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Description  |
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BACKGROUND OF THE INVENTION
The present invention generally relates to mattresses and, more
particularly, to improved air support mattresses and pads for use in the
treatment and resuscitation of patents in hospitals, nursing homes and for
home care. More specifically, the mattresses, of the present invention
provide a cushion of air between the recumbent patient and the supporting
mattress or pad, thereby eliminating possible contact therebetween.
Current types of mattresses are relatively non-conformable and cannot limit
the pressure at supported body portions supporting to permit the desired
free flow of blood and lymph.
It has long been felt desirable to eliminate contact between a patient's
body and the suporting mattress, especially in the cases of patients with
extensive burns and of patients with incipient decubitus. Living animals
of a size comparable to that of humans have been supported for indefinite
periods by a broad rising column of air. This method of support has not
proved to be practical because the high velocity of the rising column
required to support and position the animal tended to damage the healing
areas by continual erosion. Further, the level of noise is excessive.
Various systems and devices have been suggested for supporting recumbent
patients on a cushion of air. Such systems have incorporated expensive,
complicated pressure regulation devices and have required constant
adjustment. More recently, as disclosed in Chevrolet U.S. Pat. No.
3,942,202 there has been suggested the use of an elastomeric plate formed
with a pressurizable passage connectable with an array of vents. Upon
deformation of the plate the vents open into the passage to provide for
air flow from the passage through the vents. Accordingly, deflection of
the plate caused by the weight of a patient causes air flow from the vents
which, according to the Chevrolet disclosure, takes over at least part of
the supporting function of the mattress. This prior art device has a
disadvantage in that it comprises a relatively thick sheet of rubber
material that is quite unyielding to light pressure and unresponsive to
small areas of contact.
SUMMARY OF THE INVENTION
The principal object of the present invention is to provide an air cushion
that avoids the problems of the prior art and that is characterized in
that very low air pressures are utilized to life the patient off the
surface of the mattress and in that the supporting air film is restricted
to the area of incipient contact.
Another object of the invention is to provide mechanisms locally and
automatically to adjust air flow to provide uniformly adequate life
regardless of the size, shape, thickness or position of supported objects
such as bodies or parts of bodies.
The descriptions herein are intended to apply to the applications of the
membrane, herein characterized as the upper "wall," in any of its many
uses and applications.
Other objects of the invention are to provide such an air mattress
characterized by low weight and simplicity of construction and operation.
There is provided in accordance with the present invention, an air pressure
mattress including elastic upper and lower main support walls
interconnected at a multiplicity of points by internal flexible ties that
restrain separation of the main support walls by the air pressure within
the mattress, the mattress being characterized in that the upper wall is
locally conformable to adjacent portions of a recumbent patient and
comprises an outer layer of limited stretchability and having a
multiplicity of similar perforations and an inner layer substantially
continuously adherent to the outer layer and of greater stretchability
than the outer layer such that the neutral stretchability plane defined by
the outer and inner layers lies within the outer layer, the inner layer
having a separate slit in registry with each perforation of said outer
layer to provide a thin film of air for lifting the patient at any regions
where changes in curvature occur in connection with supporting the patient
free of contact with the outer layer.
The perforations are circular in the preferred embodiment and the slits are
oriented in various directions avoiding small patterns which will favor
particular directions of stretch. This maximizes the uniformity of air
escape to form uniform films.
In the alternative embodiment, elongation of the perforations in the outer
layer, with the slits centered and oriented at 90.degree. to the long axis
of the elongated holes increases the curvature induced opening of the
slits. Both the cuts and the elongated holes are variously oriented.
Since the slits are variously oriented they open in response to curvature
in any direction as is necessary since the body curvature occurs in many
directions and changes with every change in body position.
It should be noted that a large number of slits are contemplated for
example a reasonable number and variously oriented slits in the area
affected to enable sufficient air to flow under the small area of a heel.
Heels are particularly vulnerable to decubitis.
With the air cushion lightly inflated, any incipient contact of a recumbent
body with the upper wall imposes a negative (downward or concave)
curvature of the adjacent areas of the upper wall. This curvature
stretches the inner layer more than the outer layer, opening the slits in
the inner layer and allowing air flow streams to be interposed in
supporting relation between the upper wall and the recumbent body, the air
streams, in effect, acting to lower that area of the upper wall so that it
is no longer in contact with the recumbent body.
Thus, as a further feature, the air cushion of the present invention is
extremely conformable with the shape of the body members in psuedo-contact
(or near contact) therewith. Because only those slits underlying the body
surfaces open, very small volumes and velocities of air are required to
accomplish the supporting function. This, in turn, results in little noise
being generated by the escaping air.
In accordance with a more particular aspect of the invention, the flexible
ties are attached at points spaced between the slits. Such results in a
slight positive (upward) curvature of the upper wall in the regions
between the ties, imposed by the internal air pressure. Such configuration
compresses the inner layer against the outer layer, thereby more tightly
closing the slits so that no air escapes therefrom.
Other features and advantages of the invention will be apparent from the
following description and claims, and are illustrated in the accompanying
drawings which show structure embodying preferred features of the present
invention and the principles thereof, and what is now considered to be the
best mode in which to apply these principles.
BRIEF DESCRIPTION OF THE DRAWINGS
In the accompanying drawings forming a part of the specification and in
which like numerals are employed to designate like parts throughout the
same;
FIG. 1 is an elevational view illustrating the air pad (mattress) of the
present invention being used in conjunction with a conventional bed to
support a patient;
FIG. 2 is a fragmentary top plan view of the air pad showing a typical
arrangement of perforations and slits in its upper wall;
FIG. 3 is an enlarged fragmentary sectional view taken, as indicated, along
the lines 3--3 of FIG. 2;
FIG. 4 is a more detailed fragmentary sectional view showing a typical
perforation and registering slit in a concave (negative) region of the
upper wall of the air pad;
FIG. 5 is a fragmentary top plan view showing the perforation and slit of
FIG. 4; and
FIG. 6 and 7 are views similar to FIGS. 4 and 5 and showing an alternative
embodiment using a different configuration.
DETAILED DESCRIPTION
With reference to FIG. 1 there is illustrated a conventional hospital bed 1
comprising a frame 2 with a mattress 3 supported thereby. A patient 4 is
shown supported above conventional mattress 3 by an air pad 5 constructed
in accordance with the present invention. As best shown in FIGS. 2 and 3,
the air pad or mattress 5 comprises upper and lower elastic walls 8 and 9
which are joined together by a circumambient flexible sidewall 10 so as to
jointly form an air pad or bag. Typically, the bag is slightly inflated
and may have a total thickness of about 4 or more inches. A source of
compressed air 7 is connected to the bag by means of a manifold tube 6 to
be controlled in any conventional way for recharging the air in the bag to
a predetermined positive air pressure.
The upper elastic wall 8 includes an outer layer 11 of slightly stretchable
material such as rubber, and having a thickness of approximately 1/100 of
an inch. Numerous perforations 16, preferably round holes, are of about
1/8 inch diameter. The upper elastic wall 8 further includes an inner
layer 12 of extremely stretchable material, such as gum rubber completely
bonded to the outer layer. The inner layer 12 is also of a thickness of
approximately 1/100 of an inch and is continuously bonded to the outer
layer 11. In the preferred arrangements, the thickness and stretchability
relationships of the layers 11 and 12 are such that the neutral
stretchability plane P lies well within the outer layer as shown in FIG.
4.
A plurality of slits 17, oriented at various angles with respect to each
other, are cut through the inner layer 12 and are located in registry with
the perforations 16 in the outer layer 11, there being one slit 17 for
each perforation. Typically, there are 13 or more perforations and
corresponding slits per square inch. Flexible ties 15 interconnect the
upper and lower elastic walls 8 and 9 at points spaced between the slits
of the inner layer 12. Between the ties 15, slight positive curvature of
the upper wall is imposed by the internal air pressure as shown in FIG. 3.
This action compresses the inner layer by the upwardly curving of the
outer layer, tending thereby to more tightly close the slits 17.
Attachment of the ties to the inner layer of the upper wall may require
covering one or several slits which would then be incapable of exhalation.
Positive curvature is maintained between the ties. No air escapes until
negative curvature is produced by pseudo-contact.
With reference to FIGS. 4 and 5, when the air mattress is inflated any
contact of a patient's body with the upper wall will tend to impose a
negative curvature (concave) to the adjacent areas of the upper wall. This
concave configuration tends to cause stretching of the inner layer 12 to
an extent greater than that of the outer layer 11, thereby opening the
slits 17 in the inner layer and allowing air flow to form a thin film of
air to be interposed between the upper wall 8 and the corresponding region
of the recumbent body.
The pressure of the resulting film of air is just sufficient to prevent
further contact with the body. No matter what the position of the patient,
or what surfaces of the body are presented to the upper wall of the
mattress, the product of pressure of the air film multiplied by the area
of induced negative curvature (concave) will support the portions of the
body causing the negative curvature; therefore the whole body will be
supported by the film without permitting direct contact.
As the upper wall 8 recedes, the portion of the body being so supported
sinks further into the elastic membrane reversing the curvature of larger
areas of the membrane and releasing air streams from the slits in these
areas until equilibrium is reached. In assuming a lower position, other
areas of the body may come into pseudo-contact until the entire body is
supported by the various air films.
Considering the thickest parts of the body with the patient lying on the
side, the vertical thickness is approximately eighteen inches. Its density
is approximately that of water. Disregarding the effects of tension in the
upper wall, less than one pound per square inch of air pressure in a bag
without openings would comfortably support the body. With the openings of
my invention approximately two pounds of air pressure is sufficient to
eliminate contact of the body with the mattress. Since only those cuts
adjacent to the body surfaces open, very small volumes and velocities of
air are required. Little noise is generated by the escaping air.
In the mattress of this invention, the degree to which each slit is opened,
and therefore the amount of air emerging therefrom is a direct function of
the unit weight and curvature of the body member superior to it, resulting
from the vertical column, one unit in area, of the body directly above it.
On the other hand, an arm would not depress the surface as much as a
buttock, a smaller area would be rendered concave and the total volume of
air escaping in the area lessened. This is a self correcting situation,
air being applied only where, and in the amounts required. The results
include low noise, low pressure and little air.
Since all the air streams, films or cushions formed are derived from the
common plenum of the mattress or pad there is little variation in the
character of said cushions whether a portion of the body is in shallow or
deep penetration of the mattress or pad space. Hence there is little
tendency to force the body into any conformation other than that
determined by the internal structure and tensions within the body. This
adds positional comfort to the comfort provided by the lack of contact
with surfaces.
This invention also provides several advantages, other than lack of
contact, over water beds. Neglecting the tensional effects, the unit
pressure exerted by a water bed is a direct function of the depth to which
portions of the body sink below the highest point of its upper membrane.
Hence much more unit pressure is exerted on hip or shoulder of a body
lying on its side thereby forcing that member upward into an unnatural and
uncomfortable conformation. Also, since the density of the air contained
in the air mattress is orders of magnitude less than that of water no
"sloshing" could be observed.
It should be appreciated that in the transition zone adjacent negatively
curved portions of the air mattress, where the curvature changes from
negative to positive, air from slits in such areas is not required because
the air film created by escaping air in the lower portions of the
concavity is moving outwardly and across these areas which thereby tends
to maintain the required lift. Thus there results a conservation of air
within the air cushion and a tendency to allow back pressure from the
frictional forces to filter out fluctuations which may otherwise result in
fluttering of the lips of the slits and of the transition zones.
Mattresses in present use have relatively non-conformable surfaces. The
pressure of these surfaces beneath protruding parts of the body such as
hips, buttocks, shoulders and heels often far exceeds the systolic blood
pressure even in hypertensive persons. This, like the cuff of a
sphygmanometer, cuts off the flow of blood in nearby arteries, veins and
capillaries and of the lymph. When continued for extended times decubitus
and gangrene result. This invention requires air pressures of one tenth to
one fifth of these pressures and therefore does not restrict the free flow
of blood and lymph.
Several forms of slits other than straight come to mind and allow somewhat
easier opening. If cut at an angle to vertical, cut in a slight arc, or in
a slightly "s" shape, they should be useful.
An alternative embodiment is shown in FIGS. 6 and 7 and is characterized by
elongation of the perforations 20 (oval holes) with the slits or cuts 21
centered and oriented at 90.degree. to the long axis. This arrangement
increases the curvature induced opening of the slits. In a total mattress
array both the holes 20 and slits 21 are variously oriented.
The lower wall may be constructed of any nonporous material. However for
various reasons reversability may be desirable. if so, the lower wall may
be constructed in the same manner as the upper wall.
From the foregoing it will be apparent that only a relatively low level of
positive pressure need be maintained within the air pad 5 to produce the
required air stream velocity for lifting the recumbent patient relative to
the upper elastic wall 8. Such is due to the fact that air can escape from
the air pad only through those slits in the regions of negative
deformation caused by the presence of a portion of a recumbent body.
For therapeutic reasons, oxygen or other gases may be substituted for air.
An example would be to supply oxygen to an oxygen tent arrangement by
means of an air support pillow or mattress.
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