Numerical simulations of the pulsatile blood flow in the different types of arterial fenestrations: Comparable analysis of multiple vascular geometries

Modeling pulsed dye laser treatment of psoriatic plaques by combining numerical methods and image-derived lesion morphologies

OBJECTIVES

Knowledge of the physical effects of pulsed dye laser (PDL) treatment of psoriatic lesions is essential in unraveling the remedial mechanisms of this treatment and hence also in maximizing in its disease-modifying potential. Therefore, the main objective of this study was to provide estimates of these physical effects (for laser wavelengths of 585 and 595 nm), with the aim of identifying pathogenic processes that may be affected by these conditions.

METHODS

We modeled the laser light propagation and subsequent photothermal heating by numerically solving the transient diffusion and heat equations simultaneously. To this end, we used the finite element method in conjunction with an image-derived psoriatic lesion morphology (which was defined by segmenting blood vessels from a confocal microscopy image of a fluorescently labeled section of a 3 mm punch biopsy of a psoriatic lesion). The resulting predictions of the generated temperature field within the lesion were then used to assess the possibility of stalling or arresting some suspected pathogenic processes.

RESULTS

According to our results, it is conceivable that perivascular nerves are thermally denatured, as almost all locations that reach 60°C were found to be within 18 µm (at 585 nm) and 11 µm (at 595 nm) of a blood vessel wall. Furthermore, activation of TRPV1 and TRPV2 channels in perivascular neuronal and immune cells is highly likely, since a critical temperature of 43°C is generated at locations within up to 350 µm of a vessel wall (at both wavelengths) and sustained for up to 700 ms (at 585 nm) and 40 ms (at 595 nm), while a critical temperature of 52°C is reached by locations within 80 µm (at 585 nm) and 30 µm (at 595 nm) of a vessel wall and sustained for up to 100  ms (at 585 nm) and 30 ms (at 595 nm). Finally, we found that the blood vessel coagulation-inducing temperature of 70°C is sustained in the vascular epithelium for up to 19 and 5 ms at 585 and 595 nm, respectively, rendering partial or total loss of vascular functionality a distinct possibility.

CONCLUSIONS

The presented approach constitutes a useful tool to provide realistic estimates of the photothermal effects of PDL treatment of psoriatic plaques (as well as other selective photothermolysis-based treatments), yielding information that is essential in guiding future experimental studies toward unraveling the remedial mechanisms of these treatments.

Blood flow effects in a patient with a thoracic aortic endovascular prosthesis

This work analyzes hemodynamic phenomena within the aorta of two elderly patients and their impact on blood flow behavior, particularly affected by an endovascular prosthesis in one of them (Patient II). Computational Fluid Dynamics (CFD) was utilized for this study, involving measurements of velocity, pressure, and wall shear stress (WSS) at various time points during the third cardiac cycle, at specific positions within two cross sections of the thoracic aorta. The first cross-section (Cross-Section 1, CS1) is located before the initial fluid bifurcation, just before the right subclavian artery. The second cross-section (Cross-Section 2, CS2) is situated immediately after the left subclavian artery. The results reveal that, under regular aortic geometries, velocity and pressure magnitudes follow the principles of fluid dynamics, displaying variations. However, in Patient II, an endoprosthesis near the CS2 and the proximal border of the endoprosthesis significantly disrupts fluid behavior owing to the pulsatile flow. The cross-sectional areas of Patient I are smaller than those of Patient II, leading to higher flow magnitudes. Although in CS1 of Patient I, there is considerable variability in velocity magnitudes, they exhibit a more uniform and predictable transition. In contrast, CS2 of Patient II, where magnitude variation is also high, displays irregular fluid behavior due to the endoprosthesis presence. This cross-section coincides with the border of the fluid bifurcation. Additionally, the irregular geometry caused by endovascular aneurysm repair contributes to flow disruption as the endoprosthesis adjusts to the endothelium, reshaping itself to conform with the vessel wall. In this context, significant alterations in velocity values, pressure differentials fluctuating by up to 10%, and low wall shear stress indicate the pronounced influence of the endovascular prosthesis on blood flow behavior. These flow disturbances, when compounded by the heart rate, can potentially lead to changes in vascular anatomy and displacement, resulting in a disruption of the prosthesis-endothelium continuity and thereby causing clinical complications in the patient.

Numerical flow experiment for assessing predictors for cerebrovascular accidents in patients with PHACES syndrome

There is an increased risk of cerebrovascular accidents (CVA) in individuals with PHACES, yet the precise causes are not well understood. In this analysis, we aimed to examine the role of arteriopathy in PHACES syndrome as a potential contributor to CVA. We analyzed clinical and radiological data from 282 patients with suspected PHACES syndrome. We analyzed clinical features, including the presence of infantile hemangioma and radiological features based on magnetic resonance angiography or computed tomography angiography, in individuals with PHACES syndrome according to the Garzon criteria. To analyze intravascular blood flow, we conducted a simulation based on the Fluid-Structure Interaction (FSI) method, utilizing radiological data. The collected data underwent statistical analysis. Twenty patients with PHACES syndrome were included. CVAs were noted in 6 cases. Hypoplasia (p = 0.03), severe tortuosity (p < 0.01), absence of at least one main cerebral artery (p < 0.01), and presence of persistent arteries (p = 0.01) were associated with CVAs, with severe tortuosity being the strongest predictor. The in-silico analysis showed that the combination of hypoplasia and severe tortuosity resulted in a strongly thrombogenic environment. Severe tortuosity, combined with hypoplasia, is sufficient to create a hemodynamic environment conducive to thrombus formation and should be considered high-risk for cerebrovascular accidents (CVAs) in PHACES patients.

Fluid structure interaction versus rigid-wall approach in the study of the symptomatic stenosed carotid artery: Importance of wall compliance and resilience of loose connective tissue

The purpose of this paper is to demonstrate the importance of a compliant wall approach in modeling of non-Newtonian and non-physiological blood flows. A case study of a stenosed and symptomatic carotid bifurcation was considered to show the influence of the wall-resilience assumption on the flow parameters obtained with numerical simulations. Patient-specific data concerning the geometry and flow conditions were collected and used to carry out two-way coupled fluid structure interaction simulations of the pulsatile blood flow through carotid artery. The wall compliance was considered separately as related to the wall-elasticity and as associated with the reaction of the loose connective tissue surrounding the carotid bifurcation. The obtained hemodynamic parameters were compared to those which were found in rigid-wall simulations. The difference between the results obtained for rigid-wall and compliant-wall approaches for the peak-systolic area-averaged wall shear stress achieved 35%, whereas the difference between the time-averaged local vorticity and shear strain reached, respectively, 42% and 43%. The influence of the highly resilient wall on the monitored hemodynamic parameters was significant even if time-averaged values are compared, which suggests that these metrics are considerably overestimated if the wall compliance is not considered. Moreover, the findings show that the mechanical response of the loose connective tissue cannot be neglected in blood flow simulations. Additionally, this study indicates that stiffening of the arterial wall due to atherosclerosis significantly rises hemodynamic parameters. This explains the therapeutic benefits of surgical removal of plaque lesions formed in the carotid bifurcation (endarterectomy).

Study of Non-Newtonian blood flow - heat transfer characteristics in the human coronary system with an external magnetic field

This paper proposes a novel mathematical model of non-Newtonian blood flow and heat transfer in the human coronary system with an external magnetic field. As the blood viscosity is assumed to depend not only on shear rate but also on temperature and magnet strength, the modified Carreau-Yasuda viscosity model is formulated. The computational domain includes the base of the aorta, the right coronary artery, and the left coronary artery, with the left circumflex and left anterior descending arteries. The element-based finite volume method is derived for the solution of the proposed model. Numerical simulations are carried out to investigate the magnetic field effect on the blood flow-heat transfer characteristic in the human coronary system. It is found that the magnetic field has a significant impact on fluid viscosity, leading to enhanced fluid velocity.

Computational Fluid Dynamic Technique for Assessment of How Changing Character of Blood Flow and Different Value of Hct Influence Blood Hemodynamic in Dissected Aorta

Using computer tomography angiography (CTA) and computational structural analysis, we present a non-invasive method of mass flow rate/velocity and wall stress analysis in type B aortic dissection. Three-dimensional (3D) computer models of the aorta were calculated using pre-operative (baseline) and post-operative CT data from 12 male patients (aged from 51 to 64 years) who were treated for acute type B dissection. A computational fluid dynamics (CFD) technique was used to quantify the displacement forces acting on the aortic wall in the areas of endografts placement. The mass flow rate and wall stress were measured and quantified using the CFD technique. The CFD model indicated the places with a lower value of blood velocity and shear rate, which corelated with higher blood viscosity and a probability of thrombus appearance. Moreover, with the increase in Hct, blood viscosity also increased, while the intensity of blood flow provoked changing viscosity values in these areas. Furthermore, the velocity gradient near the tear surface caused high wall WSS; this could lead to a decreased resistance in the aorta’s wall with further implications to a patient.

Hemodynamic effects of size and location of basilar artery fenestrations associated to pathological implications

Fenestration is a rare congenital abnormality that refers to a segmental duplication of arteries. It is still not clear about the role of fenestrations in the etiology and pathological evolution of vascular diseases. This study aims to investigate the hemodynamic influence brought by various sizes and locations of fenestration in basilar artery models. A series presumptive fenestration models were established based on a normal basilar artery model with various sizes and locations. Identical boundary conditions were utilized in the computational fluid dynamics simulations and different flow patterns in the fenestration and bifurcation regions were comprehensively analyzed. Wall shear stress (WSS)-related parameters such as oscillatory shear index (OSI) and aneurysm formation index (AFI) were computed and compared. The value of WSS on fenestration increased by the fenestration's tortuosity, and nearly-circular fenestration suffered higher WSS than narrow-strips one. Also, high OSI and low AFI value mainly occurred in the bifurcation region, indicating a high level of turbulence and high risk of aneurysm formation. The location of fenestration mainly changed the impact force of blood flow on the bifurcation and the disorder characteristics of blood flow, while the size of fenestration changed the WSS distribution on the proximal inner wall and bifurcation region of fenestration. In summary, the nearly-circular fenestration should be stratified carefully which may results in a high risk inducing unfavorable vascular wall remodeling.

Fluid-structure interactions (FSI) based study of low-density lipoproteins (LDL) uptake in the left coronary artery

The purpose of this study is to compare the effect of the different physical factors on low-density lipoproteins (LDL) accumulation from flowing blood to the arterial wall of the left coronary arteries. The three-dimensional (3D) computational model of the left coronary arterial tree is reconstructed from a patient-specific computed tomography angiography (CTA) image. The endothelium of the coronary artery is represented by a shear stress dependent three-pore model. Fluid–structure interaction (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$FSI$$\end{document}FSI) based numerical method is used to study the LDL transport from vascular lumen into the arterial wall. The results show that the high elastic property of the arterial wall decreases the complexity of the local flow field in the coronary bifurcation system. The places of high levels of LDL uptake coincide with the regions of low wall shear stress. In addition, hypertension promotes LDL uptake from flowing blood in the arterial wall, while the thickened arterial wall decreases this process. The present computer strategy combining the methods of coronary CTA image 3D reconstruction, \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$FSI$$\end{document}FSI simulation, and three-pore modeling was illustrated to be effective on the simulation of the distribution and the uptake of LDL. This may have great potential for the early prediction of the local atherosclerosis lesion in the human left coronary artery.

Coronary arteries hemodynamics: effect of arterial geometry on hemodynamic parameters causing atherosclerosis

Coronary arteries have high curvatures, and hence, flow through them causes disturbed flow patterns, resulting in stenosis and atherosclerosis. This in turn decreases the myocardial flow perfusion, causing myocardial ischemia and infarction. Therefore, in order to understand the mechanisms of these phenomena caused by high curvatures and branching of coronary arteries, we have conducted elaborate hemodynamic analysis for both (i) idealized coronary arteries with geometrical parameters representing realistic curvatures and stenosis and (ii) patient-specific coronary arteries with stenoses. Firstly, in idealized coronary arteries with approximated realistic arterial geometry representative of their curvedness and stenosis, we have computed the hemodynamic parameters of pressure drop, wall shear stress (WSS) and wall pressure gradient (WPG), and their association with the geometrical parameters of curvedness and stenosis. Secondly, we have similarly determined the wall shear stress and wall pressure gradient distributions in four patient-specific curved stenotic right coronary arteries (RCAs), which were reconstructed from medical images of patients diagnosed with atherosclerosis and stenosis; our results show high WSS and WPG regions at the stenoses and inner wall of the arterial curves. This paper provides useful insights into the causative mechanisms of the high incidence of atherosclerosis in coronary arteries. It also provides guidelines for how simulation of blood flow in patient's coronary arteries and determination of the hemodynamic parameters of WSS and WPG can provide a medical assessment of the risk of development of atherosclerosis and plaque formation, leading to myocardial ischemia and infarction. The novelty of our paper is in our showing how in actual coronary arteries (based on their CT imaging) curvilinearity and narrowing complications affect the computed WSS and WPG, associated with risk of atherosclerosis. This is very important for cardiologists to be able to properly take care of their patients and provide remedial measures before coronary complications lead to myocardial infarctions and necessitate stenting or coronary bypass surgery. We want to go one step further and provide clinical application of our research work. For that, we are offering to cardiologists worldwide to carry out hemodynamic analysis of the medically imaged coronary arteries of their patients and compute the values of the hemodynamic parameters of WSS and WPG, so as to provide them an assessment of the risk of atherosclerosis for their patients. Graphical abstract Theme and aims: Coronary arteries have high curvatures, and hence flow through them causes disturbed flow patterns, resulting in stenosis and atherosclerosis. This in turn decreases the myocardial flow perfusion, causing myocardial ischemia and infarction. Therefore, in order to understand the mechanisms of these phenomena caused by high curvatures and branching of coronary arteries, we have conducted elaborate hemodynamic analysis for both (i) idealized coronary arteries with geometrical parameters representing curvatures and stenosis, and (ii) patient-specific coronary arteries with stenoses. Methods and results: Firstly, in idealized coronary arteries with approximated realistic arterial geometry representative of their curvedness and stenosis, we have computed the hemodynamic parameters of pressure drop, wall shear stress (WSS) and wall pressure gradient (WPG), and their association with the geometrical parameters of curvedness and stenosis. Then, we have determined the wall shear stress and wall pressure gradient distributions in four patient-specific curved stenotic right coronary arteries (RCAs), that were reconstructed from medical images of patients diagnosed with atherosclerosis and stenosis, as illustrated in Figure 1, in which the locations of the stenoses are highlighted by arrows. Figure 1: Three-dimensional CT visualization of arteries in patients with suspected coronary disease. The arteries can be seen as a combination of various curved segments with stenoses at unspecific locations highlighted by arrows. Our results show high WSS and WPG regions at the stenoses and inner wall of the arterial curves, as depicted in Figure 2. Therein, the encapsulations show (i) high WSS, and (ii) high WPG regions at the stenosis and inner wall of the arterial curves. Figure 2: WSS and WPG surface plot of realistic arteries (a), (b), (c) and (d), wherein the small squared parts are enlarged to show the detailed localized contour plots at the stenotic regions. Therein, the circular encapsulations show (i) high WSS and (ii) high WPG regions at the stenosis and inner wall of the arterial curves. Conclusion and novelty: This paper provides useful insights into the causative mechanisms of the high incidence of atherosclerosis in coronary arteries. It also provides guidelines for how simulation of blood flow in patient coronary arteries and determination of the hemodynamic parameters of WSS and WPG can provide a medical assessment of the risk of development of atherosclerosis and plaque formation, leading to myocardial ischemia and infarction. The novelty of our paper is our showing how in actual coronary arteries (based on their CT imaging), curvilinearity and narrowing complications affect the computed WSS and WPG associated with risk of atherosclerosis. This is very important for cardiologists to be able to properly take care of their patients and provide remedial measures before coronary complications lead to myocardial infarctions and necessitate stenting or coronary bypass surgery.

Computational fluid dynamics simulations of cerebral aneurysm using Newtonian, power-law and quasi-mechanistic blood viscosity models

Cerebral aneurysm is a fatal neurovascular disorder. Computational fluid dynamics simulation of aneurysm haemodynamics is one of the most important research tools which provide increasing potential for clinical applications. However, computational fluid dynamics modelling of such delicate neurovascular disorder involves physical complexities that cannot be easily simplified. Recently, it was shown that the Newtonian simplification used to close the shear stress tensor of the Navier-Stokes equation is not sufficient to explore aneurysm haemodynamics. This article explores the differences between the latter simplification, non-Newtonian power-law model and a newly proposed quasi-mechanistic model. The modified Krieger model, which treats blood as a suspension of plasma and particles, was implemented in computational fluid dynamics context here for the first time and is made available to the readers in a C# code in the supplementary material of this article. Two middle-cerebral artery and two anterior-communicating artery aneurysms, all ruptured, were utilized here as case studies. It was shown that the modified Krieger model had higher sensitivity for wall shear stress calculations in comparison with the other two models. The modified Krieger model yielded lower wall shear stress values consistently in comparison with the other two models. Moreover, the modified Krieger model has generally predicted higher pressure in the aneurysm models. Based on published aneurysm rupture studies, it is believed that ruptured aneurysms are usually correlated with lower wall shear stress values than unruptured ones. Therefore, this work concludes that the modified Krieger model is a potential candidate for providing better clinical relevance to aneurysm computational fluid dynamics simulations.