Wall Stress

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David A. Vorp - One of the best experts on this subject based on the ideXlab platform.

  • difference in hemodynamic and Wall Stress of ascending thoracic aortic aneurysms with bicuspid and tricuspid aortic valve
    Journal of Biomechanics, 2013
    Co-Authors: Salvatore Pasta, Antonino Rinaudo, Angelo Luca, Michele Pilato, Cesare Scardulla, Thomas G Gleason, David A. Vorp
    Abstract:

    The aortic dissection (AoD) of an ascending thoracic aortic aneurysm (ATAA) initiates when the hemodynamic loads exerted on the aneurysmal Wall overcome the adhesive forces holding the elastic layers together. Parallel coupled, two-way fluid–structure interaction (FSI) analyses were performed on patient-specific ATAAs obtained from patients with either bicuspid aortic valve (BAV) or tricuspid aortic valve (TAV) to evaluate hemodynamic predictors and Wall Stresses imparting aneurysm enlargement and AoD. Results showed a left-handed circumferential flow with slower-moving helical pattern in the aneurysm's center for BAV ATAAs whereas a slight deviation of the blood flow toward the anterolateral region of the ascending aorta was observed for TAV ATAAs. Blood pressure and Wall shear Stress were found key hemodynamic predictors of aneurysm dilatation, and their dissimilarities are likely associated to the morphological anatomy of the aortic valve. We also observed discontinues, Wall Stresses on aneurysmal aorta, which was modeled as a composite with two elastic layers (i.e., inhomogeneity of vessel structural organization). This Stress distribution was caused by differences on elastic material properties of aortic layers. Wall Stress distribution suggests AoD just above sinotubular junction. Moreover, abnormal flow and lower elastic material properties that are likely intrinsic in BAV individuals render the aneurysm susceptible to the initiation of AoD.

  • effects of Wall calcifications in patient specific Wall Stress analyses of abdominal aortic aneurysms
    Journal of Biomechanical Engineering-transactions of The Asme, 2007
    Co-Authors: Lambert Speelman, Geert Willem H. Schurink, Michel S. Makaroun, Ajay Bohra, Marielle E H Bosboom, Frans N Van De Vosse, David A. Vorp
    Abstract:

    It is generally acknowledged that rupture of an abdominal aortic aneurysm (AAA) occurs when the Stress acting on the Wall over the cardiac cycle exceeds the strength of the Wall. Peak Wall Stress computations appear to give a more accurate rupture risk assessment than AAA diameter, which is currently used for a diagnosis. Despite the numerous studies utilizing patient-specific Wall Stress modeling of AAAs, none investigated the effect of Wall calcifications on Wall Stress. The objective of this study was to evaluate the influence of calcifications on patient-specific finite element Stress computations. In addition, we assessed whether the effect of calcifications could be predicted directly from the CT-scans by relating the effect to the amount of calcification present in the AAA Wall. For 6 AAAs, the location and extent of calcification was identified from CT-scans. A finite element model was created for each AAA and the areas of calcification were defined node-wise in the mesh of the model. Comparisons are made between maximum principal Stress distributions, computed without calcifications and with calcifications with varying material properties. Peak Stresses are determined from the Stress results and related to a calcification index (CI), a quantification of the amount of calcification in the AAA Wall. At calcification sites, local Stresses increased, leading to a peak Stress increase of 22% in the most severe case. Our results displayed a weak correlation between the CI and the increase in peak Stress. Additionally, the results showed a marked influence of the calcification elastic modulus on computed Stresses. Inclusion of calcifications in finite element analysis of AAAs resulted in a marked alteration of the Stress distributions and should therefore be included in rupture risk assessment. The results also suggest that the location and shape of the calcified regions--not only the relative amount--are considerations that influence the effect on AAA Wall Stress. The dependency of the effect of the Wall Stress on the calcification elastic modulus points out the importance of determination of the material properties of calcified AAA Wall.

  • effect of variation in intraluminal thrombus constitutive properties on abdominal aortic aneurysm Wall Stress
    Annals of Biomedical Engineering, 2003
    Co-Authors: Elena S Di Martino, David A. Vorp
    Abstract:

    The abdominal aortic aneurysm (AAA) is a degenerating disease for which the end stage is the rupture of the vessel Wall. Accurate prediction of the Stresses acting on the aneurysm tissue may be used to determine the actual risk of rupture of a specific aneurysm. To accomplish this, a correct constitutive model for the aneurysmal aortic Wall and any intraluminal thrombus (ILT) present within it are needed. Our laboratory has previously reported the mechanical properties of ILT. The aim of this work is to investigate the reliability of using population-mean values of ILT constitutive parameters to estimate AAA Wall Stress distribution. For this, a three-dimensional asymmetric model of an aneurysm including ILT was generated and a parametric study was conducted varying ILT constitutive properties within a physiological range. Results show that the presence of any ILT reduces and redistributes the Stresses in the aortic Wall markedly. Maximum variation in the peak Wall Stresses for all the models analyzed was 5%. Adopting a nonhomogeneous ILT did not alter the Stress distribution. On the basis of these results, we infer that population mean parameters for ILT material characteristics can be used to reasonably estimate the Wall Stresses in patient specific aneurysm models.

  • Effect of intraluminal thrombus on Wall Stress in patient-specific models of abdominal aortic aneurysm☆
    Journal of Vascular Surgery, 2002
    Co-Authors: David H. J. Wang, Marshall W. Webster, Michel S. Makaroun, David A. Vorp
    Abstract:

    Abstract Purpose: The role of intraluminal thrombus (ILT) on abdominal aortic aneurysm rupture is still not clear. Rupture of an aneurysm occurs when the Wall Stress exceeds the Wall strength at any location on the Wall. The purpose of this study was to address the hypothesis that the presence of ILT alters the Wall Stress distribution or Wall Stress magnitude in AAA. Methods: Patient-specific 3D AAA geometries were reconstructed from computed tomographic images. Two geometric features, ILT surface ratio (ILT surface area divided by the total AAA surface area) and ILT volume ratio (ILT volume divided by the total AAA volume), were calculated for each AAA. Two models were created for each patient: one with ILT and one without ILT. Systolic pressure measured at the time of computed tomographic imaging was applied to the internal surface of each model. A nonlinear large deformation algorithm was used to compute Wall Stress distribution with the finite element method. The Wilcoxon matched pairs test was used to compare the peak Wall Stress between the two models of each patient. Results: Four patients were studied with ILT surface ratios that ranged from 0.29 to 0.72 and ILT volume ratios that ranged from 0.12 to 0.66. The peak Wall Stress was reduced (range, 6% to 38% reduction; P = .067) for all models with ILT included (range, 28 to 37 N/cm2) as compared with models with no ILT (range, 30 to 44 N/cm2). Visual inspection also revealed a marked effect of ILT on the Wall Stress distribution. Conclusion: The presence of ILT alters the Wall Stress distribution and reduces the peak Wall Stress in AAA.For this reason, ILT should be included in all patient-specific models of AAA for evaluation of AAA Wall Stresses. (J Vasc Surg 2002;36:598-604.)

  • Wall Stress distribution on three-dimensionally reconstructed models of human abdominal aortic aneurysm.
    Journal of Vascular Surgery, 2000
    Co-Authors: Madhavan L. Raghavan, David A. Vorp, Michel S. Makaroun, Michael P. Federle, Marshall W. Webster
    Abstract:

    Abstract Purpose: Abdominal aortic aneurysm (AAA) rupture is believed to occur when the mechanical Stress acting on the Wall exceeds the strength of the Wall tissue. Therefore, knowledge of the Stress distribution in an intact AAA Wall could be useful in assessing its risk of rupture. We developed a methodology to noninvasively estimate the in vivo Wall Stress distribution for actual AAAs on a patient-to-patient basis. Methods: Six patients with AAAs and one control patient with a nonaneurysmal aorta were the study subjects. Data from spiral computed tomography scans were used as a means of three-dimensionally reconstructing the in situ geometry of the intact AAAs and the control aorta. We used a nonlinear biomechanical model developed specifically for AAA Wall tissue. By means of the finite element method, the Stress distribution on the aortic Wall of all subjects under systolic blood pressure was determined and studied. Results: In all the AAA cases, the Wall Stress was complexly distributed, with distinct regions of high and low Stress. Peak Wall Stress among AAA patients varied from 29 N/cm 2 to 45 N/cm 2 and was found on the posterior surface in all cases studied. The Wall Stress on the nonaneurysmal aorta in the control subject was relatively low and uniformly distributed, with a peak Wall Stress of 12 N/cm 2 . AAA volume, rather than AAA diameter, was shown by means of statistical analysis to be a better indicator of high Wall Stresses and possibly rupture. Conclusion: The approach taken to estimate AAA Wall Stress distribution is completely noninvasive and does not require any additional involvement or expense by the AAA patient. We believe that this methodology may allow for the evaluation of an individual AAA's rupture risk on a more biophysically sound basis than the widely used 5-cm AAA diameter criterion. (J Vasc Surg 2000;31:760-9.)

Elaine E Tseng - One of the best experts on this subject based on the ideXlab platform.

  • Wall Stress distribution in bicuspid aortic valve associated ascending thoracic aortic aneurysms
    The Annals of Thoracic Surgery, 2020
    Co-Authors: Axel Gomez, Yue Xuan, Zhongjie Wang, Michael D Hope, David Saloner, Julius M Guccione, Andrew D Wisneski, Elaine E Tseng
    Abstract:

    Background Bicuspid aortic valve–associated ascending thoracic aortic aneurysms (BAV-aTAAs) carry a risk of acute type A dissection. Biomechanically, dissection may occur when Wall Stress exceeds Wall strength. Our aim was to develop patient-specific computational models of BAV-aTAAs to determine magnitudes of Wall Stress by anatomic regions. Methods Patients with BAV-aTAA diameter greater than 4.5 cm (n = 41) underwent electrocardiogram-gated computed tomography angiography. Three-dimensional aneurysm geometries were reconstructed after accounting for preStress and loaded to systemic pressure. Finite element analyses were performed with fiber-embedded hyperelastic material model using LS-DYNA software (LSTC Inc, Livermore, CA) to obtain Wall Stress distributions. The 99th percentile longitudinal and circumferential Stresses were determined at systole. Results The 99th percentile longitudinal Wall Stresses for BAV-aTAAs at sinuses of Valsalva, sinotubular junction (STJ), and ascending aorta were 361 ± 59.8 kPa, 295 ± 67.2 kPa, and 224 ± 37.6 kPa, respectively, with significant differences in ascending aorta vs sinuses (P Conclusions Wall Stresses, both circumferential and longitudinal, were greater in the aortic root, sinuses, and STJ than in the ascending aorta on BAV-aTAAs. These results fill a fundamental knowledge gap regarding biomechanical Stress distribution in BAV-aTAA patients, which when related to Wall strength may provide prognostication of aTAA dissection risk by patient-specific modeling.

  • Wall Stress analyses in patients with 5 cm versus 5 cm ascending thoracic aortic aneurysm
    The Journal of Thoracic and Cardiovascular Surgery, 2020
    Co-Authors: Zhongjie Wang, Yue Xuan, Michael D Hope, David Saloner, Julius M Guccione, Andrew D Wisneski, Nick Flores, Matthew Y Lum, Justin Inman, Elaine E Tseng
    Abstract:

    Abstract Objective Current guidelines for elective surgery of ascending thoracic aortic aneurysms (aTAAs) use aneurysm size as primary determinant for risk stratification of adverse events. Biomechanically, dissection may occur when Wall Stress exceeds Wall strength. Determining patient-specific aTAA Wall Stresses by finite element analysis can potentially predict patient-specific risk of dissection. This study compared peak Wall Stresses in patients with ≥5.0 cm versus Methods Patients with aTAA ≥5.0 cm (n = 47) and Results Peak circumferential Stresses at systolic pressure were 530 ± 83 kPa for aTAA ≥5.0 cm versus 486 ± 87 kPa for aTAA Conclusions Peak patient-specific aTAA Wall Stresses overall were larger for ≥5.0 cm than aTAA

  • Wall Stress on ascending thoracic aortic aneurysms with bicuspid compared with tricuspid aortic valve
    The Journal of Thoracic and Cardiovascular Surgery, 2018
    Co-Authors: Yue Xuan, Zhongjie Wang, Raymond W Liu, Henrik Haraldsson, Michael D Hope, David Saloner, Julius M Guccione, Elaine E Tseng
    Abstract:

    Abstract Objective Guidelines for repair of bicuspid aortic valve–associated ascending thoracic aortic aneurysms have been changing, most recently to the same criteria as tricuspid aortic valve-ascending thoracic aortic aneurysms. Rupture/dissection occurs when Wall Stress exceeds Wall strength. Recent studies suggest similar strength of bicuspid aortic valve versus tricuspid aortic valve-ascending thoracic aortic aneurysms; thus, comparative Wall Stress may better predict dissection in bicuspid aortic valve versus tricuspid aortic valve-ascending thoracic aortic aneurysms. Our aim was to determine whether bicuspid aortic valve-ascending thoracic aortic aneurysms had higher Wall Stresses than their tricuspid aortic valve counterparts. Methods Patients with bicuspid aortic valve- and tricuspid aortic valve-ascending thoracic aortic aneurysms (bicuspid aortic valve = 17, tricuspid aortic valve = 19) greater than 4.5 cm underwent electrocardiogram-gated computed tomography angiography. Patient-specific 3-dimensional geometry was reconstructed and loaded to systemic pressure after accounting for preStress geometry. Finite element analyses were performed using the LS-DYNA solver (LSTC Inc, Livermore, Calif) with user-defined fiber-embedded material model to determine ascending thoracic aortic aneurysm Wall Stress. Results Bicuspid aortic valve-ascending thoracic aortic aneurysms 99th-percentile longitudinal Stresses were 280 kPa versus 242 kPa ( P  = .028) for tricuspid aortic valve-ascending thoracic aortic aneurysms in systole. These Stresses did not correlate to diameter for bicuspid aortic valve-ascending thoracic aortic aneurysms ( r  = −0.004) but had better correlation to tricuspid aortic valve-ascending thoracic aortic aneurysms diameter ( r  = 0.677). Longitudinal Stresses on sinotubular junction were significantly higher in bicuspid aortic valve-ascending thoracic aortic aneurysms than in tricuspid aortic valve-ascending thoracic aortic aneurysms (405 vs 329 kPa, P  = .023). Bicuspid aortic valve-ascending thoracic aortic aneurysm 99th-percentile circumferential Stresses were 548 kPa versus 462 kPa ( P  = .033) for tricuspid aortic valve-ascending thoracic aortic aneurysms, which also did not correlate to bicuspid aortic valve-ascending thoracic aortic aneurysm diameter ( r  = 0.007). Conclusions Circumferential and longitudinal Stresses were greater in bicuspid aortic valve- than tricuspid aortic valve-ascending thoracic aortic aneurysms and were more pronounced in the sinotubular junction. Peak Wall Stress did not correlate with bicuspid aortic valve-ascending thoracic aortic aneurysm diameter, suggesting diameter alone in this population may be a poor predictor of dissection risk. Our results highlight the need for patient-specific aneurysm Wall Stress analysis for accurate dissection risk prediction.

  • ascending thoracic aortic aneurysm Wall Stress analysis using patient specific finite element modeling of in vivo magnetic resonance imaging
    Interactive Cardiovascular and Thoracic Surgery, 2014
    Co-Authors: Kapil Krishnan, Henrik Haraldsson, Michael D Hope, David Saloner, Julius M Guccione, Elaine E Tseng
    Abstract:

    OBJECTIVE: Rupture/dissection of ascending thoracic aortic aneurysms (aTAAs) carries high mortality and occurs in many patients who did not meet size criteria for elective surgery. Elevated Wall Stress may better predict adverse events, but cannot be directly measured in vivo, rather determined from finite element (FE) simulations. Current computational models make assumptions that limit accuracy, most commonly using in vivo imaging geometry to represent zero-pressure state. Accurate patient-specific Wall Stress requires models with zeropressure three-dimensional geometry, material properties, Wall thickness and residual Stress. We hypothesized that Wall Stress calculated from in vivo imaging geometry at systemic pressure underestimates that using zero-pressure geometry. We developed a novel method to derive zero-pressure geometry from in vivo imaging at systemic pressure. The purpose of this study was to develop the first patient-specific aTAA models using magnetic resonance imaging (MRI) to assess material properties and zero-pressure geometry. Wall Stress results from FE models using systemic pressure were compared with those from models using zero-pressure correction. METHODS: Patients with aTAAs <5 cm underwent ECG-gated computed tomography angiography (CTA) and displacement encoding with stimulated echo (DENSE)-MRI. CTA lumen geometry was used to create surface contour meshes of aTAA geometry. DENSE-MRI measured cyclic aortic Wall strain from which Wall material property was derived. Zero- and systemic pressure geometries were created. Simulations were loaded to systemic pressure using the ABAQUS FE software. Wall Stress analyses were compared between zero-pressure-corrected and systemic pressure geometry FE models. RESULTS: Peak first principal Wall Stress (primarily aligned in the circumferential direction) at systolic pressure for the zero-pressure correction models was 430.62 ± 69.69 kPa, whereas that without zero-pressure correction was 312.55 ± 39.65 kPa (P= 0.004). Peak second principal Wall Stress (primarily aligned in the longitudinal direction) at systolic pressure for the zero-pressure correction models was 200.77 ± 43.13 kPa, whereas that without zero-Stress correction was 156.25 ± 25.55 kPa (P= 0.02). CONCLUSIONS: Previous FE aTAA models from in vivo CT and MRI have not accounted for zero-pressure geometry or patient-specific material property. We demonstrated that zero-pressure correction significantly impacts Wall Stress results. Future computational models that use Wall Stress to predict aTAA adverse events must take into account zero-pressure geometry and patient material property for accurate Wall Stress determination.

Julius M Guccione - One of the best experts on this subject based on the ideXlab platform.

  • Wall Stress distribution in bicuspid aortic valve associated ascending thoracic aortic aneurysms
    The Annals of Thoracic Surgery, 2020
    Co-Authors: Axel Gomez, Yue Xuan, Zhongjie Wang, Michael D Hope, David Saloner, Julius M Guccione, Andrew D Wisneski, Elaine E Tseng
    Abstract:

    Background Bicuspid aortic valve–associated ascending thoracic aortic aneurysms (BAV-aTAAs) carry a risk of acute type A dissection. Biomechanically, dissection may occur when Wall Stress exceeds Wall strength. Our aim was to develop patient-specific computational models of BAV-aTAAs to determine magnitudes of Wall Stress by anatomic regions. Methods Patients with BAV-aTAA diameter greater than 4.5 cm (n = 41) underwent electrocardiogram-gated computed tomography angiography. Three-dimensional aneurysm geometries were reconstructed after accounting for preStress and loaded to systemic pressure. Finite element analyses were performed with fiber-embedded hyperelastic material model using LS-DYNA software (LSTC Inc, Livermore, CA) to obtain Wall Stress distributions. The 99th percentile longitudinal and circumferential Stresses were determined at systole. Results The 99th percentile longitudinal Wall Stresses for BAV-aTAAs at sinuses of Valsalva, sinotubular junction (STJ), and ascending aorta were 361 ± 59.8 kPa, 295 ± 67.2 kPa, and 224 ± 37.6 kPa, respectively, with significant differences in ascending aorta vs sinuses (P Conclusions Wall Stresses, both circumferential and longitudinal, were greater in the aortic root, sinuses, and STJ than in the ascending aorta on BAV-aTAAs. These results fill a fundamental knowledge gap regarding biomechanical Stress distribution in BAV-aTAA patients, which when related to Wall strength may provide prognostication of aTAA dissection risk by patient-specific modeling.

  • Wall Stress analyses in patients with 5 cm versus 5 cm ascending thoracic aortic aneurysm
    The Journal of Thoracic and Cardiovascular Surgery, 2020
    Co-Authors: Zhongjie Wang, Yue Xuan, Michael D Hope, David Saloner, Julius M Guccione, Andrew D Wisneski, Nick Flores, Matthew Y Lum, Justin Inman, Elaine E Tseng
    Abstract:

    Abstract Objective Current guidelines for elective surgery of ascending thoracic aortic aneurysms (aTAAs) use aneurysm size as primary determinant for risk stratification of adverse events. Biomechanically, dissection may occur when Wall Stress exceeds Wall strength. Determining patient-specific aTAA Wall Stresses by finite element analysis can potentially predict patient-specific risk of dissection. This study compared peak Wall Stresses in patients with ≥5.0 cm versus Methods Patients with aTAA ≥5.0 cm (n = 47) and Results Peak circumferential Stresses at systolic pressure were 530 ± 83 kPa for aTAA ≥5.0 cm versus 486 ± 87 kPa for aTAA Conclusions Peak patient-specific aTAA Wall Stresses overall were larger for ≥5.0 cm than aTAA

  • Wall Stress on ascending thoracic aortic aneurysms with bicuspid compared with tricuspid aortic valve
    The Journal of Thoracic and Cardiovascular Surgery, 2018
    Co-Authors: Yue Xuan, Zhongjie Wang, Raymond W Liu, Henrik Haraldsson, Michael D Hope, David Saloner, Julius M Guccione, Elaine E Tseng
    Abstract:

    Abstract Objective Guidelines for repair of bicuspid aortic valve–associated ascending thoracic aortic aneurysms have been changing, most recently to the same criteria as tricuspid aortic valve-ascending thoracic aortic aneurysms. Rupture/dissection occurs when Wall Stress exceeds Wall strength. Recent studies suggest similar strength of bicuspid aortic valve versus tricuspid aortic valve-ascending thoracic aortic aneurysms; thus, comparative Wall Stress may better predict dissection in bicuspid aortic valve versus tricuspid aortic valve-ascending thoracic aortic aneurysms. Our aim was to determine whether bicuspid aortic valve-ascending thoracic aortic aneurysms had higher Wall Stresses than their tricuspid aortic valve counterparts. Methods Patients with bicuspid aortic valve- and tricuspid aortic valve-ascending thoracic aortic aneurysms (bicuspid aortic valve = 17, tricuspid aortic valve = 19) greater than 4.5 cm underwent electrocardiogram-gated computed tomography angiography. Patient-specific 3-dimensional geometry was reconstructed and loaded to systemic pressure after accounting for preStress geometry. Finite element analyses were performed using the LS-DYNA solver (LSTC Inc, Livermore, Calif) with user-defined fiber-embedded material model to determine ascending thoracic aortic aneurysm Wall Stress. Results Bicuspid aortic valve-ascending thoracic aortic aneurysms 99th-percentile longitudinal Stresses were 280 kPa versus 242 kPa ( P  = .028) for tricuspid aortic valve-ascending thoracic aortic aneurysms in systole. These Stresses did not correlate to diameter for bicuspid aortic valve-ascending thoracic aortic aneurysms ( r  = −0.004) but had better correlation to tricuspid aortic valve-ascending thoracic aortic aneurysms diameter ( r  = 0.677). Longitudinal Stresses on sinotubular junction were significantly higher in bicuspid aortic valve-ascending thoracic aortic aneurysms than in tricuspid aortic valve-ascending thoracic aortic aneurysms (405 vs 329 kPa, P  = .023). Bicuspid aortic valve-ascending thoracic aortic aneurysm 99th-percentile circumferential Stresses were 548 kPa versus 462 kPa ( P  = .033) for tricuspid aortic valve-ascending thoracic aortic aneurysms, which also did not correlate to bicuspid aortic valve-ascending thoracic aortic aneurysm diameter ( r  = 0.007). Conclusions Circumferential and longitudinal Stresses were greater in bicuspid aortic valve- than tricuspid aortic valve-ascending thoracic aortic aneurysms and were more pronounced in the sinotubular junction. Peak Wall Stress did not correlate with bicuspid aortic valve-ascending thoracic aortic aneurysm diameter, suggesting diameter alone in this population may be a poor predictor of dissection risk. Our results highlight the need for patient-specific aneurysm Wall Stress analysis for accurate dissection risk prediction.

  • ascending thoracic aortic aneurysm Wall Stress analysis using patient specific finite element modeling of in vivo magnetic resonance imaging
    Interactive Cardiovascular and Thoracic Surgery, 2014
    Co-Authors: Kapil Krishnan, Henrik Haraldsson, Michael D Hope, David Saloner, Julius M Guccione, Elaine E Tseng
    Abstract:

    OBJECTIVE: Rupture/dissection of ascending thoracic aortic aneurysms (aTAAs) carries high mortality and occurs in many patients who did not meet size criteria for elective surgery. Elevated Wall Stress may better predict adverse events, but cannot be directly measured in vivo, rather determined from finite element (FE) simulations. Current computational models make assumptions that limit accuracy, most commonly using in vivo imaging geometry to represent zero-pressure state. Accurate patient-specific Wall Stress requires models with zeropressure three-dimensional geometry, material properties, Wall thickness and residual Stress. We hypothesized that Wall Stress calculated from in vivo imaging geometry at systemic pressure underestimates that using zero-pressure geometry. We developed a novel method to derive zero-pressure geometry from in vivo imaging at systemic pressure. The purpose of this study was to develop the first patient-specific aTAA models using magnetic resonance imaging (MRI) to assess material properties and zero-pressure geometry. Wall Stress results from FE models using systemic pressure were compared with those from models using zero-pressure correction. METHODS: Patients with aTAAs <5 cm underwent ECG-gated computed tomography angiography (CTA) and displacement encoding with stimulated echo (DENSE)-MRI. CTA lumen geometry was used to create surface contour meshes of aTAA geometry. DENSE-MRI measured cyclic aortic Wall strain from which Wall material property was derived. Zero- and systemic pressure geometries were created. Simulations were loaded to systemic pressure using the ABAQUS FE software. Wall Stress analyses were compared between zero-pressure-corrected and systemic pressure geometry FE models. RESULTS: Peak first principal Wall Stress (primarily aligned in the circumferential direction) at systolic pressure for the zero-pressure correction models was 430.62 ± 69.69 kPa, whereas that without zero-pressure correction was 312.55 ± 39.65 kPa (P= 0.004). Peak second principal Wall Stress (primarily aligned in the longitudinal direction) at systolic pressure for the zero-pressure correction models was 200.77 ± 43.13 kPa, whereas that without zero-Stress correction was 156.25 ± 25.55 kPa (P= 0.02). CONCLUSIONS: Previous FE aTAA models from in vivo CT and MRI have not accounted for zero-pressure geometry or patient-specific material property. We demonstrated that zero-pressure correction significantly impacts Wall Stress results. Future computational models that use Wall Stress to predict aTAA adverse events must take into account zero-pressure geometry and patient material property for accurate Wall Stress determination.

  • algisyl lvr with coronary artery bypass grafting reduces left ventricular Wall Stress and improves function in the failing human heart
    International Journal of Cardiology, 2013
    Co-Authors: Lik Chuan Lee, Joseph H. Gorman, Robert C. Gorman, Samuel T Wall, Doron Klepach, Zhihong Zhang, Randall J Lee, Andy Hinson, Julius M Guccione
    Abstract:

    Abstract Background Left ventricular (LV) Wall Stress reduction is a cornerstone in treating heart failure. Large animal models and computer simulations indicate that adding non-contractile material to the damaged LV Wall can potentially reduce myofiber Stress. We sought to quantify the effects of a novel implantable hydrogel (Algisyl-LVR™) treatment in combination with coronary artery bypass grafting (i.e. Algisyl-LVR™+CABG) on both LV function and Wall Stress in heart failure patients. Methods and results Magnetic resonance images obtained before treatment ( n =3), and at 3months ( n =3) and 6months ( n =2) afterwards were used to reconstruct the LV geometry. Cardiac function was quantified using end-diastolic volume (EDV), end-systolic volume (ESV), regional Wall thickness, sphericity index and regional myofiber Stress computed using validated mathematical modeling. The LV became more ellipsoidal after treatment, and both EDV and ESV decreased substantially 3months after treatment in all patients; EDV decreased from 264±91ml to 146±86ml and ESV decreased from 184±85ml to 86±76ml. Ejection fraction increased from 32±8% to 47±18% during that period. Volumetric-averaged Wall thickness increased in all patients, from 1.06±0.21cm (baseline) to 1.3±0.26cm (3months). These changes were accompanied by about a 35% decrease in myofiber Stress at end-of-diastole and at end-of-systole. Post-treatment myofiber Stress became more uniform in the LV. Conclusions These results support the novel concept that Algisyl-LVR™+CABG treatment leads to decreased myofiber Stress, restored LV geometry and improved function.

Yue Xuan - One of the best experts on this subject based on the ideXlab platform.

  • Wall Stress distribution in bicuspid aortic valve associated ascending thoracic aortic aneurysms
    The Annals of Thoracic Surgery, 2020
    Co-Authors: Axel Gomez, Yue Xuan, Zhongjie Wang, Michael D Hope, David Saloner, Julius M Guccione, Andrew D Wisneski, Elaine E Tseng
    Abstract:

    Background Bicuspid aortic valve–associated ascending thoracic aortic aneurysms (BAV-aTAAs) carry a risk of acute type A dissection. Biomechanically, dissection may occur when Wall Stress exceeds Wall strength. Our aim was to develop patient-specific computational models of BAV-aTAAs to determine magnitudes of Wall Stress by anatomic regions. Methods Patients with BAV-aTAA diameter greater than 4.5 cm (n = 41) underwent electrocardiogram-gated computed tomography angiography. Three-dimensional aneurysm geometries were reconstructed after accounting for preStress and loaded to systemic pressure. Finite element analyses were performed with fiber-embedded hyperelastic material model using LS-DYNA software (LSTC Inc, Livermore, CA) to obtain Wall Stress distributions. The 99th percentile longitudinal and circumferential Stresses were determined at systole. Results The 99th percentile longitudinal Wall Stresses for BAV-aTAAs at sinuses of Valsalva, sinotubular junction (STJ), and ascending aorta were 361 ± 59.8 kPa, 295 ± 67.2 kPa, and 224 ± 37.6 kPa, respectively, with significant differences in ascending aorta vs sinuses (P Conclusions Wall Stresses, both circumferential and longitudinal, were greater in the aortic root, sinuses, and STJ than in the ascending aorta on BAV-aTAAs. These results fill a fundamental knowledge gap regarding biomechanical Stress distribution in BAV-aTAA patients, which when related to Wall strength may provide prognostication of aTAA dissection risk by patient-specific modeling.

  • Wall Stress analyses in patients with 5 cm versus 5 cm ascending thoracic aortic aneurysm
    The Journal of Thoracic and Cardiovascular Surgery, 2020
    Co-Authors: Zhongjie Wang, Yue Xuan, Michael D Hope, David Saloner, Julius M Guccione, Andrew D Wisneski, Nick Flores, Matthew Y Lum, Justin Inman, Elaine E Tseng
    Abstract:

    Abstract Objective Current guidelines for elective surgery of ascending thoracic aortic aneurysms (aTAAs) use aneurysm size as primary determinant for risk stratification of adverse events. Biomechanically, dissection may occur when Wall Stress exceeds Wall strength. Determining patient-specific aTAA Wall Stresses by finite element analysis can potentially predict patient-specific risk of dissection. This study compared peak Wall Stresses in patients with ≥5.0 cm versus Methods Patients with aTAA ≥5.0 cm (n = 47) and Results Peak circumferential Stresses at systolic pressure were 530 ± 83 kPa for aTAA ≥5.0 cm versus 486 ± 87 kPa for aTAA Conclusions Peak patient-specific aTAA Wall Stresses overall were larger for ≥5.0 cm than aTAA

  • Wall Stress on ascending thoracic aortic aneurysms with bicuspid compared with tricuspid aortic valve
    The Journal of Thoracic and Cardiovascular Surgery, 2018
    Co-Authors: Yue Xuan, Zhongjie Wang, Raymond W Liu, Henrik Haraldsson, Michael D Hope, David Saloner, Julius M Guccione, Elaine E Tseng
    Abstract:

    Abstract Objective Guidelines for repair of bicuspid aortic valve–associated ascending thoracic aortic aneurysms have been changing, most recently to the same criteria as tricuspid aortic valve-ascending thoracic aortic aneurysms. Rupture/dissection occurs when Wall Stress exceeds Wall strength. Recent studies suggest similar strength of bicuspid aortic valve versus tricuspid aortic valve-ascending thoracic aortic aneurysms; thus, comparative Wall Stress may better predict dissection in bicuspid aortic valve versus tricuspid aortic valve-ascending thoracic aortic aneurysms. Our aim was to determine whether bicuspid aortic valve-ascending thoracic aortic aneurysms had higher Wall Stresses than their tricuspid aortic valve counterparts. Methods Patients with bicuspid aortic valve- and tricuspid aortic valve-ascending thoracic aortic aneurysms (bicuspid aortic valve = 17, tricuspid aortic valve = 19) greater than 4.5 cm underwent electrocardiogram-gated computed tomography angiography. Patient-specific 3-dimensional geometry was reconstructed and loaded to systemic pressure after accounting for preStress geometry. Finite element analyses were performed using the LS-DYNA solver (LSTC Inc, Livermore, Calif) with user-defined fiber-embedded material model to determine ascending thoracic aortic aneurysm Wall Stress. Results Bicuspid aortic valve-ascending thoracic aortic aneurysms 99th-percentile longitudinal Stresses were 280 kPa versus 242 kPa ( P  = .028) for tricuspid aortic valve-ascending thoracic aortic aneurysms in systole. These Stresses did not correlate to diameter for bicuspid aortic valve-ascending thoracic aortic aneurysms ( r  = −0.004) but had better correlation to tricuspid aortic valve-ascending thoracic aortic aneurysms diameter ( r  = 0.677). Longitudinal Stresses on sinotubular junction were significantly higher in bicuspid aortic valve-ascending thoracic aortic aneurysms than in tricuspid aortic valve-ascending thoracic aortic aneurysms (405 vs 329 kPa, P  = .023). Bicuspid aortic valve-ascending thoracic aortic aneurysm 99th-percentile circumferential Stresses were 548 kPa versus 462 kPa ( P  = .033) for tricuspid aortic valve-ascending thoracic aortic aneurysms, which also did not correlate to bicuspid aortic valve-ascending thoracic aortic aneurysm diameter ( r  = 0.007). Conclusions Circumferential and longitudinal Stresses were greater in bicuspid aortic valve- than tricuspid aortic valve-ascending thoracic aortic aneurysms and were more pronounced in the sinotubular junction. Peak Wall Stress did not correlate with bicuspid aortic valve-ascending thoracic aortic aneurysm diameter, suggesting diameter alone in this population may be a poor predictor of dissection risk. Our results highlight the need for patient-specific aneurysm Wall Stress analysis for accurate dissection risk prediction.

David F Teitel - One of the best experts on this subject based on the ideXlab platform.

  • nonlinearity of the left ventricular end systolic Wall Stress velocity of fiber shortening relation in young pigs a potential pitfall in its use as a single beat index of contractility
    Journal of the American College of Cardiology, 1994
    Co-Authors: Anirban Banerjee, Michael M Brook, Robert J M Klautz, David F Teitel
    Abstract:

    Abstract Objectives. We sought to evaluate in the young heart the primary assumptions on which the current use of the mean “velocity of fiber shortening corrected for heart rate” as a noninvasive index of contractility are based. Background. End-systolic Wall Stress-velocity of fiber shortening relation has been applied as a single-beat, load-independent index of contractility in children. This use is based on poorly validated assumptions of linearity, parallel shifts with changing contractile state and inotropic sensitivity of the end-systolic Wall Stress-velocity of fiber shortening relation. Methods. In eight anesthetized young piglets, 5F micromanometric catheters were placed in the ascending aorta and balloon occlusion catheters in the descending aorta. End-systolic Wall Stress and velocity of fiber shortening were calculated from aortic pressure and M-mode echocardiography under six conditions: in three contractile states 1) baseline, 2) increased contractility during dobutamine infusion (10 μg/kg per min), and 3) decreased contractility after propranolol injection (1 mg/kg), each at two afterload states (normal and increased load by partial aortic occlusion). Results. Dobutamine increased and propranolol decreased afterloadd-matched velocity of fiber shortening corrected for heart rate significantly to 140% aid 77% of baseline, respectively. However, the slope of end-systolic Wall Stress-velocity of fiber shortening was (251% of baseline) during dobutamine infusion, which also significantly decreased Wall Stress, and was much less (27% of baseline) after propranolol injection, which increased Wall Stress. Conclusions. The velocity of fiber shortening corrected for heart rate did change predictably with changes in contractility and as such can be ued noninvasively in the temporal evaluation of individual patients undergoing therapeutic interventions or to define the natural history of a disease process. However, the relation on which it is based is not defined by parallel straight lines across contractile states, so that abnormal single measurements may reflect only the nonlinearity of the relation rather than in contractility. Thus, we recommend that the end-systolic Wall Stress-velocity of fiber shortening relation should not be used as a single-beat index of contractility.