Influence of the aortic valve leaflets on the fluid-dynamics in aorta in presence of a normally functioning bicuspid valve.

In this work, we consider the blood fluid-dynamics in the ascending aorta in presence of a normally functioning bicuspid aortic valve (BAV). In particular, we perform an unsteady finite element study in real geometries with physiological velocity boundary conditions at the inlet to assess the effect of the inclusion of the leaflets on the fluid-dynamic abnormalities characterizing BAV cases. To this aim, we perform a comparison in two geometries (a dilated and a non-dilated ones) among three scenarios which are built up for each geometry: BAV without leaflets, BAV with leaflets, and tricuspid case with leaflets. For each case, we compute four indices quantifying flow asymmetry, reversal flows, helical patterns, and wall shear stresses. Our results show that the inclusion of the leaflets increases the fluid-dynamics abnormalities, especially for the non-dilated configuration, which presents a greater increment of the indices. In particular, we observe that the values of the time-averaged wall shear stress and of the systolic jet asymmetry increase by approximatively 100 and 40%, respectively, when considering the leaflets.

Computational models to predict stenosis growth in carotid arteries: which is the role of boundary conditions?

This work addresses the problem of prescribing proper boundary conditions at the artificial boundaries that separate the vascular district from the remaining part of the circulatory system. A multiscale (MS) approach is used where the Navier-Stokes equations for the district of interest are coupled to a non-linear system of ordinary differential equations which describe the circulatory system. This technique is applied to three 3D models of a carotid bifurcation with increasing stenosis resembling three phases of a plaque growth. The results of the MS simulations are compared to those obtained by two stand-alone models. The MS shows a great flexibility in numerically predicting the haemodynamic changes due to the presence of a stenosis. Nonetheless, the results are not significantly different from a stand-alone approach where flows derived by the MS without stenosis are imposed. This is a consequence of the dominant role played by the outside districts with respect to the stenosis resistance.

Expansion and drug elution model of a coronary stent.

The present study illustrates a possible methodology to investigate drug elution from an expanded coronary stent. Models based on finite element method have been built including the presence of the atherosclerotic plaque, the artery and the coronary stent. These models take into account the mechanical effects of the stent expansion as well as the effect of drug transport from the expanded stent into the arterial wall. Results allow to quantify the stress field in the vascular wall, the tissue prolapse within the stent struts, as well as the drug concentration at any location and time inside the arterial wall, together with several related quantities as the drug dose and the drug residence times.

Mathematical explanation of the buckling of the vessels after twisting of the microanastomosis.

BACKGROUND: To obtain free flap success, microvascular anastomosis must be perfectly constructed. External compression, twisting (torsion) of the anastomosis site, tension on the anastomosis site, and kinking of the pedicle must be avoided. Few experimental studies report the patency rates of rat vessels after twisting (torsion) of the microanastomosis: these results recently opened a discussion for the maximal angle of torsion, which can be impressed to a vessel in order to have the best patency rates. MATERIALS AND METHODS: To describe specifically the changing of shape of the vessels after the twisting of the microanastomosis, we extrapolate, to our experimental model (constituted by the femoral vessels of Wistar rats), the mathematical formula that engineers use to calculate the torsion of a beam when a torsion force is applied. The mathematical model used is the shell theory. Then, with a computer program using MATLAB, we could obtain the representation of these shapes at any degree of torsion. RESULTS: If a small load is applied to the vessels, it maintains its straight geometry. However, as soon as the load exceeds a critical value, which is a function of the vessel geometry and its mechanical characteristics, it snaps suddenly to a different equilibrium configuration. This phenomenon is called "buckling." When buckling occurs, wave-like deformations appear on the wall of the vessels. We calculate, in our experimental rat model, the critical twisting angle that induces buckling: maintaining a constant length of dissection of 25 mm, a minimum twisting angle of 360 degrees + 161 degrees, or 105 degrees, is required, respectively, for the femoral artery or vein, to have the buckling phenomenon and the appearance of two waves and decreased section area. CONCLUSIONS: In surgical practice, with the parameters of our experimental Wistar rats model (vessel diameter, length of dissection), it is fundamental to be below 105 degrees of torsion angle for the vein microanastomosis, in order to decrease its risk of failure.

ViVa: the virtual vascular project.

The aim of the virtual vascular project (ViVa) is to develop tools for the modern hemodynamicist and cardiovascular surgeon to study and interpret the constantly increasing amount of information being produced by noninvasive imaging equipment. In particular, we are developing a system able to process and visualize three-dimensional (3-D) medical data, reconstruct the geometry of arteries of specific patients, and simulate blood flow in them. The initial applications of the system will be for clinical research and training purposes. In a later stage, we will explore the application of the system to surgical planning. ViVa is based on an integrated set of tools, each dedicated to a specific aspect of the data processing and simulation pipeline: image processing and segmentation; real-time 3-D volume visualization; 3-D geometry reconstruction; 3-D mesh generation; and blood flow simulation and visualization.