Vent system for CPAP patient interface used in treatment of sleep disordered breathing

A vent assembly for use with a mask assembly includes a first vent, a second vent and a selector to switch the flow of exhaled gas from a patient between the first and second vents.

FIELD OF THE INVENTION

The invention relates to a vent system for use with a Continuous Positive Airway Pressure (CPAP) patient interface, e.g. a mask, used in treatment of Sleep Disordered Breathing.

BACKGROUND

The use of nasal CPAP apparatus to treat “snoring sickness” was pioneered by Sullivan and taught in U.S. Pat. No. 4,944,310. Nasal CPAP apparatus typically comprises a blower, an air delivery conduit and a patient interface. The blower provides a supply of air or breathable gas at positive pressure. The conduit interconnects the blower and the patient interface. A variety of nasal masks, nose & mouth masks, full face masks, nasal prongs and nasal pillows are used to provide an interface with the patient.

A typical mask comprises;

(i) a rigid or semi-rigid portion, termed a shell or frame, which defines a nose-receiving cavity; and

(ii) a soft patient contacting portion, termed a cushion or membrane.

Cushions have been constructed from silicone, foam, gel and combinations of these materials.

Since a patient typically exhales into the same mask cavity wherefrom they inhale, the possibility of rebreathing of carbon dioxide (CO2) exists. In conjunction with a sufficient continuous flow of fresh air or breathable gas, a vent can allow a controlled leak from the mask cavity and hence provide for the washout of CO2. Unfortunately, the noise of air or breathable gas from the vent can disrupt anyone within earshot attempting to sleep. Hence there is an advantage in providing a low-noise vent.

One form of known vent is described in U.S. Pat. Nos. 6,561,190 (Kwok) and 6,561,191 (Kwok). These patents describe the use of grommet in a mask frame. The contents of these patents are hereby incorporated by cross-reference. A vent in accordance with embodiments of these inventions is found in the MI/RAGE™ mask, manufactured by ResMed Limited.

Another known form of vent is described in International Patent Application PCT/AU00/00636 (Drew et al.) published as WO 00/78381. This patent application describes the use of a connector for a mask having a vent along a smooth continuing surface. The contents of this patent application are hereby incorporated by cross-reference. A vent in accordance with an embodiment of this invention is found in the ULTRA MIRAGE™ mask, manufactured by ResMed Limited.

Another known form of vent is described in U.S. Pat. No. 6,581,594 (Drew et al.). This patent describes the use of a vent which, in one form, comprises a thin air permeable membrane. The contents of this patent application are hereby incorporated by cross-reference.

Another known form of vent is described in International Patent Application PCT/AU01/01658 (Dantanarayana et al.) published as WO 02/051486. This patent application describes the use of a flow regulation vent. The contents of this patent application are hereby incorporated by cross-reference.

U.S. Pat. No. 6,557,555 (Hollis) describes a vent valve apparatus. The contents of this patent application are hereby incorporated by cross-reference.

Another known vent is the Respironics WHISPER swivel.

European Patent No. 0 697 225 discloses a vent formed from a porous sintered material.

A known vent, manufactured by Gottleib Weinmann Geräte Für 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 GmbH (the Draeger vent). The Draeger vent comprises a stack of 21 annular disks, which have slots in their adjacent surfaces for gas to flow therethrough. Each slot has a length of 5 to 7 mm as measured along the path from the interior of the vent to atmosphere.

Typically vents are designed with sufficient porosity to provide enough vent flow at a low pressure (e.g. 4 cm H2O) to ensure adequate washout of CO2.

Reducing the pore size of a vent can make the vent quieter, but can also increase the chances that the vent will clog.

Problems with prior art vents include that they can be too noisy, that they clog with dirt and moisture (particularly when used with humidifiers), that they are awkward or difficult to clean or assemble and that they have designs which are sensitive to very small changes in the manufacturing process which can lead to variation in the pressure flow relationship.

SUMMARY OF THE INVENTION

In accordance with a first aspect of the invention there is provided a vent for a CPAP patient interface.

In accordance with a second aspect of the invention there is provided a vent assembly comprising at least two alternative vents each having substantially the same pressure-flow characteristics.

In accordance with a third aspect of the invention there is provided a vent assembly comprising at least two alternative vents each having different pressure-flow characteristics.

In accordance with another aspect of the invention there is provided a vent assembly comprising at least two alternative vents and a mount adapted to support at least one vent in a venting position.

In accordance with another aspect of the invention there is provided a vent assembly comprising at least two alternative vents and a mount adapted to support at least one vent in a venting position and a locking mechanism adapted to retain said at least one vent in a venting position.

In accordance with still another aspect, there is provided a mask assembly for a patient comprising a frame, a cushion provided to the frame, and a vent assembly including a first vent, a second vent, and a selector to switch the flow of exhaled gas from the patient between the first and second vents.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1shows a blower10connected to an air delivery conduit20and the air delivery conduit20connected to a patient interface30. In the view shown inFIG. 1, the patient interface30is a nasal mask. The patient interface30includes a vent40. The vent40includes one or more holes, e.g., six holes50.

FIG. 2shows an alternative nasal mask, the MIRAGE® ACTIVA™ nasal mask. This mask includes a swivel elbow60. The swivel elbow is described in further detail in the Applicant's co-pending International Patent Application PCT/AU03/01162, the contents of which are hereby incorporated by cross-reference. The swivel elbow60includes a vent cover70having a number of holes50therethrough.

FIG. 3shows a cross-section of a patient interface30in position on a face of a patient80. A swivel elbow60is shown detached and in front of the patient interface30. The cavity90into which the patient80can exhale nasally can accumulate carbon dioxide unless it is washed out through the vent40included in the elbow60.

In a first embodiment of the invention, a vent assembly is provided with two alternative vents, vent a and vent b as shown inFIG. 4a-5c. Both vent a and vent b provide approximately the same total flow. Vent a provides relatively fewer large vent holes, whereas vent b provides a matrix of relatively smaller holes (e.g. below 0.5 mm diameter, preferably approximately 0.1 mm in diameter). Selection between vent a and vent b is made by rotating or sliding a cover so that either the small or large holes are lined up with an orifice on a mating surface.

As shown inFIGS. 4aand4bin exploded views, a vent assembly90in accordance with an embodiment of the invention comprises a generally cylindrical first portion100and a generally cylindrical sleeve portion110. The first portion100includes an orifice or window102. The sleeve portion110includes, in one embodiment, two alternative sets of holes corresponding to vents a and b respectively. Vent a uses three large holes. Vent b uses a series of smaller holes. In use the sleeve portion110rotatingly fits over an end of the first portion100. In the embodiment of the invention shown inFIG. 4a, the sleeve is free to rotate through 180° degrees as shown by the arrows inFIG. 5a-5c, although in other embodiments the sleeve may rotate through fewer degrees. As shown inFIG. 4a-4b, both the first portion100and sleeve portion110are hollow which allows air to pass between the interior of the first portion100through window102and thence through either of vent holes a or b.FIG. 4cshows a detail of the vent with small holes.

In a second embodiment of the invention the vent assembly is formed as part of a swivel elbow120, for example, the swivel elbow used on the MIRAGE® VISTA™ mask, manufactured by ResMed Limited, as shown inFIG. 6-9. The elbow120includes a shaft130with an orifice132therein. The shaft130includes an alignment tab134. A sleeve140includes a pair of alternative vents142,144and a pair of slots146,148, each one associated with one vent, each adapted to receive the alignment tab of the shaft. In use, the orifice132of the shaft130aligns with either vent142or vent144. In order to change from one vent to another, the vent assembly is pulled apart, rotated 180°, and re-assembled. In this way, at least one of and only one of vents142or144is used at one time.

In a third embodiment of the invention the vent assembly includes a moving part. The moving part can be located in each of two positions by having a protrusion on one part match a depression on the matching part. Alternatively, the two positions can simply be defined by use of appropriate positioning structure, e.g., detents, ratchets, etc. When the vent assembly is partway between the two vent positions, the protrusion can act to separate the matching parts so that the vented airflow is greater than in either of the two correct positions. This provides a fail-safe mechanism where an incorrect position results in high airflow (a safe condition) and also higher noise (warning the user of the mistake). Generally speaking, the assembly can be configured such that a warning, e.g., a noise, can be created when the vent parts are misaligned.

A typical vent comprises a number of vent holes. For example, three vent holes with a diameter of 2.7 mm. The effective area of a vent hole is generally smaller than the actual cross-sectional area of the vent hole. Small holes have a relatively smaller effective area than large holes, e.g. about 10% smaller. The effective area of a vent is the sum of effective areas of its constituent vent holes. In one form the alternative vents have the same effective areas.

In another embodiment of the invention, alternative vent constructions are used instead of using holes. For example, vent a and vent b are laminar flow elements, such as used in the ULTRA MIRAGE® mask. In another form sintered materials are used to construct the vent. In another form, vents are constructed from foam polymers. Combinations of different vents may be used, for example, a vent with holes and a vent constructed from a sintered material. The assembly may comprise more than two vents, for example a vent with holes, a sintered vent and a laminar flow element-type vent.

In some cases, such as clinical studies, it is desirable to test the effectiveness of a particular treatment regime, or mask and compare it with a suitable control. For example, it might be desired to test the effectiveness of an algorithm for providing nasal CPAP therapy. In such a situation, it would be desirable to be able to discount the effect of wearing the mask per se. This could be achieved by using a “sham” mask, for example, a mask with a very large vent hole. An example of a sham mask is taught in published PCT patent application WO 02/066,105. A difficulty of using a dedicated “sham” mask is that the patient may be aware that they are using the sham mask, or that it may be necessary to disturb their sleep in order to don such a sham mask.

The vent assembly may include a sham vent as an alternative. Such a sham vent would have a very high permeability, e.g. a large hole. By use of the invention, it would be possible for a clinician to switch from a “treatment” vent to a “sham” vent, with minimal disturbance to a sleeping patient and thus obtain clearer results for a clinical study.

Whilst in a preferred form the different vents are alternatives, in one form more than one vent may be used at once, for example, ½ vent a and ½ vent b.

In a vent comprising vent holes, increasing or decreasing the number of holes in the vent allows the vent flow to be set to any desired level. In this way a vent assembly in accordance with the invention can be designed to have pressure flow characteristics that mimic prior art masks which use vents with holes.

A variety of materials may be used to construct the vent assembly, for example, polycarbonate (e.g. MAKROLON), or other polymers, stainless steel, sintered ceramic or PTFE, and foam polymers. It may be particularly advantageous to use hydrophobic materials such as PTFE for small pored vents to reduce clogging of pores.

In an alternative form, instead of being mounted on a swivel elbow, a vent assembly200in accordance with an embodiment of the invention is mounted on or formed as part of a patient interface frame210.FIGS. 11a-14show a frame for a patient interface which comprises two generally cylindrical end portions220interconnected by a generally rectangular backbone230. Nozzles211may be included to interface with the nostrils of a user. A clip240is slidably positioned on the backbone230. The clip240includes at least two alternative vents250,260. One or more orifices or windows in the backbone230, similar to orifice or window102, provides for fluid communication to an interior of the patient interface. By sliding the clip240to alternatively align vent250or260with the orifice, exhaled air can be vented via vent250or260.FIG. 11a shows the clip240in a first position in which the vent260is aligned with an orifice in the backbone, and one or both vents250are sealed.FIG. 11bshows the clip240in a second position in which one or both vents250are aligned with respective orifices in the backbone, and the vent260is sealed.

FIGS. 22 and 23show an alternative embodiment of the invention in a nasal mask300. This form of the invention includes a slidable vent cover310which in a first position305exposes a set of large vent holes320and in a second position315exposes a set of small vent holes330. In one form the large and small vent holes are molded into a silicone grommet325which is removably insertable into a mask frame, in a similar manner to U.S. Pat. Nos. 6,561,190 and 6,561,191 (Kwok). When holes are exposed the passage of air between the interior of the mask and the exterior of the mask can occur therethrough.

FIG. 23aillustrates another embodiment of the present invention having a mask assembly700with a shell702and a cushion attached or otherwise provided to the shell702. The shell702includes an aperture706by which pressurized breathable gas is provided to an interior chamber defined by the shell702end cushion. Alternatively, a swivel elbow may be provided to a frontal aperture of the shell702, in which case the elbow would include a conduit that delivers breathable gas from a source to the frontal aperture.

The shell702includes at least one aperture708, in this case formed in a rectangular shape to make it easily visible. The aperture708is structured to continuously vent CO2during administration of CPAP or NIPPV therapy, for example. A slidable vent plate710includes first, second and third aperture portions712,714,716that may be selectively aligned (via sliding along the direction of arrows A) with the aperture708. As shown inFIG. 23a, the second aperture portion714is aligned with shell aperture708, whileFIG. 23bshows the plate710in a shifted position in which third aperture portion716is aligned with shell aperture708. Therefore, the clinician or patient may change the venting characteristics of the mask.

As shown inFIG. 23c, a partial schematic cross-section ofFIG. 23a, the vent plate710may be releasably held by the shell702. For example, the shell702may include a pair of legs702aeach forming a groove702bwith which a leg portion710aof the plate710may slidingly engage.

FIG. 24shows an alternative form of the invention in a nasal mask400. This form of the invention includes a hinged vent cover410. In the form shown inFIG. 24, the vent cover is generally rectangular and one side is hinged. Similarly to the vent assembly shown inFIGS. 22 and 23, the holes ofFIG. 24may be moulded into a removably insertable grommet425. The vent cover410can alternatively block the set of small vent holes430and the set of large vent holes420.

FIGS. 25aand25bshow an embodiment of the invention500incorporating a rotating vent cover510in a first and second position respectively on a vent elbow. The vent cover510is generally disc shaped having a window525therethrough. By rotating the vent cover510through, for example 120° different sets of holes are exposed. In the view shown inFIG. 25a, a set of large holes520are exposed. In the view shown inFIG. 25ba set of small holes530are exposed. Each respective set of holes520,530provides a conduit communicating with an interior of the mask. In an alternative form (not shown) the rotatable vent cover includes different sets of holes and there is a fixed position window to which the vent cover is attached. Rotating the vent cover presents a different set of vent holes to the window resulting in a different vent characteristic.

FIGS. 25c-25eillustrate yet another embodiment of the present invention. As shown in the assembled view ofFIG. 25c, a frame800includes a swivel elbow802that may rotate with respect to the frame800. A rear end803of the swivel elbow is connected or provided to the frame800, while the a lower end805is connected to a source of pressurized air or other breathable gas. A vent assembly806may be provided to a front portion of the elbow802.

FIG. 25dshows the frame800and elbow802without the vent assembly806. Front portion807of elbow802is similar to that shown inFIG. 7, in that it includes a vent opening809that continuously exhausts CO2to atmosphere. In the case ofFIG. 7, exhausted air is initially directed to vent cover70(seeFIG. 2) provided to cover the front portion of the elbow, and then the exhausted air is directed to atmosphere via one or more apertures50.

As shown inFIG. 25d, at least a portion810is closed or blocked, so that air may not pass therethrough. Thus, exhausted air is directed solely through that portion of the elbow including vent opening809. Once air is exhausted through opening809, it is directed to vent assembly806. In particular, the exhaust can be selectively directed to either first vent portion812or second vent portion814, as shown inFIG. 25c.

First vent portion812may be similar to the vent cover inFIG. 2, in that it can be made of an elastomeric material that is stretched to fit over a lip813provided to the front portion807of elbow802. The first vent portion812may include one or more apertures816to exhaust exhaled gas. The first vent portion812, unlike the vent cover inFIG. 2, may rotate with respect to the elbow802. Rotation allows the user or clinician to select whether exhausted gas is directed to the first or second vent portion812,814.

FIG. 25eshows vent assembly806in isolation. Vent assembly806an opening818adapted to be engaged with the rim813positioned on front portion of elbow802. Vent assembly includes an interior wall member820which partially divides the second vent portion814from a chamber822in communication with first vent portion812. The chamber822and the second vent portion814can be in communication with one another via interior aperture824, depending on the relative position of the vent assembly806with respect to the elbow802.

For example, if the vent assembly is rotated so that the interior wall member820is aligned with blocked portion810of elbow802(FIG. 25d) and the aperture824is aligned with aperture809, then exhausted gas can be directed through second vent portion814. In this position, a portion of the exhaust could also be vented through first vent portion812. If the aperture824is aligned with blocked portion810, then exhausted air would be directed solely to first vent portion810. Preferably, the blocked portion810may include an elastic material that can easily form an air tight seal with respect to aperture824.

The second vent portion808may be in the form of a cylinder that could be filled with foam815, to reduce noise and/or the possibility of cross-infection. As an alternative to foam, a ceramic material or GORE-TEX™ could be used.

FIGS. 25fand25gshow yet another vent assembly830, which, e.g., is adapted for use with the frame and elbow shown inFIG. 25d. Vent assembly includes a first vent portion832(FIG. 25g) like first vent portion shown inFIG. 25c. Vent assembly830includes a second vent portion834which includes a plurality of apertures836. Exhausted air is selectively directed to the first or second vent portion, depending on the member838being selectively aligned with either the aperture809or the blocked portion810of elbow802(FIG. 25d). InFIG. 25f, the second vent portion834can be seen through aperture840.FIG. 25falso shows opening842adapted to be engaged with rim813(FIG. 25d). The vent assembly830is more compact than the vent assembly shown inFIG. 25e.

FIGS. 26,27aand27bshow an alternative form of the invention including a replaceable vent cartridge. In this form of the invention the vent assembly comprises a shaft600, a rotatable sleeve620including a window625and a replaceable cartridge630with holes therethrough. The vent assembly is shown in exploded view inFIG. 26. When assembled, the cartridge630is slid into position over the shaft600and under the sleeve620. In the form shown inFIG. 27a-27b, in use the cartridge630is designed to be not rotatable about a longitudinal axis of the shaft600. In contrast, the sleeve620is designed to be so rotatable exposing a different set of holes in the cartridge630as shown inFIGS. 27aand27b. In use the holes of the cartridge630provide for fluid communication from the interior of the shaft600to atmosphere. Because small vent holes can become clogged with use, the sleeve620can be rotated after a suitable period (e.g. overnight). One cartridge might thus provide each night a clean set of vent holes for a week without requiring cleaning. At the end of the week, the cartridge may be disposed of a replaced with a clean one.

Advantages of the invention include:

When in the quiet position (fine holes) the mask will be extremely quiet, and with no discernable air jets. This makes the mask far less disturbing to both the wearer and any bed partner.

When in the normal (large holes) position, the mask will be suitable for use with a humidifier which might clog smaller holes. When the humidifier is not needed, the vent assembly can be switched easily to the quiet, small hole vent.

The use of a moveable part means that the patient does not need to keep spare parts and is precluded from losing components or not being able to fit them.

Use of the invention enables masks to be compatible with a range of different flow generators or blowers. For example, a first flow generator or blower may be pre-programmed to operate assuming a first vent characteristic and a second blower, a second vent characteristic. Since the same mask can mimic different vent characteristics, the same mask can be used on both blowers once set to the appropriate vent.

Another advantage of the invention is to provide different vents for different pressure ranges. For example, at low pressures, it may be appropriate to have a vent with large holes in order to provide sufficient vent flow. The same vent at higher pressures would have unnecessarily high vent flow which leads to increased noise. Hence in accordance with an embodiment of the invention, when a patient is using a generally low pressure treatment, they can utilize a first vent, but when treatment pressures are higher they can use a second vent.

Another advantage of the invention is that it provides a quick and simple system of replacing disposable vents. For example, certain styles of vents may clog easily and be designed for a single night's use. In accordance with an embodiment of the invention a vent assembly can comprise a set of “single use” vents. After a first night's use, the patient can switch to the second vent. After a second night's use, the patient can switch to a third vent, and so on.

In another form of the invention, sensors and/or indicators are included in the vent assembly as shown inFIGS. 20 & 21. The vent assembly300includes a shaft302and a sleeve304. The shaft302includes an orifice306which allows air to pass through. By rotating the sleeve304alternative vents308and310are aligned over the orifice306. The sensor detects which of the vents is being used and conveys the information to a flow generator controller. In one form the sensor has a different electrical resistance, depending on the vent being used, as shown inFIG. 21and discussed further below. Sensor information may be conducted to the flow generator controller via wires along the air delivery conduit, or wirelessly, for example via a BLUETOOTH™ compatible system. The flow generator controller receives the sensor information and adjusts the parameters for the algorithms controlling therapy. Alternatively or additionally the vent assembly includes an indicator of vent position which may be visual, aural, tactile or some combination. As shown inFIG. 20, the vent assembly300includes an alignment arrow312moulded on the shaft302. Each vent308,310has an adjacent indicator (e.g. an arrow, dot or some other shape)309,311molded onto the sleeve304. The indicators may present a characteristic feel depending on the vent position so that they can be recognized in the dark. Additionally or alternatively, the vent assembly may exhibit a characteristic “click” as its vent is changed as shown inFIG. 20. The vent assembly may display a tag of different color depending on the vent position.

FIG. 21shows schematic of a slidable cover350forming part of the vent assembly similar toFIG. 11-14. When the appropriate vent352or354is aligned over an orifice (not shown), a corresponding resistor353or355electrically connects to a connector356which is in electrical communication with a flow generator controller358. Thus the flow generator controller358can detect which vent is being used and adjust pressure, flow or some other parameter of the blower as necessary.

This ability to communicate the selected vent to the flow generator allows for the flow generator to provide an appropriate response. A response may be to make an adjustment to its control algorithm taking into account the characteristic of the recognized selected vent. In addition or alternatively the flow generator may not operate in treatment mode or only operate within a predetermined pressure range when the user attempts to commence treatment having selected the less than optimum vent or the characteristics of the selected vent is not recognized by the flow generator.

In addition or alternatively the flow generator may prompt the selection of the optimum vent for a given control algorithm or air circuit configuration. Having detected the selection of a vent the flow generator may present a messages to the user. The message may be by way of an auditory or visual alarm. Through use of the flow generator status display (typically an alpha-numeric LCD panel) the flow generator may present a statement as to the detected vent condition and either confirm its appropriateness or suggest corrective action.

As the invention allows for a selection to be made between vents the flow generator may communicate to the user that a selected vent is satisfactory or unsatisfactory depending on the treatment pressure range it is set to deliver. For a higher pressure range the flow generator may prompt the use of a small hole vent while suggesting a larger hole vent where it is to operate in the lower pressure range.

If the flow generator can detect a deterioration of vent performance over time (for example due to the vent becoming blocked during one treatment session or over a number of sessions) then a prompt may be given for the selection of an alternative vent.

Such a system is of use where available air circuit configurations may include a humidifier. If the flow generator detects that a small hole (e.g. mesh vent) is selected while the air circuit is set up to operate with a humidifier the flow generator may send a message to the user in order to prompt the selection of a more suitable vent.

Flow and noise levels may thus be adjusted in accordance with the above embodiments. For example, by switching from a vent with large holes to a vent with small holes and/or foam, the flow and/or noise level can be reduced about 5-50%, preferably about 15-35%, and most preferably about 20-30%. In the embodiment ofFIGS. 11a-14, the flow for large holes may be in the range of about 45-55 l/min, while the flow for the small holes may be about 55-65 l/min. In other embodiments, the difference of flow between the smaller and larger holes may be more or less pronounced, depending on patient requirements and mask configuration.

Although the invention has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the application of the principles of the invention. Numerous modifications may be made therein and other arrangements may be devised without departing from the spirit and scope of the invention.

For example, in the embodiment shown inFIGS. 28aand28b, the mask, e.g., mask30inFIG. 1, may be provided with two or more elastic vent inserts each having different flow characteristics. InFIG. 28a, the vent31has a plurality of relatively larger holes33, while the vent35inFIG. 28bmay have a larger number of relatively smaller holes37. The clinician/patient may change the vent to best suit the desired noise and/or flow characteristics.