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Otolithic activation on visceral circulation in humans: effect of aging

Heart and Vascular Institute, General Clinical Research Center, Pennsylvania State University College of Medicine, The Milton S. Hershey Medical Center, Hershey, Pennsylvania

Submitted 12 July 2008 ; accepted in final form 7 August 2008

Engagement of the otolith organs elicits differential activation of sympathetic nerve activity and vascular responses to muscle and skin in humans. Additionally, aging attenuates the otolith organ-mediated increases in muscle sympathetic nerve activity in older adults. In this study, we hypothesized that 1) the vestibulosympathetic reflex (VSR) would elicit visceral vascular vasoconstriction and 2) visceral vascular response to the VSR would be attenuated in older subjects compared with young. To test these hypotheses, heart rate, mean arterial blood pressure, and renal, celiac trunk, and superior mesenteric arterial blood velocity (Doppler ultrasound) were measured in 22 young (25 ± 1 yr) and 18 older (65 ± 2 yr) healthy subjects during head-down rotation (HDR), which selectively activates the otolith organs. Mean arterial pressure and heart rate did not change from baseline during HDR in young or older subjects. Renal blood velocity ( –2 ± 1 cm/s) and vascular conductance ( –0.03 ± 0.01 cm·s^–1·mmHg^–1) significantly decreased from baseline during HDR (P < 0.05) in young subjects. In contrast, renal blood velocity and conductance did not change in older subjects ( –0.2 ± 1 cm/s and 0.02 ± 0.08 mmHg·cm^–1·s^–1, respectively) during HDR. Superior mesenteric and celiac blood velocity and vascular conductance did not change in response to HDR in either the young or older subjects. These data suggest that renal vasoconstriction occurs during otolith organ activation in young but not older humans. Together with our previous studies, we conclude that the VSR elicits a diverse patterning of sympathetic outflow that results in heterogeneous vascular responses in humans and that these responses are significantly attenuated in older humans.

renal; splanchnic; blood flow; vestibulosympathetic reflex; vasoconstriction