A Comparison of Changes in Rhythms of Sacral Skin Blood Flow in Response to Heating and Indentation

Abstract

Brienza DM, Geyer MJ, Jan Y-K. A comparison of changes in rhythms of sacral skin blood flow in response to heating and indentation. Arch Phys Med Rehabil 2005;86:1245–51. 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. Setting A university research laboratory. Participants Ten healthy, young adults (5 men, 5 women; mean age ± standard deviation, 30.0±3.1y). Intervention Incremental heat (35°−45°C, 1° 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.