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Changes in the diurnal rhythms during a 45-day head-down bed rest
Xiaodi Liang1, Lin Zhang, Yufeng Wan
1Key Laboratory of Gene Engineering of the Ministry of Education, State Key Laboratory of Biocontrol, School of Life Sciences, Sun Yat-sen University, Guangzhou, China.
Plos One
|October 31, 2012
Summary
Head-down bed rest (HDBR) alters physiological diurnal rhythms, affecting hormone levels like cortisol and melatonin. This study reveals significant changes in bodily functions during simulated microgravity, impacting astronaut health.
Area of Science:
- Physiology
- Space Medicine
- Chronobiology
Background:
- Spaceflight alters human circadian rhythms and sleep, impacting physiology and performance.
- Mechanisms linking microgravity to sleep and circadian clock changes are not well understood.
Purpose of the Study:
- To analyze the influence of 45-day head-down bed rest (HDBR) on physiological diurnal rhythms.
- To investigate changes in urinary electrolyte and hormone excretion, and urination/defecation frequencies during simulated microgravity.
Main Methods:
- Volunteers underwent 45 days of head-down bed rest (-6° prone position) to simulate microgravity.
- Collected and analyzed urinary samples for electrolyte and hormone excretion (cortisol, melatonin, testosterone).
- Monitored urination and defecation frequencies throughout the study period.
Main Results:
- Head-down bed rest (HDBR) significantly elevated cortisol levels during the study and recovery phases.
- Increased diuresis, melatonin, and testosterone excretion were observed during HDBR.
- Urinary frequency rhythmicity increased during lights-off periods (during and after HDBR), while defecation rhythmicity was disrupted post-HDBR.
Conclusions:
- Head-down bed rest (HDBR) demonstrably alters physiological processes linked to diurnal rhythms.
- Simulated microgravity impacts key hormones and excretory functions, with potential implications for astronaut health and performance.
- Further research is needed to fully understand the underlying mechanisms of these HDBR-induced changes.
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