The blood flow through an aortic coarctation before and after corrective surgery was simulated using computational fluid dynamics (CFD) with a state-of-the-art scale-resolving turbulence model (Large eddy simulation, LES). In this manner, the transitional and turbulent effects in the pulsating blood flow could be accounted for. Aortic geometry and in-plane velocity profiles in the ascending and descending aorta were measured using MRI. The velocity profiles provided patient-specific flow boundary conditions for the fluid model. The simulation computed the turbulent kinetic energy (TKE) of the flow, which is a measure of the turbulent velocity fluctuations. High levels of TKE are undesirable, as the increased fluctuations removes energy from the mean flow.

Surgery was performed to widen the coarctation and catheter measurements showed a decrease in pressure drop, which resulted in an increased flow rate. As a consequence of the increased flow, the local Reynolds number also increased. The results from the CFD-simulations confirmed the pressure drop, but also showed that for the post-surgery model TKE levels increased at peak systole in the immediate downstream region of the coarctation.

The relationship between pressure drop, flow rate, coarctation diameter and Reynolds number is non-linear, and if both the flow rate and coarctation diameter increase as an outcome of surgery, the local Reynolds number may also increase. This, in turn, can result in an elevation of TKE levels after surgery.

Figure 1

Volume rendering of TKE in pre- and post-surgery models