Relation of Molecular Size of Dextran to its Effects on the Rheological Properties of Blood.

Abstract

Summary The viscosity of heparinized dog blood at 37°C was studied with the Brookfield cone-plate viscometer at shear rates from 230 sec^-1 down to 5.8 sec^-1 and with the Polarad couette viscometer from 2.0 sec^-1 down to 0.2 sec^-1. The relation of viscosity at various shear rates to red cell concentration was determined on samples of blood in which the hematocrit values were adjusted from 8.0% to 88%. Several fractions of dextran with mean molecular weights ranging from 15,000 to 250,000 were tested for their effects on sedimentation rate and on the viscosity of whole blood and of washed red cells suspended in Ringer-Locker solution. Some dextran fractions contained osmotically active impurities that caused a slight lowering of the hematocrit value. When the viscosity data were corrected for differences in hematocrit values the results showed that all dextran fractions raised blood viscosity, the increase being related to the mean molecular weight of the dextran fraction added. This effect cannot be explained by the change in viscosity of the plasma. Low molecular dextran does not reduce the viscosity of blood samples below the control value.