Fluid flow in cardiovascular devices and surgical pathways

Almost 1% of neonates are born with a clinically significant congenital heart disease each year in the world. Among these, single-ventricle heart defects are the most serious ones which lead to death in case of no treatment. A series of surgical interventions is typically performed to directly connect the superior and inferior vena cavae (SVC and IVC) to the pulmonary arteries (PA) with the purpose of using the single ventricle solely for pumping the oxygenated blood to the body. This creates a vascular conduit called total cavopulmonary connection (TCPC). The hemodynamic in TCPC is of paramount importance and can lead to serious postoperative complications if not designed properly. Cardiopulmonary bypass (CPB) is the crucial component of these operations requiring aortic cannulation. Cardiopulmonary bypass provides short-term support during these cardiac surgical procedures and the patients with severe cardiorespiratory failure would need an intervention that allows time for intrinsic recovery of the lungs and heart. In this case, Venovenous extracorporeal membrane oxygenation (VV-ECMO) is the preferred clinical intervention as it provides single-site access by using a double-lumen cannula (DLC) with a higher level of mobilization and physical rehabilitation. This thesis will investigate the fluid dynamics in these cardiovascular catheters as well as the total cavopulmonary connections. The current thesis is divided into two main parts with five chapters. The first part of this thesis is dedicated to the experimental and computational investigation of fluid dynamics in two important cardiovascular catheters: aortic and double-lumen cannulae. Different novel designs considering the size constraints for the neonatal and pediatric population are designed and proposed. Time-resolved particle image velocimetry (TRPIV) is then employed as a non-invasive whole-field measurement technique to experimentally quantify the flow characteristics in these cannulae. The same experimental modalities are then performed for the baseline or commercial cannulae and the performance parameters are compared with the proposed models. Finally, computational fluid dynamics (CFD) is employed to investigate the DLC performance inside the right atrium. Following that, 14 parametric cannula configurations considering the arrangement of drainage holes and infusion port are proposed. The computational upshots revealed that the currently used clinical cannulae have room for further optimization. In the second part of the thesis, the fluid flow inside TCPCs is analyzed using in vitro experiments and computational simulations. This part presents a simple and low-cost experimental method that can be utilized for the quantification of hepatic flow distribution (HFD) in complex TCPCs. More importantly, it provides a thorough key experimental data such as power loss (PL), total pulmonary flow split (TPFS), and HFD for a reference idealized TCPC which can be used for validation of CFD simulations of blood flow in complex vascular connections. Finally, CFD simulations using different solvers are performed for the idealized TCPC and also a real patient-specific model and their prediction accuracy is compared against the in vitro data. Our results revealed that turbulent models can predict the key flow parameters with a great level of accuracy and also significantly lower computational cost for both the idealized and real patient-specific models.