Abstract:
We describe the use of a flow directing apparatus for incorporation into a patient mask or adjacent to it and for use with a source of pressurized breathable gas such as electronically or electronically controlled fan blower or positive displacement ventilator to provide nasal or oro-nasally administered continuous positive airway pressure or bi level therapies. Such therapies are commonly used to treat sleep disordered breathing including sleep apnea and other syndromes, as well as ventilatory insufficiency. The valve apparatus includes means to direct expired air to atmosphere and inspired air from a pressure source to a user&#39;s airway. In this way advantage is provided compared to alternative means as described in the prior art which vent a user&#39;s expired gas to atmosphere through a fixed open vent.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This patent is a full specification based on Australian provisional patent applications with numbers 2006904948, 2006904950 
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    Not Applicable 
       REFERENCE TO SEQUENCE LISTING, A TABLE, OR A COMPUTER PROGRAM LISTING COMPACT DISK APPENDIX 
       [0003]    Not Applicable 
       BACKGROUND TO THE INVENTION 
       [0004]    The prior art in relation to exhaust valves used with nasally administered continuous positive airway pressure (CPAP) or active ventilation techniques, where a range of pressures are often used, a lower pressure for a substantial period of exhalation compared to inspiration, are related commercially to a fixed leak to atmosphere; that is a vent of fixed cross sectional area and the flow varies in proportion to the applied pressure (square root of pressure) within the circuit comprising the flow and pressure source, a connecting tube, nasal mouth mask and the users airway and lung network. The users is able to exhale expired carbon dioxide, a by product of metabolism, through the vent, usually placed in the mask or adjacent to it and then to atmosphere. Such systems are typically used with single tube delivery systems, that is the flow and pressure sources is connected to the mask and vent by a single tube. 
         [0005]    One of the significant issues with this arrangement is to ensure the adequate removal of carbon dioxide, a waste gas of metabolism, from the patient circuit. Because the flow is proportional to the administered pressure, a minimum pressure must be applied to avoid accumulation of waste gas in the circuit and rebreathing in inhalation by the patient. Typically administered pressures can range between 4 cm water (a lower pressure is possible but the designer must ensure adequate leak flow to wash out CO2—the figure is a typical minimum value and up to 40 cm H2O in some ventilation applications. It can be immediately appreciated that if the vent must be designed, in terms of its cross sectional area, to permit adequate outflow at 4 cm H2O, the outflow therefore at higher pressures, say 20 cm will constitute excess flow, which provide no useful medical or other benefit. For example, if the vent is designed to provide a vent flow of 20 l/min at 4 cmH20 then at 20 cmH20 it will provide a flow of 45 l/min. Furthermore, other factors such as increased air flow noise, air flow cooling and blowing and nasal drying are worsened as the pressure, and hence flow, is increased. 
         [0006]    Despite this deficiency a fixed size vent remains the usual method of providing exhaust venting in commercially available mask system for nasal or oro-nasally administered CPAP, for example as used to treat sleep apnea (Sullivan C E, Berthon Jones M and Issa FG. “Treatment of obstructive apnea with continuous positive airway applied through the nose” Am Rev Respir Dis 1982 125. p 107 and bi-level ventilation such as described in U.S. Pat. No. 5,148,802. 
         [0007]    The prior has attempted to improve the design of the vent in this application to provide a vent flow that is independent of flow i.e. either the flow remains constant with pressure or even reduces to some extent, albeit small extent during inhalation. These are disclosed in U.S. Pat. Nos. 5,685,296, 6,584,977, 6,889,692. These devices provide a means for flow regulation and differ to pressure regulators as described in U.S. Pat. No. 4,821,767, which provides a means for regulating a high pressure source to a low pressure constant source on a patient demand principle. However, this device is not applicable to low pressure sources such as fan driven/electrically controlled device 
         [0008]    U.S. Pat. No. 7,066,175 B2 describes a mask apparatus for use with a pneumatically controlled CPAP device to deliver breathable gas such as 100% oxygen for acute care emergency care situations. This device uses a disc valve to direct flow to the atmosphere during expiration. This device represents a novel approach over the constant flow devices described above and is aimed at preserving oxygen use from a pressurized source such as an oxygen bottle. 
       SUMMARY OF THE INVENTION 
       [0009]    We describe the use of a flow directing apparatus for incorporation into the patient mask or adjacent to it and for use with electronically or electronically controlled fan blowers or positive displacement ventilators to provide nasal or oro-nasally administered CPAP or bi level therapies. These devices will provide a pressured source of breathable gas (usually room air or oxygen enriched room air) Typical source pressures are in the range 0 to 50 cm H20, the exact pressures or combinations being determined by individual patient requirements. Applicable conditions can include but not limited to treatment of sleep apnea, sleep hyperventilation syndromes, lung disease. The device is able to direct exhaust gases to atmosphere during expiration, while directing air to patients airway during inhalation. Hence the device is unique compared to the constant or variable flow exhaust area devices as described in the prior art and does not depend at all on a continuous bias flow. The operation of the device can be most easily described as an automatically adjusting PEEP (positive end expiratory pressure) valve, where the PEEP pressure is governed by the pressure delivered by an electrically operated and hence variable pressure source as opposed to a manually adjusted mechanical design. This device has important implications for use in positive pressure therapies particularly those that are administered via a face mask and hence includes the upper airway, as opposed users who are acutely intubated. Specifically, such as system may be used where the pressure is constant (CPAP) or varying i.e. pressures are varied during the respiratory cycle being higher to actively inflate long and reduced to deflate the lung to varying degrees and needs of the treatment. For example, during active assisted inhalation, pressurized air from the source is actively directed exclusively to the patients airway in the absence of unintended mask leaks. Conversely when the pressure source senses or preempts an expiratory emptying, the system is able to direct air exclusively to the atmosphere. In this context only tidal air is expired to atmosphere in the absence of a mask leak or perfectly sealed system. This is contrast to the prior art wherein bi level devices, such as described in U.S. Pat. No. 5,148,802 where the mask system described is of a fixed vent size type. This means that during exhalation expired air will be partially transmitted down the gas delivery tube from the pressure source and only partially out the exhalation vent. It will require fixed period of time to adequately wash out the CO2 from the tube prior to the next inhalation cycle. This is a significant disadvantage of the prior art and the need to optimize the vent size to ensure rapid CO2 washout prior to the next inspiration. Clinically, it has been observed in nasal ventilation bi-level systems at rapid respiratory rates, as much as 50% of the expired tidal volume is rebreathed. Clearly in acute situations where patients may be very hypercapnic and in respiratory distress, rebreathing such a high proportion of their tidal volume may lead to treatment failure and need for more complex intubation. Despite this shortcoming, in view of the added management issues with intubation nasal ventilation will be the preferred line of treatment. Furthermore the invention disclosed here will require an alternative arrangement for triggering specifically from expiration to inspiration. Hence the prior art does not anticipate the invention when used in a bi level mode and it provides the advantages which include superior CO2 removal and potential for less rebreathing, reduced source flow requirements, reduced need for humidification or when external humidification is required improved efficiency, improved noise characteristics, and absence of biased flow onto sleeping partners. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIGS. 1A-C  and  3 A-B show an intermittent exhaust vent based on a pivoting valve, in accordance with a first embodiment of the invention. 
           [0011]      FIGS. 2A-D  show an intermittent exhaust vent based on a valve with linear motion which is an embodiment of the prior art . . . . 
           [0012]      FIGS. 3C-D  show a further embodiments as to sealing the pivoting valve element to the primary chamber. 
           [0013]      FIGS. 4A-D  show a pivoting valve intermittent exhaust vent in accordance with a further embodiment of the invention. 
           [0014]      FIG. 5  shows an intermittent exhaust vent assembly installed into a mask system. 
           [0015]      FIGS. 6A-C  show embodiments as to sealing the valve sealing face to the exhaust passage. 
           [0016]      FIGS. 7A-D  show an intermittent exhaust vent assembly integrated into a nasal mask frame. 
           [0017]      FIGS. 8A-D  show an intermittent exhaust vent assembly integrated into a nose-mouth mask frame. 
           [0018]      FIGS. 9A-B  show a pivoting valve intermittent exhaust vent in accordance with a further embodiment of the invention wherein contact switches or sensors are provided to detect extreme positions of valve movement. 
           [0019]      FIGS. 9C-D  show a pivoting valve intermittent exhaust vent in accordance with a further embodiment of the invention wherein proximity sensors are provided to detect near extreme positions of valve movement. 
           [0020]      FIGS. 10A-B  show a pivoting valve intermittent exhaust vent in accordance with a further embodiment of the invention wherein a rotary sensor is provided to detect degrees of valve movement. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0021]      FIGS. 1A-1D  illustrate a first embodiment of the invention. Referring to  FIG. 1A , a valve assembly  16  comprises a rigid valve body  1  which includes an inlet passage  6  which is supplied with breathable gas under pressure. Inlet passage  6  terminates at an inner peripheral wall  5  where it intersects primary chamber  17 . A non-return valve  7  is applied at the junction between the inlet passage  6  and the primary chamber  17 . Non-return valve is attached to the rigid valve body  1 . In the example shown, non-return valve  7  comprises a resilient flap weakly biased to the closed position and structured to deflect into two halves about a central line defined by mounting bar  20  which symmetrically bridges the junction between inlet passage  6  and primary chamber  17 . Means of attachment comprising a barb-through-hole arrangement as widely used for this type of valve. It will be appreciated that the non-return valve  7  may take alternate forms such as a resilient flap weakly biased to the closed position and structured to pivot about a peripheral line tangent to the junction between inlet passage  6  and primary chamber  17 . Non-return valve  7  prevents or minimizes backflow of patient exhalation from exiting via the inlet passage  6 , thereby forcing a majority of exhaled air to work towards actuating the exhaust valve. 
         [0022]    Also intersecting primary chamber  17  is patient connection passage  3  which provides a route for the transmission of breathable gas to and from the patient and primary chamber  17 . Features, such as groove  4  provide a means whereby the entire valve assembly  16  may be retained to a mask frame (not shown), which is in turn, sealably attached to the patient&#39;s airway. 
         [0023]    Atop inner peripheral wall  5  is valve pressure plate  10  which is attached to flexible elastic membrane  12  either by mechanical means, or alternatively by adhesive or magnetic bond, or alternatively being co-molded with flexible membrane. Alternatively, pressure plate may further be an extension of and integral with membrane  12 , and having increased stiffness against bending by virtue of geometric section such as increased thickness or ribs. 
         [0024]    When in contact with inner peripheral wall  5 , valve pressure plate  10  seals and separates primary chamber  17  from communication with exhaust passage  9 . 
         [0025]    Membrane  12  is attached to a semi-rigid backing plate  8  by mechanical means, or alternatively by adhesive or magnetic bond, or alternatively being co-molded with flexible membrane. Alternatively, backing plate may further be an extension of and integral with membrane  12 , and having increased stiffness against bending by virtue of geometric section such as increased thickness or ribs. The compression of the backing plate and membrane between the lid  2  and supporting surface of valve body  1  forms a gasket style seal against the escape of breathable gas. 
         [0026]    For all embodiments discussed herein, the lid is retained to the valve body or mask frame either by integral mechanical means such as clips, or by external mechanical means such as a separate clip or by the headgear, which spans the top of the lid and applies force towards the patient&#39;s face. 
         [0027]    For all embodiments discussed herein, membrane  12  features compliant geometry which permit it to deflect in a manner which offers minimal resistance to rotation of the valve pressure plate  10  and maximizes the work of exhalation in actuating the valve. Convoluted section(s)  11  is an example of said compliant geometry. 
         [0028]    For all embodiments discussed herein; P 1  denotes the inlet pressure supplied by the flow generator, P 2  denotes the bias pressure applied on the upper side of the membrane  12 , P 3  denotes the primary chamber pressure and is in communication with the patient via patient connection passage  3 . P 4  denotes the ambient atmospheric pressure. 
         [0029]    For all embodiments discussed herein, bias pressure passage(s)  15  connect inlet  6  to bias pressure chamber  19 , which is defined between lid  2 , and membrane  12 . Bias pressure passage  15  is sized to have a cross-sectional area sufficiently large such that pressure drops between P 1  and P 2  are minimized. Hence, P 2  is assumed to be equal at all times to P 1 . 
         [0030]    Elastic membrane  12  may have a thicker and stiffer portion  14  which makes an abrupt transition  13  to the thin general membrane thickness. Transition  13  acts as an elastic hinge about which valve pressure plate  10  pivots. Alternatively pressure plate  10  may rotate about a classical pivot or hinge for example of a pin-in-hole type. Alternatively, membrane  12  may be of constant thickness and the pivot defined at the line  13  which would be located adjacent to the edge of the rigid backing plate  8 . 
         [0031]    Peripheral chamber  18  is external to inner peripheral wall  5 , and connects primary chamber  17  to exhaust passage  9  when valve pressure plate  10  pivots open. 
         [0032]      FIG. 1B  shows the configuration of the valve of  FIG. 1A  under patient inhalation. During inhalation, the pressure P 3  within the primary pressure chamber decreases to a level below inlet pressure P 1  and forces open the non-return valve  7 , thereby admitting a flow of breathable gas from the flow generator into the primary chamber  17 . P 2 , which equals P 1 , exceeds P 3 . The resulting pressure difference presses valve pressure plate  10  closed against inner peripheral wall  5 . Consequently, flow from the flow generator is directed from the primary chamber  17  via patient connection passage  3 , to be inhaled by the patient. 
         [0033]      FIG. 1C  shows the configuration of the valve of  FIG. 1A  under patient exhalation. During exhalation, P 3 , the pressure within the primary pressure chamber increases above bias pressure P 2  and inlet pressure P 1 . Non-return valve  7  is forced closed, and valve pressure plate  10  is forced open, permitting exhaled air to escape into peripheral chamber  18 , then to be released via exhaust passage  9  out to atmosphere at lower ambient pressure P 4 . 
         [0034]      FIGS. 2A-2D  reflect prior art embodiment of the valve described in U.S. Pat. No. 7,066,175 B2 and focus on details immediately surrounding the primary chamber with other features shown in minimal detail. The membrane  21  shown in  FIGS. 2A-2C  is analogous to the membrane  12  shown in  FIGS. 1A-1C , and pressure plate  22  in  FIGS. 2A-2C  is analogous to the pressure plate  10  shown in  FIGS. 1A-1C . It should be noted that in the embodiments shown in  FIGS. 2A-2C , the membrane performs 2 functions; firstly that of a flexible barrier or seal between the bias chamber  19  at P 2  and the primary chamber  17  at P 3 , and secondly that of aligning the sealing plate such that it minimizes misalignments denoted by x as shown in  FIG. 2C . These misalignments may be due to the lateral forces incurred by the weight of the sealing plate, and would be intensified in the event that the valve is oriented as shown in  FIG. 2C , which is possible if the patient is wearing the valve in a mask during sleep. 
         [0035]    As shown schematically in  FIG. 2D , the degree of misalignment is dependent on the stiffness of the membrane in the plane of misalignment. 
         [0036]    In contrast,  FIGS. 3A-3B  show that the addition of a pivot  13  takes up the reaction to lateral forces during sleep movement, thereby freeing the membrane of the requirement to react lateral forces. Consequently membrane thickness and corresponding stiffness may be minimized. Minimizing the membrane stiffness maximizes its sensitivity, and thereby decreases the amount of respiratory effort required by the patient in order to actuate the valve. 
         [0037]      FIGS. 3C-3D  show a further embodiment for sealing the pressure plate  10  to the primary chamber  17  by means of a flexible elastomeric seal  27  which is compressed between the sealing plate  10  and the inner peripheral wall  5 . As shown the flexible seal  27  is attached atop the inner peripheral wall  5 . Alternatively flexible seal  27  may be attached to the pressure plate  10 . The means of attachment may be mechanical, adhesive, by co-molding, or alternatively if the sealing plate is a molded integral extension of the membrane  12 , the flexible seal  27  may be a molded extension of sealing plate  10 . 
         [0038]      FIG. 4A  shows a further embodiment of the valve; valve assembly  39 , wherein the primary chamber  17  features no inner peripheral wall  5 . Instead, the valve pressure plate  10  forms a ‘rocker’  30  arrangement about pivot  13 , and a sealing face  32  lies on the other side of the pivot and acts to block or open the exhaust outlet  9 . 
         [0039]      FIG. 4B  shows a further embodiment of the valve shown in  4 A; valve assembly  46 , wherein the rocker  45  rotates about a classical (pin-in-hole style) pivot  40  as opposed to the elastic pivot  13  shown in  4 A. 
         [0040]      FIG. 4C  shows the valve of  4 B under patient inhalation. During inhalation, P 3  within the primary pressure chamber decreases to a level below inlet pressure P 1  and forces open the non-return valve  7 , thereby admitting airflow from the flow generator into the primary chamber  17 . P 2  which equals P 1 , exceeds P 3 . 
         [0041]    For all embodiments herein, the projected area of pressure plate  10  greatly exceeds that of sealing face  32 . Therefore, the positive pressure difference of P 2  relative to P 3  creates a net moment that tends to rotate rocker  45  anti-clockwise as shown in  FIG. 4C , forcing sealing face  32  to block exhaust outlet  9 . Consequently, flow from the flow generator is directed from the primary chamber  17  via patient connection passage  3 , to be inhaled by the patient. 
         [0042]      FIG. 4D  shows the valve of  4 B under patient exhalation. During exhalation, P 3  within the primary pressure chamber increases above bias pressure P 2  and inlet pressure P 1 . Non-return valve  7  is forced closed, and the pressure difference of P 3  relative to P 2 , creates a net moment that tends to rotate rocker  45  clockwise as shown in the  FIG. 4D , forcing sealing face  32  away from, and thereby opening exhaust outlet  9  permitting exhaled air to be released via exhaust passage  9  out to atmosphere at lower ambient pressure P 4 . 
         [0043]      FIG. 5  illustrates a valve assembly  46  installed in a mask system  53  comprising a mask frame  50 , retaining means such as a collar  49  which engages grooves  4  in valve assembly. Collar  49  and connection passage  3  may be generally circular in cross-section, thereby permitting the valve assembly  46  to rotate relative to the mask system  53 .  FIG. 5  also illustrates a silencer  48  attached to the exhaust passage  9  and including a converging exit nozzle(s)  47  shaped to further reduce exhaust vent noise. Silencer  49  may be elastomeric in construction, or feature an elastomeric interface, to reduce noise transmitted by the semi-rigid structures of the mask frame  50  and valve assembly  46  to the exit nozzle(s)  47 . Silencer  49  and exhaust passage  9  may be of generally circular cross-section, permitting the direction of venting via exit nozzle(s) to be selected by the patient. 
         [0044]    Mask system  53  includes a cushion  51  for sealing against the patient&#39;s face and also includes headgear  52  for retaining the mask system  53  to the patient&#39;s face. It should be noted that many alternative patient interfaces may be applied to mask system  53  including nasal, individual nares seals, full-face or nose-and-mouth. 
         [0045]      FIGS. 6A-6C  illustrate an alternative sealing arrangements between valve sealing face  32  and exhaust outlet  9 .  FIG. 6A  shows a plain elastomeric gasket  54 .  FIG. 6B  shows an elastomeric gasket  55  including a projecting lip  56 .  FIG. 6C  shown an elastomeric gasket  57  including a lip  58 . 
         [0046]      FIGS. 7A-7D  illustrate an embodiment of a valve assembly integrated into a mask system including a nasal patient interface ie. enclosing the patient&#39;s nose within a sealed pressurized area. 
         [0047]      FIG. 7A  shows a perspective view of the mask system  60 . 
         [0048]      FIG. 7B  shows an exploded view of the mask system of  FIG. 7A . comprising a mask frame  67 , soft, elastomeric forehead support  65  which is rotatable and installed onto forehead support post  66 , and cushion mounting rim  68  (cushion and headgear are not shown). Mask system  60  also includes components required to effect the functions of an intermittent exhaust valve, including, non-return valve  7 , valve rocker  64  which includes pivot  40 , pressure plate  10  and sealing face  32 . 
         [0049]    Mask system  60  also includes a membrane  63  which includes a convolution  11 , bias pressure passage  15  and gasket seal  54 . Mask system  60  also includes a lid  59  which includes an exhaust passage  9  separated from bias chamber  19  by a dividing wall  61 , and includes an exhaust vent nozzle  62 . 
         [0050]      FIG. 7D  shows a front view of the integrated mask valve system, and  FIG. 7C  shows a sectional view derived from  FIG. 7D . 
         [0051]    Inhalation and exhalation functions of the valve follow that described for the valve illustrated in  FIGS. 4B-4D . It should be noted that although a nasal mask embodiment is illustrated, the general configuration shown in  FIGS. 7A-7D  may be adapted to nasal or full-face mask configurations. 
         [0052]      FIGS. 8A-8D  illustrate an embodiment of a valve assembly integrated into a mask system including a nose and mouth patient interface ie. enclosing the patient&#39;s mouth within a sealed pressurized area and also including projections for sealing in and/or around the nares. 
         [0053]      FIG. 8A  shows a perspective view of the mask system  70 . 
         [0054]      FIG. 8B  shows an exploded view of the mask system of  FIG. 8A . comprising a mask frame  75  (headgear is not shown). 
         [0055]    Mask system  70  also includes componentry required to effect the functions of an intermittent exhaust valve, including, non-return valve  7 , valve rocker  74  which includes pivot  40  and pressure plate  10  and sealing face  32 . 
         [0056]    Mask system  60  also includes membrane  73  which includes a convolution  11 , bias pressure passage  15  and gasket seal  54 . Mask system  70  also includes a lid  72 . 
         [0057]    Mask system  70  also includes a cushion  71  including portion to seal around the mouth  51  and projections to seal in or around the nares  69 . 
         [0058]      FIG. 8D  shows a side view of the integrated mask valve system, and  FIG. 8C  shows a sectional view derived from  FIG. 8D . 
         [0059]    Inhalation and exhalation functions of the valve follow that described for the valve illustrated in  FIGS. 4B-4D . 
         [0060]      FIG. 9A-B  show further embodiments of the valve assembly shown in  FIG. 1A ; wherein contact switches  80  are provided to be activated upon contact with pads  81 . It may be appreciated that the positional arrangements of  80  and  81  shown may be reversed, that pads  81  may be integral features of valve components and that a similar sensor configuration may be applied to a valve assembly of the style shown in  FIG. 4A . Contact switches  80  detect actuation of the valve mechanism to extreme positions of either fully open or fully closed. 
         [0061]      FIG. 9C-D  show further embodiments of the valve assembly shown in  1 A; wherein proximity sensor  82  are provided to be activated upon contact with targets  83 . It may be appreciated that the positional arrangements of  82  and  83  shown may be reversed, that a range of sensor types may be used including magnetic, optical or acoustic and that a similar sensor configuration may be applied to a valve assembly of the style shown in  FIG. 4A . Proximity sensors  82  detect actuation of the valve mechanism to near extreme positions of either fully open or fully closed. 
         [0062]      FIG. 10A-B  show further embodiments of the valve assembly shown in  1 A; wherein a rotational position sensor  84 , capable of detecting changes in angular displacement is provided for detecting angular displacement of the valve rocker or pressure plate  10 . The rotational position sensor  84  may be connected to the pressure plate  10  by links  85 ,  87  which rotate about pivots  86 . Alternatively a link pivoting at the sensor  84  and running in a slot provided in pressure plate  10  may be used. Rotational position sensor  84  may be either, but not limited to, a rotary potentiometer, a binary encoder or grayscale encoder. It may be appreciated that a similar sensor configuration may be applied to a valve assembly of the style shown in  FIG. 4A . It may also be appreciated that if the rotational position sensor  84  acts as the pivot  13  for the valve rocker or pressure plate  10 , then further links  85 ,  87  and pivots  86  are unnecessary. It may further be appreciated by those skilled in the art that the rotational sensor arrangement described may be substituted, for example by sensors based on relative linear motion or bending. 
         [0063]    It is will be clear to those skilled in the art that the apparatus and embodiments described above provides means to direct flow from a user to atmosphere during exhalation and from the source of pressurized breathable gas to a user&#39;s respiratory system during inhalation. It will be further evident that during unintentional leaks, such as may be attributable to mask leaks or other mating surfaces, such as movable fittings and valves, air will flow from the pressure source to atmosphere independently of gas flow initiated by the user into or out of their respiratory system. Naturally it will be the aim of the mask system including the apparatus described to minimize these leaks by optimizing for example engineered mating surfaces as well optimizing the seal between the mask and user&#39;s facial tissues. Notwithstanding issues associated with unintentional leaks, it may be further appreciated that small intentional may be introduced into the apparatus if required. This may, for example, be advantageous to remove small amounts of retained carbon dioxide from within the mask frame if desired. The amount or intended leak would be set at a designer&#39;s discretion. 
         [0064]    While the invention has been described with reference to a range of embodiments as described above, it will occur to those skilled in the art that various modifications and additions further to the disclosed methods discussed herein may be made without departing from the spirit and scope of the invention. 
       MPEP 706/707 STATEMENT 
       [0065]    If for any reason this application is not believed by the Examiner to be in full condition for allowance, applicants respectfully requests constructive assistance and suggestions of the Examiner, pursuant to M.P.E.P. 706.03 (d) and 707.070) in order that the applicants can place this application in allowable condition as soon as possible.