Dynamic interface pressure between seated users and their wheelchairs

Little is known about the dynamic pressure distribution changes that take place on the sitting surface of a wheelchair while one propels oneself on a level surface. An understanding of these dynamic pressure changes may influence the design of wheelchair seat cushions to minimize pressure sores in wheelchair users. This research investigated the dynamic interfacial pressure changes on the seated wheelchair user during short bursts of locomotion on a level surface. The pilot project included only able-bodied subjects who sat in sling-seat wheelchairs. Pneumatic bladders arranged in a flexible grid matrix (50 elements covering a 7.5″ × 15″ area) were instrumented with miniature piezoresistive pressure transducers and placed between the user and the wheelchair seat. One half of the subject/seat interface was instrumented: one-half-inch-thick foam covered the remaining half of the seat. Dynamic pressure distribution in the left and right halves was measured in separate trials for every subject. Each sensor element was sampled 10 times per second during the time it took the subject to traverse approximately 25 feet from start to stop. A trial lasted 5.6 seconds on average. The greatest shift in center of pressure observed for any trial was 3.15 inches. The lowest, static, and highest average pressures obtained were 14.2 mmHg, 27.8 mmHg, and 36.5 mmHg, respectively. The lowest, static, and highest maximum pressures were 42.0 mmHg, 135.0 mmHg, and 178.8 mmHg, respectively. There was no significant difference in location between the lowest and highest maximum pressures. The sizes of the buttock area in which pressure exceeded 35 mmHg were determined for smallest area, static, and largest area conditions. These were 2.25 sq.in., 27.0 sq.in, and 47.25 sq.in., respectievly.