Oscillatory pattern of acral skin blood flow within thermoneutral zone in healthy humans

The acral skin contains arteriovenous anastomoses, which probably is the main part of skin microcirculation for blood flow adjustments and thermoregulation in the thermoneutral zone. The objective was to investigate if an increase in sympathetic activation during cooling influences the oscillatory pattern of acral skin blood flow. We had measurements of bilateral acral skin blood flow (n  =  12) during lowering of ambient temperature from 32 °C to 18 °C. We quantified the oscillatory pattern as the time averaged wavelet spectral powers, coherence and phase angles in three frequency intervals (0.01-0.02 Hz, 0.02-0.05 Hz and 0.05-0.08 Hz). The differences were tested by Wilcoxon signed rank sum method between adjacent intervals. The absolute fluctuations in laser Doppler flux at 0.01-0.02 Hz, 0.02-0.05 Hz and 0.05-0.08 Hz were similar at 32 °C and 25 °C, and decreased at 18 °C (p  <  0.001). The relative fluctuations (amplitude of the fluctuations relative to median flux value) in laser Doppler flux at 0.01-0.02 Hz, 0.02-0.05 Hz and 0.05-0.08 Hz were higher at 25 °C and 18 °C as compared to 32 °C (p  <  0.002). The coherence between the oscillations of signals from right and left finger tips was highest (median coherence  >  0.89) at 25 °C, and lower at 32 °C and at 18 °C.The median phase angles between the flux signals from right and left finger tips were close to 0 radians. We found that the relative fluctuations in acral skin blood flow increased during vasoconstriction due to cooling. Wavelet analysis of acral skin blood flow oscillations could serve as a future clinical tool.