A new hydrodynamic interaction mechanism for the formation of rouleaux

Abstract

The tendency of red cells to stack axially and form aggregates, or rouleaux, in their passage through the microcirculation is a well documented phenomenon. The mechanism for the formation of rouleaux is commonly attributed to London–Van der Waals attractive forces and to intercellular bridging by macromolecular monolayers. While these short range forces and other assumed mechanisms are unquestionably important for red cells that are almost touching, they do not explain the mechanism by which the red cells achieve their nearly touching configuration.

The paper describes a simplified theoretical model for the time-dependent behavior of a closely spaced, neutrally-buoyant chain of identical red cells in Poiseuille flow. The results of this model predict a new hydrodynamical mechanism for the formation of rouleaux in the microcirculation which is of comparable importance to the statistical variation in size of the red cells. This model suggests that the long range forces responsible for the red cell aggregation may be hydrodynamic in origin and due to unequal multi-particle Stokes flow interaction effects. Toward that end, the interaction theory developed by the authors for gravity-driven Stokes flow is extended to the time-dependent, axisymmetric motion of finite chains of neutrally-buoyant spheres in unbounded Poiseuille flow at low Reynolds number. This theory predicts that individual particles in a finite chain of identical cells travel at different velocities due to particle interactions and that these effects are most pronounced for 16–80μ diameter arterioles and venules.