Engineering Optimization of Roller Pump Cardiopulmonary Bypass: High Fidelity In Silico Model of Blood Shear Stress

Roller pump Cardiopulmonary Bypass (RP-CPB) is the predominant form of pediatric CPB worldwide, where an artificial heart-lung machine pumps and oxygenates blood during open-heart surgeries. However, RP-CPB exposes blood to non-physiological high shear stress, which can trigger hemolysis and systemic inflammation. We hypothesize that such shear stresses can be mitigated by data-driven optimization of parameters such as hematocrit (Hct), roller occlusion, and rotational speed (Ω). This study aims to delineate the effect of the parameters on peak shear outcomes.

To test this, we developed 3D in silico closed-loop models incorporating fluid-structure interaction to capture tubing deformation and computational fluid dynamics to resolve internal flow. We conducted 68 simulations across a matrix of Hct (5-60%), occlusion (66, 76%), and Ω (38-95 rpm), and analyzed trends in peak shear and cardiac index (CI). Sensitivity analyses were performed to examine how parameter combinations affected RP-CPB outcomes.

Results show that peak shear stresses and CI increase with occlusion, Hct, and Ω. For both occlusion levels, CI shows strong nonlinear dependence on all parameters, while being more sensitive to Ω at high Hct (>40%) and to Hct at low Hct (<35%). Peak shear stress is primarily driven by Ω, with Hct effects emerging at higher values. Higher occlusion consistently elevates peak shear across all CI levels. The nonlinear relationships reveal potential to reduce peak shear while preserving oxygen delivery. For instance, reducing Hct from 40% to 30% and occlusion from 76% to 66%, while raising Ω from 54 to 95 rpm, lowered peak shear by 15% with slight increase in CI. Similarly, increasing Ω and Hct with less occlusion raised CI with constant shear.

These high-fidelity models offer a platform to optimize RP-CPB settings, minimize supraphysiologic shear stresses, and resolve the multifactorial effects of the parameters on blood flow, providing reference for future clinical strategies.