Shear rate gradient in arteriolar bifurcations: theoretical and experimental

Our purpose was to determine whether the shear rate gradient through arteriolar bifurcations in vivo could be predicted from a model of low Reynolds (Re) divergent flow. The computational model (CFD-ACE) numerically solved 3D Navier-Stokes equations for a range of bifurcation angles (30-150/spl deg/) at low Re (0.01). The branch to feed diameter ratio was 4/5; the segment intersection shape was not held constant. Velocity profiles were determined in the feed, and at the start and end of the intersection. Calculated shear rate (dv/dr) predicted a significant increasing gradient along the branch wall, but not along the corresponding lateral wall, especially for the 90/spl deg/ angles. In vivo data were obtained from cremaster preparations of the anesthetized hamster. Fluorescently labeled red blood cells were flow tracers; velocity profiles were obtained at corresponding positions through a sequential series of arteriolar bifurcations, sampling the same range of angle and vessel dimensions. Calculated dv/dr showed an increasing gradient along the branch wall when angle was 80-120/spl deg/, but not for smaller angles, which generally occur further downstream in the network. The data suggest that both bifurcation shape and location within a flow network, together determine the shear gradient in vivo.