Spiral blood flow in aorta-renal bifurcation models

Optimal Renal Artery-Aorta Angulation Revealed by Flow Simulation

INTRODUCTION

In the circulatory system, the vessel branching angle may have hemodynamic consequences. We hypothesized that there is a hemodynamically optimal range for the renal artery's branching angle.

METHODS

Data on the posttransplant kinetics of estimated glomerular filtration rate (eGFR) were analyzed according to the donor and implant sides (right-to-right and left-to-right position; n = 46). The renal artery branching angle from the aorta of a randomly selected population was measured using an X-ray angiogram (n = 44). Computational fluid dynamics simulation was used to elucidate the hemodynamic effects of angulation.

RESULTS AND DISCUSSION

Renal transplant patients receiving a right donor kidney to the right side showed faster adaptation and higher eGFR values than those receiving a left donor kidney to the right side (eGFR: 65 ± 7 vs. 56 ± 6 mL/min/1.73 m2; p < 0.01). The average branching angle on the left side was 78° and that on the right side was 66°. Simulation results showed that the pressure, volume flow, and velocity were relatively constant between 58° and 88°, indicating that this range is optimal for the kidneys. The turbulent kinetic energy does not change significantly between 58° and 78°.

CONCLUSION

The results suggest that there is an optimal range for the renal artery's branching angle from the aorta where hemodynamic vulnerability caused by the degree of angulation is the lowest, which should be considered during kidney transplantations.

Flow visualisation study of spiral flow in the aorta-renal bifurcation

The aim of this study was to analyse the flow dynamics in an idealised model of the aorta-renal bifurcation using flow visualisation, with a particular focus on the effect of aorta-to-renal flow ratio and flow spirality. The recirculation length was longest when there was low flow in the renal artery and smaller in the presence of spiral flow. The results also indicate that patients without spiral flow or who have low flow in the renal artery due to the presence of stenosis may be susceptible to heightened development of atherosclerotic lesions.

Recirculation zone length in renal artery is affected by flow spirality and renal-to-aorta flow ratio

Haemodynamic perturbations such as flow recirculation zones play a key role in progression and development of renal artery stenosis, which typically originate at the aorta-renal bifurcation. The spiral nature of aortic blood flow, division of aortic blood flow in renal artery as well as the exercise conditions have been shown to alter the haemodynamics in both positive and negative ways. This study focuses on the combinative effects of spiral component of blood flow, renal-to-aorta flow ratio and the exercise conditions on the size and distribution of recirculation zones in renal branches using computational fluid dynamics technique. Our findings show that the recirculation length was longest when the renal-to-aorta flow ratio was smallest. Spiral flow and exercise conditions were found to be effective in reducing the recirculation length in particular in small renal-to-aorta flow ratios. These results support the hypothesis that in renal arteries with small flow ratios where a stenosis is already developed an artificially induced spiral flow within the aorta may decelerate the progression of stenosis and thereby help preserve kidney function.