Modeling of antegrade and retrograde flow into a branch artery of the aorta: implications for endovascular stent-grafting and extra-anatomical visceral bypass.

PURPOSE: To compare antegrade and retrograde flow characteristics in a branch of a conduit under typical pulsatile pressure and flows, seeking an answer to the question: "Does it matter whether inflow to a branch vessel is antegrade or retrograde?" METHODS: A model was built to simulate an abdominal aorta with a branch designed to approximate a typical renal artery. Experiments were conducted to measure the flow rates from 40- and 200-mm-long inflow conduit tubes simulating a branch with antegrade and retrograde inflow configurations. For the base case with a flush origin of the branch, the pressure difference between the main conduit and branch vessel was adjusted so that the average branch flow rate was 1.22 L/min, representing average renal artery flow. A pump produced a pulsatile 5-L/min flow of a glycerol/water solution through a tube to mimic blood flow through the aorta at a mean inlet pressure of 97 mmHg, with systolic and diastolic pressures of 121 and 78 mmHg, respectively. Computational fluid dynamics (CFD) simulations were performed for the flush, antegrade inflow, and retrograde inflow cases. The CFD-predicted flow rates at the branch vessel outlet for all 3 geometries were compared with the experiments. RESULTS: From the experiments, the mean time-average branch vessel outflow rate through a 40-mm conduit for the antegrade case was 1.22+/-0.01 L/min, which was the same as the retrograde case (1.21+/-0.01 L/min; within the experimental error). However, the branch vessel outflow flow rate through a 200-mm conduit for the retrograde case was 0.07 L/min lower than the antegrade. The results from the CFD model were in good agreement with the experiments. CONCLUSION: The experiments and CFD results suggest that there is negligible difference in the outflow rates to a branch vessel in antegrade and retrograde directions for 40-mm-long conduits. However, for a 200-mm conduit, the flow to a branch vessel through the retrograde path is lower than for the antegrade direction, which has implications for the insertion of branches to stent-grafts and extra-anatomical surgical bypass for visceral revascularization.