Effects of erythrocyte aggregation and venous network geometry on red blood cell axial migration

Axial migration of red blood cells in small glass tubes can cause blood vis cosity to be effectively independent of shear rate. However, this phase sep aration may not occur to the same degree in the venous network due to infus ion of cells and aggregates at branch points. To investigate this hypothesi s, we followed trajectories of fluorescently labeled red blood cells in the venular network of the rat spinotrapezius muscle at normal and reduced flo w with and without red blood cell aggregation. Cells traveling near the wal l of an unbranched venular segment migrated similar to1% of the longitudina l path length without aggregation and migrated slightly more with aggregati on. Venular segment length between branch points averaged three to five tim es the diameter. Cells in the main vessel were shifted centrally by up to 2 0% of diameter at branch points, reducing the migration rate of cells near the opposite wall to <1% even in the presence of aggregation. We conclude t hat formation of a cell-free marginal layer in the venular network is atten uated due to the time dependence of axial migration and the frequent branch ing of the network.