Hemodynamics of the renal artery ostia with implications for their structural development and efficiency of flow.

Background: Energy losses at tube or blood vessel orifices depend on the extent of flare as measured by the dimensionless ratio of the fillet radius of curvature to diameter (r/D).

Objective: The goal of this study was to assess the effect of ostial fillet radii on energy losses at the aorta-renal artery junctions since as much as a quarter of cardiac output passes through the kidneys.

Method: Pressure loss coefficients K for the renal artery ostia as a function of r/D have been determined for representative anatomical variants using finite volume simulations. Estimates of fillet radii in humans from image analysis were employed in simulations for comparison of loss coefficients.

Results: Values for K drop 45% as r/D increases over the range 0-1.3. Image analysis indicates that the ostia are not symmetric in humans with (r/D)superior much larger than (r/D)inferior. Simulations show the loss coefficient depends almost entirely on the superior fillet radius.

Conclusions: Superior fillet radii for both renal arteries are similar to the optimal value to reduce energy losses while the inferior radii are not. Ostial asymmetry may have been induced by higher levels of shear stress present on the superior portion of a developing symmetric ostium of small r/D.