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Technical Considerations
Seat Cushion Selection
by Martin W. Ferguson-Pell, PhD
. Ferguson-Pell is Director, Center for Rehabilitation Technology and Chief of Rehabilitation Engineering Unit,
Orthopedic Engineering and Research Center, Helen Hayes Hospital, West Haverstraw, NY.
t is natural to ask why the selection of wheelchair
cushions warrants any detailed discussion
. One
would assume that the two or three cushions which
do the job well for most people would survive the
rigors of the medical marketplace
. Surprisingly, this
is not the case
: engineers and others have not
developed a universal cushion that meets the needs
of the majority of users
. In addition to different
wheelchair cushions on the market, there are many
custom designs which offer hundreds of options.
Usually only one or two will "do the job well" for a
given client
. As a result, clinicians face the task of
matching an individual's needs with the properties
of a confusing array of available cushions. To make
matters worse, our basic knowledge of how the
seated subject and the cushion mechanically interact
is very limited, owing to the mechanical complexity
of the tissues involved. Therefore, a scientific
approach to designing cushions, and instruments to
help fit them has been slow to develop, but real
progress has been made in the last decade.
A wealth of information does exist through the
clinical observations and experience of expert cush-
ion prescribers
. But a central data/knowledge base
or any other mechanism allowing us to learn
through collective experience, has not yet been devel-
. Thus, much of the advice given to therapists
new to this field is anecdotal and parochial
The objective of this chapter is to give practical
guidelines and necessary background for approach-
ing the problem in a systematic and rational way.
The primary role of a wheelchair cushion is to
provide an effective platform from which the user
may perform a wide range of tasks
. It is difficult to
work at a table or desk or to propel the wheelchair,
if the sling seat is the only support
. The wheelchair
cushion also improves comfort, aids posture, and
absorbs shock during propulsion over uneven sur-
. For many, the cushion performs a crucial
function by reducing the concentration of pressure
in tissues, thereby helping to prevent the formation
of pressure sores.
Selecting a seat cushion should be considered an
integral part of the process of prescribing the correct
. Failure to recognize that the wheelchair
and the seat cushion should be prescribed at the
same time can waste human and material resources,
and result in a far-from-optimal seating system
. All
too often, the seat cushion (and other critical
"accessories") are prescribed as an afterthought;
choice is then restricted to accommodate constraints
introduced by the dimensions of the wheelchair.
Some wheelchair users with skeletal deformity
or very limited postural control, require seat inserts
that help control the position and stability of the
trunk and hips (36)
. Seat inserts frequently require
special components and shapes
. Recent develop-
ments using modular components are expanding on
JRRD Clinical Supplement No
. 2
: Choosing a Wheelchair System
the traditional fabrication techniques involving
plywood and foam construction
. Custom-shaped
shells can now be produced by
: 1) vacuum forming
of sheet plastics
; 2) resin-bonded vacuum consolida-
tion of glass or styrofoam beads
; 3) forming
shapable matrices of lockable plastic components;
and, 4) foam molding may be performed around a
user while he/she is held in an optimum sitting
position in the wheelchair
. In a few hours, these
methods can provide a finished custom-formed
postural support which intimately follows complex
curvatures and may also help to reduce localized
pressure (19).
Specialized seat inserts are normally prescribed
by seating specialists who have received comprehen-
sive training in clinical evaluation, the biomechanics
of sitting, and fabrication techniques
. However,
some of the basic principles used in prescribing
sophisticated seat inserts also apply to prescribing
wheelchair cushions
. A review of these principles
will certainly be useful.
The information in this chapter is organized
into three main categories:
General Principles
Evaluating the Client
Some Useful Techniques for
. Matching
Cushion with Client
with the addition of two short categories:
Wheelchair Cushion Fitting Clinics,
ing what is needed to establish an effective
; and
describing an expert system pro-
gram that guides the novice through the fitting
When we sit on a cushion, a number of
interacting factors determine whether it is comfort-
able, functional, and clinically safe
. Many of these
factors are interrelated
; some factors are attributed
to the properties of the cushion, and others due to
the characteristics and needs of the user.
Factors that affect comfort include:
poor distribution of stresses in soft tissues
moisture accumulation
heat accumulation and loss
compromised stability
Factors that determine functionality include:
stability provided
weight of the cushion
frictional properties of the cushion and
cushion thickness
durability and the need for user mainte-
Factors that determine clinical safety include:
poor distribution of stresses on soft tissues
stability provided
frictional properties of the cushion and
moisture accumulation
heat accumulation and loss
durability and the need for user mainte-
tress is defined as force divided by the area over
which it acts
. Higher stresses occur if either the
force acting over a given area becomes larger or if a
given force acts over a smaller area
(Figures la and
Localized stresses in soft tissues are an inevita-
ble consequence of sitting
. Only when we are
suspended in water or are weightless in space, are
the stresses on our tissues evenly distributed
. When
our body weight is supported on a solid surface such
as a cushion, localized stresses are generated which
compress and deform the soft tissues
. The changes
in the shape of the soft tissues result in occlusion of
blood vessels and lymphatics, and stimulate nerve
endings which may signal discomfort to the central
nervous system.
The stresses can be divided into two groups:
those that act perpendicular to the skin, called
normal stresses (in everyday speech we use the term
pressure) and those that act parallel to the skin,
called shear stresses.
When a person is in the sitting position in a
wheelchair, the total force acting on the buttocks
: Seat Cushion Selection
Force F
I x b
Normal stress =
Figure la.
Normal stress
will be increased if F is made larger or if the area is made smaller
. Normal stress causes materials to compress
(compression) or expand (tension) without significant change in shape
Force F
h x b
Figure lb.
Shear stress
will be increased if F is made larger or if the area over which it acts is made smaller
. Shear stresses cause the shape of
materials to be changed without significant change in thickness.
and thighs is body weight minus the supporting forces
of the footrest and backrest
. The greatest propor-
tion of body weight, when sitting, is therefore sup-
ported by the area over the ischial tuberosities (ITs).
Bone resists even large forces with barely
perceptible deformation
. Muscle and fat are far
more vulnerable because they deform more readily,
causing blood vessels to be occluded
. The force due
to body weight, when sitting, is imposed by the ITs
on the gluteal muscles and fat, which become
deformed due to the compressive force
. In addition
to the force of the ITs and the amount of tissue
supporting them, tissue stiffness or tone also deter-
mines how much deformation (and therefore dam-
age potential) is developed in the fat and muscle.
Wheelchair users with little muscle tone in their
gluteal area are less able to resist tissue deformation,
and are therefore more vulnerable to discomfort and
tissue damage.
It is important to note that heavy individuals
are not necessarily more vulnerable to tissue break-
down (17)
. They normally have more fat and muscle
padding, which compensate for the additional body
weight that has to be supported
. At greater risk is an
emaciated person with flaccid gluteal tissues
. The
combination of inadequate padding and poor mus-
cle tone produces higher than average deformation
in the tissues that remain
. Those who have
JRRD Clinical Supplement No
. 2
: Choosinga
Wheelchair System
Shaped cushions help share the supporting forces F, and F
more equally between the ischial tuberosities (F,) and the trochanters
. On cushions with no shaping F, is considerably larger than F
and the ITs have to compress the cushion nearly 2 inches before
the trochanters make contact.
Convex base filler accommodates sling seat sag
tissue overlying the ITs due to previous pressure
sores are also particularly vulnerable.
Stresses in the soft tissues are not usually evenly
distributed, and are thought to be greatest in the
muscle close to the ITs, the area in which pressure
sores seem to start
. Necrosis migrates outward to the
skin as cell constituents are released and cause
damage to nearby compromised tissue.
If weightbearing can be shared equally by the
ITs and the nearby lateral posterior aspect of the
trochanters, the force at each IT is half of that when
only the ITs are loaded, and more soft tissues can
share the burden
. Weight distribution is, therefore,
an important principle used for designing cushions
that are shaped to encourage trochanteric and thigh
(Figure 2)
oisture accumulation results in discomfort
and, in some cases, an increased risk of soft
tissue damage
. Many factors determine the causes
and prevention of moisture accumulation.
Generation of excessive quantities
Sweat is normally generated to assist in the
thermoregulation of the body by the evaporation of
moisture to cool the surface of the skin
. Normally,
sweating is suppressed locally by pressure
. Following
spinal cord injury, however, sweating can occur in
an uncontrolled manner independent of thermo-
. The reduction of pressure by use of
sophisticated cushion systems can, in effect, reduce
suppression of sweating due to pressure, and thus
: Seat Cushion Selection
pose potential difficulties in keeping the skin dry
and free from damage due to maceration.
Poor exchange of air
If there is poor exchange
of air in the supported area and the supported area
is thermally insulated by the cushion, the interface
temperature can exceed 38 degrees Centigrade,
whereupon sweating increases rapidly with increas-
ing temperature.
Use of impermeable covers
Moisture accu-
mulation can also occur if materials in close con-
tact with the skin do not "breathe
." Vapor-
impermeable covers prevent moisture-laden air
from being diluted by drier air, thereby preventing
newly-formed sweat from evaporating or being
. Furthermore, because sweat is not being
evaporated, natural environmental cooling cannot
occur, resulting in more heat build-up and more
Continuous humidity or moisture monitors
have not proved to be reliable in measuring the
microclimate between the skin and cushion
. A
simple moisture-sensing patch is available* that has
been used successfully in research projects (14,35).
We are not aware of any centers using humidity
sensors in routine clinical evaluation
: common
sense, direct client feedback, and experience seem to
be adequate.
Methods for preventing moisture build-up in-
clude the use of cushion and cover materials that
encourage air exchange between the cushion and
. Cushions with good heat dissipation character-
istics help to reduce moisture build-up, if they are
appropriately covered with absorbent materials like
sheepskin or jersey knit fabrics
. Wearing
cotton/flannel underwear also helps to reduce mois-
ture build-up.
Water vapor permeability, absorbency, heat
capacity, and thermal insulation of materials used in
cushions are readily measured in the laboratory, but
are rarely quoted by manufacturers
. As we become
more sophisticated and learn how to apply this
information, disclosure of such data should become
more routine.
*Humidial Model HHH-20-90, Humidian Corp. 465 Mt
. Vernon Ave
. Box 464, Colton, CA 92324
Some cushions naturally pump air that is
trapped in their structure when compressed (e
. The Jay cushion may now be ordered with
an Air-exchange cover that uses this principle
(Figure 3)
This effect can contribute to maintaining
comfortable moisture levels at the cushion/skin
interface, if the cushion is fitted with an air-
permeable cover
. Air exchange is an added incentive
to encourage "push-ups," even for those who are
not particularly at risk of developing pressure sores,
but who do experience discomfort due to moisture
When a warm buttock makes contact with a
cold cushion, the buttock will cool down and the
cushion will warm up until the cushion-tissue inter-
face reaches an equilibrium temperature
. Some
cushions (e
., gels) feel colder than others (e
foam) because fluids and gels conduct heat more
rapidly than foams and air.
Another important thermal property of a cush-
ion is its heat capacity, or the amount of heat
required to raise its temperature one degree
. Heat
capacity varies with the mass of the cushion and the
type of material.
In principle, heat accumulation can be mea-
sured using thermistors or thermocouples
. However,
several problems reduce practicability for routine
clinical evaluation
. As indicated in the studies of
et al
(35) and Ferguson-Pell
et al
equilibrium of skin temperature requires sitting for
more than an hour.
It is still unclear how we might quantify heat
build-up for clinical interpretation
. We could mea-
sure the equilibrium temperature, but the transitory
coolness of a cushion that has not reached equilib-
rium may give considerable relief
. We could mea-
sure the area under the time-temperature plot for a
typical sitting period, but this requires a fairly
sophisticated data-logging system
. Similarly, we
could measure the time taken to reach a critical skin
temperature—38 degrees Centigrade—above which
sweating becomes increasingly profuse in able-
JRRD Clinical Supplement No
. 2
: Choosing
Wheelchair System
Figure 3.
"Standard" Jay cushion with cover removed.
bodied individuals
. Whichever method is used,
prolonged monitoring is required, preferably over a
range of environmental temperatures
. In practice, it
is sufficient to predict how different cushions
respond to heat build-up by knowing their thermal
properties as reported in the studies of Stewart
et al.
Ferguson-Pellet al
. (14),
Figure 4.
Foams are poor conductors of heat and have a
low heat capacity
. A thin layer of foam (plus cover)
warms up to skin temperature when one sits on it,
but does not draw much heat from the body's
. In warm environments, or during physical
exercise, the body attempts to lose heat but is
prevented from doing so in the buttocks area due to
the insulating foam of the cushion
. This region may
therefore begin to heat, resulting in uncomfortable
On the other hand, gels and fluid-filled cush-
ions are moderate conductors of heat and have a
high heat capacity
. They drain heat from the
buttocks and continue to do so for a long time
. For energetic wheelchair users, the
thermal properties of the gel help to dissipate
metabolic heat
. Gel cushions are also beneficial in
warm environments if effective water vapor and
sweat removal can be assured
. However, in cold
environments or for weak individuals who have
difficulty in staying warm, these cushions make
additional demands on the metabolic system
. Fur-
thermore, gels and fluid-filled cushions are heavy
: Seat Cushion Selection
Figure 4.
Changes in skin
temperature and moisture content of the
buttock/cushion interface for an able-bodied subject for 2
hours continuous sitting
. (Reproduced with permission, Oxford
University Press, 1986
(up to 35 pounds), which can reduce wheelchair
performance as well as present problems in stowing
the wheelchairs in the car
. Some cushions are
designed to obtain the best properties of both
materials by using a modular approach, with the gel
close to the skin, and foam for the bulk of the
. Because the mass of the gel is relatively
small, the heat capacity is smaller than a total gel
. It achieves less cooling with less metabolic
heat drain
. Studies completed by Stewart
et al
and Ferguson-Pell (14) discuss experiments on the
thermal properties of cushions in detail.
he effect that the cushion has on stability, real
or perceived, can be critical—especially for users
with poor trunk control.
A number of mechanical properties of the
cushion influence the stability of the support sur-
. The ability of the cushion to deform, both in
direct compression (vertical loading) and in shear,
must be considered.
Highly compressible cushions offer very little
resistance to body weight and tend to function like
an overcompressed spring
. If one rides over a bump
in a wheelchair the "hardness" of the sling seat can
be felt through the cushion
. Overcompressed cush-
ions are said to "bottom out
At the other extreme, incompressible cushions
are ineffective in preventing pressure localization.
Because they are less compressed, the user often
feels as if he/she is sitting on a cushion that is too
. In addition, the cushion may appear to be
moderately deformable in shear, and may feel
unstable during manual propulsion.
Cushions that fall between these two extremes
have advantages, such as improved pressure distri-
bution, but may also feel "springy." Compromises
between cushion stability and pressure distributing
capacity often have to be made in practice—usually
by accepting a small increase in the accepted
pressure over bony areas.
Material thickness can influence the sense of
instability, the cushion's compressibility, and its
pressure distributing properties.
At present we are unaware of any routine meth-
od to measure trunk stability
. We rely upon direct
feedback from the user
. Persons with spinal lesions
at a high level often have acute awareness of their
trunk stability that is far more subtle and complex
than position measurement systems are able to detect.
In the laboratory, we test the effectiveness of a
material or cushion in absorbing impact energy by
measuring hysteresis, which is represented by the
area between the load-deformation curves for load-
ing and unloading conditions
(Figure 5)
is normally expressed as a percentage, representing
the energy lost during the loading/unloading cycle.
Deformability and cushion thickness alone do
not control the destabilization of the user
. Some
cushions have the capacity to absorb energy when
they are deformed
. Gels, fluid-filled cushions, some
foam cushions, and simple air pillows behave fairly
elastically when sat upon, and create a feeling of
instability during propulsion or when riding over
rough ground
. Because they are elastic, they tend to
Time (min)
JRRD Clinical Supplement No
. 2
: Choosing a Wheelchair System
Figure 5.
Energy dissipation of cushion materials can be determined by
performing a simple mechanized test
. The area within the
load-deformation curve when the sample is loaded and then
unloaded provides a measure of energy dissipation
. The greater
the shaded area the more energy is dissipated by the cushion
transmit the energy of dynamic loading to the body
via the gluteal tissues for dissipation.
Viscoelastic materials (Temperfoam is an exam-
ple) have the capacity to absorb energy on impact,
like shock absorbers, which results in a real and
perceived sense of stability
. Viscoelastic materials
are time-dependent, their stiffness depending upon
the rate of loading
. Impact loads do not cause as
much cushion deformation as slowly applied loads,
and may therefore tend to produce high, localized,
instantaneous pressure
. Another consideration is
that because viscoelastic materials compress increas-
ingly over time, after an hour of sitting they may
bottom out, producing areas of localized pressure.
The deformation of these materials is also
dependent upon the temperature of the material.
When cold, they may feel very hard until softened
by body heat
. When very warm, viscoelastic foams
easily bottom out
. Caution should be exercised in
using these materials above or below the normal
room temperature range.
Some air-filled and water-filled cushions behave
viscously, too
. Roho cushions, for example, consist
of interconnected air bladders
(Figures 6a and 6b).
Energy dissipated:
Energy dissipated:
Figure 6a.
Roho wheelchair cushions (upper "normal" and lower "low" profiles)
: Seat Cushion Selection
Figure 6b.
Roho "high" profile cushion.
If a sudden localized force is applied, the air in the
loaded cells is forced into neighboring cells, thereby
absorbing the impact energy
. In practice, Roho
cushions provide far more stability than might be
expected, because rapid destabilizing movements are
damped by the cushion due to air flow resistance
between the cells.
eavy cushions are of particular concern to users
with limited upper limb strength, those who
transfer independently from chair to car, and
athletes who require minimal wheelchair weight for
maximum performance
. Gel or fluid cushions are
usually heaviest, weighing in some cases over 20
pounds (9 kg)
Table 1
is derived in part from Jay
(21) and lists the weights of some commercial
cushions that weigh more than 3 pounds.
rictional properties are particularly important
during transfers, as the user can easily fall if the
cushion slips away
. Yet, moderately low top surface
friction is helpful during transfers, for users whose
upper limbs are weak
. One solution to this problem
is to anchor the cushion with ties or Velcro.
Although ties are useful in maintaining the position
of the cushion during sitting, they are difficult if not
impossible for the user to install independently prior
to the transfer
. For clients who have to fold the
JRRD Clinical Supplement No
. 2
: Choosing
Wheelchair System
Table 1.
Weight of Selected Commercial Cushions*
Cushion Name
. Weight
Sculptured foam
.5 2
Sculptured foam
6 .0 2 .8
+ sheepskin
10 .0 4 .5
Reston Flotation
Solid gel
.0 6
Spence Omega 5000
Solid gel
14 .0 6
Thixotropic gel
14 .0 6
SML Comfort
Thixotropic gel
12 .0 5
Carter's Carterflow
6 .0 3
Grosvenor Medical
.0 4
Knoche Silicone Gel-foam
6 .0
Jay reg
. adult
.0 3
.0 9
Western Medical
Jobst Hydrofloat
25 .0
Ardo Water
.0 7
10 .0
.0 2
Foam-air mechanical
12 .0
Foam-air mechanical
12 .0
Healing Environment Alternating air pressure
*Derived from Jay P
Choosing the Best Wheelchair Cushion
Washington, D
: RESNA, 1984.
chair frequently, ties are not practicable and most
wheelchair users do not use them even when they are
supplied by the cushion manufacturer.
Mating strips of hook-and-loop fastener (e
Velcro) may be sewn to the underside of the cushion
cover and attached to the sling seat
. We have
experienced difficulty achieving a reliable long-term
bond between the fastener strip and the sling seat,
and when they fail, an ugly residue is left that is
difficult to remove.
Instead, we use three of the sling seat attach-
ment screws on each side of the frame for holding
the loop fastener strip to the frame
. A secondary
advantage of using hook-and-loop fasteners is that
the orientation of the cushion (top-bottom/front-
back) is automatically defined.
Jay (1984) suggests that friction can be increased
between the cushion and sling seat by using anti-skid
netting, as used with rugs
. Often, however, friction
alone is not sufficient to prevent the cushion from
being knocked out of place during the transfer
henever possible, the cushion and wheelchair
should be prescribed at the same time in or-
der that wheelchair dimensions accommodate the
thickness of the cushion
. It is important to recognize
that the cushion will be compressed in use when
determining the position of the user with respect to
the seat and back
. This compression is uneven
because of the localized distribution of pressure
owing to the weight and anatomy of the individual
(22, 31).
For users with critical requirements, the cushion
should be seen as an extension of his/her gluteal
padding and the wheelchair dimensions selected
in accordance with the prescribed cushion
. For
those with less critical needs, compromises can be
made in both cushion and chair specifications,
when they are evaluated together
. Correct sitting
height is crucial for optimal performance in the
: Seat Cushion Selection
or many people, appearance is quite important
and should not be overlooked
. Strategic use of
cover materials, colors, and designs can be em-
ployed to disguise the utilitarian appearance of the
"core" of the cushion.
t should be remembered by prescriber, user, and
insurer that the cheapest cushion is not necessarily
the most economical
. Some cushions are less durable
than others, and for most wheelchair users, long-
term rather than crisis economics should be em-
. Many clinicians have expressed great con-
cern over the cost of some cushions, especially those
designed specifically for users vulnerable to pressure
. In most cases, these costs are fully justified
when the complexities of manufacture, development
and distribution costs, and the relatively small size
of the market are considered
. According to a study
by Noble (29), the average number of inpatient days
required to heal an ischial pressure sore is 74 days.
With per diem rates in rehabilitation hospitals
exceeding $500, the expense of a correctly prescribed
cushion can be easily justified in economic terms
alone, since it is likely to significantly reduce the risk
of tissue breakdown.
aterials used in the construction of wheelchair
cushions vary greatly in their durability and
longevity, and some cushion types require user
All foam cushions deteriorate with time, even
when they are not used
. This is caused by increased
brittleness of the polymer matrix, leading to frac-
tures in the foam and softening of the cushion.
et al
. (30),
found that storage over a even few
months caused changes in the properties of foam
Fatigue is a deterioration in the supportive
properties of the cushion due to prolonged use, and
is a function of the time in use and the magnitude
and number of stresses
. Most foam cushions do not
tolerate tension ("pulling") and shear ("tearing")
. Certain cushion designs, particularly those
incorporating cut-outs, can produce very high ten-
sion and shear in the foam matrix, requiring them to
be replaced more often than simple slabs of foam.
Exposure to moisture also shortens the life of
foam cushions
. Viscoelastic (Temperfoam) cushions
are particularly susceptible to moisture, fatigue, and
. Gels also age by developing hard or consol-
idated local regions
. Sometimes these regions can be
"kneaded" to break up the lumps and prolong the
life of the cushion
. Both prescriber and user should
be alerted to deterioration in gels, as these hard
regions can pose a risk to tissue integrity.
Some cushions require the user to actively
monitor and service them
. Roho and other air-filled
cushions require that the amount of air in the
cushion be at a specific level for that individual.
Alternating pressure (ripple) cushions incorpo-
rate a battery-powered air pump and valve manifold
to control the inflation of different panels or regions
of the cushion
. Maintenance for these cushions
centers on regularly charging the battery.
Cushions requiring maintenance to ensure prop-
er function should be prescribed only when the user
or caregiver is physically able and willing to do so.
he cover is an important component in the
cushion system
. Some of the contributions to
the performance made by the cover have already
been referred to
: moisture build-up, frictional
properties, and appearance
. Mechanically, the
cover can modify the stiffness of the cushion
core due to the "hammock effect" (7,15,34)
. Un-
less the cover is stretchable, it will not follow
the surface of the compressed cushion, causing
JRRD Clinical Supplement No
. 2
: Choosing a Wheelchair System
the cushion to be harder than without the cover and,
in turn, producing higher localized pressures over
bony areas.
Users who experience frequent incontinence
require some waterproofing to protect the core of
the cushion if it is an absorbent type (e
., foam).
Otherwise, frequent washing should be all that is
. (It should of course be noted that good
medical programs to manage incontinence are far
more preferable than waterproof covers
.) Most users
with only infrequent accidents may prefer to risk
wetting their cushion than to using a vinyl type
. Simple foam cushions can be rinsed and spun
dry, although it should be remembered that this
shortens their useful life
.* Viscoelastic foams should
not get wet because they are irreparably damaged by
. Jay (21) points out that one of the difficulties
with waterproof, nonabsorbent covers is that should
an accident occur, puddling of urine on the cover
can be very embarrassing
. One approach is to use an
inner waterproof liner (e
., plastic waste-bin line)
wrapped around the core of the cushion which can
then be covered with a stretchable water absorbent
Sheepskin covers are widely used and offer
many advantages
. They absorb moisture (there-
by reducing wetness due to sweating), contain
lanolin, are washable, and have intrinsic mechan-
ical properties that offer support and help to re-
duce pressure localization and shear. Lanolin,
when in direct contact with skin, provides addi-
tional protection from moisture and friction.
The appearance of sheepskin is highly acceptable to
most users and it can be dyed
. Denne (9,10)
undertook studies that describe in detail both
the pressure-distributing properties of sheepskin and
the changes that can occur following repeated
Brushing or combing the fleece helps to pre-
vent felting of the wool fibers. Jay (21) and Menec
et al
(27) discuss in depth the benefits of sheep-
skin, compare natural and synthetic fleeces, and
recommend methods for washing and caring for
*Editor's Note
Washing a foam cushion will severely damage the
foam's integrity
. A soiled foam cushion can be `dry' wiped clean and
then dusted with cornstarch or crushed mothballs, or a mixture of the
two to remove dampness and odor
a noninstitutional setting, flammability stan-
dards for cushions and covers need be no more
stringent than for ordinary furniture and clothing,
unless the user is confused, or has severe disabilities
and is unable to get out of the chair unassisted
. The
greatest dangers arise in institutions where large
numbers of cushions and mattresses can present a
very serious fire hazard
. When burned, plastic
foams produce extremely poisonous gases that may
incapacitate even more rapidly than the fire they
Smoking presents the greatest fire hazard to
foam cushions in the home
. Some covers can form
an effective barrier between a dropped cigarette and
the cushion, but may lose their fire retardant
properties with frequent washing.
Roho, air-filled, and fluid-filled cushions are
more resistant to burning
. Plastic foams that have
been treated with a fire retardant can be obtained.
"Scott Foams" produce a foam called "Pyrell" that
is particularly resistant to burning.
Before attempting to fit a cushion, it is impor-
tant to identify the needs of the prospective user
. A
simple evaluation form may be helpful, ensuring
that key points are covered and the goals for the
user (and cushion) are understood and documented.
Techniques for achieving these goals come with
experience, but we hope with the help of expert
system computer programs such as CUSHFIT
(13,20), that we can make the process less special-
ized and more systematic in the future.
Many of the most difficult problems faced by
wheelchair prescribers are associated with attempts
to prevent pressure sores
. When evaluating users
vulnerable to pressure sores, it is important to
determine whether:
sensation is total, partial, or absent,
any clinical conditions exist, placing them at
higher than normal risk,
they regularly relieve tissue stresses by move-
they spend prolonged periods of time sitting
in their chair,
: Seat Cushion Selection
they produce unacceptably high localized
stresses over bony prominences,
they are subject to heat and moisture accu-
mulation due to exertion, environmental
temperatures, and/or reflex sweating,
they have a good sitting posture,
they have good trunk stability,
an adverse skin condition exists.
Our approach to cushion fitting divides these
factors into two groups
. Type I are those that can be
modified by a cushion/seating system, and Type II,
those that are intrinsic to the user and place him/her
at greater risk for breakdown.
Type I factors include:
highly localized stresses
heat accumulation
moisture accumulation
poor sitting posture and positioning
poor trunk stability.
Type II factors include:
degree of sensation
regular relief of stresses by movement.
: some cushions accomplish weight
shifting by alternating air pressure in local
regions of the cushion
Establishing Maximum Allowable Interface
Reswick and Rogers (32) developed guidelines
for maximum acceptable pressures at the
skin/cushion interface, associated with a range of
time intervals for which the pressure is applied
. A number of important assumptions
underlie these guidelines and should be seriously
considered when implementing them clinically:
Their guidelines are intended for use with
spinal cord injured outpatients.
They are intended to be used by associating
the total sitting time with a maximum
pressure over ischial tuberositates
. It is as-
sumed that the client performs push-ups,
., with a frequency typical of the average
spinal cord injured wheelchair user
. This
average frequency is not indicated nor is a
correction factor given for other frequencies.
Some users may be at a higher risk for
breakdown than others due to clinical fac-
tors (such as diabetes, presence of scar tissue
Hours continuous pressure
Acceptable pressure/time interval guideline
: Reswick and
Rogers (1976).
or persistent skin redness, recent spinal cord
injury) and reducing the maximum recom-
mended pressure may be indicated.
Differences in the tolerance of tissues overly-
ing different bony prominences (e
., coccyx
is much less tolerant than ischial
tuberositates) are not reflected in the guide-
Presence of other stresses—particularly shear
(coccygeal sitters) or repetitive loading (very
active user)—should be accommodated by
reducing the maximum recommended pres-
Users with a tendency for self-neglect, taking
physical risks, or whose family, social, or
career commitments are unusually demand-
ing, may tend to ignore or delay responding
to precursors or actual breakdown
. They
require a recommended pressure-time guide-
line which pulls them back further from the
threshold conditions for breakdown
. This
can be accomplished by taking rests from
sitting during the day, by really performing
push-ups, by reducing interface pressure—or
preferably all three.
For many years, there has been a debate in the
literature concerning maximum allowable pressures
[see for example: Kosiak (24)
; Cochran and Slater
; Edberg
et al
. (11)
Reswick and Rogers (32);
Shaded area represents
margin of uncertainty
JRRD Clinical Supplement No
. 2
: Choosing a Wheelchair System
Agris and Spira (1)
; Graebe (18); Noble (29)].
Discussion has centered on linking maximum al-
lowable interface pressures with physiological
parameters such as capillary perfusion pressure.
These arguments are fraught with difficulty
. For
example, there is a large pressure drop across
a capillary ranging from 30 + mmHg on the
arteriole side to nearly zero on the venule side.
Presumably, if sufficient pressure is applied to close
off the outlet (venule) side of the capillary, no blood
will flow.
I believe that interface pressure is only a rela-
tive indicator of the stresses and deformations
occurring deep in the tissue, and that we should not
attempt to link absolute values of interface pressure
to physiological processes
. Reswick and Rogers (32)
contribute positively to the clinical use of pressure
measurement, by at least emphasizing that in all
probability, there is no one maximum allowable
pressure to suit all individuals. They also expand the
clinical guidelines to include a second variable—
At Helen Hayes Hospital we have expanded this
concept to include other factors, and have estab-
lished a simple scoring system that provides a
maximum allowable pressure for each bony area at
risk (Table 2)
The basis for our scoring system is
purely pragmatic, based on extensive experience
with large numbers of spinal cord injured individu-
. Part of our current research is designed to form,
in collaboration with five other centers, a large
database that will determine how effective this
scoring system is, and whether additional factors
need to be included
Sitting Posture and Positioning
Scoliosis and pelvic obliquity cause uneven
pressure distribution over the ischial tuberositates
and greater trochanters, while rotation of the pelvis
will result in excessive sacrococcygeal pressure.
Methods for controlling these problems are dis-
cussed in depth by Zacharkow (37).
Wheelchair adjustments are critical during eval-
uation for the cushion, if the optimal posture and
positioning of the user are to be preserved
. If special
supports are required, they should be in place during
the evaluation
. The use of an adjustable evaluation
wheelchair, such as that described by Shapcott
et al.
may prove to be helpful in optimizing concur-
rent cushion and wheelchair prescription.
Armrests and footrests can affect cushion per-
formance dramatically
. Support for the arms can
reduce ischial pressures 25-35 percent (4)
. Footrests
should be set, if possible, so that the thighs are
horizontal and not bearing their own weight
. If the
footrests are too high, they transfer much of the
weight of the thighs to the ischial tuberositates
. If
they are too low, they can promote sacrococcygeal
Bush (6) and Brattgard and Severinson (4) have
also demonstrated marked reductions in ischial
pressure (up to 25 percent) by reclining the backrest
. Zacharkow (37) suggests that a seat angle of
10 degrees and backrest angle of 15 degrees are good
average values to assure good posture, stability,
comfort, and function
. Increasing the seat angle
excessively can transfer thigh weight to the ITs, and
increasing backrest angle can produce greater shear
Table 2.
Recommended Maximum Acceptable Pressure
40 60
<20 <20
60 80 40 40
80 80 40 40
Note—These maximum recommended pressures assume a normal clinical status, push-ups performed every 15 minutes and no other factors that
would increase the risk of breakdown
. Prolonged sitting( > 10 hrs) and infrequent pressure relief are weighted by reducing each of the maximum
allowable pressures by 10 mmHg per factor
. If risk is already high, then sitting time and/or pressure relief frequency
be brought to normal
Level of risk
High—no sensation
; history of sores at site
of measurement
Moderate—no sensation
; no history of
tissue breakdown
Low—partial or full sensation
; no history
of tissue breakdown
: Seat Cushion Selection
In routine clinical evaluations, we normally rely
upon the client's description of residual sensation.
Pressure Relief by Movement and Total Sitting
Pressure relief by movement and total sitting
time are factors at the technological threshold of
being directly monitored for routine evaluation.
Fisher and Patterson (16), Merbitz
et al
. (28),
et al
(5) are developing portable devices that
will provide information about pressure relief and
total sitting behavior
. Merbitz
et al
(28) and Fisher
and Patterson (16) have collected sequential data in
the hospital environment for up to 1 month
. Burn
(5) now have a device capable of measuring
pressure relief behavior and habitual sitting asym-
metry, for more than a month in the
home/workplace, without the need for battery re-
charging or data downloading
. Until these systems
complete preliminary development and clinical eval-
uation, we must rely upon the reports of the user.
Adverse Skin Condition
Adverse skin condition is monitored by direct
. Intense activity continues in an attempt
to identify methods for detecting early signs of
tissue breakdown
. These on-going studies involve
measurements of
: skin pO
, laser Doppler assess-
ment of skin blood flow
; ultrasonic properties of
; and local temperature using thermography or
liquid crystal film
. In the meantime, the following
scale is used for classifying skin condition associated
with the development of pressure sores (3):
Class 1
: skin discoloration
Class 2
: superficial pressure sore
Class 3
: destruction of skin—no cavity
Class 4
: destruction of skin—cavity.
We also recommend that the presence of scar-
ring be recorded
. An instant photograph of prob-
lematic skin conditions kept in the medical record, is
valuable for the review of progress and planning.
Devices for Measuring Interface Pressure
Devices for measuring the pressure (normal
stress) between the skin and the cushion can be used
to locate regions of localized pressure, and indicate
how they are distributed by a cushion
. It is
important to remember, however, that pressure
measurements made at the skin's surface are
thought to be much lower than those deep in the
tissues, where pressure sores initially develop
. For
users with sensation, subjective feedback of comfort
is far more desirable than rigid adherence to a
method involving maximum interface pressure.
Pressure sensors fall into the following catego-
discrete sensor, single measurement
multiple sensor, single measurement
discrete sensor, continuous measurement
4) multiple sensor, continuous measurement.
Until recently, sensor types (1) and (2) have
been most widely used in cushion-fitting clinics.
Two discrete sensor systems providing single or
snapshot type measurements are currently available
commercially in the USA:
Type (1) Skin Pressure Evaluator (SPE)
(Figure 8)
Camp International Inc.
PO Box 89
Jackson, MI 49204
[A fuller technical description of this device is given
by Reswick and Rogers (32)
One multiple sensor snapshot or single reading
device is commercially available:
Type (2) TIRR Pressure Evaluator Pad (PEP)
(Figure 9)
Tee Kay-Applied Technologies
11915 Meadowtrail Lane
Stafford, TX 77477
(713) 495-6838
[A fuller technical description of this device is given
by Krouskop
et al
. (25)
One suitable continuous reading device is com-
mercially available:
Type (3 and 4) Oxford Pressure Monitor
Camp International Inc.
PO Box 89
Jackson, MI 49204
JRRD Clinical Supplement No
. 2
: Choosing a Wheelchair System
Figure 8.
Skin Pressure Evaluator.
Appropriate configuring of the OPM can pro-
vide single sensor continuous measurement (type 3)
or multiple sensor (type 4) capability.
The SPE consists of a 4-inch diameter polyeth-
ylene sack lined on its inner surface with an
electrically conductive grid
. It is inflated manually
using a sphygmomanometer which also indicates the
pressure inside the sack
. The grid functions as a
switch which controls a small light on the sphygmo-
. When the pressure inside the sack
exceeds the pressure applied by the body, the two
grids are separated and the light is extinguished
. As
air pressure is reduced using the bleed screw on the
sphygmomanometer, a critical point is reached
where the light is suddenly illuminated
. Bleeding of
air from the sack is stopped by the operator and the
air pressure measured indicating the maximum
(peak) pressure over the bony area
. In fact, the air
sack does provide some support for the tissues
surrounding the center of the pressure distribution.
This results in readings that are somewhat lower
than the true peak pressure
. The size of this error
depends upon how localized the peak pressure is
. In effect, this means that unacceptably high
pressures are even higher than measured, whereas
"acceptable" pressures may be marginally greater
than indicated.
The PEP pressure monitor consists of an array
of 144 discrete pressure sensors approximately 1
inches between centers
. A similar principle of
operation is used in this device in that the sensor
matrix is formed from a flexible sheet of plastic,
each divided from the next using a welded seam
. All
the air cells are, however, interconnected and are
inflated from a single air pressure source
. Each cell
: Seat Cushion Selection
Figure 9.
TIRR Pressure Evaluation Pad.
is coated with a ribbon of electrically conductive
paint that functions in a similar way to the metal
grid of the SPE
. The commercially produced system
is designed to provide a readout using an array of
. Several research centers have connected the
matrix of sensors to a personal computer and have
developed software that can plot pressure contours
directly using a printer
. The matrix is inflated to
80-90 mm Hg at which point it is assumed that the
lights on the display array will be extinguished
. If
the local pressures are higher than the maximum
inflation pressure, cells that are "on" are recorded
as ">90 mm Hg
." The pressure in the matrix is
then reduced using a bleed screw in increments of
5-10 mm Hg and the pattern of lights are recorded
at each increment
. This system, therefore, provides
a direct contour map of the interface pressures
. Its
disadvantages include relatively high cost, a maxi-
mum pressure range limited to about 90 mm Hg,
and only moderate durability of the sensor matrix
(which is subject to replacements due to fatigue in
the conductive paint).
The OPM consists of a 3 x 4 matrix of sensors,
again incorporating air cells sealed into a flexible
plastic sheet
. This design does not, however, utilize
electrical contacts and the sensors are therefore
more robust than the SPE or PEP
. The control unit
that provides the inflation source for the cells and
for a readout display automatically scans the sen-
sors, rapidly reading the pressure at each sensor
every 2 to 3 seconds
. The device employs the
following principle
. When a cell is collapsed due to
the pressure applied by the body, the flow rate of air
to the cell is very small
. Suddenly, when the air
pressure in the cell is equal to the applied pressure,
the cell inflates and the flow rate of air increases
JRRD Clinical Supplement No
. 2
: Choosing a Wheelchair System
. By monitoring both the inflation pressure
and the flow rate of air to the cell during the
inflation cycle, a "knee" in the pressure versus the
flow rate curve can be detected and the pressure
. The output can be displayed using a serial
interface to a personal computer or by using the
small printer provided to produce a hard copy
Measuring Interface Pressure
The number and location of the sites for
pressure measurement should be guided by clinical
. Most often, pressures are measured un-
der the Ischia, trochanters, and coccyx, and fre-
quently, one or two sites are of particular concern.
To save time, usually only the pressure at problem
areas is measured until a cushion has been identified
that provides adequate readings at these sites
. We
then check the remaining areas of interest, which
will invariably be satisfactory
. Two exceptions exist,
scoliosis is present
. Relieving the high-pres-
sure side may well overload the opposite side
. Both
should be measured throughout the evaluation.
the user is a coccygeal sitter
. Relieving
sacrococcygeal pressure by reducing posterior pelvic
tilt can also result in a substantial increase in ischial
. The sacrococcyeal region and at least one
IT should be monitored throughout the evaluation.
All sites clinically determined to be vulnerable
to breakdown must be measured, and the results
documented, prior to issuing the cushion.
The air cell may be inserted from either side of
the wheelchair, or from behind. The transducers are
located by palpation under bony prominences
. It is
often helpful to remove screws from the lower-back
upholstery and bend it up
. This is particularly
helpful in checking the fit and pressures on cut-out
To measure pressure on each cushion:
ask or assist the user to lift his/her buttocks
off the cushion;
palpate the bony prominence and place the
pressure sensor pad under the center of this area;
hold it in place as the user resumes a relaxed sitting
remove your hand without disrupting the
placement of the pressure sensor pad (sometimes a
little talcum powder for your hands will make this a
little easier);
4)check the user's posture;
close the valve and inflate the sensor pad
until the indicator lamp goes off
; slowly release the
air and record the pressure reading at the moment
the lights go on;
repeat the process of palpation, placement
and measurement.
Usually, two readings suffice for each site
. If
successive readings are significantly different (>5
mm Hg), check placement and the user's posture,
and take readings until consistent values are ob-
. Occasionally, the indicator lamp may fail to
go out, even if inflated to high pressures, because of
a fold in the sensor pad or possibly because it has a
damaged cell
. If this happens, reposition the sensor
pad and repeat the measurement
. If this does not
resolve the problem after two or three attempts,
inspect the metal grid of the cell for damage
. When using viscoelastic foams
(Temperfoams) wait 5-10 minutes after placement of
the air cell before taking your set of readings to
ensure that the material has conformed to the shape
of the client.
When evaluating cushions of different thick-
nesses, it is important to remember that the
footplates, armrests, and/or other wheelchair com-
ponents must be readjusted for each cushion.
Location of Bony Prominences
Location of bony prominences should be deter-
mined when fitting cushions which have been, or
will be, custom-formed to provide local relief of
bony areas (cut-out cushions
; ideally commercially
preformed contoured cushions such as the
Vasiopara and the Jay,
Figure 10)
It is wise to
accurately measure the location relative to the
wheelchair, and the separation of the two ITs, and
possibly the coccyx.
A number of techniques can be employed:
With the user side-lying, hips and
knees flexed to 90 degrees, with a 90-degree thigh to
trunk angle, the ischial tuberositates are palpated.
The distance is measured from the most prominent
part of one tuberosity to the corresponding point on
the other. This technique is extremely simple and
requires no equipment, but unlike the methods
: Seat Cushion Selection
Figure 10.
Jay "Combi Posture Seat
described below it does not provide an indication of
the location of the ITs relative to the seat and back
of the wheelchair, and hence their location on the
cushion to be prescribed.
Carbonized paper
Carbonized paper can be
used to produce an imprint of bony areas
. One of
the difficulties with this technique can be the
smearing of the imprint in the process of achieving
the normal sitting position.
A simple way to reduce this problem involves
constructing an air pillow from vinyl or other heat
sealable plastic and fitting it with a suitable inflation
tube and valve. A sheet of the carbonized paper (we
use Shutrak gait analysis paper*) is placed on a firm
surface in the chair (seatboard plus 1 inch foam
*Notecare Inc
., 2435 Professional Dr
., Suite C, Santa Rosa, CA 95401
works well), and the air pillow is then placed on top
and inflated sufficiently to support the user's weight
without bottoming out
. Thus, no localized pressure
is transmitted to the carbonized paper
. It is desirable
to make the impression with the user sitting at the
normal sitting height in the chair, with armrests and
footrests adjusted appropriately.
With the user correctly positioned, the air is
released from the pillow and an imprint is made.
The pillow is then reinflated using a hand-pump and
the person carefully transferred. The measurements
of inter-IT distance and location of bony areas
relative to the chair can be made, and if required, a
hard copy kept for the record.
This technique is used to make
temporary "casts" of users for molding custom
postural seating systems
. It can also be used to
obtain an impression of the gluteal region. The areas
of deepest impression correspond to the bony
. This technique works best with indi-
viduals who are not "well-padded
A thin, flexible sack preferably made from
latex, is filled with enough glass or Styrofoam beads
to produce a layer 1-inch thick when the bag is
. The user is asked to sit on the sack, again
on a firm surface, and the air is then evacuated
using a vacuum pump
. This leaves a hard shell-like
impression of the gluteal region, and the deep
indentations of the ITs can be identified.
This device is described in full by
Mayo-Smith and Cochran (26)
. A Plexiglas plate,
which is illuminated from the side with fluorescent
lamps, supports a rubber sheet which has been
molded to form conical projections on one surface.
When viewed from below, cones which have been
compressed reflect more brightly than the
uncompressed cones
. When sat upon, areas of
highest pressure cause greatest compression of the
cones, and the result is an image with a bright region
corresponding to the bony areas
. It produces a
dynamic image indicating the effects caused by
changes in posture, reduced pelvic obliquity, rota-
tion, and other factors.
TIRR PEP Pressure evaluator
One of the
attributes of this sensor is its capacity to produce a
direct pressure map of the gluteal region
. Bony areas
can therefore be identified easily as areas of peak
pressure, and their location measured
JRRD Clinical Supplement No
. 2
Choosing aWheelchair System
Removing Sling-Seat Sag
We frequently encounter wheelchairs with ex-
cessive sling seat sag, and often, it is severe enough
to justify replacing the seat canvas
. The following
techniques are helpful in eliminating the conse-
quences of sag
: knee adduction, high trochanteric
pressures, reduced stability, and discomfort.
One technique that has been used for many
years is to place a plywood board across the seat
frame or use drop-hooks to suspend it from the
. Thin boards can also be placed in the base of
the cushion, but they have to be manageable and
they tend to flex
. These methods are effective, but
they can make independent transfers more difficult
when the chair has to be folded
. Also, bases that are
screwed to the frame of the chair tend to affect the
. Wheelchairs need to flex when traveling over
uneven terrain because, unlike automobiles, they are
not routinely fitted with a suspension system.
Our solution to this problem has been to form a
base for the cushion from Plastazote or Ethafoam.
The base is cut to a convex shape on its lower
surface, so that it fills the concave space generated
by the sling-seat
. The base can be attached to the
cushion and placed within the cover
. As an integral
part of the cushion, it is lightweight and doesn't
interfere with transferring
The Cut-Out Cushion
The principle of load distribution has already
been discussed
. Cut-out cushions help by
redistributing the body weight normally borne by
the ITs, more equally with the posterior aspect of
the greater trochanters
. The concept was first
introduced by Reswick and Rogers (32) and has been
discussed in depth by Ferguson-Pell et al
. (12,13),
Key and Manley (23), and Zacharkow (38).
A rectangular region from a slab of firm
polyurethane foam (density 3
.75 pounds/cubic
; indentation load deflection (ILO) (25 percent)
60-80 pounds) is removed with an electric carving
. The size of the cut-out is determined precisely
for each individual, based on the measured location
and separation of the ITs
. A margin of 1
.25 inches
lateral and 1
.5 inches anterior to the center of each
IT is allowed, making the cut-out slightly larger in
width and depth than the inter-ischial and seatback-
*Alimed, 297 Hyde St
., Dedham, MA 02026 (800-966-4262), supplies
these bases, preformed for easy use
to-ischia distances
. Persons with a natural tendency
to sit obliquely, or those who sit slightly off-center,
should be accommodated with a correspondingly
shaped cut-out, if correction is not indicated
. The
depth of the cut-out should not exceed half the
thickness of the cushion
. Cushions should not be
less than 3 inches thick and at least 4 inches is
. To reduce shear at the margin of the
cut-out, a chamfer 1 inch deep at 30 degrees can be
cut along the periphery.
Variations of this design include using low
density foam fillers and cut-outs on the under-
surface of the foam instead of the top
. Undercut-
outs can also be filled with low density foam
. We
recommend that an Ethafoam base be used with all
cut-out cushions so that the cushion does not
"fold" when placed in a sagging sling seat
. The
Ethafoam base itself could be cut, in addition to, or
instead of the cushion, allowing for more foam
between the buttocks and base while benefiting from
the modified shape, without gaining additional total
This approach requires experience to use effec-
tively, but provides fine control of the relative
loading of the trochanters and ITs
. Cut-outs can
also be used to provide sacrococcygeal sitters with-
out independently controlling anterior pelvic rota-
. Zacharkow (37) suggests that this can often be
achieved using a lumbar pad and a 95-degree
thigh-to-trunk angle.
When using cut-out cushions it should be noted
: 1) a flexible cover should always be used with
cut-out cushions
; 2) a firm base is always required to
prevent inwards folding of cut-out dimensions due
to sling seat sag
; 3) the overall dimensions of the
cushion should be cut precisely, to ensure that the
cushion is located securely in the same place each
. Velcro attachment as described above is
; 4) dimensions of the cut-out must be
measured for each individual
; 5) the durability of
cut-out cushions is not as good as plain foam
. They should be replaced on the average of
every 6 months
. Thus, this type of cushion should
only be prescribed when the means for reliable
follow-up are present, and the user can be relied
upon to meet scheduled appointments
; and, 6) both
trochanteric and ischial pressures must always be
measured when evaluating cut-out cushions, because
it is crucial that goal pressures for both sites are
. Where possible, an accepted pressure a little
: Seat Cushion Selection
lower than the goal pressure should be attempted, in
order to allow for changes in the foam in the first
few weeks of use.
Despite these constraints, we find that cut-out
cushions are extremely useful for users with pro-
nounced tissue wasting in the gluteal region, when
more straightforward cushion systems fail to reduce
interface pressures sufficiently, or are not applicable
for other reasons.
The Modular Cushion
The modular cushion is designed to assist those
at low-risk for pressure sores whose needs cannot be
met by the simple foam cushion
. The modular
cushion concept (15) consists of up to four layers of
component materials
. Each layer is selected to
contribute to the overall properties of the cushion
A wide range of commercially produced materials is
. The system makes use of combinations of
three classes of materials ordinarily used alone:
foams, temperfoams, and gels
. The construction of
a typical cushion is described below and illustrated
Figure 11.
: to provide a cover that is adequate for
carrying, as well as contacting body surface.
Support Segment (bottom, sides, back)
: a
smooth, strong, light, flexible, easily cleaned mate-
rial that is adequate to support and transport the
Body Contact Segment
: a durable, porous,
two-way stretch, absorbent, easily cleaned, cotton/
polyester jersey-type fabric.
Figure 11.
Schematic of a modular cushion showing
: A) body contact segment of cover
; B) support segment of cover
; C) top layer of support
; D) middle and bottom layers
; and, E) convex base
. (Reprinted from Ferguson-Pell
et al
., J Rehabil Res Dev 23(3):65,
JRRD Clinical Supplement No
. 2
: Choosing a Wheelchair System
: to encourage air circulation and re-
duce sitting pressure
. (This layer may be omitted
when heat dissipaters such as gels are used for the
middle layer
.) A soft open-cell or reticulated foam;
thickness 0
.0 inches is recommended
. If pressure
relief is a critical factor, a denser, easily washable or
disposable material may be selected instead
. (Note:
if necessary for the protection from fluids, the
underlying middle and bottom layers may be en-
closed in a thin, loose, waterproof plastic bag
: to reduce pressure and shear forces,
and control heat dissipation
. The qualities of this
layer may be selected to suit the most urgent needs
of the user
. Various medium or high density foams
and gel components
; 1
.0 inches thick can be
: similar to middle layer, but this layer
is selected primarily to augment the favorable
qualities of the middle layer, and offset any unfa-
vorable qualities
. Viscoelastic foams may be used to
improve conformance and reduce pressures
; firm
foams may be used to counter a tendency to bottom
An Ethafoam base, as described above, is
required to reduce the effects of sling seat sag.
Reswick and Rogers (32) established the first
wheelchair cushion fitting clinic at Rancho Los
Amigos Hospital
. Their clinic focused primarily on
the needs of spinal cord injured patients at risk for
developing pressure sores
. Through this clinic
evolved the design and application of the SPE
pressure evaluator and the cut-out cushion.
The clinic was established, not only to prescribe
wheelchair cushions but also to provide a focus for
developing and reinforcing self-help methods of
pressure sore prevention, to monitor skin condition
on a regular basis, and to provide ongoing educa-
et al
. (12),
Key and Manley (23),
Noble (29), Krouskop
et al
. (25),
and others devel-
oped similar clinics around the world, with many
local variations in techniques and materials
. Each
clinic claims marked reductions in pressure sore
. Ferguson-Pell
et al
(1985a), monitoring a
spinal cord injured population, noted a reduction in
admission for treatment of ischial pressure sores
from 12 percent to 5 percent following adoption of
the cushion fitting clinic concept
. Similar successes
were reported at the other clinics.
The following components are required to
establish an effective cushion fitting clinic:
Human resources
Most clinics operate within a
team approach framework
. Although details of
fitting the cushion may have to be resolved by one
or two cushion-fitting specialists, it is important that
the rehabilitation team be involved in setting goals.
In general, physical and occupational therapists
have the primary skills and training required to be
responsible for the clinic, and to work closely with
the physician.
It is important to assign one or two therapists
to be responsible for the clinic, and to develop an
experience-base which will be vital in solving more
difficult cases
. This leaves the clinic vulnerable,
because should key personnel leave, the skill-base is
lost and the clinic will take several steps backwards
while the new staff develops experience
. These are
the dangers of specialization. But the alternative—
rotating responsibility for the clinic—can lead to
communication problems, lack of continuity for the
client, and a reduced skill-base
. CUSHFIT (see
following section in this chapter) has been designed
to reduce the problems of specialization
. It is
recommended that the clinic be open at regular
times each week (half-day blocks will be needed) and
that new evaluations, which take longer, should be
separated from follow-ups.
Material resources
Instruments for measuring
interface pressure and the location of the ITs will be
. In addition, an ample supply of various
densities of foam and frequently prescribed com-
mercial cushions should be available
. If the cushion
prescribed is commercially produced, an order
should be placed in the usual way, keeping the
evaluation stock intact
. Custom-made cushions can
often be made on the spot and fitted with one of a
number of standard covers
. Temporary foam cush-
ions may also be supplied while waiting for the
: Seat Cushion Selection
commercial cushion to be delivered or a special
fabrication to be completed.
It is crucial that detailed
records be kept for each evaluation
. Results from
previous evaluations can save many hours of fol-
low-up by avoiding duplication of effort
. Documen-
tation should include
: 1) summarizing the clinical
evaluation of the user
; 2) setting goals that are
acceptable to the team and the user
; 3) recording the
observations and measurements made during the
; and, 4) reporting use protocols, fol-
low-up frequency, precautions, etc.
The clinic should have the means to
reliably follow clients on a long-term basis. This
may have to be a rather paternalistic process, but
necessary since clients may be using cushions which
deteriorate rapidly
. Their awareness of the need to
follow-up must be reinforced continuously, backed
up by telephone calls and reminder cards
solution for a minimum number of different cush-
ions evaluated (critical path approach).
CUSHFIT offers a number of benefits:
it automatically documents, stores on disk,
and prints in approved medical format all
observations made during the evaluation;
it ensures that consistent goals and protocols
are maintained in the clinic, thereby provid-
ing quality assurance;
automatically develops a database for the
clinic which may be used for administrative
and research purposes;
reduces the need for specialist therapists to
operate the clinic and reduces the impact of
staff turnover;
incorporates a scheduling program to auto-
matically keep track of clients by generating
form letters and updating central ambula-
tory care records.
CUSHFIT is an expert system computer pro-
gram that has been developed by the Orthopaedic
Engineering and Research Center of the Helen
Hayes Hospital (13,20)
. Recognizing the problems
of therapist specialization discussed above,
CUSHFIT has been designed to guide the less
specialized therapist through the fitting procedure in
an effective and efficient manner.
The program operates on the IBM PC and XT
personal computers equipped with 256K resident
memory, two disk drives, color graphics display,
and a printer.
Initially, basic clinical and administrative infor-
mation is collected
. Observations of skin status at
each bony site, and other factors, are used to weigh
the prospective user's level of risk for developing
pressure sores
. Maximum acceptable pressures (goal
pressures) are then established, as described in
. At all times, the therapist has full control of the
program and is able to interactively modify both the
goals recommended by the program, and cushions
that it specifies.
Pressure readings are obtained on two reference
cushions (medium and firm foam) and are used by
the program to establish a sequence of cushions,
commercial and custom, to be evaluated
. The
sequence has been designed to reach a satisfactory
hen selecting a seat cushion, basic physical
and clinical principles should be applied to
ensure that the best choice is made
. Unless there is
no alternative, the seat cushion should always be
prescribed simultaneously with the wheelchair
. This
ensures that we do not have to compromise our
goals unilaterally (to either the cushion or chair,
whichever happens to be prescribed last) and that
dimensional adjustments can be made to accommo-
date ergonomic and functional needs.
It should be recognized that seat cushion
selection is not a simple process—no single cushion,
at present, meets the needs of all users
. The number
of parameters which have to be controlled is
considerable, and unless we adopt a highly struc-
tured approach to cushion selection, one of two
frequently encountered problems can occur
. We
could limit our choice of candidate cushions to a
small, manageable number with consequent compro-
mises in the final result
. Alternatively, we could try
to juggle all the factors at once, and become so
confused by options that the "best fit" would be
made by chance rather than design.
This article has discussed ways of keeping our
options open while maintaining a professionally
based strategy for selection
. Pivotal to the process is
an understanding of the properties of cushions and
JRRD Clinical Supplement No
. 2
: Choosing a Wheelchair System
the principles of correct seating and positioning.
Success has been catalyzed by the availability and
correct use of measurement tools that provide both
quantitative and qualitative feedback of how the
client and the cushion interact.
Drawings for
Figures 1,
2, 4,
7, were done by
Samuel McFarland
. Photographs for
8, 9,
are printed with permission of the
The author acknowledges that many aspects of
the information in this article were developed from
programs begun in 1970 by Dr
. G
. Cochran at
the Helen Hayes Hospital and supported by the
Veterans Administration and the Paralyzed Veterans
of America.
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... Heat capacity varies with the mass of the cushion and the type of material. Thermal conductivity is also another parameter of the thermal absorbency and the thermal absorptivity should be as low as possible; otherwise a car seat feels cold in the winter time or hot during summer [1,5]. Although this initial feeling may last only a few minutes, it is nevertheless very important for the user's acceptance, as it is being repeated frequently. ...
... This region may therefore begin to heat, resulting in uncomfortable dampness. A car sit with impermeable foam can increase the skin temperature 10 °C in 2 hours and increase of the temperature of the skin will cause sweating [5]. ...
... Some cushions naturally pump air that is trapped in their structure when compressed. This effect can contribute to maintaining comfortable moisture levels at the cushion/skin interface, if the cushion is fitted with an air permeable cover [5]. One solution to reduce the degree of discomfort can be ventilation of the car seat. ...
The comfort performance of car seat is important factor while producing car seats, each layer of the car seat is tested separately on classical testing machines, which lacks the real car seat performance when all layers are sandwiched. The complication of car seat design and the testing method bring a great demand of portable device which can measure the comfort performance of the real car seat. In this research a novel portable device is designed which work with special heat flux sensor and the device is connected to computer by USB port and values of heat flux temperature of the water and temperature of the surface is provided by the software. Heat flux sensors measure the heat transfer through a surface, and are expressed in kw/m2. The software controls the heating plate adjustment using PID controller. The device is tested with real car seat and shows repeatable and reproducible results.
... It is comfortable for one, will not be necessarily for another. For example, people with smaller muscles, less resistant to deformation of tissue and it is easily, therefore, to be discomfort and tissue damage [9]. The weight is obviously considered and the Body Mass Index (BMI) of a person is calculated are greater than the increase of the pressure on the cushion [10][11]. ...
... The time factor strongly influences the feeling of comfort and can leads to fatigue. One static position for many hours, compress the tissues of the buttocks area and will be perceived as very unpleasant [9]. There are several interacting factors influence to the comfort [9]: (i) poor distribution of stresses in the soft tissue, (ii) the accumulation of moisture, (iii) the accumulation or heat loss, (iv) less stability. ...
... One static position for many hours, compress the tissues of the buttocks area and will be perceived as very unpleasant [9]. There are several interacting factors influence to the comfort [9]: (i) poor distribution of stresses in the soft tissue, (ii) the accumulation of moisture, (iii) the accumulation or heat loss, (iv) less stability. The aim of this study is to investigate the mechanical behavior of seat in a wheelchair, especially on a Stimulite cushion thermoplastic polyurethane honeycomb (TPU). ...
Full-text available
The cushions assistance to the pressure ulcers (PUs) prevention has like objective to improve wheelchair users by decreasing the effects of pressure between the both surfaces. Innovating honeycomb cushion (HC) containing thermoplastic polyurethane (TPU) which has many advantages was studied using a biomechanical and digital model for simulation. We used the finite element method (FEM) for the cushion simulation and modelization. This method led to the structural decomposition of the cushion in the aim to evaluate his mechanical behavior. This comportment was simulated numerically by FEM on cell of the cushion, then on the whole cushion. The tests of compression carried out with the electromechanical press (INSTRON 33R4204 machine) on HC permitted to determine curves related to his mechanical behavior. The result helps the comparison with the numerical model developed in this study. This result permits to study the distribution of pressure, shearing, friction and the microclimate which are sources of PUs through HC. The idea following this work is to optimize the HC in the aim to present a new product satisfying the needs for wheelchair users. The design of HC for prevention assistance of the scabs in only one layer is possible and present many advantages: optimization of the manufacturing process, improved ventilation, facilitated cleaning and decreasing cost.
... The concept of FCC, designed to alleviate pressure, traces its roots back to John Rogers, a pioneering rehabilitation engineer at the Tissue Trauma Group in Rancho. He established the first pressure clinic in the early 1970s (6,10,11), and the development of the FCC cutting and fitting technique by John Rogers and Dr. Shannon Stauffer preceded the establishment of this clinic. During this period, pressure injuries were prevalent, affecting 68% of individuals with SCI and 35% of geriatric nursing home residents (12). ...
... As a result, it was possible to maintain safe pressure levels, with a maximum sub-ischial pressure of approximately 30 mmHg and a safe pressure of 60 mmHg (10). The concept of FCCs, along with patient education, fitting techniques, and pressure measurement, was shared globally, reaching countries like Scotland and South Africa through collaboration and information exchange (10,11,13). Publications from various clinics echoed the approach developed at Rancho, with some variations in the fitting technique (10,13). ...
Full-text available
This paper explores the efficacy of the cushion fitting technique using foam cut out cushions for off-loading bony prominences in the sitting position, with a particular focus on reducing the high risk of developing pressure injuries among aging wheelchair users. This technique, historically employed at Rancho Los Amigos National Rehabilitation Center, has shown promising results in reducing pressure injuries for patients with spinal cord injuries. However, its widespread adoption remains limited. This manuscript aims to raise awareness about foam cut out cushions, its historical context, and its contemporary relevance by presenting customized solutions for individual patients with specific deformities. Key clinical points are highlighted, emphasizing the importance of skilled clinicians in the fitting process and the need to consider foam cut out cushions alongside other preventive measures. Case examples illustrate successful outcomes, demonstrating improved pelvic stability, posture, and off-loading of bony prominences. By promoting foam cut out cushions as a valuable cushioning option, this manuscript equips clinicians with knowledge to utilize this technique effectively. LAY ABSTRACT This paper investigates the effectiveness of using foam cut out cushions to relieve pressure on bony areas while sitting, especially for elderly wheelchair users who are prone to developing pressure injuries. This study delves into the historical background of foam cut out cushions and emphasizes their relevance in addressing the needs of modern patients. By customizing the cushions according to individual requirements, this research highlights a successful alternative for providing personalized cushion solutions to wheelchair users. The findings underscore the importance of adopting the cushion fitting technique to reduce pressure-related health risks, making it a valuable approach for enhancing the comfort and well-being of aging wheelchair users.
... Certaines zones anatomiques, caractérisées par une pression plus importante, interagissent de façon plus importante, définissant la stratégie d'assise adoptée (tubérosités ischiatiques ou grands trochanters pour l'assise, lombaire, uniforme ou dorso-scapulaire pour le dossier) ( Figure 15). Le chargement des grands trochanters est recherché et recherché pour les sièges où la posture assise est maintenue longtemps, en particulier sur fauteuils roulants (Ferguson-Pell, 1990). La pression sous les cuisses est toujours minimisée (Sanders et McCormick, 1987 ;Floyd, 1967). ...
... La mousse recouvrant le siège est un élément-clé pour le confort dans tous types de sièges (Ferguson-Pell, 1990;Staarink, 1995). En effet, elle influence la stabilité et la répartition de pression à l'interface entre le siège et le corps. ...
Le transfert assis-debout est une des activités journalières les plus courantes, prérequis à la marche et crucial pour l'autonomie. Cette tâche nécessite une coordination importante entre les mouvements des segments corporels, et donc des activités musculaires. S'il a beaucoup été investigué par différents moyens (analyses dynamique et cinématique, électromyographie), il existe peu de standardisation sur ses déterminants. Le transfert assis debout peut être séparé en 2 phases, une posturale durant laquelle le tronc est fléchi et une focale durant laquelle les membres inférieurs sont étendus. Cette tâche est influencée par les caractéristiques du siège dans lequel la posture assise est adoptée. Certains de ses déterminants relevant du siège (e.g. la hauteur et la présence d'accoudoirs) sont connus, mais de nombreux paramètres n'ont à notre connaissance pas été investigués. En particulier, ceux qui favorisent son ergonomie en posture assise semblent présenter une dualité avec la tâche de STS. Cette thèse s'est intéressée à l'influence de l'inclinaison du dossier, de la mousse recouvrant le siège et de la présence d'une rangée de sièges à l'avant. Dans les différentes conditions, des variations des paramètres biomécaniques analysés par une plateforme de forces et des actions musculaires quantifiées par l'électromyographie ont été observées dans la phase posturale, avec ou sans conséquence sur la phase focale. Une posture initiale avec le dossier incliné vers l'arrière a nécessité une variation des niveaux d'activité des muscles actifs dans la phase posturale, principalement les muscles du tronc, sans effet sur la phase focale. Un coussin constitué d'une mousse plus dense a réduit la durée de la phase posturale et mené à des variations des actions des muscles du haut du tronc (sternocléidomastoïdien et trapèze supérieur) et de la cuisse (vaste médial), ainsi qu'à une vitesse verticale maximale plus importante lors de l'extension des membres inférieurs. Lorsque le champ avant était occupé par une rangée de sièges, la stratégie de STS s'est révélée modifiée, avec les muscles jambiers et les extenseurs du tronc plus actifs en phase posturale, action associée au contrôle plus strict du mouvement, et les muscles droit fémoral et tibial antérieur (plan ventral) plus actifs en phase focale pour l'extension. Cette stratégie plus coûteuse a permis d'obtenir une vitesse verticale à la décharge du siège plus importante, compensant la vitesse horizontale plus faible. Ces résultats mettent en avant les adaptations à des contraintes variées des paramètres de la phase posturale pour la réussite de la tâche de transfert assis-debout. Les caractéristiques étudiées sont également liées au confort statique ressenti par le sujet. Ainsi, les caractéristiques optimales tenant compte également de la performance dynamique et permettant un compromis avec celle-ci peuvent être déduites. Ces travaux amènent donc un nouvel éclairage sur le contrôle du STS, avec des implications directes sur l'ergonomie des différentes catégories de sièges, et en particulier ceux utilisés pour le transport aérien.
... Due to the sizeable empty spaces present between the interlocking pieces of AMMS, airflow is higher in these systems than in conventional seating, so temperatures can be maintained at lower values for longer periods of sitting than in foam seating systems (20,21). The lower temperature at the user-seat interface can help lower the risk of pressure injury development (22). ...
... This may be attributed to this method's low level of manual labour component. CNC carving, however, uses foam materials like a majority of the common seat production methods, which are known to exacerbate high-temperature and high-moisture environments, raising the risk of pressure injury to users (6,21,39). Additionally, the cost of completed CNC seating systems is generally higher than that of plaster moulded or FIPS seating systems. ...
Background: Custom-contoured wheelchair seating lowers risk of pressure injury and postural deterioration while custom-contoured wheelchair seating lowers risk of pressure injury and postural deterioration while increasing the stability and functional activity of the wheelchair occupant. Producing custom-contoured seating systems has historically been a labour-intensive process custom-contoured seating systems is historically labour-intensive. Objectives: Evaluate the strengths and limitations of current manufacturing processes for custom-contoured wheelchair seating to suggest potential future manufacturing processes. Study design: Literature review of the state of the art. Methods: Research conducted through a literature review focused on the performance of different types of custom-contoured wheelchair seating products and processes over the last 40 years. Recent literature in orthotics and prosthetics was also consulted to assess future trends in seating. Results: There are five main manufacturing processes currently used to produce custom-contoured wheelchair seating systems. No single process is yet suitable for all wheelchair users, but many manufacturers are transitioning to computer numerical controlled (CNC) milling to reduce manual labour. Adjustable micro-modular seating and moulded seat insert manufacturing are also prevalent and offer alternative seating to soft foam carving. Conclusion: There is a need in the custom wheelchair seating sector for processes that are fast, cost-effective, produce little to no material waste, and that can effectively maintain a comfortable seating micro-climate. Additive manufacturing may meet these criteria, but further evaluation is required. Clinical relevance: This review suggests that the custom-contoured wheelchair seating manufacturers are moving away from labour-intensive processes towards digital techniques, like CNC foam milling. Additive manufacturing is a potential new process that may reduce overall costs, the lead time in preparing seats and has the potential to better manage the seating micro-climate.
... It is possible that a lower infill percentage would exhibit a stiffness, collapse stress, and densification stress closer to VPF, but further investigation is needed to determine the optimum infill percentage range. Printing a TPU material with such a low infill that its stiffness, collapse stress, and densification stress are below those of VPF may not be possible, nor advisable due to the possibility of "bottoming-out", or the deformation of a support surface to the extent that pressure redistribution benefits of that would prevent pressure injury development are lost (Ferguson-Pell, 1990;Wang and Dal Nevo, 2016; European Pressure Ulcer Advisory Panel, National Pressure Injury Advisory Panel and Pan ...
Purpose Most support surfaces in comfort applications and sporting equipment are made from pressure-relieving foam such as viscoelastic polyurethane. However, for some users, foam is not the best material as it acts as a thermal insulator and it may not offer adequate postural support. The additive manufacturing of such surfaces and equipment may alleviate these issues, but material and design investigation is needed to optimize the printing parameters for use in pressure relief applications. This study aims to assess the ability of an additive manufactured flexible polymer to perform similarly to a viscoelastic foam for use in comfort applications. Design/methodology/approach Three-dimensional (3D) printed samples of thermoplastic polyurethane (TPU) are tested in uniaxial compression with four different infill patterns and varying infill percentage. The behaviours of the samples are compared to a viscoelastic polyurethane foam used in various comfort applications. Findings Results indicate that TPU experiences an increase in strength with an increasing infill percentage. Findings from the study suggest that infill pattern impacts the compressive response of 3D printed material, with two-dimensional patterns inducing an elasto-plastic buckling of the cell walls in TPU depending on infill percentage. Such buckling may not be a beneficial property for comfort applications. Based on the results, the authors suggest printing from TPU with a low-density 3D infill, such as 5% gyroid. Originality/value Several common infill patterns are characterised in compression in this work, suggesting the importance of infill choices when 3D printing end-use products and design for manufacturing.
Newly developed wheelchair cushions, nowadays, promise to offer more comfort and protection against injury for wheelchair users. Therefore, developing novel wheelchair cushions has become a real challenge for manufacturers in recent years. In particular, thermal properties of the wheelchair cushion and their effect on the user’s comfort are very important factors in the design and optimization. This paper reports the findings of an investigation into the thermal properties of wheelchair cushions using an infrared thermography system. The experimental results showed a variation in the temperature behavior of different trademarks of cushions depending on the heating zones and the C1 cushion made in TPU material has more advantages than the other cushions made in PU foam, pharmform, and visco-foam. The results and analysis from this research will help to find a better type of cushion and contribute to collecting useful medical information to prevent pressure ulcers for bedridden patients.
A series of super-soft polyurethanes was prepared by synthesizing lightly crosslinked polyurethane with low isocyanate:hydroxyl ([NCO]:[OH]) molar ratios. The starting materials were polymeric isocyanate (pMDI), polypropylene glycol (PPG), and 1,1,1-tris(hydroxymethyl)propane (TMP). The effects of the [NCO]:[OH] molar ratio and concentrations of the crosslinking agent TMP on the crosslink density and the thermal, dynamic-mechanical, and mechanical properties of the polyurethanes were determined. In addition, TMP generates chemical and physical crosslinks within polyurethane; therefore, data calculated using the Flory-Rehner equation and the rubber elasticity were compared. The success of the reaction between pMDI and PPG was confirmed using Fourier-transform infrared spectroscopy. The synthesized polyurethanes exhibited a mixing phase between soft and hard segments. The addition of TMP increased the crosslinking density, resulting in increased glass transition temperature, tensile properties, and hardness; however, the pressure distribution was suppressed. The synthesized polyurethane showed effective properties for pressure ulcer relief applications.
Instead of a monolayer, multi-layered cushion can be promising to develop more comfortable automotive seat if the layer materials are properly selected. In this study, we have examined the seating comfort of different types of multilayer seat cushions. Polyurethane foams (PUFs) of three different hardness, memory foam, and technogel were used in different combination to prepare four types of multilayer seat cushions. The short-term seating comfort of the seat cushions has been investigated in terms of hardness, initial hardness factor (IHF), modulus irregularity factor (MIF), sag factor (SF), and hysteresis loss as derived from the indentation force deflection (IFD) curves. Long-term comfort has been compared to the respective stress relaxation behavior of the seat cushions. It has been observed that both the short and long-term conditions of comfort are not only influenced by the characteristics of the upper layer, but also by the bottom layer (i.e., supporting material). The present work will help the seat designer to consider the material characteristics for fabricating a good automotive seat on the basis of the desired features needed to provide traveling passengers with proper short- and long-term comfort.
Automotive textiles happen to be one rewarding sector, which extensively uses technical textiles, namely for interior trims, safety devices like seatbelts and airbags, carpets, filters, battery separators, hood liners, hoses, and belt reinforcement. The potential for the growth of the automotive textile business is considered one of the most progressive sectors in over the world, as car production is exponentially increasing in almost all developing countries. Most of the developments of components, parts, pieces, and materials used in a car are primarily governed by comfort, functionality, safety, economy, and ecology. Comfort is the first criterion that values the customer. In the case of a car's upholstery, both psychological comfort and thermo‐physiological comfort are considered. The incorporation of 3D woven composites is changing automotive design and the development process; instead of one level, the textile industry will be engaged at all stages of the automotive development process.
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This paper discusses a modular wheelchair cushion system intended for patients at moderate or low risk for developing pressure sores. With the use of components with different mechanical and physical properties the modular cushion produces improved performance compared with cushions comprising the individual components alone. In addition to achieving clinically acceptable interface pressures, this approach to wheelchair cushion prescription helps to accommodate individual preferences associated with stability, temperature dissipation, and resiliency. Mechanical tests were performed to demonstrate the underlying principles of the modular cushion. Tests with able-bodied subjects identified specific cushion configurations for different weight groups, offering alternative material configurations that may be selected at the discretion of the therapist or patient.
The present paper reports a portion of a rather comprehensive study of the transmission of forces to the human body through pads of various types and specifications (Chow, 1974). The basic objective of such pads is, of course, to impart the necessary forces without causing damage to the human tissue. Problems commonly arise in the case of handicapped individuals who are unable to shift their bodies so as to alter the force distribution with sufficient frequency to prevent tissue damage in the form of decubitus ulcers. Although the force transmission problem was considered in a general and fundamental way, particular attention was given to the special case of transmitting body weight to a seat cushion. An important phase of this general study was the investigation of the effects and characteristics of membranes which are usually interposed between the body of a resilient pad and the human skin (as pad covers, clothing, etc.) The characteristics of these membranes profoundly influence the stresses and strains within the loaded portion of the anatomy.
Since this paper is a contribution to a symposium dealing with many aspects of tissue trauma, we propose to limit our discussion to experience only at Rancho Los Amigos Hospital in Downey, California. We do not wish to imply that our methods are superior to all others but we hope that some different and useful ideas may obtain from our limited experience. The Tissue Trauma Group of the Rehabilitation Engineering Center has been actively involved in research, development and patient service for both the sitting and the recumbent (or prostrate) patient. The approaches to these two types of problem are fundamentally different for the following reasons: (i) The projected area of support of a prostrate human being, when divided into his body weight, yields an average pressure of around so mm Hg. This is below the 30-35 mm Hg usually accepted as necessary to cause ischaemia. (ii) The projected area of support, including the feet (but not the back) of a sitting person when divided into his body weight, yields an average pressure of about 50 mm Hg. This is above the 30-35 mm Hg ‘ischaemic pressure’. The logic of reason (i) has led us to develop devices to attempt to distribute the support pressure of the recumbent patient as uniformly as possible, so that such patients may lie in any position in definitely (usually through the night) without being turned. This approach has resulted in the Rancho Flotation Bed (mud bed) and the Poly-Flotation Mattress to be described later. The problems of the seated patient suggested in reason (ii) have led to an approach that involves the development of optimum seat cushions, coupled with clinical service which relies on special pressure measurement techniques and procedures for custom modification of seat cushions and sit­ting positions. These will be discussed in detail. Research and development have focused on new instrumentation to indicate the potential for tissue damage, studies of various support material characteristics and the development of support systems, both passive (viscoelastic seat cushions with or without cutouts, and flotation systems) and active (devices requiring external power) systems.
A survey was made by questionnaire of the prevalence and severity of pressure-sores on a given date among all hospital inpatients and all patients visited by a district nurse within the Greater Glasgow Health Board area. 8.8% of patients had a pressure-sore. Those aged 70 and over accounted for 70% of the patients with sores. Chairfast patients consistently had a higher pressure-sore frequency than bedfast patients of a similar degree of helplessness.
SUMMARY The mechanical properties of four commonly used sheepskin-like interface materials have been investigated to assess their relative effectiveness in preventing decubitus sores. The samples were resilient and silky varieties of natural sheepskin, resilient wool woven into a fabric backing and a pure polyester simulation of sheepskin. Consideration of the factors which cause skin breakdown suggested that the relevant mechanical properties to be measured were compressibility, frictional behaviour, ability to absorb water vapour and porosity under load. The four samples exhibited similar ability to distribute load; the polyester material produced greatest friction; the resilient wool fabrics showed both greatest porosity under load and ability to absorb water vapour. It was found that the latter was the more important property for keeping the patient's skin dry. The general conclusion arising from this work is that resilient natural sheepskins are the best interface for the prevention and management of decubitus sores.
A survey of the first 200 cases supplied with a "Paracare" pressure redistribution wheelchair cushion. The rationale of the design and material used is discussed. The method of application and follow-up studies are given and a total evaluation of the results achieved to date are presented.
Even though easily prevented, pressure sores occur frequently. The consequences of allowing pressure sores to develop are great. Pressure sores are costly and disabling, both physically and psychologically. his article presents 1) criteria for recognizing the stages of potential skin breakdown: hyperemia, ischemia, necrosis, and ulceration; 2) areas most vulnerable to skin lesions when the patient is in different positions; 3) responsibility for pressure sore prevention; 4) prevention of pressure sores by routine relief of pressure from susceptible areas; and 5) treatment of pressure sores.