The recovery characteristics of soft tissues following repeated loading.

Pressure relief at the patient support interface is important to avoid tissue breakdown by ischemia, particularly with debilitated subjects. However, there are still few guidelines to indicate the level of relief required for specific tissue areas. This paper examines the nature of the tissue recovery to repeated loading in compression. Loading was produced by (1) external application using an experimental system attached to the sacrum and (2) ischial support on a dynamic cushion. In both cases, the interface pressures applied for a prescribed time were related to changes in transcutaneous gas tension, the latter being an index of tissue viability. Results indicate two distinct responses to repeated loading. The normal response provides rapid and complete tissue recovery to unloaded values of transcutaneous oxygen tension. This was observed with all normal subjects and some of the debilitated subjects. There was also a group of debilitated subjects who demonstrated impaired and delayed tissue recovery. It is proposed that they are at most risk of developing tissue breakdown.