Central cardiovascular pressures during graded water immersion in humans.

Thermoneutral (34.9 degrees C) water immersion (WI) was conducted with 12 upright seated normal males at four consecutive water levels (5-10 min each): knee (reference), xiphoid process, fourth intercostal space, and sternoclavicular notch. Thereafter, water was let out of the tank and the experiment was repeated from the neck to the knees at the same levels. Arterial pulse pressure (PP), central venous pressure (CVP), and transmural CVP (TCVP = CVP - esophageal pressure; n = 4) gradually increased with increasing water levels (P < 0.05). Heart rate (HR) decreased at WI to the xiphoid process (P < 0.05) and thereafter remained at this level, whereas mean arterial pressure remained unchanged. There was a closer linear correlation between HR and PP (r = -0.35, P < 0.01) than between HR and CVP (r = -0.13, P > 0.05). Furthermore, there was a significant positive linear correlation between CVP and TCVP (r = 0.83, P < 0.01). We conclude that WI in humans induces an increase in cardiac filling pressures with an increase in PP and a consequent decrease in HR. Furthermore, changes in CVP accurately reflect changes in cardiac distension (TCVP) during WI.