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[Orthostatic tolerance after spaceflight or simulated weightlessness by head-down bed-rest]
Claude Gharib1, Marc-Antoine Custaud
1Université Claude Bernard Lyon 1, Faculté de Médecine Lyon Grange-Blanche, Laboratoire de Physiologie de l'Environnement, 8 avenue Rockefeller-69373 Lyon. gharib@pop.univ-lyon1.fr
Bulletin De L'Academie Nationale De Medecine
|November 5, 2002
Summary
Orthostatic intolerance (OI) affects astronauts and those on head-down bed rest, but mechanisms differ despite similar symptoms like tachycardia. This study compared OI after spaceflight and bed rest, finding distinct physiological responses.
Area of Science:
- Cardiovascular Physiology
- Space Medicine
- Autonomic Nervous System Function
Background:
- Spaceflight and prolonged head-down bed rest (HDBR) induce cardiovascular deconditioning, notably orthostatic intolerance (OI).
- The precise mechanisms underlying OI post-spaceflight and HDBR remain debated.
- Understanding these mechanisms is crucial for astronaut health and developing countermeasures.
Purpose of the Study:
- To compare the mechanisms of orthostatic intolerance (OI) following a 42-day head-down bed rest (HDBR) study with those experienced after 90 to 198 days of spaceflight.
- To investigate autonomic and baroreflex responses during orthostatic stress in both conditions.
Main Methods:
- A comparative study involving 7 subjects after 42-day HDBR and 10 astronauts post-spaceflight.
- Orthostatic stress was assessed using a 10-minute stand test after supine and sitting rest.
- Measurements included blood pressure (Finapres), ECG for RR interval analysis, autonomic indexes via spectral analysis, and spontaneous baroreflex sensitivity.
Main Results:
- Both HDBR and spaceflight groups exhibited common profiles of tachycardia and reduced parasympathetic index and baroreflex sensitivity.
- Approximately 30% of subjects in both groups experienced OI.
- However, distinct underlying mechanisms contributed to OI, despite a shared postural orthostatic tachycardia syndrome (POTS) presentation.
Conclusions:
- While both spaceflight and HDBR can lead to orthostatic intolerance (OI) with similar symptoms like POTS, their physiological mechanisms differ.
- Spaceflight duration did not appear to be a determining factor for OI severity.
- Predictive indicators for OI remain elusive, highlighting a need for further research.