Depth of Immersion as a Determinant of the Natriuresis of Water Immersion

Summary

Water immersion to the neck has been demonstrated to produce a profound natriuresis in normal seated subjects. Since an immersion-induced hydrostatic pressure gradient with a resultant redistribution of circulating blood volume has been postulated to produce this natriuresis, it was of interest to examine this postulate by sequentially assessing renal sodium handling at varying depths of immersion. Renal sodium handling was assessed in nine normal subjects on four occasions while in balance on a 150 mEq Na diet; control, waist immersion, chest immersion and neck immersion, under identical conditions of diet, posture and time of day. Immersion to the mid-chest was associated with a significant increase in U_NaV compared to waist immersion (P < 0.05). Immersion to the neck resulted in a further increment in U_NaV compared to chest immersion (P < 0.05).

These data are consistent with the hypothesis that the immersion-induced hydrostatic pressure gradient acting on the vascular beds of the lower extremities and body trunk participates in mediating the natriuresis of water immersion.