Frequency dependence of blood viscosity in oscillatory flow 1

Abstract

Womersley’s theory of oscillatory flow is used to derive a parameter, the equivalent viscosity, which characterizes the rheological state of a non-Newtonian fluid under oscillatory conditions. The equivalent viscosity so obtained is analogous to the apparent viscosity determined from Poiseuille’s Law in steady flow, and reduces to apparent viscosity at zero frequency. Experimental studies of the oscillatory flow of blood at different frequencies but the same flow amplitudes show that the equivalent viscosity is frequency dependent. The effect is demonstrated in tubes of radii ranging from 0.0304 to 0.162 cm. This frequency dependence is associated with a marked deviation in hydraulic resistance from that of a Newtonian fluid, but with a negligible effect on inertial reactance.