Rheology of blood and flow in the microcirculation

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Abstract
Rheological properties of normal human blood as a homogeneous substance: its yield stress and the stress-shear rate function under creeping shear rates, were directly measured for the first time in a Couette type viscometer, the cylinders of which were grooved to minimize heterophase effects (defined herein). The experimental data are well fitted by the Casson equation, which implies reversible aggregation of red cells into rouleaux at low shear rates. In particular, the value of yield stress extrapolated from the Casson equation is found to be equal to the directly measured yield stress within ± 10%. The yield stress is almost independent of temperature over the range 10–37 C. The following questions related to flow in the microcirculation are considered: the relation of yield stress to pressure drop and to the critical closing pressure, the significance of the Casson model to slow flow, and use of rheological parameters in general for microcirculatory flow calculations. Note: (With the collaboration of C. S. Draper, P. J. Gilinson, Jr., C. R. Dauwalter, M. Grove-Rasmussen, and R. Shaw) Submitted on July 10, 1962

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