Modal Decomposition and Lagrangian Coherent Structures Analysis of Flow Past a Dysfunctional Mechanical Aortic Valve

Aortic valve replacement is a viable approach in patients with severe aortic stenosis. Patient outcomes are often suboptimal due to valve dysfunction. This is more critical when mechanical heart valves are used where the inherent complexity of the induced flow field gives limited information on the underlying dynamics. Modal decomposition techniques can extract the dominant structures of such a complex flow, by describing an array of driving flow phenomena in just a few modes. Moreover, Finite time Lyapunov exponents (FTLE) are useful to locate Lagrangian coherent structures (LCS) within the flow.  In this in vitro work, time-resolved 2D particle image velocimetry was performed in the aorta downstream of a mechanical aortic valve under different configurations of dysfunctions. The underlying coherent dynamics of the flows were extracted using proper orthogonal (POD) and dynamic mode decomposition (DMD). While POD ranks coherent structures based on their energy content, DMD ranks them based on temporal coherence and provide information on the global stability characteristics of the flow. Furthermore, FTLE gives a description of LCS’s dynamics. The results show the ability of these techniques to assess mechanical aortic valve dysfunction and in revealing sub-optimal flow patterns.