Continuous monitoring of change in hemodilution during water immersion in humans: Effect of water temperature

Background: The present study was designed to examine whether water tempera ture during head-out immersion (HOI) modifies hemodilution dynamics. Method s: We made continuous measurements of blood density (rho b) during HOI at 3 different water temperatures; the lower critical (32 degrees C), neutral ( 34.5 degrees C), and upper critical (36 degrees C) temperatures in 6 health y male volunteers. Blood was withdrawn continuously from the antecubital ve in for measurement of rho b during 60 min of water immersion with a 10-min control period before the immersion. The density was measured with the mech anical oscillator technique. Hematocrit (Hct), plasma density (rho p), and osmolality were measured at 5-min intervals. Erythrocyte density (rho e) wa s calculated from rho b, rho p and Hct. Cardiac output and BP were measured to calculate total peripheral resistance. Results: Hct, rho h, and rho p d ecreased rapidly in the first 20-25 min of immersion and were maintained at a reduced level during immersion. Plasma volume calculated from rho p and Hct increased with the rho b reduction. These immersion-induced changes wer e independent of these water temperatures. Plasma osmolality and rho e rema ined constant throughout the experimental period in the three temperature c onditions, indicating that the increase in plasma volume and hence hemodilu tion was induced by an isotonic fluid shift from extravascular space. The t otal peripheral resistance increased inversely in proportion to the water t emperature during HOI. Conclusion: In the present condition, water temperat ure did not modify the net transcapillary fluid transfer during HOI in the presence of the temperature dependent increase in vascular tone.