Flow field characteristics of surgical bioprosthetic valves vs bileaflet mechanical heart valves under different physiological states: A comparative PIV study

The hemodynamic performance of prosthetic heart valves is critical to long-term postoperative outcomes. This study systematically compares the detailed flow field characteristics of aortic surgical bioprosthetic valves (SBV) and bileaflet mechanical heart valves (BMHV) under different physiological conditions, aiming to provide a fluid-dynamics-based rationale for personalized valve selection. An in vitro pulsatile left heart mock circulatory loop was established using a transparent silicone aortic root model reconstructed from the computed tomography data, with a refractive index-matched working fluid to eliminate optical distortion. Time-resolved particle image velocimetry was employed to quantify transient velocity fields, vortex evolution, and viscous shear stress (VSS) distributions downstream of both valve types under healthy, heart failure, and exercise conditions. The results show that the SBV consistently generates a broad, uniform, and stable central jet across all conditions, whereas the BMHV produces a characteristic triple-jet structure accompanied by pronounced wake separation. Under heart failure conditions, the low-velocity wake region downstream of the BMHV expands markedly, increasing the likelihood of flow stagnation. In contrast to the relatively stable vortex dynamics observed in the SBV, the BMHV induces strong shear layers and pronounced vortex shedding, particularly during late systole. Furthermore, the BMHV exhibits significantly higher VSS levels than the SBV in all cases, with a substantial increase under exercise conditions, suggesting potentially elevated risks of hemolysis and platelet activation. Overall, these findings indicate that the SBV provides more favorable hemodynamic performance, while the BMHV may be associated with increased risks of blood damage and thrombogenesis under specific physiological states.