A study on skin blood flow control mechanisms using wavelet analysis: Implications for alternating pressure support surfaces

The benefits of using alternating pressure (AP) support surfaces for pressure ulcer prevention are associated with providing periodic pressure relief and stimulating a protective increase in skin blood flow (SBF). The physiological mechanisms responsible for the increase in SBF are not well understood; however, these protective mechanisms may be assessed through study of SBF oscillations.;A computer-controlled system has been designed to apply various stimuli and loading conditions on the sacrum with simultaneous measurement of physiological responses (i.e. SBF and skin temperature). The results indicate that the system provides reliable data for use in the study of the relationship between tissue biomechanical and physiological characteristics and loading methods.;A time-frequency approach using wavelets was used to decompose SBF into frequency bands reported to be associated with metabolic, neurogenic, myogenic, respiratory and cardiac SBF control mechanisms. The method was used to differentiate blood flow control mechanisms responding to indentation from those responding to heating. Incremental heat (35--45°C, 1°-step/minute) and pressure (0--60 mmHg, 5-mmHg step/3 min) were applied to the sacrum in ten healthy subjects. The results suggest that skin blood flow is mediated by myogenic control after application of incremental external pressure and is mediated by metabolic control after incremental local heat exposure (p < 0.01).;The study of blood flow responses is confounded by temporal variability in blood flow measurement. This study investigated the effectiveness of our wavelet analysis technique in reducing week-to-week variability in SBF. The results show that coefficients of variation for the power in each frequency band are smaller than that of baseline SBF or maximal blood flow ratio (p < 0.05).;Ten healthy participants were subjected to both constant loading for 20 min at 30 mmHg and AP for 20 min (5-min cycle x 4) at either 60 or 0 mmHg on their sacrum. The results indicate AP stimulates an increase in SBF compared to constant loading (p < 0.01). SBF during the high-pressure phase of four AP cycles shows an increasing trend. Our study suggests that optimization of AP parameters to compensate for impaired control mechanisms in pathological populations may be possible using wavelet analysis of blood flow oscillations.