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Moderate sodium restriction does not alter lower body negative pressure tolerance
L R Davrath1, R W Gotshall, A Tucker
1Department of Physiology, Colorado State University, Fort Collins, CO 80523, USA.
Aviation, Space, and Environmental Medicine
|June 18, 1999
Summary
Moderate sodium restriction did not negatively impact orthostatic tolerance in healthy men during lower body negative pressure (LBNP) testing. This suggests dietary sodium adjustments may be safe for spaceflight adaptation.
Area of Science:
- Cardiovascular physiology
- Space medicine
- Human physiology
Background:
- Space travel causes reduced orthostatic tolerance upon return to Earth.
- Current countermeasures for orthostatic intolerance are not fully effective.
Purpose of the Study:
- To investigate the effect of a moderate dietary sodium restriction on orthostatic tolerance.
- To assess tolerance to lower body negative pressure (LBNP) under different dietary sodium conditions.
Main Methods:
- Eight healthy men participated in the study.
- Subjects underwent LBNP after 5 days on a typical diet (C) and 5 days on a sodium-restricted (SR) diet.
- Diet sequence was randomized, and adherence was verified by 24-hour urine sodium excretion.
Main Results:
- All subjects reached presyncope during LBNP, irrespective of diet.
- Urinary sodium excretion was significantly lower on the SR diet compared to the C diet.
- No significant differences were observed in LBNP stress index, cardiac volumes, blood pressure, or catecholamines between the diets.
- Plasma renin activity was significantly higher during the SR diet.
Conclusions:
- Moderate dietary sodium restriction is not detrimental to orthostatic tolerance.
- This finding suggests that sodium restriction may be a viable strategy for mitigating orthostatic intolerance.
- Further research is warranted to explore the long-term effects and applicability in astronaut populations.