Abstract
To elucidate the influence of heat stress on the cutaneous vascular response in the lower extremities during orthostatic stress, a head-up tilt (HUT) test at angles of 15°, 30°, 45°, and 60° for 4 min each, was conducted under a normothermic control condition followed by whole-body heat stress produced by a hot water-perfused suit in healthy volunteers. Skin blood flows (SkBF) in the forearm, thigh and calf were monitored using laser-Doppler flowmetry throughout the experiment. Additionally, to elucidate the effects of increased core and local skin temperatures on the local vascular response in calf skin under increasing orthostatic stress, the thigh was occluded at 20, 30, 50, 70, and 80 mmHg with a cuff in both the normothermic condition and whole-body or local heating condition. Significant decreases in forearm SkBF during HUT were observed at an angle of 60° during normothermia and at 30° or more during heating. SkBF in the thigh and calf was decreased significantly by HUT at 15° and above during normothermia, while whole-body heating diminished a significnt reduction of SkBF in these sites during HUT at the lower angles (15°–45°). Both whole-body and local heating diminished a significant reduction in calf SkBF at a low cuff pressure (20 mmHg). These results suggest that SkBF in the lower extremities show a marked reduction compared with those in the upper extremities during low orthostatic stress in normothermia, and the enhanced skin vasoconstrictor response in the lower extremities is diminished by both whole-body and local heat stress.
