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Body fluid regulation in micro-gravity differs from that on Earth: an overview
C Drummer1, R Gerzer, F Baisch
1Institut für Luft-und Raumfahrtmedizin, Deutsches Zentrum für Luft-und Raumfahrt, Cologne, Germany. christian.drummer@dlr.de
Pflugers Archiv : European Journal of Physiology
|February 24, 2001
Summary
Astronauts experience altered fluid shifts in microgravity, leading to weaker kidney responses than predicted. Body mass changes are linked to nutrition, not just fluid loss, requiring a revised understanding of spaceflight fluid balance.
Area of Science:
- Space physiology
- Renal function
- Fluid balance
Background:
- The Henry-Gauer mechanism predicts diuresis and natriuresis in response to fluid shifts during microgravity.
- Observed kidney responses in space missions differ from Earth-based hypervolemia simulations.
Purpose of the Study:
- To investigate the discrepancies in fluid and kidney responses between microgravity and simulated hypervolemia.
- To re-evaluate the classical "micro-gravity fluid shift" hypothesis.
Main Methods:
- Analysis of fluid balance and kidney function data from space missions.
- Comparison of in-flight data with ground-based simulations of hypervolemia.
Main Results:
- Kidney responses to microgravity are attenuated compared to Earth simulations, potentially due to fluid redistribution to extravascular spaces.
- Body mass deficits post-flight may result from hypocaloric nutrition rather than absolute fluid loss.
- Sodium-retaining humoral systems are activated, leading to increased body sodium during spaceflight.
Conclusions:
- The classical "micro-gravity fluid shift" model requires revision.
- Understanding altered fluid dynamics and metabolic changes is crucial for astronaut health.
- Nutrition plays a significant role in body mass regulation during space missions.