PIV and CFD Insight into the Hinge and Near-Hinge Flow Fields of Bileaflet Mechanical Heart Valves

Abstract

Regurgitant flow in mechanical heart valves (MHVs) can generate blood trauma (hemolysis, platelet activation), depending on the jets’ type and energy. In the present study, regurgitant flow in MHVs is studied with Particle Image Velocimetry (PIV) as well as with computational fluid dynamics (CFD) to determine mechanical stresses in blood. The valve under study, a 27-mm MHV, was mounted coaxially with a suitably built in-vitro tester, which allowed easy optical access. This tester was inserted in a closed flow loop, with regurgitant steady flow. The transvalvular pressure was set at a value representative of the mean aortic pressure during diastole. The 2D PIV measurements were performed in a series of planes parallel to the hinge recess plane, defined as Z = 0 mm. The model of investigated MHV was accurately reconstructed with an optical scanner, and the valve model was completed with the same adjacent chambers of the experimental setup, in order to replicate with CFD the PIV experiments. A turbulent stationary flow model was used. The distribution of jets exiting the valve, mainly from hinge corners, was observed with PIV. A repeatability analysis in vivo was performed, with a variation around 5% across 5 repetitions. The averaged experimental data were used as a guideline for model selection and mesh independence analysis in CFD simulations. The findings confirm the importance of the experimental validation of CFD studies in the challenging biomechanical issues of cardiovascular engineering. At the same time, the results emphasize the potential contribution of the CFD approach in areas not easily measurable with experimental techniques.