Relative Residence Time Research Articles

The Hemodynamics of Aneurysms Treated with Flow-Diverting Stents Considering both Stent and Aneurysm/Artery Geometries

Flow diverting stents are deployed to reduce the blood flow into the aneurysm, which would thereby induce thrombosis in the aneurysm sac; the stents prevent its rupture. The present study aimed to examine and quantify the impacts of different flow stents on idealized configurations of the cerebral artery. In our study, we considered a spherical sidewall aneurysm located on curved and tortuous idealized artery vessels and three stents with different porosities (70, 80 and 90%) for deployment. Using computational fluid dynamics, the local hemodynamics in the presence and absence of the stents were simulated, respectively, under the assumption that the blood flow was unsteady and non-Newtonian. The hemodynamic parameters, such as the intra-aneurysmal flow, velocity field and wall shear stress and its related indices, were examined and compared among the 12 cases simulated. The results illustrated that with the stent deployment, the intra-aneurysmal flow and the wall shear stress and its related indices were considerably modified depending on both stent and aneurysm/artery geometries, and that the intra-aneurysmal relative residence time increased rapidly with decreasing stent porosity in all the vessel configurations. These results also inform the rationale for selecting stents for treating aneurysms of different configurations.

A Mixture Theory Model for Blood Combined With Low-Density Lipoprotein Transport to Predict Early Atherosclerosis Regions in Idealized and Patient-Derived Abdominal Aorta.

Genesis and onset of atherosclerosis are greatly influenced by hemodynamic forces. Two-phase transient computational fluid dynamic (CFD) simulations are performed using a mixture theory model for blood, and a transport equation for low-density lipoprotein (LDL), in idealized and patient-derived abdominal aorta to predict the sites at risk for atherosclerosis. Flow patterns at different time instants and relevant hemodynamic indicators-wall shear stress (WSS)-based (time-averaged wall shear stress (TAWSS), oscillatory shear index (OSI), and relative residence time (RRT)), and LDL concentration-are used concurrently to predict the susceptible sites of atherosclerosis. In the case of idealized geometry, flow recirculations are observed on the posterior wall opposite the superior mesenteric artery and below the renal bifurcations. Low TAWSS, high OSI, high RRT and high concentration of LDL are observed in these regions. This suggests that in idealized abdominal aorta, the posterior wall proximal to the renal artery junction is more prone to atherosclerosis. This matches qualitatively with the experimental and simulation data in the literature. In the case of patient-derived geometry, flow reversal, low TAWSS, high OSI and high RRT are observed infrarenal on the anterior wall. Further, high concentration of LDL is observed at the same location on the anterior wall suggesting anterior wall distal to the renal artery junction is more prone to atherosclerosis. These findings demonstrate the use of a novel method to predict the sites at risk for atherosclerosis in geometries where complexities like junctions and curvature play a major role.

Gender differences of morphological and hemodynamic characteristics of abdominal aortic aneurysm

BackgroundGender difference in cardiovascular diseases (CVDs) is an important topic in the field of cardiovascular medicine. In this study, we focused on the mortality difference of abdominal aortic aneurysms (AAA), which is higher for female than that of male. The aim of this study was to verify whether morphological and hemodynamic factors play their roles in this phenomenon.MethodsPatient-specific AAA models of 11 females and 23 males with similar age and body mass index (BMI) have been reconstructed based on clinical computed tomography (CT) data. Firstly, the morphological parameters (diameters, curvature, intraluminal thrombus volume, etc.) of AAA models and lumbar vertebrae models were collected and analyzed. Then, based on statistical results of morphological parameters, uniformed male and female AAA models were reconstructed, and hemodynamic simulations were conducted respectively. In post-processing, the hemodynamic performances induced by gender-different morphological geometries were analyzed and compared.ResultsThe comparison of morphological parameters revealed that the average curvature of lumbar vertebrae and AAA centerline of female AAA models were obviously higher than that of the male. The amount of intraluminal thrombus in female AAA models was relatively lower than that of the male. According to the hemodynamic simulation, the uniform female AAA model has higher peak pressure, lower oscillatory shear stress index (OSI), and lower relative residence time (RRT) than that of the male model, all of which put female AAA to a relatively higher risk hemodynamic situation.ConclusionsThe morphological and hemodynamic features of AAA have very obvious gender differences that would induce higher risk of rupture for female AAA biomechanically. These findings would help to explore the mechanism of gender differences in AAA and draw attention to gender-specific consideration for AAA treatment. More morphological and hemodynamic indictors are suggested to be involved in the future guidelines.

Probabilistic characteristics of nonlinear waves in nondispersive media of the hydrodynamic type.

The paper considers the probability distributions of the nonlinear wave characteristics in nondispersive media that satisfy the Riemann- and the Kardar-Parisi-Zhang-type equations. By using the Lagrangian and Euler relations of statistical descriptions, expressions are obtained for the probability density of the Riemann wave (displacement) integral through the initial probability density of displacement, velocity, and acceleration. The case of Gaussian initial statistics is considered when multivalued sections in nonlinear waves arise at arbitrarily small distances from the entrance. The expressions obtained in this case should be interpreted as the relative residence time of the process in a certain displacement range. It is shown that, due to the Riemann equation locality, the appearance of ambiguity in the wave profile, which occurs mainly at negative values, does not affect the probability density form at positive bias values.

Influence of Artery Straightening on Local Hemodynamics in Left Anterior Descending (LAD) Artery after Stent Implantation.

Objectives The study investigates local hemodynamic environment changes caused by straightening phenomenon and the relationship between straightening phenomenon and in-stent restenosis. Background Intravascular intervention is an effective treatment in restoring the normal flow conditions and vascular lumen. Unfortunately, in-stent restenosis often occurs in a subset of patients after stent implantation and limits the success of stent implantation outcomes. The implanted stent usually causes artery straightening locally, rather than coinciding and adjusting to the physiological curve exactly. Artery straightening would apparently modify the artery geometry and therefore alter the local hemodynamic environment, which may result in intimal hyperplasia and restenosis after stenting implantation. Methods In the current investigation, we verify the hypothesis that the artery straightening influences the local hemodynamic state using the different 3D CT models. Flow analysis for blood in the left anterior descending coronary artery and the straightening model is simulated numerically. Result The current results reveal that the straightening phenomenon alters the distribution of wall shear stress and flow patterns, decreases the wall shear stress (WSS), and increases the oscillatory shear index (OSI) and the relative residence time (RRT), especially at the proximal and distal areas of stenting. Conclusions The local straightened geometry established after stent implantation was likely to generate portions of the stenting area to a high risk of neointimal hyperplasia and subsequent restenosis.

Computational prediction of hemodynamical and biomechanical alterations induced by aneurysm dilatation in patient-specific ascending thoracic aortas.

The aim of the present work is to propose a robust computational framework combining computational fluid dynamics (CFD) and 4D flow MRI to predict the progressive changes in hemodynamics and wall rupture index (RPI) induced by aortic morphological evolutions in patients harboring ascending thoracic aortic aneurysms (ATAAs). An analytical equation has been proposed to predict the aneurysm progression based on age, sex, and body surface area. Parameters such as helicity, wall shear stress (WSS), time-averaged WSS, oscillatory shear index, relative residence time, and viscosity were evaluated for two patients at different stages of aneurysm growth, and compared with age-sex-matched healthy subjects. The study shows that evolution of hemodynamics and RPI, despite being very slow in ATAAs, is strongly affected by morphological alterations and, in turn could impact biomechanical factors and aortic mechanobiology. An aspect of the current work is that the patient-specific 4D MRI data sets were obtained with a follow-up of 1 year and the measured time-averaged velocity maps and flow eccentricity were compared with the CFD simulation for validation. The computational framework presented here is capable of capturing the blood flow patterns and the hemodynamic descriptors during the various stages of aneurysm growth. Further investigations will be conducted in order to verify these results on a larger cohort of patients and with long follow-up times to finally elucidate the link between deranged hemodynamics, AA geometry, and wall mechanical properties in ATAAs.

Influence of Hemodialysis Catheter Insertion on Hemodynamics in the Central Veins.

Central venous catheter (CVC) related thrombosis is a major cause of CVC dysfunction in patients under hemodialysis. The aim of our study was to investigate the impact of CVC insertion on hemodynamics in the central veins and to examine the changes in hemodynamic environments that may be related to thrombus formation due to the implantation of CVC. Patient-specific models of the central veins with and without CVC were reconstructed based on computed tomography images. Flow patterns in the veins were numerically simulated to obtain hemodynamic parameters such as time-averaged wall shear stress (TAWSS), oscillating shear index (OSI), relative residence time (RRT), and normalized transverse wall shear stress (transWSS) under pulsatile flow. The non-Newtonian effects of blood flow were also analyzed using the Casson model. The insertion of CVC caused significant changes in the hemodynamic environment in the central veins. A greater disturbance and increase of velocity were observed in the central veins after the insertion of CVC. As a result, TAWSS and transWSS were markedly increased, but most parts of OSI and RRT decreased. Newtonian assumption of blood flow would overestimate the increase in TAWSS after CVC insertion. High wall shear stress (WSS) and flow disturbance, especially the multidirectionality of the flow, induced by the CVC may be a key factor in initiating thrombosis after CVC insertion. Accordingly, approaches to decrease the flow disturbance during CVC insertion may help restrain the occurrence of thrombosis. More case studies with pre-operative and postoperative modeling and clinical follow-up need to be performed to verify these findings. Non-Newtonian blood flow assumption is recommended in computational fluid dynamics (CFD) simulations of veins with CVCs.

Computational Comparison between the Altura Aortic Endograft Configuration and the Classic Bifurcated Idealized Designs

The Altura (Alt) endograft is a new design, lacking the classic main body with the flow divider. Instead, 2 proximal D-shaped endografts form a round circumference in the aortic neck for secure sealing and land in the iliac arteries in a cross-limb fashion. The aim of this computational study was to compare hemodynamically this model with the classic bifurcated (Bif) and cross-limb (Cx) endograft designs of equal total length. All 3D endograft models were created using the finite volume analysis application ANSYS CFX (Ansys Inc., Canonsburg, PA, USA). The Alt inlet was constructed as 2 opposing D-shaped sections. The flow was quantified by time-averaged wall shear stress (TAWSS), oscillatory shear index (OSI), relative residence time (RRT), and helicity. The displacement forces were also compared for all models with computational fluid dynamics analysis. The Alt design was associated with lower forces (range 4.0-5.9Ν) than Bif (4.17-6.15N) and Cx (4.43-6.53N). The 2-piece inlet site of the separated limbs of Alt has higher TAWSS than the uniform inlet segment of the Cx and the Bif model. Most importantly, the mid-segment and distal segment of the limbs in the Alt design present higher TAWSS in a greater area than the other 2 models. The inlet of the Alt design showed higher OSI than the other accommodations and similar or comparable OSI values along their mid-limb and distal limb segments. The range, location, and values or RRT were comparable between the 3 models. Helicity in the iliac limbs is more prominent in the crossed accommodations (Alt and Cx). Only small differences in the hemodynamic indices and displacement forces were detected between the Alt and classic accommodations. From this point of view, the Alt design could be theoretically considered not inferior to other widely used endograft configurations.

Elevated Lipid Infiltration Is Associated With Cerebral Aneurysm Rupture.

Background: Intracranial aneurysm wall degradation can be associated with lipid infiltration. However, the relationship between lipid infiltration and aneurysm rupture has not been explored quantitatively. To investigate the correlation between lipid infiltration and aneurysm rupture, we utilized patient-specific simulation of low-density lipoprotein (LDL) transport to analyze lipid infiltration in the cerebral aneurysm wall.Methods: Sixty-two aneurysms were analyzed. Patient blood pressure, plasma LDL concentration, and three-dimensional angiographic images were obtained to simulate LDL transport in aneurysms. Morphological, hemodynamic, and lipid accumulation parameters were compared between ruptures and unruptured groups. Multivariate logistic regression was also performed to determine parameters that are independently associated with rupture.Results: Size ratio, wall shear stress, low shear area, relative residence time, area-averaged LDL infiltration rate, and maximum LDL infiltration rate were significant parameters in univariate analysis (P < 0.05). Multivariate analysis revealed that only average LDL infiltration remained as a significant variable (P < 0.05). The prediction model derived showed good performance for rupture prediction (AUC, 0.885; 95% CI, 0.794–0.976).Conclusions: Ruptured aneurysms showed significantly higher LDL infiltration compared to unruptured ones. Our results suggested that lipid infiltration may promote aneurysm rupture. Lipid infiltration characteristics should be considered when assessing aneurysm rupture risk.

THE COMPARISON OF VENOUS SEQUENTIAL AND NORMAL GRAFT PATENCY BASED ON HEMODYNAMICS

Background: In coronary artery bypass grafting (CABG), the patency of venous sequential graft remains controversial. Hemodynamic factors have been proved to be the important factors influencing graft patency. The objective of this study is to compare the patency of sequential grafts and normal grafts by hemodynamic environment. Methods: This study used a patient’s clinical data to construct a 0D/3D coupled multi-scale model, and used this model to calculate graft’s hemodynamics under two grafting methods. Meanwhile, CABG ideal models were constructed based on grafts’ flow data of 60 patients (63 normal grafts, 19 sequential grafts) to calculate grafts’ hemodynamics. Results: Based on the multi-scale model, it was found that the sequential graft flow and time average wall shear stress (TAWSS) were higher than normal graft, which was good for graft patency. But there were a flow separation region, some regions of high oscillatory shear index (OSI) and relative residence time (RRT) in sequential graft, which could lead to intimal hyperplasia. Based on ideal CABG models, it was known that failure rate of sequential and normal grafts were 36.8% and 36.5%, and there were significant differences between them in flow rate, TAWSS and OSI (sequential versus normal: flow rate (ml/min): [Formula: see text] versus [Formula: see text], TAWSS (Pa): [Formula: see text] versus [Formula: see text], OSI: 0.[Formula: see text] versus [Formula: see text]). Conclusion: For saphenous venous graft (SVG), although the normal graft has similar patency with the sequential graft, the hemodynamic mechanism behind it is different. In flow rate and WSS, sequential grafts have an advantage over normal grafts. But there are high OSI and RRT regions in sequential grafts.

Experimental Investigation of the Effect of Heart Rate on Flow in the Left Ventricle in Health and Disease-Aortic Valve Regurgitation.

There is much debate in the literature surrounding the effects of heart rate on aortic regurgitation (AR). Despite the contradictory information, it is still widely believed that an increase in heart rate is beneficial due to the disproportionate shortening of the duration of diastole relative to systole, permitting less time for the left ventricle to fill from regurgitation. This in vitro work investigates how a change in heart rate affects the left ventricular fluid dynamics in the absence and presence of acute AR. The experiments are performed on a novel double-activation left heart simulator previously used for the study of chronic AR. The intraventricular velocity fields are acquired via time-resolved planar particle image velocimetry (PIV) in a clinically relevant plane. Considering fluid dynamic factors, an increase in heart rate was observed to have a limited benefit in the case of mild AR and a detrimental effect for more severe AR. With increasing heart rate, mild AR was associated with a decrease in regurgitant volume, a negligible change in regurgitant volume per diastolic second, and a limited reduction in the fraction of retained regurgitant inflow. More severe AR was accompanied by an increase in both regurgitant volume and the fraction of retained regurgitant inflow, implying a less effective pumping efficiency and a longer relative residence time of blood in the ventricle. Globally, the left ventricle's capacity to compensate for the increase in energy dissipation associated with an increase in heart rate diminishes considerably with severity, a phenomenon which may be exploited further as a method of noninvasive assessment of the severity of AR. These findings may affect the clinical belief that tachycardia is preferred in acute AR and should be investigated further in the clinical setting.

Hydrochemical evolution of groundwater in gabbro of the Troodos Fractured Aquifer. A comprehensive approach

Ophiolites often form complex, fractured, multi-lithological and highly compartmentalized aquifers that are difficult to characterize. Groundwater chemistry reflects water-rock interactions and can provide insights to groundwater recharge mechanisms, flow paths and relative residence time. A comprehensive hydrogeochemical modelling approach with PHREEQC has been developed to identify water-rock interactions and simulate groundwater evolution and mixing with connate water in fractured aquifers. The methodology was applied in the gabbro aquifers of Troodos Massif (Cyprus). The geochemical processes generating the most frequently observed water types were reproduced through modelling. Based on the overall results, a generic evolution path has been identified: CaMgHCO3 → MgCaHCO3 → CaMgNaHCO3 → Ca/Mg/Na/HCO3/SO4 → NaMgHCO3SO4 → NaSO4/Cl group. CaMgHCO3 and MgCaHCO3 types were modelled to occur predominantly in early stages of recharge. Deep unsaturated zones and longer flow paths result in gradual removal of Ca+2 and Mg+2 from groundwater, through secondary mineral precipitation, and in an increase of Na+2 and SO4−2. The most frequently occurring water types, CaMgNaHCO3 and MgCaNaHCO3, were modelled to occur at later stages of hydro-chemical evolution, after secondary mineral precipitation, and in closed conditions. In regional flow, where closed conditions with secondary mineral precipitation prevail, water types progressively shift from the HCO3 to the NaSO4 end-member group. In 38% of the 536 samples from gabbro aquifers in Troodos, groundwater mixing with connate water at a ratio of ≥0.999:0.001 occurs.

Assessing the Risk of Intracranial Aneurysm Rupture Using Morphological and Hemodynamic Biomarkers Evaluated from Magnetic Resonance Fluid Dynamics and Computational Fluid Dynamics.

Purpose:Evaluate in vivo hemodynamic and morphological biomarkers of intracranial aneurysms, using magnetic resonance fluid dynamics (MRFD) and MR-based patient specific computational fluid dynamics (CFD) in order to assess the risk of rupture.Methods:Forty-eight intracranial aneurysms (10 ruptured, 38 unruptured) were scrutinized for six morphological and 10 hemodynamic biomarkers. Morphological biomarkers were calculated based on 3D time-of-flight magnetic resonance angiography (3D TOF MRA) in MRFD analysis. Hemodynamic biomarkers were assessed using both MRFD and CFD analyses. MRFD was performed using 3D TOF MRA and 3D cine phase-contrast magnetic resonance imaging (3D cine PC MRI). CFD was performed utilizing patient specific inflow–outflow boundary conditions derived from 3D cine PC MRI. Univariate analysis was carried out to identify statistically significant biomarkers for aneurysm rupture and receiver operating characteristic (ROC) analysis was performed for the significant biomarkers. Binary logistic regression was performed to identify independent predictive biomarkers.Results:Morphological biomarker analysis revealed that aneurysm size [P = 0.021], volume [P = 0.035] and size ratio [P = 0.039] were statistically significantly different between the two groups. In hemodynamic biomarker analysis, MRFD results indicated that ruptured aneurysms had higher oscillatory shear index (OSI) [OSI.max, P = 0.037] and higher relative residence time (RRT) [RRT.ave, P = 0.035] compared with unruptured aneurysms. Correspondingly CFD analysis demonstrated significant differences for both average and maximum OSI [OSI.ave, P = 0.008; OSI.max, P = 0.01] and maximum RRT [RRT.max, P = 0.045]. ROC analysis revealed AUC values greater than 0.7 for all significant biomarkers. Aneurysm volume [AUC, 0.718; 95% CI, 0.491–0.946] and average OSI obtained from CFD [AUC, 0.774; 95% CI, 0.586–0.961] were retained in the respective logistic regression models.Conclusion:Both morphological and hemodynamic biomarkers have significant influence on intracranial aneurysm rupture. Aneurysm size, volume, size ratio, OSI and RRT could be potential biomarkers to assess aneurysm rupture risk.

Rupture risk assessment for multiple intracranial aneurysms: why there is no need for dozens of clinical, morphological and hemodynamic parameters.

Introduction:A multitude of approaches have been postulated for assessing the risk of intracranial aneurysm rupture. However, the amount of potential predictive factors is not applicable in clinical practice and they are rejected in favor of the more practical PHASES score. For the subgroup of multiple intracranial aneurysms (MIAs), the PHASES score might severely underestimate the rupture risk, as only the aneurysm with the largest diameter is considered for risk evaluation.Methods:In this study, we investigated 38 patients harboring a total number of 87 MIAs with respect to their morphological and hemodynamical characteristics. For the determination of the best suited parameters regarding their predictive power for aneurysm rupture, we conducted three phases of statistical evaluation. The statistical analysis aimed to identify parameters that differ significantly between ruptured and unruptured aneurysms, show smallest possible correlations among each other and have a high impact on rupture risk prediction.Results:Significant differences between ruptured and unruptured aneurysms were found in 16 out of 49 parameters. The lowest correlation were found for gamma, aspect ratio (AR1), aneurysm maximal relative residence time (Aneurysm_RRT_max) and aneurysm mean relative residence time. The data-driven parameter selection yielded a significant correlation of only two parameters (AR1 and the Aneurysm_RRT_max) with rupture state (area under curve = 0.75).Conclusion:A high number of established morphological and hemodynamical parameters seem to have no or only low effect on prediction of aneurysm rupture in patients with MIAs. For best possible rupture risk assessment of patients with MIAs, only the morphological parameter AR1 and the hemodynamical parameter Aneurysm_RRT_max need to be included in the prediction model.

Numerical Investigation of an Idealized Total Cavopulmonary Connection Physiology Assisted by the Axial Blood Pump With and Without Diffuser

In order to improve the surgical treatment of the congenital heart disease patient with single ventricle defect, two axial flow blood pumps, one with diffuser and the other without diffuser, were designed and virtually implanted into an idealized total cavopulmonary connection (TCPC) model to form two types of Pump-TCPC physiological structure. Computational fluid dynamics (CFD) simulations were performed to analyze the variations of the hemodynamic characteristics, such as flow field, wall shear stress (WSS), oscillatory shear index (OSI), relative residence time (RRT), between the two Pump-TCPC models. Numerical results indicate that the Pump-TCPC with diffuser has better flow field stability, less damage on endothelial cell of vessel wall, and lower risk of vascular injury and thrombosis formation than that without diffuser.

Computational analysis of the coronary artery hemodynamics with different anatomical variations

Abstract Hemodynamic parameters have been identified as a significant determinant in the development and progression of plaque, which leads to coronary artery disease (CAD). This study aims to use computational modeling to investigate how geometrical variations influence intravascular and near-wall hemodynamics. Branch angles and tortuosities were varied in idealized models of both bifurcations and trifurcations. Four patient-specific models with bifurcation (70°, 95°, and 135°) and trifurcation (90°) geometries were also computed. Computational fluid dynamics (CFD) analysis was performed for idealized and patient-specific geometries to simulate physiological conditions, enabling the quantification of local hemodynamics, including threshold analysis. The branch angle has a significant impact on the locations of adverse hemodynamics in the idealized and patient-specific cases. The angulation of different geometries influences the formation of low-velocity regions, which is more prominent in the trifurcation geometries opposite to the carina. Helicity intensity demonstrates a significant positive correlation with bifurcation (r = 0.94, P 0.2, and relative residence time (RRT) > 4.17 Pa-1 is observed with increasing branch angles, and the magnitude is more prominent for trifurcation arteries. Arterial tortuosity influences the formation of helicity intensity and promotes atheroprotectivity by decreasing the area exposed with near-wall descriptors. In conclusion, geometrical changes, including the branch angle and tortuosity, have a significant impact on local hemodynamics of the left coronary artery (LCA) and its correlation with atherosclerosis formation.

Structure-Kinetic-Relationship Reveals the Mechanism of Selectivity of FAK Inhibitors Over PYK2

There is increasing evidence of a significant correlation between prolonged drug-target residence time and increased drug efficacy. Here, we report a structural rational for kinetic selectivity between two closely related kinases: Focal Adhesion Kinase (FAK) and Proline-rich Tyrosine Kinase 2 (PYK2). We found that slow off-rate FAK inhibitors induce helical structure at the DFG motif of FAK but not PYK2. Binding kinetic data, high resolution structures and mutagenesis data support the role of hydrophobic interactions of inhibitors with the DFG helical region providing a structural rational for slow dissociation rates from FAK and kinetic selectivity over PYK2. Our experimental data correlated well with computed relative residence times from molecular simulations providing a feasible strategy for rationally optimizing ligand residence times. We suggest that the interplay between the protein structural mobility and ligand-induced effects is a key regulator of the kinetic selectivity of inhibitors of FAK versus PYK2.

Hemodynamic consequences of TEVAR with in situ double fenestrations of left carotid artery and left subclavian artery

The aortic major branches after thoracic endovascular aortic repair (TEVAR) could be preserved by in situ fenestration (ISF). This study aims to explore the hemodynamic consequences of ISF-TEVAR with double fenestrations. Two patients with aortic dissection and aneurysm, respectively, were treated by ISF-TEVAR and both the left carotid artery (LCA) and left subclavian artery (LSA) were reconstructed by fenestration technique. The blood was considered a non-Newtonian fluid and the Windkessel model was adopted at the aortic outlets. Simulations were performed in two postoperative models to analyze the effects of the double fenestration stents on the hemodynamics. The postoperative wall pressure of the LCA and LSA is relatively low and the pressure difference between the inner and outer walls of the protruding segment of the LSA stent is found. Acceleration occurs when blood flows around the fenestration stents and the shear-thinning rheological behavior is observed at the aortic arch. Moreover, regions susceptible to thrombosis are identified and the surface exposed to high relative residence time is located at the aortic arch after the LSA stent. The presence of the double fenestration stents has a profound impact on the postoperative hemodynamics, and the aortic arch and rebuilt branches should be closely watched during follow-up.

Novel Models for Identification of the Ruptured Aneurysm in Patients with Subarachnoid Hemorrhage with Multiple Aneurysms.

In patients with SAH with multiple intracranial aneurysms, often the hemorrhage pattern does not indicate the rupture source. Angiographic findings (intracranial aneurysm size and shape) could help but may not be reliable. Our purpose was to test whether existing parameters could identify the ruptured intracranial aneurysm in patients with multiple intracranial aneurysms and whether composite predictive models could improve the identification. We retrospectively collected angiographic and medical records of 93 patients with SAH with at least 2 intracranial aneurysms (total of 206 saccular intracranial aneurysms, 93 ruptured), in which the ruptured intracranial aneurysm was confirmed through surgery or definitive hemorrhage patterns. We calculated 13 morphologic and 10 hemodynamic parameters along with location and type (sidewall/bifurcation) and tested their ability to identify rupture in the 93 patients. To build predictive models, we randomly assigned 70 patients to training and 23 to holdout testing cohorts. Using a linear regression model with a customized cost function and 10-fold cross-validation, we trained 2 rupture identification models: RIMC using all parameters and RIMM excluding hemodynamics. The 25 study parameters had vastly different positive predictive values (31%-87%) for identifying rupture, the highest being size ratio at 87%. RIMC incorporated size ratio, undulation index, relative residence time, and type; RIMM had only size ratio, undulation index, and type. During cross-validation, positive predictive values for size ratio, RIMM, and RIMC were 86% ± 4%, 90% ± 4%, and 93% ± 4%, respectively. In testing, size ratio and RIMM had positive predictive values of 85%, while RIMC had 92%. Size ratio was the best individual factor for identifying the ruptured aneurysm; however, RIMC, followed by RIMM, outperformed existing parameters.

Impacts of Internal Carotid Artery Revascularization on Flow in Anterior Communicating Artery Aneurysm: A Preliminary Multiscale Numerical Investigation

The optimal management strategy of patients with concomitant anterior communicating artery aneurysm (ACoAA) and internal carotid artery (ICA) stenosis is unclear. This study aims to evaluate the impacts of unilateral ICA revascularization on hemodynamics factors associated with rupture in an ACoAA. In the present study, a multiscale computational model of ACoAA was developed by coupling zero-dimensional (0D) models of the cerebral vascular system with a three-dimensional (3D) patient-specific ACoAA model. Distributions of flow patterns, wall shear stress (WSS), relative residence time (RRT) and oscillating shear index (OSI) in the ACoAA under left ICA revascularization procedure were quantitatively assessed by using transient computational fluid dynamics (CFD) simulations. Our results showed that the revascularization procedures significantly changed the hemodynamic environments in the ACoAA. The flow disturbance in the ACoAA was enhanced by the resumed flow from the affected side. In addition, higher OSI (0.057 vs. 0.02), prolonged RRT (1.14 vs. 0.39) and larger low WSS area (66 vs. 50 mm2) in ACoAA were found in the non-stenotic case. These acute changes in hemodynamics after revascularization may elevate the rupture risk of ACoAA. The preliminary results validated the feasibility of predicting aneurismal hemodynamics characteristics in revascularization procedures by using multiscale CFD simulations, which would benefit the management of this group of patients.