title: Effect of thermal stress on the vestibulosympathetic reflexes in humans.
abstract: 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 (Delta5 +/- 1 bursts/min; Delta53 +/- 14 arbitrary units/min), whereas no change was observed in MAP, HR, or internal temperature. Whole body heating significantly increased internal temperature (Delta0.9 +/- 0.1 degrees C), MSNA (Delta10 +/- 3 bursts/min; Delta152 +/- 44 arbitrary units/min), and HR (Delta25 +/- 6 beats/min), but it did not alter MAP. HDR during whole body heating increased MSNA (Delta16 +/- 4 bursts/min; Delta233 +/- 90 arbitrary units/min from normothermic baseline), which was not significantly different from the algebraic sum of HDR during normothermia and whole body heating (Delta15 +/- 4 bursts/min; Delta205 +/- 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.
authors.affiliation: Division of Cardiology, Department of Medicine, General Clinical Research Center, Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033 -2390, USA. tew12@psu.edu
authors.forename: Thad E
authors.initials: TE
authors.lastname: Wilson
authors.forename: Chester A
authors.initials: CA
authors.lastname: Ray
mesh_terms: D000328:Adult; D004244:Dizziness / Q000209:etiology / Q000503:physiopathology*; D005260:Female; D018882:Heat Stress Disorders / Q000150:complications / Q000503:physiopathology*; D006801:Humans; D008297:Male; D018482:Muscle, Skeletal / Q000294:innervation* / Q000503:physiopathology*; D012021:Reflex, Abnormal; D012027:Reflex, Vestibulo-Ocular; D013223:Statistics as Topic; D013564:Sympathetic Nervous System / Q000503:physiopathology*