SEAT DESIGN FOR OPTIMAL LOAD TRANSFER TO SOFT TISSUES

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Pressure sores continue to be a common complication and costly clinical problem. Improved seat design using computer-aided technology has the potential to provide cost-effective seating systems that reduce risk of pressure sore development. The goal of this research is to improve custom seat design methods by investigating the biomechanics of the human buttocks-seat interface and applying the in vivo information to a computer-aided design process. The research hypothesis is that tissue viability can be enhanced using support surfaces systematically designed to optimize load transfer to buttock's soft tissue and reduce tissue distortion. In a preliminary study, a prototype of a computer-aided seating system (CASS) was designed to control support surface shape and measure interface forces. An adaptive control algorithm was developed and implemented on the prototype. Evaluation using tissue simulating test bodies demonstrated the feasibility to this approach. The resulting optimal support surfaces displayed the desired interface force and tissue stiffness characteristics. The specific aims of the proposed investigation are to: (1) complete the CASS development and implement the control algorithm on human subjects; (2) verify the characteristics of the support surfaces during and after the optimization procedure; (3) determine the clinical efficacy of realizing the optimal contours in polyurethane foams. An initial experiment using 10 able-bodied subjects (5 male and 5 female; ages 18 to 40) will be conducted to fine tune the control algorithm. The optimization criteria are based on in vivo force-deflection measurements of human buttocks' soft tissue. The algorithm is designed to iteratively update support shape to optimize load transfer using force and tissue stiffness measurements. Intermediate and final support surface force and tissue stiffness distributions will be analyzed using multivariate analysis of vectors (Hotelling's T2 statistic) for quantitative comparison. The optimal support surface will be carved into polyurethane foam using a personal computer based manufacturing system. The tissue stiffness distribution of the subject's buttocks while seated on the custom contoured foam will be compared to that on the rigid support of the CASS. This evaluation will determine the appropriateness of using compliant materials to implement the prescribed tissue load bearing characteristics. The second phase of the proposed investigation is to clinically prescribe custom contoured foam cushions for spinal cord injured, and elderly subjects. The protocol described above will be conducted on 20 paraplegic subjects (10 male add 10 female), 20 quadriplegic subjects (10 male and 10 female), and 30 elderly subjects (15 male and 15 female, age equal to or greater than 65), who depend on wheelchairs for mobility.