A nasal mask

Abstract: A CPAP system is described for improved respiratory therapy of patients. In particular a patient interface is disclosed with an outlet vent with lower noise levels and more diffused outlet flow over prior art outlet vents. The outlet vent includes a main vent which is diffused and muffled and a higher resistance vent provided in case the main vent is blocked. The outlet vent is removable for easy maintenance and provides indication to the user when maintenance is required. The outlet vent described may be used on nasal masks, mouthpieces and patient interfaces generally.

Description: This invention relates to patient interfaces particularly though not solely to nasal mask for use in providing CPAP therapy to patients suffering from obstructive sleep apnoea (OSA). BACKGROUND OF THE INVENTION In the art of respiration devices, there are well known a variety of respiratory masks which cover the nose and/or mouth of a human user in order to provide a continuous seal around the nasal and/or oral areas of the face such that gas may be provided at positive pressure within the mask for consumption by the user. The uses for such masks range from high altitude breathing (i.e., aviation applications) to mining and fire fighting applications, to various medical diagnostic and therapeutic applications. One requisite of such respiratory devices has been that they provide an effective seal against the user's face to prevent leakage of the gas being supplied. Commonly, in prior mask configurations, a good mask-to-face seal has been attained in many instances only with considerable discomfort for the user. This problem is most crucial in those applications, especially medical applications, which require the user to wear such a mask continuously for hours or perhaps even days. In such situations, the user will not tolerate the mask for long durations and optimum therapeutic or diagnostic objectives thus will not be achieved, or will be achieved with great difficulty and considerable user discomfort. Where such masks as those used above are used in respiratory therapy, in particular treatment of obstructive sleep apnea (OSA) using Continuous Positive Airway Pressure (CPAP) therapy, there is generally provided in the art a vent for washout of the bias flow or expired gases to the atmosphere. Such a vent may be provided for example, as part of the mask, or in the case of some respirators where a further conduit carries the expiratory gases, at the respirator. The washout of gas from the mask is essential to ensure that carbon dioxide build up does not occur over the range of flow rates. In the typical flow rates in CPAP treatment, usually between 4cm H 2 O to 20cm H 2 O, prior art attempts at such vents have resulted in excessive noise causing irritation to the user and concentrated flows of gases irritating any bed partners. Various approaches have been developed in the prior art to attempt to reduce the noise when CPAP therapy is provided. For example, in PCT Patent Application No. WO98/34665 it has been proposed that the vent include a resilient plug with rounded edges at the apertures to reduce noise. In PCT patent application no WO00178382 a vent is provided with a semi annular flap. However, these prior art methods are not entirely satisfactory in eliminating the extra noise created by a vent at the mask. In WO98/48878 discloses a breathing mask including a muffled air discharge opening that is connected to the tubing supplying gases to a mask. The discharge opening is muffled by way of a tubular shaped exchangeable filter sitting within a tubular pipe extending from the opening. SUMMARY OF INVENTION It is an object of the present invention to attempt to provide a nasal mask which goes some way to overcoming the abovementioned disadvantages in the prior art or which will at least provide the industry with a useful choice. Accordingly the invention consists in a device for delivering a supply of gases to a user as defined in claim 1. Preferred embodiments are defined in claims 2-8. To those skilled in the art to which the invention relates, many changes in construction and widely differing embodiments and applications of the invention will suggest themselves without departing from the scope of the invention as defined in the appended claims. The disclosures and the descriptions herein are purely illustrative and are not intended to be in any sense limiting. The invention consists in the foregoing and also envisages constructions of which the following gives examples. BRIEF DESCRIPTION OF THE DRAWINGS One preferred form of the present invention will now be described with reference to the accompanying drawings in which; Figure 1 is a block diagram of a humidified continuous positive airway pressure (CPAP system) as might be used in conjunction with the present invention, Figure 2 is an illustration of a nasal mask which may be used with the present invention, Figure 3 is a front view of a nasal mask illustrating a headgear securement to the mask, Figure 4 is a perspective view of a mask illustrating a plurality of engaging clips to connect to the sliding strap Figure 5 is a perspective view of a mask showing a sliding strap clipped into the engaging clips, Figure 6 is a side view showing the sliding strap, Figure 7 is a perspective view of the mask illustrating the outlet vents in accordance with the present invention, Figure 8 is a perspective view of the mask illustrating the vent cap in place, and Figure 9 is a perspective view of the vent cap. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention provides improvements in the field of CPAP therapy. In particular an outlet is described which is quieter and has a more diffused outlet flow. It will be appreciated that the nasal mask as described in the preferred embodiment of the present invention can be used in respiratory care generally or with a ventilator but will now be described below with reference to use in a humidified CPAP system. It will also be appreciated that the outlet vent described is equally applicable to all forms of patent interface, in particular a mouth piece. With reference to FIG. 1 a humidified Continuous Positive Airway Pressure (CPAP) system is shown in which a patient 1 is receiving humidified and pressurised gases through a nasal mask 2 (or other types of patient interface as appropriate) connected to a humidified gases transportation pathway or inspiratory conduit 3. It should be understood that delivery systems could also be VPAP (Variable Positive Airway Pressure) and BiPAP (Bi-level Positive Airway Pressure) or numerous other forms of respiratory therapy. Inspiratory conduit 3 is connected to the outlet 4 of a humidification chamber 5 which contains a volume of water 6. Inspiratory conduit 3 may contain heating means or heater wires (not shown) which heat the walls of the conduit to reduce condensation of humidified gases within the conduit. Humidification chamber 6 is preferably formed from a plastics material and may have a highly heat conductive base (for example an aluminium base) which is in direct contact with a heater plate 7 of humidifier 8. Humidifier 8 is provided with control means or electronic controller 9 which may comprise a microprocessor based controller executing computer software commands stored in associated memory. Controller 9 receives input from sources such as user input means or dial 10 through which a user of the device may, for example, set a predetermined required value (preset value) of humidity or temperature of the gases supplied to patient 1. The controller may also receive input from other sources, for example temperature and/or flow velocity sensors 11 and 12 through connector 13 and heater plate temperature sensor 14. In response to the user set humidity or temperature value input via dial 10 and the other inputs, controller 9 determines when (or to what level) to energise heater plate 7 to heat the water 6 within humidification chamber 5. As the volume of water 6 within humidification chamber 5 is heated, water vapour begins to fill the volume of the chamber above the water's surface and is passed out of the humidification chamber 5 outlet 4 with the flow of gases (for example air) provided from a gases supply means or blower 15 which enters the chamber through inlet 16. Exhaled gases from the patient's mouth are passed directly to ambient surroundings in FIG. 1. Blower 15 is provided with variable pressure regulating means or variable speed fan 21 which draws air or other gases through blower inlet 17. The speed of variable speed fan 21 is controlled by electronic controller 18 (or alternatively the function of controller 18 could carried out by controller 9) in response to inputs from controller 9 and a user set predetermined required value (preset value) of pressure or fan speed via dial 19. Nasal Mask Referring to Figure 2 a nasal mask, which may be used with the present invention, is shown in detail. The mask includes a hollow body 102 with an inlet 103 connected to the inspiratory conduit 3. The mask 2 is positioned around the nose of the user 1 with the headgear 108 secured around the back of the head of the patient 1. The restraining force from the headgear 108 on the hollow body 102 and the forehead rest 106 ensures enough compressive force on the mask cushion 104, to provide an effective seal against the patient's face. The hollow body 102 is constructed of a relatively inflexible material for example, polycarbonate plastic. Such a material would provide the requisite rigidity as well as being transparent and a relatively good insulator. The expiratory gases in the preferred embodiment of the present invention are expelled through a valve in the mask 300, or alternatively a further expiratory conduit (not shown), or any other such method as is known in the art. Mask Headgear Referring now to Figures 2 and 3 the headgear 108 is shown connected to the hollow body 102. Rather than traditional fixed or adjustable attachments the present invention utilises a sliding engagement between the headgear 108 and the hollow body 102. This is achieved with a loop 120, running through harnessing clips 122, 124 on either side of the headgear 108 and over the top of the hollow body 102. The loop 120 is reciprocally engaged with guides 126, 128 mounted on the top surface of the hollow body 102. The guides constrain the loop 120 but allow it to slide in and out, meaning the headgear 108 can move laterally, independently of the hollow body 102. The advantage to this is as the face is contorted during various sleeping positions the headgear is able to move with the changes in position while the mask is left in the correct position on the nose of the user and an effective seal is maintained. Additional guides 129, 130, 131 allow the user to adjust position of loop 120, giving ability to get different pressure on the seal depending on loop 120 position. To further ensure user comfort and effective pressure on the mask cushion 104, the headgear 108 may be constructed either using two straps running around the back of the user's head as shown in Figure 2 or with a partial skull cap or any other configurations as are known in the art. In this case the straps or partial skull cap would be constructed using neoprene but may also be constructed using any material as is known in the art which will be comfortable for the user. In a further example shown in Figures 4, 5 and 6 a nasal mask is illustrated using a sliding strap to attach the headgear 108 to the hollow body 102. The strap 200, shown in Figure 6 in isolation, is constructed of polyacetal (Delrin 500P NC010) using injection moulding techniques to give a polished finish. This material, similar to other nylon based derivatives, with its polished finish has a particularly low friction co-efficient, slides with respect to the hollow body 102 with very little resistance. As shown in Figure 4, the hollow body 102 includes a number of engaging clips 202, in use the sliding strap 200 snaps into place into the engaging clips 202 and can only be removed therefrom using a substantial force. This means that with any normal use the sliding strap 200 will stay retained within the engaging clips 202. It will also be appreciated from Figure 4 that a number of clips are so provided, in order to allow pressure from different angles for different face shapes. As shown in Figure 6 the sliding strap includes a mid-section 204 intended to reciprocate with the engaging clips 202, terminated at each end by loops 206, 208 which attach to the headgear. The first loop 206 is a full loop through which the headgear 108 is permanently attached with for example, a velcro strap. The loop 208 at the other end, is only a partial loop 210 designed so that a strap or loop from the headgear 108 can be easily slipped in or out of the open section 212 to allow easy removal and attachment of the mask. It must be noted that the claims appended relate specifically to the patient interface and outlet vent, to be described below. The above description related to the mask and mask headgear are intended to describe a specific embodiment of a patient interface which may be included in a patient interface with an outlet vent as described below. Outlet Vent As shown in Figures 7 to 9 the present invention includes an outlet vent 300 as part of the body portion. The outlet vent 300 includes a number of apertures 302 either moulded in the body portion 102 or drilled through after moulding. The apertures 302 are separated and to some extent surrounded by a number of partitions 304 which provide support for a filter cap which is installed over top of the apertures 302. The filter cap is designed primarily prevent what would otherwise be the noise generated from the flow of gases through the apertures 302 externally. This filter cap comprises a frame member 306 (shown in Figure 9) which snaps on over top of the partition 304 and holds in place a piece of filter medium 308 which sits over top of the partitions 304. The frame 306 includes large vents 307 such that the expiratory or bias flow from the mask flows out the apertures 302 through the filter medium 308 and out the vent 307. The piece of filter medium 308 is preferably Ecofilt brand filter medium (PM135) which is less prone to blocking from the humidity levels often found in such applications. The structure of the outlet vent allows for the filter medium to be replaced as and when necessary in an easy and efficient manner. The frame 306 can be easily removed, the filter medium 308 replaced and the frame 306 snapped on back in place. Further in the rare event of the filter medium blocking, auxiliary vents 310 are provided in the frame 306 which match up with gaps 312 in the partitions 304. As the auxiliary vents 310 are much smaller than the main vents 307 during normal use very little flow passes through them. If the filter medium 308 becomes blocked the flow is then forced through the auxiliary vents 310. This will be significantly more noisy than normal and will indicate the need for maintenance to the user. It will be appreciated that by providing such a system the present invention effectively minimises the noise generated by the outward flow of expiratory gases from the mask. The present invention is of a low maintenance type and when replacement of the filter medium is required, it is an easy and simply exercise. As well as reducing the noise level the flow through the outlet vent is more diffused. This avoids for example, a flow of gases directed at a sleeping partner or a similar flow directed at the patient, either of which causing restlessness or waking. The features disclosed in the foregoing description, in the claims and/or accompanying drawings may, both separately and in any combination thereof, be material for realising the invention in diverse forms thereof.

Claims: A device for delivering a supply of gases to a user (1) comprising: a patient interface (2) including a body portion (102), in use in fluid communication with said supply of gases and supplying said gases to said user (1), said body portion (102) having an outlet vent (300), at least one aperture (302) to allow passing of gases to the atmosphere and a removable diffusing member (308), characterised in that said outlet vent (300) includes a frame member (306) mountable over said at least one aperture (300), said diffusing member (308) juxtaposed between said frame member (306) and said at least one aperture (300) and wherein said frame member (306) and said body portion create a low resistance outlet (307) in parallel with a high resistance outlet (310), where said low resistance outlet (307) allows said gases to exit to said atmosphere through said diffusing member (308) and said high resistance outlet (310) allows gases to exit directly to said atmosphere. A device for delivering a supply of gases to a user (1) as claimed in claim wherein said diffusing member (308) in use diffuses and audibly muffles a substantial portion of the expired gases of said user (1). A device for delivering a supply of gases to a user (1) as claimed in claim 1 or 2 wherein during normal use the majority of said expired gases pass from said vent (300) and out through said low resistance outlet (307), whereby if the majority of said expired gases are substantially prevented from passing through said low resistance outlet (307), the majority of said expiratory gases pass out said high resistance outlet (310). A device for delivering a supply of gases to a user (1) as claimed in any one of claims 1 to 3 wherein said high resistance outlet (310) comprises apertures formed in said frame member (306) or in the intersection between the frame member (306) and said body portion (102). A device for delivering a supply of gases to a user (1) as claimed in any one of claims 1 to 4 wherein said high resistance outlet (310) is adapted such that in use if said low resistance outlet (307) is blocked or has significant increase in resistance said high resistance outlet (310) vents a sufficient flow gas so as to prevent rebreathing of carbon dioxide by said user (1). A device for delivering a supply of gases to a user (1) as claimed in any one of claims 1 to 5 wherein said diffusing member (308) is a disposable medium (308) that reduces the external audible noise level and diffusing the flow pattern that would otherwise occur from said gases flowing through said vent (300). A device for delivering a supply of gases to a user (1) as claimed in claim 6 wherein said disposable medium (308) is a filter material. A device for delivering a supply of gases to a user (1) as claimed in any of the proceeding claims wherein said patient interface (2) comprises a nasal mask (2) having a hard body portion (102), an inlet (3) to said body portion (102) receiving said supply of gases, sealing means (104) engaged with said body portion (102), and adapted to seal against the facial contours of said user (1), and means of securement (108) to said user (1) providing a compressive force on said sealing means (104) to ensure said supply of gases is delivered to a user 1 without significant leakage, said vent (300) comprising at least one aperture (302) in said body portion (102).

Inventors: GRADON LEWIS GEORGE, HAYCOCK MARK JOSEPH, MCAULEY ALASTAIR EDWIN, NIGHTINGALE CHRIS EARL, SMITH NICHOLAS CHARLES ALAN, GRADON, LEWIS, GEORGE, HAYCOCK, MARK, JOSEPH, MCAULEY, ALASTAIR, EDWIN, NIGHTINGALE, CHRIS, EARL, SMITH, NICHOLAS, CHARLES, ALAN
Applicants: FISHER & PAYKEL HEALTHCARE LTD, FISHER & PAYKEL HEALTHCARE LIMITED
Application year: 2001
Main classification: A61M16
IPC codes: A61M16, A62B18