Study of Erythrocyte Aggregation by Blood Viscometry at Low Shear Rates Using a Balance Method

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Abstract
Abalance method was used to investigate the viscometric behavior and aggregation properties of blood at very low shear rates. The system was essentially a parallel-plate viscometer, consisting of a thin brass plate suspended by a fine wire from one end of an analytical beam balance. The yield shear stress of a sample was obtained directly by recording stress relaxation curves. Results were obtained for homogeneous Newtonian and non-Newtonian fluids and for blood and various red cell suspensions. It was found that human and canine blood behave as fluids exhibiting a yield stress. Suspensions of red cells in saline had much smaller values of yield stress, which is consistent with greatly diminished erythrocyte aggregation when fibrinogen is lacking. Measured values of the yield stress were in the range of 0.001 to 0.1 dynes/cm2.