GB2424182A - Person Support System - Google Patents

Abstract

A personal support system (PSS) for use as a mattress or seat cushion has an intermediate layer (1a) sandwiched between upper and lower compressible support layers (2, 3). The support layer acts as a flexible, variable aspect hard-surface datum layer which can conform to a person's body. The layer may be a spacer fabric which may be essentially inextensible in its plane. The properties of flexibility and inextensibility of the spacer fabric may be isotropic. The system is particularly concerned with the support of persons susceptible to pressure (decubitus) ulcers.

Description

PERSON SUPPORT SYSTEM

This invention relates to a person support system (PSS), that is a compressible flexible structure formed as a composite of multiple layers with an upper support surface, which may be of the form of a mattress or seat cushion, constructed to provide a comfortable contact reaction between the person's body and the support surface. The invention is particularly, although not exclusively, concerned with the support of persons who are susceptible or vulnerable to pressure (decubitus) ulcers, and particularly those who are subject to extended immobile periods on beds or chairs.

Equally, the invention is concerned with assisting the management and healing of persons already afflicted with pressure ulcers.

The most important step to prevent pressure ulcers is to avoid prolonged pressure differentials on any one part of the body. Even when the blood flow is only partially interrupted, friction and other kinds of damage to the outer skin 1 5 layer can cause ulcers. Ill-fitting clothing and wrinkled bedding, rubbing against the skin may contribute to skin injury. Extended periods of minimal pressure with no relief can be as harmful as intense pressure over a short period of time.

Critical features of an ideal PSS, are: * distributes pressure evenly; * conforms to body weight; * minimises friction and shearing forces; provides a well ventilated, comfortable surface that does not unduly restrict movement; * maintains skin at a constant optimal temperature; * is acceptable to the patient; * is easily cleaned and maintained For a PSS to meet the ideal, it must conform to body contours, thus Increasing the area of the body supporting its weight and avoiding local point pressure. The harder the support surface, the higher the pressures experienced.

A soft support surface is better able to distribute pressure evenly and to reduce the pressure gradients that lead to tissue distortion. However, low tissue distortion support needs to take account of the difference between uniaxial and hydrostatic loading (Figs. 1, 2 & 3).

A well conforming plaster bed may produce high pressures, but so long as the bed conforms exactly to the body contours it would cause no tissue distortion. However a foam mattress might register lower pressure than the plaster bed, but if its volume or density was too low for true hydrostatic support, pressure gradients would exist. Tissue distortion (resulting in capillary occlusion), the main cause of pressure ulcers, would occur (Fig. 4).

Generally a PSS is required to have sufficient compressive strength to support the person without "bottoming out".

One object of this invention is to provide a PSS which emulates hydrostatic support, in that the patient is buoyant and "floats" e.g. to a depth of approximately 100mm, without "bottoming out", and the top face conforms to a body profile without creasing or puckering. In this way the interface force can be distributed uniformly across the "submerged" part of the body, and at a minimum value; the top face fabric moves with the patient's body, and does not contribute to shear or friction on the body tissues and conversely, it does not emulate a drum skin, and risk localised high pressure points on the patient's body by "hammocking" (FIg. 5).

A conventional PSS depends on a vertical distribution of body load through the support medium, where the interface reaction at any one point is proportional to the degree of vertical compression of the support medium below that point. This is the case, whether the support is a single element (e.g. a polyurethane foam), or multi-layer (e.g. a spring interior or multi-layer foam). Consequently where the body penetrates the support medium the most, the interface reaction experienced is the greatest. This can create high interface reaction differentials in neighbouring body tissue, with the resultant 1 5 damage to those tissues. This is the case where the hard-surface datum for the media compression is the bed/seat frame on which the bottom face of the PSS is supported (Fig. 6).

According to one aspect of the present invention there is provided a person support system comprising a flexible structure formed as a composite of multiple layers with an upper support surface characterised in that said layers include an intermediate layer which creates a flexible variable aspect hard-surface datum within the flexible structure beneath the support surface.

According to a second aspect of the present invention there is provided a person support system comprising a compressible, flexible structure formed as a composite of multiple layers with an upper support surface characterised in that said layers include a flexible intermediate layer which is substantially inextensible so as to create a variable aspect hard-surface datum within the flexible structure beneath the support surface.

This intermediate layer can serve to support the upper layer or layers of the composite in such a way that the compression of the upper layer or layers can be more or less uniform over the area of contact in use with a person's body. Consequently the interface reaction with the body can be also more or less uniform. This can result in minimal body tissue distortion.

To enable the variable aspect hard-surface datum to flex, it is preferably mounted on a flexible, compressible bottom layer.

The variable aspect hard-surface datum layer is constructed in such a way as to be flexible, but at the same time to provide a firm variable datum 1 5 for the upper layers.

The intermediate layer acts to provide a hard-surface datum, that is, it provides a support surface which, as a consequence of its variable aspect flexibility can change its surface shape (i.e. flex in its own plane) to conform to the weight distribution and shape of a loading applied thereto e.g. by the body of a person sitting or lying on the PSS, and, as a consequence of this, and where appropriate its substantial inextensibility, it can ensure that the person's body is substantially equally supported throughout the surface of the intermediate layer.

Most preferably the said flexibility, and where appropriate the substantial inextensibility of the intermediate layer, is substantially isotropic in the plane of the surface of the layer.

The substantial inextensibility is such that the layer is less extensible than the other layers of the multilayer structure and preferably, when supporting typical loadings applied by a person's body would extend by a percentage which is a minority of the dimensions of the layer in the direction of extension, say 20% or less. Where isotropic, the inextensibility is such that the layer cannot be stretched to any significant extent in any direction.

It is however to be understood that the layer may have limited extensibility so that it will stretch in use to a certain extent but in that case the layer preferably has properties of substantially complete recovery when unloaded.

Preferably the intermediate layer is relatively thin relative to the other layers and may also be relatively incompressible.

1 5 Preferably also the intermediate layer is supported by a layer therebeneath, and may be fixed relative to one or more of the other layers so as to be held in position relative thereto, although other arrangements are also possible.

In a preferred embodiment the datum layer is a fabric layer, particularly a spacer fabric having upper and lower fabric faces with spacer threads, particularly mono-filament threads, extending transversely therebetween.

An important property of the intermediate fabric layer is its high shear modulus giving high structural stability, preferably isotropically as mentioned above. With a spacer fabric this can be achieved by use of transverse spacer threads which cross each other i.e. which are arranged in at least two sets of threads which are inclined in opposite directions. The threads are also preferably relatively densely distributed to give a structure which is resiliently compressible and preferably retains much of its thickness under typical loading.

Other layers may comprise resiliently compressible foam layers and/or fabric layers or other constructions.

The various layers may be united with or without bonding and/or in any other suitable manner.

With the arrangement of the invention the composite structure can conform to the person's body, with an even distribution of interface load reaction. The intermediate hard-surface datum can be supported in its reactive profile by a "softer" bottom layer.

1 5 The composite structure may be in the form of a mattress or seat cushion and may have a casing. The casing may have a top surface which has the ability to contain and protect the composite structure mechanically, to transmit water vapour, and to conform, with the encased composite structure, to the applied body profile without puckering or creasing. For medical applications the casing should also protect hygienically, be breathable and not transmit liquids.

The PSS may also comprise a removable, launderable, synthetic or natural fleece, or 3-dimensional structure top cover, which can replace the usual top sheet; and may be compressible to provide an additional element of interface reaction load spreading.

The invention will now be described further by way of example only and with reference to the accompanying drawings in which:- Figs. 1 & 2 are schematic cross-sections through a limb supported on two contrasting surface types; Figs. 3a-b are diagrams which illustrate the concept of unilateral loading of body tissue versus hydrostatic loading; Fig. 4 is a view similar to Figs. 1 and 2 which illustrates the effect of a support medium with insufficient volume or density for true hydrostatic support; Fig. 5 is a schematic sectional view which illustrates the concept of a conforming composite support system but showing pressure points; 1 5 Fig. 6 is a schematic sectional view which illustrates the distribution of body load through the support medium, where the interface reaction at any one point is proportional to the degree of vertical compression of the support media below that point; Fig. 7 is a schematic sectional view which shows the role of the variable aspect hard-surface datum in accordance with this invention; Fig. 8 is a schematic sectional view of the variable aspect hard-surface datum of Fig. 7; Fig. 9 is a schematic sectional view which shows the near uniform distribution of interface load reaction with the arrangement of Fig. 7; Figs. 1 0 & 11 are diagrammatic sectional views of the construction of the composite and the complete PSS in accordance with the embodiment of the invention; and Fig. 12 is an enlarged schematic sectional view of the variable aspect hard-surface datum of Fig. 7.

Fig. 1 illustrates idealised conforming support of a person's limb. The supporting medium conforms to the shape of the limb and there is therefore no tissue distortion.

Fig. 2 illustrates the tissue distortion affect of a non-conforming rigid support medium.

1 5 Figs. 3a-c show how loading causes tissue distortion.

Fig. 3a illustrates blood vessels in a cube of tissue without loading.

Fig. 3b illustrates how the blood vessels stretch and compress with uniaxial pressure (loading in one direction).

Fig. 3c illustrates how triaxial pressure, such as would occur with hydrostatic loading, gives an idealised lack of distortion.

Fig. 4 shows how tissue is loaded and is distorted with a soft support medium such as a foam mattress on a rigid base which can compress to conform to the limb shape but has insufficient volume or density for true hydrostatic support whereby bottoming out' occurs and causes high tissue compression.

Fig. 5 shows conceptually how the use of a hard-surface datum layer 1 within a flexible support medium can prevent bottoming out but could give rise to hammocking' whereby localised high pressure points are formed.

That is, the datum layer can distribute pressure to approach conditions of near-hydrostatic support with near uniform compression of the support medium above the datum layer, but if insufficiently flexible complete uniformity may not be realised.

Fig. 6 illustrates the tissue-damaging forces which can arise at the interface between the support medium and the person's limb where an inadequately flexible hard-surface datum layer, such as a rigid base e.g. a bed or seat frame is used. The support force is proportional to vertical corn pression.

1 5 Fig. 7 shows conceptually the hydrostatic-like support which can be achieved with a variable aspect hard-surface datum layer 1 a in accordance with the present invention, on a flexible compressible bottom layer 3.

In accordance with the present invention, as shown by way of example in Figs. 8-1 1, a support medium is constructed as a multi-layer flexible composite structure having a datum layer 1 a between upper and lower flexible resiliently compressible layers 2, 3.

The datum layer la is preferably a textile layer e.g. as described hereinafter and is firm and stretchable with substantially complete recovery - 10- at least at its faces 4, 5. This layer has internal connective structure 6 to act both as a constraint and support for the material to enable bending/deformation in three axes with minimal loss of thickness.

As shown in Fig. 9 this datum layer 1 a can support the person's limb with non-shearing, near uniform, near hydrostatic support. The flexible compressible bottom layer 3 assists flexing of the datum layer to conform to the limb shape. Shear forces are absorbed at the layer 1 a and nonshearing, near uniform, near hydrostatic support is established at the top surface of the flexible compressible top layer 2.

As shown in Fig. 10 the layers above and below the datum layer may be 3D textile constructions and/or foam materials and/or other materials.

As shown in Fig. 11, the composite multi-layer structure of Fig. 10 may be enclosed within an outer mattress/seat-cushion case 6 which may comprise, for medical applications, 5 faces of welded reinforced polymer 1 5 sheeting with a top face of reinforced stretchable flexible breathable waterproof polymeric membrane which is spongeable/sterilisable for hygienic maintenance.

A two-way stretch fleece 7 may be fitted over the cased composite in the manner of a fitted top sheet.

For domestic applications different traditional casing constructions with reinforced stretchable flexible/breathable top face may be used.

In a particularly preferred construction the variable aspect hard-surface datum layer is a spacer material, which is a 3-dimensional spacer material, consisting of a face and a back flexible surface separated by transverse mono-filament threads which impart the specific properties to the structure, as illustrated in Fig. 12. As shown the spacer threads cross each other and are relatively densely distributed.

The spacer material is isotropic in behaviour, which denotes that the properties such as breaking strength or tenacity, breaking extension and modulus are very similar in all directions. The structure also possesses high shear modulus in all directions, particularly determined by the cross-over conformation of the spacer threads, which also means that the structure provides evenly distributed pressure around a portion of the periphery of the patients' body. The structure also imparts superior resilience properties.

Some properties of the spacer material are listed below: Structure: 1 00% polyester spacer 1 5 Property Material 1. Area Density 373.8 gm2 2. Thickness 2.25 mm 3. Density 0.166 gcm3 4. Tenacity: Machine Direction 0.045 N tex1 Cross Direction 0.042 N tex1 45 Direction (bias) 0.055 N tex1 5. Breaking Extension: Machine Direction 55.2% - 12- Cross Direction 55.1% 450 Direction (bias) 56.5% 6. Modulus (stiffness): Machine Direction 0.03 N tex1 Cross Direction 0. 03 N tex1 45 Direction (bias) 0.05 N tex1 The spacer material may also have the following modulus properties (force distribution required to give a 5% extension): 1 5 Cross direction 1.85 N tex1 Machine direction 1.37 N tex1 45 direction 1.67 N tex1 Thus, the material has a high shear modulus in all directions in the plane of the fabric.

Spacer materials are also breathable and hence comfortable as they transport both water vapour and evaporative heat around the patient, thus making him or her feel comfortable.

The load-bearing performance characteristics of the PSS of the invention can be varied and predicted by the selection of component materials with differing characteristics. The application markets of the invention can also be tailored for by the selection of alternative casing and covering materials.

The main performance features of the invention are: 1. maximum conformity and area of support contact for the person's - 13- body, and thus; 2. the minimum differential of interface pressure on the body, and thus; 3. reduction of the pressure forces generating pressure ulcers and; 4. reduction of shear forces which can also generate tissue damage; 5. no hard edges or surfaces to risk impact damage; 6. PSS surfaces suitable for hygiene maintenance in medical variant; 7. breathable, waterproof upper face of PSS casing in medical variant; It is of course to be understood that the invention is not intended to be restricted to the details of the above embodiments which are described by way of examples only. Thus, for example, although reference is made to medical and pressure ulcer treatment applications, the structure and principles of the invention may also be used in the broader arena of person support and for other support purposes. - 14-

Claims (12)

1. A person support system comprising a flexible structure formed as a composite of multiple layers with an upper support surface characterised in that said layers include an intermediate layer which creates a flexible variable aspect hard-surface datum within the flexible structure beneath the support surface.

2. A person support system according to claim 1 characterised in that the flexibility of the intermediate layer is substantially isotropic.

3. A person support system comprising a compressible, flexible structure formed as a composite of multiple layers with an upper support surf ace characterised in that said layers include a flexible intermediate layer which is substantially inextensible so as to create a variable aspect hard-surface datum within the flexible structure beneath the support surface.

1 5

4. A person support system according to claim 3 characterised in that the inextensibility of the intermediate layer is substantially isotropic in the plane of the layer.

5. A person support system according to any one of claims 1 to 4 characterised in that the intermediate layer comprises a fabric layer.

6. A person support system according to claim 5 characterised in that the intermediate layer comprises a spacer fabric.

7. A person support system according to any one of claims 1 to 6 characterised in that the said multiple layers comprise compressible - 15foam layers above and below the said intermediate layer.

8. A person support system according to any one of claims 1 to 7 characterised in that the multiple layers are enclosed within a casing which is liquid proof but breathable.

9. A person support system according to any one of claims 1 to 8 characterised in that a removable compressible cover is provided over the said upper support surface.

10. A person support system according to any one of claims 1 to 9 characterised in that it is in the form of a mattress.

11. A person support system according to any one of claims 1 to 10 characterised in that it is in the form of a cushion.

12. A person support system according to claim 1 substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.