Patent Publication Number: US-2012037161-A1

Title: Nasal mask assembly

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. Ser. No. 10/781,949, filed Feb. 20, 2004, which claims the benefit of U.S. Provisional Patent Application Nos. 60/448,533 filed Feb. 21, 2003 and 60/465,790 filed Apr. 28, 2003, each of which is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a nasal mask assembly for use with non-invasive positive pressure ventilation (NIPPV) applied to small adults or pre-adults with sleep disordered breathing (SDB). 
     2. Description of Related Art 
     Sleep-disordered breathing is a general term for a sleep disorder with apneas and hypopneas. Apneas are generally taken to be a cessation of airflow for ten seconds or longer. Hypopnea are generally taken to be a 50% or greater decrease in air flow for ten seconds or longer. Both apneas and hypopneas cause sleep arousals—moments when an individual wakes enough to resume breathing but not enough to remember any interruption of sleep. Some arousals simply cause the sleeper to shift into a lighter stage of sleep. In either case, the arousal lessens the quality of sleep. Apneas and hypopneas may cause blood oxygen levels to drop. Apneas and hypopneas result from upper airway obstruction, either full or partial, or a dysfunction of the body&#39;s automatic drive to breathe. 
     Obstructive Sleep Apnea (OSA) is a common disorder. Estimates for the number of Americans with OSA vary depending on the criteria researchers use for the study. Conservative estimates, however, put the number of adult Americans with OSA at approximately 20 million. OSA occurs because of upper airway obstructions that can cause you to snore or to stop breathing. Obstructions occur during sleep for two primary reasons: lack of muscle tone and/or gravity. Excess tissue in the upper airway and anatomic abnormalities compound these factors. During sleep, especially in REM sleep, our bodies relax, and muscle tissues like the tongue and soft palate lose their slight rigidity. Because we tend to sleep lying down, gravity pulls these tissues toward the back of the throat and closes the upper airway. 
     The use of nasal Continuous Positive Airway Pressure (nasal CPAP) to treat obstructive sleep apnea (OSA) was taught by Sullivan in U.S. Pat. No. 4,944,310. Today apparatus for OSA typically comprises (i) a blower which provides a supply of air or breathable gas at positive pressure, (ii) an air delivery conduit connected to the blower, and (iii) a patient interface, such as a nasal mask, which is connected to the air delivery conduit. 
     A variety of nasal masks have been developed. One such mask is the MIRAGE® mask, manufactured by ResMed Limited and described in U.S. Pat. Nos. 6,112,746; 6,357,441; 6,119,693 and 6,463,931, amongst others. Another such mask is the ULTRA MIRAGE® mask, also manufactured by ResMed Limited. The ULTRA MIRAGE® mask is described in U.S. Pat. Nos. 6,112,746, 6,357,441, 6,374,826, 6,412,487, 6,439,230 and 6,463,931. 
     The American Academy of Pediatrics, in a Technical Report on the Diagnosis and Management of Childhood Obstructive Sleep Apnea Syndrome (OSAS) (PEDIATRICS Vol. 109 No. 4 April 2002) noted that “Snoring is a common occurrence in childhood, with reported prevalence between 3.2% and 12.1%. The prevalence of childhood OSAS is difficult to estimate, largely because published studies use different PSG criteria for its ascertainment. Reports range from 0.7% to 10.3%.” 
     A key factor in the efficacy of therapy and compliance of patients with therapy is the comfort and fit of masks. Whilst there are a large number of masks designed for adults, there are relatively few designed to suit children. 
     One mask designed for children is the SULLIVAN® Nasal CPAP system, Infant Nasal Bubble Mask System with Sensor tubing, manufactured by ResMed Limited. See  FIG. 1 . In addition, Respironics Inc. manufactures a “Comfort Flap Small Child” product. 
     Other infant masks are shown in the following patents: FR 2775905; GB 2277688; US 2002/0104531; U.S. Pat. No. 3,827,433; U.S. Pat. No. 4,232,476; U.S. Pat. No. 4,406,283; U.S. Pat. No. 4,774,946; U.S. Pat. No. 4,896,666; U.S. Pat. No. 4,832,015; U.S. Pat. No. 5,271,391; U.S. Pat. No. 5,318,590; U.S. Pat. No. 5,462,050; U.S. Pat. No. 5,509,408; U.S. Pat. No. 5,535,741; U.S. Pat. No. 5,813,423; U.S. Pat. No. 5,660,174; U.S. Pat. No. 6,418,929; WO 01/32250 ;WO 02/05883 ;WO 95/09023 
     One adult mask is the VISTA™ mask, manufactured by ResMed Limited, and described in Australian Provisional Patent Application PS1926, filed 23 April 2002; U.S. 60/377,254 filed 3 May 2002; U.S. 60/397,195 filed 22 Jul. 2002; U.S. 60/402,509 filed 12 Aug. 2002; and U.S. Ser. Nos. 10/391,440, 10/390,682, 10/390,681, 10/390,720 and 10/390,826, all filed 19 Mar. 2003, the contents of which are hereby incorporated by cross-reference. An ornamental design applied to the VISTA™ mask is shown in design patent application U.S. Des Pat. No. 29/166,190, the contents of which are hereby incorporated by reference. 
     The VISTA™ mask includes a cushion, a frame, an elbow and headgear including a yoke. 
     While the VISTA™ mask is particularly suitable for adults, the problem arises as to how such an adult mask can be adapted to suit children. 
     International Patent Application WO2001/32250 (Sullivan &amp; Wilkie) describes a mask for supplying gas under pressure to the nasal airway of an infant human. In that application, the following is stated:
     “. . . until now, infant masks have been developed on the basis of scaling down the adult mask to approximate to the infant face and nose. The problems with this scaling down process are threefold.   First, the adult nose and middle third of the face is very different in shape from that of the infant. The adult nose is more elongated than, and protrudes far more from the surface of the face compared to the infant nose which is relatively flat with no bridge, with the nares (nostril passages) pointing outwards. Therefore in order to fit the adult nose the base of the mask has a triangular shape elongated in the vertical axis. In contrast, with an infant, the width at the base of the nose approximates the height from the base of the nose (nares) to the apex of the nose (nasion). The proportional shape of the nasal area of an adult is rectangular compared with a square proportional shape for an infant. In addition to this basic difference in proportional shape, the adult face has quite marked contours especially around the nose and cheek area which are absent in the infant. The adult mask must therefore have acute angles which accommodate these facial contours. Thus, when an adult mask is scaled down for an infant, not only are the proportions wrong for the infant nose and face, but the angles which are unnecessarily incorporated, inadvertently introduce a new problem. Because the infant has a relatively flat nose, and virtually no bridge, the angles promote formation of channels in the sealing margin of the mask, especially in the region of the nasal bridge.   Secondly in adult mask designs, the straps of the head harness connect with lugs on the rigid manifold in the order of 20 mm away from the surface of the face to allow the mask to accommodate the height of the adult nose. Because of this a potential fulcrum effect is created. In the adult this fulcrum effect is not as problematic as in the infant, not only because the adult is less mobile during sleep . . . but also because the contours of the adult face and cheeks can offset this rise. In the infant, when the mask used is merely a scaled down adult mask, the elevation of the straps lugs above the face is about 12 mm. This by itself creates a potential fulcrum as it does on the adult but the effect is enhanced by the fact that there is no offset from the infant cheek due to the smaller facial area. Consequently, the straps holding the mask in place come into contact with the side of the face in the infant, compared to the cheek in the adult.   Thirdly, because the attachment of the paediatric mask to the face and head mimics that of the adult mask, the torsional forces are increased. The greater torsional effect is due to the decreased surface area of the mask face contact relative to the air delivery pipe. Thus relatively minor movements can result in sufficient torsional forces to cause movement at the interface between the mask and the infants face.”   

     SUMMARY 
     In accordance with a first aspect of the invention a mask assembly suitable for pre-adults is provided. 
     In accordance with a second aspect of the invention a system of cushions, frames, headgear, yokes and other mask components are provided which fit a wide range of pre-adults with a good seal and which are economic to bring to market. 
     In accordance with another aspect of the invention, a system of mask cushions is provided for pre-adults in which the cushion for children aged generally 2-6 years has a shallower nasal bridge region than the cushion for pre-adults aged generally 6-16 years. 
     In accordance with another aspect of the invention, a system of mask cushions is provided for pre-adults in which the cushion for children aged generally 2-6 years has larger radius lower corner edges of the membrane than the cushion for pre-adults aged generally 6-16 years. 
     In accordance with another aspect of the invention, a system of mask cushions is provided for pre-adults aged generally 6-16 years which are adapted to be mounted to corresponding adult sized frames. 
     In one preferred embodiment, headgear for use with a respiratory mask includes first and second straps each adapted to be provided to a mask frame of the mask, where each of the first and second straps includes a yoke, each said yoke being constructed and arranged to accommodate at least one of a pre-adult patient or a small sized adult patient. 
     In another embodiment, which can be used with the headgear described above, a cushion for use with a nasal mask includes an outer membrane including a face-contact portion to form a seal with the patient; and an underlying rim positioned below the membrane, wherein the membrane and the rim are formed and positioned with respect to one another to accommodate at least one of a pre-adult patient or a small sized adult patient. 
     These and other aspects will be described in or apparent from the following description. 
    
    
     
       BRIEF DESCRIPTION OF FIGURES 
       Preferred embodiments will be described in relation to the following drawings, in which: 
         FIG. 1  shows related art infant bubble mask; 
         FIG. 2  shows a perspective view of a related art VISTA™ mask on an adult patient; 
         FIG. 3  shows a side view of the VISTA™ mask; 
         FIG. 4  shows a front view of the VISTA™ mask; 
         FIG. 5  shows a side view of a headgear yoke of the VISTA™ mask; 
         FIG. 6  shows a plan view of a headgear yoke in accordance with a first embodiment of the invention; 
         FIG. 7  is a cross-sectional view taken along section  7 - 7  in  FIG. 6 ; 
         FIG. 8  is a bottom view of the yoke shown in  FIG. 6 ; 
         FIG. 9  is a plan view of a side headgear strap according to an embodiment of the present invention; 
         FIG. 10  is a plan view of a central rear headgear strap according to an embodiment of the present invention; 
         FIG. 11  is a plan view comparing the central rear headgear strap of  FIG. 10  and the VISTA™; 
         FIGS. 11   a - 11   c  illustrate a headgear crossover according to an embodiment of the present invention; 
         FIG. 12  shows a plan view of a cushion, mounted on a frame, in accordance with an embodiment (the “Kid cushion”) of the invention; 
         FIG. 13  shows a top elevation view of the “Kid” cushion; 
         FIG. 14  shows a side elevation view of the “Kid” cushion (without the frame); 
         FIG. 15  shows a bottom elevation view of the “Kid” cushion; 
         FIG. 16  shows a perspective view of the “Kid” cushion; 
         FIG. 17  shows a plan view of the “Kid” cushion compared to other cushion shapes; 
         FIG. 18  shows a rear review of an underlying rim of the “Kid” cushion showing the change in dimension compared with an adult VISTA™; 
         FIG. 19  shows of a membrane of the “Kid” cushion showing the change in dimension compared with an adult VISTA™ cushion; 
         FIG. 20  shows the edge of the membrane of the “Kid” cushion and the more rounded lower corners of the “Mini” cushion; 
         FIG. 21  shows a sketch plot of a system of masks in accordance with an embodiment of the invention; 
         FIG. 22  illustrates a rear view of a “Kid” cushion in accordance with the present invention; 
         FIG. 23  illustrates a bottom view of a “Kid” cushion in accordance with the present invention, in comparison to the VISTA™ and/or other earlier embodiments; 
         FIG. 24  illustrates a top view of a “Kid” cushion in accordance with the present invention; 
         FIG. 25  illustrates a side view of a “Kid” cushion in use, in accordance with the present invention; 
         FIG. 26  illustrates features of the upper lip design for a cushion according to an embodiment of the present invention; 
         FIG. 27  illustrates a sample fitting chart plotting nose width v. nose or bridge height in accordance with the present invention, comparing the VISTA™, the Kidsta Small and the Kidsta Extra Small; 
         FIG. 28  illustrates cross-sectional views comparing the cushions of the “Kid”, the Kidsta Small and the VISTA™; 
         FIG. 29  illustrates partial plan views comparing the “Kid”, Kidsta Small and VISTA™ cushions; 
         FIG. 30  illustrates a sample fitting chart based on bridge center depth, in accordance with an embodiment of the present invention; 
         FIG. 31  illustrates partial cross-sectional views comparing the cushions of the “Kid”, Kidsta Small and VISTA™; 
         FIG. 32  illustrates a plan view of a Kidsta Small cushion in accordance with an embodiment of the present invention; 
         FIG. 33  is a rear view thereof; 
         FIG. 34  is a side view thereof; 
         FIG. 35  is a cross-sectional view taken along section  35 - 35  in  FIG. 32 ; 
         FIGS. 35   a - 35   g  illustrate exemplary cross-sections shown in  FIG. 32 , including dimensions and/or to-scale relative locations of the membrane relative to the rim; 
         FIG. 36  is a detailed view taken from  FIG. 35 ; 
         FIG. 37  is another detail view taken from  FIG. 35 ; 
         FIG. 38  illustrates a plan view of a Kidsta Extra Small cushion in accordance with an embodiment of the present invention; 
         FIGS. 38   a - 38   f  are various cross-sections thereof; 
         FIG. 39  is a rear view thereof; 
         FIG. 40  is a side view thereof; 
         FIG. 41  is a cross-sectional view taken along section  41 - 41  of  FIG. 38 ; 
         FIG. 42  is a detail view (scale: 2 to 1) taken from  FIG. 41 ; 
         FIG. 43  is a top view of a frame in accordance with an embodiment of the present invention; and 
         FIG. 44  shows the frame of  FIG. 43  in a different position. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       FIGS. 2-5  illustrate a related art mask known as the VISTA™, manufactured by ResMed Incorporated. Mask assembly  100  comprises (i) a soft face-contacting cushion  110 , (ii) swivel elbow  130 , (iii) headgear clips  140 , (iv) a frame  120  adapted to receive the cushion  110  and support swivel elbow  130  and headgear clips  140 , and (v) headgear  150  including straps  160  and a headgear yoke  170 . 
     Stabilization of the cushion  110  and frame  120  on the face  220  of an adult patient  200  is assisted by the size, shape and positioning of the yoke  170  on the headgear  150 . In spite of the problems identified by Sullivan &amp; Wilkie concerning the fulcrum and torsional effects of prior art masks, greater stability can be achieved in pre-adults with a mask in accordance with the present invention. In one embodiment, the present inventors have redesigned the VISTA™ mask in  FIGS. 2-5  to be suitable for use with pre-adults, or adults with small or child-like facial features. 
       FIGS. 6-16  illustrate components of a mask system for use with pre-adults, in accordance with preferred embodiments of the present invention, in which like elements are referenced by like elements compared to the VISTA™ shown in  FIGS. 2-5 . 
     The US Food &amp; Drug Administration (FDA) makes the following classifications for pre-adults: 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
             
            
               
                   
                 Neo-natal 
                 0-1 month 
               
               
                   
                 Infant 
                 1 month-2 years 
               
               
                   
                 Child 
                 2 years to 12 years 
               
               
                   
                 Adolescent 
                 12 years to 16 years 
               
               
                   
                   
               
            
           
         
       
     
     In accordance with an aspect of the invention, a mask system is provided which uses a different classification: 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 2 
               
               
                   
                   
               
             
            
               
                   
                 Infants 
                 0-2 
               
               
                   
                 Mini 
                 2-6 
               
               
                   
                 Kid 
                 6-16 
               
               
                   
                   
               
            
           
         
       
     
     The mask system can fit the same range of pre-adults defined by the FDA, however, four separate mask systems are not required. 
     In adults, a system of masks suitable for fitting a range of people should take into account body mass and racial nose characteristics. For example, the East Asian-shaped nose typically has a lower nasal bridge region compared to the Caucasian-shaped nose. However, below the ages of 5-7 there are few racial distinctions in children. In particular, neo-nates, infants and young children have no nasal bridge. Not only do children have smaller heads and faces than adults, their heads and faces are differently shaped. In accordance with an aspect of the invention, a system of mask &amp; headgear sizes has been developed in which a minimal set of components can be used to fit the widest range of people: 
     
       
         
           
               
               
               
               
               
               
             
               
                   
                 TABLE 3 
               
               
                   
                   
               
               
                   
                 Cushion 110 
                 Frame 120 
                 Yoke 170 
                 Clips 140 
                 Elbow 130 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Mini (2- 
                 2-3 sizes 
                 50-70% of 
                 Extra- 
                 50-70% of 
                 50-70% of 
               
               
                 6YO) 
                   
                 standard 
                 small 
                 standard 
                 standard 
               
               
                 Kid (6- 
                 2-3 sizes 
                 Standard 
                 Small 
                 Standard 
                 Standard 
               
               
                 16YO) 
               
               
                   
               
            
           
         
       
     
     An advantage with the mask system described herein is that a very wide range of pre-adults can find a mask which fits well with little leak, is comfortable, and yet is economic for manufacturers to produce and bring to market. Since the pediatric, small adult, or pre-adult market is relatively small in comparison to the standard adult market, there is a reduced economic incentive for business to bring product to the market. However, when a system in accordance with the invention is produced, it becomes more economically viable to produce such masks. 
     Headgear Yoke Design 
       FIGS. 6-8  illustrate (left hand) headgear yoke  170  suitable for pre-adults in accordance with an embodiment of the invention. Yoke  170  includes vertical finger  310 , ladder lock  320  to receive a headgear strap, lower yoke finger  330  and key-shaped recess  311  to receive a clip  140  (see  FIG. 3 ). Headgear yoke  170  preferably should have one or more of the following features:
     1. yoke vertical finger  310  located midway between eye-line  230  and earlobe  240  (refer to  FIG. 2 ).   2. yoke ladderlock  320  located ⅓ of the distance between the eye-line  230  and crown of the head  250 .   3. a gap of 5 mm maintained between lower yoke finger  330  and lowest point of earlobe  240 .   4. lower yoke finger  330  positioned about 15 mm behind the lowest point of the earlobe  240 .   5. a lower yoke finger  330  positioned at an angle of about 15-20°, preferably 17°, like the VISTA™.   

     Table 4 compares dimensions of related art VISTA™ headgear yoke with two “small” headgear yokes, referred to as the “Mini” and “Kid,” in accordance with preferred embodiments of the invention. The first row of Table 4 identifies four features (A, B, C and D) of the headgear yoke. These features are shown in  FIG. 6 , while  FIGS. 7 and 8  show additional views of the yoke  170 . The dimension values can be varied up to ±20%, and preferably up to ±10%, of the dimensional values listed in Table 4 below and shown in the Figures. For example, distance A can be about 90-100 mm, distance B can be about 80-100 mm, distance C can be about 25-40 mm, and distance D can be about 45-55 mm, although other distances are possible. 
       FIGS. 11   a - 11   c  illustrate a headgear crossover  80  that can be used instead of the crossover shown in  FIG. 4 . The crossover  80  includes a main body  82  which may have a substantially square appearance, although other shapes are possible. Each side may include a slot  84  to receive one of the straps  160  shown in  FIGS. 10 and 11 . Exemplary dimensions are shown in  FIGS. 11   a - 11   c,  although other dimensions are possible. Crossover  80  has an improved appearance compared to crossover in  FIG. 4 . Further, crossover  80  provides greater friction to the straps running through it and so resists slipping out of place more than the crossover in  FIG. 4 . For example, the sliding force for the crossover  80  may be increased between about 100-150%. 
     
       
         
           
               
             
               
                 TABLE 4 
               
             
            
               
                   
               
               
                 Yoke Comparison 
               
            
           
           
               
               
               
               
               
            
               
                   
                 “A” (mm) 
                 “B” (mm) 
                 “C” (mm) 
                 “D” (mm) 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
            
               
                 VISTA ™ (related art) 
                 130 
                 110 
                 43 
                 48.5 
               
               
                 “Small” 1st 
                 100 
                 86 
                 28 
                 46 
               
               
                 embodiment - “Mini” 
               
               
                 “Small” 2 nd   
                 100 
                 95 
                 37 
                 49 
               
               
                 embodiment - “Kid” 
               
               
                 “Small 3 rd   
                 100 
                 90 
                 37 
                 49 
               
               
                 embodiment - “Kidsta-S” 
               
               
                   
               
            
           
         
       
     
     Headgear Strap Design 
       FIG. 9  illustrates a side headgear strap  162  suitable for use with yoke  170  shown in  FIG. 6 . Strap  162  includes vertical portion  163  and lower portion  164 . The yoke is mounted on strap  162  in a manner similar to that shown in relation to the VISTA™ yoke and strap, as shown in  FIG. 5 . For example, the yoke and strap can be secured to one another via stitching, adhesives, etc. 
     The headgear strap  162  may include the dimensions as shown in  FIG. 9 . However, those dimension are exemplary only, as other dimensions could be used instead. For example, the strap  162  could have dimensions that are varied up to ±20%, but preferably no more than up to ±10%, of the dimensional values shown in the example in  FIG. 9 . Other variations to the yoke are described below, which may also impact the dimensions of the headgear strap. 
       FIG. 10  shows a center strap  160  for the headgear  150 . Preferred dimensions of the center strap  160  are illustrative only, and may be adjusted up to +/−10%-20% of the values shown.  FIG. 11  shows the center strap  160  of the “Kid” in side-by-side comparison with the VISTA™ center strap. The rear width of the center strap  150  shown in  FIG. 10  can be reduced by about 30 mm, as compared to the VISTA™ center strap. Further, the center strap  150  can accommodate a label (in label area  161 ) and ladder locks. 
     Cushion Design 
       FIGS. 12-16  illustrate a cushion  110  in accordance with an embodiment (e.g., the “Kid”) of the present invention.  FIGS. 12-13  and  15  show the cushion mounted on a standard VISTA™ frame  120 . Cushion  110  includes a double-walled face contacting portion. As shown in  FIG. 12 , the double wall includes a thin flexible outer membrane  910  which forms a sealing structure, and an underlying rim  920  which forms a support structure. In  FIG. 12 , the rim  920  is indicated with a broken line as it is seen through and/or below the membrane  910 . As shown in  FIG. 13 , a top view, cushion  110  has a patient contacting region  1110  and a frame-engaging region  1120 . The cushion  110  and frame  120  are adapted to engage with one another as in the VISTA™ mask, as described in U.S. Patent Application No. 60/402,509, or other ones of the applications listed above, although other engagement methods are possible. Both the membrane  910  and rim  920  preferably include a nasal bridge notch  930 , a pair of side portions  940 , and a curved lip region  950 , as shown in  FIG. 12 . 
     The cushion  110  is constructed from a silicone material, such as that used for the VISTA™ mask, although other materials could be used, e.g., gel, foam, silicone and combinations thereof. 
     In accordance with an embodiment of the invention, 2-3 “Kid” cushion sizes and 2-3 “Mini” cushion sizes can be used to fit pre-adults from 2 to 16 years. 
     Since the “Kid” range of cushions fit adult VISTA™ frames, e.g., see frame  120  in  FIGS. 2-5 ,  12 ,  13  and  15 , they have a generally inwardly sloping outer wall  1130  (see  FIGS. 13-16 ) that provides a transition between the relatively smaller patient-contacting region  1110  and the frame-engaging portion  1120  of the cushion  110 . The outer wall can also be stepped as well. In either case, the area of the bottom of the cushion (where it connects to the frame) is projected wider than the area where the membrane contacts the facial tissue. The difference in area (i.e., the projected area of the bottom of the cushion) can help reduce the pressure needed to maintain a seal with the face. This is an advantage especially in regard to fitting pre-adult or small adult patients, where the available patient contact area may be limited. 
     Moreover, the smaller area covered by the Kidsta Small and Kidsta Extra Small masks results in reduced headgear loading. The smaller area of face exposed to the air pressure in the mask results in a smaller overall reaction force, as force is equal to pressure by area. The reaction force from the pressure in the mask is a significant component of the load on the mask, especially at higher air pressures. Hence the total load on the mask, and the headgear strap loads required to match this load, will be less with the small mask area. 
     Both the “Kid” and “Mini” range of cushions are not only smaller than adult range of VISTA™ cushions, they have a different shape. For example, both the “Kid” and “Mini” cushions have relatively shallower notches in the nasal bridge region and relatively shallower curves in the lip region compared to an adult VISTA™ cushion. See also  FIGS. 27 ,  28 ,  31 ,  32  and  34 . 
     Table 5 shows the change in size of a “Kid” cushion in accordance with one embodiment of the invention. The membrane  910  of the cushion  110  has an orifice  975  ( FIGS. 12 and 17 ) defined by the edge  970  of the membrane  910 . There is a corresponding orifice  985  (visible through the membrane  910 ) defined by the edge  980  of the rim  920 . In use, the nose of the patient  200  passes through the orifice  975 . 
     As compared to the VISTA™ cushion, the orifice  985  of the rim  920  is about 3 mm smaller all around its perimeter, however the membrane  910  is smaller by an amount varying from about 0 to 3 mm.  FIG. 17  shows broken line  972  which indicates the general position of the edge of the membrane in a corresponding adult size VISTA™ cushion with its corresponding larger orifice.  FIG. 18  schematically shows relative changes of the rim of the “Kid” cushion compared to the VISTA™ cushion, while  FIG. 19  schematically shows relative change in the membrane of the “Kid” compared to the VISTA™. The relative changes in height of the cushion reflect the relatively shallower notch in the nasal bridge region and the relatively shallower curve in the lip region. 
     
       
         
           
               
             
               
                 TABLE 5 
               
             
            
               
                   
               
               
                 “Kid” v. VISTA ™ - Cushion Comparison 
               
            
           
           
               
               
               
            
               
                   
                 Membrane 
                 Rim 
               
               
                   
                   
               
            
           
           
               
               
               
            
               
                 Orifice span 
                 0 mm in nasal 
                 −3 mm in all regions 
               
               
                   
                 bridge region 
               
               
                   
                 −2 mm in lip region 
               
               
                   
                 −3 mm in side region 
               
               
                 Height of patient 
                 +6 mm in nasal 
                 +3 mm in nasal 
               
               
                 contacting region 
                 bridge region 
                 bridge region 
               
               
                 from frame- 
                 +3 mm in lip region 
                 +3 mm in lip region 
               
               
                 engaging portion. 
                 +2 mm in side region 
                 +1 mm in side region 
               
               
                 Kid Orifice span 
                 nasal bridge region - 23 
                 nasal bridge region - 35 
               
               
                   
                 lip region - 31 
                 lip region - 33 
               
               
                   
                 side region - 19 
                 side region - 43 
               
               
                 Kid Height of 
                 nasal bridge region - 28 
                 nasal bridge region - 14 
               
               
                 patient contact- 
                 lip region - 20.7 
                 lip region - 16 
               
               
                 ing region from 
                 side region - 34 
                 side region - 26 
               
               
                 frame-engaging 
               
               
                 portion 
               
               
                   
               
            
           
         
       
     
     In accordance with another embodiment of the invention, a “Kid” cushion has a further 3-4 mm increase in height of the membrane in the patient contacting-portion from the frame-engaging portion in the nasal bridge region, hence a total of 9-10 mm when compared to an adult cushion. There is a corresponding change in the rim. 
     In accordance with another embodiment of the invention, a “Mini” cushion has a further 6-7 mm increase in height of the membrane in the patient contacting-portion from the frame-engaging portion in the nasal bridge region, hence a total of 12-13 mm when compared to an adult cushion. There is a corresponding change in the rim. In this way, a “Mini” cushion has an even shallower notch in the nasal bridge region compared to a “Kid” cushion. Since a “Mini” cushion uses a smaller frame than a “Kid” cushion, it does not have the generally sloping outer wall in the transition region between the face-contacting portion and the frame-engaging portion. Furthermore, the “Mini” cushion is generally closer to the face for better stability. Such a shallower notch is indicated by broken line  990  in  FIG. 15 . Furthermore, as shown in  FIG. 20  the lower corners of the “Mini” cushion  1510  are more rounded (i.e. larger radius) than the corresponding corners of the “Kid” cushion. The cushion includes a nasal ridge region, a top lip region and two side regions. In this example, the membrane and rim each have an orifice in which a width of the membrane orifice is between about 30 and 32 mm in the lip region, between about 18 and 20 mm in each side region, and between about 22 and 24 mm in the nasal bridge region, a width of the rim orifice is about 34 and 36 mm in the nasal bridge region, between about 32 and 34 mm in the lip region, and between about 42 and 44 mm in each side region of the cushion. The membrane and the rim each have a height as measured from a portion of the cushion that engages the frame. The membrane height is about 27 and 35 mm in the nasal bridge region, between about 19 and 22 mm in the lip region, and between about 33-35 mm in each said side region, the rim height is between about 13 and 18 mm in the nasal bridge region and the lip region, and the rim height in each said side portion is between about 25 and 27 mm. 
     In general the materials used to construct a mask assembly in accordance with the invention are the same as those used to construct the VISTA™ mask. 
     As shown in  FIG. 21 , there may be some overlap in ages between the different masks and cushions. For example, some pre-adults aged 7 years may find a “Mini” (shown as “Mini-” in  FIG. 21 ) mask too small and it may be appropriate for them to be fitted with a “Kid” (shown as “Kid” in  FIG. 19 ). Of course, the Mini and Kid may be used for adult patients having smaller facial shapes or pre-adult features. 
     Further Embodiments 
     Further cushion embodiments of the invention are described in relation to  FIGS. 22-45 . These embodiments also relate to shrinking and/or re-proportioning the VISTA™, Kid or Mini cushion to create “small” (“Kidsta Small”) and “extra small” (“Kidsta Extra-Small (XS)”) cushion sizes, while preferably maintaining the same basic architecture for fitting the cushion to the VISTA™ mask frame. The new embodiments have been developed as a result of conducting testing on the “Kid” and “Mini” cushions described above. 
     The underlying rim  920  should preferably have the same cross section as the VISTA™, e.g., where it attaches to the frame as shown in  FIG. 37 , while the cross section of the membrane  910  and/or its relationship with the underlying rim  920  should be very similar to the VISTA™, bearing in mind that both should be tweaked at the nasal bridge area  930 —the membrane  910  in particular. The cushion height (e.g., the distance measured from the underlying rim  920  (i.e., the upper lip (below the nose) to the top of the cushion as shown in  FIG. 22 ) should be maintained if at all possible the same as the height of the VISTA™, keeping in mind that the height may be affected by having to fit the cushion  110  onto the frame  120 . 
     As to the underlying rim  920 , one aspect is to reduce the size of the opening  985  substantially along an entire extent thereof so that the width and effective height dimensions correspond to Table 6, all dimensions being in mm. For example, the width of the Kidsta S and XS may be in the range of about 30-42 mm, the effective height may be in the range of about 32-42 mm, and the effective bridge depth may be about 13-24 mm, although other dimensions are also possible. See  FIG. 22 , which shows the width and height of opening  985 . The membrane  910  size follows the underlying rim  920  if proportions are maintained. 
     
       
         
           
               
             
               
                 TABLE 6 
               
             
            
               
                   
               
               
                 VISTA ™, Kidsta S + Kidsta XS - Cushion 
               
            
           
           
               
               
               
               
            
               
                   
                 Width 
                 Eff. Height 
                 Bridge Depth 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 VISTA ™ 
                 45 
                 about 30 
                 &lt;11 
               
               
                   
                 KIDSTA - S 
                 39-40 
                 about 35 
                 &lt;15 
               
               
                   
                 KIDSTA-XS 
                 34-35 
                 about 40 
                 20 
               
               
                   
                   
               
            
           
         
       
     
     The top lip  950  area should be raised so that a distance z is about 2 mm. See  FIG. 23 . The membrane bridge  930  should have an effective depth (i.e., the distance from the underlying rim  920  to the bottom of the nasal bridge region of the membrane  910 , as shown in  FIG. 24 ) that is preferably adjusted as shown in Table 6. See  FIG. 24 . The underlying rim  920  may be raised too if this helps with seating to frame  120 . It may be desirable to adjust only the vertical dimension, although additional adjustment may be desirable. 
       FIG. 25  shows a side view of the “Mini” or “Kid” described above, in use on a pre-adult. As shown, the vertical finger  310  of the yoke  170  may be too close to the user&#39;s eyes, and/or the yoke lower finger  330  may impinge on the lower part of the ear lobe. Accordingly, for the Kidsta-S, the dimension “C” from Table 4 can be increased by about 9 mm (i.e., a total of about 37 mm) to move the vertical finger closer to the ear, thereby increasing field of view. To better avoid or help avoid impinging on the lower ear lobe, dimensions “B” and/or “D” from  FIG. 6  can be altered, for example, by increasing these dimensions by about 4 mm each, i.e., total dimension “B” would be about 90 mm and total dimension “D” would be about 50 mm (or a bit less than the VISTA™). The lower finger  330  may include a full radius. 
     The “Kid” or “Mini” can also be better dimensioned and/or shaped to avoid leak at the nasal bridge region, especially for kids under age 11 years old, to avoid intrusion into the eyes, to avoid discomfort stemming from a “hard-edged” cushion, and/or to reduce the size of the cushion, e.g., to avoid dead air space. 
     To better avoid intrusion into the eyes, the Kidsta XS cushion can be further shortened (compared to the Kidsta S) by about 5 mm to avoid the eye sockets. As mentioned, the frame size preferably remains the same. 
     The Kid or Mini cushion depth was about 3 mm deeper than the VISTA™, which may introduce possible instability and make headgear difficult to fit. In the Kidsta S, the height is reduced approximately to the height of the VISTA™. 
     In the Kid or Mini, the radius was smaller across the top lip (compared to the VISTA™) with no leaks or discomfort reported. Thus for the Kidsta S according to the present embodiment, maintain the 2 mm smaller radius compared to the VISTA™. For the Kidsta XS, the radius should be further reduced another 2 mm, in proportion, which may help accommodate patients with smaller lips. See  FIG. 26 . 
     As for sizing strategy, one aim is to use only 2 sizes with roughly equal population coverage. The dimensions which have the most impact on sizing are the maximum nose width (limits mask width), the minimum nose height from septum to eye line (limits mask height) and the minimum nasal bridge depth (limits shallowness of the mask). The inventors have found that width and height growth is approximately linear for the 5-16 age group. The masks are designed to fix approximately 5 year age blocks, and to fit the largest width and smallest height within each block. The data from the middle of the nasal bridge region is not widely available, so it is also assumed to be linear within each block. See Table 7, below. 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 7 
               
               
                   
                   
               
               
                   
                   
                   
                 Bridge Depth 
               
               
                   
                 Inner Cushion 
                 Inner Cushion 
                 Difference 
               
               
                   
                 (Nose) Width 
                 (Nose) Height 
                 c.t. Vista 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                 VISTA ™ Standard 
                 45 
                 40 
                 0 
               
               
                 Kid or Mini 
                 40 
                 36 
                 5.5 
               
               
                 Kidsta Small 
                 40 
                 35 
                 8.5 
               
               
                 Kidsta Extra Small 
                 35 
                 30 
                 12.5 
               
               
                   
               
            
           
         
       
     
       FIG. 27  is a sizing chart based on nose width and nose or bridge height. In accordance with an aspect of the invention, a mask (e.g., the Kidsta Small or the Kidsta XS) can be selected for a patient by measuring or otherwise obtaining one or more nose dimensions. For example, a Kidsta S or XS would be selected for a pre-adult or small sized adult patient having a nose width of less than about 40 mm and/or a nose/bridge height of less than about 35 mm. The Kidsta S and XS include cushions and/or headgear that are structured to provide a good fit for those patients. If the nose width is below about 35 mm and/or the nose/bridge height is below about 30 mm, then the Kidsta XS would appear to be the appropriate mask for that patient. 
       FIGS. 28-29  show various other features of the Kidsta S in conjunction with other cushions, for comparison purposes, VISTA™ and the Kid or Mini. 
       FIG. 30  shows the bridge center depth versus cushion type, e.g., of the Kidsta S, Kidsta XS, the Kid or Mini, the VISTA™ (S-W) and the VISTA™ (Standard). The information in  FIG. 30  can be combined with the information in  FIG. 27  to select the most appropriate mask given one or more dimensions (and/or the age)of the patient. Compared to the Kid or Mini, the nasal bridge depth is reduced by about 3 mm for the Kidsta S, and 7 mm for the Kidsta XS. Also, the vent is the same as or similar to VISTA™. See  FIG. 31 . 
       FIGS. 32-37  show various views of the Kidsta S, while  FIGS. 38-42  show various view of the Kidsta XS, including exemplary dimensions. The dimensions can be changed up to about ±20%, but preferably no more than up to about ±10%, of the exemplary values shown.  FIGS. 32-42  are drawn to scale, or at least shown the relative distances between cushion parts to scale. 
     As shown in  FIGS. 32 and 38 , the cushion may include one or more markers  911 , e.g., in the form of a diamond or other shape. The markers may be provided in conjunction with similar or complimentary markings on the frame, to provide a visual indication to facilitate alignment. 
     Headgear Clip 
     The headgear clip  140  as shown in the VISTA™ ( FIGS. 2-5 ) can be made of PBT, a plastic, resilient material, although other materials can be used. For the present embodiments, the clips can be made of polypropylene, preferably available under the trade name “BOREALIS.” Clips made for polypropylene can be more flexible than PBT, which facilitates operation, e.g., assembly and disassembly, of the clip, especially by pre-adults, e.g., 5 year old girls can operate polypropylene clips. This can help increase compliance of the patient. 
     Frame 
     The existing VISTA™ type frame  120  includes cheek pieces (see  FIGS. 2-5 ) that support the mask both vertically and from side to side movement. These cheek pieces preferably remain in light contact with the cheeks and/or jowls to provide the maximum stability with maximum comfort. 
     A problem may arise because different people have different face widths. A frame width that provides optimal contact for one person will be too tight for another person and too loose for a third. 
     If the frame is too tight, the patient may suffer from pain or skin damage, or will adjust the mask so that it is no longer too tight, but it will no longer seal or provide effective treatment. If the mask is too loose, the mask will have excessive side to side movement, especially when the patient turns to the side and presses one cheek into the pillow. 
     Another aspect of the invention is to chose a size that suits the largest number of patients, with a bias towards being too loose in preference to being too tight. It is envisaged that a range of sizes may be introduced so that customers may choose from a narrow, medium or wide mask frame. 
       FIGS. 43-44  show a frame  120  having movable rather than rigid connections  121  between the cheek pieces  123  and the main body  125  of the mask frame. This enables the width of the frame between the cheek pieces to be adjusted to fit the patient. 
     There are a number of different ways that this idea can be implemented. For example, the cheek pieces  123  can be mounted on a hinge so that they can swing in or out. The cheek pieces  123  may be either free to move or they could be locked into one or more predetermined positions, via detents, friction, and/or a pin and slot arrangement. 
     Alternatively, the cheek pieces  123  can be flexibly mounted, so that they can bend in or out without requiring much force. If they are set so that the neutral position is wider than the patient&#39;s face, the tension in the headgear will pull the cheek pieces in towards the ideal position for that person. 
     In a further alternative, if the cheek pieces  123  are set so that the neutral position is narrower than the patient&#39;s face, the cheeks will push the cheek pieces out towards the ideal position for that person. In another method, the cheek pieces could be adjusted in or out using some sort of adjustment mechanism, such as a screw adjustment. 
     With movable cheek pieces, the mask can be more comfortable for a wider range of patients. Those patients with wide faces would no longer suffer from excessive pressure on the cheeks. 
     It would also be more securely mounted on the face, resulting in less mask movement for those with thin faces, or for people with wide faces who may adjust the mask poorly in an attempt to make it more comfortable. This greater security will result in less leakage, leading to greater comfort and more effective treatment. 
     This will make the VISTA™ type mask easier to fit onto a variety of different face shapes. Because one mask will fit such a large range, less inventory will be required. 
     Use of an adjustable mask frame will stop the need for having more than one frame size. This will reduce inventory and tooling costs. 
     The ease of fitting a wide variety of facial shapes will increase the range of people to whom the masks will be attractive. Although the invention has been described with reference to particular embodiments, it is to be understood that this embodiment is merely illustrative of the application of the principles of the invention. Numerous modifications may be made therein and other arrangements may be devised without departing from the spirit and scope of the invention.