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, Huntsville, AL) numerically solved 3-D Navier-Stokes equations for a range of bifurcation angles (30-150°) 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° angles. In vivo data were obtained from cremaster preparations of the anesthetized (pentobarbital, 70 mg/kg) hamster (n = 48). 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°, 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.