensional, as shown in  FIG. 13 . When the free ends of the left and right portions  220 ,  222  of the top strap  212  are connected to each other, by the adjustment mechanism  228 , a three-dimensional closed loop is formed. In use the closed loop is configured to encircle at least a portion of the user&#39;s head. In the illustrated embodiment the closed loop encircles an upper front portion of the user&#39;s head, from the bottom of the nose up to the parietal bone, forward of the ears. In alternative embodiments the closed loop may encircle a larger or smaller portion of the user&#39;s head. 
     The use of a rigid, semi-rigid, inelastic or substantially inextensible material for the top strap  212 , side arms  214  and yoke  216  allows the closed loop, which they form, to transfer forces effectively between the patient interface  202  and the user&#39;s head. For example, if, in use, the gas delivery conduit is pulled on by the user, bedding or a CPAP supply conduit a force may be applied to the patient interface  202  that pulls it away from the user&#39;s face. This force can be translated from the yoke  216  through the side arms  214  to the top strap  216  and then to the user&#39;s head, in order to resist the seal  206  being dislodged from the user&#39;s face by a rotation of the seal  206  in a vertical direction. 
     The closed loop allows the headgear  204  to be separated from the patient interface  202  without changing the tightness settings of the top strap  212 . This is advantageous because the user does not need to undo and do up the headgear  204 , and refit the strap with the correct tightness every time that the headgear  204  is removed from the patient interface  202 . This saves time and makes fitting the headgear easier for the user. The closed loop arrangement also provides a single connection point between the headgear  204  and the patient interface  202 . 
     In other words, the integrally formed component that forms the closed loop is rigid, semi-rigid, inelastic or substantially inextensible. In the illustrated embodiment the top strap  212 , side arms  214  and yoke  216  are integrally formed from a plastic material that forms a plastic core and is covered in a textile casing, wherein the textile casing is permanently bonded to the plastic core. The plastic core provides the structure required in the headgear  204  and the textile casing provides a soft and comfortable finish to contact the user. In the illustrated embodiment the textile casing is a circular knitted tube. In alternative embodiments the textile casing may comprise several layers of textile that are cut to shape and joined along the edges, or any other tubular textile that may include, but is not limited to, woven or braided tubes. In some embodiments at least a portion of the integrally formed top strap  212 , side arms  214  and yoke  216  are formed by an intra-moulding process, examples of which are described in the Applicant&#39;s application PCT/NZ2015/050149, the entirety of which are incorporated herein. “Intra-moulding” comprises forming a component as a plastic core and a textile casing as an integral structure by the application of molten plastic into the textile casing. A strap or any other component that has been “intra-moulded” is a component formed by the application of molten plastic into the textile casing. 
       FIG. 13  shows that the headgear  204  of the illustrated embodiment has a top strap  212 , and side arms  214  that comprise soft edges  250 . The soft edges  250  are configured to extend along one or both of the longitudinal edges of the top strap  212  and the side arms  214 . The soft edge is formed by a longitudinal edge portion of the textile casing that protrudes from the edges of the plastic core and is not filled by the plastic core. The soft edges provide a cushioned edge that may improve user comfort, by softening any contact between the edges of the rigid, semi-rigid, inelastic or substantially inextensible top strap  212  and side arms  214  and the user&#39;s head. This may be of particular benefit on a lower edge of the side arms  214  that sits above the user&#39;s ears in use. 
     In alternative embodiments the closed loop may be formed from any material that provides suitable rigidity, inelasticity or inextensibility. Materials may include but are not limited to thermoplastics and silicone. In some embodiments the material may or may not have a textile casing. 
     Top Strap 
     In the illustrated embodiment the top strap  212  comprises two strap portions, a left portion  220  and a right portion 222 . The left and right portions  220 ,  222  are separate from one another and have a free end and a fixed end. The free ends are configured to be adjustably connected by an adjustment mechanism  228 . The fixed ends are configured to extend at an angle from the side arms  214  at the junction  224 . 
     The adjustment mechanism  228  is configured to provide a means to adjust and secure the top strap  212  in a desired adjusted length and thus adjust the size and/or tightness setting of the headgear  204 . Adjustment of the length of the top strap  212  can define the positioning, in use, of the side arms  214  relative to the top of a user&#39;s ear. Shortening the length of the top strap  212  may position the side arms  214  higher above the user&#39;s ears thus avoiding contact between the side arms  214  and the user&#39;s ears. This may improve comfort for the user, as contact between the side arms  214  and the top of the user&#39;s ears may cause irritation or pressure points that over time can lead to pressure sores. 
       FIG. 13  shows the adjustment mechanism  228  in a disengaged position. The free end of the left portion  220  includes a guide loop  230  and plurality of holes  232  spaced along the length of the strap. The holes  232  extend through the thickness of the top strap  212 . The free end of the right portion  222  includes a pip or post  234  that protrudes from an internal surface  236  of the strap. 
     The guide loop  230  comprises a loop structure that forms an aperture at the end of the left portion  220 . The free end of the right portion  222  is configured to pass through the aperture formed by the guide loop  230 . Thus, the left portion  220  and the right portion  222  can be slid relative to one another to vary an overlapping distance of the left and right portions  220 ,  222  and, thus, vary a length of the top strap  212 . The guide loop  230  also maintains a link between the left and right portions  220 ,  222  when the adjustment mechanism  228  is not engaged. This may improve ease of use. The guide loop  230  is angled away from the internal surface  236  such that the aperture is at least partially offset from the thickness of the strap. This allows the right portion  222  to pass through the guide loop  230  and overlap with the left portion  220  without the left portion  222  having to bend or deform. 
     The post  234  is configured to pass through any of the holes  232 . As shown in  FIG. 14 , the post  234  comprises a stem  238  and a head or cap  240 . The illustrated post  234  is generally T-shaped; however, other shapes can also be used, such as a cylindrical stem  238  and disc-shaped or spherical head  240 , for example. The holes  232  are sized, shaped and/or otherwise configured to allow the head  240  of the post  234  to pass therethrough and to retain the post  234  once passed through the holes  232 , at least in response to normal or expected forces. However, the post  234  can be deliberately removed from the holes  232  to permit separation of the left and right portions  220 ,  222  of the top strap  212 , to allow for re-sizing of the headgear  204 . Passing of the post  234  through the holes  232  can be accomplished by deformation of one or both the post  234  and holes  232 . That is, the heads  240  of the posts  234  can flex or otherwise deform and the holes  232  can stretch or enlarge to facilitate passage of the head  240  of the post  234 . In alternative embodiments there may be a plurality of posts. 
     In alternative embodiments the adjustment mechanism  228  may comprise any other suitable means of adjustably connecting the free ends of the top strap 212 , such as but not limited to hook and loop fasteners, buckles. 
     In an alternative arrangement, an internal surface  236  of the left portion  220  can comprise a hook portion of a hook-and-loop fastener and an external surface  242  of the right portion  222  can comprise a loop portion of the hook-and-loop fastener. This arrangement can also be reversed. In some configurations, a material of the top strap  212  can define the loop portion of the hook-and-loop fastener. In other words, the loop portion may not be a discrete element of the top strap  212 . 
     Side Arms 
     The pair of opposing side arms  214  are configured, in use, to link the yoke  216  to the top strap  212  on each side of a user&#39;s face. This arrangement allows rotational forces that are applied to the patient interface  202  to be translated from the yoke  216  to the top strap  212  and the user&#39;s head in order to resist rotation of the seal  206  relative to the user&#39;s face. 
     The side arms  214  comprise elongate straps that are shaped to curve across a user&#39;s cheeks towards the temple and over the ear, in use. The curvature is such that the side arms  214  avoid the eyes to provide an uninterrupted field of view and improved comfort for the user. The curvature can follow the line of a user&#39;s cheek bones so that contact between the side arm  214  and the user&#39;s cheeks transfers forces away from the patient interface  202  so that the seal with the user&#39;s face is not disturbed. 
     The side arms  214  further comprise a buckle  226  that is integrally formed at a free end of each of the side arms  214 . In use, the free ends of the side arms  214  extend rearward beyond the junction  224  with the top strap  212 , and the buckle  226  is positioned either above or behind the user&#39;s ear. 
     The buckle  226  comprises an extension of the free ends of the side arms  214  and an aperture that extends through the thickness of the side arms  214 . The aperture is configured to receive the rear strap  218 . In alternative embodiments the buckle  226  may comprise a hook or any other geometry suitable for adjustably tethering the rear strap  218  to. 
     The side arms  214  may be resiliently flexible towards and away from the face of the user in an approximately horizontal plane (when worn), to accommodate different face sizes, but are relatively inflexible in an approximately vertical plane. The illustrated side arms  214  are solid, but other versions of the side arms could include one or more apertures or cut-outs extending lengthwise of the side arms to increase the resilient flexibility of the side arms towards and away from the face of the user, but to retain relative inflexibility in an approximately vertical plane (when worn). The vertical inflexibility of the side arms  214  allows the side arms  214  to transfer forces that may be applied to the patient interface  202 , such as but not limited to blow-off forces or hose drag/pull, to the top strap  212  and rear strap  214 . This may help to reduce the likelihood of the seal  206  being dislodged from the user&#39;s face and interrupting the delivery of the therapy. 
     Yoke 
     In use, the yoke  216  is symmetrical about a sagittal plane and comprises a substantially “U” shaped structure when viewed from above, as in  FIG. 16 . The yoke  216  follows the curvature of the frame  100  and is configured to connect the patient interface  202  to the headgear  204  via the frame  100 . The yoke  216  comprises a central bridge  244  and a pair of lateral rearward portions  248  that extend laterally and rearwardly from each side of the central bridge  244 . The yoke  216  provides a single connection between the headgear  204  and the frame  100  that is independent of any other features of the frame  100 . This allows the headgear  204  to be disconnected from the frame without interfering with or disconnecting any other part of the patient interface  202 . 
     The yoke  216  is configured to provide a connection between the frame  100  and the headgear  204  that supports the patient interface  202  in a vertical and horizontal direction relative to the user when the respiratory mask  200  is worn. By supporting the patient interface  202  in vertical and horizontal directions rotation of the seal  206  relative to the user&#39;s face is reduced and thus leaks may be reduced. 
     The central bridge  244  is shaped such that it fits within the recessed channel  106  of the frame  100  (described above). The central bridge  244  is configured to temporarily or permanently connect to the recessed channel  106  by means such as but not limited to a snap-fit connection, a friction-fit connection, a clip mechanism, adhesives or welding. The central bridge  244  curves over the inlet collar  114  of the frame  100  and transitions into the lateral rearward portions  248 . 
     The lateral rearward portions  248  form an integrally formed transition between the central bridge  248  and the side arms  214 . The lateral rearward portions  248  are positioned laterally of the central bridge  244  and curve around the frame  100  in a rearwards direction, when the respiratory mask  200  is worn by a user. 
     As shown in  FIG. 16 , the central bridge  244  has a height H 1  that is less than a height H 2  of the lateral rearward portions  248  of the yoke  216 . Height H 1  is less than height H 2  in order to minimize the size of the frame  100 . Height H 2  is greater than height H 1  in order to provide a desired level of structure in the vertical direction to prevent rotation of the patient interface  202  relative to the user&#39;s face. H 1  may be between 1 mm and 12 mm, or between 4 mm and 7 mm. In the illustrated embodiment H 1  is 5.5 mm. H 2  may be between 5 mm and 16 mm, or between 8 mm and 13 mm. In the illustrated embodiment H 2  is 12.5 mm. 
     The side arms  214  may continue from the lateral rearward portions  248  at the same or greater height than H 2 . In some embodiments the height of the side arms  214  increases in a direction moving away from the yoke  216 . The transition between H 1  and H 2  occurs between the central bridge  244  and the lateral rearward portions  248 . The lateral rearward portions  248  are configured to contact the frame  100  until the height has transitioned fully to that of H 2 . This configuration allows the frame  100  to provide structural support to the yoke  216  over the maximum height such that there are no parts of the yoke  216  or side arms  214  with a small height that are unsupported and may form a weak point. This enables forces to be translated from the frame  100  through the yoke  216  to the side arms  214  without passing through a weak point that may cause the side arms  214  or yoke  216  to twist or bend a vertical direction allowing rotation of the patient interface  202 . In some embodiments the height of the side arms  214  is no greater than  16 mm; in order provide a minimal respiratory mask. 
     It can be seen in  FIG. 16  that the soft edges  250  of the side arms  214  are transitioned out so that they do not exist in the yoke  216 . This may provide an improved connection between the yoke  216  and the frame  100 , by providing rigid, semi-rigid, inelastic or substantially inextensible edges that can be engaged by the recessed channel  106  of the frame  100 . The soft edges  250  are not required on the edges of the yoke  216  as they are not likely to come into contact with the user and cause discomfort or irritation. The size of the yoke  216  may be minimized by transitioning out the soft edges  250 ; therefore the size of the frame  100  may be minimized to provide a less obtrusive respiratory mask system  200 . 
       FIG. 17  shows that in the illustrated embodiment, the lateral rearward portions  248  of the yoke  216  have a greater wall thickness T 1  in a direction perpendicular to the internal surface  236  than a wall thickness T 2  at a center of the yoke  216  and the side arms  214 . The increased thickness provides increased structure at the lateral most part of the yoke  216  that contacts the frame  100 . This allows for the effective translation of forces from the side arms  214  to the frame to minimize vertical rotation of the patient interface  202 . The lateral rearward portions can have a thickness T 1  of between 1 mm and 4 mm. In the illustrated embodiment the thickness T 1  is 2.9 mm. The central bridge  244  and side arms  214  have a thickness T 2  of between 0.5 mm and 3 mm. In the illustrated embodiment T 2  is 2.1 mm. 
     The reduced thickness T 2  of the side arms  214  relative to the greater wall thickness T 1  of the lateral rearward portions  248  of the yoke  216  can facilitate horizontal flexibility in the side arms  130  relative to the yoke  216  (when worn). This enables the side arms  214  to flex in a horizontal direction to cater for differing facial geometries, whilst providing stability in the vertical direction, when the respiratory mask  200  is worn by a user. 
     Rear Strap 
     The rear strap  218  comprises an elongate strap that extends between and is connected about the buckles  226  of the side arms  214 . The ends of the rear strap  218  are adjustably tethered through the apertures of the buckles  226  such that the length of the rear strap  218  can be adjusted. Adjustment of the length of the rear strap  218  can further adjust the overall size of the headgear  204  to fit each individual user. 
     In the illustrated configuration, the rear strap  218  is elastic or extensible. Such an arrangement allows the rear strap  218  to stretch to adjust a circumferential length of the headgear  204 . The amount of stretch of the rear strap  218  can be limited and, thus, the rear strap  218  can also be adjustable in length, as previously described. In some configurations, it is preferable for circumferential length adjustment to occur at the back of the user&#39;s head, which is less susceptible to lengthening in response to blow-off forces. The rigid, semi-rigid, inelastic or substantially inextensible nature of the junctions  224  and side arms  214  positioned on the side and forward portions of the user&#39;s head assists in maintaining a desired circumferential length of the headgear  204  despite the elastic nature of the rear strap  218 . In some cases, frictional forces between the portions of the headgear  204  and the side and forward portions of the user&#39;s head inhibit movement or lengthening of the headgear  204  in response to blow-off forces. However, in other arrangements, the rear strap  214  can be rigid, semi-rigid, inelastic or substantially inextensible and, in such cases, may be adjustable in length. 
     In the illustrated embodiment the rear strap  218  comprises a length of laminated textile and foam, such as but not limited to Breathoprene®. The rear strap is elastic such that it can be stretched to allow the headgear  204  to be pulled over a user&#39;s head without adjusting the length of the rear strap  218 . This improves ease of use. In alternative embodiments the rear strap may comprise any suitable textile or fabric material. 
     The rear strap  218  has two lateral ends  244  that are configured to pass through the buckles  226  and fold back on themselves (shown in  FIG. 12 ) where they can be fastened at a user defined position. The lateral ends  226  of the rear strap  218  can be fastened to an outer surface of the rear strap  218  by a fastening means such as but not limited to a hook and loop fastener. The overlap between the folded over lateral ends  244  and the rest of the rear strap  218  determines the length of the rear strap  218  and the sizing of the headgear  204 . In the illustrated embodiment the lateral ends  244  of the rear strap  218  include a fastener tab in the form of a hook component of a hook and loop fastener (such as but not limited to Velcro® brand hook and loop fastener). The fastener tab is configured to be fastened to a loop component on the outer surface of the rear strap  218 . In the illustrated embodiment the outer surface of the rear strap  218  comprises a material that provides the loop component of the hook and loop fastener. In alternative embodiment this arrangement of hook and loop fastener can be reversed such that the hook component is on the outer surface of the rear strap  218 . 
     Alternative Headgear Embodiment 
       FIGS. 18 and 19  show another non-limiting exemplary embodiment of a headgear  304 . For the purposes of this description, features of this embodiment that are substantially similar to those of the previous embodiment of headgear  204  are allocated reference numerals that are the same plus one hundred. For example headgear  204  becomes headgear  304  in the present embodiment. For the sake of brevity only those features which differ substantially from the previous embodiment will be described in detail here. It is to be understood that all other features are substantially as described in relation to the headgear  204 . 
     Headgear  304  comprises a top strap  312 , pair of opposing side arms  314 , yoke  316  and a rear strap  318 . As in the previous embodiment the top strap  312 , side arms  314  and yoke  316  are rigid, semi-rigid, inelastic or substantially inextensible and formed as a single integrally formed component. The single integrally formed component can be arranged to form a closed loop that, in use, encircles an upper front portion of a user&#39;s face. The top strap  312 , side arms  314  and rear strap  318  are substantially the same as the top strap  212 , side arms  214  and rear strap  218  as previously described. As shown, the rear strap  318  can extend between and be connected to buckles  326  of the side arms  314 . One or both ends of the rear strap  318  can include a grip tab  319  that can advantageously allow the user to more easily grip the end(s) of the rear strap  318  to adjust and/or secure the rear strap  318 . The top strap  312  can be adjustment via an adjustment mechanism  328 . 
     The yoke  316  of the present embodiment is configured to provide a connection between the headgear  304  and patient interface (not shown, but can be similar to patient interface  202 ). The yoke  316  is symmetrical about a sagittal plane (shown in  FIG. 19 ), in use, and comprises a loop structure formed by an upper bridge  350  and a lower bridge  352  that are joined at lateral ends by a front end of each of the side arms  314 . The upper and lower bridges  350 ,  352  are configured to removably connect to a frame (not shown, but may be similar to frame  100 ) about an inlet collar or connection of the frame. The upper and lower bridges  350 ,  352  are curved such that the loop structure they form is continuous and defines an aperture configured to encircle the inlet collar. This curved shape may be configured to fit within a perimeter of the frame, so as to reduce the overall size of the patient interface. 
     The upper and lower bridges  350 ,  352  are configured to resist rotational forces that may be applied to the patient interface. The upper and lower bridges  350 ,  352  provide two paths through which forces can be transferred from the frame to the headgear  300 ; this may evenly distribute rotational forces so that the there is no bias towards upwards or downwards rotation. 
     Alternative Frame Embodiment 
       FIG. 20  shows another non-limiting exemplary embodiment of a respiratory mask assembly  400 . The respiratory mask assembly  400  includes a patient interface  402  and a headgear  404 . The patient interface  402  includes a seal  406  configured to connect to a frame  410  and a gas delivery conduit  408 . In some embodiments, the frame  410  has a reduced or smaller overall profile compared to the frame  100 . The headgear  404  and frame  410  are configured to secure the seal  406  in a stable position below the nose of a user in use. 
     The seal  406  can be substantially similar to the seal  6  described above and has a reduced contact area with the user&#39;s face in comparison to more traditional nasal masks that seal around the user&#39;s nose, crossing the nose near or on the nasal bridge. The reduced contact area may result in reduced seal stability, which may require counteraction from the headgear  404 , in order to prevent leaks and loss of therapy. The headgear  404  is configured to provide support to counteract forces that may act to break a seal between the seal  406  and the user&#39;s face. Forces that may interrupt the seal may include, but are not limited to, blow-off forces induced by the pressure of the CPAP therapy provided, hose drag forces, and/or contact between the patient interface  402  and bedding caused by movement of the user. 
     The frame  410 , illustrated in  FIGS. 21-23B and 26A-32B  provides a connection between the seal  406  and the headgear  404 . Like the frame  100 , the frame  410  has an exterior surface  412 , an interior surface  413 , and a fluid path  415  extending therethrough as shown in  FIGS. 21-23B . The exterior surface  412  and interior surface  413  span from a first lateral edge  422  to a second lateral edge  424 . The exterior surface  412  faces away from the user in use and acts as an interface among the frame  410 , a headgear (such as headgear  404 ), and a gas delivery conduit (such as gas delivery conduit  408 ). The interior surface  413  faces the user in use and may contact the seal  406  and/or a coupling structure connected to the seal  406 . In use, the gas delivery conduit  408  is coupled to the frame  410  such that the gas delivery conduit  408  is in fluid communication with the fluid path  415 . 
     The exterior surface  412  includes a recessed surface  426  and an elevated surface  428 . In some embodiments, a portion of the headgear  404 , for example, a yoke  416 , can be placed adjacent the recessed surface  426  when assembled. In the illustrated embodiment, the recessed surface  426  is above the elevated surface  428  and/or adjacent a top edge of the frame  410 , while the elevated surface  428  is below the recessed surface  426  and/or adjacent a bottom edge of the frame  410 . An inlet collar  430  projects outwardly (away from the user in use) from the exterior surface  412 . The inlet collar  430  surrounds the fluid path  415 . In the illustrated embodiment, a border between the recess surface  426  and the elevated surface  428  is partially defined by the inlet collar  430 . The inlet collar  430  includes an inlet collar interior surface  432  (that defines the fluid path  415 ) and inlet collar surface  434  (located on an outside of the inlet collar  430 ). In some embodiments, the inlet collar surface  434  can be considered a part of or to partially define the exterior surface  412 . In the illustrated embodiment, the inlet collar  430  includes a conduit retaining projection  436  (shown in  FIG. 22 ). The inlet collar  430  can include one or more bias flow holes  438 . 
     An outlet collar  440  projects inwardly (toward the user in use) from the interior surface  413 . The outlet collar  440  has an outlet collar surface  444 , which in some embodiments, can be considered a part of or to partially define the interior surface  413 . The outlet collar  440  can include one or more seal retaining recesses  446 . The seal retaining recesses  446  allow for interaction and/or connection between the frame  410  and the seal  406 . In some embodiments, the seal retaining recess  446  allow for interaction and/or connection between the frame  410  and a coupling structure, such as a clip, that connects to the seal  406 . In the illustrated embodiment, the outlet collar surface  444  includes the seal retaining recesses  446 . 
     The fluid path  415  is defined or formed by the inlet collar  430  and the outlet collar  440 . In use, the gas delivery conduit  408  is coupled to the inlet collar  430  and the seal  406  is coupled to the outlet collar  440 . Gases can be delivered from the gas delivery conduit  408 , through the fluid path  415  (i.e., through the inlet collar  430  and outlet collar  440 ), to the seal  406  to be delivered to the user. 
     In the illustrated embodiment, the inlet collar  430  can be oval and have a major axis  113  and a minor axis  111 . In some embodiments, the inlet collar  430  can have a circular, triangular, “D”, or other shape. In the illustrated embodiment, the frame  410  is symmetric about the minor axis  111  or vertical axis  105 . In the illustrated embodiment, a major dimension D major  (illustrated in  FIG. 23B ) of an aperture defined by the inlet collar  430  is 21.9 mm or approximately 21.9 mm, and a minor dimension D minor  of the aperture is 16.7 mm or approximately 16.7 mm. In other words, a ration between the major dimension and the minor dimension is 1.31:1 or approximately 1.31:1. 
     In the illustrated embodiment, a lateral dimension (or a width) W of the frame  410  (illustrated in  FIG. 23B ) is 49.3 mm or approximately 49.3 mm. The ratio between the major dimension of the aperture defined by the inlet collar  430  and the lateral dimension W of the frame  410  is therefore 1:2.25 or approximately 1:2.25. The lateral dimension of the frame  410  can be selected to optimize or enhance the function of the frame  410  when assembled with the seal  406  and headgear  404 . In some embodiments, the lateral dimension of the frame  410  can be in the range of 30 mm (or approximately 30 mm) to 75 mm (or approximately 75 mm). 
     In the illustrated embodiment, a vertical dimension (or a height) H of the frame  410  (illustrated in  FIG. 23B ) is 28.0 mm or approximately 28.0 mm. The ratio between the minor dimension of the aperture defined by the inlet collar  430  and the vertical dimension of the frame  410  is therefore 1:1.68 or approximately 1:1.68. One consideration in selecting the vertical dimension of the frame  410  is the area needed for the recessed surface  426  and/or headgear retaining features as described herein to maintain an effective connection between the frame  410  and the headgear  404 . The vertical dimension of the frame  410  can be selected to provide adequate structure to enable the headgear  404  to connect effectively to the frame  410  and/or to provide adequate structural and rotational integrity required by the seal  406 . In some embodiments, the vertical dimension of the frame  410  can be in the range of 20 mm (or approximately 20 mm) to 50 mm (or approximately 50 mm). The vertical dimension can be varied to accommodate different seal sizes, headgear profiles, and/or headgear connection methods or mechanisms. 
     In the illustrated embodiment, a proximal dimension (or a thickness) T of the frame  410  (illustrated in  FIG. 26B ) is 17.05 mm or approximately 17.05 mm. As shown in the side views of  FIGS. 26A and 26B , an entirety of a periphery or distal end of the inlet collar  430  (in other words, a rim of the inlet collar  430  farthest away from the user in use) is not aligned with the illustrated vertical axis  105 . Vertical extremes (in other words, the top and bottom) of the inlet collar  430  intersect the vertical axis, but central portions (in other words, sides or lateral extremes) of the inlet collar  430  are displaced proximally (or toward the user in use). In other words, when viewed from the side (as in  FIGS. 26A-26B ), the periphery of the inlet collar  430  is distally facing concave (or concave facing away from the user in use). The concave profile can advantageously allow the frame  410  to have reduced material requirements. In some embodiments, the oval shape of the inlet collar  430  and/or the offset vertical and lateral extremes of the distal end of the inlet collar  430  provide beneficial behavior when a gas delivery conduit, such as gas delivery conduit  408 , is coupled to the inlet collar  430 . For example, if the gas delivery conduit  408  is removably coupled to the inlet collar  430 , for example, via a press fit, snap fit, or other connection that cooperates with the conduit retaining projection  436 , it can be difficult to unintentionally remove the gas delivery conduit  408  if a force is applied axially (in an axial direction of the inlet collar  430  and/or gas delivery conduit  408 ). The oval shape and/or concave distal end of the inlet collar  430  can therefore inhibit unintentional removal of the gas delivery conduit  408 . However, the gas delivery conduit can be detached from the frame  410  more easily or with less effort if the gas delivery conduit is twisted about the axial axis of the inlet collar  430 . 
     The frame  410  can include various headgear retaining features. The retaining features are used to couple the frame  410  to the headgear  404  as shown in  FIG. 25 . In the illustrated embodiment of  FIGS. 21-23B , the frame  410  includes two retaining features  450  located in the recessed surface  426 . More or fewer retaining features  450  are also possible. As shown, each retaining features  450  is displaced laterally with respect to or spaced laterally from the vertical axis, with one of the retaining features  450  on each side of the vertical axis. In the illustrated embodiment, the retaining features  450  are circular holes. In some embodiments, the retaining features  450  are holes having an oval, rectangular, “D” (for example, as shown in  FIG. 24C ), or other shape. In some embodiments, the two retaining features  450  are different from each other. Differing shapes for the right and left headgear retaining features  450  can help guide the user in properly connecting the headgear  404  to the frame  410 . In some embodiments, the headgear retaining features  450  have anti-rotation shapes and/or features. The headgear  404  can include projections that correspond to the retaining features  450  and are designed to fit into the retaining features  450 . The projections can be secured to the retaining features  450  and the frame  410  via a snap-fit or other suitable means. In some embodiments, the retaining features  450  can be structures projecting outwardly from the recessed surface  426 , for example as shown in  FIG. 24D . In some such embodiments, the headgear  404  can include corresponding holes that receive the retaining features  450 . In the illustrated embodiment, each of the retaining features  450  is a circular projection with a central channel that extends between and/or divides the retaining feature  450  into two semi-circular or approximately semi-circular sides or portions. The projections can be secured to correspondingly sized holes in the headgear  404  via a snap fit or other suitable means. In some embodiments, the retaining features  450  can includes one or more magnets or a magnetic material that attract to one or more magnets or magnetic material in the headgear  404 . 
     As described above, in the illustrated embodiment the frame  410  includes two retaining features  450 . The inclusion of two retaining features  450  and/or the use of circular retaining features  450  can advantageously allow for ease of donning and doffing the headgear  404  from the frame  410 . As shown in  FIG. 24A , a first of the retaining features  450  can be used to connect the frame  410  and headgear  404  at an angle. The frame  410  can then be rotated about the first retaining feature  450  so that a second of the retaining features  450  can be connected to the headgear  404  as shown in  FIG. 24B . 
     In the illustrated embodiment, the inlet collar  430 , or the inlet collar surface  434 , is angled by an angled surface angle θ A  such that a diameter of a base of the inlet collar  430  nearest the user in use is greater than a diameter of the periphery of the inlet collar  430  farthest away from the user in use, as shown in  FIGS. 28 and 29C . The inlet collar  430  may resemble a hollow frustum. The angle of the inlet collar  430  causes or allows air passing through the bias flow holes  438  (generally or approximately perpendicularly to the angled inlet collar  430  or inlet collar surface  434 ) to be directed away from the user&#39;s face. This advantageously prevents or reduces the likelihood of the user feeling a draft resulting from air flow through the bias flow holes  438  and/or entrainment. 
     A first angled surface angle can be defined as the angle between the top (or upper vertical extreme) of the inlet collar  430 , or inlet collar surface  434 , and an axis parallel to the proximal axis and located at an intersection of the inlet collar  430  and the exterior surface  412  or recessed surface  426  of the frame  410  as shown in  FIG. 28 . A second angled surface angle θ A2  can be defined as the angle between the lateral side of the inlet collar  430 , or inlet collar surface  434 , and an axis parallel to the proximal axis and located at an intersection of the inlet collar  430  and the exterior surface  412  or elevated surface  428  of the frame  410  as shown in  FIG. 29C . In some embodiments, the angled surface angles can be in the range of approximately 10° to about 15°. In the illustrated embodiment, the first angled surface angle is approximately 10°, the second angled surface angle is approximately 15°, and the angled surface angle transitions from approximately 10° to about 15° between the top and side of the inlet collar  430 . In some embodiments, the angled surface angle can be constant around the entirety of the inlet collar  430 . In some embodiments, the angled surface angle can vary around the inlet collar  430 . In some embodiments, the angled surface angle can be in the range of approximately 0° to approximately 90°, for example, approximately 0°, approximately 45°, or approximately 90°. 
     In the illustrated embodiment, each bias flow hole  438  is displaced or spaced equally from the distal end of the inlet collar  430 . In other words, an arrangement of the bias flow holes  438  follows the profile of the distal end or periphery of the inlet collar  430 , with bias flow hole(s)  438  located at or proximate a vertical extreme (top or bottom) of the inlet collar  430  being distal to or farther away from the user in use than bias flow hole(s)  438  located at or proximate lateral sides of the inlet collar  430 . In some embodiments, an arc connecting the bias flow hole(s)  438  is parallel or generally parallel to the periphery of the inlet collar  430 . Maintaining a constant and controlled distance between the bias flow holes  438  and the periphery of the inlet collar  430  can allow for better and easier control of noise produced by flow through the bias flow holes  438 . The distance between the bias flow holes  438  and the periphery of the inlet collar  430  can be selected to reduce or minimize noise produced by flow through the bias flow holes  438 . In the illustrated embodiment, the bias flow holes  438  are positioned 3.1 mm or approximately 3.1 mm from the periphery of the inlet collar  430 . In the illustrated embodiment, the bias flow holes  438  are located at or approximately at a mid-point of a length of the inlet collar  430 . 
     In the illustrated embodiment, as shown in  FIG. 26D , bias flow holes  428  are disposed about or in a portion of the inlet collar  430 . The portion of the inlet collar  430  including bias flow holes  428  can be defined by an exhaust angle BE, which is defined with respect to an origin centered at the intersection of the vertical axis  105  and the lateral axis  107  of the inlet collar  430  as shown. In some embodiments, the exhaust angle and/or the bias flow holes  428  can span from approximately 4:00 to approximately 8:00 (as on a clock). In some embodiments, the exhaust angle and/or the bias flow holes  428  can span from approximately 5:00 to approximately 7:00 or from approximately 3:00 to approximately 9:00. In some embodiments, the exhaust angle can be approximately 220°, approximately 218°, in the range of approximately 180° to approximately 270°, in the range of approximately 190° to approximately 260°, in the range of approximately 200° to approximately 250°, in the range of approximately 210° to approximately 240°, or in the range of approximately 220° to approximately 230°. In some embodiments, the exhaust angle can be 360°. In other words, in some embodiments, the bias flow holes  428  can span the circumference of or entirely encircle the inlet collar  430 . 
     As shown in  FIG. 26C , in the illustrated embodiment, the bias flow holes  438  extend through the inlet collar  430  perpendicularly or approximately perpendicularly to the inlet collar surface  434  and/or the inlet collar interior surface  432 . In some embodiments, as indicated by the dashed lines in  FIG. 26C , the bias flow holes  438  can extend through the inlet collar  430  at an angle θ relative to perpendicular. Angle θ can be in the range of approximately ±10° to approximately ±45°, for example, ±10°, ±25°, or ±45°. As illustrated, bias flow holes  438  oriented at a positive angle extend such that the hole is closer to the periphery of the inlet collar  430  on the inlet collar surface  434  than on the inlet collar interior surface  423 . Angles greater than or equal to 0 can advantageously direct flow through the bias flow holes  438  away from the user in use. 
     As shown in  FIG. 27B , the outlet collar  440  has a major axis  119  and a minor axis  121 . In the illustrated embodiment, the outlet collar  440  has a “D” shape. A major axis dimension D o-major  of the outlet collar  440  is the dimension of an aperture defined by a proximal-most end or edge of the inlet collar  440  along the major axis  119  at a position at which the aperture has a maximum lateral dimension. In some embodiments, the outlet collar  440  can have a circular, triangular, or other shape. A minor axis dimension D o-minor  of the outlet collar  440  is the dimension of the aperture along the minor axis  121 , which is parallel and/or aligned with the vertical axis, shown in  FIG. 27A , in the illustrated embodiment. As shown in  FIG. 27A , the vertical axis and lateral axis intersect at an origin at or corresponding to the center of the aperture of the inlet collar  430 . In the illustrated embodiment, the outlet major axis corresponds to or is located at the same position as the lateral axis. In some embodiments, the outlet major axis can be vertically displaced or spaced from the lateral axis. In other words, in some embodiments, a center of the aperture of the inlet collar  430  is offset from a center of the aperture of the outlet collar  440 . 
     In the illustrated embodiment, the outlet major axis dimension D o-major  is 25.9 mm or approximately 25.9 mm, and the outlet minor axis dimension D o-minor  is 20.7 mm or approximately 20.7 mm. In other words, a ratio between the outlet major axis dimension D o-major  and the outlet minor axis dimension D o-minor  is 1.25:1 or approximately 1.25:1. In the illustrated embodiment, the aperture of the outlet collar  440  is larger than the aperture of the inlet collar  430 . 
     In some embodiments, the outlet collar  440  or a portion of the outlet collar  440 , e.g., a rim  441  of the outlet collar in the illustrated embodiment, is a different color compared to other portions of the frame  410 . In some embodiments, the majority of the frame  410  can be transparent, and the outlet collar  440  or a portion of the outlet collar  440  can be a transparent blue color. In some embodiments, the majority of the frame  410  can be transparent, and the outlet collar  440  or a portion of the outlet collar  440  can be opaque. In some embodiments, the majority of the frame  410  can be opaque and the outlet collar  440  or a portion of the outlet collar  440  can be transparent. The different color (and/or transparency) of the outlet collar  440  or portion thereof can advantageously provide an indication to the user that the outlet collar  440  is designed to engage with another component of the assembly, e.g., a coupling structure, such as a clip, of the seal  406 , in use. As shown in  FIG. 29B , a proximal rim  441  extending to a certain depth of the outlet collar  440  can have a different color. In some embodiments, the different color can be produced using a Pad Printing process. In some embodiments, the inlet collar  430  or a portion of the inlet collar  430  is a different color compared to other portions of the frame  410 . In some embodiments, the outlet collar  440  and/or inlet collar  430  can be made from a material that differs in at least one property from a material of the majority of the frame  410  or of other portion(s) of the frame  410 . For example, the outlet collar  440  can be made from a material that differs in at least one property from a material of the inlet collar  430 . In such an embodiment, the frame  410  can be formed using, for example, a two-shot molding, co-molding, or over-molding process. In some embodiments, the frame  410  can be formed using a two-shot molding, co-molding, or over-molding process even if the frame  410  is made of a single material and/or the material of the inlet collar  430  does not differ from a material of the outlet collar  440 . 
       FIG. 32A  illustrates a section view taken along line  32 A- 32 A in  FIG. 31 . The section line is centrally located with respect to the frame  410  and is aligned with the vertical axis.  FIG. 32B  illustrates a  2 D view of the section of  FIG. 32A . A thickness of the frame  410 , or thicknesses of various parts of the frame  410 , can be selected to provide sufficient rigidity to the frame  410  in use while reducing or minimizing the weight and/or profile of the frame  410 . In some embodiments, the recessed surface  426  (or the frame  410  in the region of the recessed surface  426 ) has a thickness t rs  of 1.5 mm or approximately 1.5 mm. In some embodiments, the inlet collar  430  has a thickness t ic  of 1.46 mm or approximately 1.46 mm. In some embodiments, the conduit retaining projection  436  projects inwardly from the inlet collar interior surface  432  0.5 mm or approximately 0.5 mm. In the illustrated embodiment, the conduit retaining projection  436  extends around an entirety of the periphery of the inlet collar  430 . In some embodiments, the outlet collar  440  has a thickness t oc  of 1.5 mm or approximately 1.5 mm. Other thicknesses for the inlet collar  430 , recessed surface  426  (or frame  410  in the region of the recessed surface  426 ), and/or outlet collar  440  are also possible. In some embodiments, the frame  410  is made of or includes Nylon 12. Altering characteristics of the compound can allow the frame  410  to exhibit the same or similar rigidity when the inlet collar  430 , recessed surface  426  (or frame  410  in the region of the recessed surface  426 ), and/or outlet collar  440  have thicknesses in the range of 0.6 mm or approximately 0.6 mm to 2 mm or approximately 2 mm or greater than 2 mm. 
     Alternative Headgear Embodiment 
       FIGS. 33-34  show an exemplary embodiment of the headgear  404  that can be used with frame  410 . In the illustrated embodiment, the headgear  404  has a bifurcated configuration. The headgear  404  can be similar to the headgear  204  in some ways. Features of the headgear  404  that are the same as or similar to corresponding features of the headgear  204  are indicated by reference numerals that are the same plus  300  herein (e.g., the headgear  404  includes a top strap  512 , a pair of opposing side arms  514 , a yoke  516 , and a rear strap  518 ). The top strap  512  and rear strap  518  form the bifurcated configuration. 
     The side arms  514  and/or top strap  512  can include a core  549  and an outer casing  551 . In some embodiments, the core is made of or includes a plastic material. In some embodiments, the outer casing is or includes a textile. The outer casing can be permanently bonded to the core. A textile outer casing can advantageously provide a soft and comfortable finish for contacting the user in use. A longitudinal edge portion of the outer casing  551  that protrudes from edges of the core  549  and is not filled by the core  549  can form a soft edge  550  as shown in  FIG. 37 . Soft edges  550  can advantageously provide a cushioned edge that can improve user comfort, for example, by softening potential contact between edges of the top strap  512  and/or side arms  514  and the user&#39;s head. In some cases, having a cushioned edge can be of particular benefit on a lower edge of the side arms  514  that sit above the user&#39;s ears in use. A thickness of the soft edge  550  can vary along a length of each side arm  514 . In the illustrated embodiment, the thickness of the soft edge  550  varies from a maximum of 2 mm or approximately 2 mm at lateral ends of the side arms  514  (indicated by D 2  in  FIG. 37 ) to a minimum of 1 mm or approximately 1 mm on an upper ridge of the yoke  516  (indicated by Di in  FIG. 37 ). In some embodiments, a lower edge of the yoke  516  does not include a soft edge, for example, because the lower edge of the yoke  516  is not intended to be in contact with the user&#39;s face in use, for aesthetic and/or industrial design benefits, to allow for tolerances between parts, and/or other reasons. The omission of a soft edge in this region provides additional space to allow for increasing a thickness of the core  549  of the yoke  516  to improve or increase the structural integrity of that region. 
     In the illustrated embodiment, the outer casing  551  is made of a textile that is a non-stretch or low-stretch yarn. A non-stretch or low-stretch yarn requires a relatively high force for elastic deformation. In some cases, yarns having a high elasticity perform poorly (or worse compared to yarns having a lower elasticity) in an intra-molding process used to form the top strap  512  and/or side arms  514  as the yarn fibers may stretch to an extent that the molten plastic can escape outside of the outer casing. Using a non-stretch or low-stretch yarn for the side arm  514  outer casing advantageously improves the finish and/or consistency of the finished side arms  514 . A non-stretch or low-stretch yarn reduces or minimizes the amount or degree to which the fibers of the yarn can stretch, which can prevent or reduce the likelihood of the plastic stretching and escaping from the textile outer casing during the intra-molding process. The use of a non-stretch or low-stretch yarn can therefore also help improve the reliability of the manufacturing process. In some embodiments, the textile outer casing can be made of or include a yarn having a degree of elasticity. A yarn having a low elasticity (i.e., that requires a relatively high force to elastically stretch) may perform adequately in the molding process. In some embodiments, a gate  501  for the molding process is located at or near a central point on the yoke  516  of the headgear  404  as shown in  FIG. 35B . 
     As described herein, the frame  410  can include headgear retaining features  450  in the form of holes that are designed to receive projections  515  of the headgear  404 . As shown in  FIG. 35A , the projections  515 , also referred to as frame retaining features herein, can be located on either side of the yoke  516 . In the illustrated embodiment, each of the projections  515  includes two retaining portions  517  separated by a channel  519  as shown in  FIGS. 35A and 36A-36B . The channel  519  is formed by a projection  619  in the mold tool  600  that fills the region forming the channel  519  as shown in  FIG. 36C . During molding, molten plastic forces itself through the outer casing  551  under pressure or is allowed to exit the outer casing  551  to form the retaining portions  517 . The projection  619  of the mold tool  600  also restrains the outer casing  551  fabric or material to prevent or inhibit the outer casing  551  fabric or material from expanding beyond the base of the channel  519  as the plastic exits to form the retaining portions  517 , as indicated by  553  in  FIG. 36C . The outer casing  551  can also or alternatively be restrained in other ways. For example, if the retaining portions  517  (and/or other projections that protrude from the outer casing  551 ) have a thin profile or dimension relative to a profile or dimension of the textile outer casing  551 , the outer casing  551  may not be able to protrude onto the projection to a large extent. This advantageously prevents or inhibits deformation of the outer casing  551  and/or helps ensure the retaining portions  517  include or are made of only plastic. Having the retaining portions  517  made only or primarily of plastic, rather than including the outer casing, can advantageously improve the function of the frame retaining features  515 , e.g., by allowing the frame retaining features  515  to snap into the headgear retaining features  450  more securely. The channel  519  can also or alternatively allow the retaining portions  517  to flex relative to each other to improve performance of the frame retaining features  515 , e.g., to allow the frame retaining features  515  to flex to snap into the headgear retaining features  450 . 
     As shown in  FIG. 38A , each side arm  514  includes a buckle  526 . The buckle  526  is formed by an extension of the free end of the side arm  514  and includes an aperture  527  extending through the thickness of the side arm  514 . The aperture  527  is configured to receive the rear strap  518 . In the illustrated embodiment, the buckle  526  is integrally formed with the side arm  514 . In some embodiments, the structure of the buckle  526  can be maintain by the core  549 , and the outer casing  551  can make the buckle  526  soft to the touch. The buckle can be formed by intra-molding the entire buckle structure with a complete plastic core, including the location of the aperture  527 , and then die cutting the aperture  527 . Alternatively, the aperture  527  can be formed in the intra-molding process, where the outer casing  551  of the side arm  514  splits into two tubes at the end of the aperture  527  adjacent the side arm  514 , and then the tubes re-combine on the opposite side of the aperture  527 . In some embodiments, the buckle  526  can be formed by plastic (or other core  549  material) that bursts through an end of the casing  551 , such that the buckle  526  does not include an outer casing  551 . In some embodiments, the soft edge  550  of the side arms  514  extends on the top and bottom of the side arms  514  and the buckle  526 , and the lateral end  525  of the buckle  526  does not include a soft edge  550 , for example as shown in  FIG. 38B . In the illustrated embodiment, the buckle  526  is coplanar or in line with the side arm  514  when the headgear  404  is laid flat. In some embodiments, the buckle  526  is offset from the side arm  514 , for example, away from or toward the user in use. 
     Similar to headgear  204 , the top strap  512  of the headgear  404  includes a first (or left) portion  520  and a second (or right) portion  522  as shown in  FIGS. 39-40 . The first  520  and second  522  portions are separate from each other. Each of the first  520  and second  522  portions has a free end and a fixed end. The fixed ends extend at an angle from the side arms  514  at the junctions  524 . The free ends are configured to be adjustably connected by an adjustment mechanism  528 . The adjustment mechanism  528  allows the top strap  512  to be adjusted and secured at a desired length. 
     As shown in  FIGS. 39-41 , the free end of the second portion  522  includes a guide loop  530 , and the second portion  522  includes a plurality of holes  532  spaced along a length of the second portion  522  proximate the free end. In the illustrated embodiment, the guide loop  530  is plastic. The guide loop  530  can be formed by a burst-through molding process. “Burst-through molding” is described in the Applicant&#39;s co-pending Applications US62/309,400, US62/323,459, US62/364,767, and US62/401,462. Burst-through molding is a variation of intra-molding as described above. The burst-through molding process comprises introducing molten plastic into a textile casing and pushing the molten plastic through a portion of the textile casing. A component formed by the burst-through molding process comprises a unitary plastic core that is integrally formed with a textile casing and the unitary plastic core has a portion that extends through the textile casing. In some embodiments, the guide loop  530  can be coupled to the free end of the second portion  522 . In some embodiments, the guide loop  530  includes an outer casing, such as an extension of the outer casing  551 . In some embodiments, the guide loop  530  is made of or includes only the outer casing material and no plastic (or other core material). The first portion  520  includes a projection  534  that protrudes from an internal surface of the first portion  520  (i.e., a surface of the first portion  520  that faces the second portion  522  in use) proximate the free end. The first portion  520  can also include a number of position indicators. To adjust and/or secure the first  520  and second  522  portions relative to each other, the free end of the first portion  520  is passed through the guide loop  530 , and the projection  534  is passed through and/or secured in one of the holes  532 , for example, via a snap-fit connection. 
     The holes  532  can be formed using a burst-through intra-molding process. In some embodiments, the outer casing  551  of the second portion  522  can split into two parallel (and enclosed) casing portions adjacent (on the junction  524  side of) the first hole  532  (i.e., the hole  532  closest to the junction  524 ), and the parallel casing portions can extend along the length of the second portion  522  including the holes  532 . The parallel casing portions can recombine into a single casing after (or on the free end side of) the last hole  532  (i.e., the hole  532  farthest away from the junction  524 ). The parallel casing portions can bend towards each other between holes  532  such that a gap in the fabric or material of the casing  551  may not be easily observed by the user. In some embodiments, the parallel casing portions do not recombine after the last hole  532 . In some such embodiments, pressure from the plastic or core  549  material can force the parallel casing portions to move closer together after the final hole  532  such that a gap in the fabric is not easily observed. In some embodiments, the outer casing  551  includes the holes  532 , and the mold tool is designed to restrict the flow of molten plastic (or other core  549  material) from extending into the holes  532  during molding. In some embodiments, the second portion  522  can be intra-molded without holes  532 , and the holes  532  can be created via post-processing, for example, via die cutting. In some embodiments, the outer casing  551  can terminate proximate or adjacent (on the junction  524  side of) the first hole  532 , and the remainder of the second portion  522  can be formed using the burst-through process to include only plastic (or other core  549  material). 
     In some embodiments, each hole  532  is at least partially surrounded (on one or both of an internal and external surface of the second portion  522 ) by a surrounding channel  533 . The surrounding channel  533  can assist with forming the hole  532  via intra-molding. The mold tool can include a projection that applies pressure on the outer casing  551  during molding to form the channel  533 . The mold tool projection can restrict movement of the outer casing  551  during molding. Restricting movement of the outer casing  551  advantageously helps ensure that a periphery of the hole  532  (in other words, the plastic, or other core  549  material, structure inside the boundary of the surrounding channel  533 ) is entirely or substantially entirely plastic (or other core  549  material). An entirely plastic (or other core  549  material) hole  532  periphery can improve the function of the adjustment mechanism  528  and/or help maintain tolerances associated with the holes  532 . 
     In some embodiments, each of the first  520  and second  522  portions of the top strap  512  is integrally formed with the adjacent side arm  514 , for example, via the burst-through intra-molding process. In some embodiments, each of the first  520  and second  522  portions is an independent component that is coupled or connected, permanently or removably, to the respective side arm  514 . For example, as shown in  FIG. 42 , the junction  524  of each side arm  514  includes a junction projection  560 . The junction projections  560  can be formed during molding of the side arms  514 , for example, using the burst-through intra-molding process. Each of the first  520  and second  522  portions of the top strap  512  includes a recessed surface  562  at or proximate the junction end. The recessed surfaces  562  have a profile that is inverse (or approximately inverse) of or corresponds to a profile of the junction projections  560 . After molding, each of the junction projections  560  is inserted into the outer casing  551  of the junction end of the respective first  520  or second  522  portion of the top strap  512  and positioned within the recessed surface  562 . Each side arm  514  and the respective one of the first  520  and second  522  portions can then be welded together, for example, using ultrasonic welding, RF welding, or other suitable means. After welding, the side arms  514  and top strap  512  form a single plastic (or other core material) component. The outer casing  551  of the top strap  512  can be welded to the outer casing  551  of the side arm  514 . In some embodiments, an area of the top strap  512  adjacent to the junction  524  does not include a soft edge  550 . In such an embodiment, welding the core  549  of the side arm  514  and top strap  512  sufficiently secures the outer casings  551  together without needing to weld the outer casings  551  of the side arm  514  and top strap  512 . In some embodiments, the junction projections  560  are approximately the same thickness as a remainder of the core  549  of the side arms  514 . In some embodiments, the junction projections  560  have a reduced thickness. In some embodiments, the junction projections  560  are offset from a central plane of the side arms  514 . A reduced thickness and offset junction projection  560  can allow the core  549  of the side arm  514  and top strap  512  to be flush at the boundary between the junction projection  560  and recessed surface  562  when the junction projection  560  is seated in the recessed surface  562 . 
     In some embodiments, the first portion  520  of the top strap  512  includes location guides  570  to assist the user in setting and retaining a particular headgear setting, length, or size. As shown in  FIGS. 43A-43B , the location guides  570  can include a series of protruding edges  572 . A central portion  574  of the first portion  520  has a reduced lateral profile compared to the protruding edges  572 . The protruding edges  572  have a slightly greater profile or width than a diameter or width of the guide loop  530 . Therefore, as the first portion  520  of the top strap  512  is slid through the guide loop  530  of the second portion  522 , the contact and interaction between the protruding edges  572  and the guide loop  530  provides a friction force or resistive force. The resistive force can prevent or reduce the likelihood of passive movement of the first portion  520  through the guide loop  530 . The user can therefore disengage the projection  534  from the holes  532 , and the resistive force can help resist relative movement between the first  520  and second  522  portions to maintain the length of the strap  512  unless and until the user applies sufficient force to overcome the resistive force. In the illustrated embodiment, the protruding edges  572  are curved or domed outwardly convex. Other shapes or configurations for the protruding edges  572  are also possible. For example, the protruding edges  572  can be triangular. 
       FIGS. 44-45  show another non-limiting exemplary embodiment of a respiratory mask assembly  600 . The respiratory mask assembly  600  includes a patient interface and a headgear  604 . The patient interface includes a seal  606  configured to connect to a frame  610  and a gas delivery conduit  608 . The frame  610  is similar to and/or include some or all of the features of frame  410 . The headgear  604  and frame  610  are configured to secure the seal  606  in a stable position below the nose of a user in use.  FIGS. 46-47  show an exemplary embodiment of the headgear  604  that is used with frame  610 . In the illustrated embodiment, the headgear  604  has a bifurcated configuration. The headgear  604  is similar to the headgear  404  in some ways, e.g., the headgear  604  has the same or a similar overall shape as the headgear  404  and includes a top strap  612 , a pair of opposing side arms (or bottom or front strap)  614 , a yoke  616 , and a rear strap  618 . The top strap  612  and rear strap  618  form the bifurcated configuration. In some embodiments, one or more of the top strap  612 , bottom strap  614  and yoke  616 , and/or rear strap  618  are a different color than one or more of the other straps. 
     The side arms  614  and/or top strap  612  include a core and an outer casing, for example, similar to the headgear  504 . In some embodiments, the core is made of or includes a plastic material. In some embodiments, the outer casing is or includes a textile. 
     The top strap  612  of the headgear  604  includes a first (or left) portion  620  and a second (or right) portion  622  as shown in  FIGS. 47A-49B . The first  620  and second  622  portions are separate from each other. Each of the first  620  and second  622  portions has a free end and a fixed end. The fixed ends extend from, e.g., at an angle from, the front strap  614 . In the illustrated embodiment, the front strap  614 , first portion  620  of the top strap  612 , and second portion  622  of the top strap  612  can be formed independently from each other via intra-molding and then joined together via over-molded joints. As shown, each of the first  620  and second  622  portions is coupled to the front strap  614  via an over-molded joint  624 . 
     The free ends of the first  620  and second  622  portions of the top strap  612  are configured to be adjustably connected by an adjustment mechanism  628 . The adjustment mechanism  628  allows the top strap  612  to be adjusted and secured at a desired length. The adjustment mechanism  628  includes inter-engaging portions provided on respective first and second top strap portions  620 ,  622 . The inter-engaging portions are selectively engaged in one of a plurality of discrete configurations to set the length of the top strap  612 . When the inter-engaging portions are engaged, the first and second top strap portions  620 ,  622  are in a partial overlapping configuration. In this overlapping configuration, a portion of an internal surface of the first portion  620  of the top strap overlays a portion of an external surface of the second portion  622  of the top strap  612 . The internal surface of the top strap first portion  620 , in use, faces towards the user and the external surface of the top strap second portion  622 , in use, faces away from the user. The inter-engaging portions can be disengaged and re-engaged in a different configuration to facilitate adjustment of the length of the top strap. For the different lengths of the top strap  612  the first and second portions  620 ,  622  overlap in differing lengths or to differing extents. In the illustrated embodiment, the inter-engaging portion of the first portion  620  includes a male connector  628 a and the inter-engaging portion of the second portion  622  includes a female connector  628 b; although in some embodiments, the inter-engaging portion of the first portion  620  includes a female connector and the inter-engaging portion of the second portion  622  includes a male connector. 
     As shown in  FIGS. 47A-48B , the free end of the second portion  622  includes a guide loop  630 . The inter-engaging portion of the second portion  622  includes a plurality of recesses in the form of holes  632  spaced along a length of the second portion  622  proximate the free end. As illustrated, each of the holes  632  extends through the second portion  622  of the top strap  612 . In other embodiments, the inter-engaging portion of the second portion  622  includes recesses extending into the top strap second portion through its external surface. As shown in  FIGS. 47A, 49B, and 50B  the inter-engaging portion of the top strap first portion  620  includes a projection  634  that protrudes from the internal surface of the first portion  620  proximate the free end. To adjust and/or secure the first  620  and second  622  portions relative to each other, the free end of the first portion  620  is passed through the guide loop  630 , and the projection  634  is inserted into and/or secured in one of the holes  632 , for example, via a snap-fit connection. 
     In the illustrated embodiment, the inter-engaging portions of the adjustment mechanism  628  (i.e., the male connector  628   a  and female connector  628   b ) are not covered by the outer casing. This can advantageously provide a neater finish (e.g., hiding loose thread ends) and/or ease of manufacturing. 
     As shown in  FIGS. 50A-50C , the first portion  620  of the top strap is provided with or includes a thumb grip  629  on and/or in the external surface of the first portion (e.g., on and/or in the external surface of the male connector  628   a ) (i.e., a surface that faces away from the top strap second portion and the user  622  in use). The thumb grip  629  is provided on the opposite side of the top strap first portion  620  to or from the projection  634 . The thumb grip  629  can include a recessed portion (e.g., as shown in  FIG. 50C ) and/or a raised rib (e.g., a raised ring as shown in  FIG. 50A ). The first portion  620  is provided with or includes a finger grip  631  on and/or in the internal surface of the top strap first portion  620  (e.g., on and/or in the internal surface of the male connector  628   a ). In the illustrated embodiment, the finger grip  631  includes an indent or recessed portion. The finger grip  631  is located on the top strap first portion beyond or distal to (i.e., toward the free end) the projection  634 . The finger grip  631  is provided on the same side of the top strap first portion  620  to or as the thumb grip  629 . The finger grip  631  is thus on the opposite side of the top strap first portion  620  to or form the thumb grip  629 . The thumb  629  and/or finger  631  grips advantageously allow a user to grip the male connector  628   a  more easily. The thumb  629  and/or finger  631  grips also or alternatively provide visual and/or tactile cues to the user as to how to grip and use the adjustment mechanism  628 , which improves ease of use. The indent or recessed portion of the finger grip  631  thins or reduces the thickness of that portion of the top strap first portion  620 . This thinning can make the inter-engaging portion of the top strap first portion  620  more flexible, which advantageously allows the user to disengage the inter-engaging portion. For example, the user is able to more easily flex and/or lift the male connector  628   a  away from the female connector  628   b . In use, the thumb grip  629  can be gripped by the user&#39;s thumb or finger and/or the finger grip  631  can be gripped by the user&#39;s thumb or finger, depending on what is comfortable for the user.  FIG. 51A  illustrates a user gripping the finger grip  631  with a finger and the thumb grip  629  with a thumb, whereas  FIG. 51B  illustrates a user gripping the finger grip  631  with a thumb and the thumb grip  629  with a finger. In this respect, the thumb and finger grips  629 ,  631  are first and second grips that can be engaged interchangeably by a user&#39;s thumb and finger to clamp the free end of the top strap first portion therebetween. 
     As described above, the front strap  614 , first portion  620  of the top strap  612 , and second portion  622  of the top strap  612  are formed independently from each other via intra-molding and then joined together via over-molded joints  624 . As shown in  FIGS. 52A-52B , the top strap  612  includes at least one alignment post  660  (e.g., two alignment posts  660   a  in the illustrated embodiment) proximate each of the fixed ends. As shown in  FIG. 53A-53B , the bottom strap  614  includes at least one alignment post  660  (e.g., two alignment posts  660   b  in the illustrated embodiment) proximate each end. The bottom strap  614  includes at least one alignment post  660  (e.g., one alignment post  660   c  in the illustrated embodiment) positioned in each of two tabs  662  extending from an upper or top edge of the bottom strap  614 . In some embodiments, the tabs  662  are formed via a burst-through process. The alignment posts  660  protrude through the outer casing on the internal and/or external surface of the top strap  612 . The alignment posts  660  abut internal surfaces of an over-molding tool cavity to assist with alignment and positioning of the ends of the first portion  620  and second portion  622  (e.g., in a thickness direction) with respect to the front strap  614  within the over-molding tool during manufacturing. The alignment posts  660  also or alternatively increase the surface area of the top strap  612  available for the over-molding material to bond with. 
     The top strap  612  and/or bottom strap  614  include one or more pin holes  664  extending partially into the thickness of the strap from the inner surface of the strap. In the illustrated embodiment, the first portion  620  and second portion  622  of the top strap  612  each include a pin hole  664  near the fixed ends, and the bottom strap  614  includes a pin hole  664  near each end and a pin hole  664  near each burst-through tab  662 . The pin holes  664  are designed to receive pins that form part of the over-molding tool during manufacturing. The pins and pin holes  664  engage each other to retain the straps in predetermined positions within the over-molding tool and inhibit the straps from moving within the over-molding tool, for example, as the over-molding material (e.g., plastic) is injected into the tool. 
     During manufacturing, each of the fixed ends of the first portion  620  and second portion  622  is aligned with one of the burst-through tabs  662  as shown in FIGS.  54 A- 55 B. As shown, the burst-through tabs  662 , the fixed ends of the top strap  612 , and/or the ends of the bottom strap  614  include indents  666  in the outer and/or inner surface. The indents  666  advantageously provide an increased thickness of over-mold material in the over-mold joints  624 , as shown in  FIG. 57 , and/or an increased surface area for the over-mold material to bond with to improve the mechanical connection between the over-mold joint and the straps, thereby strengthening the joint  624 . As shown in  FIGS. 54A-55B , the burst-through tab  662  can have a reduced thickness compared to the thickness of a main body of the bottom strap  614 . This reduced thickness forms a recess for the over-mold material to fill and allows the finished over-mold joint  624  to have a thickness that is the same as or similar to the thickness of the main body of the bottom strap  614  and/or top strap  612 , as shown in  FIGS. 56A-58 . This inhibits the formation of protrusions that could apply force or pressure to the user&#39;s head and cause discomfort. In some embodiments, the alignment posts  660  have the same or a similar thickness as the over-mold joint  624 , for example as shown in  FIG. 57 . In such embodiments, the alignment posts  660  may leave witness marks  661  in the over-mold joints  624 . In some embodiments, the over-mold joint  624  overlaps the edge of the bottom strap  614 , for example as shown in  FIGS. 56A-56B . This improves the strength of the joint  624  between the top  612  and bottom  614  straps. The over-mold joints  624  advantageously provide improved strength to the joints between the top  612  and bottom  614  straps, and provide a neater and more aesthetically pleasing finish (e.g., compared to an intra-molded connection). 
       FIG. 59  illustrates an example embodiment of a variation in the geometry of the alignment posts  660 . In the illustrated embodiment, the alignment posts are conical. This shape minimizes or reduces witness marks on the finished over-molded joints  624 . The distal end or surface of the alignment posts  660  (the end or surface of the alignment posts  660  away from the strap body) has a reduced diameter, which provides a smaller contact area with the internal surfaces of the over-mold tool cavity. This allows the over-mold material to cover a greater area of the alignment posts  660 , which reduces the size of witness marks while still allowing the strap(s) to be positioned vertically within the over-mold tool. 
     As shown in  FIGS. 50C and 58 , each of the first and second top strap portions have a textile encased portion and an exposed or plastic portion incorporating the inter-engaging portion. Each textile encased portion can be produced by intra-molding as described above. Each textile encased portion has a tab to which the respective exposed portion is over-molded. 
     As shown in  FIGS. 47A-49B and 56A-56B , a buckle or rear strap connector  626  can be over-molded onto each end of the bottom strap  614 . Each buckle  626  includes an aperture  627  configured to receive the rear strap  618 . In the illustrated embodiment, the buckle  626  is not covered by the outer casing. The over-molded buckles  626  allow the rear strap  618  to be drawn through the buckles  626  more easily during assembly and/or adjustment due to the over-molded buckle  626  having a lower coefficient of friction than a textile covered buckle. 
     As shown in  FIG. 64 , each buckle  626  has a greater width W 2  than a width W 1  of the bottom strap  614 , such that the rear strap  618 , which has a width substantially the same as the bottom strap  614 , can pass through the aperture  627  of the buckle  626 . The upper edge  626   a  of each buckle  626  is offset from an upper edge  614   a  of the bottom strap  614 . However, the lower edge  626   b  of the buckle  626  is in alignment with a lower edge  614   b  of the bottom strap  614 . This provides a smooth and continuous lower edge of the headgear, which reduces the likelihood of the headgear digging into a user&#39;s ears when worn. The aperture  627  of the buckle  626  has a width that is substantially equal to a width of the rear strap  618 . In some embodiments, the rear strap  618  is of substantially the same width as the bottom strap  614 . 
     Similar to frame  410  and headgear  404 , the frame  610  includes headgear retaining features  650  in the form of holes that are designed to receive projections  615  of the headgear  604 . As shown in  FIGS. 60A-62A , the projections  615 , also referred to as frame retaining features or frame retention features herein, can be located on either side of the yoke  616 . In the illustrated embodiment, the projections  615  have a horseshoe shape or “U” cross-section with an inlet  619  extending from the perimeter of the projection  615  toward, to, and/or through a center of the projection  615 . The inlets  619  allow the projections  615  to flex to allow the projections  615  to snap into and/or out of the headgear retaining features  650 . 
     In some embodiments, for example as shown in  FIG. 63 , the bottom strap  614  includes a thumb pad  652  surrounding and/or extending laterally outwardly from each of frame retaining features  615  (toward the ends of the bottom strap  614  and the buckles  626 ). The thumb pads  652  are thicker than surrounding or remaining portions of the bottom strap  614 . The thumb pads  652  advantageously provide increased strength and/or resilience to the yoke  616  such that the yoke  616  is less likely to permanently deform and/or become fatigued due to repeated removal from and/or attachment to the frame  610 . The thumb pads  652  also or alternatively provide a visual indication to the user to grip the headgear  604  at this location (at the thumb pads  652 ) to disconnect the headgear  604  from and/or couple the headgear  604  to the frame  610 . In the illustrated embodiment, the frame retention features  615  are oriented such that the inlets  619  (i.e., mouths of the inlets  619  in the perimeters of the frame retention features  615 ) face laterally outward (or toward the ends of the bottom strap  614  and the buckles  626 ). The inlets  619  are therefore aligned with the elongated portions of the thumb pads  652 , which may be aesthetically pleasing. In some embodiments the thumb pads  652  provide an enhanced visual indicator in the form of a different coloured and/or textured region in the textile outer casing. The different coloured and/or textured region is integrally formed with the rest of the textile casing in some embodiments. 
       FIG. 65  shows another non-limiting exemplary embodiment of a respiratory mask assembly  700 . The respiratory mask assembly  700  includes a patient interface and a headgear  704 . The patient interface includes a seal  706  configured to connect to a frame  710  and a gas delivery conduit  708 . The mask assembly  700  can be similar to and/or include some or all of the features of previously embodiments, such as mask assembly  600  and/or  400 . The headgear  704  and frame  710  are configured to secure the seal  706  in a stable position below the nose of a user in use. 
     The headgear  704  is similar to the headgear  604 ,  404 , and/or  204  in some ways, e.g., the headgear  704  has the same or a similar overall shape as the headgear  604 ,  404 , and/or  204  and includes a top strap  712 , a pair of opposing side arms (or bottom or front straps)  714 , a yoke  716 , and a rear strap  718 . A buckle or rear strap connector  726  can be secured, e.g., over-molded, onto each end of the bottom strap  714 . In an embodiment in which the headgear  704  is made of a core material, e.g., plastic, covered by a casing, e.g., a textile, the buckles or rear strap connectors  726  can be formed from the core material of the headgear  704 . For example, the buckles or rear strap connectors  726  can be formed via a burst-through process. In the illustrated embodiment, the buckles  726  are closed loops. The buckles  726  can be wider than the front  714  and/or rear  718  straps as shown. Each buckle  726  is configured to couple to the rear strap  718 . The top strap  712  and rear strap form a bifurcated configuration. The top strap  712  can include a first portion  720  and a second portion  722  that are adjustably connected to each other by an adjustment mechanism  728  to allow the top strap  712  to be adjusted and secured at a desired length, similar to top strap  612 . 
     In use, the top strap  712  is configured to pass over the top of the user&#39;s head from one side to the other. The rear strap  718  is configured to pass around the back of the user&#39;s head. The top strap  712  and rear strap  718  are joined at the ends by the side arms  714  to form the bifurcated structure. In the illustrated arrangement, the top strap  712  joins the side arms  714  on each side of the headgear  704  at a junction  724 . Each one of the pair of side arms  714  extends forwardly, in use, from the junction  724  towards the nose of the user and transitions into the yoke  716 . In use, the headgear  704  is configured such that the junction  724  is positioned above the user&#39;s ear. It may sit forward of or rearward of the ear depending on the size of the user&#39;s head. As shown, the buckles  726  are therefore positioned behind the user&#39;s ears. 
     The mask assembly  700  also includes a headgear connector or clip  770  coupled to the yoke  716  as shown in  FIGS. 66-69B . The clip  770  can be permanently coupled, attached, or mounted to or integrally formed with the yoke  716 . In the illustrated arrangement, a portion of a front surface or side of the clip  770  faces, contacts, abuts, and/or is secured to a rear surface or side of the yoke  716 . The clip  770  couples the headgear  704  to the frame  710  in use. 
     The clip  770  includes a body having a lip  772 , e.g., a bottom lip  772 , that projects forward from the body and is visible in  FIG. 66 . A front surface  770   a  of the lip  772  is exposed or not covered by or in contact with the yoke  716 . In other words, the lip  772  projects below the bottom surface or edge of the yoke  716 . The lip  772  can be generally curved, arcuate, horseshoe, or part-elliptical shaped. In some configurations, the lip  772  protrudes from the body of the clip  770  by a distance, or has a thickness, that is equal to or approximately equal to the thickness of the yoke  716  (as measured from a front surface of the yoke  716 , visible in  FIG. 66 , to a rear surface of the yoke  716 , which contacts the clip  770 ). Therefore, the front surface of the lip  772  is flush or substantially flush with the front surface of the yoke  716 . In other configurations, the lip  772  can be thicker than or extend forward beyond the yoke  716 . In other words, the lip  772  can protrude from the body of the front surface of the clip  770  by a distance that is greater than the thickness of the yoke  716 , as illustrated in  FIG. 67B . Locking protrusions  774  protrude inwardly toward a center of the arc or horseshoe. The locking protrusions  774  are positioned at, adjacent, or proximate ends, e.g., lateral ends, of the lip  772 . 
     A rear surface  770   b  of the clip  770  includes a frame contacting portion  776  and a raised portion  778  as shown in  FIGS. 67-68 . The frame contacting portion  776  is curved, arcuate, horseshoe, or part-elliptical shaped. The frame contacting portion  776  extends along or proximate the bottom edge of the clip  770  and follows the shape and/or contour of the lip  772 . A raised edge  780  extends along and/or defines a boundary between the frame contacting portion  776  and the raised portion  778 . In the illustrated arrangement, the raised edge  780  is in the form of a shoulder or surface that extends in a substantially perpendicular direction relative to the surface of the frame contacting portion  776  and/or the surface of the raised portion. The frame contacting portion  776  is therefore defined between two elliptical arcs—the raised edge  780  forms a first, larger elliptical arc, and the inner or bottom edge of the rear surface of the clip  770  forms a second, smaller elliptical arc. The inner or bottom edge, or second, smaller elliptical arc, is shaped to correspond to or match the geometry of the frame  710 . The raised portion  778  is thicker than the frame contacting portion  776 . A top edge of the clip  770  and/or raised portion  778  can follow or correspond to the contour of the top edge of the yoke  716  as shown in  FIG. 67 . Preferably, the raised portion  778  is sized to have a large enough surface area to allow a secure connection to the yoke  716 , but to not extend beyond the bounds or upper perimeter of the yoke  716 . 
     To assemble the clip  770  and yoke  716 , the clip  770  can be manufactured with one or more mounting recesses or apertures  782 , as shown in  FIG. 69A , (also shown in  FIGS. 87 and 88 ), and the yoke  716  can be manufactured with one or more corresponding protrusions  784 . The protrusions  784  can be formed by a burst-through process as described herein. In the illustrated embodiment, the clip  770  includes three mounting recesses or apertures  782 , and the yoke  716  includes three corresponding protrusions  784 . More or fewer recesses or apertures  782  and corresponding protrusions  784  are also possible. The clip  770  and yoke  716  are placed together with the protrusions  784  extending into the recesses or apertures  782 , and a connecting structure is over-molded or otherwise formed over the clip  770  and yoke  716  assembly to secure the clip  770  and yoke  716  together. The over-mold portion  787  (shown in  FIG. 69B  and indicated by outline  786  in  FIG. 69A ) extends across at least a portion of the rear surface of the clip  770  and over the protrusions  784 . Such an arrangement can securely connect the clip  770  and yoke  716  while also providing a clean and attractive appearance by covering the recesses or apertures  782  and the protrusions  784 . In other configurations, the clip  770  and yoke  716  can be coupled by a snap-fit or other suitable type of connection. Furthermore, the locking protrusions  774  can be integrally formed with the yoke  716  via a burst-through process. In some configurations, portions of or the entire clip  770  can be formed via a burst-through process and/or burst-through material. In some configurations, the entire clip  770  can be over-molded to the yoke  716 . 
     As shown in  FIGS. 70-73 , the frame  710  includes a surrounding wall, skirt, or flange  735 , an inlet collar  730  projecting outwardly (away from the user in use) from a front surface of the surrounding wall  735 , and an outlet collar  740  projecting inwardly (toward the user in use) from a rear surface of the surrounding wall  735 . The surrounding wall  735  extends around a perimeter or circumference of an outer surface of the frame  710 . A fluid path  715  extends generally or substantially along a longitudinal axis of the frame  710  through the inlet collar  730  and the outlet collar  740 . The longitudinal axis can be substantially straight or linear, or could be curved. An internal shape of the frame  710  defining the fluid path  715  can vary along a length of the frame  710 . Thus, the longitudinal axis can be defined as an average centerline or by the geometric center of multiple axial locations within the fluid path  715  of the frame  710 . The inlet collar  730  can include one or more bias flow holes, for example as shown and described with respect to other embodiments herein. The bias flow holes can be arranged similar to bias flow holes  729  shown in  FIG. 83 . 
     In use, the seal  706  is coupled to the outlet collar  740 , and the gas delivery conduit  708  is coupled to the inlet collar  730 . As shown in  FIGS. 71 and 76 , a top of the inlet collar  730  can be longer than a bottom of the inlet collar  730 , while a top and bottom of the outlet collar  740  have the same or approximately the same length. When the seal  706  is coupled to the outlet collar  740  and the mask assembly  700  is disposed on the user&#39;s face in use, such a configuration causes the inlet collar  730  and/or gas delivery conduit  708  to point somewhat downward (when the user&#39;s head is in an upright position) rather than directly outward. This configuration can help reduce possible hose drag by the gas delivery conduit  708  on the frame  710 . 
     For use, the clip  770  is coupled to the inlet collar  730 . The inlet collar  730  includes one or more locating features that help align the clip  770  with and/or couple the clip  770  to the frame  710 . For example, the inlet collar  730  can include a locating feature  732 , which can be in the form of a tab or partial wall protruding from the inlet collar  730  along a portion of a top or upper surface of the inlet collar  730 . The inlet collar  730  can include recessed portions  734  in the outer or lateral surface of the inlet collar  730 . As shown, recessed portions  734  can be disposed on opposing sides of the inlet collar  730 . The recessed portions  734  are sized, shaped, and positioned to receive the locking protrusions  774  of the clip  770 . The inlet collar  730  can further include a lead-in or alignment recess, or scalloped portion  736 , associated with and positioned proximate and above (or closer to the top) each of the recessed portions  734 . Each scalloped portion  736  is separated from its associated recessed portion  734  by a ridge  738 . Each scalloped portion  736  is formed by a recess that increases in depth in a direction moving from an end furthest from the ridge  738  toward an end closest to the ridge  738 . Each of the scalloped portions  736  can act as a lead-in to the respective recessed portion  734  to help guide and align, or maintain alignment, of the locking protrusions  774  of the clip  770  with the recessed portions  734  during assembly or connection of the clip  770  with the frame  710 . The ridges  738  can help retain the locking protrusions  774  in the recessed portions  734  once assembled by limiting or inhibiting upward movement of the locking protrusions  774  relative to the frame  710 . 
     To couple the clip  770  to the frame  710 , the clip  770  can be slid into the space between the locating feature  732  and the surrounding wall  735  as shown in  FIGS. 74-77 . The scalloped portions  736  help guide the locking protrusions  774  into the recessed portions  734 . Movement of the locking protrusions  774  over the ridges  738  into the recessed portions  734  can provide tactile feedback to the user that the clip  770  is secured to the frame  710 . The surrounding wall  735 , locating feature  732 , recessed portions  734 , and/or locking protrusions  774  help guide connection of the clip  770  and yoke  716  to the frame  710  and/or help secure the clip  770  and yoke  716  to the frame  710  when assembled. When the clip  770  is coupled to the frame  710 , the frame contacting portion  776  of the clip  770  contacts the front surface of the surrounding wall  735  of the frame  710 . The raised edge  780  contacts the front surface and/or an outer edge of the surrounding wall  735 . The locating feature  732  contacts the front surface of the clip  770 , e.g., the lip  772 . The frame contacting portion  776  is recessed from the raised portion  778  by a distance D (shown in  FIG. 67B  equal to or approximately equal to the thickness T (shown in  FIG. 71 ) of the surrounding wall  735 . Therefore, when the clip  770  is coupled to the frame  710 , a recess defined by the frame contacting portion  776  and the raised edge  780  receives the surrounding wall  735  such that the raised portion  778  is level or flush (or substantially level or substantially flush) with the rear surface of the surrounding wall  735  as shown in  FIGS. 75-76 . 
     As shown in  FIGS. 78A and 78B , the shape of the clip  770  is designed to follow or complement the aesthetics of the yoke  716  and frame  710  by blending into the overall profile curve of the yoke  716  and frame  710 , as indicated by the curve profile  798  shown in  FIG. 78A . 
     The outlet collar  740  includes an engagement portion/member, seal element or connector  742 . The connector  742  helps secure the seal  706 , and/or a coupling structure  790 , such as a seal clip, coupled to the seal  706 , to the frame  710 .  FIGS. 79 and 80  show an example embodiment of a seal  706  and coupling structure  790 . The cushion module therefore includes the seal  706  and the coupling structure  790 . The coupling structure  790  couples the seal  706  to the frame  710 . The coupling structure  790  can be in the form of a seal clip. The seal clip can clip to the seal  706  to secure the seal  706  to the seal clip. Alternatively, the seal  706  can be overmolded onto the coupling structure and/or joined to the coupling structure via other suitable means. As shown in  FIG. 79 , lateral ends or edges  792  of the coupling structure  790  are thickened relative to a remainder of the coupling structure  790 . For example, the lateral ends or edges  792  can have a thickness of about 2 mm-6 mm. For example, the lateral ends or edges  792  can have a thickness of about 4 mm at the lateral-most edges. In the illustrated embodiment, the lateral-most edges are the thickest portions of the coupling structure  790 , and the coupling structure  790  tapers or narrows from the lateral-most edges toward a center of the coupling structure  790 . In some embodiments, lateral portions of the coupling structure  790  include recessed or scalloped portions  793  in the inner or outer surface of the coupling structure  790 , which can help reduce the weight of the coupling structure  790 . The thickened ends or edges  792  can help avoid sharp edges that could contact the patient&#39;s face in use to improve comfort. That is, the blunt edges created by the thickened ends  792  are less painful in the event that the ends  792  of the coupling structure  790  make contact with the user&#39;s face. The blunt edges can also or alternatively help prevent or inhibit sharp edges from contacting the seal  706  and potentially causing holes or tears in the seal  706 . 
     As shown in  FIG. 80 , the coupling structure  790  includes an internal surface  794  that extends into and/or defines a central aperture of the seal  706 . For use, the internal surface  794  slides over or onto the outlet collar  740  of the frame  710  to couple the seal  706  to the frame  710 . The internal surface  794  can be smooth, e.g., without any bumps, which can help the coupling structure  790  slide onto the outlet collar  740 . The surrounding wall  735  provides a stop for the seal  706  and coupling structure  790  as the seal  706  and coupling structure  790  are pushed onto the outlet collar  740 . 
     As the coupling structure  790  is pushed onto the outlet collar  740 , the internal surface  794  also slides over the connector  742 . The connector  742  can be made of a compressible, compliant, and/or resilient material. For example, the connector  742  can be made of TPE or a silicone material, which in some configurations can be a self-adhesive silicone that adheres to the surface of the outlet collar  740 . The connector  742  can be permanently coupled or bonded to the frame  710 . In some configurations, the connector  742  can be over-molded onto the outlet collar  740 . As the coupling structure  790  slides over the connector  742 , the connector  742  compresses. The compression of the connector  742  creates a friction fit between the coupling structure  790  and frame  710  and creates a sealed passage through the frame  710  and coupling structure  790  and therefore the seal  706 . The connector  742  can take the form of an annular seal or flange, such as or similar to an o-ring, that extends around an entire circumference of the outlet collar  740  as shown. However, the connector  742  can be of any suitable cross-sectional shape, including but not limited to circular. In the illustrated arrangements, as described further below, the connector  742  includes a semi-circular or part-circular sealing/connector portion (e.g., protrusion  745 ) and a non-circular base portion (e.g., bonding portion  743 ). Alternatively, the connector  742  may not extend around the entire circumference of the outlet collar  740 . In some configurations, the connector  742  is provided in a color (e.g., blue) that matches a color (e.g., blue) of the coupling structure  790  (or a portion thereof) to indicate to the user that the coupling structure  790  should be assembled onto the outlet collar  740 , which contains the connector  742 . Alternatively, another portion of the outlet collar  740  could contain the color (e.g., blue). 
     As shown in  FIGS. 71 and 73 , the connector  742  can be disposed in a groove  744 . As shown in  FIGS. 81A-81D , the groove  744  can have a cross-sectional shape that is generally or substantially similar to a trapezoid or trapezium. The inner diameter of the groove  744  can have a smaller axial length compared to the outer diameter of the groove  744 . The cross-sectional shape of the groove  744  can be symmetrical about its central axis or can be asymmetrical, as in the configuration of  FIG. 81D . Other suitable cross-sectional shapes can also be used, including rectangular (square) and circular (e.g., semi-circular), for example and without limitation. With additional reference to  FIGS. 81A-81D , the connector  742  can include a bonding portion  743  and a protrusion  745  protruding from the bonding portion  743 . A bottom or inner surface of the bonding portion  743  can have a cross-sectional shape that corresponds to the cross-sectional shape of the groove  744 . The connector  742 , e.g., the bonding portion  743  of the connector  742 , can be molded into place on the frame  710 , e.g., in the groove  744 . Alternatively, the connector  742  can be formed separately and coupled to the frame  710 .  FIGS. 81A-81D  show various embodiments of the connector  742 .  FIG. 81A  illustrates a moderately sized bonding portion  743  and the protrusion  745  generally centered within the bonding portion  743 .  FIG. 81B  illustrates a larger bonding portion  743  (compared to the bonding portion  743  of  FIG. 81A ) and the protrusion  745  displaced away from a center of the bonding portion  743  toward a rear or distal edge of the outlet collar  740  (i.e., the edge of the outlet collar  740  farthest from the surrounding wall  735 ). This protrusion  745  position can help provide greater haptic feedback to the user when the coupling structure  790  is coupled to the frame  710  because a greater portion of the coupling structure has to travel over the protrusion during coupling.  FIG. 81C  illustrates a moderately sized bonding portion  743  and a relatively wider or thicker protrusion  745  (compared to the protrusions  745  of  FIGS. 81A and 81B ) that spans the width of the bonding portion  743 .  FIG. 81D  illustrates a moderately sized bonding portion  743  the extends and/or opens to the rear or distal edge of the outlet collar  740 . This configuration can allow for simplified tooling.  FIGS. 82A and 82B  illustrate another example embodiment of the connector  742 . In this embodiment, the connector  742  has a dual-protrusion configuration with a recess between the two protrusions. In other words, the connector  742  includes a bonding portion  743  bounded by two protrusions  745 . In some or all of the illustrated configurations, a cross-section of the bonding portion  743  defines a surface length in contact with the outlet collar  740  that is greater than a surface length of a cross-section of the protrusion  745 . Accordingly, the connector  742  has a greater surface area for bonding or otherwise connecting with the outlet collar  740  than if the connector  742  were to be symmetrical such that the bonding portion  743  was a mirror image of the protrusion  745 . Such an arrangement can advantageously provide for improved bonding or other coupling of the connector  742  to the outlet collar  740 . 
     As shown in  FIG. 71 , the connector  742  is spaced from the surrounding wall  735 . For example, the connector  742  may be spaced approximately 4-5 mm from the surrounding wall  735 . The spacing from the surrounding wall  735  advantageously allows for a sufficient length of travel, after contact with the connector  742 , as the seal  706  is slid onto the outlet collar  740 , which can provide haptic feedback to the user as the seal  706  is connected to the frame  710 . 
       FIGS. 83-86  show another example of a frame  710 ′ that can be used in the respiratory mask assembly  700  of  FIG. 65 . Frame  710 ′ is similar to frame  710  in many ways. The frame  710 ′ includes a tab or guide wall  739  positioned along the side of each recessed portion  734 , scalloped portion  736 , and ridge  738  closest to the front edge of the inlet collar  730  (in other words, the side away from the surrounding wall  735  such that the recessed portion  734 , scalloped portion  736  and ridge  738  are at least partially bordered by the surrounding wall  735  and guide wall  739 ). The guide walls  739  advantageously help guide the locking protrusions  774  into place when connecting the yoke  716  and clip  770  to the frame  710 ′, as shown in  FIGS. 87-88 . 
       FIGS. 99-102  show another example of a frame  710 ′″ that can be used in the respiratory mask assembly  700 , and  FIGS. 93-98  show the frame  710 ′″ assembled in the respiratory mask assembly  700 . Frame  710 ′″ is similar to frame  710 ′ in many ways. For example, the frame  710 ′″ includes recessed portions  734 , scalloped portions  736 , ridges  738 , guide walls  739 , and a locating feature  732 . The frame  710 ′″ also includes two bottom projections  741 . In the illustrated embodiment, each bottom projection  741  extends from below a respective recessed portion  734 . A connecting portion  741   b  extends between the bottom projections  741  around the bottom of the outer circumference or perimeter of the inlet collar  730 . In this embodiment, the bottom projections  741  and connecting portion  741   b  form a unitary projection around the bottom of the inlet collar. Each bottom projection  741  includes a corner portion  741   a  ( FIG. 99 ) adjacent or proximate the respective recessed portion  734 . Each corner portion  741   a  projects laterally outward and downward from the body of the inlet collar  730 . In other words, lateral edges  741   c  (shown in  FIG. 99 ) of the projection  741  extend laterally outward and downward from the body of the inlet collar  730  adjacent or proximate the bottom edge of the recessed portions  734 . In other configurations, the frame  710 ′″ can include only the corner portions  741   a  without the connecting portion  741   b.  As shown, the connecting portion  741   b  can blend or merge into (aesthetically and/or structurally) the surrounding wall  735 . As shown in  FIGS. 95-98 , each projection  741  aesthetically blends into and forms an extension of the clip  770 . In the illustrated embodiment, the lateral edges  741   c  of each projection  741  abut bottom edges  771  (shown in  FIG. 66 ) of the clip  770 , and a bottom edge of each projection  741  generally follows or continues the curvature of lateral edges  769  (also shown in  FIG. 66 ) of the clip  770 . The projections  741  advantageously act as a barrier to prevent or inhibit a user from attempting to attach the clip  770  from or to the bottom of the frame  710 ′″ rather than the top. 
       FIGS. 103-125  show another example of a frame  710 ″″ that can be used in a respiratory mask assembly, such as the respiratory mask assembly  700 . Frame  710 ″″ is similar to frame  710 ′″ in many ways. For example, the frame  710 ″″ includes recessed portions  734 , scalloped portions  736 , ridges  738 , guide walls  739 , a locating feature  732 , two bottom projections  741 , and a connecting portion  741   b  extending between the bottom projections  741  around the bottom of the outer circumference or perimeter of the inlet collar  730 . In other configurations, however, the frame  710 ″″ may not include all of these features. 
     As shown in, for example,  FIGS. 112-115 and 122-125 , the frame  710 ″″ also includes a connector  742  disposed around a perimeter or outer surface of the outlet collar  740 . As shown, the connector  742  can be positioned at an intermediate location between an outlet end or edge of the outlet collar  740  and the surrounding wall  735 . The connector  742  extends around the entire perimeter of the outlet collar  740 . In at least one alternative configuration however, the connector  742  can extend around only a portion or portions of the perimeter of the outlet collar  740 . The connector  742  can be made of a compressible, compliant, and/or resilient material. For example, the connector  742  can be made of TPE or a silicone material, which in some configurations can be a self-adhesive silicone that adheres to the surface of the outlet collar  740 . In the illustrated embodiment, the connector  742  is disposed in a groove  744 . The groove  744  can form a channel in the outlet collar  740 . The connector  742  can include a bonding portion  743  and a protrusion  745  protruding from the bonding portion  743 . The protrusion  745  also protrudes outwardly from or relative to the outer surface of the outlet collar  740  to form a bump or ridge. The connector  742 , e.g., the bonding portion  743  of the connector  742 , can be molded into place on the frame  710 , e.g., in the groove  744 . Alternatively, the connector  742  can be formed separately and coupled to the frame  710 . The connector  742  can bond to the surface of the outlet collar  740  via a chemical bond. In another alternative, the connector  742  can be connected to the outlet collar  740  with a mechanical bond. For example, the outlet collar  740  can include through-holes through the groove  744 . The connector  742  can include portions that extend through these through-holes to facilitate a mechanical connection between the connector  742  and the outlet collar  740 . 
     A bottom or inner surface of the bonding portion  743  of the connector  742  can have a cross-sectional shape that corresponds to the cross-sectional shape of the groove  744 . In the illustrated embodiment, the groove  744  and the bottom or inner surface of the bonding portion  743  have a generally rectangular cross-section. In some embodiments, in at least a portion of the groove  744 , and therefore the connector  742 , the distal and proximal walls of the groove  744  are parallel or substantially parallel. This configuration advantageously improves the durability of the connection between the connector  742  and the groove  744 . Having as great a proportion of the walls as possible extending at or approximately at a right angle to the outer surface of the frame can reduce stress concentrations that may negatively affect the functional lifespan of the connector  742 . 
       FIGS. 103 and 113-115  show an example embodiment of a coupling structure  790  that can be used with frame  710 ″″, for example, in the respiratory mask assembly  700 . In the illustrated embodiment, the coupling structure  790  includes an outer clip  990  and an inner clip  890 . The outer clip  990  and inner clip  890  can be integrally formed (i.e., to form a one piece coupling structure) or permanently or removably coupled together. The coupling structure is relatively hard, for example, compared to the connector  742 . In other words, one or more of the inner clip  890  and the outer clip  990  is harder than the connector  742 . In the illustrated embodiment, the outer clip  990  has an inner wall, arm, portion, or flange  791  and an outer wall, arm, portion, or flange  795  extending radially outwardly from the inner wall  791 . In the illustrated embodiment, the inner clip  890  includes an internal surface  794  that extends into and/or defines a central aperture of the seal  706 . In the illustrated embodiment, the inner clip  890  has an inner wall  891 , an outer wall  893 , and a connecting wall  895  extending between the inner wall  891  and the outer wall  893 . The outer wall  893  is displayed or positioned away from the fluid path more than the inner wall  891 . As shown, an inner surface of the inner wall  891  forms the internal surface  794 . 
     The outer clip  990  and inner clip  890  couple the seal  706  to the frame  710 ″″. When coupled, the outer clip  990  and inner clip  890  are disposed around and encircle the outlet collar  740 . In the illustrated embodiment, the outer clip  990  is disposed on a patient-distal side of the connecting wall  895  of the inner clip  890 . When the outer clip  990  and inner clip  890 , along with the seal  706 , are fully connected to the frame  710 ″″, as shown in, for example,  FIG. 115 , a patient-distal end or edge of the inner wall  891  of the inner clip  890  and/or a patient-distalmost surface of the outer clip  990  may abut the surrounding wall  735  as shown. The outer clip  990  and the inner clip  890  can be coupled to each other. For example, the outer clip  990  and the inner clip  890  can be coupled via ultrasonic welding, adhesive bonding, and/or a permanent or removable snap fit. In the illustrated embodiment, an inner surface of the inner wall  791  of the outer clip  990  abuts and/or is coupled to a portion of an outer surface of the inner wall  891  of the inner clip  890 . 
     The seal  706  is coupled to the outer clip  990  and/or inner clip  890 . In some embodiments, a portion of the seal  706  is sandwiched between the outer clip  990  and the inner clip  890 . The seal  706 , inner clip  890 , and outer clip  990  therefore form an integrated unit. In the illustrated embodiment, a portion of the seal  706  is positioned in a cavity at least partially formed, defined, and/or bounded by an outer surface of the inner wall  791  of the outer clip  990 , a patient-proximal surface of the outer wall  795  of the outer clip  990 , a patient-distal surface of the connecting wall  895  of the inner clip  890  and/or a patient-distal surface of the outer wall  893  of the inner clip  890 , as shown in  FIG. 115 . The portion of the seal  706  positioned in the cavity can have a generally T-shaped cross-section. For example, in the illustrated embodiment, the portion of the seal  706  positioned in the cavity has an axial elongate collar portion  707  and a wall  705  extending radially outwardly from the collar portion  707  to a body of the seal  706 . The collar portion  707  is captured in the cavity to resist radial outward force. In the illustrated embodiment, the collar portion  707  is captured in an area bounded by the outer surface of the inner wall  791  of the outer clip  990 , a patient-proximal surface of the outer wall  795  of the outer clip  990 , and a patient-distal surface of the connecting wall  895  of the inner clip  890 . In the illustrated embodiment, the wall  705  is captured between a patient-distal surface of the outer wall  893  of the inner clip  890  and an end surface of the outer wall  795  of the outer clip  990 . 
     The connector  742  helps couple the seal  706  to the frame  710 ″″. Specifically, in the illustrated embodiment, the connector  742  helps couple the inner clip  890  to the frame  710 ″″. As the inner clip  890  is pushed onto the outlet collar  740 , the internal surface  794  of the inner clip  890  slides over the connector  742 , and the connector  742  compresses. The compression of the connector  742  creates a friction fit between the inner clip  890  and frame  710 ″″ to help retain the inner clip  890  on the frame  710 ″″ and creates a sealed passage through the frame  710 ″″ and inner clip  890  and therefore the seal  706 . 
     The inner wall  891  of the inner clip  890  includes a first portion  892  and a second portion  894 . The first portion  892  extends away from the connecting wall  895 . The second portion  894  extends away from the connecting wall  895 . The first portion  892  extends away from the connecting wall  895  in a direction that is away from the user of the interface when in-use. The second portion  894  extends away from the connecting wall  895  in a direction that is towards the user of the interface when in-use. In other words, the first portion  892  extends away from the connecting wall  895  in a direction that is generally opposite to the direction that the second portion  894  extends away from the connecting wall  895 . Together, the first portion  892  and the second portion  894  define the internal surface  794 . In the illustrated configuration, the first portion  892  and the second portion  894  are offset to define a transition portion  896 . The first portion  892  and the second portion  894  are radially offset with respect to a center of the fluid path  715 . The second portion  894  is radially offset from the first portion  892  such that the second portion  894  is displaced from the center of the fluid path  715  by a greater amount than the first portion  892 . A dimension (e.g., circumference, diameter, perimeter length, or cross-sectional dimension) of the first portion  892  is less than a corresponding dimension of the second portion  894 . For example, a perimeter defined by the region of the internal surface  794  that is defined by the first portion  892  is less than a perimeter defined by the region of the internal surface  794  that is defined by the second portion  894 . The perimeter of the internal surface  794  changes across the transition portion  896 . In the illustrated configuration, the perimeter of the internal surface  794  increases across the transition portion  896  as the transition portion transitions from the first portion  892  to the second portion  894 . As the inner clip  890  is slid onto the frame  710 ″″ to couple the seal  706  to the frame  710 ″″, the portion of the internal surface  794  defined by the first portion  892  slides over the connector  742 , as shown in  FIGS. 122 and 124 . When the inner clip  890  is fully coupled to the frame  710 ″″, the connector  742  is in contact with the portion(s) of the internal surface  794  defined by the transition portion  896  and/or the second portion  894 , as shown in  FIGS. 123 and 125 . 
     The first portion  892  can have a constant or non-constant dimension (e.g., circumference, diameter, perimeter length, or cross-sectional dimension) along a length (e.g., axial length along the direction of gases flow) of the first portion  892 . The second portion  894  can have a constant or non-constant dimension (e.g., circumference, diameter, perimeter length, or cross-sectional dimension) along a length (e.g., axial length along the direction of gases flow) of the second portion  894 . In other words, either or both of the first portion  892  and the second portion  894  can taper, e.g., toward the transition portion  896 , along its length. The dimension of the internal surface  794  changes in the transition portion  896 . Because the dimension of the first portion  892  is less than that of the second portion  894 , the compression of the connector  742  as the inner clip  890  is coupled to the frame  710 ″″, and therefore the interference between the connector  742  and the inner clip  890 , is greater at the first portion  892  than the second portion  894 . The interference between the connector  742  and the inner clip  890  is therefore greater when the inner clip  890  is in the process of being coupled to the frame  710 ″″ (and the connector  742  is therefore in contact with the first portion  892 ), for example as shown in  FIGS. 122 and 124 , compared to when the inner clip  890  is fully connected to the frame  710 ″″ (and the connector  742  is therefore in contact with the transition portion  896  and/or the second portion  894 ), for example as shown in  FIGS. 123 and 125 . 
     The interference between the connector  742  and the inner clip  890  is therefore less in a connected position compared to during assembly or disassembly. To remove the inner clip  890  from the frame  710 ″″, the inner clip  890  and frame  710 ″″ must be pulled apart from or relative to each other into a partially connected position. In the connected position, the connector  742  is in contact with the transition portion  896  and/or second portion  894  and there is therefore less interference between the inner clip  890  and the connector  742 . The peak removal force required to separate the frame  710 ″″ and the coupling structure  790  is therefore at least partially determined by the interference between the first portion  892  and the connector  742  in the partially connected position. 
     Having less interference between the connector  742  and the inner clip  890  (and therefore the coupling structure  790 ) in the connected position compared to the partially connected position and/or during assembly or disassembly can advantageously help maintain the long term performance of the connection between the frame  710 ″″ and the inner clip  890 . The cushion module (the seal  706  and the coupling structure  790 ) and the frame  710  can be stored in the connected position. The cushion module and the frame  710  are also in the connected position during overnight use. Sustained greater deformation of the connector  742  (as when in the partially connected position or if portion of the inner clip in contact with the connector  742  during storage and/or use had a smaller diameter) could result in decreased long term performance of the connector  742 , for example, because the resilience of the connector  742  may decrease if compressed to a greater extent for extended periods of time. The reduced interference between the connector  742  and the inner clip  890  (and therefore the coupling structure  790 ) can therefore extend the useful life of the mask assembly. 
       FIGS. 89-90  show another example embodiment of a frame  710 ″ and clip  770 ″ that can be used in the respiratory mask assembly  700  of  FIG. 65 . Frame  710 ″ is similar to frame  710  in some ways. As shown, the surrounding wall  735 ″ of the frame  710 ″ is a partial surrounding wall  735 ″ and does not extend around the entire circumference/perimeter of the frame  710 ″. The partial surrounding wall  735 ″ is sized and shaped to match or correspond to the geometry and size of the clip  770 ″. The partial surrounding wall  735 ″ does not extend substantially beyond (further downward) the lateral ends of the clip  770 ″ when the clip  770 ″ is coupled to the frame  710 ″. 
     The frame  710 ″ includes two channels  737  extending circumferentially around a portion of the outer surface of the inlet collar  730 . As shown, each channel  737  starts proximate a top of the inlet collar  730  and extends adjacent to the surrounding wall  735 ″ downward around the circumference of the inlet collar  730  to or toward the recessed portion  734 . The frame  710 ″ can include a locating feature  733  at the top of the inlet collar  730  adjacent the surrounding wall  735 ″. As shown, the locating feature  733  can be flush with or slightly raised relative to a body of the inlet collar  730  between the channels  737  and the front edge of the inlet collar  730 . In some configurations, the upper surface of the locating feature  733  is flat, while the surface of the inlet collar  730  forward of the locating feature  733  is curved. The channels  737  are therefore recessed relative to the locating feature  733  and body of the inlet collar. A bump  731 , which is level with or raised relative to the body of the inlet collar  730 , is disposed between the end of each channel  737  and the associated recessed portion  734 . The channel  737  can provide the same or similar functionality as the lead-in or alignment recess, or scalloped portion  736 , described above. The bump  731  can provide the same or similar functionality as the ridges  738 , described above. 
     As shown in  FIG. 91 , the clip  770 ″ includes a recess  773  in the lower surface or inner arc of the clip  770 ″ positioned at the lateral center of the clip  770 ″. Locking protrusions  774  extend inwardly from the inner arc at or proximate lateral ends of the clip  770 ″. The clip  770 ″ can also include a recess  775  positioned adjacent to, and closer to the lateral center than, each locking protrusion  774 . The recess  775  can be configured to accommodate the bump  731  such that the locking protrusion  774  can fully engage the recessed portion  734  without interference between the bump  731  and the clip  770 ″. 
     As the clip  770 ″ is coupled to the frame  710 ″, the channels  737  help guide the clip  770 ″ into place. The depth of the channels  737  helps provide horizontal or axial support to the clip  770 ″ to inhibit or prevent undesired separation in directions other than vertical or directly away from the channels  737 , which is perpendicular to the upper surface of the locating feature  733  in the illustrated arrangement. The recess  773  is aligned with and receives the locating feature  733 . The locating feature  733  serves as a visual and/or tactile guide to help the user properly align the clip  770 ″ with the frame  710 ″. The engagement of the locating feature  733  with the recess  773  helps secure the clip  770 ″ to the frame  710 ″ by inhibited or preventing lateral movement of the clip  770 ″ relative to the frame  710 ″. 
       FIGS. 92A-92C  illustrate variations of the clip  770  and frame  710 . These variations may be combined with features of any the above described embodiments. In  FIG. 92A , the clip  770  sits in a recess  796  in the inlet collar  730  of the frame  710 , and an upwardly-extending wall portion that defines the frame contacting portion  776  of the clip  770  contacts the inlet collar  730  side of the surrounding wall  735 . In  FIG. 92B , a portion of the clip  770  wraps over the top of the surrounding wall  735  and therefore contacts both sides of the surrounding wall  735 . This arrangement can secure the clip  770  to the frame  710  without the need for a recess  796  and/or a locating feature  732 . In  FIG. 92C , the clip  770  includes a channel  797  that receives the surrounding wall  735  to align the clip  770  with and secure the clip  770  to the frame  710 . 
     Unless the context clearly requires otherwise, throughout the description and the claims, the words “comprise”, “comprising”, and the like, are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense, that is to say, in the sense of “including, but not limited to.” Where, in the foregoing description reference has been made to integers or components having known equivalents thereof, those integers or components are herein incorporated as if individually set forth. 
     The disclosed methods, apparatus and systems may also be said broadly to comprise the parts, elements and features referred to or indicated in the disclosure, individually or collectively, in any or all combinations of two or more of said parts, elements or features. 
     Reference to any prior art in this specification is not, and should not be taken as, an acknowledgement or any form of suggestion that that prior art forms part of the common general knowledge in the field of endeavour in any country in the world. 
     Language of degree used herein, such as the terms “approximately,” “about,” “generally,” and “substantially,” as used herein represent a value, amount or characteristic close to the stated value, amount or characteristic that still performs a desired function or achieves a desired result. The deviation from the stated value, amount or characteristic could, for example, reflect acceptable tolerances, conversion factors, rounding off, measurement error, or other factors known to those of skill in the art. For example, the terms “generally parallel” and “substantially parallel” refer to a value, amount or characteristic that can depart from exactly parallel by less than or equal to 15 degrees, 10 degrees, 5 degrees, 3 degrees, 1 degree, 0.1 degree, or otherwise. 
     Although the present disclosure has been described in terms of certain embodiments, other embodiments apparent to those of ordinary skill in the art also are within the scope of this disclosure. Thus, various changes and modifications may be made without departing from the spirit and scope of the disclosure. For instance, various components may be repositioned as desired. Moreover, not all of the features, aspects and advantages are necessarily required to practice the present disclosure. Accordingly, the scope of the present disclosure is intended to be defined only by the claims that follow.