IMPROVED SLEEP APNOEA MASK ADAPTER

Abstract

A nasal adapter for a sleep apnoea mask that is adapted to fit into an existing mask or onto an existing air-line and adapted to make a close-fitting engagement with at least part of a patient's nose, wherein said adapter is constructed from a relatively hard material.

Claims

1-16. (canceled)

17. A nasal adapter for a nasal patient interface that delivers breathable gas to an entrance of a patient's airways during sleep, at a pressure elevated above atmospheric pressure in a range of 4 to 20 cm H.sub.2O, the nasal adapter comprising: a mask engaging side configured to attach to the nasal patient interface connected with an air supply tube and mask straps; and a nose-engaging side comprising a seal-forming structure made from a rigid material, wherein the nose-engaging side is personalised to the patient's nose contour using a digitising process; wherein the seal-forming structure is non-deformable in response to tightening of the mask straps or pressurised air received within the nasal adapter.

18. The nasal adapter of claim 17, wherein the nose-engaging side comprises a projection extending from the adapter in the form of a ring.

19. The nasal adapter of claim 18, wherein said ring is roughly triangular with curved vertices.

20. A nasal adapter for a sleep apnoea mask that is adapted to receive pressurized air from a pressurized air-line, and is adapted to engage with at least part of a patient's nose including the nostrils via a soft cushion, wherein said adapter is constructed from a relatively rigid material, and wherein the adapter is constructed such that the largest cross-sectional area of said soft cushion that engages with the pressurized air-line, and the cross-sectional area of the skin contact region of said adapter engaged with said patient's face have relative sizes such that a positive sealing coefficient for the mask is achieved, the cross-sectional area of the skin contact region being generally normal to the engaging force, said positive sealing coefficient arising where the rate of change of pressure experienced toward the patient's skin is greater than the rate of change of supplied air pressure.

21. The nasal adapter of claim 20, wherein the cross sectional area of the largest pressurised air cross section within the soft cushion (A.sub.A) minus the sum of the cross sectional areas defined by the internal edges of the skin contact region around the patient's nostrils (A.sub.N) is greater than the cross sectional area of the outer edge of the skin contact region (A.sub.S) minus the sum of the cross sectional areas defined by the internal edges of the skin contact region around the patient's nostrils (A.sub.N); said cross sections being defined as being normal to the axis along which the sealing force acts to press the nasal adapter onto the patient's face.

22. The nasal adapter of claim 21, wherein (A.sub.A-A.sub.N) is at least 5% larger than (A.sub.S-A.sub.N).

23. The nasal adapter of claim 21, wherein (A.sub.A-A.sub.N) is at least 10% larger than (A.sub.S-A.sub.N).

24. The nasal adapter of claim 21, wherein (A.sub.A-A.sub.N) is at least 20% larger than (A.sub.S-A.sub.N).

25. The nasal adapter of claim 21, wherein (A.sub.A-A.sub.N) is no more than 50% larger than (A.sub.S-A.sub.N).

26. The nasal adapter of claim 17, wherein the rigid material is a material selected from the group comprising: acrylonitrile butadiene styrene (ABS) plastic, polycarbonate plastic, polyurethane, polylactic acid (PLA) plastic and polyethylene plastic.

27. The nasal adaptor of claim 17, wherein said nasal adaptor has been manufactured by a process of 3D printing.

28. The nasal adaptor of claim 17, wherein said adaptor is coated in a biocompatible and bacterially resistant material.

29. The nasal adaptor of claim 28, wherein said adaptor is coated in polyurethane.

30. The nasal adaptor of claim 17, further comprising a pad for contact with the patient's nose bridge, the pad being made from a low to moderate durometer material.

31. The nasal adaptor of claim 17, wherein the mask engaging side is configured to securely attach to the nasal patient interface.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0032] FIG. 1 is a diagram of a mask adapter according to the invention, shown from the CPAP mask engaging side.

[0033] FIG. 2 is a diagram of the adapter of FIG. 1 shown from the nose-engaging side.

[0034] FIG. 3 is a diagram of an alternative mask adapter according to the invention, shown from the CPAP mask engaging side.

[0035] FIG. 4 is a diagram of the adapter of FIG. 3 shown from the nose-engaging side.

[0036] FIG. 5 is a diagram of the adapter according of FIG. 1 fitted to a CPAP nasal mask.

[0037] FIG. 6 is a frontal schematic view illustrating the cross sectional areas of a mask adapter according to the invention.

[0038] FIG. 7 is a schematic side view that illustrates the overall sealing force applied to a nasal adapter according to the invention.

[0039] FIG. 8 is a schematic graph illustrating the general relationship between air pressure at the skin and in the mask at different sealing coefficients.

DETAILED DESCRIPTION OF THE INVENTION

[0040] One embodiment of the invention resides in a relatively rigid adapter that may be applied to a sleep apnoea treatment apparatus, said apparatus comprising a CPAP machine, an attached air delivery line and a nasal mask adapted to deliver the air to a patient's nostrils, in the form of a nasal mask adaptor that delivers air from the air-line to the patient's nostrils in a more comfortable an efficient manner that known in the prior art.

[0041] The adapter is shaped to fit snugly to the patient's nose on one side, and adapted to fit on to the pliable silicone nose-piece or mask of existing CPAP equipment, such as those produced by Fisher & Paykel Healthcare, ResMed and Philips Respironics.

[0042] In a preferred embodiment the nasal mask interface geometry is shaped so as to maintain an airtight seal over as wide a range of movement as possible of the mask body in relation to the adapter and so provide a robust seal as dislodging forces act on the mask body. A suitable retaining lip may be provided at the opening of the nasal mask interface to conveniently prevent the adapter from falling out of the mask whenever the mask is taken off the face. During night-time movement the silicone skirt typically does not slide on the adapter but rather tends to freely roll over the surface.

[0043] In other preferred embodiments the relatively rigid skin contact portion is connected to the rigid mask platform with a flexible tube-like member securely attached to both the rigid skin contact portion and the rigid mask platform. The rigid mask platform can move around due to dislodging forces from the straps and the air supply tube while the air pressure and possibly the spring-like nature of the flexible tube-like member keep the relatively rigid skin contact member in place on the patient's face.

[0044] In other embodiments a spring-like member may be used to keep the relatively rigid skin contact member in place on the patient's face.

[0045] Turning to FIGS. 1 and 2, there is shown a nasal adaptor according to the invention, from various angles.

[0046] FIGS. 3 and 4 show similar views of an alternative design for the nasal adapter that is adapted to fit to a differently configured CPAP mask.

[0047] The nasal adapter 5 is constructed from a hard, bio-compatible polymer such as acrylonitrile butadiene styrene (ABS) plastic, polycarbonate plastic, polyurethane, poly lactic acid (PLA) plastic and polyethylene plastic. It attaches to the mask body on the air supply side, and has a surface 10 adapted to the exact contour of the patient's nose and nostrils on the patient side, as illustrated in FIG. 2. This contour is achieved by digitising the surface of the patient's nose and creating an exact match for their nose by e.g. 30 printing.

[0048] This embodiment of the adapter further features a continuous wall 15 that extends from the machine side surface 20. The profile of the wall 15 is in the shape of a rounded triangle and it is shaped to fit sealingly inside the CPAP nasal mask shown on FIG. 5.

[0049] The wall 15 also features a lip 25 at the periphery to assist in retention of the adapter in the pliable nasal mask when the mask is removed from the face.

[0050] FIG. 4 shows the adapter fitted in to a pliable silicone nasal mask 30. The patient-side is contour may be achieved by using a digitising process to capture the exact contours of the patient's face, which is then used to create the mask via a 30 printing process.

[0051] In engineering the concept of a free body diagram is commonly used to analyse forces on a rigid body. The forces on the main mask body are due to the straps, the pressurized air, the skin contact pressure and the tugs from the air supply tube. Contact of the mask with a pillow or bedding is also a consideration. Comfort is increased by minimizing the maximum skin contact pressure by providing an even and light pressure over a large skin area. The ala, i.e. the outer soft rounded portion of the nostril, will itself tend to bellow out into a rigid nose adapter that seals around the nostril openings.

[0052] Nasal pillow masks typically have a strap either side of the mask that each pull up somewhere over the ear. The plane formed by the two strap forces needs to be positioned to deliver a retaining force resulting in as even as possible a pressure where the mask and skin form an airtight seal. Masks with three or more straps, or even with a rigid member extending to contact the forehead, provide a more robust placement but with greater obstruction of the area in front of the face.

[0053] The mask's internal air pressure exerts an ejection force onto the adapter. This force can be approximated by multiplying the cross-section of the air cavity in the silicone cushion that is normal to the ejection force direction by the air pressure. The larger the cross-section of the pressurised air, the greater the ejection force and therefore the greater the strap force needed to oppose it. The minimum pressurized cross section of a theoretically ideal mask is equal to the nostril opening cross section.

[0054] Turning to FIGS. 6 and 7, one can see frontal and side views of an adapter according to the invention that illustrates the overall sealing force, F.sub.A, applied to the nasal adapter by both the silicone cushion and the pressurized air and the equal and opposite opposing force, F.sub.S, resulting from both skin contact pressures and any pressurized air acting on the face side of the nasal adapter.

[0055] The instantaneous sealing coefficient is defined as the rate of change of the average skin contact pressure to the rate of change of the pressurized air pressure minus one. The formula is

C.sub.S=(P.sub.S|P.sub.A)1

where [0056] C.sub.S is the sealing coefficient [0057] P.sub.S is the average skin contact pressure [0058] P.sub.A is the pressurized air pressure

[0059] A positive sealing coefficient has the average skin pressure increasing and decreasing faster than changes to the pressurized air pressure. Conversely a negative sealing coefficient has the average skin pressure increasing and decreasing more slowly. The sealing coefficient is generally fairly constant over the pressure ranges used with CPAP therapy. The use of a constant sealing coefficient simplifies the following explanation. A constant sealing coefficient, although common, is not necessary for the present invention as the same principles would still apply.

[0060] The average skin contact pressure can be written as a function of the air pressure as

P.sub.S=(1+C.sub.S)P.sub.A+K

where K is a constant.

[0061] To provide an airtight seal the skin contact pressure just adjacent to the boundary where the skin, the nasal adapter and the pressurized air meet must be greater than the pressurized air pressure otherwise the air will push the skin aside until it leaks out. A nasal adapter with a negative sealing coefficient will eventually leak at some point as the pressurized air pressure is increased while a nasal adapter with a positive sealing coefficient will not, as in the latter case the force applied by the inflation of the mask tends to push the adapter toward the face and as that pressure (and therefore the force) increases, its effect is to seal the adapter ever-tighter on to the face. This is illustrated by the graph shown in FIG. 8.

[0062] Skin contact pressures are very difficult to measure. It is more convenient and practical to use cross sectional areas to estimate the sealing coefficient. FIG. 6 shows cross sectional areas that are normal to the axis along which the forces F.sub.A and F.sub.S act. The cross sectional area specifying the area measurement A.sub.A is the largest cross section of the pressurized air cavity. The cross sectional area specifying the area measurement A.sub.S is that of the outside of the skin contact region. The sum of the cross sectional areas defined by the internal edges of the skin contact region specify the area measurement A.sub.N.

[0063] The sealing and reaction forces, F.sub.A and F.sub.S, are a function of pressurized air pressure, P.sub.A, average skin contact pressure, P.sub.S, and the relevant cross sectional areas.

F.sub.A=P.sub.A(A.sub.AA.sub.N)

F.sub.S=P.sub.S(A.sub.SA.sub.N)

For equilibrium

F.sub.S=F.sub.A

So, for changes in pressurized air pressure

P.sub.S(A.sub.SA.sub.N)=P.sub.A(A.sub.AA.sub.N)

hence

P.sub.S|P.sub.A=(A.sub.AA.sub.N)|(A.sub.SA.sub.N)

Substituting to make C.sub.S a function of the three cross sectional areas;

C.sub.S=(P.sub.S|P.sub.A)1

C.sub.S.sub._.sub.AREA=((A.sub.AA.sub.N)|(A.sub.SA.sub.N))1

where C.sub.S.sub._.sub.AREA is an approximation of C.sub.S.

[0064] FIG. 8 is a graph representing a plot of pressure force applied at the patient's skin as the pressure supplied by the CPAP machine is increased, for different theoretical adapter designs.

[0065] In plot 1, the force increase at the patient's nose is equal to the force applied by increase in pressure from the CPAP machine. This represents a neutral sealing coefficient of zero.

[0066] In plot 2, the force at the patient's nose rises less sharply than the force applied by the pressurized air. It begins above plot 2 by virtue of e.g. the additional force applied by the mask straps. However, as the air pressure is increased the likelihood of leakage increases, and the point at which plot 2 intersects with plot 1, the air pressure force applied by the CPAP machine has overcome the mask's ability to seal to the patient's face, and so leakage will occur.

[0067] In plot 3, the force at the patient's nose rises more sharply than the force applied by the pressurized air from the CPAP machine. So the plot always remains above plot 1, meaning that within practical bounds, the mask will be unlikely to leak because the increase in CPAP pressure will simply cause the adapter to adhere more robustly to the patient's face.

[0068] The practical upshot of this phenomenon is that, because force is a function of area times pressure, it has been found that where the cross sectional surface area of the part of the adapter that contacts the patient's face is smaller than the cross sectional surface area that is in contact with either the pressurized air or the silicone cushion the greater the increase in average skin contact pressure for an increase in air pressure. This makes it harder for the mask to be dislodged by random movements of the patient during sleep, and makes for a more comfortable overall experience for the patient.

[0069] It also means that a relatively small adapter can be designed that still adheres well to the face.

[0070] For example, it has been observed that where the contact area on the face of the adapter is about 20% smaller than the contact area with the mask on the of the air supply line side of the adapter, the balance of forces in the system resolve to a net force pushing the adapted toward the patient's face.

[0071] One process for manufacturing a preferred embodiment involves digitizing the patient's nose and surrounding face to create a 30 computer surface. This surface is used to create a 30 model of the custom nose adapter including any features to attach it to the mask.

[0072] Preferably, the adaptor is made from a material selected from the group comprising: Acrylonitrile butadiene styrene (ABS) plastic, polycarbonate plastic, polyurethane, poly lactic acid (PLA) plastic and polyethylene plastic. Other bio-compatible materials may also be used.

[0073] As stated above, the adaptor may be made from a rigid material selected from the group comprising: Acrylonitrile butadiene styrene (ABS) plastic, polycarbonate plastic, polyurethane, poly lactic acid (PLA) plastic and polyethylene plastic. The foam pad on the nose bridge is made from a low to moderate durometer material such as neoprene and polyolefin. Other bio-compatible materials may also be used.

[0074] Advantageously, the nasal adaptor may be produced by a combination of digitisation of the patient's nose and fabrication via a process of 30 printing followed by surface preparation to provide a smooth and hygienic surface. This technique provides a very closely fitting and comfortable rigid nasal adaptor, due to the accuracy and precision of the digitisation and 30 printing process, and which tends not to be susceptible to bacterial or other fouling due to the hygienic surface finish.

[0075] A 30-printed material may have tiny air-filled voids and some surface porosity that can harbour bacteria. In a preferred embodiment the 30 printed part is coated in a biocompatible and bacterially resistant material, for example polyurethane. The coating could be sprayed, brushed, dipped or otherwise applied to the 30 printed part. In another embodiment the 30 printed part is dipped in a liquid solvent or bathed in a solvent gas to partially liquefy and reform the exterior surface to form a hygienic and non-porous surface finish.

[0076] Even though there are benefits in a rigid nose adapter there may be a market preference for a semi-rigid or soft nose adapter.

[0077] In other embodiments the nose adapter includes the air diffuser. In one such embodiment a second wall with small holes forming the air diffuser is offset from the wall that is in contact with the outside of the nose. This provides a larger diffuser area than is common in existing masks and so will have slower air movement for the same airflow rate.

[0078] In other embodiments the nose adapter includes the air diffuser. In one such embodiment a second wall with small holes forming the air diffuser is offset from the wall that is in contact with the outside of the nose. This provides a larger diffuser area than is common in existing masks and so will have slower air movement for the same airflow rate.

[0079] It will be appreciated by those skilled in the art that the above described embodiments are merely a few examples of how the inventive concept can be implemented. It will be understood that other embodiments may be conceived that, while differing in their detail, nevertheless fall within the same inventive concept and represent the same invention.