A new method for the fabrication of custom contoured cushion using pressure mapping

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A new method for the fabrication of custom contoured cushion using pressure mapping


Author: Sy, Pui-lam Carmen
Title: A new method for the fabrication of custom contoured cushion using pressure mapping
Degree: M.Sc.
Year: 2000
Subject: Bedsores -- Prevention
Cushioning materials
Hong Kong Polytechnic University -- Dissertations
Department: Multi-disciplinary Studies
Jockey Club Rehabilitation Engineering Centre
Pages: ix, 65 leaves : ill. (some col.) ; 30 cm
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b1541818
URI: http://theses.lib.polyu.edu.hk/handle/200/2338
Abstract: Wheelchair users commonly spend about 12 to 16 hours a day in sitting. In order to prevent pressure sore, they usually use a pressure relief cushion. Pressure relief characteristics, provision of seating stability and cost are important factors in choosing seating cushion. Although different degrees of pressure relief and seating stability could be provided by air, gel and custom-made contoured cushions, there is still a need to explore alternative methods to produce cushion of acceptable degrees of pressure relief and seating stability at a reasonable cost. With the advancement of technology, pressure mapping system is readily available for interface pressure assessment which is becoming one of the standard procedures for seating evaluation. With the aid of a pressure mapping system, interface pressure distribution and locations of high pressure areas could be quantitatively documented. The aim of this study was to explore the feasibility of using interface pressure data for fabricating custom-made contoured cushion at relatively low cost. Ten normal subjects (5 males and 5 females with mean age 30 and mean body mass 56kg) participated in this study. They were asked to sit on the pressure mat of a pressure mapping system (Tekscan System, USA) placed at the buttock-foam cushion interface. The pressure distribution was captured and outputted in actual physical dimension to produce a pressure contour map on paper. A simple mathematical model was devised for determining the cutting depth using the interface pressure data. The model utilized the mechanical properties of the foam material and the average pressure at the buttock/flat foam interface. The pressure contour map was then used as the template for a manual foam copying machine (Manual Contour Copier) to produce the required contoured cushion. In this study, the effects of the variable, "further deformation" (d), of the mathematical model were evaluated experimentally. Three contoured cushions with different cutting depths were made for each subject with the d value set at 1, 3 and 5mm. In order to evaluate the performance of the contoured cushion made by the new method, pressure relief characteristics of the contoured cushions were compared with those of air (Roho), gel (Jay) and ordinary foam (flat foam) cushions. The pressure relief characteristics were quantified by the peak and average pressures over left and right ischial tuberosities and the total buttock-cushion contact area. The data were compared using repeated measures ANOVA. It was shown that flat foam cushion was the least effective in pressure relief. Contoured cushion with d=1mm was less effective in pressure relief than air and gel cushions. However, contoured cushions with d=3mm and d=5mm were more effective in pressure relief than the air and gel cushions. Both the air and gel cushions were found to have similar pressure relief characteristics. No significant difference in pressure relief was found between contoured cushions with d=3mm and d=5mm. It was observed that when the cutting depth of the contoured cushion was increased, the peak pressures at both ischial tuberosities tended to decrease whereas the peak pressure over the sacral region and total contact area tended to increase. As both the ischial tuberosities and the sacral region are areas of high risk of development of pressure sore, contoured cushion with d=3mm was recommended in order to obtain a good balance between the peak pressures at the ischial tuberosities and the sacral region. Further investigation of the effects of the contoured cushion made by the new method on relieving pressure for subjects with physical disabilities is suggested.

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