Abstract:
A face mask has a relatively soft canopy and a more rigid reinforcement member moulded together from different plastics as two shots in a dual-shot moulding process. The peripheral sealing edge of the canopy is tapered to a reduced thickness to increase its flexibility. The reinforcement member is a frame with radially-extending arms supporting respectively a gas port by which gas can enter the mask, a valve that allows air into the mask when there is an inadequate supply at the gas port and a selectively closable vent. The mask is secured to the patient&#39;s head by a harness attached to ends of the harness arms.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     This invention relates to face masks.  
         [0002]     Face masks are used to supply gas to a patient for various purposes and are designed to seal with the skin surface around the nose and mouth. There are many different forms of face mask currently available but often these suffer from disadvantages such as large bulk, weight, discomfort in use or poor sealing.  
       BRIEF SUMMARY OF THE INVENTION  
       [0003]     It is an object of the present invention to provide an alternative face mask.  
         [0004]     According to one aspect of the present invention there is provided a face mask of a plastics material comprising a relatively soft canopy member having a peripheral sealing edge providing a seal with the skin around the nose and mouth of a patient, the canopy member being moulded as one shot in a dual-shot moulding process, a relatively rigid reinforcement member being moulded integrally with the canopy member as another shot in the dual-shot moulding process, and the mask having a gas port by which gas can enter the mask.  
         [0005]     The peripheral sealing edge of the canopy preferably is tapered to a reduced thickness and an increased flexibility at its edge. The gas port is preferably provided on the reinforcement member. The gas port may have a connector projecting therefrom for connection to a gas supply tube, the port being located in line with the mouth of the patient and the connector being angled such that it projects down when the mask is applied to the patient&#39;s face in an upright position. The face mask preferably includes a valve separate from the gas port, the valve being arranged to allow air to flow into the mask when there is an inadequate supply at the gas port. The valve may be provided on the reinforcement member. The mask preferably includes selectively closable vent means that can be opened to allow flow of gas out of the mask, and the vent means may include a cap member movable between two discrete positions where the vent is open or closed respectively. The vent means is preferably provided on the reinforcement member. The reinforcement member is preferably a frame with a plurality of radially-extending arms. Two of the arms may extend towards opposite edges of the mask and be terminated by lateral bars extending substantially parallel to the edge of the mask. The lateral bars may support fastening means for a harness extending around the head of the patient. The mask preferably includes three arms supporting respectively a gas port, a valve to allow gas to enter the mask and a vent that can be opened to allow gas to flow out of the mask. The mask may include a harness adapted to extend around the head of the patient and attached at opposite ends with the reinforcement member. Opposite ends of the harness may be of triangular shape having a free end extending rearwardly, the free end being adjustably attachable with a part of the harness.  
         [0006]     According to another aspect of the present invention there is provided a method of making a face mask comprising the steps of moulding a first component in a mould from a relatively high temperature plastics material and subsequently moulding a second component from a relatively low temperature plastics material directly on the first component while the first component is in the mould.  
         [0007]     According to a further aspect of the present invention there is provided a face mask made by a method according to the above other aspect of the invention.  
         [0008]     A face mask according to the present invention will now be described, by way of example, with reference to the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]      FIG. 1  is a front view of the mask;  
         [0010]      FIG. 2  is a side elevation view of the mask on the face of a patient;  
         [0011]      FIG. 3  is a sectional side elevation view of the mask;  
         [0012]      FIGS. 4 and 5  are sectional side elevation views of a part of the mask to an enlarged scale indicating how it seals on the face;  
         [0013]      FIG. 6  is a perspective view of a controlled leak device;  
         [0014]      FIG. 7  is a sectional side elevation view of an anti-asphyxia valve;  
         [0015]      FIG. 8  shows two straps used in the mask harness;  
         [0016]      FIG. 9  is a side elevation view of the mask showing an alternative harness;  
         [0017]      FIG. 10  is an elevation view of the edge of the mask showing a tube access; and  
         [0018]      FIG. 11  is a sectional view of the tube access of  FIG. 10 . 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0019]     With reference first to FIGS.  1  to  5 , the mask comprises two parts, namely a canopy  1  and a support frame  2 . The canopy  1  is moulded of a relatively soft, flexible plastics material, such as, SEBS styrene ethylene butadiene styrene, whereas the support frame  2  is moulded of a harder material, such as a polypropylene copolymer. The canopy  1  and support frame  2  are moulded integrally with one another by a dual-shot moulding process in which the higher temperature plastics material forming the frame  2  is moulded first in a mould cavity, then the mould is enlarged to form a cavity for the canopy, which is subsequently moulded from a lower temperature plastics material. This results in the canopy and support frame being integrally bonded together.  
         [0020]     The canopy  1  is of generally triangular shape with a peripheral edge  10  shaped to extend under the mouth, up the cheeks, along the sides and across the nose. The canopy  1  has a domed internal cavity  11  in which the nose is received. The edge  10  is curved inwardly into the cavity in a C shape so that, when the mask is placed against the face, as shown in  FIGS. 4 and 5 , a curved contact region  12  contacts the skin with the lip  13  being on or spaced slightly above the skin. The canopy  1  varies in thickness from about 2 mm across most of its surface tapering to about 1.5 mm in the contact region  12  and to about 0.7 mm at the lip  13 . This makes the edge  10  very flexible. The seal with the patient&#39;s skin could be further enhanced by an adhesive material on the contact region.  
         [0021]     The frame member  2  has a generally star shape with three radially-extending arms  20 ,  21  and  22 . One arm  20  projects down and is formed with a gas connector port  23  positioned in line with the patient&#39;s mouth and angled downwardly at an angle of about 20° to the horizontal when mounted on the patient&#39;s face in an upright position. A second arm  21  projects upwardly to the left, as viewed in  FIG. 1 , and includes a controlled leak device  30  to be described in greater detail later. The second arm  21  is terminated by a lateral bar  24  extending parallel to the edge of the mask in the region of the patient&#39;s right cheek. The third arm  22  projects upwardly towards the right and includes an anti-asphyxia valve  25 , as described in greater detail later. The third arm is terminated by a lateral bar  26  extending parallel to the edge of the mask in the region of the patient&#39;s left cheek.  
         [0022]     Moulding the face mask in a dual-shot process gives various advantages. It enables the mask to made very thin and light in weight with a very flexible seal whilst having sufficient rigidity across its central portion to support the connector and the various other components without deformation. Because the mask can be made thin, the upper part of the mask can be shaped to follow closely the profile of the nose. This reduces interference to the patient&#39;s eyesight and can make the mask less claustrophobic than some previous masks. The dual-shot process also enables the mask to be made with high transparency so that the part of the face enclosed by the mask can be seen clearly by the clinician.  
         [0023]     The controlled leak device  30  is shown most clearly in  FIGS. 6 and 7  and is formed of two components, namely a base  31  and a cap  32 . The base  31  comprises a circular plate  33  secured in an aperture in the frame  2 . The plate  33  has three gas passages  34  extending through it and a central stem  35  projecting from the external surface. The stem  35  is hollow and cylindrical with a male luer slip surface to receive a female connector. The stem  35  also has key formations  36  on its outer surface. The cap  32  has a plate  37  of the same diameter as the base plate  33  and with three openings  38  spaced in the same manner as the passages  34 . A hollow sleeve  39  projects from the centre of the plate  33 . The sleeve  39  is shaped to fit on the stem  35  and has keyway formations on its inner surface (not shown). The key and keyway formations are arranged to prevent rotation of the cap  32  on the base  31  and to ensure that the cap can only be fitted on the base either with the openings  38  aligned with the gas passages  34  or with them not aligned and thereby preventing flow of gas. When the cap  32  is mounted on the base with the openings  38  aligned with the gas passages this permits a small flow of gas through the leak device. This is sufficient to allow air exhaled by the patient to flow out through the leak without enabling pressure of gas supplied to the mask to fall below the level needed for CPAP ventilation. When the cap  32  is removed, a tube (not shown) can be connected to the tapered stem  35  for carbon dioxide sampling purposes.  
         [0024]     The anti-asphyxia valve  25  is shown in  FIG. 7  and includes a rigid plate  70 , which is flat on its upper, outer surface  71  and has a concave, domed recess  72  on its lower, inner surface. Four holes  73  extend through the plate  70  between the recess  72  and the outer surface  71  and are equally distributed around the edge of the recess. A narrow ledge  74  extends around the outside of the recess  72 . The valve  25  also includes a flexible, resilient diaphragm  75  providing a valve member for the valve. The diaphragm  75  has a peripheral ledge  76 , which is clamped on the ledge  74  by a ring (not shown), and a domed central portion  77  with a central aperture  78 . The radius of curvature of the domed portion  77  in its natural state is greater than that of the recess  72  so that it is spaced away from the recess and allows free flow of gas through the aperture  78  and holes  73 . When the internal pressure within the mask is raised, the domed portion  77  is forced outwardly, that is, upwardly into contact with the recess  72 , thereby sealing the holes  73  closed. The valve  25 , therefore, closes when there is high gas pressure within the mask but opens when gas pressure drops, thereby permitting the patient to breath atmospheric air in through the valve. Other, conventional forms of valve could be used to allow the patient to inhale via the valve should there be an obstruction to gas flow to the inlet port  23 . Previous anti-asphyxia valves have been incorporated into the gas inlet port connection but this has the disadvantage of increasing the bulk at the inlet and thereby increasing the bending moment exerted on the mask by the associated inlet tubing.  
         [0025]     Attached to both lateral bars  24  and  26  is a strip  27  and  28  of a hook fastening material, such as of the kind sold under the Velcro trade mark (Velcro is a Registered Trade Mark of Velcro BV), which is used to secure an end of a harness  40 . The harness  40  comprises two flexible, elastic straps  41  and  42 , as shown in  FIG. 8 , which both have a pad  43  and  44  of a loop fastening material at one end so that they can be secured with the strips  27  and  28  on the mask frame  2 . At their other ends, one strap  41  has a pad  45  of a hook material and the other strap  42  has a pad  46  of a loop material. Opposite ends of the straps  41  and  42  are enlarged laterally to accommodate the pads  43  to  46 . In this way, the straps  41  and  42  can be secured with one another at one end at the back of the patient&#39;s head and can be secured at their other ends with the mask frame  2 . The arrangement allows for the straps to be secured to the frame and to one another at any angle, thereby allowing flexibility in positioning of the harness so as to accommodate a variety of patients.  
         [0026]     An alternative harness arrangement  140  is illustrated in  FIG. 9 . This harness  140  has two straps  141 , only one of which is shown, which are fastened together at the back of the head by hook and loop fastening material (not shown). The straps  141  are fastened to the mask itself by means of two posts  142  and  143  projecting from the side of the mask and spaced one above the other, which extend through apertures  142 ′ and  143 ′ in the straps. The forward end of the straps  141  is of triangular shape having a lateral portion  144  extending upwardly at an angle of about 90° to the main part of the strap, and a rearwardly-extending portion  145  extending rearwardly and downwardly at an angle of about 45° to the upper end of the lateral portion. The rearwardly-extending portion  145  has a free rear end to which is attached a pad  146  of a hook or loop material, which attaches to a cooperating pad  147  on the main part of the strap. This arrangement enables the pressure exerted by the mask on the face to be adjusted to alter its distribution. Pressure exerted by the upper part of the mask can be increased or reduced by appropriately moving the end of the portion  145  to attach it to a part of the pad  147  that is further back or further forwards. The straps  141  each have a quick-release tab  148  in the region of the upper aperture  142 ′. One or both of these tabs  148  can be pulled down to release the harness  141  from the mask.  
         [0027]     Various modifications are possible to the mask. The edge seal of the mask may be modified to allow a nasogastric tube  90  to pass through the edge  10 , as shown in  FIGS. 10 and 11 . In this arrangement the edge of the mask is moulded with a keyhole-shape formation  91  of reduced thickness, which can be easily torn or cut. The keyhole-shape formation  91  has a very narrow entrance portion slit  92  extending to the edge, and a circular sleeve portion  93  located above it and projecting a short distance inwardly. When used without a nasogastric tube, this formation is left in place so that there is no path for gas leakage in this region. When a nasogastric tube is to be used, the keyhole-shape formation is torn or cut to form a keyhole-shape aperture so that the tube  90  can be pushed sideways in through the narrow part of the aperture, which may be self-closing, and located in the circular, sleeve part of the aperture where it is a close, sealing fit. If the mask needs to be removed at any time, the tube can be easily peeled out of the aperture so that its patient end can be left in place in the patient and its machine end need not be disconnected from any apparatus to which it is connected. The mask can be subsequently replaced on the patient after having pushed the nasogastric tube into the aperture.