SPECIFICATIONWheelchair cushion monitor and alarm apparatusThe present invention relates particularly, but not exclusively, to monitors and alarms for use in reminding patients with limited movement to perform movements at regular intervals in order to reduce the risk of developing pressure sores.
The invention is particularly suited for use with wheelchair bound patients.
The development of pressure sores is principally dependent on the amount of movement of the patient at the support surface and on the magnitude of pressure developed thereat. Knowledge of the amount of movement, the pressure magnitude and the time over which the movement and/or magnitude is maintained can indicate whether the patient is likely to develop pressure sores; the less movement and the greater the pressure time product the more likely the patient is to develop pressure sores.
There have been proposed several devices which monitor the movement and the pressure magnitude over a period of time and which provide an alarm if an insufficient amount of movement occurs or if a particular level of pressure has been exceeded for too long (Fordyce and Simons (1968), U.S. Public Health Rep. 83, 527-528; Malamentetal (1975), Arch. Phys.
Med. Rehab, 56, 161-165; and Chawla,Andrews and Bar (1978), Paraplegia 16, 413419).
In addition, in the Chawla device the patient was given an opportunity to prevent the audible alarm by performing a push-up in a predetermined time after a visual indication was presented. A counter was also used which actuated the alarm if a push-up of the required duration was not achieved. A further counter also counted the time by which the patient exceeded the predetermined time, called the error time.
The results obtained with these devices indicate that despite the alarm signal, which may be audible or visual, wheelchair patients do not tend to relieve pressure at regular intervals. In addition, the relatively rapid frequency of the alarm reminders (usually at a predetermined interval up to 20 mins.) is tiresome for the patient and is often socially embarrassing. Furthermore these devices showed that although push-ups of sufficient duration were performed these tended to be at unregular intervals.
An object of the present invention is to obviate or mitigate the abovesaid disadvantages.
According to a first aspect of the present invention there is provided a feedback method for monitoring and controlling the duration of pressure relief between a supporting surface and a supported surface comprising, monitoring the duration of pressure relief with sensing means located in the supporting surface or in the supported surface, continuously accumulating the duration of pressure relief and comparing the accumulated value with a first predetermined value of time over a first period of time in a counting and comparison means, at the end of said first period of time providing an output signal from said counting and comparison means to variable timing and control means, said output signal actuating said variable timing and control means from a first timing mode into a second timing mode for a second timing period when the value of the accumulated duration of pressure relief, at the end of the first period, is less than the first predetermined value of time, said variable timing and control means actuating an alarm after a preset time interval in said second timing mode.
Preferably, when said accumulated duration of pressure relief at the end of said first period is greater than said first predetermined value of time, said variable timing and control means is reset in the first timing mode.
Alternatively, the monitored parameter may be representative of pressure, and at the end of the first period of time when the accumulated duration of pressure is greater than a second predetermined value of time, the variable timing and control means switches to the second timing mode.
Preferably, when the accumulated duration of time is representative of pressure and, at the end of the first period of time, is less than the second predetermined value of time, the variable timing and control means is reset in the first timing mode.
According to another aspect of the present invention there is provided apparatus for monitoring a parameter representative of pressure or pressure relief between a support surface and a supported surface comprising,a sensor responsive to said parameter and adapted to be located in the support or the supported surface,counting and comparison means connected to the sensor output for counting the duration of said parameter and for comparing said duration with a predetermined value of time,variable timing and control means connected to the output of the comparison means, and to theinput of the counting means,alarm means having one input connected to the output of the counting and comparisonmeans, and another input being connected to theoutput of the timing and control means whereby,in use, when the duration of pressure relief sensedin a first preset time is less than thepredetermined value, a first output signal is fed tothe alarm means, and at the end of said firstpreset time said variable timing and controlmeans switches to said second timing modewhen the duration of pressure relief sensed in asecond preset time is less than the predeterminedvalue of time, a second output signal from thevariable timing and control means is fed to theinput of the alarm means actuating the alarm.
Preferably, said apparatus has a second timingmeans connected to the output of the countingand comparison means said second timing meansbeing connected to said alarm means and beginning timing when sensor detects movements indicating a pressure relieved state and which stops timing when the sensor indicates a pressure applied state.
Preferably also, said sensor is a pressureactuated switch.
Alternatively, the sensor may be a pressure transducer.
Preferably also, said alarm means is an audible alarm.
According to yet another aspect of the present invention there is provided apparatus for monitoring the pressure or pressure relief between a support surface and a supported surface over a preset period of time comprising,a weight-actuated sensor for switching from a first state to a second state in response to applied weight,a first timing means having an input connected to the output of the sensor, said first timing means being actuated to count for a predetermined period when said sensor is in the second state, said timing means having a first output connected to one input of an alarm means, and producing an output signal at the end of said predetermined period,variable timing and control means having an input connected to the output of said first timing means, and an output connected to another input of said alarm means, said variable timing and control means counting the number of output signals from said timing means and comparing the number counted with a preset value, whereby, in use, when the number of output signals counted exceeds the preset value a second output signal is fed to the other input of the alarm means actuating the alarm, and in the first or second period when the number of counts is less than the preset value the apparatus remains in the respective period.
Preferably also, said sensor is a pressureactuated switch. Alternatively, the sensor may be a pressure transducer.
Preferably also, said alarm means is an audible alarm.
According to yet another aspect of the present invention there is provided apparatus for determining the movement of an individual with respect to a support over a preset period of time comprising, a sensor responsive to the movement or to the weight of an individual,a signal processing circuit connected to the output of the sensor controlling the apparatus to operate between a first period and a second period, said signal processing circuit being connected to an alarm means, the apparatus being insertable within tbe support surface and being free of connections to the exterior of the support surface whereby, in use, when less than a first predetermined number of movements is performed in said first period said apparatus is switched to said second period and when less than a second predetermined number of movements is performed in said second period said alarm means is actuated.
The apparatus is particulary envisaged for use in wheelchair cushions.
Embodiments of the present invention will now be described by way of example with reference to the accompanying drawings in which:~Fig. 1 is a block diagram of one circuit for use with the apparatus according to the first aspect of the present invention;Fig. 2 is a block diagram similar to Fig. 1 with a push-up timing circuit added;Fig. 3 is a block diagram of another circuit for use with the apparatus according to the second aspect of the present invention;Fig. 4 is a block diagram similar to Fig. 3 with some additional circuit components;Fig. 5 is a schematic diagram of the apparatus according to the present invention shown in place in a wheelchair cushion;Fig. 6 is a schematic diagram similar to Fig. 5 showing an alternative arrangement in the wheelchair cushion.
Referring now to Figs. 1 and 2 of the drawings, apparatus for determining the movement of an individual with respect to a support surface over a preset period of time comprises a movement sensor 1, an electrical circuit 2 for processing the signals from the sensor and an alarm connected to the circuit 2 for indicating when the required amount of movement has not been achieved.
The movement sensor 1 is a pressure-actuated switch which changes from an 'off-state' to an 'on-state' in response to weight being applied.
The weight of an individual or patient is sufficient to effect this change of state, and upon removal of this weight the switch reverts to the 'off-state'.
The sensor 1 and the other parts of the apparatus are located within the wheelchair cushion 21 shown in Figs. 5 and 6.
The electronic circuit 2 has a counter 4 with one input 4a connected to the output of the sensor 1 , the output 4b of the counter is connected to one input of a comparator 5, the other input Sb of the comparator being fed from the preset counter (not shown).
The output of the comparator is connected to one input 3a of the alarm 3 and to one input 7a of a flip-flop 7. The flip-flop 7 has a second input 7b connected to one output 8a of a mode timer 8.
The mode timer 8 has a second output 8b connected to a second input 4c of the counter 4.
In use there are two conditions: a first condition when the switch is loaded, i.e. in the onposition, and a second condition when there is no load applied, i.e. in the off-position. In the first condition the counter 4 is enabled and every time the patient moves to relieve load on the sensor 1, the counter 4 is incremented by 1. The number of movements is accumulated over a predetermined period of time and the accumulated number is continuously compared in the comparator 5 with the preset number. If the accumulated number does not equal or exceed the preset number within the predetermined time the comparator 5 produces an output signal which enables the flipflop 7 and the alarm 3.
When the switch is initially loaded into the onposition the timer 8 is in a first state called the monitor state. When this period expires the number of push-ups is counted and compared with the predetermined number. If the predetermined number is equalled the timer is reset in the monitor state. If the counted number is less than the preset number the timer switches to a second timing state called the alarm state. In the alarm state when a predetermined time has elapsed, say 10 minutes, and a push-up of a predetermined time has not been performed, the alarm is actuated. Each time the patient does a push-up of the required time the alarm is postponed for 10 minutes.At the end of the monitor period if the accumulated pressure relief time in the memory is still insufficient, the timer is reset in the alarm mode, if the accumulated pressure relief time is sufficient the timer is reset to the monitor mode.
This circuit is easily modifiable as shown in Fig.
2 to give an indication of the quality of 'push-ups achieved by wheelchair patients; the sensor is fed to a timer 9 in parallel with the counter 4 which only begins timing when the switch is opened.
The time for which the switch is opened is accumulated and compared with the preset value of time, and the output of the comparator 5 and timer 9 are combined, via a gate 10, so that the alarm actuates if less than the required number of push-ups are achieved within the given time or if the total push-up time is less than the preset value. This enables the quality of push-ups to be monitored and also stimulates the individual to provide push-ups of the correct quality.
Referring now to Fig. 3 of the drawings, apparatus for determining the movement of an individual with respect to a support surface comprises a pressure actuated switch 11, an electronic circuit 12 and an audible alarm 13. The electronic circuit 12 has a movement interval timer (MIT) 14 connected to the output of the sensor 1 The output 1 4a of the MIT 14 is connected to one input 1 3a of the alarm 13 and to one input 1 5a of a push-up error counter (PEC) 15. The PEC 15 has an output 1 5b connected to one input 1 6a of a flip-flop 16. The other input 1 6b of the flip-flop is fed from one output 1 7a of a mode timer (MT) 17. Another output 1 7b of the mode timer 17 is connected to another input 1 sic of the PEC 1 5. The output from the flip-flop 1 6 is connected to the other input 1 3b of the alarm 13.
In use there are two conditions; when the switch is loaded, i.e. in the on-position and when the switch is not loaded, i.e. in the off-position. In the first condition the MIT 14 is actuated and begins to count for a predetermined period, for example 15 minutes. If there is no movement during the counting an output signal is fed to the input 1 3a from the MIT 14 at the end of the counting period. If there is movement of a sufficient duration during the counting which interrupts the sensor output the timer is reset. The output signal is also fed to the PEC 15 and when the PEC receives the signal the counter is incremented by 1. After subsequently timed periods without a movement, successive output signals are fed to the alarm 13 and to the PEC 15, the counter accumulating the number of output signals and continuously comparing the accumulated number with a predetermined value.
If the predetermined value is exceeded the PEC provides an output signal which enables the flipflop 16. When this occurs the flip-flop 16 sends an output to the alarm 13 which actuates the alarm to produce an audible signal. The audible signal continues until the individual moves to relieve the load on the sensor, by doing a 'push-up' for example. When this occurs the MIT 14 is reset and the PEC 1 5 is also reset by the MT.
Thus this circuit provides an indication of the interval between movements, i.e. of the length of time for which the individual has been supported.
As shown in Fig. 4, a general reset timer (GRT) 18 can be connected to the sensor output. In the pressure relieved condition, or when the wheelchair is not in use, if this condition is maintained for a short preset time, called the push-up valid interval, e.g. 5 seconds, the MIT 14 is reset and the GRT 18 enabled. The GRT 18 causes the system to be reset if the pressure relieved state is maintained for a continuous preset period, e.g. 3 minutes.
Furthermore, the circuits shown in Figs. 1 4 could be easily modified to be actuated only when a particular level of pressure is exceeded. Thus a pressure/time profile could be monitored for each individual, the alarm being actuated when a particular value of the pressure/time integral is exceeded. This arrangement could be implemented by the insertion of a pressure monitoring circuit PMC (not shown) between the sensor and the timer or counter, with the PMC having a threshold so that an output signal is provided when the threshold is exceeded. An example of such a PMC would be an operational amplifier wired for differential amplifier operation, with one input being adjustable to set a variable threshold.
Referring now to Fig. 5 the apparatus is shown inserted in a wheelchair cushion 21, the cushion 21 having a cut-out 22 in which the electronics are located and being connected to the sensor 12 by leads 23. An alternative arrangement is shown in Fig. 6 with the sensor and electronics located in the one unit, in the centre of the cushion 21.
It may be understood that several modifications may be made to the apparatus as hereinbefore described without departing from the scope of the invention. For example, the sensor can be of any type responsive to weight or any other parameter which varies underload such as temperature. The alarm could be visual or audio/visuai. The circuitry hereinbefore described is designed to operate on power consumptionCMOS technology (complementary-metal-oxidesemiconductor) although it could be based on any other suitable logic system, e.g. TTL.
Thus there is provided apparatus for determining the quality and quantity of movement of an individual with respect to a support surface.
The combination of the portable autonomous device and the facility to switch between monitor and alarm modes depending on the movement history of the patient gives the apparatus according to the present invention advantages in that patients find it less tiresome and it produces a better patient response reducing the risk of pressure sores developing.
Claims (filed on 14 July 1982)1. A feedback method for monitoring and controlling the duration of pressure relief between a supporting surface and a supported surface comprising, monitoring the duration of pressure relief with sensing means located in the supporting surface or in the supported surface, continuously accumulating the duration of pressure relief and comparing the accumulated value with a first predetermined value of time over a first period of time in a counting and comparison means, at the end of said first period of time providing an output signal from said counting and comparison means to variable timing and control means, said output signal actuating said variable timing and control means from a first timing mode into a second timing mode for a second timing period when the value of the accumulated duration of pressure relief, at the end of the first period, is less than the first predetermined value of time, said variable timing and control means actuating an alarm after a preset time interval in said second timing mode.
2. A method as claimed in claim 1 wherein when said accumulated duration of pressure relief at the end of the said first period is greater than said first predetermined value of time, said variable timing and control means is reset in the first timing mode.
3. A method as claimed in claim 1 wherein the monitored parameter may be representative of pressure, and at the end of the first period of time when the accumulated duration of pressure is greater than a second predetermined value of time, the variable timing and control means switches to the second timing mode.
4. A method as claimed in any one of claims 1-3 wherein when the accumulated duration of time is representative of pressure and, at the end of the first period of time, is less than the second predetermined value of time, the variable timing and control means is reset in the first timing mode.
5. Apparatus for monitoring a parameter representative of pressure or pressure relief between a support surface and a supported surface comprising,a sensor responsive to said parameter and adapted to be located in the support or the supported surface,counting and comparison means connected to the sensor output for counting the duration of said parameter and for comparing said duration with a predetermined value of time,variable timing and control means connected to the output of the comparison means, and to the input of the counting means,alarm means having one input connected to the output of the counting and comparison means, and another input being connected to the output of the timing and control means whereby, in use, when the duration of pressure relief sensed in a first preset time is less than the predetermined value, a first output signal is fed to the alarm means, and at the end of said first preset time said variable timing and control means switches to said second timing mode when the duration of pressure relief sensed in a second preset time is less than the predetermined value of time, a second output signal from the variable timing and control means is fed to the input of the alarm means actuating the alarm.
6. Apparatus as claimed in claim 5 including a second timing means connected to the output of the counting and comparison means said second timing means being connected to said alarm means and beginning timing when sensor detects movements indicating a pressure relieved state and which stops timing when the sensor indicates a pressure applied state.
7. Apparatus as claimed in claim 5 or 6 wherein said sensor is a pressure-actuated switch.
8. Apparatus as claimed in claim 5 or claim 6 wherein the sensor may be a pressure transducer.
9. Apparatus for monitoring the pressure or pressure relief between a support surface and a supported surface over a preset period of time comprising,a weight-actuated sensor for switching from a first state to a second state in response to applied weight,a first timing means having an input connected to the output of the sensor, said first timing means being actuated to count for a predetermined period when said sensor is in the second state, said timing means having a first output connected to one input of an alarm means, and producing an output signal at the end of said predetermined period,variable timing and control means having an input connected to the output of said first timing means, and an output connected to another input of said alarm means, said variable timing and control means counting the number of output signals from said timing means and comparing the number counted with a preset value, whereby, in use, when the number of output signals counted exceeds the preset value a second output signal is fed to the other input of the alarm means actuating the alarm, and in the first or second period when the number of counts is less than the preset value the apparatus remains in the respective period.
10. Apparatus as claimed in claim 9 wherein said sensor is a pressure-actuated switch.
11. Apparatus as claimed in claim 9 wherein the sensor may be a pressure transducer.
12. Apparatus for determining the movement of an individual with respect to a support over a
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