Otolithic activation on visceral circulation in humans: effect of aging

Abstract

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 (Delta -2+/-1 cm/s) and vascular conductance (Delta -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 (Delta -0.2+/-1 cm/s and Delta0.02+/-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.

Endurance training reduces renal vasoconstriction to orthostatic stress

“…We have demonstrated (18) that engagement of the VSR can elicit renal vasoconstriction. If the VSR is attenuated after endurance training, this would cause less renal vasoconstriction.…”

Effect of healthy aging on renal vascular responses to local cooling and apnea

“…This pressor response in older adults was coincident with an augmented renal vasoconstriction (Fig. 2), which is often considered to be evidence of increased renal sympathetic nerve activity (6,43,61), but one must consider that augmented renal vasoconstriction with aging could be the cause or consequence of an augmented MAP in these subjects. This caveat is particularly important because the older subjects had higher RVRI at baseline.…”

“…These parameters were sampled at 200 Hz by a data acquisition system (PowerLab; ADInstruments, Colorado Springs, CO) and were synchronized with the Doppler images using verbal and written time stamps. Transabdominal Doppler ultrasound (HDI 5000; Advanced Technology Laboratories Ultrasound, Bothell, WA) was used to measure renal blood flow velocity (RBV), as described previously (43,61). Briefly, the depth and angle of insonation (Ͻ60°) were held constant within each subject, and images were acquired and saved at end expiration (end of spontaneous respiratory cycle).…”

“…The same investigator (M. D. Muller) performed all RBV measurements and was not blinded during data analysis. RVRI was calculated offline as MAP/RBV; an increase in RVRI is considered to indicate renal vasoconstriction (6,41,43,61). Thermal sensation (0 ϭ neutral/no sensation of cold, and 11 ϭ unbearable cold) and pain perception (0 ϭ no pain, and 10 ϭ unbearable pain) were obtained immediately after each stimulus (17,20).…”

“…Therefore, a better understanding of the renal circulation in older adults may have clinical relevance. However, there is currently little experimental data (42,61) regarding the effect of healthy aging on renal vasoconstriction during sympathoexcitatory stress.…”