Haemorheological changes during pregnancy.

Haemorheology is concerned with whole blood viscosity and its determinants, i.e. plasma viscosity, haematocrit and shear-dependent flow behaviour of the red cells due to their tendency to aggregate at low and to deform at high shear rates. The basic principles and definitions of haemorheology are explained in Chapter l, section .|.1. In section't .2. the haemodynamicr elevance of the changes in whole blood viscosity are discussed. The haemodynamics ignificance of whole blood viscosity depends on the shear forces exerted on the blood. Under normal circulatory circumstances the local shear forces are always so high, that whole blood viscosity will be low and hardly able to cause circulatory troubles. However, whole blood viscosity may become important when the shearing forces fall below a certain level and are not compensated for by vasomotor control.