Repeatability of subject/bed interface pressure measurements

The repeatability of a technique for measuring interface pressures has been assessed. Pressure was measured using a Talley SA500 Pressure Evaluator under six anatomical sites (occiput, scapula, elbow, sacrum, buttock, and heel) of six healthy subjects lying supine on a Clinifloat mattress (trademark, SSI). For each site of each subject, four repeat readings were taken per day on four separate days. Mean pressures varied significantly between subjects (p < 0.02), though differences in mean pressures between sites were greater. Pressure was not significantly related to subject mass. The overall repeatability of the technique was +/- 0.77 kPa (+/- 5.8 mm Hg) which was much smaller than the range of pressures found under different sites (2.72 kPa or 20.4 mm Hg at the sacrum to 9.00 kPa or 67.5 mm Hg at the heel). Repeatability varied from site to site, from +/- 0.47 kPa (+/- 3.5 mm Hg) at the buttocks to +/- 1.20 kPa (+/- 9.0 mm Hg) at the heel. Measurements were found to vary significantly more between days than between repeats on the same day (p < 0.02).