Fluid-structure interaction simulation of tissue degradation and its effects on intra-aneurysm hemodynamics

Tissue degradation plays a crucial role in vascular diseases such as atherosclerosis and aneurysms. Computational modeling of vascular hemodynamics incorporating both arterial wall mechanics and tissue degradation has been a challenging task. In this study, we propose a novel finite element method-based approach to model the microscopic degradation of arterial walls and its interaction with blood flow. The model is applied to study the combined effects of pulsatile flow and tissue degradation on the deformation and intra-aneurysm hemodynamics. Our computational analysis reveals that tissue degradation leads to a weakening of the aneurysmal wall, which manifests itself in a larger deformation and a smaller von Mises stress. Moreover, simulation results for different heart rates, blood pressures and aneurysm geometries indicate consistently that, upon tissue degradation, wall shear stress increases near the flow-impingement region and decreases away from it. These findings are discussed in the context of recent reports regarding the role of both high and low wall shear stress for the progression and rupture of aneurysms.

Asymptotic limits for a nonlinear integro-differential equation modelling leukocytes’ rolling on arterial walls

We consider a nonlinear integro-differential model describing z, the position of the cell center on the real line presented in Grec et al (2018 J. Theor. Biol. 452 35–46). We introduce a new ɛ-scaling and we prove rigorously the asymptotics when ɛ goes to zero. We show that this scaling characterizes the long-time behavior of the solutions of our problem in the cinematic regime (i.e. the velocity z ˙ tends to a limit). The convergence results are first given when ψ, the elastic energy associated to linkages, is convex and regular (the second order derivative of ψ is bounded). In the absence of blood flow, when ψ, is quadratic, we compute the final position z ∞ to which we prove that z tends. We then build a rigorous mathematical framework for ψ being convex but only Lipschitz. We extend convergence results with respect to ɛ to the case when ψ′ admits a finite number of jumps. In the last part, we show that in the constant force case [see model 3 in Grec et al (2018 J. Theor. Biol. 452 35–46), i.e. ψ is the absolute value)] we solve explicitly the problem and recover the above asymptotic results.

Assessment of New Coronary Features on Quantitative Coronary Angiographic Images With Innovative Unsupervised Artificial Adaptive Systems: A Proof-of-Concept Study

Background and Purpose: The Active Connection Matrixes (ACMs) are unsupervised artificial adaptive systems able to extract from digital images features of interest (edges, tissue differentiation, etc.) unnoticeable with conventional systems. In this proof-of-concept study, we assessed the potentiality of ACMs to increase measurement precision of morphological structures (e.g., stenosis and lumen diameter) and to grasp morphological features (arterial walls) from quantitative coronary angiography (QCA), unnoticeable on the original images.Methods: Archive images of QCA and intravascular ultrasound (IVUS) of 10 patients (8 men, age 69.1 ± 9.7 years) who underwent both procedures for clinical reasons were retrospectively analyzed. Arterial features derived from “IVUS images,” “conventional QCA images,” and “ACM-reprocessed QCA images” were measured in 21 coronary segments. Portions of 1-mm length (263 for lumen and 526 for arterial walls) were head-to-head compared to assess quali-quantitative between-methods agreement.Results: When stenosis was calculated on “ACM-reprocessed QCA images,” the bias vs. IVUS (gold standard) did not improve, but the correlation coefficient of the QCA–IVUS relationship increased from 0.47 to 0.83. When IVUS-derived lumen diameters were compared with diameters obtained on ACM-reprocessed QCA images, the bias (−0.25 mm) was significantly smaller (p < 0.01) than that observed with original QCA images (0.58 mm). ACMs were also able to extract arterial wall features from QCA. The bias between the measures of arterial walls obtained with IVUS and ACMs, although significant (p < 0.01), was small [0.09 mm, 95% CI (0.03, 0.14)] and the correlation was fairly good (r = 0.63; p < 0.0001).Conclusions: This study provides proof of concept that ACMs increase the measurement precision of coronary lumen diameter and allow extracting from QCA images hidden features that mirror well the arterial walls derived by IVUS.

Image processing to delineate the boundaries of peripheral arterial walls

The analysis of the arterial wall properties is vital in the prediction of stroke events and arterial hypertension in humans. Numerous researchers have experimented with several approaches to model arterial vessels and to analyse their biomechanical behaviour for many years now. Our study is focussed on image processing of peripheral arterial cross sections to detect and isolate the distinct layers. These boundaries will enable the creation of FEM models for further analysis of arterial wall properties. In a clinical setting, it facilitates doctors to identify the optimum pressure that can be applied to the artery for the treatment of stenosis without damaging the morphology of the blood vessels. This paper aims at distinguishing the various layers of arterial walls from images by minimizing human intervention. Cross section images of arteries from various sources were collected[10][11]. The boundaries from the image were obtained using image processing techniques of MATLAB(R2021a). The approach identified was to convert the input RGB images to grayscale, thresholding and applying morphological operators to delineate the Intima, Media, and Adventitia. These regions of interests (ROI) were then superimposed to generate an image with differentiated boundaries and void of unnecessary noise and inhomogeneity. This approach gave us an insight of the differences in various methods of boundary detection and to infer the optimum approach for accurate demarcation of boundaries of the three layers of arterial walls. It paves a pathway for forward modelling and to perform detailed FEM analysis in in-vitro diagnostics. In a nutshell, it was observed that the edge detection procedure implemented could be used for healthy and stenotic arteries. Further studies must be conducted to test the efficiency across a wide range of images and hence generalise its usage. Upon satisfactory boundary detection, forward modelling could be performed using the identified geometric forms.

Symptomatic arterial hypertension in extrasystolic arrythmia

Funding Acknowledgements Type of funding sources: None. Within the main causes of the secondary arterial hypertensions the main roles play renal, endocrine and hemodynamic. In the list of reasons of the secondary hemodynamic arterial hypertension there’re no extrasystoles. Purpose. To determine the relationship between different types of extrasystoles and the the secondary hemodynamic arterial hypertension. Materials and methods. We observed 132 patients with supraventricular and ventricular extrasystoles. Extrasystoles were divided into groups due to the moment of their appearance in cardiocycle: 1. Extrasystoles before the mitral valve opening. 2,3. Exstrasystoles in phase of fast ventricules filling before and after the peak of transmitral blood flow. 4. Extrasystoles in slow ventricules filling phase. 5. Other extrasystoles (allorrhythmias and group extrasystoles). The reason for that dividing was the different contribution of each type into the hemodynamics and heart output. We analyzed the regular, extraordinary and first post-extrasystolic contractions. Intra-arterial blood flow was estimated by ultrasound-doppler. The moment of extrasystoles appearance was determined by echocardiography, electrocardiography and 24-hours ECG monitoring. The kinetics of vessel wall was calculated by sphygmograms and included speed, acceleration, power and work parameters. The BP measuring was made by Korotkov method that the moment of measuring was in the first post-extrasystolic wave on sphygmogram. We duplicated it after the normalization and calibration of carotid arteries sphygmograms. Results. The main importance to the hemodynamic changes has the moment of extrasystole appearance in cardio cycle and the ability of the first post-extrasystolic contraction to reestablish an adequate resulting blood flow. It is characterized by: stroke volume rising from 5 to 40%; systolic BP increase up to 30% (with formation of the secondary hemodynamic AH) compared with the systolic BP with normal heart rate; rising of arterial walls kinetic parameters (speed, acceleration, power, work); blood flow velocity rising; grown arterial wall deformation. The maximum of these parameters was in first post-extrasystolic contraction with extrasystoles before the mitral valve opening and extrasystoles before the transmitral peak blood outflow. The special hemodynamic situation appears when there’re allorrhythmias when, for example, in case of constant bigeminia, BP is increased in 50% of time, and in case of trigimenia – in 1/3 of time. Conclusion. We believe it’s necessary to include extrasystoles into the list of the reasons of the secondary hemodynamic arterial hypertension. The main features of this type of AH are: unstable BP rising, prevalence growth of systolic BP, direct relationship with extrasystoles’ appearance moment. The risen blood flow of first post-extrasystolic contraction can be the reason of additional arterial walls deformation and complications that may cause the any AH.