Three-dimensional flow structures past a bio-prosthetic valve in an in-vitro model of the aortic root

Abstract

The flow field past a prosthetic aortic valve comprises many details that indicate whether the prosthesis is functioning well or not. It is, however, not yet fully understood how an optimal flow scenario would look, i.e. which subtleties of the fluid dynamics in place are essential regarding the durability and compatibility of a prosthetic valve. In this study, we measured and analyzed the 3D flow field in the vicinity of a bio-prosthetic heart valve in function of the aortic root size. The measurements were conducted within aortic root phantoms of different size, mounted in a custom-built hydraulic setup, which mimicked physiological flow conditions in the aorta. Tomographic particle image velocimetry was used to measure the 3D instantaneous velocity field at various instances. Several 3D fields (e.g. instantaneous and mean velocity, 3D shear rate) were analyzed and compared focusing on the impact of the aortic root size, but also in order to gain general insight in the 3D flow structure past the bio-prosthetic valve. We found that the diameter of the aortic jet relative to the diameter of the ascending aorta is the most important parameter in determining the characteristics of the flow. A large aortic cross-section, relative to the cross-section of the aortic jet, was associated with higher levels of turbulence intensity and higher retrograde flow in the ascending aorta.

Turbulent Systolic Flow Downstream of a Bioprosthetic Aortic Valve: Velocity Spectra, Wall Shear Stresses, and Turbulent Dissipation Rates

“…For validation of the present model, we will show in the following that the computational model yielded results which were consistent with experimental observations. In particular, we will compare our results to experimental results by Hasler and Obrist (2018) and Vennemann et al (2018) who studied the same bovine BHV as in the present work.…”

“…Hedayat and Borazjani ( 2019 ) showed that small vortical structures in systolic flow of a bileaflet MHV contribute significantly to their thrombogenic potential. Experimental investigations by Hasler et al ( 2016 ) and Hasler and Obrist ( 2018 ) presented three-dimensional PIV data of the flow past a BHV. The measured fields showed turbulent flow with instantaneous shear strain rates beyond 2, 000 s −1 ( Figure 1 ).…”

“… Shear rates in the systolic flow behind a BHV. Adapted from experimental results by Hasler and Obrist ( 2018 ). …”

Performance analysis of the transcatheter aortic valve implantation on blood flow hemodynamics: An optical imaging‐based in vitro study

“…Despite scarcity of literature on in vivo studies on hemodynamics of patients with TAVI valves, there have been some reports using in vitro settings. However, most of the in vitro studies assume non‐physiological geometry, ie, rigid aorta and no aortic arch and two‐dimensional flow . Stühle et al showed that peak systolic velocity of the Edwards Sapien TAVI is slightly higher than that of the native aortic valve, whereas the vorticity and strain rate are considerably higher in the systolic phase .…”

“…Currently, there are multiple TAVI devices in the market, which have different material designs and characteristics. Hatoum et al, Hasler and Obrist, and Giese et al compared the flow patterns of different TAVIs in a rigid model in vitro. Hatoum et al showed that higher rates of RSS was found in the Medtronic Evolut compared to Edwards Sapien 3 (161.27 ± 3.45 Pa vs. 122.84 ± 1.76 Pa), which is explained as the interaction between the Evolut’s distal stent structure and the flow.…”