Les variations du rythme cardiaque lors de l'immersion

When young adult males, well trained to vertical immersion, are introduced in tap water, cardiac rhythm is modified according to the importance of the hydrostatic pressure and to the bath temperature. At thermoneutrality (34.2° C), in vertical immersion to the neck, a tachycardia appears first in 1-2 minutes, followed by a bradycardia of longer duration. Both are reflex in origin, as consequences of blood mechanical translocation to the intrathoracic reservoirs. Auricular distension provokes a Bainbridge type tachycardia which is suppressed by the baroreceptors effects of an subsequent increase in systemic blood pressure due to a Frank-Starling mechanism. Immersion in cold water for 30 minutes, reinforces the bradycardia as systemic blood pressure is more increased by direct and reflex vasoconstriction. In warm water, tachycardia is observed as blood pressure falls by vasodilatation. Signification of these changes as adaptation processes is discussed. A dissociation can be observed between the vasomotor and the cardioaccelerator orthosympathetic centres.Lecomte Jean, Lagneaux Denise. Les variations du rythme cardiaque lors de l'immersion. In: Bulletin de la Classe des sciences, tome 1, 1990. pp. 295-311