Abstract:
A mask for use with the administration of CPAP therapy includes a mask body for connection with a supply of breathable gas pressurized above ambient; and a compliant patient contacting element including a multilayered cushioning interface. The interface has an interior layer and an exterior layer provided in spaced relation to the interior layer when the mask is not in use. The exterior layer is elastically and resiliently movable towards and away the interior layer in use. Only the exterior layer forms a contacting seal with the patient in use.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 10/068,963, filed Feb. 11, 2002, allowed, which is a continuation of U.S. application Ser. No. 09/230,491, filed Aug. 11, 1999, now U.S. Pat. No. 6,357,441, which claims the benefit of Australian Patent Application No. P01265, filed Jul. 26, 1996, through PCT Application No. PCT/AU97/00450, filed Jul. 16, 1997 (published as WO 98/04310 on Feb. 5, 1998). This application contains subject matter related to U.S. application Ser. No. 08/791,212, filed Jan. 31, 1997, now U.S. Pat. No. 6,112,746, incorporated by reference in its entirety, which also claims priority to Australian Provisional Patent Application No. PO 1265, filed Jul. 26, 1996. 
    
    
     FIELD OF THE INVENTION 
     The invention relates generally to a nasal mask and to a cushion therefor, for example, for use in the treatment of respiratory conditions and in assisted respiration. 
     BACKGROUND OF THE INVENTION 
     Nasal masks are commonly used in the treatment of respiratory conditions and sleep disorders (e.g., obstructive sleep apnea) by delivering a flow of breathable gas for, or to assist patient respiration. These nasal masks typically receive a gas supply line which delivers gas into a chamber formed by walls of the mask. The walls usually are semi-rigid and have a face contacting portion including an aperture which is aligned with the wearer&#39;s nostrils. The face contacting portion can comprise a soft, resilient elastomeric material which may conform to various facial contours. The mask normally is secured to the wearer&#39;s head by straps. The straps are adjusted to pull the mask against the face with sufficient force to achieve a gas tight seal between the mask and the wearer&#39;s face. Gas is thus delivered to the mask and through the aperture to the wearer&#39;s nasal passages. 
     Problems often arise with masks of the above configuration. For example, the mask may be dislodged, thereby breaking the seal between the mask and wearer. This may occur if the wearer rolls over when sleeping thereby creating a drag force on the gas supply line which is transmitted to the mask, breaking the seal. In the case of a mask being used for the administration of Continuous Positive Airway Pressure (CPAP) treatment for the condition obstructive sleep apnea, such a leak can result in the pressure supplied to the entrance of the wearer&#39;s airway being below the therapeutic value, and the treatment becoming ineffective. 
     Another problem is that the face contacting portion may apply excessive pressure to the wearer&#39;s face resulting in discomfort and possibly skin irritation. This excessive forces. In some cases these excessive pressures and forces may cause the face to distort to conform with the face contacting portion to increase wearer discomfort, facial soreness and ulceration. 
     Other types of devices exist whereby small nostril nosepieces (pillows) are held in place by a harness strapped over the wearer&#39;s head, for example as shown in prior art U.S. Pat. No. 4,782,832. While this arrangement may alleviate some problems regarding seal breakage and skin abrasion, the harnesses associated with such devices are quite cumbersome for the wearer, as are the gas supply lines. Also, air ‘jetting’ into the nostrils can be irritating to the patient making such devices generally uncomfortable to use. 
     In  FIGS. 1-3 , a prior art nasal cushion  10 . generally equivalent to that shown in prior art U.S. Pat. No. 5,243,971, is first described. 
     As shown, the cushion  10  generally includes a base  11  from which depends a semi-rigid cushion frame  12  formed of elastomeric material. Attached over the outside of the frame  12  is a membrane  15 , also of elastomeric material, having at its distal end a face contacting portion  14 . The frame  12  and the membrane  15  generally form a chamber  17  into which the wearer&#39;s nose can be received. The frame  12  has a notch  19  to accommodate the bridge of the wearer&#39;s nose. The base  11  includes slots  13  to accommodate straps (not shown) to secure the cushion  10  and a mask body (not shown) in combination to the wearer&#39;s head. 
     An aperture  16  is formed at the end of the membrane  15  distal from the frame  12  providing access for a wearer&#39;s nose  20  to the chamber  17  as noted. As shown, the aperture  16  in an unflexed state is generally circular (or elliptical) and is large enough to allow partial entry of the wearer&#39;s nose. The resilience of the membrane material allows the face contacting portion  14  and the aperture  16  to invert when the nose is received. The inverted membrane arrangement relies upon a positive pressure of supplied gas within the mask to effect a seal to the wearer&#39;s face. The seal is characterised as a “rolling edge seal”, in that there can be motion of the cushion  10  relative to the patient&#39;s face yet the seal is maintained. Even so, a tuck  22  arises in the vicinity of the upper lip due to the circular shape of the aperture, and it is from this tuck that leaks can arise due to head and body movement during sleep. 
     It is an object of the invention to overcome or at least substantially ameliorate one or more of the foregoing disadvantages. 
     SUMMARY OF THE INVENTION 
     In one broad form, the invention discloses a nasal mask cushion to sealingly connect a mask to a wearer&#39;s face, the cushion comprising: 
     a substantially triangularly-shaped frame of resilient material having a rim to surround the wearer&#39;s nose; 
     a membrane also of resilient material, the membrane being relatively more flexible than the frame, and being of the same general shape as said rim and fixed to and extending away from the frame so as to have an outer surface spaced from the rim, a portion of said outer surface forming a face contacting seal; and 
     a nose-receiving cavity bounded by said frame and said membrane; 
     and wherein said seal portion is generally coterminous with respect to said rim and is resiliently deformable towards the rim in use of the cushion. 
     Preferably, the rim and seal portion are shaped to generally match facial contours of the facial tissue around the sides and over the bridge of the nose and between the base of the nose and the top lip. 
     In one particularly advantageous form, the membrane is substantially saddle-shaped. The membrane further has a centrally located aperture through which the wearer&#39;s nose passes to enter said cavity. 
     It is preferred that the cushion and membrane each include a co-located notch to accommodate the bridge of the nose of the wearer. Typically, the seal portion contacts at least the wearer&#39;s nose, and preferably, also the facial tissue around the sides and over the bridge of the nose and between the base of the nose and the top lip. 
     The invention further discloses a nasal mask for connection to a wearer&#39;s face comprising: 
     a mask body for connection with a supply of breathable gas; and 
     a nasal cushion, the body and cushion defining a nose-receiving cavity, the cushion including: 
     a substantially triangularly-shaped frame of resilient material having a rim to surround the wearer&#39;s nose; 
     a membrane also of resilient material, the membrane being relatively more flexible than the frame, and being of the same general shape as said rim and fixed to and extending away from the frame-so as to have an outer surface spaced from the frame, a portion of said outer surface forming a face contacting seal; 
     and wherein said seal portion is generally coterminous with respect to said rim and is resiliently deformable towards the rim in use of the mask. 
     The mask body can further include attachment points from which securing straps can be attached, and by which the mask can be secured to the wearer&#39;s head. The nasal mask can yet further comprise an arm depending from said body from which a further securing strap(s) can be attached. 
     The invention further discloses nasal CPAP treatment apparatus comprising a flow generator for the supply of gas at a pressure elevated above atmospheric pressure to a gas delivery conduit, the conduit in turn coupled to a nasal mask as described immediately above. 
     In one particularly preferred form, a supply of gas can be provided to said cavity, said supply of gas assisting, but not solely causing maintenance of a seal by said seal forming portion of said membrane to the face of the wearer in use of the cushion. 
     Advantageously, because the membrane and the rim are substantially shaped to the facial contour, and the membrane does not need to turn in on itself, as in the prior art, thus contacting the face without folds or creases. With the cushion/mask secured to the wearer&#39;s head, the headstraps need only to be tensioned to balance the force due to mask gas pressure that tends to lift the mask off the face. Such relatively lower mask-to-face pressure results in greater patient comfort, and a reduction in the likelihood of skin irritation. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       An embodiment of the invention will now be described with reference to the accompanying drawings, in which: 
         FIG. 1  is an exploded perspective view of a prior art nasal mask; 
         FIG. 2  is a perspective view of the prior art nasal mask of  FIG. 1 ; 
         FIG. 3  is a perspective view of the prior art nasal mask attached to a wearer; 
         FIG. 4  is a rear perspective view of a mask cushion embodying the present invention; 
         FIG. 5  is a cross-sectional view along line  5 - 5 ; 
         FIG. 6  is a perspective view of a nasal mask including the cushion of  FIGS. 4 and 5 ; and 
         FIG. 7  is a perspective view of the nasal mask of  FIG. 6  secured to a wearer&#39;s head. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 4  shows a perspective view of a nasal cushion  30  embodying the invention.  FIG. 5  shows the cross-sectional view along line  5 - 5 . The cushion  30  comprises a substantially triangularly shaped frame  32  from which extends a rim  40  (otherwise referred to as a first membrane, a first molded layer or an interior layer, with the first membrane having a first rim) and a membrane  34  (otherwise referred to as a second membrane, a second molded layer or an exterior layer, with the second membrane having a second rim). The frame  32  has a scalloped edge  36  by which the cushion  30  is affixed to a mask body, as presently will be described. 
     The membrane  34  has an aperture  38  into which the wearer&#39;s nose is received in use of the cushion  30 . The membrane  34  is spaced away a distance from the rim  40  of the frame  32 , and its outer surface  41  is of substantially the same shape as the rim  40 . The outer surface  41  of the membrane  34  and the rim  40  of the frame  32  also can be described as generally saddle shaped. The shaping of the outer surface  41  of the membrane  34  and the rim  40  of the frame  32  also include respective notches  42 ,  44  that receive the bridge of the wearer&#39;s nose in use of the cushion  30 . 
     As is best seen in  FIG. 5 , the frame  32  and the membrane  34  are integrally formed, typically by in a one-shot molding process. The frame  32  and the membrane  34  are fabricated from a resilient material. One suitable such material is Silastic™ silicone elastomer manufactured by Dow Corning. The frame  32 , in one preferred embodiment, has a typical thickness at its rim  40  of 1.5 mm. The membrane  34 , in a preferred embodiment, has a typical thickness of 0.35 mm. In this way, the membrane  34  is relatively more flexible than the rim  40 . 
     In use of the cushion  30 , a wearer&#39;s nose will be inserted in the aperture  38  to engage a seal forming portion  45  (formed between the dashed lines) of the outer surface  41  to cause deformation of the membrane  34 . Depending upon the securing force supplied to the membrane  34 , it may deform to appoint where it butts against the rim  40  of the frame  32 . The frame  32  has a rigidity. sufficient to withstand usual securing pressures in use of the cushion  30  to tend to retain its shape and resist deformation. It thus acts as a supporting structure. 
     Referring now to  FIG. 6 , the nasal cushion  30  is shown attached to a mask body  46  by the edge  36  of the frame  32 , adhered or otherwise secured to a flange  48  of the mask body  46 . Only the outer surface  41  of the membrane  34  can be seen. The flange  48  includes three slots  50 ,  52  and  54  from which tensioning straps can be attached to secure the cushion  30  and the mask body  46  (in combination) to the head of a wearer. 
     The mask body  46  forms a cavity that can receive the nose of the wearer by the aperture  38 . A port  56  is provided at the top of the mask body  46  by which breathable gas can be supplied to the chamber. 
     Referring now to  FIG. 7 , there is shown a nasal mask  60  including the mask body  46  and the mask cushion  30 . A coupling tube  62  is connected at one end with the inlet port  56 , and at the other to a socket  64  into which can be received a gas delivery tube (not shown) for the supply of breathable gas to the chamber internal of the mask body  46 . The mask body  46  also has two vent openings  66  by which expired gas is exhausted. A first fastening strap  68  is fixed between to the lower two slots  50 , 54 . The upper slot  52  receives an arm  70 , the top end of which has a resilient pad  72  to engage the forehead of the wearer. The arm  70  has two slots  74 , 76  along its side edges, by which a second fastening strap  78  is secured. 
     In fitting the nasal mask  60 , the wearer&#39;s nose is received through the aperture  38  into the chamber within the mask body  46 . The seal forming portion  45  thus contacts both the surface of the wearer&#39;s nose and a portion of the wearer&#39;s face in the region between the base of the nose and the upper lip, and around the sides and over the bridge of the nose. The shape of the seal forming portion  45  is particularly suited to effectively seal the difficult region of the facial contour that is the crease between the sides of the nose and the face. Depending upon the tension applied by the fastening straps  68 , 78 , a seal is formed with the membrane  34  remaining spaced from the rim  40  of the cushion frame  32 . While the provision of pressurised gas to the chamber of the mask body  46  assists in the maintenance of a seal between the membrane  34  and the wearer&#39;s nose and face, it is not essential in most cases, and an effective seal will be formed absent any such pressurised gas. The seal formed between the membrane  34  and the wearer&#39;s nose and face is not in the nature of a rolling seal in the manner of prior art as shown in FIGS. I to  3 , as on relative movement of the mask  60  in relation to the wearer&#39;s head, the nose will be restrained by contacting the frame  32 . Thus only limited relative motion between the mask  60  and the wearer&#39;s nose and face occurs. 
     The membrane  34  closely imitates the facial contour, and because of its relatively lesser stiffness than the frame  32 , can conform to particular facial structures with minimum force, and without a tendency to fold or crease. 
     If the fastening strap  68 , 78  are tensioned to excess, the membrane  34  deforms to abut the rim  40  of the cushion  32 , the frame  32  thus acting as an “end limit”. In such a configuration, almost zero relative movement can occur between the mask  60  and the wearer&#39;s head. 
     The nasal cushion  30  and nasal mask  60  has been described with reference to CPAP or assisted respiration treatment, however it is to be understood that the invention generally is applicable to any application where gas and/or atomised liquid is to be supplied to the entrance of the nasal airways. Such applications include nebulisers, gas masks and anaesthetic machines.