Relationship between blood flow direction and endothelial cell orientation at arterial branch sites in rabbits and mice.

The orientation of endothelial cells near arterial branch sites has been compared with flow streamlines near the arterial wall. We detected cell orientation by examining cell impressions in vascular casts of rabbit and mouse arterial branch sites. Flow streamlines were assessed in glass models with flow parameters approximating mean in vivo values. At high Reynolds numbers (large arteries), secondary flow develop near branch sites, and this was reflected in the pattern of streamlines near the vessel wall. At symmetrical Y bifurcations, streamlines originating near the inner wall of the branches are directed toward the lateral wall; thus they appear to wind around the daughter vessels and merge on the lateral wall. A similar phenomenon was observed on a 90 degree side branch. When flow conditions in the Y bifurcation and side branch models approximated those at the iliac bifurcation and renal artery origin, respectively, the streamlines near the walls were almost identical to the patterns of endothelial cell orientation. At very low Reynolds numbers, no secondary flow phenomena occurred and streamlines followed branch geometry. This mimicked endothelial cell orientation in very small vessels. Hence the influence of mean blood flow on endothelial cell was well predicted by the model studies.