Abstract:
A respiratory mask having a variable flow venting is provided according to the invention, including a gas supply hose, a mask shell adapted to output a gas to a respiratory system of a person, the mask shell adapted to be connected to the gas supply hose, and an exhaust gas flow volume regulating device which maintains a substantially constant gas flow volume out of the respiratory mask independent of an internal gas pressure inside the respiratory mask.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates generally to the field of respiratory masks.  
           [0003]    2. Description of the Background Art  
           [0004]    A respiratory mask is a device used to deliver a gas or gases to a person. FIG. 1 shows a respiratory mask  100  of the related art. The respiratory mask  100  includes a mask shell  104 , a gas supply hose  107 , a vent aperture  112 , and an optional gasket  115 . The mask shell  104  is fitted over a face of the person in order to supply a gas to a respiratory system of the person.  
           [0005]    The respiratory mask  100  may be used to deliver any variety of gases, including air or oxygen, and a variety of medicines or treatments. Preferably, the mask shell does not allow a supplied gas to escape. A strap or other attaching means may be affixed to the mask shell and may be fitted over the head of the person. Constant pressure gas is therefore delivered, with the vent aperture  112  maintaining a substantially constant pressure in the mask. This is referred to as a continuous positive airway pressure (CPAP) mask. The vent aperture  112  allows expired carbon dioxide to escape from the mask. It is important that the vent aperture  112  be of a sufficient size to exhaust substantially all expired carbon dioxide under normal conditions of use.  
           [0006]    In the related art, the need for venting has meant simply an aperture on or close to the mask shell, whereby exhaled air is flushed out of the respiratory mask by the positive pressure generated by the gas supply hose. This is taught by Rapaport U.S. Pat. No. Re. 35,339.  
           [0007]    Several drawbacks exist with the venting of the related art respiratory mask  100 . First, the air circulation within the mask  100  and vent aperture  112  may create annoying noises. Second, a jet of air from the vent aperture  112  may impinge on the wearer or on nearby persons. This can be seen in FIG. 1, where the vent aperture  112  and a resulting air jet are relatively close to the face of the wearer, and will in all likelihood be in the region of persons near to or sleeping with the wearer. As a result, these drawbacks may affect compliance with a therapy.  
           [0008]    Therefore, there remains a need in the art for an improved respiratory mask.  
         SUMMARY OF THE INVENTION  
         [0009]    A respiratory mask having a variable flow venting is provided according to the invention, comprising a gas supply hose, a mask shell adapted to output a gas to a respiratory system of a person, the mask shell adapted to be connected to the gas supply hose, and a gas flow volume regulating device which maintains a substantially constant gas flow volume out of the respiratory mask independent of an internal gas pressure inside the respiratory mask.  
           [0010]    The above and other features and advantages of the present invention will be further understood from the following description of the preferred embodiment thereof, taken in conjunction with the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    [0011]FIG. 1 shows a vented respiratory mask of the related art;  
         [0012]    [0012]FIG. 2 shows a first embodiment of a variable aperture vented respiratory mask of the present invention;  
         [0013]    [0013]FIG. 3 shows a second embodiment of a variable aperture vented respiratory mask of the present invention; and  
         [0014]    [0014]FIG. 4 shows a third embodiment of a variable aperture vented respiratory mask of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0015]    [0015]FIG. 2 shows a first embodiment of a variable aperture vented respiratory mask  200  of the present invention. The variable aperture vented respiratory mask  200  includes a mask shell  206 , a gas supply hose  209  attached to the mask shell  206 , an optional gasket  213 , and a gas flow volume regulating device  220 . The gas flow volume regulating device  220  further includes a hollow elastomeric truncated cone  222  having an internal diameter, an outer aperture  225  in the mask shell  206 , and an inner aperture  228  disposed inside the mask shell and forming a truncated end of the hollow elastomeric truncated cone  222 . The gas flow volume regulating device  220  forms a variable aperture that responds to the internal pressure of the CPAP mask  200  in order to maintain a substantially constant gas flow volume out of the mask  200  regardless of pressure differences between the inside and the outside of the mask  200 . In the preferred embodiment, the gas flow volume regulating device  220  is designed with aperture sizes such that the resulting gas flow volume is adequate at the lowest CPAP working pressure, which is typically a pressure of about three to four cm H 2 O. In the preferred embodiment, a minimum gas flow volume ten to fifteen liters per minute at a pressure of four cm H 2 O air pressure is sufficient to vent the exhaled air from the mask  200 . Suitable aperture sizes are dependent on the cross-sectional geometry and depth of the hole. For example, with a round aperture and a wall thickness of 0.05 inch, to achieve a flow rate of 10-15 liter/min, the aperture diameter can be 0.157 inch at 4 cm H 2 O pressure, and 0.101 inch at 18 cm H 2 O pressure. Aperture sizes can fall between these values for intermediate pressures.  
         [0016]    In use, the variable aperture vented respiratory mask  200  receives a gas from the gas supply hose  209  at an essentially constant pressure. In the shown embodiment of FIG. 2, the exhaust gas flow is regulated by the deformation of the hollow elastomeric truncated cone  222 . As the internal pressure in the mask  200  increases (i.e., during exhalation by the wearer), the hollow elastomeric truncated cone  222  is increasingly deformed, decreasing the internal diameter. By regulating the size of the vent aperture, a volume of gas escaping from the gas flow volume regulating device  220  is kept below an objectionable level. It should be understood that a gas flow volume regulating device of any of the embodiments is preferably located on the mask shell, but alternatively may be located near the mask or on the gas supply hose.  
         [0017]    The gas flow volume regulating device  220  in this embodiment may be set to a desired flow volume by the choice of material composing the hollow elastomeric truncated cone  222 , which can be, for example, silicone, polyurethane or the like.  
         [0018]    [0018]FIG. 3 shows a second embodiment of a variable aperture vented respiratory mask  300 . The main components are identical to the mask  220 , and the reference numbers of the identical components are retained. The mask  300  includes a gas flow volume regulating device  310 , which further includes an elastic flap  316  that is positioned over an aperture  313 . The gas flow volume regulating device  310  therefore includes a variable aperture that responds to the internal pressure of the CPAP mask  300 .  
         [0019]    In a normal state, such as when the internal pressure is low, the elastic flap  313  is normally displaced away from he aperture  313 , allowing an uninhibited gas flow through the aperture  313 . As the internal pressure increases, the elastic flap  316  is displaced closer and closer to the aperture  313 , regulating the gas flow volume through the aperture  313  and therefore regulating the internal pressure.  
         [0020]    The gas flow volume regulating device  310  in this embodiment may be set to a desired flow volume by the choice of material composing the elastic flap  313 , which can be, for example, silicone, polyurethane or the like. The closing pressure on the flap can be varied, depending on the hardness of the material from which it is made, and the flap geometry.  
         [0021]    [0021]FIG. 4 shows a third embodiment of a variable aperture vented respiratory mask  400 . The main components are identical to the mask  200 , and the reference numbers of the identical components are retained. The mask  400  includes a gas flow volume regulating device  408 , which further includes an aperture  411 , an electronically actuated member  414 , an actuator  418 , a pressure sensor  421 , and a controller  424  connected to the actuator  418  by a control line  427  and to the pressure sensor  421  by a signal line  429 . The gas flow volume regulating device  408  therefore includes a variable aperture that responds to the internal pressure of the mask  400 .  
         [0022]    The controller  424  may be any type of general purpose controller, including a programmable device such as a microcontroller, a custom-built chip, or a hard-wired logic circuit. The actuator  418  may be any type of general purpose actuator, such as a servo-type actuator or solenoid-type actuator. In the preferred embodiment, the actuator  418  is a servo-type actuator that extends and retracts the electronically actuated member  414  so as to cover or uncover the aperture  411 . Alternatively, the actuator  418  may move the electronically actuated member  414  in some other manner, such as displacing it to a side of the aperture  411  or away from the aperture  411  into the interior of the mask shell  206 .  
         [0023]    In use, the controller  424  receives a pressure signal from the pressure sensor  421  over the signal line  429 . The controller may then adjust the placement of the electronically actuated member  414  in relation to the aperture  411 . The controller may do this by sending a control signal to the actuator  418  over the control line  428 . The actuator, in response to the control signal, may move the electronically actuated member  414  to cover or uncover the aperture  411 , thereby varying an effective size of the aperture  411 . In the preferred embodiment, the electronically actuated member  414  may move anywhere from a fully covering position to a fully uncovering position and anywhere in between. Alternatively, the actuator  418  may have only covering and uncovering positions, with gas flow volume regulation being accomplished by repeatedly covering and uncovering the aperture  411 .  
         [0024]    While the invention has been described in detail above, the invention is not intended to be limited to the specific embodiments as described. It is evident that those skilled in the art may now make numerous uses and modifications of and departures from the specific embodiments described herein without departing from the inventive concepts.