Hemorheology

Hemorheology is the study of flow properties of blood and its elements (plasma and formed elements, including red blood cells, white blood cells and platelets). There is increasing evidence indicating that flow properties of blood are among the main determinants of proper tissue perfusion and alterations in these properties play significant roles in disease processes; hence, knowledge of them is vital to any understanding of hemorheology. Blood is a suspension of cellular elements in plasma, therefore exhibit non-Newtonian flow behavior. That is, its viscosity is shear rate dependent. Blood viscosity decrease with increased shear rate, known as shear thinning. Blood viscosity is determined by plasma viscosity, hematocrit (volume fraction of red blood cell, which constitute 99.9% of the cellular elements) and mechanical behavior of red blood cells. Therefore, red blood cell mechanics is the major determinant of flow properties of blood. Red blood cells have unique mechanical behavior, which can be discussed under the terms “erythrocyte deformability” and “erythrocyte aggregation”.