The influence of non-Newtonian behaviors of blood on the hemodynamics past a bileaflet mechanical heart valve

TL;DR

This study uses detailed simulations to show that blood's non-Newtonian properties significantly affect flow dynamics and shear stresses around a mechanical heart valve, especially at low Reynolds numbers and during peak cardiac cycles.

Contribution

It provides new insights into how shear-thinning and yield stress behaviors of blood influence hemodynamics around bileaflet mechanical heart valves under various flow conditions.

Findings

Non-Newtonian blood increases wall shear stress compared to Newtonian models.

Differences in pressure recovery decrease as Reynolds number increases.

Peak shear stress and blood damage are higher during cardiac cycle peaks with non-Newtonian blood.

Abstract

This study employs extensive three-dimensional direct numerical simulations (DNS) to investigate the influence of blood non-Newtonian behaviors on the hemodynamics around a bileaflet mechanical heart valve under both steady inflow and physiologically realistic pulsatile flow conditions. Under steady inflow conditions, the study reveals that blood rheology impacts velocity and pressure field variations, as well as the values of clinically important surface and time-averaged parameters like wall shear stress (WSS) and pressure recovery. Notably, this influence is most pronounced at low Reynolds numbers, gradually diminishing as the Reynolds number increases. For instance, surface-averaged WSS values obtained with the non-Newtonian shear-thinning power-law model exceed those obtained with the Newtonian model. At $Re = 750$, this difference reaches around 67\%, reducing to less than 1\% at $Re = 5000$. Correspondingly, pressure recovery downstream of the valve leaflets is lower for the shear-thinning blood than the constant viscosity one, with the difference decreasing as the Reynolds number increases. On the other hand, in pulsatile flow conditions, jets formed between the leaflets and the valve housing wall are shorter than steady inflow conditions. Additionally, surface-averaged wall shear stress and blood damage (BD) parameter values are higher (with differences more than 13\% and 47\%, respectively) during the peak stage of the cardiac cycle, especially for blood exhibiting non-Newtonian yield stress characteristics compared to the shear-thinning or constant viscosity characteristics. Therefore, blood non-Newtonian behaviors, including shear-thinning and yield stress behaviors, exert a considerable influence on the hemodynamics around a mechanical heart valve.