scholarly journals The impact of wall thickness and curvature on wall stress in patient-specific electromechanical models of the left atrium

2019 ◽  
Vol 19 (3) ◽  
pp. 1015-1034 ◽  
Author(s):  
Christoph M. Augustin ◽  
Thomas E. Fastl ◽  
Aurel Neic ◽  
Chiara Bellini ◽  
John Whitaker ◽  
...  
Keyword(s):  
Left Atrium ◽  
Wall Thickness ◽  
Wall Stress ◽  
Sensitivity Analyses ◽  
Patient Specific ◽  
Cauchy Stress ◽  
Contraction Phase ◽  
Relative Contribution ◽  
Complex Anatomy ◽  
The Impact

AbstractThe left atrium (LA) has a complex anatomy with heterogeneous wall thickness and curvature. The anatomy plays an important role in determining local wall stress; however, the relative contribution of wall thickness and curvature in determining wall stress in the LA is unknown. We have developed electromechanical finite element (FE) models of the LA using patient-specific anatomical FE meshes with rule-based myofiber directions. The models of the LA were passively inflated to 10mmHg followed by simulation of the contraction phase of the atrial cardiac cycle. The FE models predicted maximum LA volumes of 156.5 mL, 99.3 mL and 83.4 mL and ejection fractions of 36.9%, 32.0% and 25.2%. The median wall thickness in the 3 cases was calculated as $$1.32\, \pm \,0.78$$1.32±0.78 mm, $$1.21\, \pm \,0.85$$1.21±0.85 mm, and $$0.74\,\pm \,0.34$$0.74±0.34 mm. The median curvature was determined as $$0.159\,\pm \,0.080$$0.159±0.080 $$\hbox {mm}^{-1}$$mm-1, $$0.165\,\pm \,0.079\,\hbox {mm}^{-1}$$0.165±0.079mm-1, and $$0.166\,\pm \,0.077\,\hbox {mm}^{-1}$$0.166±0.077mm-1. Following passive inflation, the correlation of wall stress with the inverse of wall thickness and curvature was 0.55–0.62 and 0.20–0.25, respectively. At peak contraction, the correlation of wall stress with the inverse of wall thickness and curvature was 0.38–0.44 and 0.16–0.34, respectively. In the LA, the 1st principal Cauchy stress is more dependent on wall thickness than curvature during passive inflation and both correlations decrease during active contraction. This emphasizes the importance of including the heterogeneous wall thickness in electromechanical FE simulations of the LA. Overall, simulation results and sensitivity analyses show that in complex atrial anatomy it is unlikely that a simple anatomical-based law can be used to estimate local wall stress, demonstrating the importance of FE analyses.

scholarly journals End-systolic wall stress in aortic stenosis: comparing symptomatic and asymptomatic patients

Open Heart ◽  
2019 ◽  
Vol 6 (1) ◽  
pp. e001021 ◽  
Author(s):  
Rasmus Carter-Storch ◽  
Jacob Eifer Moller ◽  
Nicolaj Lyhne Christensen ◽  
Lars Melholt Rasmussen ◽  
Redi Pecini ◽  
...  
Keyword(s):  
Aortic Valve ◽  
Aortic Stenosis ◽  
Wall Thickness ◽  
Global Longitudinal Strain ◽  
Wall Stress ◽  
Left Ventricular ◽  
Volume Index ◽  
Aortic Valve Area ◽  
The Impact ◽  
Systolic Wall Stress

AimsIn aortic stenosis (AS), there is poor association between symptoms and conventional markers of AS severity or left ventricular (LV) systolic function. This may reflect that symptoms arise from LV diastolic dysfunction or that aortic valve area (AVA) and transvalvular gradient do not reflect afterload. We aimed to study the impact of afterload (end-systolic wall stress [ESWS]) on the presence of symptoms in AS and to test whether symptoms are related to increased ESWS or LV remodelling.Methods and resultsIn a prospective study, ESWS was estimated by measuring LV wall thickness from MRI and estimated LV end systolic pressure from echocardiographic mean gradient and systolic blood pressure in 78 patients with severe AS scheduled for aortic valve replacement and 91 patients with asymptomatic severe AS. Symptomatic patients had lower indexed AVA (0.40±0.11 vs 0.45±0.09 cm2/m2, p=0.009). They had undergone more extensive remodelling (MRI LV mass index [LVMi]: 85±24 vs 69±17 g/m2, p<0.0001), had higher tricuspid regurgitant gradient (24±8 mm Hg vs 19 ± 7 mm Hg, p=0.0001) and poorer global longitudinal strain (−15.6±3.8 vs −19.9±3.2%, p<0.0001). ESWS was higher among symptomatic patients (96±51 vs 76±25 kdynes/cm2, p=0.003). Multivariate logistic regression identified echocardiographic relative wall thickness, tricuspid gradient, mitral deceleration time, early diastolic strain rate, MRI LVMi, MRI LV end-diastolic volume index and ESWS as independently associated with being symptomatic.ConclusionESWS can be estimated from multimodality imaging combining MRI and echocardiography. It is correlated with LV remodelling and neurohormonal activation and is independently associated with symptomatic status in AS.

scholarly journals Fluid-Structure Simulations of a Ruptured Intracranial Aneurysm: Constant versus Patient-Specific Wall Thickness

2016 ◽  
Vol 2016 ◽  
pp. 1-8 ◽  
Author(s):  
S. Voß ◽  
S. Glaßer ◽  
T. Hoffmann ◽  
O. Beuing ◽  
S. Weigand ◽  
...  
Keyword(s):  
Intracranial Aneurysm ◽  
Wall Thickness ◽  
Ex Vivo ◽  
Thickness Distribution ◽  
Wall Stress ◽  
Patient Specific ◽  
Fluid Structure ◽  
Aneurysm Wall ◽  
Ruptured Intracranial Aneurysm ◽  
Rupture Site

Computational Fluid Dynamics is intensively used to deepen the understanding of aneurysm growth and rupture in order to support physicians during therapy planning. However, numerous studies considering only the hemodynamics within the vessel lumen found no satisfactory criteria for rupture risk assessment. To improve available simulation models, the rigid vessel wall assumption has been discarded in this work and patient-specific wall thickness is considered within the simulation. For this purpose, a ruptured intracranial aneurysm was prepared ex vivo, followed by the acquisition of local wall thickness usingμCT. The segmented inner and outer vessel surfaces served as solid domain for the fluid-structure interaction (FSI) simulation. To compare wall stress distributions within the aneurysm wall and at the rupture site, FSI computations are repeated in a virtual model using a constant wall thickness approach. Although the wall stresses obtained by the two approaches—when averaged over the complete aneurysm sac—are in very good agreement, strong differences occur in their distribution. Accounting for the real wall thickness distribution, the rupture site exhibits much higher stress values compared to the configuration with constant wall thickness. The study reveals the importance of geometry reconstruction and accurate description of wall thickness in FSI simulations.

A Comparative Study of Biomechanical and Geometrical Attributes of Abdominal Aortic Aneurysms in the Asian and Caucasian Populations

2020 ◽  
Vol 142 (6) ◽  
Author(s):  
Tejas Canchi ◽  
Sourav S. Patnaik ◽  
Hong N. Nguyen ◽  
E. Y. K. Ng ◽  
Sriram Narayanan ◽  
...  
Keyword(s):  
Wall Thickness ◽  
Gaussian Curvature ◽  
Wall Stress ◽  
Aneurysm Rupture ◽  
Aortic Aneurysms ◽  
Patient Specific ◽  
Backward Elimination ◽  
Abdominal Aortic ◽  
Highly Correlated ◽  
Peak Wall Stress

Abstract In this work, we provide a quantitative assessment of the biomechanical and geometric features that characterize abdominal aortic aneurysm (AAA) models generated from 19 Asian and 19 Caucasian diameter-matched AAA patients. 3D patient-specific finite element models were generated and used to compute peak wall stress (PWS), 99th percentile wall stress (99th WS), and spatially averaged wall stress (AWS) for each AAA. In addition, 51 global geometric indices were calculated, which quantify the wall thickness, shape, and curvature of each AAA. The indices were correlated with 99th WS (the only biomechanical metric that exhibited significant association with geometric indices) using Spearman's correlation and subsequently with multivariate linear regression using backward elimination. For the Asian AAA group, 99th WS was highly correlated (R2 = 0.77) with three geometric indices, namely tortuosity, intraluminal thrombus volume, and area-averaged Gaussian curvature. Similarly, 99th WS in the Caucasian AAA group was highly correlated (R2 = 0.87) with six geometric indices, namely maximum AAA diameter, distal neck diameter, diameter–height ratio, minimum wall thickness variance, mode of the wall thickness variance, and area-averaged Gaussian curvature. Significant differences were found between the two groups for ten geometric indices; however, no differences were found for any of their respective biomechanical attributes. Assuming maximum AAA diameter as the most predictive metric for wall stress was found to be imprecise: 24% and 28% accuracy for the Asian and Caucasian groups, respectively. This investigation reveals that geometric indices other than maximum AAA diameter can serve as predictors of wall stress, and potentially for assessment of aneurysm rupture risk, in the Asian and Caucasian AAA populations.

Negative Correlation of Wall Thickness With Wall Blood Pressure in a Patient-Specific Atherosclerotic Coronary Artery: A Case Report

2012 ◽  
Author(s):  
Biyue Liu ◽  
Jie Zheng ◽  
Richard Bach ◽  
Dalin Tang
Keyword(s):  
Blood Pressure ◽  
Shear Stress ◽  
Wall Shear Stress ◽  
Wall Thickness ◽  
Patient Specific ◽  
Artery Wall ◽  
Atherosclerosis Progression ◽  
Wall Shear ◽  
Intensive Investigation ◽  
The Impact

There are two major hemodynamic stresses imposed at the blood-arterial wall interface by flowing blood: the wall shear stress (WSS) acting tangentially to the wall, and the wall pressure (WP) acting vertically to the wall. These forces influence the artery wall metabolism and correspond to the local modifications of artery wall thickness, composition, microarchitecture, and compliance [2]. The role of flow wall shear stress in atherosclerosis progression has been under intensive investigation [4], while the impact of local blood pressure on plaque progression has been under-studied.

scholarly journals Fluid-structure interaction in intracranial vessel walls: The role of patient-specific wall thickness

2018 ◽  
Vol 4 (1) ◽  
pp. 587-590
Author(s):  
Samuel Voß ◽  
Sylvia Saalfeld ◽  
Thomas Hoffmann ◽  
Oliver Beuing ◽  
Gábor Janiga ◽  
...  
Keyword(s):  
Wall Thickness ◽  
Wall Stress ◽  
Medical Community ◽  
Patient Specific ◽  
Stress Distributions ◽  
Fluid Structure ◽  
Intracranial Vessel ◽  
Wide Variability ◽  
Specific Configuration ◽  
Vessel Walls

AbstractComputational Fluid Dynamics studies try to support physicians during therapy planning of intracranial aneurysms. However, multiple assumptions (e.g. rigid vessel walls) are required leading to a sparse acceptance of numerical approaches within the medical community. This study incorporates multiple fluid-structural simulations for an intracranial basilar artery bifurcation. Based on a patient-specific dataset, which was acquired using optical coherence tomography, minimum, mean, maximum, and diameter-dependent thicknesses were generated and compared w.r.t. hemodynamic and wall stress parameters. The comparison of different wall thickness models revealed a strong variability among the analyzed parameters depending on the corresponding assumption. Using the patient-specific configuration as a reference, constant thicknesses lead to differences of up to 100 % in the mean wall stresses. Even the diameter-dependent thickness results in deviations of 32 %, demonstrating the wide variability of computational predictions due to inaccurate assumptions. The findings of this study highlight the importance of geometry reconstruction including accurate wall thickness reproduction for fluid-structure simulations. Patient-specific wall thickness seems to be out of alternatives regarding the realistic prediction of wall stress distributions.

scholarly journals Uncertainty quantification and sensitivity analysis of left ventricular function during the full cardiac cycle

2020 ◽  
Vol 378 (2173) ◽  
pp. 20190381 ◽  
Author(s):  
J. O. Campos ◽  
J. Sundnes ◽  
R. W. dos Santos ◽  
B. M. Rocha
Keyword(s):  
Uncertainty Quantification ◽  
Wall Thickness ◽  
Cardiac Cycle ◽  
Fibre Orientation ◽  
Left Ventricular ◽  
Sensitivity Analyses ◽  
Patient Specific ◽  
Model Parameters ◽  
Fibre Direction ◽  
Active Stress

Patient-specific computer simulations can be a powerful tool in clinical applications, helping in diagnostics and the development of new treatments. However, its practical use depends on the reliability of the models. The construction of cardiac simulations involves several steps with inherent uncertainties, including model parameters, the generation of personalized geometry and fibre orientation assignment, which are semi-manual processes subject to errors. Thus, it is important to quantify how these uncertainties impact model predictions. The present work performs uncertainty quantification and sensitivity analyses to assess the variability in important quantities of interest (QoI). Clinical quantities are analysed in terms of overall variability and to identify which parameters are the major contributors. The analyses are performed for simulations of the left ventricle function during the entire cardiac cycle. Uncertainties are incorporated in several model parameters, including regional wall thickness, fibre orientation, passive material parameters, active stress and the circulatory model. The results show that the QoI are very sensitive to active stress, wall thickness and fibre direction, where ejection fraction and ventricular torsion are the most impacted outputs. Thus, to improve the precision of models of cardiac mechanics, new methods should be considered to decrease uncertainties associated with geometrical reconstruction, estimation of active stress and of fibre orientation. This article is part of the theme issue ‘Uncertainty quantification in cardiac and cardiovascular modelling and simulation’.

Advanced Human Coronary Plaque Wall Thickness Correlates Positively With Flow Shear Stress and Negatively With Plaque Wall Stress: An IVUS-Based FSI Study

2013 ◽  
Author(s):  
Dalin Tang ◽  
Chun Yang ◽  
Joseph D. Petruccelli ◽  
Jie Zheng ◽  
Richard Bach ◽  
...  
Keyword(s):  
Shear Stress ◽  
Wall Thickness ◽  
Wall Stress ◽  
Coronary Plaque ◽  
Stress Conditions ◽  
Patient Specific ◽  
Plaque Progression ◽  
Flow Shear ◽  
Flow Shear Stress

Atherosclerotic plaque progression is believed to be associated with low and oscillating flow shear stress conditions [1–3]. In vivo image-based coronary plaque modeling papers are relatively rare because clinical recognition of vulnerable coronary plaques has remained challenging [3–4]. Samady et al. [3] published their seminal patient follow-up coronary plaque progression study and indicated that flow shear stress (FSS) was associated with plaque progression and remodeling. We have published results based on follow-up studies showing that advanced carotid plaque had positive correlation with flow shear stress and negative correlation with plaque wall stress (PWS) [4]. In this paper, patient-specific intravascular ultrasound (IVUS)-based coronary plaque models with fluid-structure interaction (FSI), on-site pressure and ex vivo biaxial mechanical testing of human coronary plaque material properties were constructed to obtain flow shear stress and plaque wall stress data from six patients to investigate possible associations between vessel wall thickness and both flow shear stress and plaque wall stress conditions.

MRI-Based Inflow Boundary Conditions for Patient Specific Fluid Structure Interaction Modeling of Abdominal Aortic Aneurysms

2012 ◽  
Author(s):  
Santanu Chandra ◽  
Samarth Raut ◽  
Anirban Jana ◽  
Robert W. Biederman ◽  
Mark Doyle ◽  
...  
Keyword(s):  
Boundary Condition ◽  
Boundary Conditions ◽  
Wall Thickness ◽  
Wall Stress ◽  
Patient Specific ◽  
Structure Interaction ◽  
Outflow Boundary Conditions ◽  
Abdominal Aortic ◽  
Outflow Boundary ◽  
Fully Coupled

Rupture of abdominal aortic aneurysm (AAA) is the 10th leading cause of death for men over age of 50 in US. The decision for surgical intervention is currently based on aneurysm diameter or its expansion rate. However, the use of these criteria for all patients is debatable. For example, small aneurysms do rupture or become symptomatic before reaching the critical diameter. Computationally predicted mechanical wall stress is considered a viable alternative criterion for rupture risk assessment. Hence, it is important to evaluate the effect of different modeling approaches on the accuracy of the predicated AAA wall stress. For computational solid stress (CSS) analysis or finite element analysis (FEA), a uniform static or transient intraluminal pressure is generally applied on the wall-lumen surface whereas in fluid-structure interaction (FSI) modeling the wall-lumen surface experiences transient and non-uniform fluid stress. An earlier comparison on idealized AAA models [1] revealed that static and transient CSS underestimate the peak wall stress (PWS) by an average 20–30% for variable wall thickness and 10% for uniform wall thickness when compared to fully coupled FSI. However, FSI-predicted stresses and strains were observed to be sensitive to inflow and outflow boundary conditions, warranting further study on a more accurate approach for FSI modeling. Though significant work has been performed on modeling outflow boundary conditions [2], studies on the sensitivity of computed stress or strain to the type of FSI inflow boundary condition is scarce [2–4]. We hypothesize that a FSI framework with a patient specific velocity boundary condition derived from magnetic resonance imaging (MRI) data applied to patient specific AAA geometry would provide better accuracy of PWS calculations compared to a FEA model. In this work, we present a framework where the AAA geometry is reconstructed from computed tomography (CT) images, on which FSI simulations were performed with inlet velocity components extracted from patient MR images of the abdominal aorta. Fully coupled FSI simulations were performed and results were compared with CSS simulations with uniform transient pressure boundary conditions.

Abstract 107: Increased Peak Wall Stress in Women With Abdominal Aortic Aneurysms

2017 ◽  
Vol 37 (suppl_1) ◽  
Author(s):  
Eric Shang ◽  
Grace Wang ◽  
Ronald Fairman ◽  
Benjamin Jackson
Keyword(s):  
Wall Thickness ◽  
Aortic Wall ◽  
Wall Stress ◽  
Aortic Aneurysms ◽  
Patient Specific ◽  
Rupture Risk ◽  
Intraluminal Thrombus ◽  
Abdominal Aortic ◽  
Aortic Wall Thickness ◽  
Peak Wall Stress

Objective: Women with abdominal aortic aneurysms (AAA) exhibit more rapid aneurysm growth and greater rupture risk at equivalent diameters relative to men. Evidence suggests that biomechanical peak wall stress (PWS) derived from finite element analysis of AAAs is a superior predictor of rupture compared to maximum transverse diameter (MTD). This study aimed to investigate differences in the calculated PWS of AAAs between men and women. Method: Men (n=35) and women (n=35) with infrarenal AAAs with 45-55mm MTD undergoing CTA were identified. Customized image processing algorithms extracted patient-specific AAA geometries from raw DICOM images. The resulting aortic reconstructions incorporated patient-specific and regionally resolved aortic wall thickness, intraluminal thrombus, and wall calcifications. Aortic models were loaded with 120mmHg blood pressure using commercially available FEA solvers. Results: Peak wall stress was found to be significantly higher in women (299±51 vs 257±53 kPA, P=0.001, see Figure). Neither MTD (50.5±3.1 vs 49.8±2.9 mm, P=0.34), mean aortic wall thickness (2.38±0.52 vs 2.34±0.50 mm, P=0.69), nor wall thickness at location of PWS (2.36±0.60 vs 2.20±0.46 mm, P=0.20) varied by sex. While there were no sex-associated differences in aneurysm volume (86.6±27.0 vs 94.8±25.5 cm 3 , P=0.76) or intraluminal thrombus volume (14.2±11.7 vs 16.3±13.4 mm, P=0.33), women’s AAAs had significantly increased maximum Gaussian curvature (0.032±0.011 vs 0.025±0.015 mm -2 , P=0.03). Conclusion: Comparably sized AAAs in women were shown to have significantly higher peak wall stress. Maximum gaussian curvature, a measure of aneurysm morphology, was significantly different between the two groups. These results suggest that men and women possess distinct aneurysm geometries, and that PWS-derived rupture risk prediction may provide a more reliable estimator of rupture risk in all patients.

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