In vitro analysis of the fluid dynamics in the superior vena cava – pulmonary artery anastomosis with an additional systemic to pulmonary shunt

Babies with one pumping ventricle need a series of medical and surgical procedures in order to have an adequate blood flow to the lungs and consequently to survive and grow. The Fontan operation is usually the final stage of surgeries and isolates the systemic and pulmonary circulation. This study focuses on the second stage of surgeries, in which the superior vena cava (SVC) is connected directly to the pulmonary artery (PA). To improve the pulmonary perfusion, it is suggested to connect an additional systemic to pulmonary shunt (SPS) to the SVC-PA anastomosis, which should work as an ejector. The SPS as an ejector is regarded in this report. The objective is to investigate the fluid dynamics in different shunt models. In shunt model 1, the SPS is connected at an angle of 45o and in shunt model 2 the SPS is connected perpendicularly to the left pulmonary artery. Two approaches were applied: in vitro experiments and computational fluid dynamics (CFD) simulations. The influence of the SPS flow on the flow in the SVC (Qsvc), the flow distribution in the lungs and the pressure in the SVC was determined at three different conditions: continuous SPS flow with rigid and with distensible shunt models and pulsatile SPS flow with rigid shunt models. At continuous condition, also the influence of the pulmonary resistance and the upper body pressure is measured. With the CFD model, simulations based on the experiments with continuous SPS flow and rigid shunt models and simulations with increased pulmonary resistance were performed. The experimental and computational results at each condition showed that with an increasing SPS flow the pressure in the SVC did not become too high (maximum increase of 13.5 %), but the total flow (Qtot) in the pulmonary arteries did not increase much either (maximally 23.7%) with respect to the strong decrease of Qsvc (87.4%). Imposing a higher pressure in the SVC led to a higher flow in the SVC and a higher Qtot and a high pulmonary resistance resulted in the opposite. The flow distribution appeared to be determined by the configuration of the shunt model and the pulmonary artery resistance. When the major part of the pulmonary resistance was defined after the pulmonary arteries, in SM1 a recirculation in the pulmonary arteries developed. With a higher resistance at the pulmonary arteries, the flow distribution between the right and left pulmonary artery was not influenced by the configuration anymore. From these results, it can be concluded that the SPS did not work as an ejector. The increase of Qtot was small, because Qsvc was blocked instead of entrained. The difference in angle and position of the SPS did not improve the effect of the ejector. Neither did the distensibility and the pulsatile flow through the SPS. 2 Biomedical engineering Analysis of the fluid dynamics in the SVC – PA anastomosis with an additional SPS