Internal Viscosity of the Red Cell and a Blood Viscosity Equation

Abstract

BLOOD is known to be viscous and thixotropic^1,2 and its viscosity decreases as the flow velocity, or velocity gradient, increases. While at near zero flow velocities, human blood may exhibit viscosities from 100 to 10,000 times that of water; at high flow velocities, it is only two to ten times that of water^3,4. Perhaps the most remarkable aspect of blood is the fact that it remains fluid even at haematocrits of 95–100 per cent. If the red cells were rigid particles, the consistency of blood at high haematocrits would be that of a brick. It therefore seemed⁵ both obvious and simple that the fluidity of blood and of the packed blood cells can be explained only by the very low internal viscosity of the red cell.