Effect of baroreflex loading on the responsiveness of the vestibulosympathetic reflex in humans

Dyckman, Damian J.; Monahan, Kevin D.; Ray, Chester A.

doi:10.1152/japplphysiol.00555.2007

Cited by 18 publications

(17 citation statements)

References 33 publications

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“…VSR in humans has been found to be a mediator of cardiovascular stress (Dyckman et al 2007, Saunder et al 2008 and to even have shorter response latency than the baroreflex (Kaufman et al 2002 andVoustianiouk et al 2006). The latter finding indicates that the VSR could be the first line-of-defense to cardiovascular stress and thus could play a vital role in maintaining astronaut orthostatic tolerance.…”

Section: Vestibular Motivations For Artificial Gravitymentioning

confidence: 99%

A critical benefit analysis of artificial gravity as a microgravity countermeasure

2010

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Human physiological systems, especially the cardiovascular and musculo-skeletal systems, are well-known to decondition during spaceflight. Several countermeasures that are in use today have been rigorously developed over the decades to combat this deconditioning. However, these countermeasures are system specific and have proven to be only partially effective. Artificial gravity has been persistently discussed as a countermeasure that potentially has salutary effects on all physiological systems, though few ground-based studies have been performed in comparison to other countermeasures. The current analysis attempts to elucidate the effectiveness of artificial gravity by directly comparing results of previously published and unpublished deconditioning studies with those of more traditional, ground-based countermeasures (i.e. resistive exercise, aerobic exercise, lower body negative pressure, or some variation of these). Animal studies were also evaluated to supplement the knowledge base and to fill gaps in the human countermeasure literature. Designs of published studies, such as study duration, deconditioning paradigm, subject selection criteria, measurements taken, etc., were confounding variables; however, studies that had some measure of consistency between these variables were compared, although notable differences were cited in the analysis and discussion. Results indicate that for prolonged spaceflight an artificial gravity-based countermeasure may provide benefits equivalent to traditional countermeasures for the cardiovascular system. Too few comparable, human studies have been performed to draw any conclusions for the musculoskeletal system, although animal studies show some positive results. Gaps in the current knowledge of artificial gravity are identified and guidance for future deconditioning studies is offered. Based on the results of this study, a comprehensive artificial gravity protocol is proposed and future research topics using this countermeasure are

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Section: Vestibular Motivations For Artificial Gravitymentioning

confidence: 99%

A critical benefit analysis of artificial gravity as a microgravity countermeasure

2010

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“…Collectively, these studies indicate that MSNA activation by the vestibular system is a powerful autonomic reflex, capable of stimulating MSNA in the presence of other sympathetic activators. More recently, Dyckman et al (16) examined the vestibulosympathetic reflex during baroreceptor unloading (nitroprusside infusion) and loading (phenylephrine infusion). HDR elicited increases in MSNA during the nitroprusside trial but did not change MSNA during the phenylephrine trial (16).…”

Section: Sympathetic Responses To Activation Of the Otolith Organs Inmentioning

confidence: 99%

Sympathetic responses to vestibular activation in humans

Carter¹,

Ray²

2008

American Journal of Physiology-Regulatory, Integrative and Comp

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Activation of sympathetic neural traffic via the vestibular system is referred to as the vestibulosympathetic reflex. Investigations of the vestibulosympathetic reflex in humans have been limited to the past decade, and the importance of this reflex in arterial blood pressure regulation is still being determined. This review provides a summary of sympathetic neural responses to various techniques used to engage the vestibulosympathetic reflex. Studies suggest that activation of the semicircular canals using caloric stimulation and yaw rotation do not modulate muscle sympathetic nerve activity (MSNA) or skin sympathetic nerve activity (SSNA). In contrast, activation of the otolith organs appear to alter MSNA, but not SSNA. Specifically, head-down rotation and off-vertical axis rotation increase MSNA, while sinusoidal linear accelerations decrease MSNA. Galvanic stimulation, which results in a nonspecific activation of the vestibule, appears to increase MSNA if the mode of delivery is pulse trained. In conclusion, evidence strongly supports the existence of a vestibulosympathetic reflex in humans. Furthermore, attenuation of the vestibulosympathetic reflex is coupled with a drop in arterial blood pressure in the elderly, suggesting this reflex may be important in human blood pressure regulation.

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“…However, the relative contributions of the baroreflexes and VSR during postural blood pressure regulation have not been specifically tested to date. However, our previous studies clearly indicate an additive interaction between baroreceptor unloading and the VSR (3,17).…”

Section: Discussionmentioning

confidence: 65%

Otolithic activation on visceral circulation in humans: effect of aging

Sauder

Conboy²,

Chin-Sang³

et al. 2008

American Journal of Physiology-Renal Physiology

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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.

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Effect of baroreflex loading on the responsiveness of the vestibulosympathetic reflex in humans

Cited by 18 publications

References 33 publications

A critical benefit analysis of artificial gravity as a microgravity countermeasure

A critical benefit analysis of artificial gravity as a microgravity countermeasure

Sympathetic responses to vestibular activation in humans

Otolithic activation on visceral circulation in humans: effect of aging

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