A comparison of changes in rhythms of sacral skin blood flow in response to heating and indentation

Objective: To differentiate blood flow control mechanisms associated with indentation from those associated with heating and to discern heat-induced and pressure-induced changes by comparing the effect of externally applied stress on skin blood flow (SBF) to the response to externally applied heat. Design: Repeated-measures design. Participants: Ten healthy, young adults (5 men, 5 women; mean age +/- standard deviation, 30.0 +/- 3.1y). Intervention: Incremental heat (35 degrees-45 degrees C, 1 degrees step/min) and pressure (0-60mmHg, 5mmHg step/3min) on the sacrum using a computer-controlled indenter. Sessions for heat and pressure protocols were separated by 7 +/- 2 days. Main Outcome Measures: We used a Laserflo Blood Perfusion Monitor 2 and Softip pencil probe to measure capillary blood perfusion and wavelet analysis to decompose the blood flow signal. The power spectrum was divided into 5 ranges corresponding to metabolic, neurogenic, myogenic, respiratory, and cardiac control mechanisms. The average relative (ie, normalized) power in each frequency range was computed to determine of the relative contribution of each control mechanism. Results: Power in the myogenic frequency range was higher after incremental pressure and lower after incremental heating, whereas power in the metabolic frequency range was lower after incremental pressure and higher after incremental heating (P <.01). Mean blood flow decreased as pressure increased from 0 to 15mmHg; mean blood flow increased as pressure increased from 15 to 60mmHg. Conclusions: SBF, as recorded by the laser Doppler, suggests that there may be a myogenic control mechanism mediating blood flow after incremental tissue loads and that a metabolic control mechanism may mediate blood flow after heat application to the tissue. The study of local blood flow control mechanisms and their response to pathomechanical perturbations may be possible using wavelet analysis of blood flow oscillations. More research is needed to establish the clinical utility of these findings in the development of support surfaces intended to reduce the risk of developing pressure ulcers.