Non-Newtonian blood rheology significantly alters hemodynamic predictions during cardiac looping: a computational study.

Introduction: Hemodynamic forces play a key role in early cardiac morphogenesis, yet many computational studies assume Newtonian blood behavior. Here, we evaluate the impact of non-Newtonian shear-thinning rheology on flow patterns, pressure distributions, and wall shear stress (WSS) during cardiac looping using idealized three-dimensional models of the embryonic heart tube. Methods: Five geometries representing progressive looping stages, from a linear tube to an S-shaped configuration with ventricular ballooning, were analyzed under pulsatile flow using both Newtonian and power-law viscosity models. Results and Discussion: Across all stages, Reynolds numbers (Re ≈ 1-7) and Womersley numbers (Wo ≈ 0.3) indicated laminar, quasi-steady flow consistent with embryonic conditions. Incorporating shear-thinning rheology produced substantial deviations from Newtonian predictions, with peak systolic WSS differing by up to ∼94% (range 64%-94% depending on stage) and pressure drops by up to ∼70% (range 48%-70% depending on stage). These effects were most pronounced in regions of increased curvature and geometric complexity. These findings demonstrate that non-Newtonian rheology can substantially alter predicted hemodynamic quantities during cardiac looping and should therefore be considered in future developmental hemodynamic models, particularly when wall shear stress and pressure magnitudes are used to infer mechanobiological responses.