ASSESSMENT OF BALANCE

Abstract: Apparatus for and a method of assessing balance performance has a platform (11) which overlies a baseplate (10). At least two flexible tubes (12 and 13) are positioned between the baseplate (10) and platform (11) with at least the major part of each such tube positioned below a defined area A and B respectively of the platform. Each tube (12, 13) is closed and is connected to one or more differential pressure transducers (16) in such a manner that the electrical output (17) from the or each transducer depends upon the relative pressures of the tubes (12, 13) connected thereto. The electrical outputs (17) are analysed by a processing unit which drives a display to provide real-time feedback to a user of the apparatus, indicative of the user's balance performance.

Description: ASSESSMENT OF BALANCE This invention relates to apparatus for use in the assessment of balance performance, and to methods of assessing balance performance using preferred kinds of apparatus of this invention. Physiotherapists and other clinical staff often have to treat patients having an impaired balance performance. The enhancement of balance performance, may assist in the recovery from an injury, in the treatment of various conditions, or to improve general performance for example of an athlete or gymnast. It has been established that the posture and gait of a person can often be improved by monitoring the load carried by each foot, and then displaying to the person essentially in real time those loads in such a way that he may himself ad ust the loads until they are substantially the same. In effect, a closed-loop system is set up, allowing a user to observe and correct primarily his balance and perhaps also his posture. For example, it has been established that if a person suffers from disease of the joints or from post-injury trauma, the loads carried by the two feet may differ greatly, but by allowing that person to monitor and adjust those loads in the manner described above, rapid improvements in the condition from which the person is suffering may be obtained. There have been various proposals for apparatus suitable for monitoring the balance performance of a person. Most proposals use some kind of platform on which the person stands or sometimes sits, the platform being provided with appropriate weighing devices, m order to determine the loads applied to the platform. For example, there may be provided two separate platforms, one for each foot respectively, and each platform being supported on a number of load cells, whereby a load imposed on the platform produces an electrical output indicative of the load. Another arrangement is described in our own International Patent Publication No. WO 93/21825. Here, each foot platform is supported by beams which bend resiliently under the imposed load, strain gauges providing an electrical output dependent upon the bending of the beams. A problem associated with the known forms of balance performance apparatus is that the platform tends to have a significant thickness. A person having, for example, chronic joint disease may experience considerable difficulties lifting first one foot and then the other on to the platform. Moreover, the eyes of the person using the platform will then be at an unusual level, and even though that may be only 25 to 50mm higher than usual, that can itself affect balance performance. In addition, having regard to the physical structure of the known platform arrangements described above, the apparatus for assessing balance performance tends to be somewhat complex and so also expensive. A processor for the output from the strain gauges or load cells, as appropriate, also has to be relatively sophisticated, in order to produce a useful output in real time, and also to permit proper calibration of the platform. It is an aim of the present invention to address the above problems associated with known forms of balance performance assessment apparatus, and so to provide apparatus which is relatively simple and which may be constructed with a relatively small vertical extent. According to one aspect of the present invention, there is provided apparatus for use in assisting the determination of balance performance, comprising a base plate, a platform overlying the base plate, a plurality of flexible tubes disposed between the base plate and platform with at least the major part of each tube being positioned within a respective area of the platform, each tube defining a closed volume and the tubes being connected to one or more differential pressure transducers in such a manner that the one or more transducers provide an electrical output dependent upon the relative air pressures in the tubes. In its simplest form, there are only two flexible tubes disposed between the base plate and the platform of the apparatus of this invention, with at least a major part of the length of a first tube being positioned within a first area of the platform and at least a major part of the length of a second tube within a second area of the platform. A person may then stand with one foot on each area respectively and supported by the air pressure within the first and second tubes each of which defines a closed volume and is connected to a common differential pressure transducer. Should the load on the person's two feet be different, there will be a resultant pressure difference in the tubes and the differential pressure transducer will then yield an electrical output indicative of both the magnitude of that difference and which is the greater. That output may then be used to drive a suitable real time display. As the apparatus requires only a base plate and a platform overlying that base plate with a spacing sufficient to accommodate the tubes, the overall height of the apparatus may be made very small and typically 10 to 12mm. Consequently, the apparatus itself will have a smaller influence on the balance performance of a person than is the case with known forms of apparatus . The first and second areas of the platform may be substantially rectangular and disposed immediately adjacent each other. Each area may carry suitable markings to indicate where a person should place his feet, when using the apparatus. Though the platform defining the two areas may comprise a single substantially rigid sheet, in a preferred form of the apparatus, the first and second areas of the platform are respectively defined by two separate platform sections free to move independently of one another. In this case, a common flexible membrane may be disposed over both platform sections, that membrane carrying said markings. For the arrangement described above, the first and second tubes may be defined by a single length of tubing having its two ends connected to the transducer, that single length of tubing being closed - for example by clamping or folding - at a location part-way between its two ends, thereby to define the two tubes. In a more complex form of the invention, there are three or even more flexible tubes disposed between the base plate and the platform, at least a major part of the length of each tube being disposed within a respective area of the platform and each tube being connected at its two ends to two separate differential pressure transducers. In this way, each transducer would be common to two different tubes and provide an electrical output dependent upon the pressure difference in those tubes. For example, three tubes with three differential pressure transducers may be employed generally in a circular configuration, or four tubes with four differential pressure transducers, in a generally rectangular configuration. In any of the above arrangements, the platform may be divided into as many sections as there are tubes, with each platform section being separate from and free to move independently of the others, as has been described hereinbefore. The apparatus of this invention may include processing means acting on the outputs of the or each pressure transducer, which processing means drives a display device indicative of the prevailing pressure difference or differences in the tubes. For example, a graphical display device may be employed, having a linear array of light sources. The processing means may illuminate selected light sources to show the relative pressures and so the effective balance performance. It will be appreciated that the processing means may perform a reset cycle prior to use of the apparatus to assess balance performance, and during the course of that reset cycle, any pressure imbalance with no load applied to the platform may be taken into account. Thus, the display device may electronically provide a bias so that a zero-imbalance indication may be given when no load is applied to the platform, even if the pressures in the two (or more) tubes are unequal. According to a second aspect of this invention, there is provided a method of determining balance performance using apparatus including processing means, as described above, in which method the processing means processes the electrical output from the or each differential pressure transducer and drives a graphical display device in real time to give a visual display of balance performance. Such processing may apply correction factors as appropriate to the or each electrical output, having regard to the number of transducers, the arrangement of the tubes below the platform, whether the platform is in separate sections, and the way in which the apparatus is being used. For example, in the case where there are two tubes disposed below respective separate platform sections, a person may stand with each foot wholly on a respective section. In this case, in order to determine left-to-right balance performance, no correction factor need be applied to the output obtained from the transducer. Such a platform may instead be used to determine front to back balance performance, in which case a person should stand with each foot bridging the two platforms. In this case, correct balance performance is obtained with one third of the total load in the ball area of a person's foot and two thirds in the heel area; the processing means may apply a suitable correction factor in order that the display device properly indicates balance performance for that use. In addition to the above, the processing means may be arranged to allow setting of a suitable full scale deflection for any given person. For example, and in the case of lef -to-right balance, that person may stand with no load on one foot, and then no load on the other foot. This will give maximum pressure differentials both to the left and to the right and thereafter the processing of the transducer output may be appropriately scaled in order to obtain a display of maximum use to the person. In the case of a more complex form of the apparatus, having more than two tubes, the processing means may be able to assess balance performance in more than one direction, simultaneously. In this case, the display device should appropriately be configured to allow a real time display of balance performance in all of the assessed directions simultaneously. By way of example only, one specific embodiment of the present invention will now be described in detail, reference being made to the accompanying drawings in which:- Figure 1 diagrammatically shows a plan view of a simple form of a first embodiment of apparatus of this invention; Figure 2 is a vertical section through the apparatus of Figure 1 ; Figure 3 is a vertical section through an alternative form of the first embodiment; Figure 4 diagrammatically illustrates a complete apparatus as shown in Figure 3, including a display device; Figure 5 shows use of the apparatus of Figure 4, in an alternative mode; Figure 6 further illustrates the alternative mode of use of the apparatus; Figure 7 is a plan view on a more complex form of apparatus forming a second embodiment of this invention; Figure 8 diagrammatically illustrates a complete balance performance monitor using the apparatus of Figure 7; and Figure 9 diagrammatically illustrates a third embodiment of this invention. Referring initially to Figures 1 and 2, a platform assembly for use in an overall balance performance monitor constructed and arranged in accordance with the present invention comprises a base plate 10 and a platform 11 of substantially the same shape and dimensions as the base plate. The platform 11 overlies the base plate, with two flexible tubes 12 and 13 disposed therebetween. The tubes typically may be made of silicon rubber and are closed at their one ends 14 and 15 respectively. The other ends of the tubes are connected to a common differential pressure transducer 16, which provides an electrical output 17 indicative of any air pressure difference between the two tubes. It will be appreciated that if a greater load is imposed on area A of platform 11 than is imposed on area B, the air pressure in tube 12 will rise to a higher pressure than that in tube 13. The electrical output 17 will be proportional to the difference m pressure and will also indicate on which side the greater pressure appears. For example, with zero- pressure difference a zero electrical output may be provided, and if the load imposed on area A is greater than on area B, then the electrical output may move in the positive direction. Conversely, for a lower pressure in tube 12 than in tube 13, the output may move negatively. Figure 3 shows a modified form of the apparatus of Figures 1 and 2. Here, the platform 11 is divided into two platform sections 18 and 19, with tube 12 lying below section 18 and tube 13 below section 19. In addition, the space between the base plate 10 and platform 11 is filled with a resilient foam material 20, to give additional support to the two platform sections . Figure 4 shows the platform assembly of Figure 3 incorporated in an overall balance performance monitor. It can be seen that the platform sections 18 and 19 each carry a foot marking, to assist a person in the proper placement of his feet. The electrical output 17 from the transducer 16 is supplied to a processing unit 21 , which in turn drives a graphical display device 22 including a linear array of light emitting diodes 23. Merely for the user's convenience, the LEDs 23 are contained within a double-headed arrow 24. The processing unit 21 is arranged to perform a reset cycle before a person stands on the platform assembly. During this, the processing unit applies a suitable correction to the electrical output 17 such that with no load on either platform section 18 or 19, the central LED 25 is illuminated, irrespective of the actual pressure difference within the two tubes 12 and 13. Next, a person stands on the platform assembly with each foot in the appropriate area as marked on the platform sections and places his entire weight on one platform section. The processing unit determines the pressure difference which then prevails and illuminates the associated extreme LED in the display device; this process is repeated for the other platform section to set the full scale deflection in the other direction. Following the initialisation as described above, a person may stand normally on the platform assembly and the display device 22 will, by appropriate illumination of the LEDs, give a real time display of actual balance performance. Figure 5 illustrates essentially the same apparatus as has been described above with reference to Figure 4, except that the platform sections 18 and 19 carry markings for the user's feet at 90° to those markings shown in Figure 4. The user will then have his heels on platform section 19 and the balls and toes of his feet on platform section 18. Correct front-to- back balance is achieved when a person has two thirds of his total weight supported on his heels and one third on the balls of his feet, as shown in Figure 6. Thus, a zero-imbalance indication should be given when the load imposed on platform section 19 is twice the load imposed on platform section 18. The processing unit 21 may appropriately apply a correction to the output 17, to achieve this. Figures 7 and 8 show a more complex form of the apparatus described above. Here, the platform 30 is divided into four areas A, B, C and D, respective separate tubes 31, 32, 33 and 34 being disposed in each of those areas. Four differential pressure transducers 35, 36, 37 and 38 are provided, each connected to two adjacent tubes. In this way, four electrical outputs are obtained and are supplied to the processing unit 39, which drives a display device 40 having two linear arrays 41 and 42 of LEDs. As will be appreciated from Figure 8, the apparatus allows a simultaneous display of balance performance, in both the lef t-to-πght and front-to- back senses. In other respects, the apparatus operates much as has been described above, especially in relation to the initialisation routines. Another embodiment of this invention is illustrated m Figure 9. This employs three tubes 45A, 45B and 45C arranged within a generally circular platform 46, with the tubes connected to three transducers 47. A processing unit (not shown) operates on the outputs of those three transducers, to drive a suitable display. This embodiment of the apparatus may be used for balance performance assessment, either for a person standing on the platform or for a person sitting on the platform. The processing unit may include suitable software to allow sufficient analysis of the transducer outputs in order that a meaningful display of balance performance may be given. Such software may allow the analysis of lef t-to-right and front-to-back performance simultaneously, even though only three transducers provide outputs to the processing unit.

Claims: CLAIMS 1. Apparatus for use in assisting the determination of balance performance, comprising a base plate, a platform overlying the base plate, a plurality of flexible tubes disposed between the base plate and platform with at least the major part of each tube being positioned within a respective area of the platform, each tube defining a closed volume and the tubes being connected to one or more differential pressure transducers in such a manner that the one or more transducers provide an electrical output dependent upon the relative pressures in the tubes. 2. Apparatus as claimed in claim 1, wherein there are first and second flexible tubes disposed between the base plate and platform with at least a major part of the length of the first tube being positioned within a first area of the platform and at least a major part of the length of the second tube within a second area of the platform, the first and second tubes each defining a closed volume and being connected to a common differential pressure transducer which provides an electrical output dependent upon the relative pressures in the two tubes. 3. Apparatus as claimed in claim 2, wherein the first and second areas of the platform are each substantially rectangular and are disposed adjacent each other. 4. Apparatus as claimed in claim 3, wherein the first and second areas of the platform are respectively defined by two separate platform sections free to move independently of one another. 4. Apparatus as claimed in claim 3, wherein a common flexible membrane is disposed over both platform sections. 5. Apparatus as claimed in any of claims 2 to 4, wherein the first and second tubes are defined by a single length of tubing closed at a location part way between its ends thereby to define the two tubes. 6. Apparatus as claimed in claim 1, wherein there are at least three flexible tubes disposed between the base plate and platform, a major part of the length of each tube being disposed within a respective area of the platform and each tube being connected at its two ends to two separate differential pressure transducers, each transducer being common to two different tubes. 7. Apparatus as claimed in claim 6, wherein each area of the platform is defined by a respective platform section, each platform section being separate from and free to move independently of the others. 8. Apparatus as claimed in claim 7, wherein a common flexible membrane is disposed over all of the platform sections. 9. Apparatus as claimed in any of the preceding claims, and including processing means acting on the outputs of the or each pressure transducer, the processing means driving a display device indicative of the prevailing pressure difference in the two tubes. 10. Apparatus as claimed in claim 9, wherein the display device has a linear array of light sources, the processing means driving the display device to show by illumination of selected light sources the relative pressures in the two tubes. 11. Apparatus as claimed in claim 9 or claim 10, wherein the processing means is arranged to perform a reset cycle prior to use of the apparatus to assess balance performance, to display an apparent zero imbalance in the pressures in the tubes irrespective of the actual pressures in the tubes. 12. A method of assessing balance performance using apparatus as claimed in claim 9 or any claim dependent thereon, in which method the processing means processes the electrical output from the or each differential pressure transducer and drives a graphical display in real time to give a visual display of balance performance. 13. A method as claimed in claim 12, wherein the processing applies correction factors to the electrical outputs from the or each transducer. 14. A method as claimed in claim 12 or 13, wherein the processing of the electrical output applies a bias to that output in order that a zero-imbalance display may be given when no load is imposed on the platform.

Inventors: DAUGHTERY CHRISTOPHER, MALOY PETER, STOPPS MARTIN, WENMAN ALAN, DAUGHTERY, CHRISTOPHER, MALOY, PETER, STOPPS, MARTIN, WENMAN, ALAN
Applicants: DAUGHTERY CHRISTOPHER, MALOY PETER, SMS LTD, STOPPS MARTIN, WENMAN ALAN, DAUGHTERY, CHRISTOPHER, MALOY, PETER, SMS SANDLAND MANUFACTURING SERVICES LIMITED, STOPPS, MARTIN, WENMAN, ALAN
Application year: 1996
Main classification: A61B5
IPC codes: A61B5, G01G19