Pulsatile flow characteristics in a stenotic aortic valve model: An in vitro experimental study

Aortic stenosis (AS) is one of the most common valvular heart diseases around the globe. The accurate assessment of AS severity is important and strongly associated with accurate interpretation of the hemodynamic parameters across the stenotic valve. In this study, we conducted in vitro fluid dynamic experiments to investigate the pulsatile flow characteristics of a stenotic aortic valve as a function of heart rate. An in vitro cardiovascular flow simulator was used to generate pulsatile flow with a prescribed waveform (40% systolic period and 4L/min cardiac output) under varied heart rates (50 bpm, 75 bpm and 100 bpm). The stenotic valve was constructed by molding silicone into three-leaflet aortic valve geometries wrapping around thin fabrics which increases its stiffness and tensile strength. Two-dimensional phase-locked particle image velocimetry (PIV) was employed to quantify the flow field characteristics of the stenotic valve. Pressure waveforms were recorded to evaluate the severity of the stenosis via the Gorlin and Hakki equations. Results suggest that as the heart rate increases, the peak pressure gradient across the stenotic aortic valve increases significantly under the same cardiac output. Analysis also shows the estimated aortic valve area (AVA) decreases as the heart rate increases under the same cardiac output using Gorlin equation estimation, while the trend is reversed using Hakki equation estimation. Under phase-locked conditions, quantitative flow characteristics, such as phase-averaged flow velocity, turbulence kinetic energy (TKE) for the stenotic aortic valve were analyzed based on the PIV data. Results suggest that the peak systolic jet velocity downstream of the valve increases as the heart rate increases, implying a longer pressure recovery distance as heart rate increases. While the turbulence at peak systole is higher under the slower heart rate, the faster heart rate contributes to a higher turbulence during the late systole and early diastole phases. Based on the comparison with no-valve cases, the differences in TKE was mainly related to the dynamics of leaflets under different heart rates. Overall, the results obtained in this study demonstrate that the hemodynamics of a stenotic aortic valve is complex and the assessment of AS could be significantly affected by the pulsating rate of the flow.