Cell-resolved simulation of red blood cells' behavior in high-shear organ-scale flows: a Norwood case study

A key challenge in the design and improvement of cardiovascular surgeries is preventing detrimental complications such as clot formation and hemolysis. Numerical simulation of red blood cell (RBC) membrane deformation is crucial in identifying and averting erythrocyte damage under high mechanical stresses. Hence, a multi-scale RBC solver is developed using the finite element method, fast Lagrangian particle tracking specially designed for periodic flows, and boundary element method for fluid-structure interactions. Using this framework, we can computationally study the mechanical behavior of RBCs at non-physiological stresses (up to 230Pa) present in complex biomedical applications, e.g., post-Norwood-surgery anatomy, a high-risk operation for single ventricles. The results of simulations performed on three geometries representing Blalock-Taussig (BT) shunts with 2.5 and 4mm diameters, and a 2.5mm central shunt, with more than 500 RBCs per case, suggest that RBCs under high shear stresses created due to the insertion of the shunt could experience around 10% increase in area and one-fold elongation (visualized as damage maps for comparison). Furthermore, the smaller BT shunt produces larger areal strains, proving its inferiority. Among the studied designs, the central shunt, creating the highest incidents of large areal strain, shear strain, and elongation, is the riskiest option.