Chairs and seats – Bottom or back with means to alter contour – Having a plurality of adjacent relatively adjustable sections
Reexamination Certificate
2003-04-21
2004-01-13
Cuomo, Peter M. (Department: 3636)
Chairs and seats
Bottom or back with means to alter contour
Having a plurality of adjacent relatively adjustable sections
C297S452630, C005S933000
Reexamination Certificate
active
06676215
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a seating apparatus and, more particularly, to a pressure-relieving wheelchair seating apparatus for avoidance and relief of decubitus ulcers (i.e., pressure sores).
Decubitus ulcers develop on the skin of immobilized people, particularly under bony locations like the ischial tuberosities and coccyx, when the seating pressure exceeds a typical value of 32 mm Hg for a period of time, such pressure stopping blood flow to the tissues under pressure. While other factors such as diet, moisture, and shear stress on the skin contribute to the formation of decubitus ulcers, they can generally be avoided by physically moving the immobilized person at frequent intervals to restore blood flow to the pressurized areas.
The medical industry has recognized that a general relationship exists between seating pressure and seating time. That is, the greater the seating pressure, the less time a person may sit in that same position without suffering damage to the skin and tissue located at that position. Although each person exhibits a different pressure/time relationship (based on such factors as body weight, shape and structure), a general relationship was established by J. B. Reswick and J. E. Rogers which plots the maximum suggested seating pressure vs. the maximum suggested seating time for tissue under a bony location. This relationship is commonly referred to as the Reswick/Rogers curve, and provides general seating guidelines for an average person. For example, the Reswick/Rogers curve provides that a seating pressure of 500 mm Hg will allow the immobilized person to remain seated for approximately 1.1 hours, while a seating pressure of 200 mm. H.g. will allow the immobilized person to remain seated for approximately 2 hours.
As mentioned, the seating pressure under a bony location, such as the ischial tuberosities, varies from person to person based on body weight, shape and structure. However, average seating pressures typically range from about 200 mm Hg to about 500 mm Hg. These seating pressures therefore limit the seating time to relatively short periods (i.e., 1.1 hours to 2 hours as defined by the Reswick/Rogers curve) before movement of the immobilized person is necessitated. Of course, the immobilized person can usually not move himself or herself, and must rely upon the assistance of another person.
It will be appreciated by one skilled in the medical art that typical blood pressure in the capillaries is about 32 mm Hg (0.62 psi). As a result, a seating pressure above 32 mm Hg restricts and/or obstructs blood flow in the capillaries experiencing this pressure, thus preventing blood flow to the surrounding tissues. A prolonged period of restricted and/or obstructed blood flow leads to tissue damage, and eventually to the development of a decubitus ulcer. The medical art has therefore recognized that periodic pressure relief is required (particularly a reduction in pressure below 32 mm Hg for at least five seconds thereby reestablishing capillary blood flow) with respect to body tissue experiencing pressure (e.g., seating pressure) above 32 mm Hg. However, although this requirement has been recognized by the medical art, no prior art device has been able to satisfactorily provide the necessary periodic pressure relief required by a seated immobilized person.
In this regard, the prior art has attempted to reduce the frequency of developing decubitus ulcers through the use of various seating cushions for minimizing the seating pressure under the immobilized person. For example, certain prior art cushions are provided with cut-out openings at locations corresponding to the maximum pressure points in an attempt to relieve these local pressure concentrations under the bony locations. However, the surrounding seating pressure can still be high enough to stop the blood supply in the capillaries under these bony areas. Certain other prior art cushions utilize inflatable compartments filled with air or a gel in which the pressure is alternately raised or lowered in different compartments sequentially so that the area of maximum pressure is not always in the same location. However, such prior art inflatable cushions cannot ensure that the seating pressure is adequately reduced when a particular compartment is deflated, since the deflated compartment may still remain in contact with the seated individual.
The prior art has also attempted to reduce the frequency of developing decubitus ulcers through the use of support structures including a plurality of movable elements. For example, U.S. Pat. Nos. 5,626,555 and 5,109,558 disclose support structures including a plurality of movable elements for supporting an immobilized person. The patents teach that prolonged periods of contact with a typical support structure decreases the blood circulation in the person leading to the formation of bed sores. The patents further teach that periodic relief of pressure through movement of the individual elements of the support structure can improve blood circulation and avoid soreness.
These patents, and the prior art in general, fail to recognize the complex relationship that must exist between the various aspects of a support structure for such structure to prevent development (and to actually promote healing) of decubitus ulcers. The factors to be considered include the number of individual support elements, the frequency and length of time of displacement, the sequential direction of displacement, the displacement distance of the support element, the type of cushion material, the thickness and stiffness of the cushion material, and weight, shape and bone structure of the patient, among others. A careful review of the prior art indicates that the disclosed devices fail to recognize this complex relationship and, accordingly, fail to prevent the formation of decubitus ulcers. The prior art devices are also incapable of promoting the healing of such ulcers. Finally, the mentioned prior art devices are also inadequate for retrofitting of existing wheelchairs due to their overall size and space requirements.
No single prior art seating apparatus or cushion simultaneously addresses all of the mentioned problems. There is therefore a need in the art for a seating apparatus which provides periodic pressure relief to the seated immobilized person thereby reducing the seating pressure below 32 mm Hg for at least five (5) seconds to restore and/or promote blood flow in the capillaries, which alternates this periodic pressure relief through different localities, which provides air circulation under the seated person to prevent the build-up of moisture underneath, and which allows the continued use of a wheelchair by a person with an existing decubitus ulcer.
SUMMARY OF THE INVENTION
The present invention, which addresses the needs of the prior art, relates to a seating apparatus for supporting a lower body region of an immobilized person for avoidance and relief of decubitus ulcers. The seating apparatus provides regular intervals of seating pressure reduction below a predetermined seating pressure for at least a predetermined relief period. The seating apparatus includes a plurality of rigid slats. The slats define a support plane for supporting the lower body region of the immobilized person. Each of the slats is movable between a first support position wherein each of the slats is coplanar with the support plane and a second displaced position wherein each of the slats is displaced a distance D from the support plane for the predetermined relief period whereby capillary blood pressure is reduced below the predetermined seating pressure in the unsupported portion of the lower body region. Each of the slats supports a cushion for sitting thereon, the cushion being formed from a viscoelastic material. The seating apparatus further includes a cage for supporting the slats and which is configured to allow movement of each of the slats between the first and second position. The seating apparatus further includes a plurality of mechanisms for moving each of
Ezra Arthur A.
Shah Mehendra C.
Cuomo Peter M.
Harris Stephanie
Hoffmann & Baron , LLP
The Research Foundation of State University of New York
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