Changes in body fluid compartments during hypohydration and rehydration in heat-acclimated tropical subjects

Body fluid compartments at different levels of graded hypohydration and partial rehydration were determined using radiotracers in 28 heat-acclimated, male volunteers from tropical regions of India, in hot dry conditions in a climatic chamber. These subjects were hypohydrated to varying degrees (i.e., 1%, 2%, 3%, and 4% body mass deficit) by moderate work in hot conditions in a climatic chamber maintained at 45 degrees C dry bulb temperature and 30% relative humidity. Rehydration study was carried out only in those subjects who were hypohydrated to 3% and 4% body mass and who were brought back to 2% level of hypohydration by receiving a calculated amount of water. Up to the 2% level of hypohydration, a major contribution towards sweat loss was observed from the interstitial fluid (ISF) compartment. At higher levels of hypohydration, no further significant loss from ISF was seen, though significant losses in intracellular fluid (ICF) and plasma volume (PV) were apparent. The present study also found that at the 4% hypohydration level, a maximum fluid contribution was met by the ICF compartment. Significant increases observed in sweat K+ at 3 and 4% also indicate the ICF mobilization, which is rich in K+ ions. On partial rehydration, the ISF compartment held the repletion fluid in excess, and was found to be enough to restore sweat rate to euhydration level. This study clearly indicates that sudorific gain is achieved with partial restoration alone in subjects hypohydrated to 3 and 4% levels.(ABSTRACT TRUNCATED AT 250 WORDS)