Volume studies. II. Simultaneous determination of plasma volume, red cell mass, extracellular fluid, and total body water before and after volume expansion in dog and man.

A method for the simultaneous determination of plasma volume, red cell mass, extracellular fluid volume, and total body water is described. Plasma volume and red cell mass were determined by a standard dual gamma-tracer technique using 125radioiodinated labeled human serum albumin (125RISA) and 51radiochromate-tagged red cells (51Cr-RBC). Extracellular fluid volume and total body water were determined by a dual beta-tracer technique which utilized radiosulfate-35 (35SO4) and tritiated water (THO), respectively. Kinetic studies of each radionuclide in normal and fluid expanded states demonstrated equilibration of 125RISA and 51Cr-RBC in 5 minutes, 35SO4 and THO in 30 minutes. The results of the volume studies in dog and man demonstrated less than 10 per cent variation on repetitive study, and better than 70 per cent accuracy in estimating a known fluid change. This technique will enable a more precise and simplified investigation of the physiology of body fluid volume regulation in health and disease.