WO2015132560A1

WO2015132560A1 - Heel protection mattress

Info

Publication number: WO2015132560A1
Application number: PCT/GB2015/050503
Authority: WO
Inventors: Michael Hutson
Original assignee: Rober Limited
Priority date: 2014-03-03
Filing date: 2015-02-20
Publication date: 2015-09-11
Also published as: EP3113745B1; GB201403707D0; GB2523754A; EP3113745A1; GB2523754B; DK3113745T3; ES2750076T3

Abstract

An inflatable mattress configured to reduce the incidence of bed sores by providing intermittent pressure relief to a patient sleeping on it having adaptations to improve the pressure relief provided around the vulnerable heel area. The adaptations are active deflation of the cells in the heel region, and passive deflation in the body region.

Description

Heel Protection Mattress

[0001] This invention relates to an alternating pressure mattress for preventing pressure ulcers, particularly around the heel region of a patient's limb.

BACKGROUND

[0002] Bed sores, or pressure ulcers, are likely to occur when a patient is bed ridden for a long period of time, causing parts of the body that are in contact with the mattress to be constantly subjected to pressure. This results in obstructed blood flow, which can damage the affected tissue and ultimately leads to bed sores. The reduced blood flow is especially severe in areas of skin near a protruding bone such as the heel or the hip, and accordingly bed sores are more likely to develop at these locations. Furthermore, the unobstructed blood supply to the heel is relatively poor compared to the rest of the body. The heel is therefore especially prone to bed sores. Furthermore, for the same reasons of poor blood supply in these regions, bedsores on the heel and similar areas are slow to heal.

[0003] In hospitals, patients who are deemed to be at risk of developing a bed sore are generally provided with an alternating pressure mattress having a plurality of inflatable cells which are cyclically inflated and deflated.

[0004] When cells are deflated the tissue that was supported by the deflated cells is provided with pressure relief. However, the degree of pressure relief provided depends on the extent to which the cells are deflated. For a relatively low risk patient a mattress may be provided in which the cells simply have a valve opened to allow the pressure therein to gradually reduce towards atmospheric pressure. In this event the pressure will not actually reach atmospheric pressure because the open valve still provides a resistance to the air escaping, so air is only removed by the pressure caused by the patient's weight, which is largely supported by the inflated cells once the pressure in the deflated cells has reduced. Therefore, there is a small residual pressure between the patient and the deflated cells. It is undesirable to provide a valve that would allow the pressure in the cell to reduce rapidly to atmospheric pressure because this would "jerk" the patient. Consequently, using a small valve that allows controlled deflation means that deflating cells do not reach atmospheric pressure in the time available. Such a small valve therefore does not provide complete pressure relief.

[0005] For patients who face a higher risk of developing a bed sore a mattress may be provided which actively pumps the air out of the deflated cells, ensuring that no residual pressure is applied by the deflated cells. Completely evacuating the air out of the cells makes the mattress more effective in preventing bed sores. By using active pumping a small valve can be used so that initial evacuation is not sudden but, by virtue of the pump, the rate of evacuation remains substantially the same so that complete evacuation does occur, over a relatively short period of time, without the initial sudden rush that would otherwise potentially disturb a patient sleeping on the mattress.

[0006] If the air is actively evacuated from the deflated cells it is possible that part of the patient will come into contact with the bottom surface of the mattress. Potentially, this will be uncomfortable, and will cause pressure to be applied to the area in contact with the lower surface of the mattress. One option to avoid this disadvantage is to increase the height of the cells in mattresses providing active evacuation, by making the cells generally elliptical in cross section, with the long axis arranged vertically when the mattress is in use.

[0007] Active evacuation of air from mattress cells is effective in providing total pressure relief. However, it also increases the cost of the mattress, as a more powerful pump has to be provided to fill the larger cells, and the pump has to both fill and evacuate the cells. Furthermore, if the patient faces a relatively low risk of developing a pressure ulcer it may be advantageous to provide a residual pressure between the patient and the deflated cells, as this reduces the pressure between the patient and the inflated cells, which may be more comfortable for the patient. Mattresses providing active evacuation are therefore typically reserved for patients who face an especially high risk of developing a bed sore.

[0008] The present invention aims to provide a low-cost mattress that provides complete pressure relief to areas of tissue that face a particularly high risk of developing a bed sore. BRIEF SUM MARY OF THE DISCLOSURE

[0009] According to an embodiment of the present invention there is provided an alternating pressure mattress system comprising a first compressor and a mattress having a plurality of cells lying transversely with respect to a length of the mattress and disposed in side by side relationship along the length of the mattress between first and second ends thereof, the cells divided into at least four groups of cells, a first and second of said groups of cells being located in a first section of the mattress and a third and fourth of said groups of cells being located in a second section of the mattress, which groups of cells are arranged to be cyclically inflated and deflated, wherein:

the air in the cells in said first and second groups of cells is actively evacuated when said cells are deflated;

the air in the cells in said third and fourth groups of cells is allowed to vent to atmosphere when said cells are deflated, no active evacuation being provided; and

said active evacuation comprises pumping the air out of the cells using a second compressor. [0010] In an embodiment said second compressor may be the same as said first compressor. In another embodiment the mattress may further comprise longitudinal edge cells extending along longitudinal edges of the mattress.

[0011] In a further embodiment said first section of said mattress may be located at said first end of said mattress, whereby an average patient on the mattress may be provided with periodic total pressure relief of their heel region when lying on said first end of said mattress.

[0012] In an embodiment the mattress may further comprise at least one additional cell near said second end of the mattress that is configured to remain inflated throughout said predetermined cycle, whereby a patient on the mattress may be provided with constant support of their head when lying on said at least one additional cell.

[0013] In an embodiment the system may further comprise a quick release mechanism configured to permit rapid deflation of all of the cells.

[0014] In another embodiment the quick release mechanism may be configured to fully deflate the cells within 30 seconds of being activated, preferably within 15 seconds of being activated.

[0015] In a further embodiment the cells may be divided into two groups which are cyclically inflated and deflated.

[0016] In a different embodiment the invention relates to a mattress for a system as described above, the mattress comprising said plurality of groups of cells, wherein the cells of each group comprise connections and tubing associated with said connections which are separate from the connections and tubing associated with said connections of the cells of the other groups.

[0017] A different embodiment of the invention relates to a method for the prevention or treatment of bed sores in a patient, said method comprising the steps of:

providing a mattress having a plurality of cells divided into at least two groups of cells which may be inflated or deflated;

disposing the patient on the mattress with their heels located at a first end of the mattress; and

cyclically inflating and deflating said groups of cells,

wherein:

the cells in a first section of the mattress located near said first end of the mattress are actively evacuated when said cells are deflated, said first section including cells from each of said two groups of cells; the cells in a second section of the mattress are vented to atmosphere when said cells are deflated, no active evacuation being provided, said second section including cells from each of said two groups of cells; and

said active evacuation comprises pumping the air out of the cells using a compressor.

[0018] A different embodiment of the invention relates to a pump unit for an alternating pressure mattress comprising:

first and second compressors;

first, second, third and fourth connectors;

a plurality of valves configured to control the flow of air to and from said first and second compressors and said first, second, third and fourth connectors; and a control unit configured to control said valves and said compressor,

wherein:

said control unit is configured to control said valves and said compressors to cyclically inflate and deflate mattress cells attached to said connectors;

said cells attached to said first and second connectors are arranged to be deflated by active evacuation of the air from said cells using said second compressor; and said cells attached to said third and fourth connectors are arranged to be deflated by allowance of the air in the cells to vent to atmosphere, no active evacuation being arranged.

[0019] In a further embodiment said second compressor may be the same as said first compressor.

[0020] In another embodiment the control unit may be configured to cyclically: deflate mattress cells attached to said first and third connectors; inflate mattress cells attached to said first and third connectors; deflate mattress cells attached to said second and fourth connectors; and inflate mattress cells attached to said second and fourth connectors.

[0021] In a further embodiment the pump unit may further comprise a fifth connector, wherein said control unit is configured to maintain cells attached to said fifth connector constantly inflated whilst cyclically inflating and deflating the cells attached to said first, second, third and fourth connectors.

[0022] In another embodiment the pump unit may further comprise a pressure sensor disposed between said first or second compressor and said connectors.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Embodiments of the invention are further described hereinafter with reference to the accompanying drawings, in which: Figure 1 is a prior art alternating pressure mattress for preventing bed sores;

Figure 2 shows a graph of the pressure within a cell against time for different methods of deflation;

Figure 3 shows a cross section of an alternating pressure mattress for preventing bed sores in an embodiment of the present invention;

Figure 4 shows an exemplary air circuit diagram for an alternating pressure mattress in an embodiment of the present invention; and

Figure 5 shows a pump unit in an embodiment of the present invention.

DETAILED DESCRIPTION

[0024] Figure 1 shows a prior art alternating pressure mattress configured to prevent or treat pressure ulcers by cyclically reducing the pressure applied to different areas of the body of a patient sleeping on the mattress. The mattress comprises a plurality of inflatable cells arranged perpendicular to the longitudinal axis A of the mattress (only eight being shown). The cells are divided into at least two groups of alternately disposed cells, which groups of cells are configured to be cyclically inflated and deflated in a predetermined cycle that ensures that at least one group of cells is inflated at any given time on which the patient is supported. For a typical mattress between 16 and 24 cells will be provided, and the cells will be deflated using either a "two cell cycle" or a "three cell cycle", which means that there are two or three groups respectively of cells. If a two cell cycle is used then the cells may be divided into two groups, with adjacent cells in different groups. Alternatively, a "three cell cycle" may be used, and in that case the cells are divided into three groups, for example a first group comprising cells 2i , 2₄ and 2₇, a second group comprising cells 22, 2δ and 2s and a third group comprising 23 and 2Q. In either case the groups of cells are cyclically inflated and deflated in a cycle that ensures that at least one group of cells is inflated at any given time.

[0025] Although not shown in Figure 1 , prior art mattresses also include at least one compressor for inflating the cells and a controller for selecting which cells are to be inflated or deflated. The controller may be configured to open valves to deflate selected cells at predetermined time intervals, and to actuate the pump and direct the airflow to selected cells to inflate them at predetermined time intervals.

[0026] It is known to provide mattresses similar to the one shown in Figure 1 in which the air in the cells is vented to atmospheric pressure when the cells are deflated. Venting occurs through the natural resilience of the material of the cells. However, it also provides a small residual pressure between the patient and the deflated cells. A representation of the reduction in pressure P against time T for cells that are vented to atmospheric pressure is shown by pressure profile 5 in Figure 2. Pressure initially decreases rapidly from inflated pressure PMAX. However, as the cell deflates the pressure gradient over the valve decreases, causing the rate of deflation to reduce so that the pressure never reaches atmospheric pressure, PATM and complete pressure relief is not provided.

[0027] It would clearly be possible to allow the pressure within a mattress cell to quickly reduce to atmospheric pressure without providing active deflation, simply by providing a valve with such a large flow area that the valve provides little or no resistance to air escaping. However, this is undesirable because the rapid decrease in pressure, as shown be pressure profile 4 in Figure 2 would "jerk" the patient. Consequently, using a small valve that allows controlled deflation means that deflating cells might never reach atmospheric pressure and provide complete pressure relief, as shown by pressure profile 5 in Figure 2.

[0028] It is also known to provide mattresses similar to the one shown in Figure 1 in which the air in the cells is actively pumped out of the cells when they are deflated. This ensures that no residual pressure remains between the deflated cells and the patient. A representation of the change in pressure P against time T for cells that are actively vented to atmospheric pressure is shown by pressure profile 6 in Figure 2. It is to be noted that the initial rate of deflation is slower than that shown in profile 4, so that there is no sudden loss of support for the patient and yet ultimately there is complete pressure relief.

However, because the rate of deflation is substantially constant, complete pressure relief is provided.

[0029] The cells 2 in Figure 1 have a generally circular cross section. This is typically the case for mattresses in which the cells are vented to atmosphere as illustrated by pressure profile 5 when they are deflated. These mattresses represent the lowest cost type of mattress. However, for mattresses in which the air is actively pumped out of the cells as illustrated by pressure profile 6 it is generally necessary to elongate the cells so that they have a generally elliptical cross section, with the major axis of the ellipse arranged so that it is vertical when the mattress is in use. If the air was actively evacuated from a mattress having cells with a generally circular cross section then it is probable that the patient would come into contact with the bottom surface of the mattress between inflated cells.

Potentially, this would be uncomfortable, and wake a sleeping patient when their body contacts the lower surface. Elliptical cells significantly reduce this possibility. However, providing elliptical cells increases the cost of the mattress as the cells are larger and therefore require more material to make. A more powerful pump is also required to fill the cells. [0030] The mattress shown in Figure 1 also includes longitudinally oriented side support cells 3, which help to prevent the patient from accidentally rolling off the mattress. Such side support cells remain continuously inflated when the mattress is in use.

[0031] Figure 3 shows a cross section of an alternating pressure mattress in an embodiment of the present invention. The mattress has cells inflated and deflated in a 2 cell cycle and the structure of the mattress is similar to that shown in Figure 1. However, Figure 3 shows cells 2'2 and 2 deflated to approximately zero pressure, whist cells 2Q, 2S, 2IO and 2i2 all retain some residual pressure. After a predetermined time interval the group of cells that is deflated in Figure 3 will be inflated and the group of cells comprising cells 2Ί , 2'3, 2δ, 2₇, 2g, 2i i and 2 will be deflated. A patient may be disposed on the mattress with their heels located at the first end. In this way the complete deflation of the cells near a first end of the mattress (i.e. cells 2Ί , 2'2, 2'z and 2 ) advantageously provides total pressure relief to the heel of a patient sleeping on the mattress.

[0032] Because cells 2s to 2 are not completely deflated, they provide some residual support to a patient who is unlikely to contact the under surface. Nevertheless, they still benefit from changing pressure on their body so that the risks of bed sores and pressure ulcers developing, in these less-susceptible regions of the body, are still substantially mitigated.

[0033] The timing and phasing of the inflation and deflation of the cells at the first end of the mattress (i.e. cells 2Ί , 2'2, 2'z and 2 ) may be different from the timing and phasing of the inflation and deflation of the other cells (i.e. cells 2s-2i3).

[0034] Some cells at a second end of the mattress (not shown) may be in an additional group that remains constantly inflated when the mattress is in use, thereby providing constant support to the patient's head.

[0035] Figure 4 shows an exemplary air circuit diagram for an alternating pressure mattress configured to implement a 2 cell cycle in an embodiment of the present invention. Air circuit 10 connects groups of cells A, A', B, B' and C to compressor 1 1 via filter/sliencer 12, air pipes or tubing 14 and valves 15. The valves 15 and compressor 1 1 are controlled by a control unit (not shown), which is in communication with pressure sensor 13.

Filter/silencer 12 is provided to damp away any high-frequency pulsations that are introduced by compressor 1 1 that might otherwise cause the patient discomfort.

[0036] Groups of cells A' and B' are disposed at a first end of the mattress where the heels of a patient are likely to rest. Group of cells C is disposed at a second end of the mattress opposite said first end and is configured to be continuously inflated when the mattress is in use. Groups of cells A and B are disposed between said first and second ends. Groups of cells A' and B' may each comprise between one and three cells, preferably two cells, and group of cells C may comprise between 1 and 6 cells, for example 4 cells. The remainder of the cells are in group of cells A or B. Cells preferably alternate between group of cells A (or A') and group of cells B (or B') along the length of the mattress. Referring to Figure 3, group of cells A' may comprise cells 2Ί and 2'3, group of cells B' may comprise cells 2'2 and 2'₄, group of cells A may comprise cells 2s, 2₇, 2g, 2n and 2i3 and group of cells B may comprise cells 2Q, 2S, 2io and 2i2. Group of cells C is not shown in Figure 3. Not all cells A, B, A' or B' are shown in the drawings. Typically, there are sixteen to thirty cells forming a mattress, with each cell being between 5 and 15 cm, preferably about 10 cm, in diameter. Furthermore, the cells disposed at the first end of the mattress (i.e. the cells in groups A' and B') may be of a different size to rest of the cells (i.e. the cells in groups A, B and C).

[0037] Valves 15 are controlled by the control unit to connect or disconnect cells from different air tubes. For example, valve 153 is configured to selectively connect group of cells A' either to air pipe 14, which communicates with the outlet of compressor 1 1 , or air pipe 14', which communicates with the inlet of compressor 1 1 , via valve 15i .

[0038] The control unit is configured to inflate and deflate the cells in a predetermined cycle. For example, the controller may first inflate all of the cells to a predetermined pressure. In this event valve 15i connects the inlet of compressor 1 1 to the ambient atmosphere, valve 152 connects the outlet of compressor 1 1 to air pipe 14, valves 153-156 connect the respective groups of cells to air pipe 14, and compressor 1 1 is activated. Once the cells are inflated to a predetermined pressure, which may be measured by pressure sensor 13, compressor 1 1 is stopped. After a predetermined time delay, either groups of cells A' and A, or B' and B, are deflated. Group of cells A or B is deflated by actuating one of valves 15s or 15e and connecting the group of cells to air pipe 14", which vents to atmospheric pressure. In this event, these cells deflate gradually so as to minimise disturbance of a patient whose body is supported by them, possibly asleep. On the other hand, group of cells A' or B' is deflated by actuating one of valves 153 or 15₄, thereby connecting the group of cells to air pipe 14', which communicates with the inlet of compressor 1 1 via valve 15i . Valve 152 is then actuated to connect the outlet of compressor 1 1 to vent and the compressor is then activated to deflate the group of cells. After a predetermined time delay the deflated groups of cells are re-inflated. Group of cells A' or B' may begin re-inflation before group of cells A or B to reduce pressure variations between the cells. After a further predetermined time delay whichever of groups of cells A' and A, or B' and B, was not previously deflated is deflated and then re-inflated in a similar way, and the cycle is repeated. [0039] The valves and the pump are preferably electrically actuated, and the control unit preferably includes a processor disposed on a printed circuit board that is in electrical communication with the valves and the pump. The control unit is preferably provided with software adapted to control the cyclic inflation and deflation of the cells.

[0040] Although not shown in the drawing, air circuit 10 preferably further comprises a CPR valve or switch which can be activated to quickly deflate all of the cells in the event that the patient needs CPR. Such a valve or switch is preferably in communication with the control unit, and the control unit is preferably configured to stop the cycle of inflating and deflating the cells once the CPR valve or switch is activated. Alternatively the CPR valve or switch may disconnect the cells from the rest of the air circuit, so that it is impossible for the compressor to re-inflate the cells until the CPR valve or switch is deactivated. The cells are preferably deflated within 30 seconds of the CPR valve or switch being activated, more preferably within 15 seconds of the CPR valve or switch being activated.

[0041] In Figure 4 valves 15 are shown at spatially disparate locations. However, it will be understood that this is simply for convenience of illustration, and that the valves may be located anywhere along the length of the air pipes that they connect. Indeed, in one embodiment all of the valves are located in a common manifold which is connected to compressor 1 1. Such a manifold may advantageously be located within a housing, which housing may also contain the compressor 11 and the control unit. A display and controls may be located on the outer surface of the housing. When the mattress is in use as part of a bed the housing may be disposed at an end of the bed. A housing containing

compressor 11 , a common valve manifold and a control unit may comprise a replaceable pump unit, which pump unit may be connectable to a mattress comprising a plurality of cells to control the inflation and deflation of said cells.

[0042] A pump unit may include compressor 11 , filter 12, pressure sensor 13, and at least some of the lengths of air pipes 14, 14', 14" and valves 15 as shown in Figure 4, as well as a control unit for controlling valves 15 and compressor 1 1. The pump unit further comprises at least first, second, third and fourth connectors for connecting to groups of cells A', B', A and B on a separate alternating pressure mattress, and preferably a fifth connector for connecting to group of cells C. Once such connectors are connected to the respective cells of an alternating pressure mattress the mattress may function as described above.

[0043] Figure 5 shows a pump unit 20 in an embodiment of the present invention. Pump unit 20 comprises a housing 26, a control unit 25 and valve manifold 24, first and second compressors 21 , 22, a vent 27 and first, second, third and fourth connectors 23i-23₄, valve manifold 24 being in fluid communication with compressors 21 , 22, vent 27 and first to fourth connectors 23i-23₄. Valve manifold 24 includes at least one valve to independently control fluid connections to each of the first to fourth connectors 23i-23₄. The valves controlling fluid connections to first and second connectors 23i , 232 are configured to connect each of the connectors to one of the first and second compressors 21 , 22, or to disconnect the connector from both compressors and from vent 27. The valves controlling fluid connections to third and fourth connections 233, 23₄ are configured to connect those connections either to the first compressor 21 or vent 27, or to disconnect the connectors from both compressors and from vent 27.

[0044] Control unit 25 is in electrical communication with the first and second

compressors 21 , 22 and valve manifold 24, and is configured to control the connections made by the valves in valve manifold 24 and the operation of compressors 21 ,22. In this way control unit 25 may control the inflation and deflation of mattress cells that are in fluid communication with connectors 23i-23₄.

[0045] Connectors 23i-23₄ may be connected to different groups of cells within a mattress. For example, connectors 23i and 232 may be attached to a first and second groups of cells located in a first section of the mattress where a patient's heels are likely to rest, and connectors 233 and 23₄ may be attached to third and fourth groups of cells located in a second section of the mattress. When connectors 23i-23₄ are connected in this way control unit 25 may provide pressure relief to a patient lying on the mattress by controlling the first and second compressors and the valve manifold to cyclically inflate and deflate all of the groups of cells, with the deflation of the first and second groups of cells being performed by actively pumping the air out of the cells using the second compressor 22 and the deflation of the third and fourth groups of cells being performed by venting the cells to atmospheric pressure via vent 27. In this way the patient is provided with total pressure relief in the heel region, but not around the upper body.

[0046] Although Figure 5 shows control unit 20 having a first compressor 21 for inflation of the cells and a second compressor 22 for deflation of the cells, it will be understood that a single compressor may be used for both inflation and deflation. In this event one or more valves may be included to selectively connect either the inlet or the outlet of the compressor to valve manifold 24. Furthermore, control unit 20 may also include a filter/silencer disposed between the compressors 21 ,22 and the connectors 23i-23₄ to damp away any vibrations or flow pulsations caused by the compressors. A pressure sensor may also be included between the compressors 21 ,22 and the connectors 23i-23₄, which pressure sensor preferably communicates with control unit 25 to determine when cells attached to connectors 23i-23₄ have reached a predetermined pressure, and so inflation is to be stopped.

[0047] In another embodiment the invention relates to a method for the prevention or treatment of bed sores by disposing the patient on an alternating pressure mattress similar to that shown in Figure 3 with the patient's heels located above any of the cells that are configured to be actively deflated (i.e. cells 2ι'-2₄'). Once the patient is disposed on the mattress in this way the cells are cyclically inflated and deflated, with the air in cells 2ι'-2₄' being actively pumped out when the cells are deflated and the air in the other cells being simply vented to atmosphere when the cells are deflated. The cycle in which the cells are inflated and deflated preferably maintains at least half of the cells inflated at any given time, for example by inflating all groups of cells that are deflated before deflating another group of cells.

[0048] Throughout the description and claims of this specification, the words "comprise" and "contain" and variations of them mean "including but not limited to", and they are not intended to (and do not) exclude other moieties, additives, components, integers or steps. Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

[0049] Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. The invention is not restricted to the details of any foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

[0050] The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

Claims

1. An alternating pressure mattress system comprising a first compressor and a mattress having a plurality of cells lying transversely with respect to a length of the mattress and disposed in side by side relationship along the length of the mattress between first and second ends thereof, the cells divided into at least four groups of cells, a first and second of said groups of cells being located in a first section of the mattress and a third and fourth of said groups of cells being located in a second section of the mattress, which groups of cells are arranged to be cyclically inflated and deflated, wherein:

said active evacuation comprises pumping the air out of the cells using a second compressor.

2. The system of claim 1 , wherein said second compressor is the same as said first compressor.

3. The system of claim 1 or 2, further comprising longitudinal edge cells extending along longitudinal edges of the mattress.

4. The system of any preceding claim, wherein said first section of said mattress is located at said first end of said mattress, whereby an average patient on the mattress may be provided with periodic total pressure relief of their heel region when lying on said first end of said mattress.

5. The system of any preceding claim, further comprising at least one additional cell near said second end of the mattress that is configured to remain inflated throughout said predetermined cycle, whereby a patient on the mattress may be provided with constant support of their head when lying on said at least one additional cell.

6. The system of any preceding claim, further comprising a quick release mechanism configured to permit rapid deflation of all of the cells.

7. The system of claim 6, wherein the quick release mechanism is configured to fully deflate the cells within 30 seconds of being activated, preferably within 15 seconds of being activated.

8. The system of any preceding claim, wherein the cells are divided into two groups which are cyclically inflated and deflated.

9. A mattress for a system as claimed in any preceding claim, the mattress

comprising said plurality of groups of cells, wherein the cells of each group comprise connections and tubing associated with said connections which are separate from the connections and tubing associated with said connections of the cells of the other groups.

10. A method for the prevention or treatment of bed sores in a patient, said method comprising the steps of:

a. providing a mattress having a plurality of cells divided into at least two

groups of cells which may be inflated or deflated;

b. disposing the patient on the mattress with their heels located at a first end of the mattress; and

c. cyclically inflating and deflating said groups of cells,

wherein:

the cells in a first section of the mattress located near said first end of the mattress are actively evacuated when said cells are deflated, said first section including cells from each of said two groups of cells;

the cells in a second section of the mattress are vented to atmosphere when said cells are deflated, no active evacuation being provided, said second section including cells from each of said two groups of cells; and

1 1. A pump unit for an alternating pressure mattress comprising:

first and second compressors;

first, second, third and fourth connectors;

a plurality of valves configured to control the flow of air to and from said first and second compressors and said first, second, third and fourth connectors; and

a control unit configured to control said valves and said compressor, wherein:

12. The pump unit of claim 1 1 , wherein said second compressor is the same as said first compressor.

13. The pump unit of claim 11 or claim 12, wherein the control unit is configured to cyclically: deflate mattress cells attached to said first and third connectors; inflate mattress cells attached to said first and third connectors; deflate mattress cells attached to said second and fourth connectors; and inflate mattress cells attached to said second and fourth connectors.

14. The pump unit of any of claims 1 1-13 further comprising a fifth connector, wherein said control unit is configured to maintain cells attached to said fifth connector constantly inflated whilst cyclically inflating and deflating the cells attached to said first, second, third and fourth connectors.

15. The pump unit of any of claims 10-14 further comprising a pressure sensor disposed between said first or second compressor and said connectors.

16. An alternating pressure mattress system substantially as described herein and with reference to Figures 3-5.

17. A pump unit substantially as described herein and with reference to Figures 3-5.

18. A method for the prevention or treatment of bed sores substantially as described herein and with reference to Figures 3-5.