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Dysfonctions neuromusculaires et cardiovasculaires dans les troubles posturaux orthostatiques induits par la microgravité

Abstract : Postural and orthostatic impairment are both acknowledged consequences of spaceflight. One of the factors for orthostatic and postural stability is muscle tone, which decreases within the onset of microgravity. Studies of cardiovascular, neuromuscular and postural effects of microgravity are numerous ; yet the role of neuromuscular and vascular disorders in orthostatic and postural impairment remains unclear. We aimed to investigate vascular and neuromuscular alterations induced by microgravity, as well as their relationships. We studied healthy men exposed to 6-mo spaceflight, 21-day head-down bedrest and 3-to 5-day dry immersion. These conditions differ by the level of support unloading. Cardiovascular state was assessed by orthostatic tests, neuromuscular - by myotonometry, postural stability - by stabilometry. We found that long-term spaceflight induced much deeper disorders than relatively short-term modeled microgravity. Furthermore, immersion induced more severe disorders than bedrest, despite its shorter duration. Our data, along with literature, suggest that it is the support unloading that defines the depth of disturbances. The leading role in development of postural disorders under gravitational unloading belongs to decrease in postural muscle tone. This decrease occurs mainly by a reflex mechanism (decrease in support afferentation). It might be responsible for orthostatic impairment - via decrease in the efficiency of muscle pump promoting venous return, and for postural impairment - via increase in recruitment thresholds of postural motoneurons.
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Liubov Dmitrieva. Dysfonctions neuromusculaires et cardiovasculaires dans les troubles posturaux orthostatiques induits par la microgravité. Médecine humaine et pathologie. Université d'Angers; Institut des problèmes biomédicaux de l'Académie des Sciences de Russie, 2018. Français. ⟨NNT : 2018ANGE0058⟩. ⟨tel-02324895⟩

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