Mask with gusset

Details Mask with gusset Mask with gusset

2002-12-19

2004-08-10

Lewis, Aaron J. (Department: 3761)

Surgery

Respiratory method or device

Face mask covering a breathing passage

C128S207130, C128S205250

Reexamination Certificate

active

06772760

ABSTRACT:

This invention relates generally to masks for use in respiratory therapy. One use is in CPAP treatment of Obstructive Sleep Apnea. However, the mask arrangements presented herein are useful in other types of respiratory therapy. In the quest for an improved mask arrangement for respiratory therapy, there are various design objectives—effectiveness of seal between the mask and the patient's face, good compliance with a prescribed therapy regime, and patient comfort. The present invention provides various embodiments of a novel mask arrangement, which offers several distinct advantages over known mask arrangements.
BACKGROUND
In respiratory therapy where air is delivered to the mask under pressure, it is important to maintain a good seal between the mask and the patient's face. Leaks between the mask and the patient's face can reduce the desired air pressure in the mask and create increased noise. Both can reduce the effectiveness of, and compliance with, the therapy. In the first instance, the prescribed treatment parameters are not being maintained. In the latter, the increased noise can disrupt the sleep cycle of both the patient and the patient's bed partner.
Leaks are especially prone to occur as the patient moves during the night. Drag and movement of the air delivery tube or the mask system as the patient turns or moves can alter the positioning and alignment of the mask with respect to the patient's face, which movement can be translated or transferred to the cushion seal, creating leaks. Thus, while the mask may initially be leak free when attached to the patient, leaks are prone to develop later in the night as the patient moves in bed, awakening the patient. Hence, patients may tighten straps more than is necessary for pressure requirements in order to reduce or prevent leaks that result from movement.
Many different mask systems are known. One broad group of known mask systems include a rigid shell, a face-contacting cushion and headgear. The shell typically encompasses the nose or nose and mouth. Some known shells encompass the entire face. The cushion is typically constructed from a soft material such as silicone. A headgear provides a means to secure the mask in position. One known form of headgear consists of an arrangement of straps.
Certain mask designs have been developed to increase the flexibility of the mask cushion to enhance patient comfort while maintaining an effective seal between the mask and the patient. The Bubble Cushion (a registered trademark of ResMed, Ltd.) Mask, covered by U.S. Pat. No. 5,243,971, the subject matter of which is incorporated herein by reference, uses a flexible cushion membrane attached to a mask shell and the pressure inside the mask system to assist in the seal of the cushion membrane itself against the skin or face of the user.
The ResMed Mirage (a registered trademark of ResMed, Ltd.) Mask System, is covered by, inter alia, U.S. Pat. No. 6,112,746, the subject matter of which is incorporated herein by reference, has a contoured, three-dimensionally shaped cushion having an outer face-contacting membrane spaced apart from an inner frame rim to both assist in the seal and increase the comfort of the patient. Neither of these masks incorporates an expanded gusset section for mounting the cushion to the mask to assist in sealing the mask to the patient (user).
A known fitting procedure with a known mask has been to supply the maximum air pressure to the mask that will be supplied to the mask during the therapy and to adjust the strap tension to the necessary level to prevent leaks at that maximum air pressure. However, in many therapy regimens, this maximum air pressure is often encountered only during a portion of the duration of the therapy and the mask air pressure is lower at other times during the therapy. Such is the case, for example, when using auto-titrating or variable pressure systems or during ramp-up when using CPAP systems. Thus, the strap tension is higher than necessary during significant portions of the therapy duration. Further, since leaks are disruptive of both the sleeping cycle and the prescribed therapy regimen, patients will often tighten the straps even more than is necessary to prevent leaks at the maximum encountered air pressure. In known masks, this higher than necessary strap pressure directly results in a higher than necessary force of the mask cushion on the patient's face, particularly as the pressure goes below the maximum mask air pressure.
See
FIG. 1
, which shows a force diagram for a known mask
110
having a cushion
130
attached to a rigid shell
120
. The cushion
130
includes a face-contacting portion
134
attached to a cushion sidewall
173
. The cushion sidewall
173
can be relatively flexible, as in the ResMed Bubble Cushion® mask, or relatively rigid, as in the ResMed Mirage® mask. Although the mask
110
would be in contact with the face
42
of a patient
40
(shown in phantom) in use, for purposes of clarity in this diagram (as well as the diagram of FIG.
10
), a flat foundation
43
is substituted for the patient's face
40
. The total force of prior art masks on the user's face F
m
has been found empirically to be given by the equation F
m
=F
c
+F
Ac
, where F
c
is the force of the cushion on the patient's face and F
Ac
is the force on the patient's face of the mask air pressure P inside of the perimeter of A
c
, the area of contact of the cushion with the patient's face. The force F
Ac
is given by the equation F
Ac
=PA
c
. Since the force F
c
is distributed around A
c
and is not merely located at two points on the cushion, as it might seem due to the limitations of the two-dimensional representation of
FIG. 1
, this force is shown in parentheses. Although A
c
is shown inward of the sidewall
173
as would be the case if the mask
110
had just been brought into contact with the user's face with a minimal contacting force, in practice, the face-contacting portion
134
tends to roll under when sufficient force is applied to the mask
110
to seal the mask to the user's face such that A
c
can expand outward, toward the sidewall
173
.
The force (tension) in the headgear strap F
s
for the prior art mask has been found empirically to be given by the equation F
s
=(F
c
+F
Ac
)/(2 cos &thgr;), where &thgr; is the angle of the head strap with respect to the mask
110
. Thus, the force of the cushion on the patient's face F
c
is given by the equation F
c
=2F
s
cos &thgr;−F
Ac
. The force of the mask cushion on the patient's face is difficult to distribute completely evenly around the cushion in known masks, especially at higher forces, and results in localized high pressure spots around the mask cushion. This higher force on the face, and especially the localized high pressure spots, are uncomfortable to the patient and can disrupt the sleep cycle. See, for instance,
FIG. 2
, which charts the force required to secure a mask on a face versus the air pressure in the mask (measured in centimeters H
2
O). As seen there, the force required to maintain a known mask sealed to the face throughout a mask air pressure range is most substantially affected by the maximum air pressure in the mask that will occur during therapy. That is, the force of the mask on the face remains at a fairly high level even when the pressure in the mask drops and this force of the mask on the face is directly related to the force necessary to seal the mask at the maximum mask air pressure. Misalignment of the mask will move the curve upward as higher forces are required to seal the mask to the face in light of the misalignment.
This force on the face increases as the head straps of a known mask are tightened to increase the sealing force of the mask, and thereby compressing the cushion and bringing the shell of the mask closer to the patient's face. When the straps are tightened, the shell of the mask moves a distance X between a position X
0
when a seal is first obtained t

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