Evaluation of Blood Volume Measurement Techniques

Abstract

To assess the ability of an injection of Cr⁵¹-tagged red cells and one of T 1824 to measure a standard part of the total blood volume, two types of experiments have been done. First, three or four successive injections were made, separated by the sampling period of 80 minutes, in both intact and splenectomized dogs under different anesthetic regimes. The tagged cells gave total cell volumes showing no trend away from the expected value, based on the first determination and the cells lost in the sample taken, and the standard deviation was but 3.0 per cent. There was no real difference in this error depending upon the anesthesia. The T 1824 measured plasma volume tended to become progressively greater than the expected value with each injection. This trend could not be corrected out on the basis of either a plasma specific gravity or a hematocrit change. The standard deviation was three times larger than for the cell volume. Part of this variability might be related to fluctuations in dye concentration away from the bestfit slope, as were quite common at various times during the sampling period. Yet, plasma volumes based on the concentration shown at any particular time (e.g., 10 minutes) gave slightly worse agreement with the expected. The second experiment involved measurements of cell and plasma volume after three successive bleedings. Here both volumes were greater than the expected, with the standard deviation of the cell volume still less than that of the plasma volume. Curiously enough, T 1824 could follow the changes in plasma volume in these bleeding experiments a little better than it could reproduce the same volume in essentially normovolemic dogs.