Effects of support surface relief pressures on heel skin blood perfusion.

Objective: To investigate the effect of pressure-relief magnitude on heel blood flow.

Design: 12 healthy subjects (5 male, 7 female; 21 to 43 years of age) lay on a support surface for 50 minutes with 1 heel on the end cell of the support surface. Cell pressure was computer controlled to vary cyclically at 5-minute intervals between a constant 20 mm Hg during loading and 10, 5, and 0 mm Hg during off-loading. Heel skin blood perfusion was monitored by laser Doppler probes on the heel and foot dorsum. Average skin blood perfusion during each 10-minute cycle and the hyperemic response after pressure relief were determined absolutely and relative to baseline.

Setting: University research center.

Results: An inverse relationship was found between relief pressure and heel skin blood perfusion over each pressurization-relief cycle and during the hyperemia phase. Full-cycle average skin blood perfusion associated with release to 0, 5, and 10 mm Hg were 34.1 +/- 7.5 arbitrary units (AU), 26.4 +/- 7.5 AU, and 9.3 +/- 3.3 AU, respectively (P <.001).

Conclusions: The reduced average skin blood perfusion is attributable to blunting of hyperemia when relief pressure is too high. When it corresponded to an interface pressure near diastolic pressure, little, if any, functional pressure relief or hyperemia is realized. Suitable relief pressures are likely dependent on an individual's diastolic blood pressure and the net tissue forces acting on heel blood vessels. This suggests that lower blood pressures need lower pressure-relief levels. It is suspected that if depressed vascular responsiveness and/or diminished hyperemic reserve is also present, even lower relief pressures are needed.