Nasal mask for CPAP having ballooning/moulding seal with wearer's nose and facial contours

A nasal mask which is suitable for use in a continuous positive airway pressure system. The mask has a face contacting portion mounted to a shell which is sized and shaped to overfit the nose region of an intended wearer, and the face contacting portion is in the form of a distendable membrane which is moulded from an elastic plastics material. The distendable membrane and the shell together define a chamber, and pressurised gas admitted to the chamber causes the membrane to distend outwardly from the shell. When placed in contact with the face of the wearer, the distendable membrane is caused to overlay the covered facial regions and, under the influence of the pressurised gas, to conform three-dimensionally with the contours of the overlayed regions. An orifice is formed within the membrane and is shaped and positioned to admit gas from the chamber to the nasal passages of the wearer.

FIELD OF THE INVENTION 
This invention relates to a nasal mask and, in particular, to a mask that 
has the facility to conform to the facial contours of a wearer. 
BACKGROUND OF THE INVENTION 
Nasal masks currently are employed for various purposes, including for the 
delivery of oxygen to persons who suffer lung disease or who are exposed 
to rarefied atmospheres, for administering anaesthesic gases and for 
delivering pressurised air to persons who suffer from such disorders as 
sleep apnea. The masks usually are moulded from a relatively soft, 
resilient plastics material and they are shaped during manufacture to 
match the facial contours of an average intended wearer. However, a 
problem with the known types of masks is that, because individuals vary so 
much from the average, the masks must be forced against their inherent 
resiliency to deform and so adapt to the shapes of the users in order to 
avoid gas leakage. This requires that the masks be secured firmly by 
retaining straps or harnesses in order to prevent air leakage and, 
depending on the degree of deformation required in any given case, may 
produce discomfort, irritation or even ulceration of the upper lip and/or 
the nasal bridge where there is little cushioning from subcutaneous 
tissue. Thus, the retaining force normally is distributed over a 
relatively small sealing area defined by the peripheral edge of the mask 
and this causes a relatively high localised pressure to be exerted on the 
face of the wearer. Also, because the sealing area is relatively small in 
the currently employed masks, minor dislocation of a mask may produce a 
significant leakage path for gas. 
Attempts have been made to overcome the above difficulties by shaping 
perimeter edges of some masks in such a manner that the edges tend to move 
with a rolling action when a mask is pushed into contact with a wearer's 
face. This shaping permits differential movement around the perimeter of a 
mask and facilitates adaptation of the mask to the facial contours of the 
wearer. 
Also, U.S. Pat. No. 4,971,051 discloses a mask which has been developed in 
an attempt to provide both comfortable and conformable perimeter sealing, 
the mask having a flexible pneumatic cushion formed around its perimeter 
and/or being provided with a so-called flap ring which is formed as an 
adjunct to the mask. The flap ring comprises a flexible membrane which is 
affixed to the perimeter of the mask and it acts in the manner of a flap 
valve when blown against a wearer's face by air delivered to the interior 
of the mask. 
A problem which is inherent in a mask of the type disclosed in U.S. Pat. 
No. 4,971,051 is that the flap ring is constrained by its attachment to 
the perimeter seal of the mask and its freedom to adapt to facial contours 
is limited. Moreover, again because the flap ring is attached to the 
perimeter seal of the mask, any movement of the perimeter seal may cause 
movement of the flap ring relative to the wearer's face and thereby open a 
path through which gas may leak. Similarly, movement of the flap ring may 
cause stresses to be imposed on the perimeter seal, so that a path may be 
created through which gas may leak. 
SUMMARY OF THE INVENTION 
In contrast with the prior art masks, the present invention provides a 
nasal mask which comprises: 
(a) a face contacting portion in the form of a distendable membrane which 
is shaped to define a chamber, the membrane being formed from an 
elastomeric material and the chamber having a thin walled externally 
convex end region which is arranged in use of the mask to be depressed by 
and to accommodate the nose of a wearer. 
(b) a gas supply port communicating with the chamber and connectable to a 
supply of pressurised gas which, when admitted to the chamber, causes the 
membrane to distend outwardly, 
(c) retaining means for holding the face contacting portion in contact with 
the face of the wearer whereby the end region of the chamber is caused to 
overlay at least the nose portion of the wearer's face and, under the 
influence of the pressurized gas, to conform with the contours of the 
overlayed region, and 
(d) at least one orifice formed within the membrane, the orifice being 
shaped and positioned to admit gas from the chamber to the nasal passages 
of the wearer. 
The face contacting portion of the mask according to the present invention 
may be considered as having a shape which is unrelated to that of the 
intended wearer until such time as the mask is charged with gas and fitted 
to the wearer. However, when so charged and fitted, the membrane is caused 
to distend, to overlay the covered facial regions and to conform 
three-dimensionally with the facial contours of the wearer. In so doing, 
the membrane is caused to deform locally to accommodate individual facial 
projections and depressions, and distortions of the type that might 
otherwise create peripheral air leakage passages are thereby avoided. This 
is to be contrasted with the prior art masks which are moulded or are 
otherwise constructed with a clearly defined perimeter shape which is 
intended to match that of an intended wearer and which, except in the 
event of a perfect fit, must be distorted to match the features of the 
wearer. 
Thus, the mask in accordance with the present invention may be viewed as a 
self-conforming mask which, by overlaying and conforming to the shape of 
the wearer provides an inherently large self-sealing area. 
PREFERRED FEATURES OF THE INVENTION 
The gas supply port and the retaining means may be secured to or be formed 
integrally with the distendable membrane itself. However, the distendable 
membrane is preferably mounted to a shell which is shaped to overfit the 
nose region at least of the wearer and which co-operates with the membrane 
to define the chamber. When this preferred arrangement is employed the 
retaining means would normally be connected to the shell and the gas 
supply port would normally be provided in a wall of the shell. 
The shell is preferably moulded from a rigid plastics material and the 
membrane, which normally would be moulded from an elastic plastics 
material, is preferably removably mounted to a peripheral portion of the 
shell. 
The distendable membrane is preferably secured to or moulded as an 
extension of a connector moulding which is arranged to mount the membrane 
to the shell. The connector moulding may be configured to contact facial 
regions of the wearer and, thus, be employed to locate the mask in a 
desired position on the face of the wearer. However, it is intended that 
the connector moulding should not interfere in any way with the face 
conforming feature of the distendable membrane. 
When the membrane is formed with a single orifice, such orifice may be 
formed as an aperture which is shaped and sized to permit unimpeded 
communication between the chamber and the nasal passages of a wearer to 
whom the mask is fitted. Alternatively, the aperture may be shaped and 
sized to permit communication between the chamber and the nares-mouth 
region of the wearer, so that the mask may be employed as a full face 
mask. As a further alternative, two apertures may be provided for aligning 
with the respective nasal passages. However, when the membrane is formed 
with two orifices they preferably will be provided within respective 
nipples which are shaped and positioned to project into the nasal passages 
of the wearer to whom the mask is fitted. The nipples are preferably 
moulded integrally with the remaining portion of the membrane, so that 
they may be positioned and shaped elastically to match the wearer.

DETAILED DESCRIPTION OF THE INVENTION 
As illustrated in FIG. 1, the CPAP circuit comprises a motor driven pump 10 
which is arranged to provide an air supply to a mask 11 which is fitted to 
a wearer 12 in the manner shown in FIG. 8. The air is supplied at a flow 
rate greater than the rate at which the air would normally be inspired in 
order to create backpressure within the circuit, whilst the wearer 
maintains regular breathing, in order that a membrane portion 13 of the 
mask will be caused to distend in the manner which is to be described in 
greater detail below. A motor speed controller 14 is located in circuit 
with the pump lo and functions effectively to control the air pressure in 
the system to meet the requirements of individual persons. Also, a 
modulator 15 may optionally be located in circuit with the pump for 
modulating the pressure at which the air is delivered to the mask. The 
modulator is arranged , to provide pressure modulation within the range of 
5% to 50% and at a frequency in the range 5 Hz to 60 Hz in order to effect 
stimulation of respiratory tract muscles in the wearer 12. 
The air is conveyed to the mask 11 by way of a delivery line 16 and a 
supply port 18 in a shell portion 19 of the mask. 
As illustrated, the mask is in general shaped to cover the nose area of the 
person 12 to whom the air is to be supplied and does not cover the mouth 
of the person. Thus, air from the supply port 18 is directed into the 
upper air passage of the person by way of the mask 11 and the person's 
nasal passages. However, it will be understood that the primary feature of 
the mask, namely the distendable membrane 13 may be incorporated in a full 
face mask, in which case the mask will be shaped to cover both the nose 
and mouth of the person. 
Excess air, that is air which is not inspired during normal breathing, is 
vented to the atmosphere by way of a multi-aperture orifice 20 in the 
shell portion 19 of the mask 11. The orifice 20 presents a resistance to 
the air flow, so that a continuous positive pressure is maintained within 
the circuit and, thus, within the mask. By maintaining this pressure, the 
air which is breathed by the person 12 to whom the mask is fitted causes a 
pressure to be maintained in the upper airway of the person during normal 
inspiration and expiration. 
Air which is expired by the person 12 is also vented to atmosphere by way 
of the orifice 20. 
The shell 19 of the mask is moulded from a rigid plastics material and it 
has a body portion 24 around which a flange 25 extends. As can best be 
seen from FIG. 5, a lip 26 projects forwardly of the body portion 24 and a 
connector moulding 27, which carries the distendable membrane portion 13, 
overfits the lip 26. The interior of the shell 19 forms a cavity 28 which 
is defined in part by the membrane 13 and the connector moulding 27, and 
air is admitted to the cavity 28 from the support port 18. 
An arm 29 extends upwardly from the body portion 24 of the shell and is 
angled such that an upper head engaging portion 30 of the arm will contact 
the forehead of the person 12 to whom the mask is fitted. A pad 31 of 
cushioning material is adhered to the head engaging portion 30 and slots 
32 are located in that portion to accommodate harness straps 42 which are 
used to secure the mask to the head of the person 12. Additional slots 33 
are formed within the peripheral flange 25 of the shell body portion 24 
for receiving further harness straps 43. 
The connector moulding 27 has a peripheral flange 34 in which a 
circumferential recess 35 is located. The recess 35 is positioned to 
overfit the shell lip 26 and the recess serves to hold the moulding 27 
captive to the shell 19. The moulding 27 might be configured to provide an 
elementary support for the membrane 13 or, in an alternative arrangement, 
the membrane might be formed integrally with the moulding 27. However, as 
illustrated, the moulding 27 is formed separately from the membrane 13 and 
includes an integral wall 36 which is profiled at region 37 to locate 
around the nasal bridge of the wearer 12 and at region 38 to fit against 
the upper lip of the wearer. 
The membrane 13 is formed as a thin-walled balloon-like pocket, and is 
moulded from a soft, flexible plastics material. The membrane is adhered 
to the wall 36 of the moulding 27, and an aperture 39 is formed within the 
membrane 13. The aperture 39 is shaped, positioned and sized to provide 
air passage communication between the chamber 28 of the mask and the nasal 
passages of the wearer 12, and various size membranes 13 may be provided 
to accommodate different size wearers, for example adults and children. 
A small orifice (not shown in the drawings, may be provided in the membrane 
to act as a vent for any moisture that might otherwise build up between 
the mask and the wearer's face. 
In the alternative arrangement shown in FIGS. 6 and 7, the air passage 
between the chamber 18 of the mask and the nasal passages of the wearer is 
provided by way of two orifices 40 which are located within respective 
nipples 41. The nipples themselves are shaped, positioned and sized to fit 
within the nasal passages of the wearer 12. 
As shown in the sequential illustrations of FIGS. 8A to 8C, when fitting 
the nasal mask to the wearer 12, the mask is first connected to the 
pressurised air supply so that the membrane 13 is caused to billow or 
distend outwardly from the shell 19. A face contacting portion of the mask 
is then placed in contact with the wearer's nose and is positioned such 
that the aperture 39 or the nipples 41 align with the nasal passages. In 
this condition, as shown in FIG. 8B of the drawings, the membrane 13 will 
begin moulding around the nose of the wearer. 
As the mask is pushed further into position, the shell 19 is moved closer 
to the wearer's nose and, under the influence of the air pressure within 
the chamber 28, the membrane 13 moulds completely around the nose of the 
wearer and conforms to the facial contours which are actually overlayed by 
the membrane. The mask is then pushed into its final position, as 
indicated in FIG. 8C and the retaining harness, indicated by the chain 
dotted lines 42 and 43, is positioned around the wearer's head to retain 
the mask in position.