Renal, endocrine, and cardiovascular responses during head-out water immersion in legless men

The hydrostatic pressure gradient during head-out water immersion (HOI) causes a blood shift from the legs into the thoracic cavity to stretch the receptors in the cardiac atria and results in a diuresis in hydrated subjects. The present study was conducted to examine whether the HOI-induced diuresis and related circulatory and hormonal changes were attenuated in the subjects who had no legs (legless men).

Two legless men served as the subjects. They lost both legs 15 and 17 yr ago by accidents and were otherwise healthy. Six normal males participated as controls. The experimental protocol was consisted of a 1-h control, a 3-h HOI (water temperature, 34.5 degrees C) and a 1-h recovery.

Average urine flow (0.6 ml x min(-1)), urinary excretion of sodium (90 microeq x min(-1)), and osmolal clearance (1.4 ml x min(-1)) of the legless subjects increased in the first h of immersion to 0.7 ml x min(-1), 139 microeq x min(-1), and 1.8 ml x min(-1), respectively. These values remained elevated during HOI, however, the magnitude of the increase was smaller compared with the control subjects. Plasma arginine vasopressin was significantly (p < 0.05) decreased from 1.0+/-0.4 microU x 100 ml(-1) to 0.4+/-0.2 microU x 100 ml(-1) during HOI in the normal subjects, but was not in the legless subjects (from 0.5 at control period to 0.4 microU x 100 ml(-1) during HOI). A concurrent reduction of aldosterone and plasma renin activity was observed with an increase in atrial natriuretic peptide during HOI in both subject groups, however, the magnitude of the changes was smaller in the legless subjects compared with the control subjects. Similarly, the average increase in cardiac output during HOI in the legless subjects (by 17%) was less compared with the control subjects (by 31%).

The magnitude of renal, endocrine, and cardiovascular changes in response to HOI in the legless subjects were less than in control subjects, but the responses were qualitatively similar. Accordingly, we suggest that the cephalad blood expansion during immersion is not only due to translocation of blood from the legs but also the abdominal region.