WO1995007679A2

WO1995007679A2 - Pressure relief foam mattress

Info

Publication number: WO1995007679A2
Application number: PCT/CA1994/000484
Authority: WO
Inventors: A. Ward George; J. Folkard Noel
Original assignee: Woodbridge Foam Corporation
Priority date: 1993-09-13
Filing date: 1994-09-13
Publication date: 1995-03-23
Also published as: WO1995007679A3; AU7606694A

Abstract

A mattress (10) to relieve pressure and shear forces and inhibit the formation of decubitus ulcers includes a foam body having a generally planar surface to be supported on a rigid surface such as the carriage of a bed and an upper support surface (14) on which an individual lies. The foam body includes a contoured base (18) having upstanding side rails (22, 26) formed of dense foam material and a central body portion (12) on the base and extending between the side rails. The central body portion is partitioned into a head supporting zone (30), a foot supporting zone (34) and a mid-section supporting zone (32). The head and foot supporting zones include an upper layer of very soft foam (42, 62) and a bottom layer (40, 64) of firmer foam. In the foot supporting region, the bottom layer (64) forms a cantilever to support the calves of an individual while the heels of the individual are only supported by the soft foam of the top layer. The mid-section supporting zone is contoured and is divided into a plurality of freely moving individual cells (60) to reduce the shear force between an individual and the mattress when the individual moves or the carriage is adjusted. Preferably, inserts (28) formed of foam material more resilient than the base and side rails are provided in the side rails to facilitate folding of the mattress about transverse fold lines.

Description

PRESSURE RELIEF FOAM MATTRESS

TECHNICAL FIELD

The present invention relates to mattresses and in particular to a foam mattress to relieve pressure and shear forces to inhibit the formation of decubitus ulcers.

BACKGROUND ART

Beds are well known in the art and many designs have been considered. A particular area in which innovative developments in bed design have been made is the health care industry. In the case of patients in hospitals, specifically those patients who are bed ridden, it is desired that the mattress on which a patient lay not only provide adequate support but also relieve pressure and shear forces to inhibit the incidence of decubitus ulcers forming on the patient.

Most hospital beds have an adjustable carriage which can be moved to allow the head and foot sections of the bed to be raised and lowered as required. Unfortunately, most mattress designs are unsuitable for use with such a bed due to the fact that they are relatively inflexible and cannot assume the shape of the carriage as it goes through its entire range of movement. This results in the mattress lifting from the carriage. Lifting of the mattress poses problems in that the individual lying on the mattress is not supported by the mattress in the manner intended.

Although foam mattresses are typically flexible enough to be used with the above described type of adjustable bed, conventional foam mattress do not provide adequate support especially in the areas adjacent the mattress fold lines. If the thickness of the mattress is increased to improve support, its ability to fold about the fold lines decreases. This results in the foam mattress exhibiting the same deficiencies as other prior art mattresses namely, it lifts from the carriage when the carriage assumes certain positions.

U.S. Patent Application Serial No. 08/152,173 filed on November 16, 1993 to Ward et al and assigned to the same assignee of the present invention, discloses a foldable foam mattress designed to overcome the folding problems associated with the prior art type mattresses discussed above. The mattress includes inserts formed of high resilience foam within the foam body adjacent the fold lines to assist folding of the mattress while ensuring that the mattress still provides adequate support to an individual, especially in the areas adjacent the fold lines.

Although the mattress described in the above-identified co-pending application overcomes the folding problem associated with prior art mattresses, its design was not intended to deal specifically with reducing the occurrence of decubitus ulcers forming on an individual lying on the mattress for extended periods of time. Mattress designs to deal with this problem have, however been considered. For example, U.S. Patent No. 4,580,301 to Ludman et al shows a mattress having a body of open-cell foam with air passages extending up through a central region of the mattress. The body also includes a base with supporting elements in the head and foot regions. The supporting elements are formed of foam material which is more dense and less readily compressed than the remainder of the foam material. Although this mattress is designed to reduce the occurrence of decubitus ulcers, improved designs to improve support while reducing the occurrence of decubitus ulcers are continually being sought. It is therefore an object of the present invention to provide a novel foam mattress which obviates or mitigates at least some of the above-described problems associated with prior art mattress.

DISCLOSURE OF THE INVENTION

According to one aspect of the present invention there is provided a mattress comprising a foam body including a base having a bottom surface to be supported by a generally rigid surface and being formed of a generally firm foam and a central body portion on said base and having an upper support surface on which an individual is to lie, said central body portion including a head supporting zone and a foot supporting zone with each zone having an upper soft foam layer disposed above a generally firmer foam layer, whereby the foam layers in said head and foot supporting zones are less firm than the foam of said base but provide adequate support to an individual while reducing local pressure points and minimizing shear forces to inhibit the occurrence of decubitus ulcers forming on an individual lying on said mattress.

Preferably, the firmer foam layer in the foot supporting zone extends only partially along the length of the zone and is positioned to support the calves of an individual lying on the mattress, the heels of the individual being supported only by the upper soft foam layer. It is also preferred that the head and foot supporting zones are bridged by a mid-section supporting zone formed mostly of foam material less firm than the base but more firm than the firmer foam layer between the soft foam and the base in the head and foot supporting zones. In one embodiment, the soft foam layers have an ILD co-efficient equal to about 6 lbs, the firmer foam layers have an ILD co-efficient equal to about 17 lbs, the foam in the mid-section supporting zone has an ILD co-efficient equal to about 23 lbs, and the base foam has an ILD co-efficient equal to about 35 lbs. Preferably, the mattress further includes inserts formed of high resilience foam material to facilitate folding of the mattress about at least one fold line extending normal to the longitudinal axis of the mattress. It is also preferred that the mattress further includes a pair of side rails integrally formed with the base with the inserts being located in the side rails.

Preferably, the entire upper surface of the mid-section supporting zone is divided into cells with the cells being defined by transverse and longitudinal slits formed in the upper surface. It is also preferred that the transverse slits are arranged in pairs with each pair of slits generally resembling a wishbone to define cells generally ovate in cross-section and cells generally rectangular in cross-section, the ovate cells and the rectangular cells being arranged alternately along the length of the mid-section supporting zone. Preferably, the ovate cells are slightly lower in height than the rectangular cells and the rectangular cells have inwardly curved sides whereby the rectangular cells adjacent the fold lines fold over the ovate cells when the mattress is folded about the fold lines to present a generally continuous upper surface adjacent the fold lines. It is also preferred that the longitudinal slits are only provided in the rectangular projections. The cells also reduce shear forces between an individual and the mattress since the cells are able to move freely. By reducing shear forces between the individual and the mattress, shear forces between the tissue and the bone of the individual are reduced. This is important as both shear forces and pressure applied to tissue have been identified as a cause of decubitus ulcers.

According to another aspect of the present invention there is provided a method of forming a foam product formed from a plurality of foam pieces at least one of which is preformed, said method comprising the steps of:

(i) placing the at least one preformed foam piece in a mold at a desired location; (ii) introducing unexpanded foam into said mold; and

(iii) expanding said unexpanded foam in said mold to complete said foam product, said foam when expanded acting as a binding agent to hold the pieces of foam forming said foam product together.

Preferably, the foam product includes a plurality of preformed foam pieces with the preformed pieces being fitted together in a manner so as to avoid large seams in the surface of the foam product and provide transitional regions between the zones of the mattress. It is also preferred that the foam product is a mattress having a base and a central body portion on the base, the central body portion being constituted by the foam pieces and the base being constituted by the expanded foam.

The lightweight soft foam upper layers in the head and foot supporting zones which are supported by firmer but still soft foam layers provide adequate support to an individual while relieving pressure points to inhibit the formation of decubitus ulcers. The inserts make the mattress more readily foldable than prior art designs allowing it to conform to the shape of an adjustable bed carriage without lifting of the mattress occurring and without requiring transverse cuts or contours to be formed in the foam core of the mattress. This of course maintains the structural integrity of the mattress and ensures comfort and support to an individual on the mattress. These features make the present mattress advantageous over prior art mattress.

BRIEF DESCRIPTION OF THE DRAWING

An embodiment of the present invention will now be described more fully with reference to the accompanying drawings in which:

Figure 1 is a top plan view of a foam mattress to relieve pressure and shear forces to inhibit the formation of decubitus ulcers; Figure 2 is a side elevation of the mattress shown in Figure 1 ;

Figure 3 is a sectional view of the mattress shown in Figure 1 taken along line A-A;

Figure 4 is an end elevation of the mattress shown in Figure 1 taken in the direction of arrow 4;

Figure 5 is a sectional view of the mattress shown in Figure 2 taken along line B-B; and

Figure 6 is a top plan view of an alternative embodiment of a foam mattress to relieve pressure and shear forces to inhibit the formation of decubitus ulcers.

BEST MODE FOR CARRYING OUT THE INVENTION

Referring now to Figures 1 , 2 and 4, a mattress to inhibit the formation of decubitus ulcers on an individual is shown and is generally indicated by reference numeral 10. This is achieved by designing the mattress to distribute an individual's weight over a large surface area and to reduce local pressure points to ensure adequate blood flow to all areas of the individual. The mattress also inhibits the formation of decubitus ulcers by incorporating freely moving cells on its upper surface which reduce shear forces between an individual and the mattress. The entire mattress 10 is formed of foam material and is foldable making it particularly useful with adjustable beds such as those typically found in hospitals.

The mattress 10 is generally rectangular in plan and in side elevation and includes a central foam body portion 12 having an upper surface 14 designed to support an individual. The central foam body portion 12 is disposed on a foam frame 16 formed, for the most part, of dense foam material having an Indentation Load Deflection (ILD) co-efficient equal to about 35 lbs. The frame 16 includes a contoured foam base 18 (see Figure 3) having an upper surface designed to match the postural contour of a typical individual and a planar bottom surface to be supported by a rigid surface such as the carriage of an adjustable bed. A pair of upstanding side rails 22 and 26 respectively integrally formed with the base 18, run along opposite sides of the base. The side rails 22 and 26 are reduced in height intermediate their length and are cut on their upper surface in this intermediate area to form a toothed pattern of rectangular projections 22a. An insert 28 formed of high resilience HR 29 grade foam material is included in each of the side rails 22 and 26 respectively and fills in the reduced intermediate area. The inserts 28 have a bottom complementary to the toothed pattern of projections 22a and are dimensioned so that they extend to locations which correspond with the fold lines of most adjustable bed carriages. This is generally where the hip and knee joints of an individual are positioned when an individual lies on the mattress 10. The inserts 28 facilitate folding of the mattress 10 about fold lines extending normal to the central longitudinal axis of the mattress.

The central body portion 12 is formed from a number of individual pieces of different grade foam and is partitioned into three zones, namely a head supporting zone 30, a mid-section supporting zone 32 and a foot supporting zone 34.

Referring now to Figure 3, it can be seen that within the head supporting zone 30, the central body portion 12 includes a bottom layer of foam material 40 having an ILD co-efficient equal to about 17 lbs. Above layer 40 is a very soft top layer of foam material 42 having an ILD co-efficient equal to about 6 lbs. Layer 42 covers layer 40 and extends above and overtop of the side rails 22 and 26. Both the bottom and top layers 40 and 42 respectively extend from one end of the mattress 10 and stop short of the junction between the head supporting zone 30 and the mid-section supporting zone 32. A layer of HR 23 foam material 44 having an ILD co-efficient equal to about 23 lbs is fitted to the layers 40 and 42 and extends into the mid-section supporting zone 32. The layers 40, 42 and 44 are notched and are complimentarily shaped at their ends to facilitate assembly in such a manner so as to avoid large seams and provide transitional areas between the zones of the mattress. This increases comfort and also increases the durability of the mattress 10 in high tear areas such as at the fold lines.

The layer 44 increases in thickness in the mid-section supporting zone 32 adjacent the head supporting zone 30 and slowly decreases in thickness towards the foot supporting zone 34 as it conforms with the contoured base 18. The layer 44 however, stops short of the junction between the mid-section supporting zone 32 and the foot supporting zone 34.

A plurality of narrow slits 46 arranged in pairs 48 extend across the width of the layer 44. The slits 46 are shaped so that each pair 48 resembles a wishbone. This defines generally ovate projections 50 disposed between generally rectangular projections 52. The rectangular projections 52 have inwardly curved sides and are higher than the ovate projections 50.

The spacing between adjacent pairs 48 of slits in the mid-section supporting zone 32 varies along the length of layer 44 with the largest spacing between adjacent pairs 48 of slits occurring midway along its length. The depth of adjacent pairs 48 of slits also varies along the length of layer 44 with the deepest pairs 48 of slits being located midway along its length. The spacing between and depth of the pairs of slits is chosen to provide full support to an individual by matching the contour of a typical individual. The slits 46 promote air circulation and reduce heat and moisture build-up at the skin surface of an individual. A plurality of spaced slits 58 running parallel to the longitudinal axis of the mattress 10 are also formed in the upper surface of the layer 44. The slits 46 and 58 divide the upper surface of the rectangular projections 52 into a plurality of freely moving individual cells 60 aligning and supporting an individual within the mid-section supporting zone 32 while reducing shear forces between the individual and the mattress.

Joined to the end of layer 44 near the foot supporting zone 34 are top and bottom layers of foam material 62 and 64 respectively. The mating ends of the layers 44, 62 and 64 are fitted together and are complimentary shaped in a manner so as to avoid large seams and provide transitional areas between the zones of the mattress. The bottom layer 64 is formed of foam material having an ILD co-efficient equal to about 17 lbs and extends from layer 44 partially into the foot supporting zone 34. The top layer 62 is formed of very soft foam having an ILD co-efficient equal to about 6 lbs and extends from layer 44 to the end of the mattress 10. Similar to layer 42, layer 62 also extends above and overtop of the side rails 22 and 26. Therefore, the top layer 62 is deep beyond layer 64 and contacts the base 18. The upper surface of the layer 62 has a depression 68 formed in it and is designed to receive the heels of an individual.

To construct the mattress 10, the various types of foam forming the central body portion 12 and inserts 28 can either be molded, produced in individual blocks and cut from the blocks in the required size or produced using a combination of these technologies. The pieces of foam forming the central body portion 12 are then placed in a mold. The inserts 28 are also placed in the mold and are held in place within the mold by pins or the like. Once this has been done, unexpanded polyurethane foam which is to form the remainder of the mattress (i.e. the frame 16) is placed in the mold. The polyurethane foam is then expanded to form the frame 16 and complete the mattress 10. The expanded foam in the mold acts as a binding agent to hold the central body portion 12 and the frame 16 together. In use, the mattress 10 is typically housed within a lightweight cover (not shown) to protect the foam and is placed on the carriage of an adjustable bed. When the carriage is moved to elevate the head supporting zone 30 and/or the foot supporting zone 34, the mattress 10 folds about one or both of the fold lines without the lower surface of base 18 lifting to any great extent from the carriage. This is due to the provision of the inserts 28 formed of high resilience foam material.

When the mattress 10 is folded about one or both of the fold lines, the rectangular projections 52 on both sides of the ovate projections 50 near the fold lines, fold over the ovate projections 50 maintaining a generally continuous upper surface 14 with increased support in areas typically supporting the majority of the weight of an individual lying on the mattress 10.

The individual cells 60 formed along the projections 52 help to reduce shear forces placed on the individual as the mattress 10 is articulated. When a mattress is articulated, an individual lying on the mattress tends to move relative to the mattress. With conventional mattresses, as the individual moves, the skeleton of the individual tends to move freely while the epidermis of the individual tends to remain stationary against the surface of the mattress. To inhibit this differential movement between the epidermis and the skeleton occurring, when the present mattress is articulated, the cells 60 move with the individual before any significant shear forces are placed on the individual.

The thicknesses and grades of foam material used to form the mattress 10 are selected so that an individual properly lying on the mattress does not feel the rigid frame of the underlying bed carriage. Also, the different grades of foam used in the various zones 30 to 34 of the central body portion 12, distribute an individual's weight over a large surface area to relieve local pressure points which can promote discomfort and lead to the formation of decubitus ulcers. This is achieved by providing very soft foam layers 42 and 62 in the head and foot supporting zones 30 and 34 respectively. The bottom layers 40 and 64 of firmer, but still soft foam, help to build load between the firm base 18 and the soft foam layers 42 and 62 to inhibit bottoming out when an individual is supported by the mattress 10. Moreover, the layer 64 in the foot supporting zone 34 acts as a cantilever to support the calves of an individual while the heels of the individual are received in the depression 68 and are supported by the extremely soft layer of foam material 62. This virtually eliminates the formation of decubitus ulcers on the heels of an individual. Also, the design of the mattress to virtually eliminate surface glue seams and provide transitional areas between the zones increase comfort and durability.

The ends of the mattress 10 are not provided with rails. This ensures that the soft foam layers 42 and 62 respectively remain as soft as possible. It has been found that when side rails are provided, the side rails of firmer foam constrain the soft foam layers as they are compressed. Also, because the side rails do not reach the upper surface of the mattress, if an individual has an arm and/or leg overhanging the mattress, it is not supported by the firm side rails thereby increasing comfort.

Figure 6 shows an alternative embodiment of the mattress 10'. In this embodiment, the mattress 10' is basically the same as the mattress 10 described above with the exception that a plurality of transverse ribs 80 are formed on the upper surface of layer 62' in the foot supporting zone 34' within the depression 68'.

The present invention provides advantages in that the lightweight soft foam upper layers in the head and foot supporting zones which are supported by firmer but still soft foam layers, provide adequate support to an individual while relieving pressure points to inhibit the formation of decubitus ulcers. Also, the high resilience foam inserts facilitate folding of the mattress about the fold lines. This allows the mattress to assume the configuration of an adjustable bed while minimizing lifting of the mattress from the carriage of the bed.

Claims

What is claimed is:

1. A mattress comprising a foam body including a base having a bottom surface to be supported by a generally rigid surface and being formed of a generally firm foam and a central body portion on said base and having an upper support surface on which an individual is to lie, said central body portion including a head supporting zone and a foot supporting zone with each zone having an upper soft foam layer disposed above a generally firmer foam layer, whereby the foam layers in said head and foot supporting zones are less firm than the foam of said base but provide adequate support to an individual while reducing local pressure points and minimizing shear forces to inhibit the occurrence of decubitus ulcers forming on an individual lying on said mattress.

2. A mattress as defined in claim 1 wherein the firmer foam layer in said foot supporting zone extends only partially along the length of said zone and is positioned to support the calves of an individual lying on said mattress, the heels of said individual being supported only by said soft foam layer.

3. A mattress as defined in claim 2 wherein the upper surface of said soft foam layer in said foot supporting zone is contoured to accommodate the heels of an individual.

4. A mattress as defined in claim 2 wherein said head and foot supporting zones are bridged by a mid-section supporting zone formed mostly of foam material less firm than said base but more firm than said firmer foam layers.

5. A mattress as defined in claim 4 wherein said soft foam layers have an ILD co-efficient equal to about 6 lbs and said firmer foam layers have an ILD co-efficient equal to about 17 lbs.

6. A mattress as defined in claim 4 further comprising a pair of side rails integrally formed with said base and running along opposite sides thereof and inserts formed of foam material more resilient than said base, said inserts being provided in said side rails to facilitate folding of said mattress about at least one fold line extending normal to the longitudinal axis of said mattress.

7. A mattress as defined in claim 6 wherein the upper surface of said head and foot supporting zones extends over said side rails.

8. A mattress as defined in claim 7 wherein said inserts are spaced along the length of said side rails at positions to accommodate the articulations of an adjustable bed carriage.

9. A mattress as defined in claim 7 wherein the upper surface of most of said mid-section supporting zone is divided into transverse cells defined by slits formed in said upper surface.

10. A mattress as defined in claim 10 wherein said slits are cut at depths which generally match the contour of an individual lying on said mattress.

11. A mattress as defined in claim 10 wherein said slits are arranged in pairs with each pair of slits generally resembling a wishbone to define cells generally ovate in cross-section and cells generally rectangular in cross-section, said ovate cells and said rectangular cells being arranged alternately.

12. A mattress as defined in claim 11 wherein said ovate cells are slightly lower in height than said rectangular cells and wherein said rectangular cells have inwardly curved sides whereby the rectangular cells adjacent said fold lines fold over the ovate cells when the mattress is folded about a fold line to present a continuous upper surface adjacent said fold line.

13. A mattress as defined in claim 2 wherein the different types of foam material of said central body portion abut at their junctions in a manner so as to avoid large seams and provide transitional areas between the zones within said foam body.

14. A mattress as defined in claim 2 wherein said soft foam layers in said head and foot supporting zones are free at the ends of said mattress to reduce constraining thereon.

15. A mattress as defined in claim 9 wherein said transverse cells are further divided into smaller cells by longitudinal slits formed in said mid-section supporting zone.

16. A method of forming a foam product formed from a plurality of foam pieces at least one of which is preformed, said method comprising the steps of:

(i) placing the at least one preformed foam piece in a mold at a desired location;

(ii) introducing unexpanded foam into said mold; and

(iii) expanding said unexpanded foam in said mold to complete said foam product, said expanded foam acting as a binding agent to hold the pieces of foam forming said foam product together.

17. The method of claim 16 wherein said foam product includes a plurality of preformed foam pieces and wherein said preformed pieces are glued together and overlapped to avoid large seams in said foam product.

18. The method of claim 17 wherein said foam product is a mattress having a base and a central body portion on said base, said central body portion being constituted by said foam pieces and said base being constituted by said expanded foam.