On the role of aortic valve architecture for physiological haemodynamics and valve replacement. Part I: flow topology and vortex dynamics

Abstract

Aortic valve replacement has become a growing concern due to the increasing prevalence of aortic stenosis in an ageing population. Existing replacement options have limitations, necessitating the development of improved prosthetic aortic valves.In this study, flow characteristics during systole in a stenotic aortic valve case are compared with those downstream of two newly designed surgical bioprosthetic aortic valves (BioAVs) using advanced simulations. Our findings reveal that the stenotic case maintains a high jet flow eccentricity due to a fixed orifice geometry, resulting in increased vortex stretching in the commissural low-flow regions. One BioAV design introduces non-axisymmetric leaflet motion, which reduces the maximum jet velocity and forms more vortical structures. The other BioAV design produces a fixed symmetric triangular jet shape due to non-moving leaflets and exhibits favourable vorticity attenuation and significantly reduced drag. Therefore, this study highlights the benefits of custom-designed aortic valves in the context of their replacement through comprehensive flow analyses. The results emphasise the importance of analysing jet flow, vortical structures, momentum balance and vorticity transport for evaluating aortic valve performance.

On the role of aortic valve architecture for physiological haemodynamics and valve replacement. Part II: spectral analysis and anisotropy

“…κ −5/3 ε 2/3 /dκ equals 0 over wavenumbers ranging from 4,000 to 9,000 rad/m for time instances between t = 0.12 s and t = 0.19 s. Interestingly, these instants correspond to the times at which the KHI establishes as discussed in 9 . In Fig.…”

“…3 In regards to the fluctuating enstrophy intensity I ω ′2 , the time-averaged value for the VLth30 valvular case is thrice that of the stenotic case and the Ulth0 BioAV case. The elevated levels of fluctuating enstrophy in the VLth30 case arise from the non-axisymmetric and more pronounced leaflet motion, with a displacement magnitude of approximately 2 mm during systole 27,9 . This finding is consistent with the higher levels of streamwise instantaneous vorticity highlighted in the first part of the study 9 .…”

“…Both parts utilise validated and high-fidelity computational approaches. In this paper, the analysis of blood motion strives to comprehensively characterise the turbulence by inspecting the energy carried by the vortical structures of the flow following vortex ring formation, a shedding process including vortex stretching and advection 9 . We seek to observe the typical energy decay of kinetic energy (KE) as described in the theory of turbulence 23 .…”

“…1 (a, b, c) display the distribution of the modal KE at different scalar angular wavenumbers for various time instances considered over systole, represented by thin grey lines. Details on the geometry of three valvular configurations, the stenosed aorta case and the two newly designed bioprosthetic valves (VLth30 and Ulth0), are presented in the Methods section of the first part of the study 9 .…”

“…For the VLth30 case, it is worthwhile to note that the times at which a local minimum in the fluctuating enstrophy temporal evolution is found (i.e. t=0.12, 0.156, 0.21, 0.256 s) correspond to the times at which the area at the vena contracta is maximum 9 .…”