Hematocrit of the Human Cranial Blood Pool

A technique is described utilizing the separate injection of gamma-labeled red cells and plasma, with subsequent measurement of the amount of each label found in the cranial portion of the head and in venous blood specimens. By this means the relationship between the hematocrit of the cranial blood pool and venous blood is determined. In the basic technique, Cr 51 is used separately and sequentially as the label for both red cells and plasma. A modification of this technique using I 131 human serum albumin is described also. Only antecubital venipuncture for injection and sampling was utilized. The mean hematocrit of the human cranial blood pool was found to be 0.84 times the venous hematocrit by both dual tracer methods. This technique should be applicable to other organs. The distribution ratios of any gamma emitters in brain and blood should be similarly measurable.