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Interactions vestibulo-végétatives et évolution du baroréflexe carotidien au cours de deux modèles d'impesanteur : l'alitement prolongé tête déclive et l'immersion sèche

Abstract : The removal of the gravity vector during spaceflight normally directed from the head to the feet in the standing position acts on the body fluids by the loss of the hydrostatic pressure gradient, which results in a cardiovascular deconditioning syndrome. This lack of gravity also disturbs the vestibular system, particularly otoliths that lose their ability to detect head tilts. We conducted our studies in humans using the 3-day dry immersion model and the 60-day anti-orthostatic bed rest model. The aim of our first research work is to study the influence of the otolithic system on the regulation of the cardiovascular system through the vestibulo-sympathetic reflex. For this purpose, galvanic stimulation experiments were used to evaluate otolithic sensitivity as well as neck flexion maneuvers associated with conventional cardiovascular and plethysmography measurements. In addition, an accelerometer has been used to quantify the activity and inactivity phases. The aim of our second research project is to study the evolution of the carotid baroreflex during weightlessness simulation models and to establish possible hypotheses of interaction with otolithic afferents. For this purpose, blood pressure and heart rate measurements were used in response to mechanical stimulations of carotid baroreceptors applied directly via the pressure collar technique. Our results confirmed that the neck flexion maneuver is indeed an otolithic stimulation with the appearance of otolitic changes of reactivity only in ventral decubitus and not in lateral decubitus. Nevertheless, the role of vestibulo-sympathetic reflex on cardiovascular regulation is not clearly demonstrated. Moreover, the sensitivity of the carotid baroreflex during these protocols is not modified. Our general hypothesis of a change in cardiovascular control related to the reduction of otolithic stimulation during weightless simulation protocols is not verified. It remains to understand the real meaning of the head-down neck flexion maneuver and its connection with the authentic otolithic stimulation it causes. It is likely that multiple sensory systems are involved in cardiovascular regulation in relation to gravity. The specific role of the vestibular system is likely to be better understood in situations where its plasticity is best brought into play, that is to say in real weightlessness.
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Steven De Abreu. Interactions vestibulo-végétatives et évolution du baroréflexe carotidien au cours de deux modèles d'impesanteur : l'alitement prolongé tête déclive et l'immersion sèche. Médecine humaine et pathologie. Normandie Université, 2019. Français. ⟨NNT : 2019NORMC421⟩. ⟨tel-02464575⟩

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