CA2160996A1 - Pneumatic wheel chair cushion for reducing ischemic injury - Google Patents

Abstract

A pneumatic cushion (A) for a wheel chair and the like is disclosed which comprises an air housing box (B), a plurality of air openings in the air housing box, and a plurality of air channels (16, 18, 20, 22) communicating with an air supply. The air channels communicate with the air openings to deflate and inflate individual air sacks (S) carried over the air openings. An air distribution manifold (F) includes a rotating blocking member to periodically block air distribution to the air sacks allowing them to deflate. The air sacks (S) are constructed from a fabric having a low air permeability thus allowing air to escape (70) through the sacks for deflation which cools the portion of the occupant seated on the cushion while allowing temporary pressure relief during deflation. The air sack inflation system is open so that pressure may be relieved by a backward flow of air (72) through the system.

Description

WO94/lg997 PCT~S93l02~9 21 ~099~

PNEUMATIC WHEEL CHAIR CUSHION FOR
REDUCING ISCHENIC INJURY
Background of the Invention The invention is directed to a pneumatic wheel chair cushion having a dynamic pressure relieving system for reducing ischemic injury to the weight bearing portions of the buttocks of a patient in a sitting position.
With the increasing number of wheel chair patients, the need for wheel chair cushions which provide for greater prevention of ischemic injury are needed.
Typically, wheel chair cushions have been provided in various forms and shapes cut from foam. Other wheel chair cushions have been prov~ded which include air cushions. United States Patent No. 4,864,671 discloses a controllably inflated wheel chair cushion that includes a number of independently inflatable rows of cells. The cells are inflated and deflated according to a sequence selected by the user to selectively relieve pr~ssure against the buttocks of the patient.
The cells are inflated at a predetermined pressure and may not be deflated until a valve is opened to exhaust the cell. The cells are exhausted through a manifold which delivers air between the cells in order to supply fresh air and reduce the heat from the cushion.
However, the system may not satisfactorily compensate a patient's weight causing excessive pressure on inflated portions. United States Patent No. 4,852,195 discloses a similar fluid pressurized cushion which utilizes air cells arranged in a matrix. The air cells are inflated and deflated in a sequence to shift body support from one set of cells to another for promoting blood circulation and comfort. The cells in each matrix may also be interconnected to shift fluid WO 94/lg9g7 PCT/USg3/02649 ~,~ 6~99~
pressure as the patient's weight may shift. While the above air cushions deflate to periodically alleviate pressure against the occu.pant's buttocks, the air cells are generally static and closed by valves and may not suitably allow pressure to be automatically relieved in instances where the patient's body weight shifts. The pressurized cushions are alternatir.g, but are static.
While the air cells or cushions are filled and pressurized with air, that pressure cannot change until the air pressure is released. This may not be satisfactory for severe cases of amputated wheel chair patients whose lower stump is very susceptible to acute ischemic injury and skin decay.
Accordingly, an object of the present invention is to provide an pneumatic wheel chair cushion having a dynamic air distribution system which periodically relieves pressure on portions of the occupant's buttocks.
Another object of the invention is to provide a pneumatic cushion having a dynamic air dist ibution system which is self regulating and adjusts to the shift in weight of the occupant to automatically relieve pressure and prevent ischemic injury.
Another object of the present invention is to provide a pneumatic cushion for a wheel chair and the like which utilizes individual air sacks which are inflated and deflated in a sequence to periodically reduce pressure against portions of the occupant's buttocks wherein the air sacks are controlled by a dynamic air pressurization system which allow a back flow of air to bleed from the air sacks under excessive pressure to prevent ischemic injury.
Another object of the present invention is to provide a pneumatic cushion for a wheel chair and the W094/1~97 PCT~S93/OZ~9 2~ 609~6 like which uses individual air sacks arranged in a matrix which can be alternately inflated and deflated wherein the fabric of the air sacks has a low air permeability which allows a certain amount of the air to escape to maintain the cushion dry and also to assist in automatically regulating the air pressure to shift in occupant's weight.
Summary of the Invention The purpose of this invention is to prevent lo ischemic injury to the weight bearing portions of the buttocks while in a sitting position. This object is accomplished by providing an air cushion having a number of individual air sacks or cells arranged in a matrix which are not physically connected with one another so that they act independently. Reduced air flow and therefore reduced pressure is provided within the cushion periodically so each air sack on the surface will have reduced pressure and reduced flow for 12 seconds every minute, for example, dependent on a clock motor. An air distribution is provided which at any time, is self-regulating because if pressures increase when the occupant shifts their weight or the like, the system automatically buffers the area of exerted weight by a back flow of air to a blower when the pressure of the occupant exceeds the pressure in that cushion. The cushion is self-adjusting, and prevents acute trauma to an area. The air distribution system and cushion allow spontaneous, automatic adjustment in pressure just from the patient shifting his weight so that it minimizes the potential for soft tissue injury at any point in time. There is no closed valve in the system during the inflation cycle. The system is a dynamic pressure and flow pressure system.
The air system is continually being charged so that if WO 94/19gg7 PCT/US9310264g ~,~ 6~9~ -it is overcome by weight shifts, the air pressure is bled back or outward through the pores in the air sack.
Description of the Drawings The construction designed to carry out the 5invention will hereinafter be described, together with other features thereof.
The invention will be more readily understood from a reading of the following specification and by reference to the accompanying drawings forming a part 10thereof, wherein an example of the invention is shown and wherein:
Figure 1 is a perspective view illustrating a pneumatic cushion constructed according to the invention embodied in a wheel chair;
15Figure 2 is a sectional view taken along line 2-2 of Figure 1;
Figure 3 is an enlarged sectional view of an individual air cell for a pneumatic cushion according to the invention;
20Figure 4 is a perspective view with parts separated of a pneumatic cushion according to the invention;
Figure 5 is a top plan view of individual air sacks according to the invention illustrating a prescribed inflation/deflation sequence for relieving ischemic 25injury to the occupant;
Figure 6 is a sectional view taken through an air distribution manifold according to the invention;
Figure 7 is a sectional view of an alternate embodiment of a pneumatic air cushion according to the 30ir.vention;
Figure 8 is a sectional view illustrating the construction of an air sack according to the invention;
and W O 94119997 1~CT~US93/02649 ~1~0~
Figure 9 is a perspective view showing an alternate embodiment of an air distribution manifo]d according to the invention.
Description of a Preferred Embodiment Referring now in more detail to the drawings, a pneumatic cushion A for reducing ischemic injury to a patient sitting in the wheel chair and the like is illustrated. As applied to a wheel chair, a support is provided by a wheel chair frame 10, and pneumatic cushion A is carried by the frame. Cushion A includes a dynamic, self-regulating air distribution system which periodically reduces air pressure in selected portions of the cushion. The air distribution system includes an air distribution plenum B having a plurality of air cnannels C. Plenum B includes a housing or plenum box 12 having a plurality of air compartments D formed in the box communicating with air channels C. The air compartments are arranged in an N
x N matrix where N is the number of compartments D in a row. In the illustrated embodiment, there are five rows 14a-14e, each having five air sacks S.
The system includes an air distribution manifold F
which extends centrally through air plenum box 12 with air channels C extending laterally from central air distribution manifold F. There are four major air channels 16, 18, 20, 22 extending from the manifold, as can best be seen in Figure 2. Air distribution manifold F includes a cylindrical air distribution tube 24 which is a stationary member, and an air inlet 26 formed at a first end of the air distribution manifold which includes an annular disk 28 with a plurality of circumferentially spaced holes 30 for the entry of air.
A center bearing 32 rotatably receives one end of a rotating program member which has a shaft 34. There is WO94/19997 PCT~S93/02~9 2,~6099~

a fittinq 36 carried by the air inlet for connection to a blower 38 for delivering air to the air inlet. An opposite end of shaft 34 is coupled to a clock motor 39 using a set screw 37 by which shaft 34 is rotated in a programmed manner.
As can best be seen in Figure 6 and 4, there are a plurality of air distribution ports P in air distribution manifold F which are in fluid communication with air channels C in air distribution plenum B. The air distribution ports include air ports a, b, c, d, e spaced equiangularly around cylindrical air distribution manifold F. There are five sets of the port a-e along the length of the manifold as denoted 1-5. Where N is the number of rows, the angular spacing "X" of ports P is 360/N degrees around the circumference of cylindrical manifold F. In the illustrated embodiment, the five air ports for each row of air sacks have a 72 degree spacing circumferentially and are spaced a predetermined length longitudinally along manifold F (Figure 2).
Air blocking means G is provided for periodically blocking air distribution ports P in the manifold to periodically interrupt the distribution of air in air channels C and deflate air sacks S in accordance with a preselected sequence. The air blocking means includes rotating program member 34 having rotating one-way valve means 40 with a blGcking position in which the valve means is positioned over an air port P.
In this position, valve means blocks air to deflate air sacks S while, at the same time allowing air to back flow in the system and vent from the air sack as where excessive pressure occurs from a person's shifting weight. The valve means includes flexible wipers carried at programmed positions on shaft 34 which block WO 94/199g7 PCT/US93/02649 21SO9~

air distribution ports P. The wipers are angularly spaced from one another on said shaft with same spacing as between air ports, and same longitudinal spacing.
Flexible wipers include a stem 44, and a flapper valve 46 which engages the inside diameter of cylindrical air distribution manifold F (Figure 6). As can best be seen in Figure 5, air sacks are deflated in diagonal rows from one corner to an opposite corner. Drive motor 39 carried by a second end of said air distribution manifold rotatably drives said rotating program member 34.
A top member 50 extends over the top of said air distribution plenum B having a plurality of air openings 52 in fluid communication with air channels C.
There is an air opening over each air compartment D so that there are N x N air openings 52. Sealing means 56 in the form of a matrlx gasket seals between air compartments D and top member 50, as can best be seen in Figures 4 and 2. Inflatable air sacks S are carried by top member 50 over air openings 52, and are deflated as air distribution ports P are periodically blocked in accordance with the preselected sequence shown in Figure 5. In the illustrated embodiment, there are 5 sets of circumferentially spaced ports spaced along the length of manifold F, as can best be seen in Figure 4.
The air cells and sacks controlled by ports a-e are designated in Figure 5. The air sacks are sequentially inflated and deflated for reducing ischemic injury to a person seated on the cushion. Air sacks S are constructed from a material 53 having a low air permeability to allow slight air escapement from the air sacks to relieve excessive pressure above and prevent accumulation of moisture between the cushion and occupant. For this purpose, it will be seen that WO94/19997 PCT~S93/02~9 .

2~6~

the individual air sacks are unattached to act individually during inflation and deflation for proper support and relief to prevent ischemic injury. The fabric of the air sacks and cover is characterized in that the fabric is micro-porous, having a low transmission of air and water vapor, but which blocks liquid transmission. Suitable fabrics are constructed from a fine weave pattern, and either coated, laminated, or impregnated with a material such as expanded Teflon. Suitable fabrics are sold under the commercial names of Goretex whicn is manufactured by the W. L. Gore Company, Ultrex manufactured by Burlington Industries of Greensboro, North Carolina, and Storm Shed manufactured by Reeves Brothers Manufacturing Company of Gaffney, South Carolina.
A plurality of annular flanges 57 surround air openings 52 in top member 50 having an undercut 58 for receiving a lower edge 60 of the air sacks. An elastic retaining means 62 secures the lower edge of the air sacks underneath the undercut. A cover 64 extends over the plurality of air sacks S which is secured around the periphery of top member 50. Both air sacks S and cover 64 are preferably constructed from a low air permeable fabric which allows air to escape from the air sacks to dry moisture in the buttocks area of the person seated on the cushion through flow through the cover. It will be noted that the fabric maintains air for sufficient pressure to support the person during the inflation/deflation sequences, but bleeds air to prevent excessive pressure and moisture. The air pressure in the air sacks automatically adjusts to the shifting of weight of a patient on the cushion. An open air distribution path extends from the blower to the air sacks which are not blocked which allows the WO94/lg997 PCT~S93/02~9 ~160g!~6 backwards flow of air from said air sacks to the blower in the event of over pressurization of the air sacks due to the weight of the patient. At the same time, the blocked air ports may be relieved through the open path by the flapper valves as shown in the direction of arrow 70, and the air sack fabric, having low air permeability, retains air during normal sitting pressures, but allows escapement of air outwardly in the event of excess pressure as shown by arrow 72.
lo Referring now to Figures 7 through 9, alternate embodiments of certain of the features of the invention will now be described. Figure 7 illustrates a pneumatic cushion wherein the air distribution system utilizes flexible vinyl hose at 16a, 18a, 20a, 22a, and at 23a, if necessary. The flexible conduits may be any suitable flexible hose, such as vinyl, and are substitutes for air channels 16 through 22 formed by plates in the embodiment of Figure 2. The vinyl hoses are connected to air distribution manifold F by suitable means, such as nipple fittings. The air distribution system and conduits are included in a plenum or housing B' covered by top member 50 having openings 52 as can best be seen in Figures 7 and 8.
Air permeable air sacks S' are illustrated which include a fabric as in the embodiment of Figures 1 through 6 but with an alternate construction. The construction of air sacks S' comprises a fabric covering of low permeability fabric but which has a bottom wall 80. A generally rigid bottom plate 82 is sewn or otherwise constructed within the air sacks to include a stem 84 that provides a nipple fitting for the flexible conduits, as can best be seen in Figure 8.
A soft, foam pad 86 may be carried atop generally rigid plate 82 for comfort. Stem 84 includes a wide portion W094/lgg~ PCT~S93/02~9 2~,6~9~
84a and a flange 84b that provide a means of retaining the air sacks. For this purpose, a retaining ring 88 may be employed to retain bottom plate 82 and hence air sack S by means of engagement of top member 50 and flange 84b. A sealing ring 90 may be disposed between the bottom of the air sacks and top member 50 of housing B'.
Figure 9 illustrates an alternate embodiment of a rotating air distributor according to the invention having a slightly different construction than that shown in Figure 4 wherein a stationary member or stator 92 in the form of an elongated air distribution tube is provided. A rotor shaft 94 is carried within stationary member 92 and provides a rotary valve mechanism. A plurality of valving elements 46' are provided in a staggered and longitudinally spaced relationship. Ports P' are formed in the stationary member 92 and are alternately blocked and unblocked by valve members 46' in a cyclic manner. Valve members 46' are like valve members 46 in that they may have a rigid base and a flexible wiper 48'. Ports P' are arranged in sets or groups of five as shown by numerals 1-5. Each group of ports P' correspond to a row of air sacks. There are also five ports P' in each group.
Rotor 94 is rotated in the same manner as rotor shaft 34 of Figure 4. Each of the ports a through e are connected to openings 52 in top member 50 by the flexible conduits 16'a through 23'a. The air conduits, which go from the same port of stator 92 to the same air sacks, are given like reference numerals in the embodiments of Figures 9 and 7. While the air conduits are illustrated in parallel lines, it is to be understood that the air conduits are flexed and routed WO g4/199g7 PCTlUSg3/0264g 216Qgg~

to stems 84 of the air sacks S' disposed in openings 52 in the rectangular array of Figure 5.
The rectangular array includes N rows and M columns where N=M=5 in the illustrated embodiment of Figure 5.
However, it is to be understood that the array may include any number of rows and columns as is necessary for a chair or bed cushion. The illustrated array has five deflation cycles I-V. The number of ports (a-e) corresponds to the number of columns 90, and the number of sets of ports corresponds to the number of rows 92 in the matrix. However, the matrix does not have to be square, i.e. N = M.
Other variations of the distributor may be utilized in accordance with the present invention as long as the same is allowed to be maintained in a low profile box underneath the air sacks. For example, a stationary disk and a rotating disk may be utilized as the stator and rotor elements. The stator disk may have the ports formed therein in an analogous manner to that of the embodiments of Figures 2, 7 and 9 so as to group the ports and rows of air sacks as controlled by the distributor. A rotary element may be utilized to selectively block the ports in accordance with the deflation cycle and pattern shown in Figure 5, or other suitable pattern.
Thus, it can be seen that an advantageous construction can be had for a pneumatic air cushion wherein the air blower delivers air at a constant flow rate and pressure which establishes a common system pressure in the unblocked air sacks, the air distribution conduits, and distribution manifold connected to the blower. The interruption of air flow to the blocked air sacks allows the air sacks to arrive at a pressure lost than the system pressure by escape WO94/19997 PCT~S93/02649 s~,'!,.6~9~&
of air through the air sack material and reach a stage of deflation, or equilibrium while remaining system stays at common system pressure. Air pressure in the air sacks changes for awhile as air is loss, and reaches a state of equilibrium depending on the weight, portion, and position of the body supported on the cushion. The new lower equilibrium pressure provides higher volume blood flow in the capillaries in the soft tissue overlying the cushion and air sacks. Thus, by creating this higher volume blood flow in a cyclic fashion, ischemic injury is reduced. The common system pressure may be determined primarily by the speed of the variable speed air blower.
While a preferred embodiment of the invention has been described using specific terms, such description is for illustrative purposes only, and it is to be understood that changes and variations may be made without departing from the spirit or scope of the following claims.

Claims (22)

What is claimed is:

1. A pneumatic cushion for reducing ischemic injury comprising:
a housing;
a support member extending over at least a part of said housing having a plurality of air openings;
a plurality of inflatable air sacks carried by said support member over said air openings, said air sacks being arranged in an rectangular array, where N is the number of rows and M is the number of columns in said rectangular array, and said air sacks are inflated and deflated in alternating inflation and deflation cycles according to a preselected sequence for reducing ischemic injury to a person supported on said cushion;
a dynamic air distribution system for distributing air to said air sacks and for periodically reducing air pressure in selected portions of said pneumatic cushion, said air distribution system comprising:
a plurality of air conduits carried within said housing;
a rotary air distributor carried within said housing for cycling air in said air conduits having an air inlet;
said rotary air distributor including a stationary element having a plurality of ports in fluid connection to said air conduits, and a rotary valve mechanism for periodically opening said ports during said inflation cycle, and blocking said ports to periodically interrupt the flow of air to said air sacks during said deflation cycle in accordance with a preselected sequence;
said stationary element having N sets of M ports connected to said air sacks;
a cover secured to said housing extending over said plurality of air sacks;
a blower for delivering air to said air inlet.

2. The apparatus of claim 1 wherein said housing includes a plenum box over which said support member extends.

3. The apparatus of claim 2 wherein said air conduits include a plurality of air channels formed by walls in said plenum box.

4. The apparatus of claim 1 wherein said air conduits comprise flexible hose.

5. The apparatus of claim 1 wherein said stationary element includes a cylindrical air distribution tube extending through said air housing box.

6. The apparatus of claim 5 wherein said rotary valve mechanism comprises a rotor shaft disposed coaxially with said cylindrical air distribution tube which carries N valving elements.

7. The apparatus of claim 6 wherein N=M.

8. The apparatus of claim 1 including a fitting carried by said air inlet for connection to a blower which delivers air to said air inlet and rotary air distributor.

9. The apparatus of claim 1 wherein said ports are spaced 360/N degrees around a circumference of said stationary element.

10. The apparatus of claim 1 wherein said ports are arranged together on said stationary member corresponding to a prescribed row and said ports of different rows are arranged at different axial locations on said stationary element.

11. The apparatus of claim 10 wherein said rotary valve mechanism comprises a plurality of valve elements for blocking certain of said ports in different rows during a deflation cycle according to said prescribed sequence.

12. The apparatus of claim 11 wherein said valve elements are angularly spaced from one another on said shaft corresponding to said spacing between said ports, and said valve elements include flexible valve elements which engages an inside diameter of said stationary element to block said air ports and flex away from said ports to automatically relieve pressure in a blocked air cell.

13. The apparatus of claim 1 wherein said air sacks are constructed from a material having a low air permeabllity which allows slight air escapement from said air sack during said deflation cycle, and which relieve pressure in a generally self-regulating manner during said inflation cycle.

14. The apparatus of claim 1 wherein said air sacks comprises a fabric enclosure having a bottom wall, a rigid bottom plate carried within said sack over said bottom wall, said plate having a stem extending through said sack and said openings in said support member, and said air conduit being connected to said stem.

15. The apparatus of claim 14 comprising a sealing member disposed between said bottom wall of said air sack and said support member of said housing, and a retaining member for securing said stem within said opening of said support member.

16. The apparatus of claim 1 wherein said stationary element extends longitudinally through said housing having a longitudinal axis generally parallel to said support member of said housing, said stationary element being disposed near one side of said housing, and said ports being arranged on a side of said stationary member opposite of said side of said housing, and said air conduits extending laterally from said stationary element to said air sacks.

17. A pneumatic cushion for reducing ischemic injury to a patient comprising:
a plurality of inflatable air sacks carried by a substrate which extends generally over a support area of said cushion;
a dynamic air distribution system for distributing air at a common system pressure to inflate said air sacks during an inflation cycle and for periodically reducing air pressure in selected ones of said inflated air sacks during a deflation cycle according to a predetermined sequence;

said air distribution system including an air blower establishing said common system pressure, an air distributor connected to said air blower, air conduits connected to said air distributor and to said air sacks, and said common system pressure being established in said air distributor, air conduits, and said inflated air sacks during said inflation cycle;
said air distributor including a valve mechanism disposed in said air distribution system having a blocking position which interrupts generally the entire communication of said common system pressure to said selected ones of said inflated air sacks during said deflation cycle; and said air sacks being constructed from a material having a low air permeability which allows a slight air escapement from said air sacks which allows said selected air sacks to deflate and reach an air pressure less than said common system pressure during said deflation cycle so that said pressure exerted against said patient's body is periodically reduced.

18. The apparatus of claim 17 wherein said valve mechanism has an open position in which said first plurality of air sacks remain generally at said common system pressure during said inflation cycle, and said open position of said valve mechanism allows said air in said first plurality of air sacks to flow in a reverse direction through said air distribution system and reduce the instantaneous air pressure therein in the event that air pressure in said air sacks exceeds said common system pressure so that said common system pressure is maintained in said first plurality of air sacks in a generally self regulatory manner during said inflation cycle.

19. The apparatus of claim 18 wherein said valve mechanism includes valves which block air flow through said ports in a first direction, but said valves open to deliver air through said ports in a second, opposite direction to automatically prevent excessive pressure in said air sacks.

20. The apparatus of claim 17 wherein said air sacks are arranged in a rectangular matrix comprising rows and columns, and said air sacks deflate diagonally from one corner of said matrix to another.

21. The apparatus of claim 17 wherein said valve mechanism includes a self-regulating air flow control valve having an open position for transmitting an inward air flow from said blower and air conduits to said air sacks in a first direction for inflating said sacks in a prescribed sequence during said inflation cycle, while simultaneously allowing a backward air flow in a second, opposite direction to prevent excessive pressures in said air sacks in a self-regulating manner when said air flow control valve is in said open position;
said air flow control valve having a blocked position for preventing said inward air flow during said deflation cycle, and said air flow control valve being moved from said blocked position directly by excessive pressure greater than said common system pressure in said air sack allowing a backward air flow in a second opposite direction to prevent said excessive pressures in said air sacks in a self-regulating manner.

22. A pneumatic cushion for reducing ischemic injury to a person occupying said cushion comprising:
a support;
a pneumatic cushion carried by said support;
a dynamic air distribution system which periodically reduces air pressure in selected portions of the cushion which includes means for producing an air flow, an air distributor for distributing said air flow;
a cyclic air flow controller for periodically blocking said air flow and interrupting the distribution of air in said air distributor;
a plurality of inflatable air sacks in fluid communication with said air distributor for receiving an inward air flow from said air distributor through an air port, and said air sacks are constructed from a material having a prescribed air permeability which allows an outward air flow through said air sack material;
said air flow controller having an open position in which said inward air flow is directed through said air port to said inflated air sacks during an inflation cycle to create said inflated air sacks;
said air flow controller having a blocking position for periodically blocking said air port and said inward air flow to said air sacks during a deflation cycle in accordance with said preselected sequence causing the air pressure in said air sacks to be reduced by said outward air flow through said air permeable air sack material so that reducing ischemic injury to a person seated on said wheel chair and moisture accumulation are reduced; and said air pressure in said selected air sacks being controlled by said person's anatomy and weight distribution when said air flow controller is in said blocking position during said deflation cycle.