(12) United States Patent
`Drew et al.
`
`(10) Patent N0.:
`(45) Date of Patent:
`
`US 6,581,594 B1
`Jun. 24, 2003
`
`US006581594-B1
`
`(54) RESPIRATORY MASK HAVING GAS
`
`5,937,851 A *
`6,112,746 A *
`M 21:32:: 21::
`,
`,
`
`8/1999 Serowski et a1.
`9/2000 KWOk et al.
`32332
`
`u o p
`
`
`~
`.............. ..
`
`128/205.11
`128/207.13
`1:233:12
`.
`
`(75)
`
`IHVCHIOISZ Joanne DFEVY, Balgowlah (AU);
`Alexander Vlrr, Balmain (AU);
`Ge0fi'rey Crumblin, Baulkham Hills
`(AU)
`
`(73) Assignee: ResMed Limited, North Ryde (AU)
`
`( * ) Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 0 days.
`
`(21) ApP1~ NOJ 09/570,907
`
`(22) Filed:
`
`May 15, 2000
`
`Int. Cl.7 ............................................. .. A61M 16/00
`(51)
`(52) US. Cl.
`.......................... .. 128/204.18; 128/207.12;
`128/207.13
`(58) Field of Search ..................... .. 128/200.29, 201.29,
`128/204.18, 205.11, 207.12, 207.13
`
`(56)
`
`References Cited
`
`FOREIGN PATENT DOCUMENTS
`
`AU
`EP
`
`4/1999
`71223:
`2/1996
`069722 A2
`OTHER PUBLICATIONS
`
`Instruction Brochure for “E—Vent—N” ©Aug. 1997 Dréiger
`Medjzjntecnik GmbH, 2 pages,
`*
`i
`_
`“led by exammer
`Primary Examirzer—Aaron J. Lewis
`(74) Attorney, Agent, or Firm—Pillsbury Winthrop LLP
`
`(57)
`
`ABSTRACT
`
`The present invention nievides a Vent asseinbiy Snitabie for
`use with a respiratory mask of the type used in CPAP
`treatment. In one embodiment the Vent is made of a thin air
`permeable membrane. Generally, the membrane is thinner
`than 0.5 mm. The membrane can be made of a hydrophobic
`material such as polytetrafluoroethylene (PTFE). The mem-
`brane can also be fabricated from expanded PTFE. The
`
`......... .. 128/207.15
`3,291,127 A * 12/1966 Eimer et al.
`3,850,171 A * 11/1974 Ball 61 al.
`.... ..
`128/205.11
`
`3/1981 Reber ~~~~~~~~~~ ~~
`42581710 A *
`128/20418
`........ .. 128/207.12
`4,266,540 A *
`5/1981 Panzik et al.
`5,065,756 A * 11/1991 Rapoport
`............. .. 128/204.18
`591481802 A *
`9/1992 Sanders st a1~
`~~~~~~~~ 128004-18
`5,477,852 A * 12/1995 Landis et al.
`........ .. 128/204.18
`5,560,354 A * in/1996 Benhonnones
`et al.
`................... .. 128/204.18
`8/1997 Landis et al.
`........ .. 128/204.18
`
`5,657,752 A *
`
`of 10 to 15 microns. In an alternative embodiment, the Vent
`assembly includes a Vent constructed from stainless steel. In
`another embodiment the membrane has a superficial cross-
`Secnonai area of appmximateiy 500 mm;
`in another
`~
`~
`§i?all‘iIi3IiZ“§VZ1ii 13:32 131633331siifiiflsfiminmii‘E333
`.
`’
`y
`g
`which can be removeably attached to a mask fame.
`
`8 Claims, 4 Drawing Sheets
`
`
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`22
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`RMD 1022
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`1
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`RMD 1022
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`U.S. Patent
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`30024:2n.uJ
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`Sheet 1 of 4
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`US 6,581,594 B1
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`U.S. Patent
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`Jun. 24, 2003
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`Sheet 2 of 4
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`US 6,581,594 B1
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`U.S. Patent
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`Jun. 24, 2003
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`Sheet 3 of 4
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`US 6,581,594 B1
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`U.S. Patent
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`Jun. 24, 2003
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`Sheet 4 of 4
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`US 6,581,594 B1
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`US 6,581,594 B1
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`1
`RESPIRATORY MASK HAVING GAS
`WASHOUT VENT AND GAS WASHOUT
`VENT FOR RESPIRATORY MASK
`
`BACKGROUND OF INVENTION
`
`1. Field of the Invention
`
`The present invention relates to a respiratory mask and a
`vent for a respiratory mask.
`2. General Background and Related Art
`The application of Continuous Positive Airway Pressure
`(CPAP) via a nasal mask is a common ameliorative treat-
`ment for sleep disordered breathing (SDB)
`including
`obstructive sleep apnea (OSA) as described in commonly-
`assigned US. Pat. No. 4,944,310. In CPAP treatment for
`OSA, air or other breathable gas is supplied to the entrance
`of a patient’s airways at a pressure elevated above atmo-
`spheric pressure, typically in the range 3-20 cm I120 as
`measured in the patient interface. It is also known for the v
`level of treatment pressure to vary during a period of
`treatment in accordance with patient need,
`that form of
`CPAP being known as automatically adjusting nasal CPAP
`treatment, as described in commonly-assigned U.S. Pat. No.
`5,245,995.
`Non-invasive positive pressure ventilation (NIPPV) is
`another form of treatment for breathing disorders including
`sleep disordered breathing. In a basic form, NIPPV involves
`a relatively high pressure of gas being provided in the patient
`interface during the inspiratory phase of respiration and a
`relatively low pressure or atmospheric pressure being pro-
`vided in the patient interface during the expiratory phase of
`respiration. In other NIPPV modes the pressure can be made
`to vary in a complex manner throughout the respiratory
`cycle. For example,
`the pressure at
`the patient interface
`during inspiration or expiration can be varied through the
`period of treatment as disclosed in commonly—assigned
`International PCT Patent Application No W0 98/12965 and
`International PCT Patent Application No WO 99/(H088.
`In this specification any reference to CPAP treatment is to
`be understood as embracing all of the above -described forms
`of ventilatory treatment or assistance.
`Typically, the patient interface for CPAP treatment con-
`sists of a nasal mask. The nasal mask is generally defined by
`a mask shell which forms an inner cavity defined by its
`interior surface, mask cushion and the user’s face, a gas inlet
`which may or may not include a separate component such as
`a swivel elbow. Alternatively, a nose-mouth mask or full-
`faee mask or nasal prongs or nasal pillows can be used. In >
`this specification any reference to a mask is to be understood
`as incorporating a reference to a nasal mask, nose-rnouth
`mask, full face mask, nasal prongs or nasal pillows unless
`otherwise specifically indicated. The mask incorporates, or
`has in close proximity, a gas washout vent for venting
`exhaled gases to atmosphere. The gas washout vent (the
`Vent) is sometimes referred to as a C02 washout vent.
`It is important that the apparatus is quiet and comfortable
`to encourage patient compliance with therapy. The exhaust-
`ing to atmosphere of exhaled gas through the vent creates
`noise. As CPAP and NIPPV treatments are normally admin-
`istered while the patient is sleeping, minimization of such
`noise is desirable for both the comfort of the patient and any
`bed partner.
`From a clinical perspective it is desirable for a mask and
`vent combination to maximize both the elimination of
`exhaled CO2 through the vent and also the inhalation of the
`
`_
`
`2
`supplied breathable gas. In this way, retention of exhaled
`CO2 within the mask, which is “re-breathed” by the wearer,
`is minimized. Generally by locating the vent in the mask
`shell CO2 washout will be superior to locating the same vent
`between the mask shell and the breathable gas supply
`conduit.
`It is desirable to minimize the weight of the vent assembly
`for greater patient comfort.
`Systems for the delivery of nasal CPAP treatment often
`incorporate in—line humidifiers to minimize drying of the
`nasal mucosa and increase patient comfort. Accordingly, it is
`also desirable that a vent not block when used with humidi-
`fied gas. It is also desirable that a vent be easily cleaned or
`economically disposable.
`A number of vent configurations are known. One
`approach to vent configuration is to create within the mask
`shell one or more openings that allow for the flow of exhaust
`gas from the inner cavity to atmosphere. The exhaust flow
`may be directed through the incorporation of an additional
`pipe extending out from the opening located on the mask
`shell outer surface.
`The assignee’s nasal mask system known by the name
`ResMed Modular Mask System incorporates an outlet vent
`located in the swivel elbow connected to the mask shell. The
`ports defining the vent have the same cross-sectional thick-
`ness and are formed from the same polycarbonate material
`that is used to form the swivel elbow and mask shell frame.
`The whisper swivel, manufactured by Respironics, Inc
`provides three slots on the circumference of a generally
`cylindrical attachment piece. In use, the attachment piece is
`to be interposed between the mask shell and the gas conduit.
`The attachment piece is made of the same material and
`thickness as is used to make the mask shell.
`European Patent No. 0 697 225 discloses a vent formed
`from a porous sintered material.
`A lcnown vent, manufactured by Gottleib Weinmann
`Gerate Fur Medizin Und Arbeitsschutz GmbH and Co.
`comprises a generally cylindrical insert to be interposed in
`use. between the mask shell and the gas conduit. The insert
`includes a window which is covered with a porous sintered
`material of approximately 3-4 mm thickness.
`Another type of vent intended to be inserted between the
`mask shell and the breathable gas supply conduit
`is the
`E-Vent N by Draeger medizintechnik G1nbH (the Draeger
`vent). The Draeger vent comprises a stack of 21 annular
`disks, which have slots in their adjacent surfaces for gas to
`flow therethough. Each slot has a length of 5 to 7 mm as
`measured along the path from the interior of the vent to
`atmosphere.
`The assignee produces a respiratory mask known as the
`MIRAGE® nasal mask system and the MlRAGE® full-face
`mask (the MIRAGE mask). The MlRAGE® mask has a
`crescent shaped opening in the mask shell
`in which is
`located a complementary shaped crescent elastometric insert
`with six holes therein which constitutes the Vent. The
`elastomeric inset has a cros-sectional thickness of 3 to 4 mm.
`The vent of the type used in the MlRAGE® is described in
`International Patent Application No. WO 98/34665 and
`Australian Patent No 712236.
`It is an object of the present invention to provide an
`alternative form of vent that is suitable for use in a respi-
`ratory mask.
`SUMMARY OF THE INVENTION
`
`The present invention provides a vent assembly suitable
`for use with a mask used in CPAP treatment wherein the vent
`assembly is a thin air permeable membrane.
`
`6
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`

`
`US 6,581,594 B1
`
`5
`
`3
`In one form of the invention, the membrane is thinner than
`the mask frar11e.
`In another form of the invention, the membrane is thinner
`than 05 mm.
`In another form of the invention the membrane has an
`approximate thickness of 0.05 mm.
`In another form of the invention the membrane is cori-
`structed from a hydrophobic material such as polytetrafluo-
`roethylene (PTFE).
`In another form of the invention the membrane is con-
`structed from expanded PTFE.
`In another form of the invention the expanded PTFE
`membrane is mounted on a polypropylene scrim.
`In another form,
`the pores of the membrane have a
`reference pore size of 10 to 15 microns.
`In another form of the invention the membrane is con-
`structed from stainless steel.
`In another form of the invention the membrane of the vent
`has a superficial cross—sectional area of approximately 500 '
`mm‘.
`
`In another form of the invention the vent assembly
`comprises a membrane attached to a vent frame, the vent
`assembly forming an insert which can be removeably V
`attached to a mask fame.
`
`In another form of the invention there is provided a
`respiratory mask for communicating breathable gas to the
`entrance of a wearer’s airways, the mask including mask
`shell, (ii) a gas inlet and (iii) an opening into which an insert
`constructed from a thin air permeable membrane with a
`corresponding shape may be placed. The opening may be
`positioned in the mask shell or in the gas inlet.
`In one form, the mask includes a mask shell with an
`integrally formed gas inlet and the opening is provided in the
`mask shell remote the inlet. In another form,
`the mask
`includes a mask shell with an integrally formed gas inlet and
`the opening is provided in the gas inlet. In yet another form,
`the mask includes a mask shell with a separately formed gas
`inlet attached thereto and the opening is provided in the
`mask shell remote the inlet. In still yet another form, the
`mask includes a mask shell with a separately formed gas
`inlet attached thereto and the opening is provided in the gas
`inlet.
`The present invention also provides a respiratory mask
`arrangement
`for communicating breathable gas to the
`entrance of a wearer’s airways,
`the mask arrangement
`including a vent assembly comprising an opening with a thin
`air permeable membrane extending across an opening.
`The present
`invention also provides an apparatus for ,
`delivering CPAP which apparatus includes a mask arrange-
`ment for communicating breathable gas to the entrance of a
`wearer’s airways,
`the mask arrangement including a gas
`washout vent assembly comprising an opening with a thin
`air permeable membrane extending across said opening.
`BRIEF DESCRIPTION 01“ TIIE DRAWINGS
`
`4
`FIG. 6 is a perspective view of a respiratory mask
`according to sixth embodiment of the invention;
`FIG. 7 is a perspective View of a full-face mask according
`to a seventh embodiment of the invention;
`FIG. 8 is an enlarged detailed View of an insert suitable for
`use with the masks shown in FIG. 6 and FIG. 7; and
`FIG. 9 is a perspective View of a vent assembly according
`to an eighth embodiment of the invention where the thin air
`permeable membrane is located in a cylindrical position on
`a tube suitable for attachment to the mask elbow.
`DETAILED DESCRIPTION
`
`FIG. 1 shows a nasal respiratory mask 10 according to a
`first embodiment of the invention. The mask 10 includes a
`rigid plastic mask shell 12, which has a peripheral flange 14
`for mounting of a cushion (not shown) to the shell 12. The
`cushion abuts the wearer’s face in use and is well known in
`the art. The flange 14 includes slots 15 for the connection of
`mask restraining straps (not shown) that extend around the
`head of the wearer to maintain the mask 10 adjacent to the
`wearer’s face. The straps are also known in the art. The shell
`12 also includes an arr11 16, which terminates ir1 a fitting 18
`that is adapted to connect to a forehead support (not shown),
`which is also known in the art.
`The mask shell 12 includes a breathable gas inlet 20
`which is rotatably mounted to the shell 12. The inlet 20 has
`a first end 22 which is adapted for connection with a
`breathable gas supply conduit (not shown) and a second end
`24 which is adapted to connect to, and communicate the
`supplied gas to the interior of the shell 12 for subsequent
`communication with the wearer’s airways.
`The mask 10 includes a gas washout Vent constituted by
`an opening 26 in the shell 12 across which extends a thin air
`permeable membrane 28.
`In the FIG. 1 embodiment, the thin air permeable mem-
`brane 28 is a stainless steel sheet approximately 0.45 mm
`thick having holes with a diameter approximately 0.1 rnr11 in
`diameter. The total open area is approximately 5% of the
`total superficial surface area of the sheet. The dimensions of
`the sheet are approximately 322 mmz. The holes are laser cut
`into the stainless steel. The holes are desirably laser cut or
`flame cut through the stainless steel.
`Preferably the holes have a diameter of less than 0.2 mm,
`and preferably provide a total open area of approximately
`1% to 25% of the superficial surface area of the steel. The
`holes may be tapered (in a gradual or stepped manner)
`through their internal bore. In use, if the smaller end of the
`vent’s openings are located on the atmosphere side the
`opportunity for blockage occurring by the insertion of
`particulate matter will be minimized. Alternatively,
`the
`larger end of the vent’s openings may be located on the
`atmosphere side which may make the vent quieter.
`FIG. 2 shows a nasal respiratory mask 40 according to a
`second embodiment of the invention. Like reference numer-
`als to those used in describing the first embodiment will be
`used to denote like features in respect of the second embodi-
`ment. Accordingly, the mask 40 has a shell 12 with a gas
`inlet 20. Instead of the slots 15 of the first embodiment the
`mask shell includes openings 42 which are adapted to snap
`engage with connection fittings (not shown) provided on the
`end of mask restraining straps (not shown). Further, instead
`of the arm 16 and fitting 18,
`the mask 40 includes an
`adjustable forehead support mechanism indicated generally
`by the reference numeral 44.
`The mask 40 also includes a vent constituted by an
`opening 26 formed in the gas inlet 20 across which extends
`a thin air permeable membrane 28.
`
`FIG. 1 is a perspective View of a respiratory
`according to a first embodiment of the invention;
`FIG. 2 is a perspective view of a respiratory
`according to a second embodiment of the invention;
`FIG. 3 is a perspective View of a respiratory
`according to a third embodiment of the invention;
`FIG. 4 is a partial cross-sectional view of a vent assembly
`according to a fourth embodiment of the invention;
`FIG. 5 is a partial cross-sectional View of a vent assembly
`according to a fifth embodiment the invention;
`
`mask
`
`mask
`
`mask
`
`7
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`
`US 6,581,594 Bl
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`5
`FIG. 3 shows a mask 60 according to a third embodiment
`of the present invention. Although this particular embodi-
`ment is directed to a nasal mask, it should noted that various
`vent arrangements can be used with various mask arrange-
`ments. Once again like reference numerals to those used in
`describing features of the first embodiment shall be used to
`denote like features in respect of the third embodiment. The
`mask 60 includes a mask shell 12 with an integrally formed
`fixed gas inlet 62. A cushion 64 is attached to the peripheral
`flange 14 of the shell 12. The shell 12 also includes slotted
`extensions 66 for connecting headgear (not shown) to the
`mask. The mask 60 includes an opening 26 across which is
`extended a thin air permeable membrane 28 of identical
`construction to the ePTFE membrane discussed below in
`relation to the mask 40 shown in FIG. 6.
`FIG. 4 shows a cross—section of vent assembly 110. There
`is provided a membrane 114 interposed between an outer
`element 112 and an inner element 116. This arrangement
`provides for a simple assembly. There is a corresponding
`opening 115 in the outer element 112 and inner element 116
`to allow for the passage of air through the membrane. The
`inner element ll6 may form part of the mask frame or of a
`separate insert to be positioned in an opening in the mask
`frame.
`FIG. 5 shows an alternative cross—section of a vent
`assembly 110. There is provided a stainless steel membrane '
`insert 118 positioned over the inner element 120. There is an
`opening 119 in the inner element 120 to allow for the
`passage of air through the membrane. The inner element 119
`may form part of the mask frame or of a separate insert to
`be positioned in an opening in the mask frame.
`FIG. 6 shows a nasal respiratory mask 80 according to a
`sixth embodiment of the invention. The mask 80 is similar
`to the second embodiment of the mask 40 shown in FIG. 2
`and like reference numerals have been used to indicate like
`features with respect to the second embodiment. In the mask
`40 of FIG. 2, the vent is provided in the gas inlet 20, whereas
`in the mask 80 the vent is provided in the shell 12. More
`particularly, the mask 80 includes two cylindrical inserts 82
`which have an inner opening 26 across which extends the
`thin air permeable material 28. The thin air permeable
`material is made from GORE-TEX® product attached to a
`polypropylene scrim having an area of 481 mmz. The
`membrane is constructed from expanded polytetrafluoroet-
`hylene (ePTFE). The inventors have identified GORE-
`TEX® ePTFE product manufactured by W. L. Gore &
`Associates,
`Inc. of Maryland USA (GORE-TEX®
`membrane) as being a suitable material for constructing a
`membrane. Ir1 one preferred form, the GORE-TEX® rnern-
`brane has the following characteristics:
`
`Membrane material
`Reference pore size
`Bubble Point
`Airflow
`Thickness
`Substrate
`
`100% expanded polytetralluoroethylene
`10-15 micron
`typical minirnum individual 0.02 bar
`0.37 LPM/em;
`0.05 mm
`polypropylene scrim
`
`FIG. 7 shows a seventh embodiment of a full-face respi-
`ratory mask 100 according to the invention. Once again like
`reference numerals to those used in denoting like features
`with previous embodiments have been used to denote like
`features in respect of this embodiment. The mask 100 is
`similar to the mask 80 shown in FIG. 6 in that the vent is
`provided in the inserts 82. However the mask 100 uses
`slotted extensions 66 to attach mask restraining straps (not
`shown), not openings 42.
`
`6
`As best seen in FIG. 8, which is a close—up View of the
`insert shown in FIG. 6, the insert 82 is comprises a cylin-
`drical portion 86 sized to be a snug fit into a circular orifice
`88 provided in the mask shell 12. The insert 82 located
`against the outer surface of the shell 12 by a peripheral
`flange 90. The inserts may be glued in position.
`FIG. 9 shows a further embodiment of the invention in
`which an ir1-line vent assembly is provided. Like numerals
`are used to indicate like features with previous embodi-
`merits. In this embodiment, the in-lirie vent assembly corn-
`prises a generally cylindrical shaped vent frame with “win-
`dows” or “ports” covered with a membrane as described
`above.
`The thin air permeable membrane of the present invention
`may be attached to the mask by any suitable means. For
`example, the stainless steel vent described above may be
`attached to a polycarbonate mask shell by way of hot glue
`adhesive (for example) or any other suitable adhesive. The
`durability sought to be achieved will determine the suitable
`approach for attachment.
`In a further embodiment there is provided a means to
`indicate the volume of air that has passed through the vent,
`or alternatively the time that the vent assembly has been
`used. When a sufficient volume of air has passed through the
`vent assembly, or the assembly has been used for a sufficient
`time and may have become blocked, the indicator will signal
`that the vent assembly should be replaced.
`For convenience, the thin air permeable membrane can be
`provided in an insert which is releasably attachable to the
`mask shell via a push—fit mechanism, as shown in FIG. 8.
`Preferably on at least the outer surface of the insert there is
`provided at least one cross-piece that protects the air per-
`meable membrane from being damaged as it is located into
`the receiving orifice of the mask shell. This approach will
`allow for he easy placement, removal and replacement of a
`vent inser while retaining the other components of the
`mask. While the insert may be configured to take the form
`of any recuisite shape preferably the insert has a circular
`circumferential shape defining a cylindrical insert which has
`a frictiona fit within a corresponding circular orifice in the
`mask shel or gas inlet.
`Formation of the vent through use of an insert configu-
`ration faci itates the selection and fitting of a vent to suit a
`user’s requirements. For example where a low treatment
`pressure is required the associated flow will also be rela-
`tively sma 1 compared with flow required to achieve a higher
`treatment
`ressure. In such circumstances a relatively large
`vent area may he adopted to facilitate achievement of the
`clinically desirable mask C02 washout rate. Should a higher
`treatment
`ressure be required then the previously selected
`vent may be exchanged for a vent being more restrictive to
`flow. The more restrictive vent will allow achievement of the
`clinically desirable mask CO2 washout rate While avoiding
`the intensity of noise and exhaust gas jetting that would
`occur had the previously selected low pressure vent been
`used with the higher treatment pressure.
`Locating the vent in the mask shell results in an improve-
`ment in the minimization of C02 retention within the mask
`compared to locating the vent as an inline mask component.
`Although the invention has been described with reference
`to specific examples,
`it
`is to be understood that
`these
`examples are merely illustrative of the application of the
`principles of the invention. Thus it is to be understood that
`numerous modifications may be made in the illustrative
`examples of the invention and other arrangements may be
`devised without departing from the spirit and scope of the
`invention.
`
`8
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`US 6,581,594 B1
`
`7
`
`We claim:
`1. A respiratory mask comprising:
`a mask shell that can be fitted over a user’s nose;
`a cushion positioned in proximity to an edge portion of the
`mask shell to aid in fitting the mask shell to a user’s
`face;
`a breathable gas inlet that can conduct gas through the
`mask shell to a breathing cavity formed between the
`mask shell and a user’s face when the mask is in use;
`and
`
`a gas washout vent made from a thin air permeable
`membrane formed, constructed and arranged to allow
`gas to exit from the breathing cavity,
`wherein the membrane includes a plurality of tapered
`holes.
`
`2. A respiratory mask according to claim 1, wherein each
`of the tapered holes includes a small end facing atmosphere.
`3. A respiratory mask according to claim 1, wherein each
`of the tapered holes includes a small end facing an interior
`of the mask shell.
`
`4. A respiratory mask according to claim 1, wherein the
`membrane is mounted in an insert that is selectably detach-
`able from the mask shell.
`
`5. A respiratory mask according to claim 1, wherein a
`thickness of the membrane is less than a thickness of the
`mask shell.
`
`6. A respiratory mask comprising:
`a mask shell that can be fitted over a user’s nose;
`a cushion positioned in proximity to an edge portion of the
`mask shell to aid in fitting the mask shell to a user’s
`face;
`a breathable gas inlet that can conduct gas through the
`mask shell to a breathing cavity formed between the
`mask shell and a user’s face when the mask is in use;
`and
`
`a gas washout vent made from a thin air permeable
`membrane formed, constructed and arranged to allow
`gas to exit from the breathing cavity,
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`8
`wherein the membrane is formed in an opening of the
`respiratory mask, and a cross piece is formed across the
`opening.
`7. A respiratory mask comprising:
`a mask shell fittable over a user’s nose;
`a cushion positioned in proximity to an edge portion of the
`mask shell to aid in fitting the mask shell to a user’s
`face;
`a breathable gas inlet to conduct gas through the mask
`shell to a breathing cavity formed between the mask
`shell and the user’s face when the mask is in use; and
`a gas washout vent including an air permeable member to
`allow gas to exit from the breathing cavity, wherein
`the member comprises a stainless steel sheet having a
`thickness of less than about 0.5 mm, the stainless steel
`sheet includes a plurality of holes, an area of the holes
`is substantially 5% of a total superficial surface area of
`the stainless steel sheet, a diameter of each of the holes
`is less than 0.2 mm, a total open area of the holes is
`approximately 1—25% of the superficial surface area of
`the stainless steel sheet, and an area of the stainless
`steel sheet is about 322 mmz.
`8. A respiratory mask comprising:
`a mask shell fittable over a user’s nose;
`a cushion positioned in proximity to an edge portion of the
`mask shell to aid in fitting the mask shell to a user’s
`face;
`a breathable gas inlet to conduct gas through the mask
`shell to a breathing cavity formed between the mask
`shell and the user’s face when the mask is in use; and
`a gas washout vent including an air permeable member to
`allow gas to exit from the breathing cavity, wherein
`the member comprises an expanded polytetrafluoroethyl-
`ene sheet having a thickness of about 0.05 mm, the
`sheet includes a plurality of pores in the range of 10-15
`microns, an area of the sheet is approximately 480
`mm2, a bubble point of the sheet is at least 0.02 bar, and
`an airflow capacity of the sheet is about 0.37 LPM/cm2.
`*
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`$
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`9