Jingshu Wu

Numerical Investigation of the Effects of Channel Geometry on Platelet Activation and Blood Damage

Thromboembolic complications in Bileaflet mechanical heart valves (BMHVs) are believed to be due to the combination of high shear stresses and large recirculation regions. Relating blood damage to design geometry is therefore essential to ultimately optimize the design of BMHVs. The aim of this research is to quantitatively study the effect of 3D channel geometry on shear-induced platelet activation and aggregation, and to choose an appropriate blood damage index (BDI) model for future numerical simulations. The simulations in this study use a recently developed lattice-Boltzmann with external boundary force (LBM-EBF) method [Wu, J., and C. K. Aidun. Int. J. Numer. Method Fluids 62(7):765–783, 2010; Wu, J., and C. K. Aidun. Int. J. Multiphase flow 36:202–209, 2010]. The channel geometries and flow conditions are re-constructed from recent experiments by Fallon [The Development of a Novel in vitro Flow System to Evaluate Platelet Activation and Procoagulant Potential Induced by Bileaflet Mechanical Heart Valve Leakage Jets in School of Chemical and Biomolecular Engineering. Atlanta: Georgia Institute of Technology] and Fallon et al. [Ann. Biomed. Eng. 36(1):1]. The fluid flow is computed on a fixed regular ‘lattice’ using the LBM, and each platelet is mapped onto a Lagrangian frame moving continuously throughout the fluid domain. The two-way fluid–solid interactions are determined by the EBF method by enforcing a no-slip condition on the platelet surface. The motion and orientation of the platelet are obtained from Newtonian dynamics equations. The numerical results show that sharp corners or sudden shape transitions will increase blood damage. Fallon’s experimental results were used as a basis for choosing the appropriate BDI model for use in future computational simulations of flow through BMHVs.

Simulations of Flow Through Bileaflet Mechanical Heart Valves to Assess Platelet Damage

Prosthetic heart valves have been used for over 50 years to replace diseased native valves but still lead to severe complications such as hemolysis, platelet aggregation, and thromboembolic events. The most widely implanted design is the bileaflet mechanical heart valve (BMHV). Most modern BMHV designs have better flow hemodynamics and blood damage performance than their earlier-generation counterparts. However, blood element trauma and thromboembolic events still remain as major complications of current BMHV designs. These problems have been linked to blood element damage caused by non-physiological stresses. These stresses are caused by the complex flow fields that arise due to prosthetic heart valve design, particularly in the leaflet hinge region. In order to reduce the severity of these complications, the blood damage that occurs in flows through prosthetic heart valves must be well understood.Copyright

A Numerical Investigation of Blood Damage in the Hinge Area of BMHV

Bileaflet mechanical heart valves (BMHVs) have been widely used to replace native valves. Unfortunately, the design of bileaflet MHVs produces flow fields that may cause damage to blood elements, especially at the hinge area. The objectives of this study are to analyze the flow properties around the hinge area and through the valve, to further understand the cause of blood damage and provide improved designs to reduce the adverse hemodynamic effects of valves that cause platelet activation and damage blood elements. An important part of this improvement is to understand the hemodynamic effects produced by different valve designs, and how the surrounding flow fields affect thromboembolic formation. The hemodynamics of the valve flow is characterized by complex spatial and temporal three-dimensional structures that arise from the pulsatility of the flow, the complexity of the geometry and the flow-dependent motion of the valve leaflets. High fidelity simulations of the valve flow fields throughout the cardiac cycle is required to improve and refine existing valve designs so as to ultimately develop bileaflet MHVs with minimal thromboembolic complications.Copyright