Regional blood volume in man determined by radiolabelled erythrocytes

The purpose of the present study was to develop a non-invasive method capable of measuring the regional blood volume in the peripheral circulation. External counting of autologous radiolabelled erythrocytes was performed by dynamic scintigraphy of the calf. During short venous stasis synchronous changes in segmental blood volumes were recorded by plethysmography, thereby obtaining a calibration factor. The recordings were performed with the position of the calf varying between elevated, horizontal and lowered before and after 4.5 min venous stasis with a tourniquet pressure on 57 mmHg applied above the knee. The mean blood volume comprised 3.2 (1.2 ml per 100 ml tissue in the elevated position, 6.0 (1.6) in the horizontal position and 9.8 (2.6) in the lowered position. Correspondingly, the blood volume increase during venous stasis was 120%, 60% and 20% in the three positions. Studies of the reproducibility showed a coefficient of variation of 13.5%. The present study suggests that the method of blood volume measuring should be further evaluated to study the function of capacitance vessels.