Abstract:
A CPAP system for supplying humidified gases to a user is disclosed in which various interfaces are described for gas delivery. A mask cushion including a deformable cushion and thin sheath is described. A forehead rest with a horizontal pivot that is attached to the mask is disclosed. An outlet vent to reduce the noise from exhausted carbon dioxide is described. A mouthpiece is also described with an outlet diffuser including Heat Moisture Exchanger Material.

Description:
This application is a divisional application of Ser. No. 10/297,951, which was filed on Dec. 11, 2002 and accorded a filing date under 35 U.S.C. §371 of Mar. 25, 2003, now abandoned and entitled Breathing Assistance Apparatus which is the National Stage of International Application No. PCT/NZ01/00110 which has an international filing date of Jun. 14, 2001 and which was published in English on Dec. 20, 2001 under International Publication Number WO 01/95965. 

   FIELD OF INVENTION 
   This invention relates to patient interfaces particularly though not solely for use in delivering CPAP therapy to patients suffering from obstructive sleep apnoea (OSA). 
   BACKGROUND OF THE INVENTION 
   In the art of respiration devices, there are well known variety of respiratory masks which cover the nose and/or mouth of a human user in order to provide a continuous seal around the nasal and/or oral areas of the face such that gas may be provided at positive pressure within the mask for consumption by the user. The uses for such masks range from high altitude breathing (i.e., aviation applications) to mining and fire fighting applications, to various medical diagnostic and therapeutic applications. 
   One requisite of such respiratory masks has been that they provide an effective seal against the user&#39;s face to prevent leakage of the gas being supplied. Commonly, in prior mask configurations, a good mask-to-face seal has been attained in many instances only with considerable discomfort for the user. This problem is most crucial in those applications, especially medical applications, which require the user to wear such a mask continuously for hours or perhaps even days. In such situations, the user will not tolerate the mask for long durations and optimum therapeutic or diagnostic objectives thus will not be achieved, or will be achieved with great difficulty and considerable user discomfort. 
   U.S. Pat. Nos. 5,243,971 and 6,112,746 are examples of prior art attempts to improve the mask system U.S. Pat. No. 5,570,689 and PCT publication No. WO 00/78384 are examples of attempts to improve the forehead rest. 
   Where such masks are used in respiratory therapy, in particular treatment of obstructive sleep apnea (OSA) using continuance positive airway pressure (CPAP) therapy, there is generally provided in the art a vent for washout of the bias flow or expired gases to the atmosphere. Such a vent may be provided for example, as part of the mask, or in the case of some respirators where a further conduit carries the expiratory gases, at the respirator. A further requisite of such masks is the washout of gas from the mask to ensure that carbon dioxide build up does not occur over the range of flow rates. In the typical flow rates in CPAP treatment, usually between 4 cm H 2 O to 20 cm H 2 O, prior art attempts at such vents have resulted in excessive noise causing irritation to the user and any bed partners. 
   Various approaches have been developed in the prior art to attempt to reduce the noise when CPAP therapy is provided. For example, in PCT Patent Application No. WO98/34665 it has been proposed that the vent include a resilient plug with rounded edge apertures to reproduce noise. However, this is not entirely effective in eliminating the extra noise created by a vent at the mask. 
   In common with all attempts to improve the fit, sealing and user comfort is the need to avoid a concentrated flow of air at any portion of the respiratory tracts. In particular with oral masks or mouthpieces it is a disadvantage of prior art devices that the oral cavity may become overly dehydrated by use of the device, causing irritation and possible later complications. 
   SUMMARY OF THE INVENTION 
   It is an object of the present invention to attempt to provide a patient interface which goes some way to overcoming the abovementioned disadvantages in the prior art or which will at least provide the industry with a useful choice. 
   Accordingly in one aspect the invention consists in a device for delivering a supply of gases to a user comprising: 
   a hollow body including a gases inlet and gases delivery aperture, said gases inlet in use in fluid communication with said supply of gases, 
   a resilient sealing pad adapted to engage around or adjacent to the periphery of said gases delivery aperture, and 
   a flexible sealing lip adapted to engage around or adjacent to the periphery of said gases delivery aperture between said resilient sealing pad and a user, and significantly higher in density than said resilient sealing pad, 
   said resilient sealing pad and said flexible sealing lip each including at least a portion shaped to approximate the facial contour of a user, said resilient sealing pad adapted to deform substantially independently of said flexible sealing lip. 
   In a second aspect the present invention comprises a device for delivering a supply of gases to a user comprising: 
   a hollow body including a gases inlet and gases delivery aperture, said gases inlet in use in fluid communication with said supply of gases, 
   a resilient sealing pad adapted to engage around or adjacent to the periphery of said gases delivery aperture, and 
   a flexible sealing lip adapted to engage around or adjacent to the periphery of said gases delivery aperture between said resilient sealing pad and a user, 
   said resilient sealing pad and said flexible sealing lip each including at least a portion shaped to approximate the facial contour of a user, said resilient sealing pad adapted to deform substantially independently of said flexible sealing lip. 
   To those skilled in the art to which the invention relates, many changes in construction and widely differing embodiments and applications of the invention will suggest themselves without departing from the scope of the invention as defined in the appended claims. The disclosures and the descriptions herein are purely illustrative and are not intended to be in any sense limiting. 
   The invention consists in the foregoing and also envisages construction of which the following gives examples. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     One preferred form of the present invention will now be described with reference to the accompanying drawings in which; 
       FIG. 1  is a block diagram of a humidified continuous positive airway pressure (system) as might be used in conjunction with the present invention, 
       FIG. 2  is an illustration of the nasal mask in use according to the preferred embodiment of the present invention, 
       FIG. 3  is a side elevational view of the mouthpiece as being used by a patient, 
       FIG. 4  is a perspective view from above of the mouthpiece, 
       FIG. 5  is a perspective view from one side and from an inward direction of the mouthpiece of  FIG. 4 , 
       FIG. 6  is a cross-section of the mouthpiece of  FIG. 4 , 
       FIG. 7  is a cross-sectional view of the mouthpiece of  FIG. 4 and a  user with the mouthpiece in place to demonstrate the location and positioning thereof in relation to the main features of the user&#39;s anatomy, 
       FIG. 8  is a perspective view of the mouthpiece with the outer flap in place, 
       FIG. 9  is a perspective view of the outer flap bent back, 
       FIG. 10  is a cutaway view of the mouthpiece with the outer flap in use, 
       FIG. 11  is a perspective view of the outer flap including the ventilation apertures and moisture barrier, 
       FIG. 12  shows the outlet vent sleeve installed on the elbow, 
       FIG. 13  shows the outlet vent sleeve in isolation, 
       FIG. 14  shows the elbow in isolation, 
       FIG. 15  shows the one piece elbow outlet vent interior, 
       FIG. 16  shows the one piece elbow outlet vent exterior, 
       FIG. 17  shows a cross section of the mouthpiece with a dispersing filter, 
       FIG. 18  shows a perspective view of the mask with cushion, 
       FIG. 19  is cuttaway view of the mask showing the cushion, 
       FIG. 20  is a cuttaway view of the periphery of the outer membrane, 
       FIG. 21  is a cuttaway view of the periphery of the mask body portion, 
       FIG. 22  shows a make with the forehead rest on a user, and 
       FIG. 23  shows the forehead rest in isolation. 
   

   DETAILED DESCRIPTION 
   The present invention provides improvements in the delivery of CPAP therapy. In particular a patient interface is described which is quieter for the user to wear and reduces the side leakage as compared with the prior art. It will be appreciated that the patient interface as described in the preferred embodiment of the present invention can be used in respiratory care generally or with a ventilator but will now be described below with reference to use in a humidified CPAP system. It will also be appreciated that the present invention can be applied to any form of patient interface including, but not limited to, nasal masks, oral masks and mouthpieces. 
   With reference to  FIG. 1  a humidified Continuous Positive Airway Pressure (CPAP) system is shown in which a patient  1  is receiving humidified and pressurised gases through a patient interface  2  connected to a humidified gases transportation pathway or inspiratory conduit  3 . It should be understood that delivery systems could also be VPAP (Variable Positive Airway Pressure) and BiPAP (Bi-level Positive Airway Pressure) or numerous other forms of respiratory therapy. Inspiratory conduit  3  is connected to the outlet  4  of a humidification chamber  5  which contains a volume of water  6 . Inspiratory conduit  3  may contain heater wires (not shown) which heat the walls of the conduit to reduce condensation of humidified gases within the conduit. Humidification chamber  5  is preferably formed from a plastics material and may have a highly heat conductive base (for example an aluminium base) which is in direct contact with a heater plate  7  of humidifier  8 . Humidifier  8  is provided with an electronic controller  9  which may comprise a microprocessor based controller executing computer software commands stored in associated memory. 
   Controller  9  receives input from sources such as dial  10  through which a user of the device may, for example, set a predetermined required value (preset value) of humidity or temperature of the gases supplied to patient  1 . The controller may also receive input from other sources, for example temperature and/or flow velocity sensors  11  and  12  through connector  13  and heater plate temperature sensor  14 . In response to the user set humidity or temperature value input via dial  10  and the other inputs, controller  9  determines when (or to what level) to energise heater plate  7  to heat the water  6  within humidification chamber  5 . As the volume of water  6  within humidification chamber  5  is heated, water vapour begins to fill the volume of the chamber above the water&#39;s surface and is passed out of the humidification chamber  5  outlet  4  with the flow of gases (for example air) provided from blower  15  which enters the chamber through inlet  16 . Exhaled gases from the patient&#39;s mouth are passed directly to ambient surroundings in FIG.  1 . 
   Blower  15  is provided with variable speed fan  21  which draws air or other gases through blower inlet  17 . The speed of variable speed fan  21  is controlled by electronic controller  18  (or alternatively the function of controller  18  could carried out by controller  9 ) in response to inputs from controller  9  and a user set predetermined required value (preset value) of pressure or fan speed via dial  19 . 
   Nasal Mask 
   According to a first embodiment of the present invention the patient interface is shown in  FIG. 2  as a nasal mask. The mask includes a hollow body  102  with an inlet  103  connected to the inspiratory conduit  3 . The mask  2  is positioned around the nose of the user  1  with the headgear  108  secured around the back of the head of the patient  1 . The restraining force from the headgear  108  on the hollow body  102  and the forehead rest  106  ensures enough compressive force on the mask cushion  104 , to provide an effective seal against the patient&#39;s face. 
   The hollow body  102  is constructed of a relatively inflexible material for example, polycarbonate plastic. Such a material would provide the requisite rigidity as well as being transparent and a relatively good insulator. The expiratory gases can be expelled through a valve (not shown) in the mask, a further expiratory conduit (not shown), or any other such method as is known in the art. 
   Mask Cushion 
   Referring now to  FIGS. 18 and 19  in particular, the mask cushion  1104  is provided around the periphery of the nasal mask  1102  to provide an effective seal onto the face of the user to prevent leakage. The mask cushion  1104  is shaped to approximately follow the contours of a patient&#39;s face. The mask cushion  1104  will deform when pressure is applied by the headgear (not shown) to adapt to the individual contours of any particular user. In particular, there is an indented section  1150  intended to fit over the bridge of the user&#39;s nose as well as a less indented section  1152  to seal around the section beneath the nose and above the upper lip. 
   In  FIG. 19  we see that the mask cushion  1104  is composed of an inner foam cushion  1110  covered by an outer sealing sheath  1112 . The inner cushion  1110  is constructed of a resilient material for example polyurethane foam, and can deform independently of outer sealing sheath  1112  in order to enable it to distribute pressure evenly along the seal around the user&#39;s face formed by sealing sheath  1112 . Inner cushion  1110  can also act as a secondary seal. The inner cushion  1110  is located around the outer periphery  1114  of the open face  1116  of the hollow body  1102 . The open face  1116  acts as a gases delivery aperture to deliver gases to a user. Similarly the outer sheath  1112  may be commonly attached at its base  1113  to the periphery  1114  and loosely covers over the top of the inner cushion  1110 . 
   In the preferred embodiment shown in  FIGS. 19-21  the bottom of the inner cushion  1110  fits into a generally triangular cavity  1154  in the hollow body  1102 . The cavity  1154  is formed from a flange  1156  running mid-way around the interior of the hollow body. 
   The outer sheath  1112  fits in place over the cushion  1110 , holding it in place. The sheath  1112  is secured by a snap-fit to the periphery  1114  of the hollow body. In  FIGS. 20-21  the periphery  1114  is shown including an outer bead  1158 . The sheath  1112  includes a matching bead  1159 , whereby once stretched around the periphery, the two beads engage to hold the sheath in place. 
   Forehead Rest 
   In the preferred embodiment of the present invention the nasal mask  2102  includes a hinged forehead rest  2106  (seen in FIGS.  22  and  23 ). The attachment of the forehead rest  2106  to the nasal mask  2102  effectively allows the forehead rest  2106  to move freely in proximity to the user but with no lateral movement. 
   In one form shown in  FIG. 23 , pins  2130  are provided mounted on a base  2132  attached to the nasal mask  2102 . These pins  2130  are co-axial within cylinders  2131  mounted on a bridge member  2136 . 
   At the top end  2142  (around the user&#39;s forehead) of the bridge member  2136  harnessing slots  2138  are provided which allow straps from the headgear to be inserted to secure the mask to the headgear. For the user&#39;s comfort one or more resilient cushions  2140  are provided underneath the top end  2142  of the bridge member  2136 , which rest on the forehead of the user. The cushion  2140  might be constructed of silicon or any foam materials as is known in the art for providing cushioning. 
   For example the forehead rest  2106  described previously may include a weakened section at its base  2132  which allows the joining member  2136  to pivot from the nasal mask  2102 . The bridge member extends up to the forehead of the user. In a further alternative the mask may include a vertical upwardly extending inlet. In this case the member  2136  is hinged at its base  2132  to either side of the inlet passage. Again the member would then extend to the forehead. 
   Alternatively any well-known form of hinge can be used to provide the pivoting action. 
   Mouthpiece 
   Now with reference to a further inlet embodiment of the present invention the patient interface  2  is shown in  FIGS. 3  to  10  as a mouthpiece. In this embodiment, the mouthpiece  50  includes a vestibular shield  49  being a generally flat and generally rectangularly-shaped member in front elevation having a curved profile that reflects the curvature of a user&#39;s jaw and in turn the curvature of the labial vestibule region. A gases passageway extends through the vestibular shield from an inlet  51  to an outlet  52  in much the same way as with the earlier embodiments. In the preferred embodiment the inlet  51  is provided by a flattened oval-shaped connector  53 . The outlet  52  has an even more laterally extended flattened oval shape  54 . The major differences between the mouthpiece  50  and the embodiments described above are provided on the inner face of the vestibular shield. Most prominently, the mouthpiece  50  includes a tongue depressor  55  extending from the inner face of the vestibular shield  49 . The operation of the tongue depressor will be described further on with reference to FIG.  5 . The tongue depressor includes a vertical stiffening flange  56  centrally located on its upper surface and extending from the gases outlet  52 . In use gases flow easily around the stiffening flange  56  effectively bifurcating the gases outlet  52 . The tongue depressor  55  further includes a pair of vertically extending spacers  57  which in use may abut against the roof of the wearer&#39;s mouth and ensure that the tongue cannot completely block the air passageway. In the mouthpiece  50  the sealing effect of the vestibular shield  49  against the lips of the user is enhanced by providing teeth abutments of significantly increased thickness than the raised area  20  of the earlier embodiments. In particular, an upper teeth abutment  58  and a lower teeth abutment  59  are provided, with the lower teeth abutment  59  protruding further from the inner face of the vestibular shield  49  than the upper teeth abutment  58 . This difference serves to match the typical over-bite of most users. The abutments  58  and  59  are not required to be wider than the gases outlet  52 . 
   A notch  60  is provided centrally in the upper edge of the vestibular shield  49  to accommodate the upper frenal attachment. A slight bead  61  is provided around the edge of the vestibular shield  49  for user comfort, with the vestibular shield  49  otherwise being very thin for additional suppleness. 
   Referring particularly to  FIG. 6 , in its preferred form the mouthpiece  50  is preferably formed by over-moulding a soft and supple material part  70  over a stiffer material part  67 . These can generally be termed the shield part and the passageway-forming insert. The passageway-forming insert preferably includes a pair of upper and lower vertical flanges  63  and  64  to fully engage within the supple material. The passageway-forming insert  67  includes the vertically extending stiffening flange  56  of the tongue depressor  55 , together with a curved planar portion  71  forming the backbone of the tongue depressor  55 . The vertically extending spacers  57  are of the soft and supple material and are part of the over-moulding  70 , as are the upper and lower teeth abutments  58  and  59 . 
   Referring now to  FIG. 7 , use of the mouthpiece according to  FIGS. 4  to  6  is depicted. With the present mouthpiece  50 , the upper and lower lips  85 ,  86  are further distended by the abutment action of the abutments  75 ,  76  against the upper and lower teeth  87 ,  83  respectively, thus forming a seal of greater pressure between the lips  85 ,  86  and the upper and lower portions respectively of the vestibular shield  49 . A lower face  77  of the tongue depressor  55  impinges if necessary on the upper surface  72  of the tongue  90  and retains the tongue in the lower portion of the mouth. This ensures a clear gases outlet  52  from the gases passageway through the vestibular shield. The vertically extending spacers  57 , if forced by pressure from the tongue, will engage against the roof of the user&#39;s mouth and maintain a clear air passageway. This stops the sleeping patient unconsciously blocking the oral passageway and reverting to nasal breathing. 
   Referring now to  FIGS. 8 and 9  of the present invention a mouthpiece is illustrated including an extra-oral sealing flap  110 . The flap  110  in its natural bias is tapered, the wide open end of which is shaped to conform to the facial contours around the outside of the mouth of a user. The narrow end joins to a cylindrical section, which is designed to slide over the inlet port  114  of the mouthpiece  112 . While this is one method of attachment the flap  100  might also be constructed as an integral part of the mouthpiece  112 . The flap  110  needs to be constructed of flexible material, therefore materials such as silicone rubber can be employed to fashion the flap. 
   The outer flap  110  is seen in  FIG. 9 , in a bent back position. It will be appreciated that when the mouthpiece  112  is being inserted into the mouth of a user, the outer flap  110  is intended to be in this bent back position to aid insertion. Prior to insertion, the outer flap is bent back by simply pressing on its outer periphery  116 , until it snaps into the bent back position, in which it will stay unaided. 
   In  FIG. 10  we see the outer flap  110  in use with the mouthpiece  112  in the mouth  117  of a user  119 . Once correctly positioned in the mouth  116 , the outer flap  110  may be adjusted into its operational position by pressing on its outer periphery  116  until it snaps back to press against the outside of the mouth  118 . Due to the relative position of the vestibular shield  122  and the outer flap  110 , the outer flap  110  is unable to fully reach its natural bias and thereby inflicts a compressive force on the outside of the mouth  118 . 
   It will be appreciated that as well as providing a substantially airtight seal the addition of the outer flap provides enough compressive force on the mouth to keep the mouthpiece and conduit in place without the need for straps. This allows the administering of CPAP therapy to be considerably less obtrusive than traditional methods. 
   In a further additional improvement shown in  FIG. 11 , the outer flap  300  is shown in perspective. Included are ventilation apertures  302 ,  303  either side of the gases port  304 , which are surrounded by a ridge  306  acting as a moisture barrier. The apertures  302 , 303  are provided such that any excess moisture leaking from the mouth will migrate to the apertures where they may evaporate. Small vents in the conduit may be used to direct small amounts of pressurised gas at the apertures to aid evaporation. The ridge  306  is included to ensure that no moisture migrates further into the sealing region  308 , as this would be detrimental to the sealing properties of the flap. 
   Interface Connection 
   Attention is now directed to FIG.  3 . It has been found that an additional factor in the effectiveness of any patient interface  2 , is the manner in which the interface is connected to the breathing circuit  41 . The weight of the breathing circuit  41 , and any attempted movement of one other of the breathing circuit  41  and the interface  2  relative to the other, is one of the largest influences tending to dislodge the interface  2 . It must be noted that the interface  2  must remain in position and maintain a seal during all sleep, when the user has no muscle tone. 
   The connection  40  as provided in the present invention between the breathing circuit  41  and the interface  2  decouples the interface  2  from the breathing circuit  41 . As a result, the connection  40  is effective in reducing the forces placed on the interface  2  by the breathing circuit  41  when the user moves around during sleep. In the preferred sleeping position, the breathing circuit  41  is laid across the chest  43  of the user, and may be secured to the user&#39;s bed clothes or sleeping garments. The breathing circuit  41  is preferably laid on the chest of the user to take the weight of the breathing circuit  41  off of the interface  2 . 
   To connect between the gases outlet  42  which is vertical when the user is laying on his or her back and the breathing circuit  41  which is generally horizontal, an L-shaped elbow  45  is incorporated in the connection  40 . The elbow  45  may be incorporated in the interface  2 . The elbow  45  is formed at a right angle and provides a positive pressure on the interface  2 . The elbow  45  may include a swivel joint and may be disconnected from gases outlet  42 . The connection  40  further includes an extremely flexible connecting tube  46  provided between the elbow  45  and the breathing circuit  41 . The connecting tube  46  is preferably connected to the breathing circuit  41  by a swivel joint  48  for reasons described herein. The breathing circuit  41 , while flexible, will necessarily be stiff enough to maintain its integrity over comparatively long lengths, while the connecting tube  46 , being only a short length, for example 10 centimeters, merely has to span between the user&#39;s mouth and chest, and can thereby be made in a manner that would not be suitable for long lengths. Furthermore, as a result of the short length of the connecting tube  46 , the connecting tube  46  does not need to incorporate significant insulation or heating capability. The connecting tube  46  may be formed from a thin plastic membrane supported over a helical or double helical or corrugated supporting ribs. In such a case, the support makes the connection tube  46  laterally flexible and resistant to torsion. The elbow swivel joint  45  allows for movement of the connection tube  46  relative to the interface  2 . The swivel joint  48  allows for movement of the connection tube  46  relative to the breathing circuit  41 . It is to be understood that one or both of the swivel joints  45 ,  48  could be eliminated, but the preferred embodiment includes swivel joint  48 . 
   Outlet Vent 
   The present invention will now be described with reference to the various different embodiments previously described. In order to reduce the noise caused by expiratory gases being expelled from the patient interface  2 , the present invention is illustrated in  FIGS. 12  to  17  with the elbow connector (previously designated as  45 ) including an outlet vent. It would be appreciated by one skilled in the art that the elbow connector as described herein will be equally applicable to all proceeding embodiments and all other forms of patient interface for delivering CPAP therapy. 
   Referring particularly now to  FIGS. 12  to  14 , the elbow connector is illustrated including a flexible sleeve  400  which fits overtop of the elbow connector. The sleeve  400  is preferably constructed of silicon, but it will be appreciated by one skilled in the art that a number of other flexible materials will be equally applicable. The sleeve  400  includes locating indents  402  which once installed on the elbow connector match up with and lock into locating notches  404  on the elbow connector. The location is necessary so that the outlet aperture  406  in the elbow connector always matches up with the outlet vents  408  in the outlet sleeve  400 . This then prevents the undesirable situation where the sleeve could slip and the outlet vents  408  not match up with the outlet aperture  406  with resulting consequences to the patient. 
   Referring now to  FIGS. 15 and 16 , the present invention is shown with a one-piece elbow. In this case the elbow is preferably constructed of either “Hytrel” plastic or polycarbonate. In this fashion the elbow connector is manufactured to have a thin portion  410  surrounding the outlet vents  412  in comparison to the remainder of the elbow connector which is considerably thicker. The properties of the material chosen for the elbow connector are such that its flexibility is dependent on its thickness. Therefore in the thin section  410  the elbow connector is relatively flexible and in the remainder is relatively rigid. Accordingly the outlet vents  412 , which are also rounded on their periphery are formed in a flexible portion, and therefore achieve the desirable low noise properties when expiratory gases are vented therethrough. 
   Flow Diffuser 
   Referring now particularly to the use of mouthpieces, a further improvement is shown in FIG.  17 . It is documented that when CPAP therapy is delivered to patients they often complain of drying of the airways and resulting irritation and discomfort. In particular when a concentrated airflow of under humidified gases flows past the oral or nasal cavities, or the airway of the user then drying and irritation may occur. Accordingly the present invention as illustrated in  FIG. 17  includes a mouthpiece with a flow diffuser  500 . 
   As described in the preceding embodiments, the mouthpiece sits with a vestibular shield  502  between the gums  504  and the lips  506  of a user. An outer flap  506  provides compressor force on the lips  506  to keep the mouthpiece in place in the user&#39;s mouth. Again the mouthpiece includes a tongue depressor  514  extending into the user&#39;s oral cavity. 
   In the preceding embodiments the delivered gases would flow through passageway  512  in the mouthpiece, causing a relatively concentrated flow of gases to flow through the oral cavity and down the airway. With the flow diffuser  500  fitted overtop of the passageway  512  the flow is defused over the much larger area of the diffuser  500 , and therefore both the speed and side effects are reduced. 
   Alternatively the space between the passageway  512  and the diffuser  500  could be filled with a Humidity Moisture Exchange (HME) material. This would allow moisture through on the inspiratory flow put prevent it passing out an expiration. This would further prevent against the patient&#39;s passageways drying out. Further, if the HME material was in the form of foam, then it might also act as the diffuser  500 . It will also be appreciated that the HME material could be used in the space  516  all the way out to the elbow connector (not shown) to maximise its effect. 
   It will be appreciated that by providing such a system the present invention effectively minimises the noise generated by the outward flow of expiratory gases from the mask. The present invention requires little or no maintenance. The present invention also provides a flow diffuser for use with the mouthpiece, which reduces any side effects of orally delivered CPAP therapy and improves user comfort.