Effect of body temperature on cold induced vasodilation

Cold-induced vasodilation (CIVD) is an acute increase in peripheral blood flow observed during cold exposures. It is hypothesized to protect against cold injuries, yet despite continuous research it remains an unexplained phenomenon. Contrary to the traditionally held view, we propose that CIVD is a thermoregulatory reflex mechanism contributing to heat loss. Ten adults (4 females; 23.8 +/- 2.0 years) randomly underwent three 130-min exposures to -20 degrees C incorporating a 10-min moderate exercise period at the 65th min, while wearing a liquid conditioning garment (LCG) and military arctic clothing. In the pre-warming condition, rectal temperature was increased by 0.5 degrees C via the LCG before the cold exposure. In the warming condition, participants regulated the LCG throughout the cold exposure to subjective comfort. In the control condition, the LCG was worn but was not operated either before or during the cold exposure. Results demonstrated that the majority of CIVD occurred during the warming condition when the thermometrically-estimated mean body temperature (T (b)) was at its highest. A thermoregulatory pattern was identified whereby CIVD occurred soon after T (b) increased past a threshold (approximately 36.65 degrees C in warming and pre-warming; approximately 36.4 degrees C in control). When CIVD occurred, T (b) was reduced and CIVD ceased when T (b) fell below the threshold. These findings were independent of extremity temperature since CIVD episodes occurred at a large range of finger temperatures (7.2-33.5 degrees C). These observations were statistically confirmed by auto-regressive integrated moving average analysis (t = 9.602, P < 0.001). We conclude that CIVD is triggered by increased T (b) supporting the hypothesis that CIVD is a thermoregulatory mechanism contributing to heat loss.