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Sleep restriction does not affect orthostatic tolerance in the simulated microgravity environment.
S Marlene Grenon1, Shelley Hurwitz, Natalie Sheynberg
1Division of Endocrinology, Hypertension and Diabetes, Brigham and Women's Hospital, 221 Longwood Ave., Boston, MA 02115, USA.
Journal of Applied Physiology (Bethesda, Md. : 1985)
|July 6, 2004
Summary
Orthostatic intolerance (OI) increases after simulated microgravity. However, sleep restriction did not worsen this condition or alter physiological responses in healthy men.
Area of Science:
- Space physiology
- Cardiovascular research
- Sleep science
Background:
- Orthostatic intolerance (OI) is a significant challenge for astronauts post-spaceflight.
- Astronauts commonly experience sleep restriction during space missions.
- The combined effects of microgravity and sleep restriction on OI are not fully understood.
Purpose of the Study:
- To investigate if sleep restriction exacerbates orthostatic intolerance following simulated microgravity.
- To assess the impact of sleep restriction on renal, cardioendocrine, and cardiovascular adaptations to simulated microgravity.
Main Methods:
- Nineteen healthy men underwent simulated microgravity using head-down tilt bed rest (HDTB).
- Subjects were divided into non-sleep restricted (8h/night) and sleep-restricted (6h/night) groups.
- Physiological assessments included tilt-stand tests, 24-h urine collections, hormonal measurements, and cardiovascular system identification.
Main Results:
- Simulated microgravity significantly increased the occurrence of orthostatic intolerance.
- Sleep restriction did not significantly worsen the occurrence or severity of OI compared to non-sleep restriction.
- Both groups exhibited similar physiological changes, including altered sodium and potassium excretion and increased plasma renin activity.
Conclusions:
- Simulated microgravity increases the risk of orthostatic intolerance.
- Sleep restriction does not additively worsen orthostatic intolerance in simulated microgravity.
- Renal, cardioendocrine, and cardiovascular responses to simulated microgravity are similar under sleep-restricted and non-sleep-restricted conditions.