VESTIBULOSYMPATHETIC REFLEXES IN HUMANS

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The specific goals of this study are to further our understanding of how activation of the vestibular system participates in orthostasis by its regulation of sympathetic nerve activity and peripheral vascular resistance in humans. We will investigate muscle sympathetic nerve activity (MSNA) and blood pressure responses: 1) during dynamic engagement of the otolith organs, 2) during engagement of the otolith organs in the upright posture, and 3) during engagement of the vestibulosympathetic reflex in subjects predisposed to orthostatic intolerance. Pilot data suggests that dynamic stimulation of the otolith organs elicits greater increases in MSNA during dynamic rather than static engagement of the otolith organs. This finding would support the hypothesis that the vestibulosympathetic reflex, mediated by dynamic stimulation of the otolith organs, contributes to orthostatic tolerance with changes in posture. Preliminary data also suggests that increases in MSNA by the vestibulosympathetic reflex via head-down rotation (HDR) is independent of body posture. This finding would provide the first evidence that vestibular activation in the upright posture contributes to sympathetic outflow and will support the concept that the vestibular system contributes to orthostasis in humans. Finally, pilot data suggests that vestibular activation of MSNA is attenuated in conditions that are associated with orthostatic intolerance (i.e., idiopathic orthostatic hypotension, vestibular deficient subjects, and highly trained endurance athletes), and that, blood pressure is reduced during vestibular activation in these subjects.