Numerical analysis of the pressure drop across highly-eccentric coronary stenoses: application to the calculation of the fractional flow reserve

Abstract Background Fractional flow reverse (FFR) is the gold standard assessment of the hemodynamic significance of coronary stenoses. However, it requires the catheterization of the coronary artery to determine the pressure waveforms proximal and distal to the stenosis. On the contrary, computational fluid dynamics enables the calculation of the FFR value from relatively non-invasive computed tomography angiography (CTA). Methods We analyze the flow across idealized highly-eccentric coronary stenoses by solving the Navier–Stokes equations. We examine the influence of several aspects (approximations) of the simulation method on the calculation of the FFR value. We study the effects on the FFR value of errors made in the segmentation of clinical images. For this purpose, we compare the FFR value for the nominal geometry with that calculated for other shapes that slightly deviate from that geometry. This analysis is conducted for a range of stenosis severities and different inlet velocity and pressure waveforms. Results and conclusions The errors made in assuming a uniform velocity profile in front of the stenosis, as well as those due to the Newtonian and laminar approximations, are negligible for stenosis severities leading to FFR values around the threshold 0.8. The limited resolution of the stenosis geometry reconstruction is the major source of error when predicting the FFR value. Both systematic errors in the contour detection of just 1-pixel size in the CTA images and a low-quality representation of the stenosis surface (coarse faceted geometry) may yield wrong outcomes of the FFR assessment for an important set of eccentric stenoses. On the contrary, the spatial resolution of images acquired with optical coherence tomography may be sufficient to ensure accurate predictions for the FFR value

Numerical Simulation of Multi-Span Greenhouse Structures

Greenhouses had to be designed to sustain permanent maintenance and crop loads as well as the site-specific climatic conditions, with wind being the most damaging. However, both the structure and foundation are regularly empirically calculated, which could lead to structural inadequacies or cost ineffectiveness. Thus, in this paper, the structural assessment of a multi-tunnel greenhouse was carried out. Firstly, wind loads were assessed through computational fluid dynamics (CFD). Then, the buckling failure mode when either the European Standard (EN) or the CFD wind loads were contemplated was assessed by a finite element method (FEM). Conversely to the EN 13031-1, CFD wind loads generated a suction in the 0–55° region of the first tunnel and a 60% reduction of the external pressure coefficients in the third tunnel was not detected. Moreover, the first-order buckling eigenvalues were reduced (32–57%), which resulted in the need for a different calculation method (i.e., elastoplastic analysis), and global buckling modes similar to local buckling shape were detected. Finally, the foundation was studied by the FEM and a matrix method based on the Wrinkler model. The stresses and deformations arising from the proposed matrix method were conservative compared to those obtained by the FEM

Analysis of finite element and finite volume methods for fluid-structure interaction simulation of blood flow in a real stenosed artery

This paper presents a qualitative and quantitative comparison between the finite element and the finite volume methods for the fluid-structure interaction simulation of blood flow through a real stenosed artery. The artery geometry corresponds to a severely stenosed (around 75% lumen reduction) portion of the brachiocephalic trunk, located immediately upstream of the bifurcation of this vessel into the right subclavian and right common carotid arteries. The patient-specific geometry was segmented from medical images of a computerized tomography scanner from an individual with the subclavian steal syndrome. Doppler ultrasound velocity measurements were used to determine and impose patient-specific boundary conditions. The numerical simulations were performed in commercial software, Ansys and COMSOL, with a comparative second order discretization for the pressure, velocity and displacement variables. The results of this research disclosed a reasonable overall agreement between the predicted hemodynamics for both approaches. The finite volume method software (Ansys) proved to be more efficient in computational time and memory requirements.This work was developed in the aim of the doctoral grant SFRH/BD/144431/2019, and the projects UIDB/04436/2020, UIDB/04077/2020, funded by the Portuguese Foundation for Science and Technology (FCT). Also, this work was partially funded by Junta de Extremadura through grant GR18175 (partially financed by FEDER)

3D manufacturing of intracranial aneurysm biomodels for flow visualizations: Low cost fabrication processes

There is a continuous search for better and more complete in vitro models with mechanical properties closer to in vivo conditions. In this work a manufacturing process, based on a lost core casting technique, is herein reported to produce aneurysm biomodels to perform experimental hemodynamic studies. By using real artery images combined with a lost core casting technique, three materials were tested: paraffin, beeswax and glycerin-based soap. All in vitro biomodels were compared according to their transparency and final structure. Additionally, comparisons between experimental and numerical flow studies were also performed. The results have shown that the biomodels produced with beeswax and glycerine-based soap were the most suitable in vitro models to perform direct flow visualizations of particulate blood analogue fluids. The biomodels proposed in this works, have the potential to provide further insights into the complex blood flow phenomena happening at different kinds of pathologies and answer to important hemodynamics questions that otherwise cannot be tackled with the existing in vitro modelsFCT – Fundação para a Ciência e Tecnologia within the R&D Units Project Scope: UIDB/00319/2020, UIDB/04077/2020, UIDB/00690/2020 and NORTE-01-0145-FEDER-030171, funded by COMPETE2020, NORTE 2020, PORTUGAL 2020 and FEDER, R.A and C.F.acknowledge the support of Junta de Extremadura through Grants GR18175 and IB16119 (partially financed by FEDER) This project has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No 798014. This project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 82883