Flow behavior of erythrocytes. II. Particle motions in concentrated suspensions of ghost cells

Abstract

The detailed motions of individual human red blood cells (rbc) were studied under the microscope in transparent suspensions of red cell ghosts (serving as a model for whole blood) by tracking the particles in flow through tubes having radii R 0 of 32 to 80 μm at Reynolds numbers from 10 −3 to 0.3, and volume concentrations c from 0.10 to 0.93. The rbc velocity distributions were blunted from the parabolic at c > 0.2 with a region of plug flow of radius R c in the core of the tube where the velocities u M were measurably constant. R c increased with increasing c, and decreased with increasing flow rate Q and R 0. At c > 0.4, the rbc were continuously deformed from the resting biconcave shape, and their major axes became aligned within 20° of the flow. By contrast, gluteraldehyde-hardened red cells (hbc) continued to rotate with varying angular velocities, even at c = 0.93. The paths of the rbc exhibited erratic radial displacements whose magnitude and frequency at a given c increased with increasing shear rate, and in a given tube was greatest at 0.2 < c < 0.4 and with particles at radial positions 0.4 < R/ R 0 < 0.8. Appreciable radial displacements also occurred in the plug flow region where it was shown that shear rates of the order 0.01 u M/ R c existed. The distributions of rbc across the median plane of the tube were also measured. At high Q and c < 0.43 there was a pronounced movement of rbc to the periphery, perhaps due to differences in the rates of radial migration between rbc and ghosts stemming from differences in their densities.