Note: Descriptions are shown in the official language in which they were submitted.
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ALTERNATING PRESSURE PADS
This invention relates to alterna.ting pressure pads, particularly for use in
nursing patients and others prone to bed sores.
Alternating pressure pads are lrnown 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 particularly
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 coniinuous 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 of the tube and restoring the
controlled leak
through the sensor tube. While simple in operation, a sensor tube of this
kin.d 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.
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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 alternating 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 predetermined 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 forming the conduit by
partially
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
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to increase inflation pressure in the event that the sensor pad indicates that
the sets of
cells are insufficiently inflated.
According to a further aspect of the invention, therefore, there is provided
an
alternating 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
circuit and
detecting means for detecting a pressure change in the sensor pad, or in air
conduits
connected thereto and for causing 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 tvvo sets of inter-
dispersed 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
contained within a cover which is waterproof and provides an easily cleaned
and
disinfected surface. Such an arrangement is described in the above US patent
and has
the advantage that if the cells in 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 support surface during any part of the
alternating cycle.
According to a still further aspect of the invention, therefore, there is
provided
an alternating pressure pad comprising a plurality of inflatable cells
arranged in at least
two sets of inter-dispersed cells, means for inflating and deflating the cells
alternately,
a pressure sensor arranged 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
SUBSTITUTE SNEET (RULE 26)
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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 predetermin.ed value. -
The construction 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
construction 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 i is a circuit diagram of an alternating pressure pad in accordance
with
the invention=
Figure 2 is a plan view showing the construction of the sensor pad; and
Figures 3 and 4 are circuit diagrams of modified alternating pressure pads of
the invention.
Referring to Figure 1, the alternating 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 form as described in US Patent
No.
5,396,671. A sensor pad 3 is positioned to lie 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
capacitv, whereas main inflation pump 9 may be an axial or centrifugal rotary
pump of
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higher output. Check valves l0a 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 retuins 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 arrangement 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
alternating
supply of air to pressure lines 7a and 7b. The rotation speed may be altered
to
proNide a desired delay period between inflation and deflation period.
The rotary valve 6 may include 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 partially or fully connected in a further
position when it
vents to atmosphere. This arrangement 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 starting up
the main
pump 9 for inflation of previously deflated cells.
The circuit also includes a pressure limit 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 11, as shown in Figure 3.
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A pressure sensitive switch 17 is located in the feed-back line 12 and is
arranged 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 alternating pressure
pad is in 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 start up of the apparatus.
The air
from one or both pumps enters the cells altemately, and returns to the
circulation
pump 8 via the feed-back line 12.
If the weight of the patient on the sensor pad exceeds the pressure of air
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 wiil. supply air along the line 12 to the rotary valve 6 and
restore the
pressure within the sets 1 and/or 2.
Once pressure is restored in the inflatable cells, the patient wiil 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
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= 7 insuPficient inflation of the cells 1 and 2, switch 17 may be arranged to
close under a
spring-bias to cause activation of the pump 9.
A preferred construction of the sensor pad is shown in Figure 2. Referring to
Figure 2, the sensor pad 3 comprises an inflatable envelope 21, supported on a
backing
sheet 22. The backing sheet 22 is preferably a sheet of plastics material
which has a
dimension X-X approxiinately corresponding to the width of a bed or other
suitable
base support, intended to support the inflatable mattress. Backing sheet ? is
fitted
with fising 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 support for the inflatable mattress, under a moderate lateral
tension
designed to keep the surface of the backing sheet 22 flat, and the. inflatable-
-
envelope 21 unkinked.
Envelope 21 is foimed 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
partially
thermoplastic sheets forming the envelope 21 along weld lines 27 and 28,
welding
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 =m 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
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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
transported
from one part of the hospital to another, while comfortably supported on the
inflated
mattress.
The main inflation pump will only operate intermittently. This has the
following advantages:
I. 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 part 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
transferred to the non-inflated set, there is a further 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 I with the following changes. In
Figure 3, the
same reference numerals are used for parts which are the same as those shown
in
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Figure 1. As can be seen in Figure 3, a pressure relief valve is provided by
the line
36, which bridges air lines 11 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 activated if the pressure of air flowing through the sensor pad is
restricted by
the patient's weight. Coirective 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 portion 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 reverts to
the sealed
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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
fall speed,
drawing air partly 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 arranged 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 of the pump appropriately.
