Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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THERAPEUTIC TURNING BED
BACKGROUND OF THE INVENTION
This invention relates to therapeutic beds, which are
principally of the so-called "iow air loss" type and which
facilitate the nursing of hospitalised patients.
DESCRIPTION OF THE PRIOR ART
In low air loss beds, the patient is supported on a
number of inflated sacs whose pressures are adjusted so as
to maximise the area over which the patient's weight is
supported, thereby minimising the skin contact pressures.
Typical references describing conventional low air loss
beds (hereinafter LALB's) are GH Patent No..1474018 arid US
Patent No. 4525885. Low air loss beds have been very
successful clinically in nursing patients who are prone to
development of pressure sores.
Bed-ridden and immobile patients also tend to suffer
from lung congestion and have to be turned at regular
intervals in order to assist drainage of fluid from the
lungs. Normally, this is performed manually by nurses,
who physically turn the patient at one to two hour
intervals.
Although powered turning beds exist, these are
primarily designed for spinal injury patients and are
designed so that the patient is tightly confined. In such
powered turning beds, the patient is turned slowly through
an angle of up to~60o in each direction, and the patient
is ,wedged between blocks of foam and strapped to a firm
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baseboard. This tightly confined condition is found by
many patients to be very unpleasant, can induce nausea and
encourage the development of bed sores unless the
patient's condition is constantly monitored.
SUMMARY OF THE INVENTION
According to one of its aspects, the present
invention provides a therapeutic bed which comprises:
(a) a trolley frame having floor-engaging feet or
wheels,
(b) an attitude frame pivotably mounted on the
trolley frame so as to be pivotable through a
predetermined arc about an axis extending longitudinally
of the bed,
(c) operating means .for causing the attitude frame
to pivot through said predetermined arc,
(d) a plurality of air sacs supported an said
attitude frame and inflatable to a pressure sufficient to
provide a resilient surface for supporting a patient
thereon, said air sacs together forming a cavity within
which the patient's body can be nested and supported so
that the patient does not slide off the bed during
turning, and
(2) contro l means for causing the turning movement
of the attitude frame to be arrested when reaching the end
of the predetermined movement in one direction and causing
the operating means to reverse the direction of turning
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movement.
The operating means for effecting the pivoting
movement will normally include control means, such as a
microprocessor, which can be programmed to control the
rate of pivoting movement, the dwell time at the extreme
point of the pivoting movement and the angle through which
the attitude frame is pivoted. In practice, we have found
that for the best clinical effect, the attitude fxame
should be pivoted through a total arc of at least about
40° (i.e. 20o in each direction), and that a total
pivoting arc may be as much as 80o without losing
stability.
Dwell times at the extreme point in the cycle may
vary from a few seconds to 30 minutes but is preferably
between about 1 and 5 minutes.
In order to maintain the patient in a stable position
in the bed with the minimum of straps or other,rnstraining
devices, the operative surface of the bed is preferably
made up of a plurality of individual inflatable air sacs,
which are shaped to produce a cavity corresponding to the
silhouette of the patient. Thus, the .patient can be
snugly nested in the air sacs while being supported at
minimum skin contact pressures.
Preferably, the air sacs are made partly or wholly
from water vapour permeable material, which is however
'impermeable to liquids. By using such materials and
ensuring that an air flow takes place within the sacs,
CA 02057000 1999-11-OS
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water vapour is induced to pass into the sacs and is swept away
in the air stream. In this way, the condition of the patient's
skin and his comfort generally is improved. The operation of
water vapour permeable LALB' s and the selection of suitable water
vapour permeable materials is described in GB Patent No. 1474018,
US Patent No. 452885, U.K. Patent Specification No. 2141333, WO
86/06624, US Patent No. 3822425 and "Bed Sore BioMechanics",
edited by R.H. Kennedy, J.M. Cowden and J.T. Seales, published
by Macmillan 1976, pages 259 - 299. Examples of commercially
available water vapour permeable materials are Permatex* manufac-
tured by Carrington & Dewhurst Performance Fabrics and Gortex*
manufactured by W.L. Gore & Associates.
Further improvements in patient comfort are achieved
by providing a heater in the air supply to the sacs and also
exhaust regulation valves, to control the air flow in the sacs,
as describe in the above cited references.
Although the operating means for pivoting the attitude
frame may be selected from a variety of systems, e.g. inflatable
air bags (which can be repetitively filled and exhausted) or
hydraulic rams acting between the trolley frame and the attitude
frame, such methods have various disadvantages. It has been
found that the most effective
* trade-mark
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operating means comprises a direct mechanical linkage
between the relatively movable components, i.e. the
attitude frame and the trolley frame. The mechanical
linkage may be a pinion drivably connected to an electric
motor which is arranged to mesh with a toothed gear or
quadrant, the pinion and toothed geaa- ar quadrant being
mounted respectively on the relatively movable frame
components. Where the motor can be operated at law rpm,
the pinion can be mounted directly on the motor shaft.
However, in order to provide sufficient torque from a
' motor of compact dimensions, it is normally necessary to
drive the attitude frame through a gear box. In an
alternative mechanical drive arrangement, the electric
motor may be coupled to a worm, (normally through a gear
box) ithe worm being engaged with a worm wheel mounted an
the other relatively movable component.
The various features of the improved turning bed will
become apparent from the following description and
accompanying drawings.
HRIEF DESCRIPTION OF THE DRAWINGS
Figures la, lb, lc and ld are schematic views of the
bed showing the various attitudes and functions,
Figure 2 is a side elevation of an embodiment of the
bed showing the attitude frame in the fully raised
position and the head and foot sections of the contour
frame fully raised,
WO 9114816 PC'T/~13911f(f0829
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Figures 3a, 3b and 3c show the shapes of profiled air
sacs when viewed along the sections A-A, B-B and C-C in
Figure 2,.
Figure 4 is a side elevation of the trolley frame and
attitude frame showing the actuators and associated parts
for raising and lowering the attitude frame. Figures 4a,
4b, 4c and 4d show details of the linkages between the
trolley frame and the attitude frame and are respectively
enlarged views of the areas circled by A & B in Figure 4
and sections taken on the lines B-B and D-D in Figure 4,
Figure 5 is a partial end elevation showing the
manner in which the motor for pivoting the base frame is
mounted,
Figure 6 is a plan view of the trolley frame,
Figure 7 is a side eleva~:ion of the attitude frame
showing the manner in which the motor is mounted thereon,
Figure 8 is a view taken in the direction of the
arrow X in Figure 7,
Figure 9 is a diagrammatic view of the control panel
and display arrangements for the bed,
Figure 10 is an example of the information which can
be shown an the display screen, and
Figure 11 is a diagrammatic layout of the contrpl
system for the bed.
Referring to the drawings, the general appearance and
basic functions of the bed a.re shown in Figures la to d,
and Figure 2. The bed has a trolley frame (I) which is
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fitted with
ground-engaging castors 1( 2.) and ~ ~ , supports an
attitude frame (3). Attitude frame (3) is supported from
the trolley frame (1) by means of actuating arms (4 & 5)
which can be raised and lowered separately or in unison by
actuators (15 & 16). As can be seen in Figures la and
lc, operation of the actuators (15 & 16) in unison cause
the attitude frame {3) to be raised or lowered in a
horizontal plane while Figure lb shows that if actuator
(16) is extended while actuator (15) is retracted,
attitude frame (3) takes up the Trendelenberg position.
The opposite movement of actuators (15 & 16) causes the
attitude frame to be tilted into the reverse Trendelenberg
position.
As shown schematically at (18 & 19) in Figure lc, the
attitude frame is fitted with potentiometric sensor means
to determine when sac sections 22, 23, 24 and 25 (which
together form the contour frame 8) are flat on the
attitude frame (3). The sensor means are 2 of the 3
analogue inputs shown in Figure 11. They are effectively
variable resistors, one component being linked to the head
. or foot sections (22 or 25) and the other to the frame 3.
As indicated in Figure 11, the sensors (18 & 19) are
connected via a relay board to the microprocessor coat=ol
board, so that the position of the sac sections can be
monitored.. Thus, there will be a voltage drog across the
resistor;whose value depends on the extent of pivoting of
section 22 or 25.- This voltage change is converted by the
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microprocessor to an angular display on screen C (Figures 9
to 11). This is important since the turning operation,
which is indicated schematically in Figure ld; should not
commence with the sac sections in a fully contoured
condition. However, it is generally safe to operate with
the head or foot section raised by esbout 10 to 200.
Figure ld shows diagrammatically the principle
whereby the attitude frame (3) is pivotable about a
longitudinal axis of the bed through a maximum angle in
each direction of about 400. As shown schematically in
Figure ld, the arm (4) at the head end (10) takes the form
of an A-frame (61,61a), whose legs are attached to a pair
of levers (45). Levers (45) are linked to actuator (15)
so that extension of the actuator causes the A-frame to
rise (see Figure 6). At its apex, the A-frame is
pivotably connected to the attitude frame (3) at (47) so
that the attitude frame is pivotable on-.the A-frame about
an axis, which extends longitudinally of the bed.
Supported on the attitude frame (3) so as to be pivotable
with the attitude frame is a drive motor (62). Motor
(62) drives a pinion (67) which meshes with a quadrant
shaped gear (64) fixed to the A-frame so that on operation
of the motor, the attitude frame is tilted about the
longitudinal axis of the bed with respect to the A-frame. ,
Referring particularly to Figure 2, attitude frame
('3) has suspended beneath it a blower housing (11) which
CA 02057000 1999-11-OS
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is connected via trunking (12) to a control box (13) which
incorporates valve gear for controlling the flow of pressurised
air to individual air sacs (14) and also for supplying air to
bellows (20 & 21) for raising and lowering the foot and head of
the bed sections which form the contour frame (8). The bed
sections forming the contour frame are linked together by
appropriate hinges (not shown), except for the head section (25)
of the contour frame ( 8 ) which incorporates a sliding hinge which
slides on the attitude frame (3). The general arrangement of the
air sac air flow control means, CPR emergency release handle (26)
are generally as described in our published PCT application WO
86/06624. As previously mentioned, the air sacs (14) are not all
of the same shape, although they are generally of a lozenge shape
and are removably attached to the sections forming the contour
frame (8) . In order to provide the nesting cavities within which
the patient can be supported, the air sacs are shaped as shown
in Figure 3A to 3C. As can be seen from the end views of these
air sacs, their surfaces are profiled according to their location
in the patient support surface formed by the contiguous air sacs .
The air sac shown in Figure 3C is shaped by stitching or gluing
to provide an upper surface with a single gap (31) suitable for
supporting the head of the patient whereas
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the air sac (3B) which is located further down the head
section of the contour frame is provided with a bigger gap
in its top surface (32) for accommodating the shoulders of
the patient. In a similar manner, the air sac shown in
Figure 3A incorporates two depressions (33) in its top
surface within which the patient's legs can be lifted.
It will be appreciated.that differently shaped air sacs or
air sacs of different dimensions may be selected and
fitted to the contour frame depending on th,e size and
weight of the patient.
The mechanism for raising and lowering the patient
support surface of the bed and for pivoting the attitude
frame about its longitudinal axis is shown in detail in
Figures 4, 4A to D, 5, 6, 7 and 8.
deferring particularly to Figures 4 and 6, the
actuator (15) includes an electric motor (41) drivably
engaging a threaded lead screw (42). To the free end of
lead screw (42) is pivotably connected a lever (43),
Lever (43) is fixedly attached to a shaft (44) mounted in
the trolley frame (1). A pair of spaced levers (45
45a) are also fixedly attached at one end to shaft (44)
and at their outer end pivotably connected to :,the lower
end of actuating arm (4). '.As mentioned above, actuating
arm (4) is in the form of an A-frame having legs (S1 &
61a). The lower ends of the A-frame (4) are joined by a
shaft (65), the ends of which are received in b~arings~ in
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the outer ends of levers ( 45 & 45a ) . ' .. .
As best seen in Figure 4b and Figure 5, the apex of
the A-frame (4) is welded at its upper end to a trunnion
(47) within which is mounted, within a suitable bearing, a
shaft (48). As a result, attitude frame (3) is able to
rotate about shaft (48) which comprises the longitudinal
pivoting axis of the bed.
. At its opposite end from lead screw (42) actuator
(15) is pivotably attached to a bracket (46) mounted an
the trolley frame (1). Thus, when lead screw (42) is
extended, levers (43, 45 & 45a) act together as a bell
crank lever causing shaft (44) to rotate in an anti-
clockwise direction and actuating arm (4) to rise.
A similar arrangement is provided at the foot end of
the bed where actuator (16) incorporates a motor (50) and
lead screw (52). The actuator (16) is anchored to the
trolley frame (1) by bracket (53) and at the other end is
pivotably connected to a lever (53) whose remote end is
fixed angularly to a shaft (54), which is pivotably
mounted within frame (1). Shaft (54) also carries an
angularly fixed lever (55), to the opposite end of which
is pivotably attached arm (5). At its upper end, arm (5)
is.rotatably secured within a trunnion (56) mounted on the
underside of the attitude frame (3). Details of
construction of trunnion (56) are shown in Figure 4A, from
which it will be seen that the trunnion incorporates a
universal joint (58) which enables pivoting movement of
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the attitude frame (3) about shaft (57) as-well as limited ..
angular movement between arm (5) and the plane within
which attitude frame (3) lies. Figure 4C shows the
bearing located between arm (5) and lever (55). In order
to bias the attitude frame (3) into a horizontal position
compression springs (62a & b) extend between the attitude
frame (3) and the cross shaft (65). As an alternative,
other means. of damping or biasing 'the movement of the
attitude frame may be employed such as gas struts in place
of the springs. Only one end of the gas struts or springs
is fixed so that they function only in compression.
The turning mechanism is shown in more detail in
Figures 5, 7 & 8. In principle, a quadrant (64) is farmed
with taothing to form a curved rack and is fixedly
attached to the A-frame (4). A motor (62) is carried by a
supporting plate (66) which is fixed to the attitude frame
(3). Motor (62) is arranged to drive a pinion (67) which
is engageable with the curved rack of the.. quadrant (64)
and the arrangement is such that with the pinion engaged
with the rack, operation of the motor causes the attitude
frame to turn about the axis of the trunnion (4?),
In practice, the motor (62) includes a gear box (68)
which reduces the speed of the pinion to an appropriate
rate. It has been found that an appropriate speedy for
the pinion is about 2 rpm. In an emergency'when it is
desired to return the bed rapidly to the horizontal '
WO 9()/14816 PCT/GB~)It/1)0829
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position, the pinion sgeed may be increased.
A DC electric motor is preferred for several reasons.
First, the shaft speed has a linear relationship with the
applied voltage. Therefore, the rate of turning can be
accurately determined and controlled by regulation of the
voltage. Secondly, the low voltages employed make the bed
electrically safe. Thirdly, the bed can be operated by
on-board batteries which makes the bed truly portable.
Normally, a battery charger will be . included and a
rectifier for operating from a mains voltage supply. We
currently prefer to employ a DC motor such as the
"pancake" motors manufactured by Printed Motors Limited of
Bordon, Hampshire, England. These motors deliver high
torque at low speed, e.g. 900 rpm at 6 volts and exhibit
an almost exactly linear speed/volt age relationship.
Thus, the pivoting speed of the attitude frame can be
controlled by connecting the turning motor (62) to the
central processor board via the relay board and regulating
the applied voltage in accordance with the pragrammed
turning speed (see Figures 9 to 11).
The quadrant (64) is readily manufactured by flame
cutting a disc of appropriate radius into four pieces and
milling teeth to correspond with the setting of the pinion
teeth.
The motor and gear box assembly (62 & 68) are bolted
onto a supporting plate (69) which is itself pivotably
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mounted on bracket (66) by shaft (70). Connected to the
end of plate (69) remote from shaft (70) is a push rod
(71), the opposite end of which is clamped to one 2nd of a
shaft (73) mounted in a side cheek of the attitude frame
(3). Shaft (73) can be rotated in a clockwise or anti-
clockwise direction by gushing or ;pulling on rods (74 or
75) which are actuatable by levers (76 & 77), conveniently
located at each side of the bed. Pulling on lever (76 or
77) will disengage the pinion (67) from the rack (64), so
that in an emergency, the bed can be returned manually to
a horizontal position. The engagement/disengagement
mechanism provided by rods (74 & 75) and associated
actuating rod (71) are linked by a shaft which moves over .
centre between two stable positions defining engaged and '
disengaged conditions of the motor and rack. When the
motor is disengaged, the attitude frame (3) is held in a
horizontal plane by the two compression sgrings (62A &
62B). However, for further security, a dog clutch may be
mounted on the motor gear box and engage in an apertured
bar so as to effectively lock the attitude frame to the A-
Frame (4).
The control panel is shown in Figure 9 and is mounted
on the face 80 of control box 13 (see Figure 2). This
includes an electrical mains indicator E, a blower switch
F and a CPR lever G. Operation of the CPR lever. will
cause air to be dumped from the main~air feed from the
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blower, thus causing all sacs to deflate rapidly and the
bellows to deflate. The CPR lever is also linked to the
actuator control thus bringing the bed to harizontal. The
screen A is the temperature adjustment and display and
shows the temperature of air passing through the sacs.
Knobs H are linked to the valves fo:c air supply to the
individual sections 22 to 25 and provide the control tar
individual pressure control to each group of sacs.
However, all the air sacs can be simultaneously inflated
to full blower output pressure by pulling out knob J.
This is used for assisting the patient on and off the bed.
Light B is a warning light and draws attention to an alarm
warning in the corresponding position in the display panel
C, (see also Figure 10).
The bed includes a potentiometric tilt sensor
manufactured by Penny & Giles, which sense the angle of
the attitude frame and provides a feed back to the
microprocessor unit. This operates in the same way as
the contour angle sensors (18 & 19) mentioned above. The
output from this sensor is the third analogue input
indicated in Figure 11. Alternatively, another type of
pendulum sensor, e.g. a mercury switch, may be used. In
this' way, the maximum angle of tilting can be preset so
that the bed frame will commence turning in the opposite
direction once the maximum tilt angle has been reached. A
delay may be selectable so that there is a variable dwell
at some point in the sequence.
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The control system for the bed is shown in the block
diagram of Figure 11. From Figure 11, it will be seen
that all controls, sensors and display devices are linked
to the microprocessor control board, which controls the
operation of all the functions of the bed.
Operation of the bed is divided into two main modes:
1. Standard Low Air Loss (LAL) system use,
2. Turning mode.
The system automatically enters operating mode 1 upon
power up. In this mode the control system receives input
from 'transducers which are displayed on the screen (see
Figure 10). Indicators to set desired pressures can be
set in this mode from keypad input (101). Inputs from CPR
switch, Power Loss and Full Inflate are also monitored in
this mode. All hand control functions which control the
beds standard functions, i.e. tilt, posture and high low
are available.
Upon selection of turning mode the turning parameters
can be set by keypad input (101), once parameters are set
they are displayed. The system checks all safety switches
and if found to be correct, turning can begin. While
turning is in progress all inputs including CPR Qower Loss
and Full Inflate are continually monitored.., In this
mode, the Hand Control functions may be inhibited to allow
the bed to turn safely within pre-set limits..- If these
pre-set limits are exceeded, advisory messages are also
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displayed to indicate which fault conditions exist. Alarm
messages are also displayed i:E the various alarm
conditions are met.
During the turning cycle the bed can be stopped from
turning or the dwell-time can be frozen to allow a nursing
procedure to take place. The be.d c:an then be restarted to
continue Sts last operation or returned to a level
position.
The cycle of automatic turning and dwell time
continues until either a keypad input returns the bed to
Mode 1 or the CPR switch is operated.
In order to avoid problems arising from the attitude
frame being impeded by obstructions such as furniture or.
visitors, the attitude frame is fitted with a
circumferential D-section inflated tube. This tube is
connected to a pressure sensitive switch which is
activated when the tube presses against an obstruction and
therefore increases the pressure in the tube. On
activation the switch sends a signal to the microprocessor
which in turn causes the turning motor to reverse and thus
move away from the obstruction. Simultaneously, the
display panel will indicate the presence of an
obstruction. Instead of an inflated tube, an infra-red
detector may be used.
The control system includes a third mode called the
maintanance or service mode. In this mode, the
microprocessor is programmed to check the operating
1fO 90114816 PUT/GBoll/110829 '
functions of the bed and to indicate in the display panel
A any malfunctions.
As indicated in Figure 11, the control means includes
an output port and an ancillary grinter or recording
device (e. g. a tape cassette). This enables the clinician
or nurse to print out from the microprocessor store, data
concerning the sequences which the bed has performed, e.g.
over the last few hours or days and provides a record of
the treatment.
