Fåhræus effect

[1] Robin Fåhræus was a pathologist at the University of Uppsala in Sweden, and his interest in the suspension stability of blood and later in hemorheology was motivated by the desire to understand the clinical effects of abnormalities in the aggregation and flow behavior of the formed elements.

It was Hess in 1915 who proved that blood obeys the poiseuille law at high flow and low shear.

Fahraeus entered the scene in 1917 through his observation that sedimentation velocity of red corpuscles increases during pregnancy.

He used the concept of buffy coat as the starting point of his work on red cell sedimentation and the more general problem of suspension stability of blood.

He pointed out that fibrinogen was the principal protein involved in red cell aggregation leading to the formation of regular rouleaux and that the process was quite distinct from blood coagulation.

He concluded the following results: (a) In high flow rates in tubes of diameter (< 0.3 mm) the concentration of red cells is lower than large feed tube, the reason being that, red cells are distributed in the axial core and their mean velocity is therefore more than the mean velocity of blood.

[citation needed] Considering steady laminar fully developed blood flow in a small tube with radius of

In capillary tubes, the erythrocytes are more concentrated towards the centre of the vessel, leaving significant RBC-free layer near the vessel walls. The Fahraeus effect occurs because the average RBC velocity is higher than the average plasma velocity.