2003 Advances in Skin & Wound Care  
P ressure ulcers due to sustained unrelieved or inadequately relieved pressure are an important clinical, humanitarian, and economic problem. 1-3 Pressuredependent blood flow changes play a major role in the skin breakdown process, with the greatest breakdown frequency at sites of bony prominences. The heel is particularly prone to such effects, 4 in part because of its relatively lower resting blood perfusion level 5 and higher amount of surface pressure when under load. 6-9 Local blood flow
more » ... Local blood flow decreases during heel loading 5 and flow recovery after unloading are involved in the breakdown process. [10] [11] [12] Previous work has shown that when the pressure supporting the heel was cycled at different rates, the average blood flow over complete cycles was significantly greater when the level of pres-sure was zero (full release) when compared with a nonzeropressure value (partial release). 13 However, because only 2 levels of pressure relief were investigated, the blood flow effects of intermediary levels of pressure relief are unknown. The present study sought to characterize the flow responses of the heel to 3 separate pressure-relief levels when the heel was supported with a uniform load magnitude and duration. METHODS Subjects Twelve volunteers (7 female and 5 male), randomly drawn from the medical school student and staff population, were tested after signing an approved institutional review board consent form. All subjects were free of lower-extremity vascular disease ABSTRACT 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 pressurizationrelief 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.
doi:10.1097/00129334-200305000-00013 fatcat:zwvbyk3iufe7blqie3yscpm5ki