Dynamics of fluid distribution between the blood and interstitium during overhydration.

The dynamics fluid volume distribution between the blood and interstitium was studied in 24 anephric conscious dogs by making serial measurements of blood volume, sodium space, and plasma proteins during several different states of hydration. After recovery from splenectomy and unilateral nephrectomy, the remaining kidney was removed, and intravenous infusion of lactated Ringer solution equivalent to 5%, 10%, or 20% of the body weight followed the next day. Blood volume and sodium space were elevated in each infusion group for the entire 25-h postinfusion period of measurements, while total amount of circulating proteins increased in the 10% group and decreased in the 20% group, which blunted the increase in blood volume in this group. During the first 5 h after infusion, the increase in blood volume was proportional to the increase in sodium space up to a sodium space of 50% above control. By 24 h postinfusion the relationship between blood volume (BV%) and sodium space (SS%) as percent control was linear over the entire range of sodium spaces (BV% = 68.0 + 0.32 SS%, r = 0.99).