Axial concentration in narrow tube flow for various RBC suspensions as function of wall shear stress.

The flow of RBC suspensions (Hct 25 and 30%) in a constricted section (of length 35 mm and diameter 0.20 mm) in a glass tube was photographed under dark field illumination. The wall shear stress ranged from 0 to 150 dynes/cm2. The following supensions were investigated: normal RBC in plasma (highly deformable); osmotically crenated RBC in hypertonic plasma (hardly deformable); RBC in a 4:1 mixture of plasma and Rheomacrodex (non aggregating). The thickness δ of the cell free medium at the wall was plotted as function of wall shear stress E(w). It was observed that: on increasing E(w) from zero, δ increases to a maximum for values of E(w) between 1.5 and 5.0 dynes/cm2 (maximum axial concentration), then decreases to zero at very high E(w) (no axial concentration); osmotic crenation as well as inhibition of aggregation result in decreased axial concentration for all E(w)