The present invention relates to a pressure controller, in particular, a pressure controller for controlling the fluid pressure in an alternating pressure pad. In most cases the fluid in an alternating pressure pad is air.

Alternating pressure pads are well known for the prevention and management of decubitus ulcers in bedridden patients. The formation of decubitus ulcers, commonly known as bedsores, results from, amongst other things, the pressure applied to certain portions of the skin of a bedridden patient. In addition, it is well known that should the lower reflex arc be broken by, for instance, lesion of the spinal cord or of nerve roots then decubitus ulcers of unusual severity and rapidity of onset are likely to develop.

Alternating pressure pads generally comprise two sets of alternately inflatable cells: the duration of the inflation and deflation cycles may last from under two minutes for a gentle massaging effect to over twenty minutes. Huntleigh Technology pic manufacture and supply such an alternating pressure pad system.

A high air pressure in the pads may be needed to support the bony protuberances of a patient and to ensure that the patient is lifted sufficiently away from deflated cells of the pad so that adequate pressure relief is provided. A low air pressure, however, is desirable since it provides a pad which is softer and more comfortable. Optimal pressure

support therefore not only varies from patient to patient but also during a given inflation cycle of the pad since the pressure supporting points will change during a cycle. The required optimal support pressure will vary even more as a patient changes from a supine to a sitting position.

It is known to provide a manually adjustable pressure controller to set an optimal pad support pressure. This may be a regulator for the compressor supplying air to the alternating pressure pad. It is also known to provide an automatic pressure controller comprising a convoluted compressible tube placed under the pad. In such a system a small amount of air is diverted through the tube, the passage of air being detected by a pilot valve. When the support pressure in the pad is so inadequate that the pressure exerted by a patient causes the tube to be compressed shut, the pilot valve actuates a throttle which diverts a fixed proportion of air, such as one third, from the compressor to the pad thereby to increase the support pressure. When the tube is not closed, the fixed proportion of air is vented to the air via a relief valve. Such a system, however, is complex, costly and inefficient.

W089/08438(PCT/GB89/00232) in the name Of Huntleigh Technology pic describes a pressure controller which has a means which is sensitive to fluid pressure which is adapted to open a valve when the predetermined pressure in an alternating pressure pad is reached. This pressure controller also comprises a sensor pad which is compressible in dependence upon a patient's weight distribution on the alternating pressure pad. If the patient is not suitably supported, the sensor pad will reduce the

escape of fluid from the valve thereby ensuring that more fluid is supplied to the alternating pressure pad until the patient is supported as required.

This arrangement necessitated the use of four connecting tubes between the pump and the mattress and the use of a suitable means for sensing fluid pressure. The applicants, therefore, sought to develop a pressure controller which achieved the same result with a simpler arrangement.

Accordingly, the present invention provides a pressure controller for controlling the pressure in an alternating pressure pad of alternately inflatable sets of cells, comprising an air supply line to each set of cells, a pump arrangement to inflate each set of cells alternately via the air supply lines, and a sensor, the air supply lines being further connected for air to flow through the sensor to exhaust, the sensor being arranged when located beneath the pad to reduce air flow to exhaust from each of the supply lines during inflation of the corresponding sets of cells if the pad is insufficiently inflated to support a patient thereon.

Preferably, the sensor comprises respective separate air flow reducing passages for air from each of the supply lines.

Preferably, the air supply lines are connected together via non-return valves to said sensor having a single air flow reducing passage.

Preferably, the sensor is provided with a relief valve to the atmosphere which opens at the predetermined minimum pressure to which the pad is

required to inflate.

Preferably, the pressure controller further comprises a rotary valve connected to the pump arrangement having an inlet and two outlets, each outlet being connected to an air supply line, the rotary valve connecting each set of cells alternately.

Preferably, the rotary valve can be stopped in a position such that each set of cells is inflated simultaneously as a static pressure pad.

In a further aspect, the present invention provides a pressure controller for controlling the pressure in a pressure pad comprising one or more air supply lines to the pad, a pump arrangement to inflate the pad via the supply line(s) and a sensor, the air supply line(s) being further connected for air to flow through the sensor to exhaust, the sensor being arranged when located beneath the pad to reduce air flow to exhaust from each supply line during inflation of the pad if the pad is insufficiently inflated to support a patient thereon.

A preferred embodiment of the present invention will now be described in detail, by way of example only, with reference to the accompanying drawing which is a schematic representation of a pressure controller in an alternating pressure pad system, the system further comprising a compressor supplying air to the pad via a rotary valve.

An alternating pressure pad 1 is shown comprising a first set 2 and a second set 3 of alternately inflatable cells. Both sets of cells are supplied with air from a compressor 4 via a rotary

valve 5. A pair of supply lines 6 and 7 lead from the rotary valve 5 to the pad 1 and connect on leaving the other end of the pad 1 to form a single outlet line 8. The supply lines 6 and 7 are provided with non-return valves 9 and 10 respectively. The outlet line 8 is connected to a sensor pad 11 which is located under a patient's mattress. The sensor pad comprises a single compressible tube 12 arranged in a convoluted path. Air passing through the sensor pad 11 is "blocked" by a relief valve 13 pre-set to a predetermined pressure which sets the minimum pressure to which the cells 2 and 3 inflate. The predetermined pressure is dependent upon the dimensions of the cells, i.e in general, the smaller the cells the higher the value and the larger the cells the lower the value.

In use, the compressor 4 delivers air to the pad via rotary valve 5 so that each set of cells 2 and 3 is alternately inflated and deflated. The inflation/deflation cycle may repeat over periods varying from two minutes to over twenty minutes. The rotary valve 5 operates so that during inflation of the set of cells 2, air from the set of cells 3, in addition to air from the compressor 4 passes into set of cells 2. This is the "cross-over" point. Further, when, or preferably before, the pressure difference of the air in set of cells 3 over the air from the compressor 4 becomes negligible, the air from set of cells 3 is prevented from passing into set of cells 2. Similarly, during inflation of the other set of cells 3, the air from set of cells 2 is allowed to pass into set of cells 3 for an initial period.

The rotary valve 5 includes a stator 14 having

an inlet 15 and outlets 16a and 16b and a rotor 17 which is motor driven. The inlet 15 of the stator is connected to compressor 4 and the outlets 16a and 16b are connected to sets of cells 2 and 3 respectively. The rotor 17 is provided with a vent 18 and an inlet port 19. During one revolution of the rotor 17 within the stator 14 first one set of cells and then the other is connected to the compressor 4. However, there is a point in the cycle when both sets of cells 2 and 3 are connected to each other via the rotor

17. This is the cross-over point and occurs when the rotor 17 is positioned with its inlet port 19 extending between outlets 16a and 16b. Deflation of the cells 2 and 3 is effected by a vent 18 in the rotor 20 which communicates alternately with outlets 16a and 16b.

The air leaving the pad 1 is only able to pass through the non-return valves 9 and 10 in one direction in order to prevent air leaking back through any deflated cells when the inflated cells are fully inflated. The air in lines 6 and 7 is combined to form a single outlet line 8 before passing into the compressible tube 12 in the sensor pad 11. If the weight of the patient is such that the compressible tube 12 is compressed even though the cells are inflated, the air exhausting to the atmosphere via relief valve 13 will be reduced and the air supplied from the compressor 4 will continue to inflate the cells until the weight of the patient is no longer able to compress tube 12. Thus, air exhausted to the atmosphere now depends upon the compression of the sensor pad 11 and is a function of the weight distribution of the patient. Normal operation occurs when the pressure within the cells rises to the predetermined value and air can pass

freely through the sensor pad because the alternating pressure pad is giving the required support to the patient.

It will be appreciated that the sensor could comprise separate air flow reducing passages for air from each of the supply lines.

Clearly, this is a simple and efficient arrangement which requires only a small number of connecting tubes between the compressor and mattress.

The pressure controller depicted in the drawing could easily be adapted for use with a static pressure pad system in either of the following ways:

(a) The rotary valve 5 is omitted and the compressor 4 is connected directly via supply lines 6 and 7 to the pad l; or

(b) The rotary valve 5 is retained but the rotor is stopped at the cross-over point so that the two sets of cells 2 and 3 in the pad 1 are connected in parallel making the arrangement operate as a static system.