The Microrheology of Red Blood Cell Suspensions

Abstract

The general problem of microrheology is to predict the macroscopic flow properties of a material from a detailed description of the behavior of its constituent elements. This approach has been used to study suspensions of human red cells in plasma or Ringer's solution flowing steadily in rigid tubes 8-25 times the red cell diameter by observing individual cell motions under the microscope. The results have been compared with those previously obtained with model particles under similar conditions. In very dilute suspensions single red cells rotated in orbits similar to those of rigid discs at low flow rates, but, in common with model deformable particles, were observed to migrate away from the tube wall. Linear rouleaux of red cells rotated as rodlike particles and were flexible, bending during their rotational orbits in a manner similar to that of filaments of nylon or Dacron. Transparent concentrated suspensions were produced by preparing ghost cells reconstituted in biconcave form in plasma. In these, the motions of some unhemolyzed red cells were followed. The erythrocyte velocity profiles were blunted at concentrations above 20 %; the cell paths were erratic because of frequent radial displacements, especially at the tube periphery, with the particles being markedly deformed and oriented parallel to the flow. Finally, the difference in flow pattern in large and small vessels is discussed and some relevant model experiments are described.To the rheologist, vertebrate blood is a very concentrated suspension of deformable, disclike particles which circulates in distensible vessels whose sizes range from less than 1 to 3000 red cell diameters. As shown by measurements of the viscosity, blood possesses a remarkable fluidity when compared to other model particle suspensions of spheres and discs. This appears to be due in large measure to the deformability of the red cell, which has been seen to change shape during flow in the capillaries (1, 2) and, as described below, to deform also in large vessels owing to collisions with neighboring particles (3). Fig. 1 compares the relative viscosity, -, (viscosity of suspension/viscosity of pure suspending phase), of a number of model dispersions with that of blood as a function of the volume concentration, c, of suspended particles. It is evi-5 s

TRAIL-coated leukocytes that kill cancer cells in the circulation

“…3F). The enhanced apoptotic effect suggests that blood-cell collisions under flow can promote the apoptotic effects of ES/TRAIL liposomes and agrees with our intuitive understanding of blood rheology, as the presence of erythrocytes is known to create erratic cell paths with frequent cross-streamline displacements (26) and increase the lifetime of colliding doublets to promote aggregate formation (27).…”

Influence of cell shape and aggregate formation on the optical properties of flowing whole blood

“…26 The minimum of the transmittance in microscopy studies was correlated with the presence of disaggregated and randomly oriented RBCs and increased again during the aggregation phase. 5,6 These results correspond well to those presented in Figs. 6͑a͒ and 6͑b͒.…”

“…5 This condition is followed by an increasing degree of alignment with the symmetry axis of the disk-shaped cells oriented along the shear direction, i.e., perpendicular to the flow direction and here along the direction of the probe beam. 6 Schmid-Schönbein et al used a shear rate value of 460 s Ϫ1 to represent a condition of aligned cells. 5 With increasing shear rate the RBCs are elongated to flat prolate-shaped ellipsoids oriented with their symmetry axes along the flow direction.…”

Erythrocyte Velocity and a Velocity Pulse in Minute Blood Vessels on the Surface of the Mouse Brain

“…However, with this technique, the visualization of blood flow had several limitations, as suggested by other workers (1,15). Overlapping red cells obscure textural details in the cell column (1,15). Thus cells would be visualized best either at unphysiologically low hematocrits (15) or in vessels so narrow that the cells move in single file (1,3,16).…”

“…However, with this technique, the visualization of blood flow had several limitations, as suggested by other workers (1,15). Overlapping red cells obscure textural details in the cell column (1,15).…”