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Plasma and blood volume in space.
André Diedrich1, Sachin Y Paranjape, David Robertson
1Center for Space Medicine and Physiology, Vanderbilt University School of Medicine, Division of Clinical Pharmacology, Department of Medicine, Autonomic Dysfunction Center, Nashville, Tennessee 37232-2195, USA. andre.diedrich@vanderbilt.edu
The American Journal of the Medical Sciences
|July 17, 2007
Summary
Body fluid regulation differs in space due to gravity. New hypotheses suggest fluid loss in space results from decreased intake, fluid shifts to tissues, and reduced blood volume, impacting astronaut health.
Area of Science:
- Physiology
- Space Medicine
- Gravitational Biology
Background:
- Gravity significantly impacts human body fluid regulation.
- Previous studies on hypovolemia (low blood volume) mechanisms in simulated and actual spaceflight show discrepancies.
- The Henry Gauer hypothesis regarding increased diuresis (urine output) with central blood volume expansion was not consistently observed.
Purpose of the Study:
- To explore novel hypotheses for fluid volume regulation during spaceflight.
- To understand the multifactorial causes of reduced blood volume in astronauts.
- To explain the attenuated diuresis observed during space missions.
Main Methods:
- Review and synthesis of recent findings on fluid shifts and volume regulation in microgravity.
- Analysis of factors contributing to negative fluid balance, including intake, urine output, and fluid distribution.
- Examination of physiological responses to spaceflight, such as sympathetic activation and hormonal changes.
Main Results:
- Reduced blood volume in space is attributed to decreased fluid intake, fluid shifts into interstitial spaces (due to reduced gravitational compression), and shifts into muscle interstitial space (due to decreased postural muscle tone).
- Erythrocyte (red blood cell) loss further contributes to reduced blood volume.
- Attenuated diuresis is linked to stress-mediated sympathetic activation, reduced red cell mass, and rapid blood volume contraction.
- The relationship between plasma osmolarity and vasopressin release may be altered in microgravity.
Conclusions:
- Body fluid regulation mechanisms differ significantly between Earth and space environments.
- Multiple factors contribute to hypovolemia and altered fluid balance in astronauts.
- Further research is needed to fully understand the neuroendocrine regulation of fluid balance in microgravity.
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