Flow Patterns at the Bifurcation and Curving Portion of the Human Middle Cerebral Artery

The relationship between blood flow and the localized development of atherosclerosis and thrombosis were studied at the bifurcation and curving portion of a human cerebral artery. Blood flow patterns were studied by direct observation and by photographing of tracer particles flowing through the isolated arterial segment, which had been obtained at the time of death and had been prepared in such a way that it was transparent. A standing recirculation zone consisting of a pair of secondary flow spirals, located on both sides of the common median plane of the bifurcation, was formed on the lateral side of the daughter vessels over wide ranges of inflow Reynolds numbers (Re0) and flow rate ratios (Q1: Q0; Q0 and Q1 indicating the quantity of flow in M1 and M2 segment of the middle cerebral artery, respectively). The formation and size of the recirculation zone were largely dependent on Q1: Q0 and Re0. In addition, formation of eddies was observed on the inner side of the curving portion as well as at the bifurcation of the middle cerebral artery. The results suggest that, under physiological conditions, there is a standing recirculation zone in the bifurcation and bending portion of the middle cerebral artery, which affects local mass transfer and interactions between blood cells and the vessel wall. This may contribute to the development of atherosclerosis and thrombosis in this and anatomically similar regions.