Acute head-down tilt decreases the postexercise resting threshold for forearm cutaneous vasodilation

The purpose of this study was to evaluate the role of baroreceptor control on the postexercise threshold for forearm cutaneous vasodilation. On four separate days, six subjects (1 woman) were randomly exposed to 65 degrees head-up tilt and to 15 degrees head-down tilt during a No-Exercise and Exercise treatment protocol. Under each condition, a whole body water-perfused suit was used to regulate mean skin temperature (T(sk)) in the following sequence: 1) cooling until the threshold for vasoconstriction was evident; 2) heating ( approximately 7.0 degrees C/h) until vasodilation occurred; and 3) cooling until esophageal temperature (T(es)) and (T(sk)) returned to baseline values. The Exercise treatment consisted of 15 min of cycling exercise at 70% maximal O(2) uptake, followed by 15 min of recovery in the head-up tilt position. The No-Exercise treatment consisted of 30 min resting in the head-up tilt position. After the treatment protocols, subjects were returned to their pretreatment condition, then cooled and warmed again consecutively. The calculated T(es) threshold for cutaneous vasodilation increased 0.24 degrees C postexercise during head-up tilt (P < 0.05), whereas no difference was measured during head-down tilt. In contrast, sequential measurements without exercise demonstrate a time-dependent decrease for head-up tilt (0.17 degrees C) and no difference for head-down tilt. Pretreatment thresholds were significantly lower during head-down tilt compared with head-up tilt. We have shown that manipulating postexercise venous pooling by means of head-down tilt, in an effort to reverse its impact on baroreceptor unloading, resulted in a relative lowering of the resting postexercise elevation in the T(es) for forearm cutaneous vasodilation.