Cardiovascular and renal effects of head out water immersion in man. Application of the model in the assessment of volume homeostasis

Abstract

Studies from several laboratories recently have succeeded in delineating the circulatory, renal, and endocrine changes induced in man by water immersion. These studies have demonstrated that immersion in the seated posture results in a redistribution of blood volume with a relative central hypervolemia. As a consequence, profound alterations in fluid and electrolyte homeostasis ensue, including a marked natriuresis, kaliuresis, and diuresis, as well as a suppression of the renin aldosterone system and of ADH release. Characterization of the immersion model and the demonstration that it constitutes a potent 'central volume stimulus' that does not necessitate infusing exogenous volume expanders have permitted its successful application in the investigation of abnormal sodium and water homeostasis in patients with decompensated cirrhosis and, more recently, hypertension. Examples have been described of the successful application of the immersion model, commending its future use as an investigative tool to assess dynamically the control mechanisms for the renin aldosterone system in normal man and in a wide array of disease states characterized by a deranged volume homeostasis. In an edematous or hypertensive subject, water immersion constituted a less hazardous means to evaluate the effects of volume expansion than administration of a saline load. In contrast to saline administration (1) water immersion is associated with a decrease in body weight rather than with the increase which attends saline infusion, (2) water immersion is associated with a significant, albeit slight, decrease in mean arterial blood pressure in contrast to the increase in blood pressure induced by saline administration, and (3) the 'volume stimulus' of immersion is promptly reversible after cessation of immersion in contrast to the relatively sustained hypervolemia which follows saline administration.