Evaluation of transducer performance for buttock-cushion interface pressure measurements.

To assess the performance of transducers used clinically to measure pressure at the skin-cushion interface of seated patients, transducers were placed between slabs of gel and/or foam materials compressed between platens. The recorded pressures consistently exceeded the nominal pressures calculated using the surface area of the slabs. This overestimation, observed in both miniature diaphragm transducers and air cell transducers, appeared to result from preferential loading of the transducer due to insufficient structural compliance in the environs. On the other hand, air cell transducers placed at a skin-foam interface beneath the thighs of human subjects gave readings which agreed closely with subcutaneous tissue pressure measurements obtained from a wick catheter inserted at the same location. These results suggest that, although pressure measurements are prone to error due to load sharing, results obtained clinically from subjects on soft cushions are reasonably accurate because of the high compliance of human soft tissue and the foam. Under low loads these distribute the pressure equitably and avoid concentrations of load on the transducer.