134 HEMATOCRIT AND VISCOSITY REDUCTION OF NEONATAL AND ADULT RED BLOOD CELLS IN NARROW TUBES

Abstract

In blood vessels and in artificial tubes with diameters of less than 500 μm, both the blood viscosity and the hematocrit decrease with decreasing tube diameter. The present study was designed to measure the dependence of viscosity reduction on hematocrit reduction of red blood cell (RBC) suspensions of neonates and adults by means of a capillary viscometer. RBC were suspended in buffer solution at hematocrits of 0.40, 0.50 and 0.601/l. Glass tubes with diameters of 270, 100 and 50 μm were perfused with these suspensions. Tube hematocrit and viscosity decreased significantly at each feed Hct when going from 270 μm tubes to 50 μm tubes. Hematocrit and viscosity reductions were more pronounced for neonatal RBC than for adult cells at each feed hematocrit. At a feed Hct of 0.60 l/l viscosity reduction was 37% for neonates and 29% for adults, whereas at a Hct of 401/l viscosity reductions were only 30% and 25%, respectively. Hct reductions in 50-μm tubes were 27% for neonates and 20% for adults at a feed Hct of 0.60 l/l and 45% for neonates and 40% for adults at a feed hematocrit of 0.40 l/l. Tube viscosities increased exponentially with increasing tube hematocrit. We conclude that the stronger viscosity reduction of neonatal RBC in 50-μm tubes results from the stronger hematocrit reduction of neonatal cells.