1,721,209 research outputs found
On the impact of geometry on near-wall and intravascular flow features in idealized, population-based coronary bifurcations
Full text linkPersonalized multiscale modeling of coronary plaque progression: the interaction between low-density-lipoprotein transport and cellular dynamics
Full text linkMultiscale agent-based modeling has shown promise in elucidating the mechanobiological mechanisms underlying atherosclerotic plaque formation and progression. However, the integration of advanced models of low-density lipoprotein (LDL) transport in the lumen and across the endothelium with agent-based models (ABMs) of plaque growth remains underexplored. Furthermore, patient-specific applications are lacking. This study introduces a novel agent-based modeling framework for atherosclerosis, integrating hemodynamics and LDL transport in the lumen through computational fluid dynamics simulations, a three-pore model of trans-endothelial LDL migration, and an ABM of lipid and cellular dynamics. For the first time, the framework was applied to a patient-specific coronary artery and validated against 1-year follow-up data. Furthermore, it was used to explore potential plaque evolution over 5 years and under elevated LDL concentration. The calibrated model predicted the 1-year variation in wall area in two patient-specific coronary cross-sections with an error of less than 10%. Simulated scenarios indicated that variations in blood LDL concentrations can result in distinct plaque morphologies, from localized to diffuse patterns. This study provided an innovative, advanced multiscale model of atherosclerotic plaque formation and progression. As the first patient-specific application of a multiscale agent-based modeling framework for atherosclerosis with initial validation, this study underscored the potential of the approach for deciphering the mechanobiological pathways driving coronary plaque progression. The developed model provided valuable insights into how the interplay between LDL transport and hemodynamics influences arterial wall cellular dynamics in a patient-specific context
Divergence of the normalized wall shear stress as an effective computational template of low-density lipoprotein polarization at the arterial blood-vessel wall interface
Full text linkBackground and Objective: Near-wall transport of low-density lipoproteins (LDL) in arteries plays a relevant role in the initiation of atherosclerosis. Although it can be modelled in silico by coupling the Navier–Stokes equations with the 3D advection-diffusion (AD) equation, the associated computational cost is high. As wall shear stress (WSS) represents a first-order approximation of the near-wall velocity in arteries, we aimed at identifying computationally convenient WSS-based quantities to infer LDL near-wall transport based on the underlying near-wall hemodynamics in five models of three human arterial districts (aorta, carotid bifurcations, coronary arteries). The simulated LDL transport and its WSS-based surrogates were qualitatively compared with in vivo longitudinal measurements of wall thickness growth on the coronary artery models. Methods: Numerical simulations of blood flow coupled with AD equations for LDL transport and blood-wall transfer were performed. The co-localization of the simulated LDL concentration polarization patterns with luminal surface areas characterized by low cycle-average WSS, near-wall flow stagnation and WSS attracting patterns was quantitatively assessed by the similarity index (SI). In detail, the latter two represent features of the WSS topological skeleton, obtained respectively through the Lagrangian tracking of surface-born particles, and the Eulerian analysis of the divergence of the normalized cycle-average WSS vector field. Results: Convergence of the solution of the AD problem required the simulation of 3 (coronary artery) to 10 (aorta) additional cardiac cycles with respect to the Navier-Stokes problem. Co-localization results underlined that WSS topological skeleton features indicating near-wall flow stagnation and WSS attracting patterns identified LDL concentration polarization profiles more effectively than low WSS, as indicated by higher SI values (SI range: 0.17–0.50 for low WSS; 0.24–0.57 for WSS topological skeleton features). Moreover, the correspondence between the simulated LDL uptake and WSS-based quantities profiles with the in vivo measured wall thickness growth in coronary arteries appears promising. Conclusions: The recently introduced Eulerian approach for identifying WSS attracting patterns from the divergence of normalized WSS provides a computationally affordable template of the LDL polarization at the arterial blood-wall interface without simulating the AD problem. It thus candidates as an effective biomechanical tool for elucidating the mechanistic link amongst LDL transfer at the arterial blood-wall interface, WSS and atherogenesis
The Atheroprotective Nature of Helical Flow in Coronary Arteries
Full text linkArterial hemodynamics is markedly characterized by the presence of helical flow patterns. Previous observations suggest that arterial helical blood flow is of physiological significance, and that its quantitative analysis holds promise for clinical applications. In particular, it has been reported that distinguishable helical flow patterns are potentially atheroprotective in the carotid bifurcation as they suppress flow disturbances. In this context, there is a knowledge gap about the physiological significance of helical flow in coronary arteries, a prominent site of atherosclerotic plaque formation. This study aimed at the quantitative assessment of helical blood flow in coronary arteries, and to investigate its possible associations with vascular geometry and with atherogenic wall shear stress (WSS) phenotypes in a representative sample of 30 swine coronary arteries. This study demonstrates that in coronary arteries: (1) the hemodynamics is characterized by counter-rotating bi-helical flow structures; (2) unfavorable conditions of WSS are strongly and inversely associated with helicity intensity (r = − 0.91; p < 0.001), suggesting an atheroprotective role for helical flow in the coronary tree; (3) vascular torsion dictates helical flow features (r = 0.64; p < 0.001). The findings of this work support future studies on the role of helical flow in atherogenesis in coronary arteries
Patient-specific computer modelling of coronary bifurcation stenting: The John Doe programme
Full text linkJohn Doe, an 81-year-old patient with a significant distal left main (LM) stenosis, was treated using a provisional stenting approach. As part of an European Bifurcation Club (EBC) project, the complete stenting procedure was repeated using computational modelling. First, a tailored three-dimensional (3D) reconstruction of the bifurcation anatomy was created by fusion of multislice computed tomography (CT) imaging and intravascular ultrasound. Second, finite element analysis was employed to deploy and post-dilate the stent virtually within the generated patient-specific anatomical bifurcation model. Finally, blood flow was modelled using computational fluid dynamics. This proof-of-concept study demonstrated the feasibility of such patient-specific simulations for bifurcation stenting and has provided unique insights into the bifurcation anatomy, the technical aspects of LM bifurcation stenting, and the positive impact of adequate post-dilatation on blood flow patterns. Potential clinical applications such as virtual trials and preoperative planning seem feasible but require a thorough clinical validation of the predictive power of these computer simulations
The influence of geometric factors on the wall shear stress distribution in realistic human coronary arteries
Full text linkDissertação apresentada na Faculdade de Ciências e Tecnologia da Universidade Nova de Lisboa para a obtenção do grau de Mestre em Engenharia Biomédica. A presente dissertação foi desenvolvida no Erasmus Medical Center em Roterdão, HolandaBackground:
Atherosclerosis is the main cause of death in the Western society. It is a geometrically focal disease, affecting preferentially vessel areas of low wall shear stress (SS), which induces the expression of atherogenic genes. To predict wall SS several options are available. Among them Computational Fluid Dynamics (CFD) simulations on 3D reconstructed coronaries using Finite Element Modeling (FEM). However, to perform CFD a 3D representation is needed. To obtain a 3D representation of the coronary under study different methods can be applied.
Methods:
CFD calculations were performed using FEM on ten 3D reconstructed coronary arteries by the state-of-the-art ANGUS method (biplane angiography + Intravascular Ultrasound (IVUS)). The SS outcomes of the CFD calculations were compared with SS calculated by the Poiseuille equation, and with the SS outcomes of CFD simulations of the same 3D reconstructed arteries by QCA-3D (biplane angiography – no cross-sectional information) and Straight (IVUS images stacked on a straight centerline – no curvature information) methods.
Results:
The Poiseuille equation did not have any sensitivity in predicting any low SS (<0.5 Pa) per cross-section. However, the average correlation coefficient between the average SS per cross section from the Angus geometries and SS based on the Poiseuille equation was r2 = 0.65 0.09. A strong correlation was obtained for the SS from the ANGUS and the Straight method, while only an average correlation was obtained between ANGUS and QCA-3D average SS. Bland-Altman analysis was performed to confirm the results agreement. The sensitivity and specificity of the QCA-3D and Straight method in predicting low and high SS was measured. Geometric factors, such as local curvature, area gradient and torsion were found to be related to the presence of SS peaks or to regions prone to plaque development. These geometric risk factors were utilized to give some guidelines on meshing optimization.
Conclusions:
The use of a simpler 3D reconstruction approach, such as the QCA-3D or the Straight method, in combination with the optimization of meshing based on the geometric features of the coronaries, has the potential to, in the future, bring CFD calculations of wall SS from bench to bedside
Patient-specific computer modelling of coronary bifurcation stenting: The John Doe programme
No full textJohn Doe, an 81-year-old patient with a significant distal left main (LM) stenosis, was treated using a provisional stenting approach. As part of an European Bifurcation Club (EBC) project, the complete stenting procedure was repeated using computational modelling. First, a tailored three-dimensional (3D) reconstruction of the bifurcation anatomy was created by fusion of multislice computed tomography (CT) imaging and intravascular ultrasound. Second, finite element analysis was employed to deploy and post-dilate the stent virtually within the generated patient-specific anatomical bifurcation model. Finally, blood flow was modelled using computational fluid dynamics. This proof-of-concept study demonstrated the feasibility of such patient-specific simulations for bifurcation stenting and has provided unique insights into the bifurcation anatomy, the technical aspects of LM bifurcation stenting, and the positive impact of adequate post-dilatation on blood flow patterns. Potential clinical applications such as virtual trials and preoperative planning seem feasible but require a thorough clinical validation of the predictive power of these computer simulations
Serial RV wall stress measurements:association with right ventricular function in repaired Tetralogy of Fallot patients
Full text linkBackground: Optimal timing of pulmonary valve replacement (PVR) in Tetralogy of Fallot (TOF) patients remains challenging. Ventricular wall stress is considered to be an early marker of right ventricular (RV) dysfunction.Objectives: To investigate the association of RV wall stresses and their change over time with functional parameters in TOF patients.Methods: Ten TOF patients after surgical repair with moderate/severe pulmonary regurgitation were included. At two timepoints (median follow-up time 7.2 years), patient-specific computational biventricular models for wall stress assessment were created using CMR short-axis cine images and echocardiography-based RV pressures. RV ejection fraction (RVEF), NT-proBNP and cardiopulmonary exercise tests were used as outcome measures reflecting RV function. Associations between regional RV diastolic wall stress and RV function were investigated using linear mixed models.Results: Increased wall stress correlated with lower RV mass (rrm = −0.70, p = 0.017) and lower RV mass-to-volume (rrm = −0.80, p = 0.003) using repeated measures. Wall stress decreased significantly over time, especially in patients with a stable RVEF (p < 0.001). Higher wall stress was independently associated with lower RVEF, adjusted for left ventricular ejection fraction, RV end-diastolic volume and time since initial surgery (decrease of 1.27% RVEF per kPa increase in wall stress, p = 0.029) using repeated measurements. No association was found between wall stress, NT-proBNP, and exercise capacity.Conclusions: Using a computational method to calculate wall stress locally in geometrically complex ventricles, we demonstrated that lower wall stress might be important to maintain ventricular function. RV wall stress assessment can be used in serial follow-up, and is potentially an early marker of impending RV dysfunction
Healthy and diseased coronary bifurcation geometries influence near-wall and intravascular flow: A computational exploration of the hemodynamic risk
Full text linkLocal hemodynamics has been identified as one main determinant in the onset and progression of atherosclerotic lesions at coronary bifurcations. Starting from the observation that atherosensitive hemodynamic conditions in arterial bifurcation are majorly determined by the underlying anatomy, the aim of the present study is to investigate how peculiar coronary bifurcation anatomical features influence near-wall and intravascular flow patterns. Different bifurcation angles and cardiac curvatures were varied in population-based, idealized models of both stenosed and unstenosed bifurcations, representing the left anterior descending (LAD) coronary artery with its diagonal branch. Local hemodynamics was analyzed in terms of helical flow and exposure to low/oscillatory shear stress by performing computational fluid dynamics simulations.Results show that bifurcation angle impacts lowly hemodynamics in both stenosed and unstenosed cases. Instead, curvature radius influences the generation and transport of helical flow structures, with smaller cardiac curvature radius associated to higher helicity intensity. Stenosed bifurcation models exhibit helicity intensity values one order of magnitude higher than the corresponding unstenosed cases. Cardiac curvature radius moderately affects near-wall hemodynamics of the stenosed cases, with smaller curvature radius leading to higher exposure to low shear stress and lower exposure to oscillatory shear stress. In conclusion, the proposed controlled benchmark allows investigating the effect of various geometrical features on local hemodynamics at the LAD/diagonal bifurcation, highlighting that cardiac curvature influences near wall and intravascular hemodynamics, while bifurcation angle has a minor effect
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