ALTERNATING PRESSURE PADS

Abstract: An alternating pressure pad which comprises at least two sets (1, 2) of inflatable cells, an air supply line (7a, 7b) to each set, a pump (8) to circulate pressurised air through a circuit including the sets of cells and to return air from the cells to the pump, valve means (6) for alternately causing inflation and deflation of each set, a sensor pad (3) in said circuit through which pressurised air is passed and detecting means (17) for detecting a reduction in air flow through the sensor pad which is below a predetermined level and for increasing air pressure in said sets of cells to restore the air flow above said predetermined level.

Description: ALTERNATING PRESSURE PADS This invention relates to alternating pressure pads, particularly for use in nursing patients and others prone to bed sores. Alternating pressure pads are known and have been used in the construction of mattresses, chairs, couches and other patient support devices to improve blood circulation, and thereby reduce the incidence of bed sores. US Patent No. 5,396,671 discloses an alternating pressure pad paπicularly designed for use as a mattress, in which two sets of inflatable cells are alternately inflated and deflated in order to stimulate blood circulation in a patient lying on the mattress. In this US Patent, a sensor pad is located beneath the inflatable cells in order to detect when the cells are insufficiently inflated. One sensor described comprises a flexible tube positioned beneath the mattress. One end of this tube is connected to the inflatable cells and the other discharges to atmosphere, thus providing a continuous leakage path. In the event that inflation pressure in the cells becomes insufficient to maintain the use above a base surface, the sensor tube will be compressed and reduce or entirely cut off the flow of air therethrough. As a result, more air will become available to the cells and the user will be raised off the base surface, thereby releasing the compression ofthe tube and restoring the controlled leak through the sensor tube. While simple in operation, a sensor tube of this kind has the disadvantage that there is a constant loss of air from the system, which necessitates the continuous operation of a higher capacity pump than would be required if such a leak could be avoided. According to one aspect of the present invention there is provided an alternating pressure pad having a sensor pad in which the sufficiency of inflation of the cells is sensed by detecting the change of pressure or air flow through the sensor pad or through conduits leading to it. According to another aspect of the present invention, therefore, there is provided an altemating pressure pad which comprises at least two sets of inflatable cells, an air supply line to each set, a pump to circulate pressurised air alternately through a circuit, including the sets of cells, and to return air from the cells to the pump, the sensor pad in said circuit through which pressurised air is passed and a detecting means for detecting a reduction in air flow through the sensor pad, which is below a predeteπriined level and for increasing air pressure in said sets of cells to restore the air flow of above said predetermined level. The reduction in air flow through the sensor pad caused by the patient's weight compressing the sensor pad can be detected by sensing the change of air pressure in the sensor pad or in conduits connecting the pad to the circuit. A sensor pad for use in accordance with the invention can be very simply constructed as an inflatable, flexible envelope comprising a conduit extending back and forth across the pad. The pad can be constructed from films of plastics sheet material welded at their perimeters to form the envelope and foπning the conduit by paπially welding the films together in a series of parallel weld lines. Preferably, a first pump is provided to circulate air through the circuit, and a second, larger capacity pump is connected to the circuit and is operated intermittently to increase inflation pressure in the event that the sensor pad mdicates that the sets of cells are insufficiently inflated. According to a fuπher aspect of the invention, therefore, there is provided an altematmg pressure pad which comprises at least two sets of inflatable cells, an air supply line to each set, a first pump to circulate air alternately through a circuit, including said sets, and return air to said first pump, a sensor pad positioned to detect inadequate inflation pressure in said sets, a second pump connected to said circmt and detecting means for detectmg a pressure change in the sensor pad. or in air conduits connected thereto and for causmg said second pump to be actuated in the event of reduction of pressure below a predetermined level. Preferably, the inflatable cells are arranged in at least two sets of lnter- dispersεd cells, e.g. an inter-digitated arrangement as described in US Patent No 5,396.671 Conveniently, there are one or more layers of indigitated cells, preferably contamed within a cover which is waterproof and provides an easily cleaned and disinfected surface. Such an arrangement is descπbed in the above US patent and has the advantage that if the cells m the two or more layers are disposed so that a deflating cell is juxtaposed beneath or above an inflating cell, the user of the mattress is less likely to touch the underlying suppoπ surface during any pan ofthe altematmg cycle. Accordmg to a still further aspect of the invention, therefore, there is provided an altematmg pressure pad comprising a plurahty of inflatable cells arranged in at least two sets of mter-dispersed cells, means for inflating and deflating the cells alternately, a pressure sensor ananged to sense the flow of air through the cells, a pump for inflating the cells and circulating pressurised air through the cells, and control means for controlling the operation of the pump according to the flow of air through the sensor, and to increase air pressure in the cells in the event that pressure in the sensor falls below a predetermined value. The constmction of the cells, the header tubes feeding the cells, the cover for containing the cells, means for fixing the components together, the value means for alternately deflating and inflating the cell sets and other details of the constmction of the mattress may be as described in the above US Patent No. 5,396,671. Several embodiments in accordance with the invention will now be described with reference to the accompanying drawings, in which:- Figure 1 is a circuit diagram of an alternating pressure pad in accordance with the invention; Figure 2 is a plan view showing the constmction ofthe sensor pad; and Figures 3 and 4 are circuit diagrams of modified altemating pressure pads of the invention. Referring to Figure 1 , the altemating pressure pad comprises two sets 1 and 2 of inflatable cells. These cells are preferably constructed as longitudinal headers 4 inter-digitated finger-like cells 5 having a foπn as described in US Patent No. 5,396,671. A sensor pad 3 is positioned to He beneath the mattress formed by the sets 1 and 2. The inflatable sets 1 and 2 are connected to a rotary valve 6 by air input lines 7a and 7b. Rotary valve 6 is fed with air from low power circulation pump 8 or larger powered main inflation pump 9. Circulation pump 8 may be a diaphragm pump having a relatively low output capacity, whereas main inflation pump 9 may be an axial or centrifugal rotary pump of higher output. Check valves 10a and 10b are located between air lines 7a and 7b to prevent inflation air leaking between the air lines 7a and 7b. An air line 11 feeds the pressure pad 3 and a feed-back line 12 retums air to the low output circulation pump 8. Circulation pump 8 feeds air along air line 13 and air line 14 to the rotary valve 6. Sensor pad includes a flexible, compressible tube 15. Because of the aπangement of the check valves 10a and 10b, there is always a flow of air through tube 15 of sensor pad 3, and around the circuit which includes the circulation pump 8, and the rotary valve 6. Rotary valve 6 is driven by an electric motor (not shown), at a speed which is adjustable to provide the desired altemating supply of air to pressure lines 7a and 7b. The rotation speed may be altered to provide a desired delay period between inflation and deflation period. The rotary valve 6 may mclude a position in which both sets of cells 1 and 2 are in communication, so that the inflated set equalises pressure with the deflated set, before the set to be deflated is paπially or fully connected in a fuπher position when it vents to atmosphere. This aπangement ensures a saving in the volume of air required to be fed to the circuit and thus reduces the air output capacity required from the pumps. It also reduces the pressure required in the line 12 when staπing up the main pump 9 for inflation of previously deflated cells. The circuit also includes a pressure Umit valve 16, which bridges the feed-back line 12 with the input line 14 to the valve 6. The purpose of the pressure limit valve 16 is to leak to atmosphere in the event that the pressure in the circuit reaches an unacceptably high level. Alternatively, the pressure limit valve may connect the feed back line 12 with the input line 1 1. as shown in Figure 3. A pressure sensitive switch 17 is located in the feed-back line 12 and is ananged to sense a reduction in pressure in the feed-back line 12. In the event of a reduction in pressure in this line, switch 17 causes the electrical feed to the main inflation pump 9 to be actuated, thereby causing the main inflation pump to feed air to the input line 14. The system works in the following manner. When the altemating pressure pad is m normal use, air under pressure will be supplied alternately by the pump 8 to sets 1 and 2. Pump 9 is normally actuated only on staπ up of the apparatus. The air from one or both pumps enters the cells alternately, and retums to the circulation pump 8 via the feed-back line 12. If the weight of he patient on the sensor pad exceeds the pressure of afr within the pad, the tube 15 will collapse and close off the passage of air through the line 12. This will cause the pressure to fall in the feed-back line 12 which will be sensed by the pressure switch 17. On actuation of the switch 17, the main inflation pump 9 will be actuated and this will supply air along the line 12 to the rotary valve 6 and restore the pressure vvithin the sets 1 and/or 2. Once pressure is restored in the inflatable cells, the patient will be lifted off the sensor pad and this will restore the flow of air through the lines 11, 15 and 12, and the increased pressure will open switch 17, thereby causing the main inflation pump 9 to be switched off. The switch 17 is preferably adjusted so that the switch is held in the off position when the pressure in the feed-back line 12 is sufficient to indicate a normal flow of air through line 12. On reduction of the pressure to a level indicative of insufficient inflation of the cells 1 and 2, switch 17 may be ananged to close under a spring-bias to cause activation of the pump 9. A prefened construction of the sensor pad is shown in Figure 2. Referring to Figure 2, the sensor pad 3 comprises an inflatable envelope 21, suppoπed on a backing sheet 22. The backing sheet 22 is preferably a sheet of plastics material which has a dimension X-X approximately coπesponding to the width of a bed or other suitable base suppoπ, intended to suppoπ the inflatable mattress. Backing sheet 22 is fitted with fixing means such as press-studs 23, attached through a reinforcing strip 24. The fastening means 23 are intended to be attached to the surface of the bed or other underlying suppoπ for the inflatable mattress, under a moderate lateral tension designed to keep the surface of the backing sheet 22 flat, and the pressure pad 21 urjkinked. Envelope 21 is formed with inlet and outlet connectors 25 and 26 for connection with the air line 11 and feed-back line 12. The tube effectively passing between the connectors 25 and 26 consists of an elongated tube formed by paπially welding thermoplastic sheets forming the envelope 21 along weld lines 27 and 28, thereby forming an elongated tube in zig-zag formation within the envelope 21. Although this design of sensor pad 3 is less likely to kink in use because of rucking of the sensor pad 3 beneath the patient, the over-pressure valve 16 prevents the sacs from being raised to an unacceptably high pressure, should there be an unexpected blockage in the circuit. The pressure limit valve is conveniently housed together with the rotary valve 6, and the air switch 17 in the same casing, preferably together with one or both pumps. Alternatively, the pressure limit switch is located adjacent the mattress air input or feed back connection lines. The circulation pump 8 is preferably a diaphragm-type pump which has the advantage of requiring low power and creating a low level of noise. The pressure relief may be set to relieve pressure within the system at a pressure of about 70 mm Hg water gauge. The rotary valve can also be provided with a setting in which both inflatable cells sets are inflated, and with no leakage to atmosphere. In this setting the main electrical supply to the pump can be disconnected and the patient may be transpoπed from one pan of the hospital to another, while comfoπably suppoπed on the inflated mattress. The main inflation pump will only operate termittently. This has the following advantages: 1. Because there is less air pressure dumped or leaked from the system and thus a lower power demand, this enables the equipment to be used at least for a pan of the time with a battery power supply. 2. As air is only exhausted to atmosphere at only one point in the sequence of the rotary valve, and air from the cell set to be deflated is first of all transfened to the non-inflated set, there is a fuπher economy on leakage of air to atmosphere. Figure 3 shows a modification of the circuit shown in Figure 1. In Figure 3. the air circuit is the same as in Figure 1 with the following changes. In Figure 3, the same reference numerals are used for pans which are the same as those shown in Figure 1. As can be seen in Figure 3, a pressure relief valve is provided by the line 36, which bridges air lines 1 1 and 12 and has a pressure limit valve 16 in the line 36. This pressure relief valve 16 functions in exactly the same way as the valve 16 in Figure 1. In the embodiment of Figure 3, there is only one pump 8a and this provides for circulation of air through the system- The pump 8a will be a larger output pump than the pump 8 in Figure 1 , and may, for example, be a pump able to operate at different speeds to increase the air output. In Figure 3, a pressure-sensitive control system 30 is provided. This system will be aαivated if the pressure of air flowing through the sensor pad is restricted by the patient ' s weight. Conective action will then be taken automatically. The control system comprises an air flow restrictor 31, connected to the inlet to the pump 8a. The control system also includes a control assembly 32. The assembly includes a one-way valve 33, connected to the air inlet line to the pump 8a between the restrictor 31 and the pump 8a. Valve 33 is under the control of a pressure-sensitive switch 34 and is acted on by a seal or plate 35. In use, air is pumped by the single pump 8a at, say, 5 litres per minute, to the rotary valve 6 and passed alternately to the two cell sets. If the weight of the patient causes the sensor line to be constricted, a small poπion of air is drawn via restrictor 31 to deflate valve 34, and so open valve 33. Air is now drawn into the circuit from atmosphere through valve 33, and increases the flow rate to the cell sets until the flow rate is back to the intended level, whereupon the control system reveπs to the sealed condition. If the sensor pad becomes completely blocked, air will flow via the bypass line and valve 16 to open the control system In the embodiment of Figure 4, the pump 8a is a two speed pump and the air circuit is as shown in Figure 3 except for the pressure-sensitive control system The feed-back line 12 incorporates an air operated switch 40, set to reduce the voltage to the pump when the pressure reaches approximately 50 mm Hg and increase the voltage when the pressure falls below approximately 25 mm Hg. When the air flow through the sensor is reduced, the air switch 40 is thrown and the pump then runs at full speed, drawing air paπly from the atmosphere via a valve 43 and partly by the restrictor 31. When the flow of air through the sensor is restored, air in the line 12 returns to full pressure and the switch is then actuated to reduce the voltage supplied to the pump 8a. Air will now be exhausted slowly through the circuit, the rotary valve 6 being ananged to transfer a little air at the time when the deflated cells are about to inflate, to activate the switch to run the pump at full speed, during inflation of the previously deflated cells. If at any time the sensor becomes completely blocked, the air is directed via the by-pass line to throw the switch 40 and thereby adjust the operation ofthe pump appropriately.

Claims: CLAIMS - 1. An altemating pressure pad which comprises at least two sets of inflatable cells, an air supply line to each set, a pump to circulate pressurised air through a circuit including the sets of cells and to return air from the cells to the pump, valve means for alternately causing inflation and deflation of each set, a sensor pad in said circuit through which pressurised air is passed and detecting means for detecting a reduction in air flow through the sensor pad which is below a predetermined level and for increasing air pressure in said sets of cells to restore the air flow above said predetermined level. 2. A pressure pad as claimed in claim 1 wherein the reduction in air flow through the sensor pad is detected by sensing a change in air pressure in the sensor pad or conduits connecting the pad in the circuit. 3. An pressure pad as claimed in claim 1 or 2 wherein the sensor pad comprises an inflatable flexible, envelope. 4. A pressure pad as claimed in claim 1 or 2 wherein the sensor pad comprises an elongate tube wound back and forth beneath the pressure pad. 5. A sensor pad as claimed in claims 3 or 4 wherein the sensor pad is positioned in use beneath at least one ofthe sets of inflatable cells and reduced air flow through the sensor pad is indicative of insufficient inflation pressure in the sets of inflatable cells. 6. A pressure pad as claimed in any one of the preceding claims wherein the cells ofthe different sets are interspersed one with the other. 12 7. An alternating pressure pad which comprises at least two sets of inflatable cells, an afr supply line to each set, a first pump to circulate air alternately through a circuit including said sets and return air to said first pump, a sensor pad positioned to detect inadequate inflation pressure in said sets, a second pump connected to said circuit and detecting means for detecting a pressure change in the sensor pad or air conduits connected thereto, and for causing said second pump to be actuated. 8. A pressure pad as claimed in claim 7 wherein said pressure change is indicative of insufficient inflation pressure in said sets of cells. 9. A pressure pad as claimed in claim 8 wherein the first pump is adapted to circulate air through the circuit and the second pump is adapted to be actuated mter nittently when the sensor pad senses insufficient inflation pressure in said sets of cells. 10. A pressure pad as claimed in any one of claims 7 to 9 wherein the cells ofthe different cells are interspersed one with the other. 11. A pressure pad as claimed in any one of claims 7 to 10 wherein the sensor pad comprises a flexible tube which is wound back and forth to foπn a substantially flat pad. 12. An altemating pressure pad comprising a plurahty of inflatable cells ananged as at least two sets of interspersed cells, valve means for causing inflation and deflation ofthe cells alternately, a pressure sensor ananged to sense the flow or air through the cells and connected in a continuous circuit with said pump, a pump for inflating the cells and circulating pressurised air through the cells, and control means for controlling the operation of the pump according to the flow of air through the sensor and to increase air pressure in the cells in the event that pressure in the sensor falls below a predetermined value.

Inventors: STACY PETER CHARLES, STACY, PETER, CHARLES
Applicants: KCI MEDICAL LTD, STACY PETER CHARLES, KCI MEDICAL LIMITED, STACY, PETER, CHARLES
Application year: 1996
Main classification: A47C27
IPC codes: A61G7