GB2473661A

GB2473661A - A mattress with two layers of inflated cells and a foam base

Info

Publication number: GB2473661A
Application number: GB0916533A
Authority: GB
Inventors: Richard John Baker; Gary John Baker
Original assignee: SQUIRREL MEDICAL Ltd
Current assignee: SQUIRREL MEDICAL Ltd
Priority date: 2009-09-21
Filing date: 2009-09-21
Publication date: 2011-03-23
Anticipated expiration: 2029-09-21
Also published as: GB2473661B; GB0916533D0

Abstract

A mattress comprising a base 8 made of an expanded foam material, a first layer 22 of cells positioned transversely to the body of the mattress and inflatable with gas, a second layer 24 of cells also positioned transversely to the mattress and inflatable with gas and further comprising a region of cells with perforations in and means for supplying gas to the cells wherein the overall thickness of the mattress is less than 150mm. A variety of ranges of foam thickness and density and cell diameter and gas pressure are provided. The second layer of cells 24 may also have alternating regions of static and ventilated cells. The device may be used to assist in the prevention of bed sores.

Description

I

A MATTRESS

The present invention relates to a mattress, in particular to a mattress having therapeutic and/or orthopaedic applications.

It is known to provide mattresses comprising a plurality of inflatable cells.

Mattresses of this general type are widely used in hospitals and clinics, in particular for patients with long term illnesses and difficulties requiring them to remain in bed for extended periods of time, It is known to provide such mattresses with suitable pumps and control means to selectively inflate and deflate the cells with air. In this way, the form and contours of the mattress may be varied beneath the patient, so as to avoid the patient developing pressure sores and other conditions symptomatic of extended periods reclining in bed. The mattress may be provided with cells that are permanently inflated andlor cells that may be selectively partially or wholly inflated and deflated. In addition, the mattress may be provided with cells that are provided with air-permeable portions, for example by way of laser perforations, designed to allow air to leak or bleed from the cell at a predetermined rate.

One mattress produced by the present Applicant comprises a base of expanded foam, in particular an open-cell polyurethane foam, a first layer of transverse cells permanently inflated to a predetermined pressure with air, and an upper layer of transverse air-filled cells. The total number of cells in the mattress is 84, divided between the first and upper layers. The cells in the upper layer are of two forms. First, the upper layer is provided with a region of cells of the aforementioned perforated variety, means being provided to supply air at a constant rate and * .S' pressure to replace air leaving the cells through the perforations and maintain the *. cells at a predetermined inflation pressure. Second, the upper layer is provided with a region having cells that are selectively inflated and deflated, as described :30 hereinbefore. The mattress of this type has proven to be particularly successful in forming a bed for patients that are bed-ridden or required to spend extended periods : of time in bed in a prone position. A mattress of this general type is herein referred **. to as an inflated cell mattress'. *S * * S * S **

However, a particular problem has arisen in relation to the height of the mattress. The aforementioned mattress has a general height or thickness of about cm. While easily accommodated by a wide range of beds, a mattress of this height requires the use of extended side rails on the bed, to prevent the patient from inadvertently falling out of bed. In this regard, it is a general requirement that the top of side rails fitted to beds must be at least 22 cm from the upper surface of the mattress, in order to adequately safeguard a patient lying in the bed and prevent them from inadvertently falling out of bed. Reference in this regard is made, for example, to MHRA Device Bulletin DB2006 (06) Safe Use of Bed Rails'. In order to meet this requirement, the rails fitted to bed frames generally require extensions to be fitted, in order to increase their height. The use and fitting of such extensions is inconvenient for medical staff tending the patient in the bed and is generally undesirable.

It would therefore be of advantage if a mattress having all the advantages of the aforementioned mattress could be provided, while at the same time reducing the need to use extended side rails on a bed to which the mattress is fitted. In particular, it would be advantageous if such a mattress could be provided that may be accommodated by an existing bed frame without the need to provide any extension to the side rails as provided, while at the same time providing the same level of security and comfort for the patient.

Accordingly, the present invention provides a mattress comprising: a base comprising an expanded foam material; a first layer comprising a first set of transverse cells inflated with gas to a first pressure; a second layer comprising a second set of transverse cells inflated with gas to a second pressure, the second set of cells comprising first and second regions of S...

cells, the cells of the first region of the second set having perforations therein; and *S*S means for supplying gas to the cells; wherein the density of the foam of the base and the pressure of gas within the * cells of the first and second layer are selected such that a patient may be supported :.: * as required and to provide the mattress with an overall thickness of no greater than : 150 mm.

The inventors have surprisingly found that an inflated cell mattress of the aforementioned general kind can be produced that provides all the advantages in terms of therapy and comfort to patients, while also being sufficiently thin as to be accommodated by existing bed frames and have the side rails of the bed sufficiently restrain the patient without the need for extensions to side rails. This, in turn represents a major advantage to healthcare staff and practitioners in tending to the needs of the patient safely and easily.

Further, it has been found that the mattresses of the present invention are more comfortable for patients than existing deep cell mattresses. It can also be difficult for patients to move themselves off of the existing deep cell mattresses. In addition, the cells of the mattress of the present invention are smaller than those of the known mattresses of similar construction. It has been found that the smaller cells, having lower diameters, are more stable and offer an improved support surface for rehabilitation of patients with a variety of conditions.

Finally, the mattresses of the present invention offer a significant reduction in weight, compared with known mattresses of similar configuration.

The mattress of the present invention comprises a base formed from an expanded foam material. Suitable foam materials are well known in the art and are commercially available. Preferred foam materials are polyurethane foams, in particular open-cell polyurethane foams. The density of the foam material of the base layer is selected, together with the pressure of air within the cells of the first and second layers and the dimensions of the cells of the first and second layers, to *.* provide the requisite level of support for the patient, when the mattress is in use.

Preferably, the density of the foam material of the base is in the range of from 20 to kg/rn3, more preferably from 25 to 40 kg/rn3, with a foam density in the range of from 30 to 35 kg/rn3 being especially preferred.

: * The thickness of the base is selected according to the density of the foam ** material, in turn selected as noted hereinbefore. The thickness of the foam base is **.: preferably in the range of from 2 to 6 cm, more preferably from 2.5 to 5 cm, still more preferably from 2.5 to 4 cm. A base thickness of about 3 cm is particularly suitable for the mattress of the present invention.

A particularly preferred base layer comprises a polyurethane foam having a density of between 32 and 32.5 kg/rn3 and a thickness of 3 cm.

The mattress further comprises a first layer of inflated cells. The first layer of cells extends across the upper surface of the base layer, with the mattress in use.

The cells in the first layer extend transversely, that is laterally across the mattress, substantially perpendicular to the longitudinal axis of the mattress. The cells may have any suitable shape and form. Preferably, the cells are generally cylindrical.

The cells are formed with a cell wall of flexible, gas-impermeable material. Suitable materials are known in the art and are commercially available. Preferred materials for forming the cell wall include known polymers, in particular polyurethane.

The cells of the first layer are inflated to a first pressure with gas. The cells are preferably maintained at a substantially constant gas pressure during use.

Accordingly, the cells in the first layer may be referred to as static cells'. Preferably, the gas within the cells of the first layer is kept at a constant, predetermined pressure. It is preferred that all the cells of the first layer are filled with gas to substantially the same pressure. As already noted, the pressure of gas within the cells of the first layer is selected, together with the density of the foam material of the base layer and the gas pressure within the cells of the second layer, to provide the required level of support to the patient, when the mattress is in use. Preferably, the pressure of gas within the cells of the first layer is in the range of from 20 to 80 mmHg, more preferably from 25 to 70 mmHg, still more preferably from 30 to 60 mmHg. A minimum gas pressure of 25 mmHg, more preferably 30 mmHg, has been * found to be suitable for providing the required level of support to a patient lying on the mattress for a prolonged period of time. * S S

*. .30 The pressure of gas within the cells of the first layer may be varied, according * to the size and weight of the patient using the mattress. It is preferred that all cells in the first layer are maintained at substantially the same gas pressure. However, . .: should it be required, the first layer may be divided into two or more regions, each region comprising one or more cells, the gas pressure within the cells varying from region to region. It is particularly preferred that the gas pressure within the cells of the first layer is constant.

The dimensions of the cells of the first layer will be determined by the pressure of gas within the cells, the density of the foam of the base layer and its thickness, and the gas pressure and dimensions of the cells of the second layer. The cells of the first layer extend laterally across the base. Preferably, the cells of the first layer have the relevant dimension (for example a diameter in the case of the preferred cylindrical cells) to provide the first layer with a thickness of from 3 to 6 cm, more preferably from 3.5 to 5.5 cm, still more preferably from 4 to 5 cm. A preferred thickness of the first layer of cells is about 4.75 cm.

As noted above, the cells are prepared from a suitable gas-impermeable material. The thickness of the cell wall is selected according to the material of construction to provide sufficient strength to the cell wall to resist the internal gas pressure and retain the shape and form of the cell when the mattress is in use. A typical thickness of the cell wall is from 0.2 to 1.0 mm, more preferably from 0.25 to 0.6 mm, still more preferably from 0.3 to 0.5 mm. A wall thickness of about 0.35 mm has been found particularly suitable for cylindrical cells formed from polyurethane and having a diameter of about 4.75 cm.

The cells of the first layer are preferably of a uniform shape and size.

However, if desired, the first layer may be provided with cells of different shapes and sizes, so as to accommodate the needs of the patient. Preferably, each cell of the first layer extends laterally across the entire width of the base and the mattress.

I * p. S. S

As noted, the cells of the first layer extend transversely across the base of the mattress. Preferably, the cells in the first layer are arranged so as to provide a 30 continuous layer, that is adjacent cells in the layer are touching or abut each other.

The number of cells in the first layer will be determined by the overall length of the mattress and the dimensions of the cells in the layer. Preferably, the individual cells and the mattress are sized to provide the first layer with from 20 to 40 cells, more preferably from 25 to 35 cells. It has been found that providing the first layer with from 28 to 32 cells is a particularly effective arrangement.

Any suitable gas may be used to inflate the cells of the first layer. Air is a most suitable and convenient gas. The mattress may be provided with means to provide gas to the cells of the first layer, in order to provide the required pressure of gas and/or to change the gas pressure within the cells, as required. Suitable means, such as pumps, for providing the gas are known in the art and are commercially available.

The mattress of the present invention further comprises a second layer of inflated cells. The second layer of cells extends across the upper surface of the first layer of cells, with the mattress in use. The cells in the second layer extend parallel to the cells in the first layer and transversely, that is laterally across the mattress, substantially perpendicular to the longitudinal axis of the mattress. The cells may have any suitable shape and form. Preferably, the cells are generally cylindrical.

The cells of the second layer are inflated to a second pressure with gas. The cells in the second layer are divided into a first region and a second region. The cells in the first region are provided with perforations in the cell wall, such that gas may leave the cell. Gas is provided to the cell from the gas supply means to replace the gas leaving through the perforated cell wall, thereby maintaining the gas pressure within the cell. Such perforated cells are known in the art. The cells in the second region are preferably maintained at a substantially constant gas pressure during use, that is the cells of the second region are static cells. It is preferred that all the cells of sacs the second region are filled with gas to substantially the same pressure. a... a * a. S

The pressure of gas within the cells of the first region is selected, together with the density of the foam material of the base layer and the gas pressure within the cells of the first layer, to provide the required level of support to the patient, when the mattress is in use. Preferably, the pressure of gas within the cells of the first region is in the range of from 20 to 80 mmHg, more preferably from 25 to 70 mmHg, still more preferably from 30 to 60 mmHg. A minimum gas pressure of 25 mmHg, more preferably 30 mmHg, has been found to be suitable for providing the required level of support to a patient lying on the mattress for a prolonged period of time.

The pressure of gas within the cells of the first region of the second layer may be varied, according to the size and weight of the patient using the mattress. It is preferred that all cells in the first region are maintained at substantially the same gas pressure. However, should it be required, the first region may be divided into two or more portions, each portion comprising one or more cells, the gas pressure within the cells varying from portion to portion. In use, gas is supplied under pressure to each cell in the first region, with gas being allowed to escape from the cell through the perforations at a rate determined by the size of the perforation and the gas pressure.

Such an operation is known in the art.

The second layer further comprises a second region containing cells. The cells of the second region are static cells, that is the cell wall is not perforated and the pressure of gas within the cells of the second region is maintained constant.

The pressure of gas within the cells of the second region is selected, together with the density of the foam material of the base layer and the gas pressure within the cells of the first layer, to provide the required level of support to the patient, when the mattress is in use. Preferably, the pressure of gas within the cells of the second region is in the range of from 20 to 80 mmHg, more preferably from 25 to 70 mmHg, still more preferably from 30 to 60 mmHg. A minimum gas pressure of 25 mmHg, more preferably 30 mmHg, has been found to be suitable for providing the required level of support to a patient lying on the mattress fora prolonged period of time. SIS. * * S...

The pressure of gas within the cells of the second region of the second layer *:::o may be varied, according to the size and weight of the patient using the mattress. It is preferred that all cells in the first region are maintained at substantially the same gas pressure. However, should it be required, the second region may be divided into two or more portions, each portion comprising one or more cells, the gas pressure within the cells varying from portion to portion.

In one preferred embodiment, the pressure of gas in some or all of the cells of the second layer is varied over time. In particular, it is preferred that the cells are repeatedly inflated and deflated over time. Any suitable pattern of inflation and deflation may be employed, while ensuring that the subject lying on the mattress has sufficient support. One particularly preferred arrangement is to divide the cells of the second layer into two groups, X and Y, with the cells from group X alternating with cells from group Y in the second layer. A particularly preferred alternating pattern of cells in groups X and Y is XYXYXY. The cells in group X are inflated and deflated over time, according to a predetermined regime, with the cells in group Y being inflated and deflated over time using the equal but opposite regime. Preferably, all the cells in group X are inflated and deflated at the same time according to the same regime. In one preferred regime, the cells in group X are deflated and held in the deflated state for a period of time, in particular from 1 to 5 minutes, more preferably from 2 to 4 minutes, especially about 3 minutes. During this inflation/deflation of cells in group X, the cells in group Y are held at constant pressure. Thereafter the cells in group X are inflated and all cells in the second layer held inflated for a period of time, in particular from 0.5 to 5 minutes, more preferably from 0.5 to 3 minutes, especially about 1 minute. The inflation and deflation of the cells depends upon the volume of the cell and the pressure of the gas supply. Typically, inflation and deflation times are from 15 to 60 seconds, more preferably from 20 to 40 seconds, especially about seconds. While keeping the cells in group X at a constant pressure, the cells in group Y are then inflated and deflated according to the same regime as those for group X. The regime is then repeated. This alternating pattern of inflation and deflation has been found to assist patients, in particular avoiding the occurrence of conditions, such as sores and the like, that arise from prolonged periods of time in bed. All cells in the second layer may be subjected to the inflation/deflation regime described above, that is the groups of cells X and Y may extend the entire length of S...

the mattress. In one preferred embodiment, the cells at each end of the mattress, for 0 example from 2 to 7, more preferably 5 cells at each end, are kept constantly inflated and are not subjected to the inflation/deflation regime.

The dimensions of the cells of the second layer will be determined by the ** pressure of gas within the cells, the density of the foam of the base layer and its thickness, and the gas pressure and dimensions of the cells of the first layer. The cells of the second layer extend laterally across the base. Preferably, the cells of the second layer have the relevant dimension (for example a diameter in the case of the preferred cylindrical cells) to provide the second layer with a thickness of from 3 to 6 cm, more preferably from 3.5 to 5.5 cm, still more preferably from 4 to 5 cm. A preferred thickness of the second layer of cells is about 4.75 cm.

As noted above, the cells of the second layer are prepared from a suitable gas-impermeable material. The thickness of the cell wall is selected according to the material of construction to provide sufficient strength to the cell wall to resist the internal gas pressure and retain the shape and form of the cell when the mattress is in use. A typical thickness of the cell wall is from 0.2 to 1.0 mm, more preferably from 0.25 to 0.6 mm, still more preferably from 0.3 to 0.5 mm. A wall thickness of about 0.35 mm has been found particularly suitable for cylindrical cells formed from polyurethane and having a diameter of about 4.75 mm.

The cells of the second layer are preferably of a uniform shape and size.

However, if desired, the second layer may be provided with cells of different shapes and sizes, so as to accommodate the needs of the patient. Preferably, each cell of the second layer extends laterally across the entire width of the base and the mattress.

The number of cells in the second layer will be determined by the overall length of the mattress and the dimensions of the cells in the layer. Preferably, the individual cells and the mattress are sized to provide the second layer with from 20 to cells, more preferably from 25 to 35 cells. It has been found that providing the second layer with from 28 to 32 cells is a particularly effective arrangement. * *

As noted, the cells of the second layer extend transversely across the base of the mattress. Preferably, the cells in the second layer are arranged so as to provide a continuous layer, that is adjacent cells in the layer are touching or abut each other. * *. * * * *. I I. I * * S * S.

The cells of the second layer are preferably in direct contact with the cells of the first layer. The first and second layers preferably contain the same total number of cells, with each cell in the first layer having a corresponding cell in the second layer overlying it.

Any suitable gas may be used to inflate the cells of the first layer. Air is a most suitable and convenient gas. The mattress is provided with means to provide gas to the cells of the second layer, in order to replenish the gas leaving the cells of the first region through the perforations in the walls of the cells, to provide the required pressure of gas and/or to change the gas pressure within the cells, as required. Suitable means, such as pumps, for providing the gas are known in the art and are commercially available.

The second layer may be provided with a single first region and a single second region. More preferably, the second layer is provided with a first region at each end of the mattress, with a second region of cells disposed between the two first regions. In an alternative, preferred embodiment, the second layer of the mattress is provided with a plurality of both first regions and second regions, arranged in an alternating pattern along the mattress, with a first region being disposed at each end of the mattress. For example, in a mattress comprising a second layer having a total of 29 cells therein, the mattress comprises a first region at each end having 5 cells therein, a central first region having 9 cells therein and two second regions each having 5 cells disposed therebetween.

To maintain the shape and form of the foam material of the base, the mattress is preferably provided with a covering layer extending over the surface of the base. Suitable materials for forming the covering layer are known in the art and are commercially available. A preferred material for forming the covering layer is *.S.

polyvinylchioride. * * ** *

The mattress is preferably provided with a cover extending over the outer surfaces of the mattress, including the sides, ends and the exposed surfaces of the base and the second layer of cells. Suitable materials for forming the cover are ** S * I* * S. known in the art and are commercially available. A preferred material for the cover is a combination of polyurethane and polyester (known commercially as multispandex).

In use, the mattress of the present invention is provided on a suitable bed frame. Such bed frames are very well known in the art and generally conform to standard prescribed dimensions of length and width. The mattress is oriented with the base lowermost and the second layer of cells uppermost. The patient thus lies on the mattress with their weight supported first by the cells of the second layer, then the cells of the first layer and the base layer. As noted, the pressure of gas within the cells of the first layer is generally kept constant, thus allowing the base and first layer to provide a constant support to the patient. The gas pressure within the cells of the second layer may be varied, for example by reducing or stopping the supply of gas to the cells of the first region and allowing them to partially or wholly deflate. In this way, the contours of the second layer may be varied, in turn changing the points of contact and the pressure points between the mattress and the patient, thus reducing or preventing the development of conditions such as sores and the like.

Pressure mapping of the mattress of the present invention has shown that it provides a very high degree of support for a patient while being of sufficiently low thickness to be accommodated by existing bed frames without the need for side bar extensions and the like.

Embodiments of the present invention will now be described, by way of example only, having reference to the accompanying drawings, in which: :. Figure lisa plan view of a mattress according to one embodiment of the ::..: present invention; and *S..

Figure 2 is a side view of the mattress of Figure 1 along the line II -II.

Turning to Figure 1, there is a shown one embodiment of a mattress of the *:*. present invention, generally indicated as 2. The mattress 2 comprises a base 4 comprising a layer 6 of PVC, supporting a layer 8 of polyurethane foam. The foam has a density of 32.5 kg/rn3 and a thickness of 3 cm, providing the base 4 with a total thickness of about 3.5 cm.

The mattress 2 is provided with end retaining members 10 extending vertically from each end of the base 4.

An assembly of air-filled cells 20 is provided on the base 4 between the end retaining members 10. The assembly of cells 20 comprises a first layer of cells 22 and a second layer of cells 24, the second layer disposed on the first layer, as shown in Figure 2.

The first layer 22 consists of 29 cylindrical cells 26 extending laterally across the mattress 2. The cells 26 of the first layer 22 are static cells, having dimensions of 4.75 cm diameter and 88 cm long. The cells 26 are inflated with air to a pressure of to 60 mmHg.

The second layer 24 consists of 29 cylindrical cells 28 extending laterally across the mattress 2 and overlying the cells 26 of the second layer. The cells 28 of the second layer 24 have dimensions of 4.75 cm diameter and 88 cm long. The cells 28 are inflated with air to a pressure of 30 to 60 mmHg. The cells 28 of the second layer 24 are arranged into five regions A to E along the length of the mattress 2. The layer 24 comprises a mixture of static cells and ventilated cells. The ventilated cells are provided with laser-formed perforations in their walls, to allow a constant flow of air from within the cell. The static and ventilated cells are distributed throughout the regions of the layer 24 as follows: 0*.I * S S ** S *S.. * S *S.*

REGION TYPE OF CELLS NO. OF CELLS A Ventilated 5 B Static 5 C Ventilated 9 S. * D Static 5 * E Ventilated I Air is provided to the cells of the mattress by a pump 30 of conventional design.

The mattress 2 is provided with a cover 34 (partially shown in Figure 2) extending thereover, formed from a mixture of polyurethane and multispandex.

The density of the foam of the base 4 and the size, number and arrangement of cells 26, 28, and air pressure within the cells have been selected in order to allow the mattress to provide the required support for a patient, while keeping the overall thickness of the mattress to 13 cm. This allows the mattress to be safely accommodated by existing beds with side frames, without requiring extensions to the side frames to be employed. * * * S. * * S.. * * *S5� * S. *. * * ** * . . *. . S. * * . *.

Claims

CLAIMS1. A mattress comprising: a base comprising an expanded foam material; a first layer comprising a first set of transverse cells inflated with gas to a first pressure; a second layer comprising a second set of transverse cells inflated with gas to a second pressure, the second set of cells comprising first and second regions of cells, the cells of the first region of the second set having perforations therein; and means for supplying gas to the cells; wherein the density of the foam of the base and the pressure of gas within the cells of the first and second layer are selected such that a patient may be supported as required and to provide the mattress with an overall thickness of no greater than 150 mm.
2. The mattress according to claim 1, wherein the density of the foam material of the base is in the range of from 20 to 50 kg/rn3.
3. The mattress according to claim 2, wherein the density of the foam material of the base is in the range of from 25 to 40 kg/rn3.
4. The mattress according to claim 3, wherein the density of the foam material of the base is in the range of from 30 to 35 kg/rn3.
5. The mattress according to any preceding claim, wherein the thickness of the foam base is in the range of from 2 to 6cm. * *** * p **p.
6. The mattress according to claim 5, wherein the thickness of the foam base is in the range of from 2.5 to 5 cm.
7. The mattress according to claim 6, wherein the thickness of the foam base is in the range of from 2.5 to 4 cm. ** * * p S * S.
8. The mattress according to any preceding claim, wherein the cells of the first layer are static cells.
9. The mattress according to any preceding claim, wherein the pressure of gas within the cells of the first layer is in the range of from 20 to 80 mm Hg.
10. The mattress according to claim 9, wherein the pressure of gas within the cells of the first layer is in the range of from 25 to 70 mm Hg.
11. The mattress according to claim 10, wherein the pressure of gas within the cells of the first layer is in the range of from 30 to 60 rnmHg.
12. The mattress according to any preceding claim, wherein the cells in the first layer are sized to provide the first layer with a thickness of from 3 to 6 cm.
13. The mattress according to claim 12, wherein the cells in the first layer are sized to provided the first layer with a thickness of from 3.5 to 5.5 cm.
14. The mattress according to claim 13, wherein the cells in the first layer are sized to provided the first layer with a thickness of 4 to 5 cm.
15. The mattress according to any preceding claim, wherein the first layer comprises from 20 to 40 cells.
16. The mattress according to claim 15, wherein the first layer comprises from 25 to 35 cells. * * *
17. The mattress according to claim 16, wherein the first layer comprises from **** 28 to 32 cells. *** * * ** *
18. The mattress according to any preceding claim, wherein the second layer comprises a first region comprising ventilated cells and a second region comprising L:' static cells. *e * * S * S.
19. The mattress according to claim 18, wherein the second layer comprises a plurality of first regions and/or second regions, each first region being adjacent at least one second region.
20. The mattress according to claim 19, wherein the second layer comprises three first regions and two second regions arranged in an alternating pattern, with each second region being adjacent two first regions.
21. The mattress according to any preceding claim, wherein the pressure of gas within the cells of the second layer is in the range of from 20 to 80 mm Hg.
22. The mattress according to claim 21, wherein the pressure of gas within the cells of the second layer is in the range of from 25 to 70 mmHg.
23. The mattress according to claim 22, wherein the pressure of gas within the cells of the second layer is in the range of from 30 to 60 mmHg.
24. The mattress according to any preceding claim, wherein at least some of the cells in the second layer are divided into a first group X and a second group Y, the cells in groups X and Y being subjected to a regime of repeated inflation and deflation.
25. The mattress according to claim 24, wherein the cells in groups X and Y are arranged in an alternating pattern in the second layer.
26. The mattress according to either of claims 24 and 25, wherein the cells in the region adjacent one or both ends of the mattress are maintained at a constant pressure. * S S...
27. The mattress according to any preceding claim, wherein the cells in the second layer are sized to provide the second layer with a thickness of from 3 to 6 cm.

L:''
28. The mattress according to claim 27, wherein the cells in the second layer are *:*. sized to provided the second layer with a thickness of from 3.5 to 5.5 cm.
29. The mattress according to claim 28, wherein the cells in the second layer are sized to provided the second layer with a thickness of 4 to 5 cm.
30. The mattress according to any preceding claim, wherein the second layer comprises from 20 to 40 cells.
31. The mattress according to claim 30, wherein the second layer comprises from to 35 cells.
32. The mattress according to claim 31, wherein the second layer comprises from 28 to 32 cells.
33. The mattress according to any preceding claim, having a total thickness of lessthan 140 mm.
34. The mattress according to claim 33, having a total thickness of about 130 mm.
35. A mattress substantially as hereinbefore described, having reference to the accompanying figures. * * * ** * I-.. * * **** * * * * * ** * ( 0 *.. 0. *I SO