Rheological behaviour of neonatal blood at term with or without polycythemia: A study in 0.38 mm diameter tubes

The intrinsic resistance of red blood cell (RBC) is a determining factor of the blood viscosity. Hematocrit (Ht) greater than 60% significantly contributes to an increase in this factor. This study determines the viscosity of the intracellular content of RBC in neonates with and without polycythemia. The viscosity is measured in two neonate groups, according to the absence of illness and their hematocrit values, using capillary tubes with a 0.38 mm diameter at 25° C. The internal viscosity was found to be lower in polycythemic neonates together with lower plasma viscosity and mean corpuscular hemoglobin levels. The relative viscosity was significantly greater in the polycythemic group. We draw the conclusion, that viscosity changes due to increased hematocrit are compensated by decreases in the plasma and internal viscosities of the red blood cells thus minimizing their effects on tissue blood flow.