Hemorheology, also spelled
haemorheology (from the
Greek ‘αἷμα, haima "
blood" and
rheology), or
blood rheology, is the study of flow properties of blood and its elements of
plasma and
cells. Proper tissue
perfusion can occur only when blood's rheological properties are within certain levels. Alterations of these properties play significant roles in disease processes. Blood
viscosity is determined by plasma viscosity,
hematocrit (volume fraction of red blood cell, which constitute 99.9% of the cellular elements) and mechanical properties of
red blood cells. Red blood cells have unique mechanical behavior, which can be discussed under the terms
erythrocyte deformability and
erythrocyte aggregation. Because of that, blood behaves as a
non-Newtonian fluid. As such, the viscosity of blood varies with
shear rate. Blood becomes less viscous at high shear rates like those experienced in peak-
systole. Contrarily, during end-
diastole, blood moves more slowly and becomes thicker and stickier. Therefore, blood is a
shear-thinning fluid.
