(physiology) The ratio of shear stress to shear rate in a fluid
The apparent viscosity in Newtonian fluid (homogenous) remains the same with changing shear strain rate at constant temperature and pressure. However, a non-Newtonian fluid, the apparent viscosity changes with the rate of shear strain, e.g. apparent viscosity decreases as shear rate increases, as it occurs in sheer thinning (pseudoplastic) fluid.
In blood physiology, the circulating blood is a non-Newtonian fluid, and thus the apparent viscosity describes the resistance to blood flow in small blood vessels.
- effective viscosity (non-Newtonian fluid)