Jan YK, Brienza DM, Geyer MJ; Department of Rehabilitation Science and Technology, University of Pittsburgh, Pittsburgh, PA. yij2@pitt.edu.

PURPOSE: Prevention of pressure ulcers and enhanced tissue integrity may be possible using alternating pressure (AP) support surfaces. AP appears to stimulate a protective increase in skin blood flow (SBF), but the mechanism by which this occurs is not well understood. Our studies on AP and skin blood flow are confounded by both the interrelated control mechanisms (metabolic, neurogenic, myogenic, cardiac, and respiratory) and stimuli effecting SBF. In this study we have used a technique for analyzing SBF that allows us to measure the effects mediated by specific control mechanisms. Discerning heat induced and pressure induced changes will allow us to study and develop AP technology. SUBJECTS: Ten healthy subjects (5 female, 5 male) were recruited to participate in the study. The following exclusion criteria were used: the presence of pressure ulcers on the sacrum, diabetes, vascular disease, hypertension, spinal cord injury, or use of vasoactive medications. METHODS: Participants were subjected to incremental heat (35 to 45°C, 1° step/minute) and pressure (0 to 60 mmHg, 5 mmHg step/ 3 min) on their sacrum using a computer-controlled indenter. Incremental loading was preceded by a 10-minute period for baseline measurement and a followed by a 10-minute period to observe recovery. Sessions for heat and pressure protocols were separated by 7 ± 2 days. A Laserflo Blood Perfusion Monitor 2 (BPM²) (Vasamedics, MN) and Softip pencil probe (P-435) were used to measure capillary blood perfusion. ANALYSES: Wavelet analysis was used to decompose the blood flow signal. The power spectrum was divided into five ranges corresponding to metabolic, neurogenic, myogenic, cardiac and respiratory control mechanisms. The average relative (i.e. normalized) power in each frequency range was computed for the baseline and recovery periods. Comparisons were made using paired t-tests. Trends were analyzed for incremental loading periods. RESULTS: Power in the myogenic frequency range was higher after pressure and lower after loading while power in the in the metabolic range was lower after pressure and higher after loading. Mean blood flow decreased as pressure increased from 0 to 15 mmHg and increased as pressure increased from 15 to 60 mmHg. Mean blood flow increased as temperature increased. CONCLUSIONS: Pressure induced a myogenic mediated increase in SBF and heat induced a metabolic mediated increase. FUNDING SOURCE: Department of Veterans Affairs, Rehabilitation Research and Development Service (grant no. F2181C).

Copyright 2004 by the American Physical Therapy Association

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