White blood cell plugging and blood flow maldistribution in the capillary network of cat cerebral cortex in acute hemorrhagic hypotension: an intravital microscopic study.

The behavior of white blood cells (WBCs) in the capillary network of the cat brain was studied under normal conditions and during acute hemorrhagic hypotension. A small transilluminated area of the cerebral cortex was observed directly, and blood cells flowing through the capillary network were recorded on cinefilm using a high-speed cinecamera. The cell motion was analyzed on the projection screen using a frame-by-frame method. The time during which a single WBC remained at a capillary branching, ie, stagnant time (ST) was examined in detail. In hemorrhagic hypotension, ST was much longer than that in the normal condition. WBC plugging occurred at capillary branchings, and a nonuniform flow pattern (plasma-WBC-accumulated red blood cells [RBCs]) appeared in perfused capillaries. RBC velocity in capillaries was reduced. The ST level was increased significantly with a decrease in RBC velocity. These findings suggest that acute hemorrhagic hypotension may induce flow maldistribution in cerebral microcirculation.