Fahraeus effect and cell screening during tube flow of human blood. I. Effect of variation of flow rate 1

Glass capillaries (I.D. 15–95 μm) were perfused with red cell suspensions in buffered Ringer’s solution using driving pressures which corresponded to wall shear stresses between 5 and 400 dynes/cm². The hematocrit within the capillaries (H_T), in the discharge reservoir (H_D), and in the feed reservoir (H_F) as well as the volume flow rate through the capillaries were determined. It was observed that variation of flow rate resulted in significant changes of the screening effect (H_D/H_F < 1) and the Fahraeus effect (H_T/H_D < 1): cell screening increased and the Fahraeus effect decreased upon reduction of volume flow rate ( μ ¯ -values ranging from 10 to 10³ sec⁻¹). The combined effect of both mechanisms resulted in an increase of capillary hematocrit with decreasing flow rate. It is concluded that cellular overvelocity increases with shear stress due to shear-dependent axial concentration of flowing red cells.