Head-Out Water Immersion: A Critical Evaluation of the Gauer-Henry Hypothesis

In recent years, there has been a renewed interest in the study of the physiological responses elicited during head-out water immersion (WI) in both humans and animals. This interest is based on the observation that WI leads to stereotyped cardiovascular, renal, fluid shift, and endocrine responses which develop rapidly. The homeostatic basis or rationale for this response pattern which involves the integrated responses of multiple systems is unclear at the present time. Therefore one goal of this chapter is to attempt to identify certain critical physiologic variables which may be regulated during the course of this complex response pattern which is generally elicited during the simple act of returning to the aquatic environment from whence we came. The major focus of this analysis will be on the hypothesis originally proposed by Gauer and Henry (34) concerning a physiologic link between heart and kidney and the particular role this link may play in governing the hormonal responses elicited during WI. In this regard, a number of excellent reviews representing several points of view related to this issue have been published (25,34,35,74).