Central venous pressure and plasma arginine vasopressin during water immersion in man

The influence of increased central venous pressure (CVP) on the plasma concentration of arginine vasopressin (pAVP) was examined in 7 healthy males subjected to water immersion (WI) up to the neck following overnight food- and fluid restriction. During WI the subject sat upright in a pool (water temperature = 35.0 degrees C) for 6 h. In control experiments the subject assumed the same position outside the pool wearing a water perfused garment (water temperature = 34.6 degrees C). CVP increased markedly during WI and after 20 min of immersion it attained a level which was significantly higher than the control value (10.9 +/- 1.5 (mean +/- SE) vs. 2.2 +/- 1.3 mm Hg, p less than 0.01). This increase was sustained throughout the 6 h WI period. Simultaneously, after 20 min pAVP during WI was significantly lower than control values (1.8 +/- 0.3 vs. 2.2 +/- 0.3 pg X ml-1, p less than 0.05) and sustained throughout WI. Systolic arterial pressure increased significantly by 7-10 mm Hg (p less than 0.05) after 2 h of WI, while diastolic arterial pressure was unchanged. Heart rate was decreased by 10 bpm throughout immersion. There was no change in plasma osmolality when comparing control with immersion. A pronounced osmotic diuresis, natriuresis and kaliuresis occurred during WI, counteracting an acute significant increase in plasma volume of 6.5 +/- 1.9% (P less than 0.01 within 20 min of immersion). We conclude that an increase in CVP due to WI is accompanied by suppressed pAVP.