U.S. patent application number 10/665059 was filed with the patent office on 2005-03-24 for methods and devices for reducing stress concentration when supporting a body.
Invention is credited to Rogers, John E..
Application Number | 20050060809 10/665059 |
Document ID | / |
Family ID | 34312838 |
Filed Date | 2005-03-24 |
United States Patent
Application |
20050060809 |
Kind Code |
A1 |
Rogers, John E. |
March 24, 2005 |
Methods and devices for reducing stress concentration when
supporting a body
Abstract
This invention is of a method and equipment for reducing stress
concentrations in a body supported in a horizontal or any reclining
position up to and including a fully seated position. The stress
reduction is accomplished by means of specially designed or
arranged cushioning material contained inside a membrane or bladder
wherein the pressure of a fluid inside the membrane can be
controlled as a means of varying the cushioning effect
(compressibility) of the material inside and holding the cushioning
material in specific places to reduce fight-back of the material
over supporting edges that may otherwise create undesirable shear
on the supported body tissue.
Inventors: |
Rogers, John E.; (Cameron,
TX) |
Correspondence
Address: |
David G. Henry
900 Washington Avenue
P.O. Box 1470
Waco
TX
76703-1470
US
|
Family ID: |
34312838 |
Appl. No.: |
10/665059 |
Filed: |
September 18, 2003 |
Current U.S.
Class: |
5/713 ; 5/709;
5/727 |
Current CPC
Class: |
A61G 7/05769 20130101;
A61G 7/05723 20130101; A61G 7/05753 20130101 |
Class at
Publication: |
005/713 ;
005/709; 005/727 |
International
Class: |
A47C 027/08 |
Claims
I claim:
1. A support system for supporting a body or a portion thereof,
comprising: a foam mattress, cushion, seating pad or similar
support structure containing a plurality of vacant regions and
configured to reduce local stresses on a supported body, reduce
cross contamination between a patient and a patient surroundings,
and reduce the incidence of dust mites into said support system; a
bladder or membrane impervious to gases or other fluids, completely
encasing said mattress, cushion, seating pad or similar support
structure; a passageway means allow and control the ingress and
egress of a gas or other fluid into or out of said vacant regions,
within or around the support structure encased by said bladder or
membrane; and a pressure/vacuum pump to allow continuous variation
of the fluid pressure within said bladder or membrane.
2. A support system according to claim 1 wherein the support
structure is a foam mattress in which portions of the support
structure have been removed or omitted in one or more selected
regions of the material, forming empty regions and the empty
regions are a truncated cone or a bell-shaped region.
3. A support system according to claim 1 wherein one or more of the
edges of the mattress, cushion, seating pad or other body support
surface is undercut such that the edge tapers inward toward the
bottom of the mattress, cushion, seating pad or body support
element.
4. A support system according to claim 1 wherein said mattress,
cushion, or seating pad is formed from a convoluted foam
material.
5. A support system as in claim 1 wherein said mattress, cushion,
or seating pad is formed from a convoluted foam material and said
convoluted foam material is inserted with smooth side upward and
one or more cut-outs are made for the purpose of reducing local
stresses on the body or sections thereof.
6. A support system according to claim 1 wherein the support
structure provides for reduction of localized stresses by a modular
construction technique using different types of foam material in
selected regions to form a composite foam mattress.
7. A support system according to claim 1 wherein the support
structure provides for reduction of localized stresses by a modular
construction technique using different types of foam material
encased in individual membranes in selected regions to form a
composite foam mattress.
8. A support system according to claim 1 wherein said bladder is
permanently sealed to prevent any escape or replacement of the
fluid contained therein.
9. A support system according to claim 1 wherein said bladder is
enclosed by a Ziploc.sup.7 or similar fastening means.
10. A device according to claim 1 wherein the support structure
comprises a seat cushion and wherein said seat cushion contains
provisions for localized relief of stress comprising one or more
regions where material has been removed or omitted selectively from
said seat cushion.
11. A support system as in claim 1 where a variable orifice is
contained within the encasing membrane to control the rate of
gaseous exchange from within the membrane to outside of the
membrane and vice versa.
12. A support system for supporting a body or a portion thereof,
comprising: a foam mattress, cushion, seating pad or similar
support structure containing a plurality of vacant regions and
configured to reduce local stresses on a supported body, reduce
cross contamination between a patient and a patient surroundings,
and reduce the incidence of dust mites into said support system; a
bladder or membrane permeable or semi-permeable to gases or other
fluids, completely encasing said mattress, cushion, seating pad or
similar support structure; a passageway means to allow and control
the ingress and egress of a gas or other fluid into or out of said
vacant regions, within or around the support structure encased by
said bladder or membrane; and.
13. A method for reducing the possibility of development of
deleterious body lesions in a human body under conditions of
continued bed confinement by; placing a mattress, cushion, seating
pad or similar support structure, designed or configured to
minimize localized stress concentrations caused by the weight of
the body thereon, within a bladder or membrane impervious to gases
or other fluids, completely encasing said mattress, cushion,
seating pad or similar support structure, varying the fluid
pressure in the support structure as a means of controlling the
resiliency of said support structure to the desired support
level.
14. A method for reducing the possibility of development of
deleterious body lesions in a human body under conditions of
continued bed confinement by: placing a mattress, cushion, seating
pad or similar support structure, designed or configured to
minimize localized stress concentrations caused by the weight of
the body thereon, within a bladder or membrane impervious to gases
or other fluids, completely encasing said mattress, cushion,
seating pad or similar support structure, varying the fluid
pressure in the support structure as a means of controlling the
resiliency of said material support structure to the desired
support level, wherein the support structure comprises a mattress
containing provision for reduction of localized stresses in certain
portions of the body being supported by the removal of portions of
the mattress material in one or more selected regions.
15. A A method for reducing the possibility of development of
deleterious body lesions in a human body under conditions of
continued bed confinement by; placing a mattress, cushion, seating
pad or other similar support structure, designed or configured to
minimize localized stress concentrations caused by the weight of
the body thereon, within a bladder or membrane impervious to gases
or other fluids, completely encasing said mattress, cushion,
seating pad or other similar support structure, varying the fluid
pressure in the material support structure as a means of
controlling the resiliency of said material support structure to
the desired support level, wherein the support structure contains
provisions for reduction of localized stresses by the removal of
portions of the support structure in one or more selected regions
forming a plurality of vacant regions, where said vacant regions
are in the shape of an upright truncated cone.
16. A method for reducing the possibility of development of
deleterious body lesions in a human body under conditions of
continued bed confinement by; placing a mattress, cushion, seating
pad or other similar support structure, designed or configured to
minimize localized stress concentrations caused by the weight of
the body thereon, within a bladder or membrane impervious to gases
or other fluids, completely encasing said mattress, cushion,
seating pad or other similar support structure, varying the fluid
pressure in the material support structure as a means of
controlling the resiliency of said material support structure to
the desired support level, wherein the support structure contains
provisions for reduction of localized stresses by means of cutting
or slicing portions of the mattress material in one or more
selected regions.
17. A method according to claim 13 wherein the support structure
comprises a seat cushion of suitable support material.
18. A method for reducing the possibility of development of
deleterious body lesions in a human body under conditions of
continued bed confinement by; placing a mattress, cushion, seating
pad or other similar support structure, designed or configured to
minimize localized stress concentrations caused by the weight of
the body thereon, within a bladder or membrane impervious to gases
or other fluids, completely encasing said mattress, cushion,
seating pad or other similar support structure, varying the fluid
pressure in the material support structure as a means of
controlling the resiliency of said material support structure to
the desired support level, wherein the support structure comprises
a seat cushion and said seat cushion contains provisions for
localized relief of stress comprising one or more regions where
material has been removed selectively from the seat cushion.
19. A method for reducing the possibility of development of
deleterious body lesions in a human body under conditions of
continued bed confinement by; placing a mattress, cushion, seating
pad or other similar support structure, designed or configured to
minimize localized stress concentrations caused by the weight of
the body thereon, within a bladder or membrane impervious to gases
or other fluids, completely encasing said mattress, cushion,
seating pad or other similar support structure, varying the fluid
pressure in the material support structure as a means of
controlling the resiliency of said material support structure to
the desired support level, wherein one or more of the edges of the
mattress, cushion, or seating pad is undercut such that the edge
tapers inward toward the bottom of the mattress, cushion, or
seating pad.
20. A method according to claim 13 wherein said mattress, cushion,
or seating pad comprises a plurality of modules, separated from one
another and contained within individual fluid-tight membranes or
bladders.
21. A method for reducing the possibility of development of
deleterious body lesions in a human body under conditions of
continued bed confinement by; placing a mattress, cushion, seating
pad or other similar support structure, designed or configured to
minimize localized stress concentrations caused by the weight of
the body thereon, within a bladder or membrane impervious to gases
or other fluids, completely encasing said mattress, cushion,
seating pad or other similar support structure, varying the fluid
pressure in the material support structure as a means of
controlling the resiliency of said material support structure to
the desired support level, wherein said mattress, cushion, or
seating pad is formed from a convoluted foam material.
22. A method according to claim 13 wherein the encased material
comprises a seat cushion.
23. A method for reducing the possibility of development of
deleterious body lesions in a human body under conditions of
continued bed confinement by; placing a mattress, cushion, seating
pad or other similar support structure, designed or configured to
minimize localized stress concentrations caused by the weight of
the body thereon, within a bladder or membrane impervious to gases
or other fluids, completely encasing said mattress, cushion,
seating pad or other similar support structure, varying the fluid
pressure in the material support structure as a means of
controlling the resiliency of said material support structure to
the desired support level, wherein the support structure comprises
a seat cushion and wherein said seat cushion contains provisions
for localized relief of stress comprising one or more regions where
material has been removed or omitted selectively from said seat
cushion.
24. The support system of claim 12 further comprising a
pressure/vacuum pump to allow continuous variation of the fluid
pressure within said bladder or membrane.
25. The support system of claim 12 wherein said bladder or membrane
is enclosed by a Ziploc or similar fastening means.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] Not applicable
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] Not applicable
REFERENCE TO A MICROFICHE APPENDIX
[0003] Not applicable
BACKGROUND
[0004] A person who is elderly or has some enervation and is
confined to bed for an extended period, will have a propensity to
develop tissue trauma sores (ischemic ulcers, decubitus ulcers or
bedsores). Typically these sores appear over bony prominences where
forces arising from the weight of the body are concentrated and the
lack of movement leads to tissue destruction. (Those with normal
sensation and mobility become "uncomfortable" and move to a
different position while those under anesthetics can't move) To
avoid such sores, some form of tissue pressure/shear interface
should be provided to reduce these forces to a value that the
tissue can tolerate. These tissue trauma forces may be adjusted in
a number of ways; by "putting the load where the body can tolerate
it", by attempting to control interface forces across the patient
body support surface, or by moving the patient periodically before
tissue reaches an irreversible "death" situation.
DESCRIPTION OF PRIOR ART
[0005] In recent years, inventors have approached this problem of
tissue breakdown prevention using two basic approaches for body
support, fluidic substance or polymeric foam. Each of these methods
encompasses many variations that have met with differing degrees of
success. In most instances cross-contamination or dust mite
prevention has not been considered as part of a performance
requirement until after-the-fact
[0006] 1. Fluidic Support
[0007] Water/Air. Making use of a shaped structure and air bladders
was proposed by Weinstein et al in U.S. Pat. No. 3,456,270 wherein
water was the supporting medium and a lifting inflatable bladder
interface was used for raising patient for transfer etc.
[0008] Whitney in U.S. Pat. No. 3,802,004 changed a patient
immersion depth through unique bladder arrangements inflated by
air, without changing medium volume.
[0009] Hagopian in U.S. Pat. Nos. 5,072,468 and 5,068,935 describes
a special bed frame for ease of manufacture and the use of water as
the base medium with an air bladder on its upper surface to lower
or raise the patient, as in Reswick (later), with the added ability
to provide an inflated wedge for postural trunk control of the
patient. These approaches also were an attempt to reduce
"hammocking" over bony prominences that tends to negate the
efficacy of the support medium. It should be noted that the water
bed of today is comprised of water, a supporting envelope to
"hammock" a person so that they do not sink into the bed and
appropriate baffling or channeling for stability of the water.
[0010] Air. There are a number of ways in which air has been
compressed, blown or applied to support a patient. Hart in 1926 in
U.S. Pat. No. 1,772,310, described a technique of alternating the
fluidic support points on the body by controlling the time each
support point was to be activated, while limiting interface
pressure to an acceptable value. Hart also introduced a method of
patient turning in this same patent.
[0011] Whitney, in U.S. Pat. No. 3,148,391 used a modified method
of support that was compact and introduced temperature control of
interface as well as the alternating method of support. Ford in
U.S. Pat. No. 4,711,275 opted to inflate and deflate arrays of air
cells through independent air compressors to create an alternating
pressure support system. Krouskop in U.S. Pat. No. 4,989,283 opted
to control height of the supporting bladders in his approach to
body support by measuring any changes in cell configuration through
a microprocessor using its input from internal bladder sensors to
control appropriate valving to pressure sources or exhausts to
maintain each bladder at some referenced height. Others used
lateral support tube shaping (Talley of the UK) while others
included an air loss to circumvent needle puncturing problems (3M)
with appropriate control mechanisms.
[0012] Air, as a fluidic support has been proposed in many forms
for various purposes of body positioning. A surgical table is the
subject of Canadian Patent 1035000 by Carrier where individual
bladders of air are positioned to keep the bony prominences clear
of the table, while providing a fairly stable support as each
bladder is independently inflated to a desired pressure. All are
then covered by a forgiving cover.
[0013] Air cushion machines are quite effective in supporting a
large unforgiving body against a homogenous and somewhat stiff
undersurface; however, their use as a patient support medium is
impractical. Then again, if enclosed in a container of soft tough
and highly flexible material, air is much more suitable for patient
support if designed correctly to reduce hammocking.
[0014] Consequently, by using air in tubular or oval containers and
arranging appropriately within the bed frame, a mattress of air
tubes is a reasonable approach, depending on cross sectional area
of bladders and their positioning. Shaping these air tubes and
putting holes in them to circumvent accidental needle punctures and
with a pump sufficiently large to keep ahead of the leak rate, had
its merits.
[0015] Although Armstrong, U.S. Pat. No. 2,998,817, first developed
an inflatable massaging and "cooling" system, as time passed,
materials were developed that had built in leak rates suitable for
beds and thus the current Low-Air Loss mattress approach evolved
using so-called vapor-permeable materials. Such materials may
consist of 80 denier nylon, or thereabouts, backed with a material
of choice such as a film of urethane or vinyl.
[0016] Hess, U.S. Pat. No. 4,638,519, demonstrated use of shaped
bladders using such materials with appropriate individual bladder
control and methods of bladder attachments with air supplies while
Goode, U.S. Pat. No. 4,797,962, used the process of controlling
these air bladders in groups as a means of modifying support
pressure under portions of the body as others have done in the
aforementioned. (Some of these approaches have been prone to
collapse when the patient is in the sitting position in the bed,
consequently exposing the coccyx and ischial tuberosities [sit
bones] to excess pressure and shear due to increased bladder
loading by the vertical component of the trunk.)
[0017] Some have attempted to reach suitable body support through
the use of foam on top of slats placed on top of air cylinders as
outlined by Wilkinson, in U.S. Pat. No. 5,070,560.
[0018] High Density Fluid. Reswick, in U.S. Pat. No. 3,803,647,
used a mixture of Barium sulfate ore and water (or other fluids) as
a medium of support with a loose fitting lifting interface sheet as
the top member of the unit. This sheet was inflated and allowed
access to the patient at a suitable working height for the
attendant personnel. The aqueous lution of barites was used as its
specific gravity could be much greater than "1" and thus support a
body without immersion problems of water only. This specific
gravity, eater than "1", allowed the patient to lay in the solution
and be supported up the body sides to an optimum immersion point.
If the specific gravity is too high, excess pressures can be
exhibited as area of support is drastically reduced. Keeping the
mixture sufficiently fluidic presented a maintenance problem that
led to patent disuse.
[0019] This patent also addressed shaping of the container to
reduce the contained mixture volume and of a tubular top bladder as
a stiffening method of the upper surface of contained fluid for
easier patient transfer or performing dressing changes.
[0020] Thompson, U.S. Pat. No. 4,357,722, demonstrates a flexible
open mesh approach in a special bed frame to support the patient
interfacing medium to change tension of support under various
portions of the body.
[0021] Hargest et al, U.S. Pat. Nos. 3,428,973 and 3,866,606, used
fluidized beads to create a specific gravity greater than "1".
These beads were micro-balloons approximating 100 microns in
diameter and were "fluidized" by an air plenum chamber placed at
the base of the beads separated by appropriate filtering and
restrained to remain adjacent to the patient by another optional
filter. Fluidization depends on the pressure drop across the
supporting beads and that of the filtering system. Excess drop
reduces fluidization, increases heat loss and can create ballooning
of upper cover. It is thus necessary to adjust pump flow to match
patient needs and size.
[0022] Lacoste, U.S. Pat. No. 4,481,686 controls bacteria through
bead selection.
[0023] Goodwin addresses support of beads in his U.S. Pat. Nos.
4,564,965, 4,672,699 and 4,776,050 with sequential diffusion of
beads in U.S. Pat. No. 4,637,083.
[0024] Viard in U.S. Pat. No. 5,402,542 demonstrates use of a 1
programmable EPROM and heat exchanger to control bead system
component temperatures.
[0025] River sand has also been used in place of beads and
periodically "fluidized" with marginal success.
[0026] Yet another approach that may be considered somewhat fluidic
is the use of gel and air wherein a semi fluid gel is used in place
of the fluidic bead systems in much thinner beds than the units
discussed above. Due to the nature of the gel, however, its
accommodation of high forces is somewhat limited.
[0027] 2. Use of Polymeric Foam Such as Polyurethane
[0028] Flat Stock. Polyurethane is formed through the mixing of
different polymers under controlled conditions. Some manufacturers
provide the fabricator with huge blocks of foam which are then cut
into required sizes and sold to various fabricators of furniture,
mattresses and so on. Some of this stock is sold as is or as a
finished item when placed within some acceptable cover consistent
with industry requirements. Some foam is rigid and some
flexible.
[0029] As can be readily acknowledged, flexible foam acts somewhat
like a spring. It is well known that the further a spring is
compressed the stronger is the resisting force of that spring, and
so it is with foam. The unfortunate part of this foam as a support
media is that our bodies are not flat and our hips protrude further
than our waist Accordingly, when one is sidelying on foam, the hip
sees more "spring-back" (foam fightback) or a higher load than our
waist. This hip bone (Trochanter) is poorly vascularized and thus
the tissue at its surface can be robbed of the desired blood to
keep the tissue healthy. Thus the enervated person is unaware of
the damage being incurred with this load, the tissue dies, and the
result is a "sore" where the skin integrity is forever damaged
without surgical intervention. Other parts of our bodies such as
the heels, malleolus (ankles), iliac crest (pelvis), coccyx
(tailbone), ischial tuberosities (sit bones), scapula (shoulder
blades), occiput (back of head), elbows and ears are areas that are
also poorly vascularized and prone to breakdown with small loading
of tissue in these areas.
[0030] Those with normal sensation and mobility feel this excess
tissue load as a discomfort and move away, thereby restoring
circulation in the region. It has been clinically noted that a
sleeping person will normally move more than twenty times during an
eight hour period on a "so called", standard mattress.
[0031] Thus flat stock foam, using current technology, is not very
desirable for patients at-risk of tissue breakdown or for their
comfort. Some materials tend to give way with applied load as in
the case of materials used for the Apollo astronaut couches,
however, this material known as "visco-elastic foam, is expensive,
is temperature sensitive, heavy, flaky, tends to tear readily, and
has not been generally used by the bedding industry in the
past.
[0032] Flexible polyurethane foam has been the material of choice
most recently. These materials are available in many densities and
Indention Force Deflections (IFD). Densities may range from the
soft 1.1 pounds/cubic foot up to about 7 pounds/cubic foot and an
IFD range of about 14 to 180 is commonly used for bed support
purposes. These foams are generally manufactured as a polyether,
polyester, high resiliency or other, foam, with all exhibiting
different characteristics. The polyether materials are generally
found in furniture while the polyester is used in packaging
requiring fire resistance while high resiliency may be found where
continual cycling is encountered. Other foams also include rubber
and other compounding which have not found great favor in the
bedding/cushioning industry.
[0033] Although combinations of many of these foams is common
knowledge in the industry, polyether material is less expensive and
it may be found in products where replacement is no problem or
where material is not used extensively. Its durability under
continual loading has generally been less than desirable.
[0034] Cut or Shaped Foam Stock. Reducing forces encountered in
flat stock of polyurethane was obtained through reduction of a foam
support in the bony areas by cutting the foam in a special pattern
as proposed by Rogers (the inventor herein) in U.S. Pat. Nos.
3,885,257, 3,866,252 and 4,042,987. Others also cut foam as
disclosed in U.S. Pat. No. 3,828,378 by Flam, U.S. Pat. No.
4,901,387, by Luke and later U.S. Pat. No. 5,025,519 and U.S. Pat.
No. 5,252,278 by Span. Kraft in U.S. Pat. No. 4,679,266 simulated
foam support by zones of inner (mattress) springs with varying
strengths.
[0035] Murphy in U.S. Pat. No. 4,628,557 and Rogers (inventor
herein) in U.S. Pat. No. 4,042,987 and U.S. Pat. No. 4,903,359
could make a selection of foam removal under affected areas of the
patient, and in Rogers's case, overloaded adjacent support members
rolled automatically into the vacancy to spread load gradually to
adjacent areas. Bony areas of the body can be free of all force in
foam products through use of material cutouts in mattresses,
mattress replacements, body conforming supports, or cushions, but
shearing forces at the demarcation edge of support and no support
are a harbinger of tissue death unless that demarcation is gradual
and can be overcome by the body's internal blood pressure without
creating total occlusion of the blood supply. It is then of
paramount concern that proper shaping of the edges of regions where
foam is removed is built into any design of a support surface so
that loading is transferred gradually to adjacent support areas of
the body more amenable to the applied forces (putting the load
where the body can tolerate it). Some methods to do this are
disclosed in U.S. Pat. Nos. 5,127,119 and 5,048,137 by Rogers
(inventor herein). Foam is cut away from bony areas and edge or
shear effects are accommodated by cutting foam around the removed
foam area to create supporting foam forces "normal" to the body and
give a gradual buildup of load over a reasonable area where blood
flow is not compromised. One patent discloses technique of load
spreading through shaping of the cutout conically or approaching a
bell shape.
[0036] Convoluted foam, initially used in anechoic chambers, is
formed from flat stock put through a convoluting machine, and has
been used as a mattress or pad where patient is supported by a
number of peaks and valleys, such as described by Schulper, in U.S.
Pat. No. 3,197,357. This machine can produce two products 4" thick
from one five inch piece of foam. Obviously material is spread
equally between the two halves in such a manner as to create a peak
of four inches with valleys to offset the adjacent peaks, a type of
"mirror" image.
[0037] Peak sizes were varied as well as depth of valleys in an
attempt to equalize forces without complete relief of affected
areas. In some instances manufacturers cut the peaks off some of
these convoluted pads in an attempt to control support load
distribution. Most of this type material was fabricated from
inexpensive foam and has been banned from use in many medical
facilities across the USA because of its inability to eliminate
damaging forces on body tissue when the user had expected more
protection than the material could provide without extensive
forming, cutting or modified as proposed in the subject patent.
SUMMARY OF THE PRIOR ART
[0038] From the foregoing, it is clear that many different
approaches have been used in an attempt to reduce discomfort and
injury in a bedridden patient. Such discomfort and possible injury
is a direct result of the stress concentration created by the
non-uniform shape of the human body. An ideal supporting structure
would distribute the forces due to the body weight in a way to
minimize or eliminate any localized concentrations of stress,
particularly shear, such as would occur at a discontinuity in the
underlying material.
[0039] However, this does not mean that a uniform distribution of
stress is the most desirable result. Where bony structure in the
body is near the surface and not protected by a reasonable
thickness of soft tissue, an effort should be made to greatly
reduce or even to eliminate the stress in that region, compensating
by slightly higher forces elsewhere, where the body can tolerate
it. Total elimination of stress locally is particularly important
to promote healing where a bedsore or injury already exists so that
the affected site can be readily supplied with a healthy flow of
blood. This same thinking is also appropriate for all sites of the
body where blood flow may be compromised by an inappropriate body
support medium.
[0040] The prior art has not as a rule directly addressed this
goal. Although it has been generally recognized that a support
structure for the human body needs to provide different stress
patterns in different areas, most schemes do not fully achieve it.
In fact, some have discontinuities in material and make no apparent
attempt to minimize shear stress at those points.
BRIEF SUMMARY OF THE INVENTION
[0041] This invention relates to the support of a person in the
prone, supine, sidelying, semi reclined or sitting position without
the usual stress concentrations which may lead to tissue trauma,
decubitus ulcers or bed sores. It is an object of the present
invention to provide support for a human body in a manner so that
the forces of support have fewer concentration points which are
likely to occur at or near bony prominences, nerves, or tendons,
and which, if not accommodated, can lead to serious complications
such as bed sores, nerve damage, or strained tendons.
[0042] This invention addresses the stress distribution problem by
combining several techniques. First, using a basic foam inner
material, or other that gives a similar performance, the invention
provides regions where material has been cut in some selected
manner, cut away, omitted, or formed to reduce the magnitude and
abruptness of any stress concentrations when supporting a body.
This technique is then combined with the process of applying a
membrane over the insert material to smooth out the localized
variation in stress and concomitantly, if the membrane is able to
control the amount of air or fluid surrounding the space between
the bladder and interstices of the foam, the fluid pressure may be
varied to change the characteristics of the foam itself. This can
be characterized by reviewing U.S. Pat. Nos. 5,127,119 and
5,048,137 by Rogers and observing that if these patented products
were loaded by a body, the foam will "fold" over "normally" to the
tissue of the body to reduce the shearing occurring at the tissue.
However, if a bladder were to also be placed between the body and
the supporting foam discussed, the bladder, with air control
ability, can hold the foam in its desired place without the
normally concurrent fightback of the foam and thus the "shear" or
pressure known to damage the tissue, nerves, and tendons. The body
is virtually floated by a high specific gravity through a
combination of foam, bladder and fluid pressure. But, the foam or
supporting medium must be previously pre-shaped for this system to
work as designed.
[0043] It is this combination of techniques that accomplishes, in a
superior way, the desired goal of comfort and safety of the
patient. "Comfort" has been shown to be directly related to forces
exerted on the body by Rogers in the "Hospital Materiel Management
Quarterly" article, "Body Support Testing and Rating" dated August
1992.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
[0044] FIG. 1 is an embodiment wherein a foam mattress, containing
one or more regions where foam has been cut away, is inserted into
a closely fitting bladder in which the pressure of a fluid can be
controllably varied.
[0045] FIG. 2 depicts the deformation of a foam material around a
cylindrical cut-out in the material when an irregular object is
placed thereon.
[0046] FIG. 3 shows how the material deforms when an inverted
conical hole is in the support material.
[0047] FIG. 4 shows how the material will deform if the cut-out is
tapered away from the hole progressively from top to bottom.
[0048] FIG. 5 shows a detail of the deformation around a cut-out
placed within a bladder.
[0049] FIG. 6 is a view of an insertable foam pad with undercut
edges.
[0050] FIG. 7 depicts an insert containing modules of different
types of foam in different areas with undercutting at the
joint.
[0051] FIG. 8 shows a modular device with individually pressurized
sections.
[0052] FIG. 9 shows a convoluted foam material inserted into a
bladder.
[0053] FIG. 10 shows a convoluted pad inserted with smooth side up,
containing a cut-out for localized pressure relief.
DETAILED DESCRIPTION OF THE INVENTION
[0054] The basic features of the invention can be seen in FIG. 1. A
foam pad 1 of any size or shape, containing one or more cutouts 2,
is inserted into a closely fitting airtight bladder 3. A valve 4,
is affixed to an opening 5, and an optional pumping means 6, for
pressurizing or evacuating the bladder may be attached. It should
be noted that the shape of the pad in FIG. 1 is for demonstration
only and that the pad may also be in the shape of a torus, a
circle, or a square for example, with a rectangular, or
other-shaped center portion removed, or for that matter, any
suitable body supporting shape.
[0055] As demonstrated by Rogers (inventor herein), U.S. Pat. No.
5,048,137, the deformation of a foam mattress around an opening
through the foam in the form of a truncated upright cone (small
radius at top) or bell-shaped, is such that the material around the
edges of the opening tends to "roll" into the cavity when a load is
placed upon the portion of the mattress containing the cut-out. The
result is that instead of an abrupt change in force distribution at
the edge of the cut-out, the distribution changes more gradually at
the approach to the opening. This desirable condition comes about
because the shape of the cavity is such that there is gradually
less and less material as the edge of the opening is approached,
hence the spring-constant or fight-back is reduced near the cut-out
in a manner suitable for gradual force reduction commensurate with
blood pressure supply to the supported site.
[0056] However, the gradual diminishing of the forces on the body
as the cut-out is approached only occurs where the material slopes
back away from the opening into the foam. If the sides of the
opening are vertical, whether a cylindrical, elliptical, or other
shape, the body will see a higher stress concentration near the
opening. This effect can be seen in FIG. 2. Since the force on the
body is proportional to the amount of compression of the underlying
material, when a body of irregular shape as shown, is supported
over the opening, the forces will increase near the cut-out, and
drop sharply within the opening.
[0057] On the other hand, as in FIG. 3, where the top of the
opening is larger in cross section than below, the body will see a
stress concentration near the edge of the opening, and also at the
point where the body loses contact with the underlying material and
is unsupported across the opening. But where the opening is
undercut as in FIG. 4, whether the opening is in the form of an
inverted cone or of some horizontal cross section other than
circular, as the opening is approached there is less material under
the body and the forces upon the body will be reduced gradually
because the material can bend or "roll" into the opening as shown
with a reduced "spring constant" and concomitant force on the
supported body.
[0058] Thus, FIGS. 2, 3, and 4 demonstrate how the shape of the
cut-out plays a significant role in controlling stress
concentrations in supporting a body.
[0059] Now, when the foam or other material is placed inside a
bladder wherein the fluid pressure may be varied, two additional
effects are observed. First the membrane of the bladder extends
over the opening adds support to the supported body in the form of
a "hammocking" effect. The amount of hammocking support will be
determined by bladder composition and adds considerably to the
smoothing effect, further reducing any abrupt changes of pressure
on the body.
[0060] Another factor arises from the ability to vary the pressure
of the fluid inside the bladder. Within the cells of the foam the
variation of pressure changes the spring constant of the foam. At
the same time, in the cut-out section, the pressure of the fluid
directly determines the local force distribution on the supported
body. This is shown in more detail in FIG. 5 which is a cross
section of an undercut cut-out encased in a bladder showing the
resulting deformation of the foam.
[0061] Thus, the invention disclosed herein provides for
simultaneously varying both the shape of the supporting material
and its resiliency. These variations are accomplished by
selectively cutting, removing, omitting or shaping material and by
varying the resiliency of the material with fluid pressure in the
cells of the material.
[0062] In one embodiment, the invention is a foam pad shaped as
desired for a mattress, pillow, body support device or cushion,
which contains one or more cut-outs in preselected locations. These
cut-outs will preferably have outwardly sloping sides, being
smaller at the top than at the bottom. It is obvious that the
amount of force gradation on the supporting body is directly
related not only to the type of support material but also the slope
and shape of the cutout, the bladder material, and the amount of
contained fluid. Therefore, it is possible to tailor the support
device to the needs of the body resting thereon.
[0063] If the edge of the support structure impinges on any portion
of the body, such as the heels or the back of the knees when
seated, then in order to avoid stress concentration, that edge
should be sloping inward from top to bottom as in FIG. 6. FIG. 6
shows the same type of roll-over effect as earlier shown in the
cut-outs. The same principle also applies to the inner surfaces of
a ring or a so-called doughnut. Otherwise a tourniquet effect will
reduce the blood supply in the center and create a blood flow
limiting situation and the possibility of tissue death within the
ring.
[0064] The foam insert is placed in a close-fitting bladder or
membrane containing a passageway for air or other fluid to enter or
leave. A valve or other means for controlling the internal pressure
may be fitted to the bladder as was shown in FIG. 1. This fitting
may be connected to a pressure or vacuum pump or simply left open
initially and closed when the body is in position upon the
mattress, pillow, support module, or cushion. In this latter case
the foam fight-back has been reduced over sloping edges making the
body support surface free of unwanted shear at the edges. Without
the outer membrane and with the surrounding air pressure normal
such shear is likely to be encountered.
[0065] Alternatively, it may be desirable to simply hermetically
seal the bladder either by conventional sealing means or by a
Ziploc.RTM. type closure after establishing the desired internal
pressure. On the other hand one might use a semi-permeable membrane
or a controllable orifice so that the weight of the body would
force the air out slowly, allowing the pad to assume a shape
conforming to the body. Of course cut-outs may be placed in
appropriate locations to further enhance the patient's comfort and
tissue health, however, if cross-contamination or dust mite
restriction is part of the patient physical support consideration,
appropriate filtering or support personnel regimen must be
considered in the overall performance specification of the patient
physical support system.
[0066] Another method of varying the resiliency of the support is
to cut a number of slits in the material as was shown by Flam, U.S.
Pat. No. 3,828,378. The placement of these slits will result in
varying compressibility or resiliency. By combining this technique
with the pressure variation in the bladder and optional cut-outs, a
much wider range of controllable properties can be obtained. The
foam, where slit will act like a collection of individual springs,
much as in an innerspring mattress. It will also be possible to
vary the spring effect in different areas of the mattress and then
provide the bedridden person with even greater degree of comfort by
changing the pressure in the mattress and/or adding shaped
cut-outs.
[0067] Another means of providing variable force distribution is to
use different types of foam in different areas as shown in FIG. 7.
This would not be limited to any particular shape of the foam. For
example, one could fill in one or more of the cut-outs with a
softer foam plug to get even more variation in the local
resiliency. Lateral strips of foam may be used and the different
effects of the pressure variation in the different foams would
allow a seemingly endless variety, especially if combined by the
ability to vary fight-back of the supporting material by varying
pressure. Cross-contamination between patients can be readily
controlled as can dust mite invasion into the inner core of the
unit.
[0068] A further refinement on using different foams is shown in
FIG. 8. In this embodiment, each section is encased in an
individual bladder wherein the pressure can be maintained
independently of the others. It should be noted that the principles
of undercutting have been carried over from the earlier
embodiments, as shown in FIG. 8, in order to minimize stress peaks
arising from discontinuities at the joining of different foams.
Where there are joints between two types of foam, whether or not
they are in independent bladders of the type shown in FIG. 8, the
firmer material should extend over the softer one as shown in FIGS.
7 and 8. The outer cover itself may be sloped to match the material
within and assure that gradation support transfer is acceptable to
tissue restraints.
[0069] Finally, FIGS. 9 and 10 show two different techniques for
using a convoluted foam material within the bladder. In FIG. 9 the
material is inserted with the convolutions upward. In this
configuration, the use of cut-outs is of less obvious value,
although they would still provide some pressure relief in the areas
where no material is left. FIG. 10 shows the use of the convoluted
material in an inverted position, where the cut-outs would be of
more value in reducing pressure concentrations.
[0070] The numerous embodiments covered herein are by no means 7
exhaustive. Some variation suggested by the foregoing 8 techniques
will no doubt occur to those skilled in the art, and the
application of the above principles would follow directly.
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