Inflatable support

[0001] The present invention relates to a pressure controlled inflatable pad apparatus, in particular, a pressure controlled alternating or static inflatable pressure pad apparatus.

[0002] 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.

[0003] 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.

[0004] 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 that 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.

[0005] It is known to provide an automatic pressure controller comprising a sensor pad that 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 to exhaust thereby ensuring that more fluid is supplied to the alternating pressure pad until that patient is supported as required.

[0006] The fluid flows from the fluid supply line through the pressure pad and from the pressure pad through the sensor pad to exhaust or directly from the sensor pad to exhaust.

[0007] This arrangement necessitates the use of multiple connecting tubes between the pump and the mattress. This method is purely pneumatic without any electrical or electronic content added to the mattress, and the pump has to operate continuously at full output for effective performance. The system has to be set up individually when installed. Also, where the sensor pad is within the fluid circuit supplying the pressure pad, the sensor performance is dependent both on the fluid circuit and overall system pressure drops. Moreover, the static performance of the pressure pad is not as effective as the alternating performance as the optimum static pressure cannot be set. It is also known to have a sensor pad within the air circuit as described above but where the fluid is returned back to the pump. The system is prone to the same problems as outlined above.

[0008] The present invention seeks to make improvements.

[0009] According to the present invention, there is provided a pressure pad comprising at least two sets of inflatable cells, a fluid supply line to each set of cells, a pump arrangement to inflate each set of cells via the supply lines, and a sensor, a separate supply line connected to the sensor for fluid to flow through the sensor to exhaust, the sensor located beneath the cells, and control means controlling the output of the pump to increase or decrease the supply of fluid to the cells in dependence on the rate of flow of fluid to exhaust at the sensor exit. The invention eliminates the need for maximum compressor output at all times with separate pressure control and wasted compressor output. This has the advantage of increased compressor life and lower running costs.

[0010] Preferably, the control means controls the pump's output by varying the pulse width modulated drive for the compressor(s) in dependence on the rate of flow at the sensor exit. Preferably, the sensor comprises at least one compressible tube arranged in a convoluted path within a sensor pad.

[0011] Preferably, a pressure difference across a restrictor at the sensor pad exit determines the rate of flow.

[0012] Preferably, the supply of fluid through the sensor pad to exhaust vents into the space between the cells in the pressure pad, to provide a humidity gradient across the pad for greater patient comfort.

[0013] Preferably, the cells are arranged as a plurality of inflatable segments, the supply lines to the cells being respectively further provided with valves to allow the separate segments to be inflated to different support pressures, and more preferably the valves and their control are located within the pressure pad.

[0014] Preferably, all the inflatable segments are inflated to a first support pressure, the segments supporting at least the heels maintained at the first support pressure and the segments supporting at least the torso further inflated to a second higher support pressure and maintained at that higher pressure. Preferably, the cells supporting the heel and/or the head are of a smaller size for better pressure relief.

[0015] Preferably, the valves automatically close in the event of no power, preventing deflation of the cells and providing support for a user during power failure or during transport when power is not available.

[0016] Preferably, the segment of cells supporting the torso of a user can be deflated separately to facilitate user entry or exit from the pressure pad and more preferably, the supply lines to the cells and sensor pad are located beneath the pressure pad to allow for easy exit from the side of the pressure pad.

[0017] Additionally, the segments of cells supporting the head and heels can be deflated to provide proning of the user.

[0018] Preferably, each cell can be deflated individually to provide pressure relief to the different parts of the body supported thereon.

[0019] The present invention will now be described in detail, by way of example only, with reference to the accompanying drawings in which:

[0020] FIG. 1 shows a schematic diagram of an alternating pressure pad according to the invention;

[0021] FIG. 2 shows the zoning arrangement of the alternating pressure pad in FIG. 1;

[0022] FIG. 3 shows the sacral deflate arrangement of the alternating pressure pad in FIG. 1; and

[0023] FIG. 4 shows the proning arrangement of the alternating pressure pad in FIG. 1.

[0024] Referring to FIG. 1, an alternating pressure pad 1 is shown comprising a first set 11 and a second set 12 of alternately inflatable cells. Both sets of inflatable cells are supplied with air from a pump 6 via a rotary valve 7. A pair of air supply lines 14 lead from the rotary valve 7 to the pad.

[0025] A tube 10 of a sensor pad 8 is connected at one end to the output of the pump 6 and at the other end to a solenoid 44, pressure transducer 16 and two different restrictors 15 and 15a. The tube 10 comprises a portion which is positioned under the pad 1 to receive pressure exerted by a patient and to be compressible depending on the pressure applied.

[0026] The compressible portion of the tube 10 is, in this embodiment, a single compressible tube arranged in a convoluted path and formed as a sensor pad 8. The pad 8 may be formed of two polyurethane sheets welded together to define a single convoluted tube. In an alternative embodiment (not shown), the two sheets may he welded together with foam in between to define a single or a plurality of interconnected tubes. The open celled foam may be welded inside the tube 10 to act as a spring and to keep the tube 10 open unless a positive direct force is applied, for example, a patient sinking through the cells 11 and 12. The foam prevents the tube 10 kinking and increases both accuracy and consistency of the sensor pad 8.

[0027] In use, the pump 6 includes two compressors C1, C2 to deliver air to the pad 1 by means of a rotary valve 7 so that each set of cells of the pad is alternately inflated and deflated. The two compressors C1, C2 are both run together when first switched on for maximum flow and rapid fill, then they are reduced in flow to give the required flow. A pressure transducer 5 is used to check the pressure of the output from the pump 6. Operating the pump 6 in this way means that each compressor C1 or C2 has the lowest shuttle amplitude and therefore stress. This reduces both noise and vibration, and gives a very long life. If one should fail, the other compressor operates at increased power and the service engineer alarm is activated. Thus the reliability of the overall system is increased. Of course, a single compressor can also be used. The system operates on an inflation/deflation cycle repeating over periods varying from two minutes to over twenty minutes. In a preferred embodiment the cycle time is 10 minutes.

[0028] During the inflation cycle, the rotary valve 7 is in such a position that a portion of the flow goes via the tube 10 and the rest fills the cells 11 or 12 depending on the cycle. Any change in patient position or weight, which causes an alteration in the airflow in the sensor pad tube 10, will reduce or increase the differential pressure measured at the pressure transducer 16. Based on this feedback the microprocessor directly controls the power level to the compressors C1, C2 and therefore the compressors pneumatic output, thus increasing or decreasing the air flow to the cells to either prevent bottoming or to run the pressure pad 1 at a minimum pressure.

[0029] Solenoid 44, pressure transducer 16 and restrictors 15, 15a act as a switched two range flow sensor where flow is measured via the differential pressure across the restrictors 15 or 15a depending on whether the pressure pad is in alternating or static mode. The differential pressure is measured by pressure transducer 16 by comparison to atmospheric pressure.

[0030] For optimal inflation pressures of the pressure pad in static or alternating mode, a preset pressure for the sensor pad is determined by experiment depending on the level of comfort required by the patient. A control band around the preset pressure is established where, depending on whether the actual sensor pad pressure is above or below the preset value, the output level of the compressor is varied according to the difference between the preset value and the actual sensor pad pressure measured. The air from the sensor pad exit is vented inside the pressure pad 1 to control the humidity gradient across the cover.

[0031] Additionally, as shown in FIG. 2, the pressure pad 1 is segmented into zones for a heel section (zone 1), an upper leg section (zone 2), a mid torso section (zone 3), and a head section (zone 4). The heel, upper leg and head section are inflated at one pressure P1 and the torso section is at a higher pressure P2. As shown in FIG. 1, the supply lines 14 are provided with solenoids 41, 42 and 43 and pressure transducer 45 to control the pressures P1 and P2 within the respective segments of cells 11 and 12. A control module 50 is provided inside the pad 1.

[0032] The control module 50 consists of a manifold made up from two mouldings forming air channels and upon which are mounted the solenoids, the pressure transducers and their control. Solenoid 41 prevents over inflating of the head and heel cells 11, solenoid 42 prevents over inflating of the head and heel cells 12, and solenoid 43 retains the air in the head and heel cells 11, 12.

[0033] Solenoid 44 controls the back pressure in the sensor pad by switching between restrictors 15 and 15a for static and alternating operation of the pressure pad.

[0034] Thus, the number of supply lines 14 to the pressure pad 1 are kept to the minimum.

[0035] In use, during inflation of cells 11, the pressure in the head and heel sections is monitored by pressure transducer 5 until the required pressure P1 is achieved at which point solenoid 41 or 42 operates to cut off the air flow. Pressure transducer 45 then monitors the pressure P1 in the head and heel section.

[0036] The pressures P1 in the head, upper leg and heel sections is substantially lower than the pressure P2 in the torso section. Due to the fact the desired air pressure P2 in the torso section is not established when the head, upper leg and heel pressures P1 need to be shut off, the value of P1 is set proportional to the P2 value from the previous alternating inflation cycle. The highest pressure segment is kept at its P2 pressure level by direct control from the pump 6 via feedback from the sensor pad 8, and can be sealed using the rotary valve 7 when required. The torso section can be set to different comfort pressures by adjusting the sensor pad preset pressure values controlling the compressors' output.

[0037] During the time that the cells 11 are fully inflated a combination of rotor position and solenoid operation can allow a cell segment to be opened, its pressure checked by pressure transducer 45 and then topped up with air or resealed as required. This method saves the need for multiple costly pressure transducers controlling the pressure in each segment.

[0038] Similar use of the solenoids provides additional features of the torso section being deflatable to a safety cell depth to allow patient ingress/egress off the pressure pad, as shown in FIG. 3, since it is known that patients find it difficult to get on or off a fully inflated pressure pad. This feature of torso cell deflation can be patient controlled.

[0039] Alternatively, as shown in FIG. 4, the head section can be deflated whilst the torso section first cell 51 is kept inflated and upper leg and heel sections are alternately inflated to provide a proning position for a patient. The upper leg and heel section cells may also be individually deflated to provide pressure relief where necessary. Therefore, any cell within the pressure pad may be deflated individually to provide individual areas of pressure relief.

[0040] Although the particular embodiment described above relates to an alternating pressure pad 1, the invention applies equally to a static pressure pad with a sensor pad and having head, upper leg, torso and heel sections at differing pressures P1 and P2.

[0041] The pump 6 uses powered pulse width modulated (PWM) driven compressors as opposed to the mains alternating current driven compressors of the prior art. A micro-controller creates the driving waveform for the compressors C1, C2 with variable mark space constant repetition rate and constant amplitude, so that the pump 6 is not dependent for performance on any particular mains voltage or frequency. Therefore, the pump 6 can be operated from the mains voltage of any country. The compressors output is varied by varying the PWM mark space ratio from zero to maximum. Therefore, the cell pressure P1, P2 is controlled by varying the PWM drive of the compressor C1, C2, eliminating the need for maximum compressor output at all times with separate pressure control and wasted compressor output. This has the advantage of increased compressor life and lower running costs.