EVALUATION OF BLOOD-VISCOSITY AT HIGH-SHEAR RATE WITH A FALLING BALL VISCOMETER

We tested the accuracy and the usefulness of the MT90 (falling ball) viscometer as an alternative to more expensive and sophisticated devices for physiological and clinical investigations. This instruments measures viscosity from the velocity of a ball falling through a syringe filled with less than 1 ml of blood or plasma at a shear rate of 1 000 s-1, i.e. the range of the so-called 'newtonian' behavior of blood. We postulated that this shear rate allows us to measure RBC rigidity in a completely disaggregated structure. Four indices of RBC rigidity derived from high shear rate viscometry were used: mu45r (i.e. blood viscosity at corrected hematocrit 45% divided by plasma viscosity); 'Tk' (Dintenfass); 'k' (Quemada), 'mu(RBC)' (Breugel and coll.). All were strongly correlated to each other (r=0.98 p<0.01) and easily detected in vitro rigidification of RBCs with (a) ionophore A23187 (10(-4)M); (b) heating at 56-degrees-C during 10 min; (c) 30 min incubation in hypercalcemic-hyperosmolar buffer, when used together with Hanss' hemorheometre. At this shear rate, modifications of blood viscosity induced by changes (within a physiological range) of hematocrit and RBC rigidity were correctly described by both Quemada's and Dintenfass's equations for blood viscosity. 'k' values given by the equation of Quemada at this shear rate correlated with RBC rigidity indices calculated with the Carri-Med rheometer using both Quemada's and Wang's equations. Correlations between these indices of rigidity and those given by the hemorheometre were found only for in vitro experiments of RBC stiffening, while in clinical situations viscometric and hemorheometric indices gave rather different results. The coefficient of variation for viscometric measurements was 2% (plasma viscosity) and 3% (blood viscosity). We conclude that this viscometer gives results consistent with other methods. We suggest that it is useful and accurate for physiological and clinical studies.