The role of posture in the natriuresis of water immersion in normal man.

Abstract

SummaryWater immersion to the neck has been demonstrated to produce a profound natriuresis in seated and standing subjects. Since an immersion–induced hydrostatic pressure gradient with a resultant redistribution of blood volume has been postulated to produce this natriuresis, it was of interest to examine this postulate by assessing renal sodium handling during immersion in supine subjects. Renal sodium, potassium and water handling was assessed in seven normal subjects during a control period and during water immersion under identical conditions of diet, supine posture and time of day. Although assumption of the recumbent position during immersion was associated with a gradual increase in UNaV, the resultant increase did not differ from the increase in UNaV following the assumption of recumbency during control. These data support the hypothesis that the natriuresis of water immersion is mediated by an immersion–induced hydrostatic pressure gradient acting on the vascular beds of the lower extremities an...