Alteration in fluid mechanics in porcine femoral arteries with atheroma development.

Although the relationship between the local wall shear stresses (WSS) and atheroma development has been previously studied, the effect of variable regional wall distensibility with early atherosclerotic lesions and its effect on local hemodynamics have not been well investigated. We induced early atherosclerotic lesion development in one femoral artery in a Yucatan miniswine model with the contralateral artery serving as control. Eight weeks following atheroma formation, hemodynamic and intravascular ultrasound image data were obtained. Using the measured regional arterial distension as the moving boundary condition, unsteady laminar incompressible computational analysis was performed on the reconstructed arterial segments. With the development of early atherosclerotic lesions, there was increased wall distensibility and an increase in the computed normalized wall shear stress amplitude (NWSA). Alterations in the local fluid mechanics and mass transport at these sites may need to be considered in our understanding of the continued growth of these lesions.

Two-dimensional fluid-structure interaction simulation of bileaflet mechanical heart valve flow dynamics.

BACKGROUND AND AIM OF THE STUDY: Mechanical heart valve implantation requires long-term anticoagulation because of thromboembolic complications. Recent studies have indicated that the relatively high wall shear stresses and negative pressure transients developed during the valve closing phase may be dominant factors inducing thrombus initiation. The study aim was a two-dimensional (2D) functional simulation of flow past bileaflet heart valve prosthesis during the closing phase, incorporating the fluid-structure interaction analysis to induce motion of the leaflets. METHODS: The fluid-structure interaction model used was based on unsteady 2D Navier-Stokes equations with the arbitrary Lagrangian-Eulerian method for moving boundaries, coupled with the dynamic equation for leaflet motion. Parametric analysis of the effect of valve size, leaflet density, and the coefficient of resilience at the instant of impact of the leaflet with the housing were also performed. RESULTS: Comparing the predicted motion of the leaflet with previous experimental results validated the simulation. The results showed the presence of negative pressure transients near the inflow side of the leaflet at the instant of valve closure, and the negative pressure transients were augmented during the leaflet rebound process. Relatively high velocities and wall shear stresses, detrimental to the formed elements in blood were present in the clearance region between the leaflet and valve housing at the instant of valve closure. CONCLUSION: The simulation can be potentially applied to analyze the effects of valve geometry and dimensions, and the effect of leaflet material on the flow dynamics past the valve prosthesis during the opening and closing phases for design improvements in minimizing problems associated with thromboembolic complications.