Journal of Applied Physiology, Vol 49, Issue 2 184-188, Copyright © 1980 by American Physiological Society
Characterization of renal response to prolonged immersion in normal man
M. Epstein, A. G. DeNunzio and M. Ramachandran
During the initial phase of spaceflight, there is a translocation of fluid
from the lower parts of the body to the central vascular compartment with a
resultant natriuresis, diuresis, and weight loss. Whether this natriuresis
and diuresis result in the attainment of a new steady state or whether the
circulatory adjustment is incomplete is the subject of continuing
controversy. Because water immersion is regarded as an appropriate model
for studying the redistribution of fluid that occurs in weightlessness, we
carried out an immersion study of relatively prolonged duration in order to
characterize the temporal profile of the renal adaptation to central
hypervolemia. Twelve normal male subjects underwent an immersion study of
8-h duration in the sodium-replete state. Immersion resulted in marked
natriuresis and diuresis which were sustained throughout the immersion
period. The failure of that natriuresis and diuresis of immersion to abate
or cease despite marked extrcellular fluid volume contraction as evidenced
by a mean weight loss of -2.2 +/- 0.3 kg suggests that central blood volume
was not restored to normal and that some degree of central hypervolemia
probably persisted.
