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 spac e, and sternoclavicular notch. Thereafter, water was let out of the ta nk and the experiment was repeated from the neck to the knees at the s ame levels. Arterial pulse pressure (PP), central venous pressure (CVP ), and transmural CVP (TCVP = CVP - esophageal pressure; n = 4) gradua lly increased with increasing water levels (P < 0.05). Heart rate (HR) decreased at WI to the xiphoid process (P < 0.05) and thereafter rema ined 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 TC VP (r = 0.83, P < 0.01). We conclude that WI in humans induces an incr ease in cardiac filling pressures with an increase in PP and a consequ ent decrease in HR. Furthermore, changes in CVP accurately reflect cha nges in cardiac distension (TCVP) during WI.