Journal of Applied Physiology, Vol 38, Issue 4 570-575, Copyright © 1975 by American Physiological Society
Plasma volumes and constituents of heat-exposed men before and after acclimatization
L. C. Senay Jr
Five men underwent a 2-wk exercise regimen and were then exposed to 45
degrees C db, 28 degrees C wb, wind speed 1 m/s for 12 h while at rest.
Body weight was maintained with 0.1% saline. One week later the exposure
was repeated without rehydration. After heat acclimatization, the 12-h
experiments were repeated. Frequent body weights, rectal temperatures, and
venous blood samples were obtained. Results indicated that hemodilution
upon acute heat exposure is partially due to protein influx into the
vascular volume and the hemodilution allowed considerable loss of body
water before plasma volume returned to preexposure values. Water within the
vascular volume appeared to be in equilibrium with that in other body
compartments before but not after acclimatization. Acclimatization altered
the rate of protein transfer (and water movement) such that hemodilution
was accomplished more rapidly than before acclimatization. Early
hemodilution was quite labile and depended upon subject hydration during
the first hour of heat exposure.
