Regional Variations in the Proportion of Red Cells in the Blood in Man

Summary: Surface counting techniques following the intravenous injection of 51 Cr labelled red cells and 131 I labelled human serum albumin have been used to investigate the regional haematocrit in normal subjects, subjects with splenic enlargement and after splenectomy. Regional variations in the proportions of red cells and plasma were demonstrated, the red‐cell concentration being highest at the precordium and lowest in the hepatic region. Intermediate values were obtained for the lumbar and splenic regions in normal subjects. The enlarged spleen has a definite but variable tendency to be associated with high local haematocrit values when compared with the venous haematocrit. Raised whole‐body to venous haematocrit ratios result from the pool of red cells in the spleen which shows delayed mixing with the cells of the extrasplenic circulation. The raised whole‐body to venous haematocrit ratio associated with splenomegaly is more dependent on the concentration of the pooled cells relative to the venous haematocrit than on the volume of pooled cells and spleen size. The significance of variations in regional to venous haematocrit and whole‐body to venous haematocrit ratios is discussed.