Vestibular activation does not influence skin sympathetic nerve responses during whole body heating

The cutaneous vasculature and eccrine sweat glands are modified by both thermal and nonthermal factors. To determine the effect of thermal stress on the vestibulosympathetic reflex, skin sympathetic nerve activity (SSNA) and cutaneous end-organ responses were measured in 10 subjects during static head-down rotation (HDR) and dynamic yaw and pitch (30 cycles/min) to activate the otolith organs and semicircular canals. SSNA (microneurography of peroneal nerve), cutaneous vascular conductance (CVC; laser-Doppler flux/mean arterial pressure), sweat rate (capacitance hygrometry), and body temperature were collected during normothermia and after whole body heating. Body temperature was controlled by perfusing neutral (34-35°C) or warm (44-46°C) water through a tube-lined suit. During normothermia, HDR did not alter SSNA (-0.4 ± 4.4% change), CVC (4.2 ± 6.9% change), or sweat rate (-2.7 ± 1.2% change) within the innervated area of skin. Dynamic yaw and pitch also did not elicit significant changes in SSNA, CVC, or sweat rate during normothermia. Whole body heating significantly increased internal temperature (0.8 ± 0.1°C), mean skin temperature (4.1 ± 0.2°C), CVC (322 ± 109% control), and sweat rate (0.35 ± 0.08 mg·cm^-2·min^-1). After whole body heating, HDR did not significantly alter SSNA (3.2 ± 7.6% change), CVC (-7.3 ± 3.9% change), or sweat rate (-3.3 ± 1.9% change). Dynamic yaw and pitch also did not produce significant changes in SSNA, CVC, or sweat rate after whole body heating. These data suggest that vestibular activation by head movements is not a nonthermal factor affecting SSNA and cutaneous end-organ responses in humans.