Characterization of Turbulent Flow Behind a Transcatheter Aortic Valve in Different Implantation Positions

Figure 1. Inner lumen geometry of the silicone phantom mimicking the aortic root with reference to the main geometrical parameters of Table 1.

Figure 2. Pulse replicator and its elements during the systolic phase (A) and the diastolic phase (B). The pulse replicator is a hydraulic flow loop consisting of the volumetric pump (VP), the left ventricle (LV), the transcatheter aortic valve (TAV), the stopper (ST), the compliance chamber (CC), the tunable resistor (TR), the left atrium (LA), the mitral valve (MV), and the pressure sensors (PSs). Pressure signals in the CC (PCC) are shown in (C) for the UI and the LI. The flow rate (Q) prescribed at the outlet of the VP (Pump) is shown in (D).

Figure 3. TAV axial positioning in the LI (A) and in the UI (B) and the relative positioning of the LI (OLI) and the UI (OUI) reference systems with respect to the measurement reference system (OSTJ).

Figure 4. Scheme of the Tomo-PIV hardware together with the measurement reference system. The main components for image acquisition are: two CCD Digital Camera, a set of mirrors and a dual cavity Nd:YAG laser with optics for volumetric illumination. Image storage and processing is performed with the software DaVis 8.4 installed on the PC workstation.

Figure 5. Side and axial views of the TAV in the LI (A) and in UI (B). The top views show the TAV at peak flow (tϕ = 0.17 s) and at the end of the diastole (tϕ = 0.86 s). The side view shows the TAV at peak flow. Red dashed lines highlight the TAV's leaflets tips during systole (GOA) while blue lines highlight the TAV's leaflets tips during diastole (PI). The POA is highlighted by yellow dashed lines. The white arrows denote the TAV's degree of expansion in the aortic root silicone phantom at the level of the sinus portion.

Figure 6. Mean streawise velocity v¯y in different cross-sections of the flow-domain: longitudinal plane at 45° together with transversal planes at yLI = yUI = 10, 20, 30, 40 mm for the UI (A) and for the LI (B). The core jet is highlighted by contour lines which include v¯y values higher than 0.5 m/s. High vrms′ values were found close to the aortic wall for the UI due to measurement artifacts. This portion of the flow domain was therefore discarded for subsequent analysis.

Figure 7. Root mean square of velocity fluctuations vrms′ in different cross-sections of the flow-domain: longitudinal plane at 45° together with transversal planes at yLI = yUI = 10, 20, 30, 40 mm for the UI (A) and for the LI (B). Shear layers are highlighted by contour lines which include vrms′ values higher than 0.3 m/s. High vrms′ values were found close to the aortic wall for the UI due to measurement artifacts. This portion of the flow domain was therefore discarded for subsequent analysis.

Figure 8. Turbulent kinetic energy density tke in two longitudinal planes at 45° (left) and 0° (right) for the UI (A) and for the LI (B).

Figure 9. Turbulent velocity spectra Eyy(kx) for points located at increasing distance from the valve (yLI = yUI = 10, 20, 30, 40 mm) on the centerline of the flow domain (x = z = 0 mm) for the LI (A) and for the UI (B).

Figure 10. Turbulent velocity spectra Eyy(ky) for points at different transversal locations (x = 0, 5, 10, 13 mm) on the center plane (z = 0 mm) at a distance of 10 mm from the valve's trailing edge (yLI = yUI = 10 mm) for the LI (A) and for the UI (B).