Experimental measurement of dynamic fluid shear stress on the ventricular surface of the aortic valve leaflet

Abstract

Aortic valve (AV) calcification is a highly prevalent disease with serious impact on mortality and morbidity. The exact causes and mechanisms of AV calcification are unclear, although previous studies suggest that mechanical forces play a role. It has been clinically demonstrated that calcification preferentially occurs on the aortic surface of the AV. This is hypothesized to be due to differences in the mechanical environments on the two sides of the valve. It is thus necessary to characterize fluid shear forces acting on both sides of the leaflet to test this hypothesis. The current study is one of two studies characterizing dynamic shear stress on both sides of the AV leaflets. In the current study, shear stresses on the ventricular surface of the AV leaflets were measured experimentally on two prosthetic AV models with transparent leaflets in an in vitro pulsatile flow loop using two-component Laser Doppler Velocimetry (LDV). Experimental measurements were utilized to validate a theoretical model of AV ventricular surface shear stress based on the Womersley profile in a straight tube, with corrections for the opening angle of the valve leaflets. This theoretical model was applied to in vivo data based on MRI-derived volumetric flow rates and valve dimension obtained from the literature. Experimental results showed that ventricular surface shear stress was dominated by the streamwise component. The systolic shear stress waveform resembled a half-sinusoid during systole and peaks at 64–71 dyn/cm2, and reversed in direction at the end of systole for 15–25 ms, and reached a significant negative magnitude of 40–51 dyn/cm2. Shear stresses from the theoretical model applied to in vivo data showed that shear stresses peaked at 77–92 dyn/cm2 and reversed in direction for substantial period of time (108–110 ms) during late systole with peak negative shear stress of 35–38 dyn/cm2.

In Vitro Characterization of Bicuspid Aortic Valve Hemodynamics Using Particle Image Velocimetry

“…3), to simulate pulsatile physiological flow and pressure conditions in an in vitro setup. 11,22,[40][41][42] Compliance and resistance elements were adjusted to achieve desired flow and pressure conditions. The cardiac output, ventricular pressure and aortic pressure were measured at 500 Hz using a custom LabView program for 15 cycles, to obtain statistically converged ensemble averaged flow and pressure curves.…”

Cyclic strain induces dual-mode endothelial-mesenchymal transformation of the cardiac valve

“…VECs typically align perpendicular to flow (23,24), resulting in an anisotropic alignment on the inflow surface that is oriented circumferential to the valve leaflet (23,25). VECs in the outflow surface generally exhibit no preferred orientation and are isotropic (23) due to oscillatory blood flow patterns (26).…”

Hemodynamic and Cellular Response Feedback in Calcific Aortic Valve Disease

“…For example, the normal tricuspid valve requires some amount of vorticity to facilitate rapid valve closure after systole. 71 Using a similar particle tracking and aortic valve explantation technique, Yap et al 75,76 were also able to demonstrate that the shear stresses on the ventricular side of the valve are higher than those on the aortic side. The ventricular side shear stress peaked at 64 to 71 dynes/cm 2 during systole and reversed in direction at the end of systole for only 15 to 25 milliseconds at 40 to 51 dynes/cm 2 .…”