Circulating red cell volume measured simultaneously by the radioactive iron and dye methods

The measurement of the circulating red cell volume is of considerable value in the study of the circulation in both the normal state and in ex-perimentally induced abnormal circulatory states, and in disease. Modern modifications employing Evans Blue (T-1824) (1 to 3) of the original dye method of Keith et al (4) have clearly shown that plasma volume can be measured with a high degree of accuracy in normal man and animals. Values for normal plasma volume in man deter-mined by several workers are in general agreement both as to absolute plasma volume and plasma volume per unit of body measurement (2, 5 to 7). The method has also proved reliable in the study of intravenous crystalloid (8) and colloid (9) therapy as well as in experimentally induced (10 to 12) and clinical shock (7, 12 to 14). A recent improvement in the method described by Noble (15), in which changes in dye concentration of blood samples are corrected for variations in water content as determined by serum protein measure-ments, should increase the applicability of the technique. There is no general agreement among authors that the dye plasma technique measures either the total or circulating red cell volume. The opinion that cell volume can be calculated from the deter-mined plasma volume and the hematocrit of blood samples drawn from large arteries and veins or the auricle, is based on the assumption that the hematocrit of blood flowing through the entire vascular bed is a constant at all times and under all conditions. Smith (16) found lower value