Multi-scale simulation of red blood cell trauma in large-scale high-shear flows after Norwood operation.

Cardiovascular surgeries and mechanical circulatory support devices create non-physiological blood flow conditions that can be detrimental, especially for pediatric patients. A source of complications is mechanical red blood cell (RBC) damage induced by localized supraphysiological shear fields. To understand such complications in single ventricle patients, we introduce a multi-scale numerical model to predict hemolysis risk in idealized anatomies. We employed our in-house CFD solver coupled with Lagrangian tracking and cell-resolved fluid-structure interaction to measure flow-induced stresses and strains on the RBC membrane. The Norwood procedure, known for its high mortality rate, is selected for its importance to single-ventricle population survival. We simulated three anatomies including 2.5 mm and 4.0 mm diameter modified Blalock-Taussig shunts (mBTS) and a 2.5 mm central shunt (CS), with hundreds of RBCs per case for statistical analysis. The results show that the conditions created by these surgeries can elongate RBCs by more than two-fold (3.1% of RBCs for 2.5 mm mBTS, 1.4% for 4 mm mBTS, and 8.8% for CS). Shear and areal strain metrics also reveal that CS creates the greatest deformations on the RBC membrane. These conclusions are further confirmed when strain history and different damage thresholds are considered. The central shunt is more hemolytic in comparison to the modified Blalock-Taussig shunt. Between the two mBTSs, the smaller diameter is slightly more prone to hemolysis. Spatial damage maps produced based on the studied metrics, highlighted hot zones that match the clinical images of shunt thrombosis, demonstrating their potential to enhance cardiac surgery outcomes.