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Effect of thermal stress on the vestibulosympathetic reflexes in humans

¹Division of Cardiology, Department of Medicine, and ²Department of Cellular and Molecular Physiology, General Clinical Research Center, Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033

Submitted 14 April 2004 ; accepted in final form 21 May 2004

Both heat stress and vestibular activation alter autonomic responses; however, the interaction of these two sympathetic activators is unknown. To determine the effect of heat stress on the vestibulosympathetic reflex, eight subjects performed static head-down rotation (HDR) during normothermia and whole body heating. Muscle sympathetic nerve activity (MSNA; peroneal microneurography), mean arterial blood pressure (MAP), heart rate (HR), and internal temperature were measured during the experimental trials. HDR during normothermia caused a significant increase in MSNA (5 ± 1 bursts/min; 53 ± 14 arbitrary units/min), whereas no change was observed in MAP, HR, or internal temperature. Whole body heating significantly increased internal temperature (0.9 ± 0.1°C), MSNA (10 ± 3 bursts/min; 152 ± 44 arbitrary units/min), and HR (25 ± 6 beats/min), but it did not alter MAP. HDR during whole body heating increased MSNA (16 ± 4 bursts/min; 233 ± 90 arbitrary units/min from normothermic baseline), which was not significantly different from the algebraic sum of HDR during normothermia and whole body heating (15 ± 4 bursts/min; 205 ± 55 arbitrary units/min). These data suggest that heat stress does not modify the vestibulosympathetic reflex and that both the vestibulosympathetic and thermal reflexes are robust, independent sympathetic nervous system activators.

orthostasis; otolith organs; muscle sympathetic nerve activity; microneurography; heat stress

This article has been cited by other articles:

				J. R. Carter and C. A. Ray Sympathetic responses to vestibular activation in humans Am J Physiol Regulatory Integrative Comp Physiol, March 1, 2008; 294(3): R681 - R688. [Abstract] [Full Text] [PDF]