Investigating the efficacy of the NASA fluid loading protocol for astronauts: The role of hormonal blood volume regulation in orthostasis after bed rest
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Dynamic cerebral autoregulation after bed rest: effects of volume loading and exercise countermeasures.
This study assessed effects of head-down-tilt (HDT) bed rest on dynamic cerebral autoregulation (CA) in 21 healthy young adults with volume loading and exercise countermeasures. Of these, seven underwent an 18-day bed rest without exercise countermeasures (sedentary group). Volume loading with dextran infusion was performed after bed rest to restore reduced plasma volume to levels before bed re...
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Introduction Extracellular fluid volume and arterial blood pressure are principally determined by total body sodium via osmoregulation. Dysregulation of mechanisms involved in maintaining sodium balance are therefore implicated in the development of hypertension. Hormonal mechanisms are thought to be critically involved in the regulation of natriuresis, and modification of these mechanisms may ...
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Orthostatic intolerance follows actual weightlessness and weightlessness simulated by bed rest. Orthostasis immediately after acute exercise imposes greater cardiovascular stress than orthostasis without prior exercise. We hypothesized that 5 min/day of simulated orthostasis [supine lower body negative pressure (LBNP)] immediately following LBNP exercise maintains orthostatic tolerance during b...
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This study tested the hypothesis that cardiovascular and hormonal responses to lower body negative pressure (LBNP) would be altered by 4-h head down bed rest (HDBR) in 11 healthy young men. In post-HDBR testing, three subjects failed to finish the protocol due to presyncopal symptoms, heart rate was increased during LBNP compared with pre-HDBR, mean arterial blood pressure was elevated at 0, -1...
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Humans exposed to real or simulated microgravity experience decrements in blood pressure regulation during orthostatic stress that may be related to autonomic dysregulation and/or hypovolemia. We examined the hypothesis that hypovolemia, without the deconditioning effects of bed rest or spaceflight, would augment the sympathoneural and vasomotor response to graded orthostatic stress. Radial art...
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