Patent Grant
6941602
1. Field of the Invention
The present invention relates to cushions, and in particular to seat cushions having an array of individual, expandable, fluid-filled cushioning cells for use by persons confined to wheelchairs and the like.
2. Description of the Related Art
In the United States alone, more than 247,000 individuals have complete or partial paralysis and more than 600,000 nursing home residents use wheelchairs. Many of these people require the use of a pressure-reducing cushion to minimize the risk of sitting-induced pressure ulcers. The prevalence of pressure ulcers among all nursing home residents is estimated between 7% and 23%. The incidence rate among other populations with mobility impairments is even higher; it has been estimated that between 50% and 80% of persons with spinal cord injury will develop a pressure ulcer. Even the lowest estimates indicate that pressure ulcers present a significant health care problem.
Pressure ulcers/sores are extremely dangerous and difficult to cure. These pressure sores, or decubitus ulcers, typically form in areas where bony prominences exist, such as the ischia, heels, elbows, ears and shoulders. Typically, when sitting, much of the individual's weight concentrates in the regions of the ischia, that is, at the bony prominences of the buttocks, and unless frequent movement occurs, the flow of blood to the skin tissue in these regions decreases to the point that the tissue breaks down. This problem is well known and many forms of cushions are especially designed for wheelchairs for reducing the concentration of weight in the region of the ischia. These cushions generally seek to distribute the user's weight more uniformly over a larger area of the buttocks.
Another area where pressure ulcers occur is in the trochanter area. Both cushions and bases for the cushions are often shaped so that pressure is relieved on the ischia and the trochanters. A significant problem with wheelchair-type cushions is stabilization of the user so that he has a feeling of security when sitting in the wheelchair.
Conventional cushioning devices for supporting the human body, such as the typical mattress, seat cushion or padded back rest, do not distribute the weight of the supported body evenly over the area of the body that is in contact with the cushioning device. For example, in the case of a mattress, the buttocks or hips, and likewise the shoulders, sink further into the mattress than the lumbar region of the back. Since most conventional cushioning devices exert a supporting force that is proportional to the amount they are deflected, those portions of the body which sink deepest into the cushioning device experience a resisting force per unit area that is considerably greater than those body portions that deflect the cushioning device only slightly. For those individuals who are confined to beds or wheelchairs for extended periods of time, the unequal distribution of supporting forces deforms the vascular system and reduces blood flow, which can lead to extreme discomfort and can even be debilitating in the sense that bed sores often develop at the skin areas where the supporting force is greatest.
While cushions which derive their cushioning properties from inner springs or foam material are quite common and inexpensive to manufacture, and offer good stability, they suffer the inability to distribute loads or develop restoring forces evenly to the object they are supporting. For example, expanded polymer foam of a resilient character, such as polyurethane, is a popular cushioning material for seating, and indeed finds widespread use in furniture and automotive seats. But resilient polymer foam does not produce the most desirable relationship between force and displacement. Far from this relationship being linear, it tends to be skewed, such that the force increases at a greater rate than the displacement, and this makes the material unusually stiff when an individual or object such as a bony prominence is deeply immersed in it. Thus, the region of the body that is most susceptible to injury receives the greatest resisting force per unit area, compounding the injury or increasing the risk thereof.
An effective cushion reduces pressure over bony prominences while providing stability and support, primarily through envelopment. The main types of wheelchair cushions can be described as fluid, compressive (elastic, viscoelastic), or suspension cushions. Fluid and fluid-like seat cushions achieve envelopment by accommodation of bony prominences and maintain the condition by virtue of their ability to dynamically adjust to changing loading conditions. However, the dynamic nature of fluid-filled cushions often leads to the undesirable characteristic of poor stability.
Cushions made from elastic materials such as high resilient foams must rely on pre-contouring to achieve envelopment. Such a cushion has no ability to dynamically adjust beyond the limits of the compliance of the material as defined by its material properties. That is, these cushions cannot change shape without a tendency to return to their original shape. When a person sits on the cushion both the cushion and the buttocks will deform until force equilibrium is reached. In the cushion, the counter forces will be greatest where there is the most deformation and least where there is low deformation as discussed above. Elastic cushions provide the advantage of enhanced stability due to the foam's tendency to hold its shape and, thus, hold the person in place. A fluid-like cushion instead changes its shape to accommodate changing load. The disadvantage of pre-contoured compared to fluid-like cushions is that the distribution of forces is sensitive to the relative match between the cushion and the buttock shapes, and to the positioning of the buttocks on the surface.
Cushions made from viscoelastic materials have a combination of elastic and fluid properties, giving such cushions some ability to reconfigure in a memoryless fashion and some ability to provide stability through resilience. An optimum balance of viscous and elastic response is a matter of personal preference and need, however, and may vary significantly from person to person.
Suspension cushions use the strategy of removal of material in the areas that commonly experience high pressure and use covers under tension to support these areas in a suspension-like manor. Suspension cushions remove material from the ischial area, and often the sacral area as well. The successful use of a suspension cushion also, as with a pre-contoured cushion, relies on a consistent positioning of the user on the surface.
Through clinical tests, it has been determined that one of the better methods of preventing the development of bed sores on patients is to support such persons on a series of flexible intercommunicated cells filled with a fluid such as air. Since the cells are intercommunicated all exert an equal supporting force against the engaged individual. Such an arrangement of cells is disclosed in U.S. Pat. No. 3,605,145.
Fluid cell cushions provide a uniform distribution of weight and thus provide good protection from the occurrence of pressure sores. These cushions have an array of closely-spaced air cells which project upwardly from a common base. Within the base the air cells communicate with each other, and thus all exist at the same internal pressure. Hence, each air cell exerts essentially the same restoring force against the buttocks, irrespective of the extent to which it is deflected. U.S. Pat. No. 4,541,136 shows a cellular cushion for use on wheelchairs.
The typical fluid cell cushion provides a highly displaceable surface which tends to float the user. While this reduces the incidence of pressure sores, it detracts from the stability one usually associates with a seating surface. Most of those confined to wheelchairs have little trouble adjusting to the decrease in stability, but for those who have skeletal deformities, particularly in the region of the pelvis and thighs, and for those who lack adequate strength in their muscles, lesser stability can be a source of anxiety.
The stability problem has been attacked by the use of shaped bases such as shown in Graebe, U.S. Pat. No. 4,953,913 and Jay, U.S. Pat. No. 4,726,624. These bases are generally used in conjunction with cushions. Graebe, U.S. Pat. No. 4,953,913 has been used in conjunction with a cellular cushion and a fabric cover. The stability problem also has been addressed in the cellular cushion by the use of zoned areas of inflation as shown in Graebe, U.S. Pat. No. 4,698,864, which shows a zoned cellular cushion with cells of varying height; and Graebe, U.S. Pat. No. 5,052,068, which shows another form of zoned cushions with cells of different heights. By varying the pressure between zones, one can accommodate for skeletal deformities, while still maintaining protection against pressure sores.
Graebe, U.S. Pat. No. 5,111,544, shows a cover for a zoned cellular cushion which keeps the cells from deflecting outwardly. This cover has a stretchable top, a skid resistant base, and a non-stretchable fabric side panel area.
Another problem with cushions of the prior art is the inability to accommodate individual shapes and sizes, or to be customized to provide greater support in areas needing it. One approach has been to employ cushions having separate adjustable zones, as discussed above, and such as described in U.S. Pat. No. 5,163,196.
Typically, a zoned cellular cushion has a separate filling stem and valve for each of its zones. The user opens the valve of each stem and introduces air into the zone for that stem, usually with a hand pump, and then releases the air from the zones until the desired posture is achieved. In a more sophisticated arrangement, a hose kit connects a single pump to a manifold which in turn is connected to the several valves through separate hoses. These hoses are fitted with separate hose clamps so that the air from the pump may be directed to the cells of the individual zones independently, and likewise the air can be released from them independently, all by manipulating the clamps. The hoses of the hose kit lie externally of the cushion and may become entangled in components of a wheelchair. Furthermore, by reason of their remote location, the hose clamps are difficult to manipulate. Also, such a design is not automatically adjustable, rather, may require repeated and cumbersome manual adjustment in order to achieve the desired level of comfort. In addition, while pressure may be varied from one zone to the next, all cells in a particular zone exert the same pressure, and fluid flow cannot be controlled between individual cells.
Other attempts to adjust cellular cushions include manually tying off cells in regions of the cushion, such as those regions supporting the ischia. Such efforts are cumbersome, however, and provide at best a trial and error solution to the problem.
Accordingly, an advance in the art could be realized if a cushion could be provided that offered the advantages of automatic contour adjustment, and that combined with optimum pressure-reducing and flexibility capabilities of air floatation, or cellular cushions, with stability closer to that of foam cushions.
The present invention addresses the shortcomings of the prior art by providing a cushion that automatically controls shape, interface pressure, and provides relative stiffness and seating stability.
The cushion provides the ability to produce both an isobaric surface interface with an indenting body or an a priori condition at the interface. The cushion is based on an array of interconnected cells. The accommodation of the cushion to an indenting body is accomplished by the displacement of fluid from compartments receiving the indentor to peripheral cells. This arrangement is comparable to connecting cells to a plenum chamber, but adds the novel feature of using constrictures such as miniature check valves between communicating cells. The check-valves may be selectively enabled or disabled, for example, through the use of a control pin. This feature gives the cushion the ability to selectively control flow rates and pressures (based on the amounts of fluid delivered) among communicating cells. Indeed, flow rates and pressures can be controlled for every individual cell, rather than just zones of cells.
In a preferred embodiment, the cushion conduits/valves are laminated between thin layers, which together form the “backbone” or structural continuity between cells. Collapsible (and distensible) pads on either or both sides (i.e., top and bottom) of the structural or “backbone” layer constitute the completed cellular cushion.
These and other aspects and advantages of the present invention are set forth in greater detail in the following detailed description and accompanying figures.
In the accompanying drawings, which form a part of the specification, and wherein like numbers refer to like parts wherever they occur:
FIG. 12(a) illustrates the tool of
FIG. 12(b) illustrates the tool of
The ideal cushion would support a person, while at the same time retain the buttocks in an uncompressed state, as close as possible to that of being suspended in air or floating in water. While such an ideal cushion is not likely possible, it is possible, according to the present invention, to model a customized cushion in a way to maximize contact area, optimize pressure distribution, and other parameters so as to closely approximate an ideal situation. Because each patient has unique cushioning requirements, dictated by such variables as weight, sex, posture, build, injury, etc., the ideal cushions for any given patient should be uniquely designed for that patient. Because the present invention permits cell-by-cell customization, in terms of pressure and/or flow rate of fluid from one cell to the next, it offers the ability to tailor the cushion to each patient's unique needs.
The cushion may be customized with the assistance of a software system based on data for each patient, such as weight, sex, local peculiarities, etc., in order to create optimal cushioning by taking advantage of the unique cell-by-cell customizing features of the present invention, which will now be described.
The present invention incorporates individual, expandable (i.e., vertically distensible), fluid-filled, cushioning cells. The cushion incorporates reciprocal, one-way connections between all immediately adjacent cushioning cells. The flow of fluid (gas or liquid) from any particular cell to all contiguous cells is based on the relative internal pressures among the cells. When a threshold pressure is exceeded in a cell, a one-way (e.g., duckbill) valve opens to allow fluid to flow out to one or more adjacent cells experiencing a lower internal pressure. Upon being subjected to external loading (i.e., from an indenting force) fluid flows from cells in areas of higher pressure to cells in areas of lower pressure. This process continues until a uniform or a priori pressure distribution is achieved among the cells. A concomitant effect is a change in shape of the cushion to accommodate the differential compressive forces of the indenting surface. An a priori pressure distribution (i.e., other than isobaric) can be achieved over the system of cells by having higher opening pressures for valves in selected regions of cells in the cushion array. For example, areas of the cushion supporting regions known to be prone to development of pressure sores, such as the ischia, sacrum, and coccyx can be filled with cells that have a different pressure/flow distribution than other areas of the cushion, by virtue of the opening pressures of the valves for those cells relative to opening pressures for valves for cells in other regions.
The rate of change in shape of the appliance due to an indenting force is a function of the flow rate of the fluid. The ability to control flow rate between cells provides the capability to “set” the compliance of the cushions. This, in turn, allows a measure of control over the stability of the cushion (or, perhaps more properly, the stability of a person seated on the cushion). The rate of flow is governed primarily by the external forces exerted on the cushion, the viscosity of the fluid, the lumen size (i.e., the inside diameter) of the connecting conduits, and the degree of constriction applied to these connecting links. In the case of air, the primary considerations are lumen size and constriction force. Air may, in certain circumstances, be the preferred fluid, while in other circumstances, a more viscous fluid, or even a gel, might be the preferred fluid for filling the cells of the cushion.
Referring now to
As illustrated in
In a preferred embodiment of the invention, each individual connecting link or conduit 16 is unidirectional (i.e., no backflow is permitted). This means that once air is expelled from the cell via an outflow conduit, air may only reenter that cell via a separate inflow conduit from an adjacent cell.
By introducing a selective constriction in one of the conduits between two cells, as illustrated in
Referring now to
The constrictor or clip 30 of the present invention may assume different configurations depending on the objectives desired for adjacent cells. The constrictor 30 illustrated in
The constrictor clip 30 illustrated in
A series of three (3) check-valves 20, each with an opening threshold pressure of 10 mm. of Hg (for example) is shown in FIG. 9. Thus, it should be noted that the three (3) check-valves 20, when closed, maintain a total pressure differential of 30 mm of Hg between contiguous cells 10. If only two (2) of the three (3) check-valves 20 are closed, the total differential pressure between contiguous cells 10 (i.e., across the two (2) enabled check-valves 20) would be 20 mm. Hg. Thus by selecting the opening threshold pressure for each check-valve 20 and by controlling the number of check-valves 20 that are enabled, the total differential pressure between contiguous cells 10 may be closely controlled.
In the current embodiment (as illustrated in FIGS. 9 and 10), the control pin 22 is advanced through one or more check-valves 20, thereby overcoming the checking function of the check-valves 20. By sliding the control pin 22 to open successive serial check-valves 20 within the conduit 16, it is possible to selectively disable (i.e., open) as many of the serially arranged check-valves 20 as may be desired. Accordingly, the current embodiment allows for the selection of the pressure differential between two adjacent cells 10. It should be noted that other types of valves or flow restriction devices, for example duckbill valves 21 as illustrated in
It should be noted that, to reduce the amount of flow restriction caused by the control pin 22, the elongated end 24 and the spherical end 26 may be hollow to permit fluid flow through the control pin 22. Additionally, the check-valve 20 (or other flow restriction device) may include a stand off 23 which prevents the spherical end 26 of the control pin 22 from completely blocking the inlet of the check-valve 20. It should be further be noted that the control pin 22 may also be used in conjunction with other flow restriction devices, for example duckbill valves 21 as illustrated in
As illustrated in FIG. 12(a), the tines 29 may be pushed along the conduit 16 (as shown by the directional arrow in
As illustrated in FIG. 12(b) the tines 29 may be pulled along the conduit 16 (as shown by the directional arrow in
It should be noted that other types of tools may be used to move the control pin 22 through the conduit 16 while remaining within the scope of the present invention. It should further be noted that a non-spherical shaped end may be used for the control pin 22 while remaining within the scope of the present invention.
In the current embodiment, the serial check-valves 20 are placed within one or more of the connecting conduits 16 (flexible tubes) of the reciprocally connected cells 10 described in
While the embodiment illustrated in
Another embodiment of the invention includes more than one backbone or middle layer 50, providing a “stacked” arrangement of cells potentially several layers high.
In the preferred embodiment, the cells are interconnected to one another, but not to a common plenum, as is the case with prior art designs. This cell-to-cell connection allows for more stability than cushions using a plenum.
Referring now to
While the present invention has been described in terms of specific examples and preferred embodiments, such description is illustrative only, and not intended to limit in any way the scope of the invention, which is defined by the claims and all equivalents thereof. For example, while a preferred embodiment of the cushion is a seat cushion for primary use by an occupant in a seated position, it is to be understood that the invention may be employed for other cushioning applications, including without limitation, office furniture seats and/or backs, bed mattresses, home furniture, car seats and backs, arm rests, etc.
This application is a continuation-in-part of U.S. patent application Ser. No. 09/635,954 filed 10 Aug. 2000, now U.S. Pat. No. 6,519,797, which claims the benefit of U.S. Provisional Application No. 60/148,193 filed Aug. 10, 1999.
| Number | Name | Date | Kind |
|---|---|---|---|
| 1282980 | Takach | Oct 1918 | A |
| 2434641 | Burns | Jan 1948 | A |
| 3303518 | Ingram | Feb 1967 | A |
| 3312213 | Timm | Apr 1967 | A |
| 4005326 | Suga | Jan 1977 | A |
| 4120061 | Clark | Oct 1978 | A |
| 4541136 | Graebe | Sep 1985 | A |
| 4698864 | Graebe | Oct 1987 | A |
| 4707872 | Hessel | Nov 1987 | A |
| 5009391 | Steigerwald | Apr 1991 | A |
| 5052068 | Graebe | Oct 1991 | A |
| 5152023 | Graebe | Oct 1992 | A |
| 5163196 | Graebe et al. | Nov 1992 | A |
| 5326071 | Gunness | Jul 1994 | A |
| 5364162 | Bar et al. | Nov 1994 | A |
| 5369828 | Graebe | Dec 1994 | A |
| 5456284 | Ryan et al. | Oct 1995 | A |
| 5487197 | Iskra, Jr. et al. | Jan 1996 | A |
| 5502855 | Graebe | Apr 1996 | A |
| 5561875 | Graebe | Oct 1996 | A |
| 5596781 | Graebe | Jan 1997 | A |
| 5638565 | Pekar | Jun 1997 | A |
| 5640731 | Toedter | Jun 1997 | A |
| 5845352 | Matsler et al. | Dec 1998 | A |
| 6089260 | Jaworski et al. | Jul 2000 | A |
| 6519797 | Brubaker et al. | Feb 2003 | B1 |
| Number | Date | Country | |
|---|---|---|---|
| 20030121102 A1 | Jul 2003 | US |
| Number | Date | Country | |
|---|---|---|---|
| 60148193 | Aug 1999 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 09635954 | Aug 2000 | US |
| Child | 10319156 | US |
