[Changes in plasma and extracellular fluid volumes and plasma protein mass under conditions of head-down tilt hypokinesia and immersion].

Twenty-four young volunteers were exposed to 30-56-hour head-down tilting (at -6 degrees and -15 degrees) in 5 experimental runs. The purpose of the study was to measure volumes of plasma and extracellular fluid, as well as concentrations of plasma proteins and hemoglobin. The results varied but in most cases the plasma volume decreased by 0.46-0.55 1, extracellular fluid volume by 0.75-2.15 1, and plasma proteins by 13.4-30.4 g. The hemoglobin concentration increased by 8-12% and that of plasma proteins in some cases grew and in others diminished. Water loading prevented the plasma volume decrease. The paper discusses with reference to the data in the literature the fate and role of plasma proteins in the regulation of the intravascular volume and fluid redistribution.