Abstract:
A mask ( 10 ) for use with a system for supplying breathable gas pressurized above atmospheric pressure to a human or animal&#39;s airways. The mask ( 10 ) includes a mask shell ( 12 ) which is, in use, in fluid communication with a gas supply conduit ( 30 ), and a gas washout vent assembly ( 20 ). At least the region of the mask shell ( 12 ) or conduit ( 30 ) surrounding or adjacent the vent assembly is formed from a relatively flexible elastomeric material.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 10/364,358, filed Feb. 12, 2003, now U.S. Pat. No. 7,207,335, which is a continuation of U.S. application Ser. No. 09/021,541, filed Feb. 10, 1998, now U.S. Pat. No. 6,561,190, which claims the benefit of Australian Application No. PO5045, filed Feb. 10, 1997, each incorporated herein by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a mask and a vent assembly therefor. 
     The mask and vent assembly according to the invention have been developed primarily for the venting of washout gas in the application of continuous positive airway pressure (CPAP) treatment in conjunction with a system for supplying breathable gas pressurised above atmospheric pressure to a human or animal. Such a system is used, for example, in the treatment of obstructive sleep apnea (OSA) and similar sleep disordered breathing conditions. However, the invention is also suitable for other purposes including, for example, the application of assisted ventilation or respiration. 
     The term “mask” is herein intended to include face a, nose masks, mouth masks, nasal pillows, appendages in the vicinity of any of these devices and the like. 
     BACKGROUND OF THE INVENTION 
     Treatment of OSA by CPAP flow generator systems involves the continuous delivery of air (or other breathable gas) pressurised above atmospheric pressure to a patient&#39;s airways via a conduit and a mask. 
     For either the treatment of OSA or the application of assisted ventilation, the pressure of the gas delivered to a patient can be at a constant level, bi-level (ie. in synchronism with patient inspiration and expiration) or autosetting in level to match therapeutic need. Throughout this specification the reference to CPAP is intended to incorporate a reference to any one of, or combinations of, these forms of pressure delivery. 
     The masks used in CPAP treatment generally include a vent for washout of the gas to atmosphere. The vent is normally located in the mask or in the gas delivery conduit adjacent the mask. The washout of gas through the vent is essential for removal of exhaled gases from the breathing circuit to prevent carbon dioxide “re-breathing” or build-up, both of which represent a health risk to the mask wearer. Adequate gas washout is achieved by selecting a vent size and configuration that will allow a minimum safe gas flow at the lowest operating CPAP pressure, which, typically can be as low as around 4 cm H 2 O for adults and 2 cm H 2 O in paediatric applications. 
     Prior art masks are generally comprised of a rigid plastic shell which covers the wearer&#39;s nose and/or mouth. A flexible or resilient rim (or cushion) is attached to the periphery of the shell which abuts and seals against the wearer&#39;s face to provide a gas-tight seal around the nose and/or mouth. 
     A prior art washout vent utilized one or more holes or slits in the rigid shell or in a rigid portion of the delivery conduit to allow the washout gas to vent to atmosphere. In some masks, the holes or slits were formed during the moulding process. In others, they were drilled or cut as a separate step after the shell or conduit had been moulded. 
     The flow of gas out the holes or slits in the shell or conduit to atmosphere creates noise and turbulence at the hole or slit outlet as the delivered gas, and upon expiration, the patient-expired gas (including CO 2 ) exits. Bi-level and autosetting gas delivery regimes tend to generate more noise than a constant level gas delivery regime. This is thought to be due to the extra turbulence created by the gas accelerating and decelerating as it cycles between relatively low and relatively high pressures. The noise adversely affects patient and bed-partner comfort. 
     Another prior art vent included hollow rivets or plugs manufactured from stainless steel or other rigid materials attached to openings in the rigid shell. The outer edges of die rivers were rounded to help reduce noise. However, his approach was expensive, required an extra production step and did not prove effective in reducing noise. 
     Another approach to reduce noise involved the use of sintered filters at the gas outlet of the mask shell. However, the filters were prone to blocking, especially in the presence of moisture. Accordingly, sintered filters were impractical for use in CPAP treatment as they were easily blocked by the moisture from the patient&#39;s respiratory system or humidifiers or during the necessary regular cleaning of the mask and associated componentry. 
     Foam filters wrapped around the air outlets in the shell were also attempted. However, they also suffered from the disadvantages of being prone to blocking, difficult to clean and requiring constant replacement. 
     Remote outlet tubes have been used to distance the noise source from the patient. However, these tubes are difficult to clean, are prone to entanglement by the patient and/or their bed partner and suffer the ether disadvantage that a volume of exhausted gas is retained in the tube adjacent the mask. 
     It is all object of the present invention to substantially overcome or at least ameliorate the prior art disadvantages and, in particular, to reduce the noise generated by gas washout through a mask. 
     SUMMARY OF THE INVENTION 
     Accordingly, the invention, in a first aspect, discloses a mask for use with a system for supplying breathable gas pressurised above atmospheric pressure to a human or animal&#39;s airways, the mask includes a mask shell which is, in use, in fluid communication with a gas supply conduit, a gas washout vent assembly, wherein at least the region of the mask shell or conduit surrounding or adjacent the vent assembly is formed from a relatively flexible elastomeric material. 
     In an embodiment, the entire mask is formed from the elastomeric material. 
     In another embodiment, the mask shell and/or conduit is formed from a relatively rigid material and the region surrounding or adjacent the vent assembly is formed from the relatively flexible elastomeric material. 
     In a second aspect, the invention discloses a vent assembly for the washout of gas from a mask or conduit used with a system for supplying breathable gas pressure above atmospheric pressure to a human or animal, wherein the vent assembly is formed from the relatively flexible elastomeric material. 
     In a preferred embodiment, the vent assembly is an insert of relatively flexible elastomeric material, wherein the insert is attachable to the mask shell or conduit. The insert preferably has at least one orifice therethrough. 
     In a preferred form, the rigid plastics mask shell is formed from polycarbonate and the insert is formed from SILASTIC™ or SANTOPRENE™. 
     Desirably, the insert is substantially crescent-shaped and includes a plurality of orifices therethrough. 
     The insert preferably includes a groove around its periphery, the groove adapted to locate the insert against a correspondingly sized rim of an opening formed in the mask shell or conduit. 
     In other embodiments, the insert is substantially circular, triangular, cross or peanut shaped. 
     The mask shell and/or the conduit can desirably also include one or more inserts. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Preferred embodiments of the invention will now be described, by way of examples only, with reference to the accompanying drawings in which: 
         FIG. 1  is a perspective view of a first embodiment; 
         FIG. 2  is a perspective view of a second embodiment; 
         FIG. 3  is a perspective view of a third embodiment; 
         FIG. 4  is a perspective view of a fourth embodiment; 
         FIG. 5  is a perspective view of a fifth embodiment; 
         FIG. 6  is a perspective view of a sixth embodiment; 
         FIG. 7  is a perspective view of a seventh embodiment; 
         FIG. 8  is a partial cross-sectional view of the first embodiment along the line  8 - 8  of  FIG. 1 ; 
         FIG. 9  is a perspective view of an eighth embodiment; 
         FIG. 10  is a plan view of the insert of the third embodiment; 
         FIG. 11  is a cross-sectional view of the third embodiment insert along the line  11 - 11  of  FIG. 10 ; and 
         FIG. 12  is a partial cross-sectional view of the third embodiment insert along the line  12 - 12  of  FIG. 10 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring firstly to  FIG. 1 , there is shown a mask  10  for use with a system (not shown) for supplying breathable gas pressurised above atmospheric pressure to a human or animal&#39;s airways. The mask includes a rigid plastics shell  12  having an inlet tube  14  for connection to a supply conduit to communicate breathable gas from a flow generator (not shown) to the nasal passages of the mask wearer. The mask shell  12  also includes a flexible sealing membrane  16  which is used to provide a gas tight seal between the face of the wearer and the interior of the shell  12 . The shell  12  also includes lugs  18  for connecting the mask  10  to a head strap (not shown) to retain the mask in place. 
     The mask includes a SILASTIC™ insert  20  through which is provided an orifice  22  for gas washout. As best shown in  FIG. 8 , the insert  20  has a recess or groove  24  around its periphery. A correspondingly sized opening  26  bounded by a rim  28  is provided in the shell  12  to enable the insert  20  to be retained in place in the fashion of a grommet. The opening  26  can be moulded in the shell  12  or drilled or punched as a post-moulding step. The flexibility of the SILASTIC™ allows the insert  20  to be initially squeezed through the opening  26  before resiliently expanding to the configuration shown in  FIG. 8  and engaging the rim  28 . 
     As seen in  FIG. 8 , orifice  22  has a cross-sectional contour from a face side of the orifice to an atmosphere side of the orifice. In  FIG. 8 , the contour is shown as being symmetrical between the face side of the orifice and the atmosphere side of the orifice with a central portion of the orifice contour being of constant diameter. After the insert  20  is positioned in opening  26  of mask shell  12 , the contour remains substantially constant in size as gas is passed therethrough. 
       FIGS. 2 to 7  show further embodiments in which corresponding reference numerals are used to indicate like features. In all these embodiments the insert  20  has an external groove or recess  24  which engages the rim  28  of a corresponding shaped opening  26  in the mask shell  12  to retain the insert  20  in place. 
     In the embodiment shown in  FIGS. 2 to 5  and  7  the insert  20  includes more than one orifice  22 . In the embodiment shown in  FIG. 6 , two inserts  20  are provided in the shell  12 . 
     In the embodiment shown in  FIG. 9 , the insert  20  is provided in a gas supply conduit  30 . 
       FIGS. 10 to 12  show the insert  20  of the third embodiment of  FIG. 3 . The dimensions  32 ,  34 ,  36 ,  38 ,  40 ,  42  and  45  are approximately diameter 1.73 mm, diameter 3.30 mm, 28.80 mm, 19.00 mm, 1.20 mm, 1.20 mm and 3.60 mm respectively. 
     The side  44  of the insert  20  faces the patient&#39;s face in use and the side  46  faces atmosphere. 
     The mask shell  12  is manufactured from polycarbonate. Other rigid plastics materials can equally be used. The insert  20  can be manufactured from an elastomer sold as SILASTIC™ produced by the Dow Corning Corporation) or a thermoplastic elastomer sold as SANTOPRENE™ (produced by Monsanto). Other flexible elastomeric materials can be used also. 
     The mask  10  produces less noise than an identical mask having a similar sized and shaped orifice(s) formed directly in the mask shell  12  instead of formed in the flexible insert  20 . It is thought that the noise reduction occurs due to the flexible insert  20  damping vibrations caused by air passage through the orifice(s)  22  which produce vibrations or similar in the mask shell  12 . 
     A prototype of the embodiment of the invention shown in  FIG. 3  has been tested over a range of constant and bi-level CPAP treatment pressures. For comparison purposes, an identical mask to that shown in  FIG. 3  but formed entirely from polycarbonate and having six identical arcuately spaced holes  22  drilled directly through the mask shell was also tested. In both masks the six holes had a diameter of 1.7 mm. The results of the test are summarised in the Tables below: 
     
       
         
               
             
               
               
               
             
               
               
               
             
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Constant level gas delivery 
               
             
          
           
               
                 Pressure 
                 Noise levels 1 m from mask (dBA) 
                   
               
             
          
           
               
                 (cm H 2 O) 
                 With flexible insert 
                 Without flexible insert 
               
               
                   
               
             
          
           
               
                 4 
                 26.8 
                 35.2 
               
               
                 10 
                 33.4 
                 43.1 
               
               
                 18 
                 39.3 
                 49.2 
               
               
                   
               
             
          
         
       
     
     
       
         
               
             
               
               
               
             
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 Bi-level gas delivery 
               
             
          
           
               
                 Pressure 
                 Noise levels 1 m from mask (dBA) 
                   
               
             
          
           
               
                 (cm H 2 O) 
                 With flexible insert 
                 Without flexible insert 
               
               
                   
               
               
                  5-10 
                 30.8-38.5 
                 37.2-43.0 
               
               
                 10-15 
                 38.6-43.7 
                 42.9-47.9 
               
               
                   
               
             
          
         
       
     
     As the result show, the mask shown in  FIG. 3  produced less radiated noise than a similar mask not including the flexible elastomeric insert  20  representing a significant advantage in terms of the comfort of the mask wearer and their bed partner. 
     In addition to the noise reduction discussed above, the masks  10  possesses other advantages over those of the prior art. Firstly, the insert  20  is very easy to install into the mask shell  12  during either assembly of the mask which, is often supplied in kit form, or before and after cleaning which is regularly required and often carried out in the home environment. Secondly, the mask shell  12  may be produced with a single size of opening  26  and provided with a range of different inserts  20  which allows the outlet size to be “tuned” to give an optimum gas washout rate for a particular patient&#39;s treatment pressure level. 
     Although the invention has been described with reference to specific examples, it will be appreciated by those skilled in the art, that the invention may be embodied in many other forms.