INFLUENCE OF EXERCISE INTENSITY AND PLASMA-VOLUME ON ACTIVE CUTANEOUSVASODILATION IN HUMANS

The influence of dynamic exercise on active cutaneous vasodilation was evaluated in eight male subjects. We measured the increase in interna l body temperature (esophageal temperature, T-es) required to elicit a ctive cutaneous vasodilation and the slope of the linear relationship between increases in forearm skin vascular conductance (Delta FVC) and T-es during indirect heating (legs immersed in 44 degrees C water for 30 min), 30 min of light exercise (LEX; 75 +/- 5 W = 30% maximal oxyg en uptake, VO2max), and 20 min of moderate exercise (MEX, 149 +/- 7 W = 60% VO2max) Studies were conducted in the supine position at 30 degr ees C (RH <30%) and mean skin temperature averaged 35.09 +/- 0.12 degr ees C. During indirect heating and LEX, cutaneous vasodilation occurre d after a similar increase in T-es, 0.03 +/- 0.02 degrees C and 0.11 /- 0.02 degrees C, respectively. During MEX, T-es increased 0.42 +/- 0 .06 degrees C before the onset of cutaneous vasodilation (P < 0.05, di fferent from rest and LEX). The relationship between the increase in T -es threshold for vasodilation and exercise intensity was nonlinear, i ndicating that some minimal exercise intensity was required to elicit a delay in active cutaneous vasodilation. That minimal exercise intens ity was greater than 30% VO2max (75 +/- 5 W). During MEX the increase in T-es threshold for vasodilation was inversely related to resting pl asma volume (ml . kg(-1)) with a larger initial plasma volume associat ed with a smaller increase in T-es threshold for cutaneous vasodilatio n (r(2) = 0.67, P = 0.03). In addition, peak cutaneous vasodilation re presented as the peak Delta FVC/peak Delta T-es, was directly related to plasma volume (r(2) = 0.64, P = 0.03). We conclude that the influen ce of exercise on the threshold for active cutaneous vasodilation is d ependent on an interaction between exercise intensity and the size of the intravascular compartment. This conclusion is consistent with the hypothesis that blood volume expansion is an important adaptation of e xercise training and contributes to improved thermoregulatory control during exercise in the heat.