Numerical investigation of turbulent features past different mechanical aortic valves

Abstract

Flow through mechanical aortic valves (MAVs) has been constantly associated to higher haemolysis and platelet activation levels with respect to native valves, due to non-physiologic haemodynamic features. Both computational and experimental investigations have correlated the blood damage to augmented levels of turbulent stress downstream of MAVs. This study provides a computational estimation, drawn from high-resolution direct numerical simulations, of turbulent and fluctuating viscous stresses in three different MAV configurations, at subsequent stages of the cardiac cycle. The configurations comprise a St. Judes Medical Regent valve (SJMV), a Lapeyre-Triflo FURTIVA valve (LTFV) with three leaflets, and a SJMV with vortex generators (VGs). Non-standard configurations are expected to mitigate the mean stress level on blood constituents reducing the turbulent production. Computations are carried out by means of a finite-difference flow solver with a direct-forcing immersed boundary technique to handle fixed and moving bodies. The VGs are found to provide instabilities which corrupt the Kármán-like vortex shedding downstream of the leaflets, reducing the intensity of turbulent kinetic energy at the peak flow rate, thus lowering the local Reynolds shear stress. Conversely, the LTFV configuration provides comparable haemodynamic performance at peak flow rate but further reduced stress level in the deceleration phase. These interpretations are supported by probability density distributions from three-dimensional fields, and further corroborated by a pointwise mapping of the Taylor length scale and local energy spectra. The outcomes of this study might potentially be exploited to improve the design of new-generation MAVs, with the aim of decreasing the risk of thromboembolic complications.

Electro-fluid-mechanics of the heart

“…A very similar dynamics for the aortic root was recently reported by Nitti, De Cillis & de Tullio (2022) who investigated the flow downstream of several valves by direct numerical simulation. During peak systole, the highest Reynolds number of the cardiovascular system was attained () and yet the energy spectra were not characterized by the small-scale content of statistically steady turbulence at the same .…”

Fluid-structure interaction simulation of mechanical aortic valves: a narrative review exploring its role in total product life cycle

“…A crucial consideration involves deciding whether to represent the entire geometry under investigation as a two-dimensional (2D) or three-dimensional (3D) geometrical model ( Figure 2A ). Since the flow structures downstream of a BMAV are highly 3D ( 33 , 86 ), the vast majority of FSI studies opted for a 3D representation ( 27 , 28 , 31 , 33 – 35 , 37 – 72 , 74 – 83 ) ( Table 1 ). Nevertheless, 2D simulations were conducted in previous studies focusing on the FSI approach ( 43 , 85 ).…”

“…Concerning the geometrical modelling of the BMAV, in the majority of FSI studies the device’s geometry was reconstructed to replicate commercially available designs, such as the Bicarbon valve (Corcym Srl, Milan, IT) ( 58 , 59 , 67 , 71 ), the ATS Open Pivot valve (Medtronic, Dublin, IR) ( 54 – 56 , 63 , 75 , 79 ), the On-X valve (Artivion, Kennesaw, GA, USA) ( 38 , 45 ) and valves from St. Jude series (Abbott Laboratories, Chicago, IL, USA) ( 27 , 28 , 31 , 33 , 35 , 37 , 49 – 53 , 57 , 60 – 62 , 64 – 66 , 68 – 70 , 72 – 77 , 81 – 85 ). Nevertheless, idealized valve models, which do not refer to specific commercial designs, are sometimes considered ( Figure 2C ) ( 42 ).…”

“…Generally, the BMAV sewing cuff is not included in the structural domain, nor it is accounted for in determining model geometry, as it does not alter blood flow patterns ( 45 ). Consequently, the BMAV geometrical model can include valve leaflets and housing ( 28 , 31 , 33 , 35 , 37 – 41 , 44 – 72 , 75 – 81 , 83 – 85 ) or valve leaflets only ( 27 , 34 , 36 , 42 , 43 , 73 , 74 ), ( Table 1 ). Typically, only the FSI between valve leaflets and blood is of interest, and therefore only valve leaflets are included in the structural domain of the simulation.…”

“…However, PIV-based approaches are extremely time-consuming and require an expensive equipment, in particular when four-dimensional (4D) velocity measurements have to be performed to fully characterize the fluid dynamics through BMAVs. Therefore, it is advisable to complement PIV measurements with CM&S, which can provide 4D flow fields with adequate spatial and temporal resolution, enabling comprehensive fluid dynamic analyses and thromboembolic risk prediction ( 31 , 32 ). The integration of experimental and computational approaches is particularly recommended for evaluating thrombogenicity and hemolysis risk associated with heart valve prostheses ( 29 ).…”