Maximum Oscillatory Shear Index Research Articles

Wall Shear Stress Measured with 4D Flow CMR Correlates with Biomarkers of Inflammation and Collagen Synthesis in Mild-to-Moderate Ascending Aortic Dilation and Tricuspid Aortic Valves.

Understanding the mechanisms underlying ascending aortic dilation is imperative for refined risk stratification of these patients, particularly among incidentally identified patients, most commonly presenting with tricuspid valves. The aim of this study was to explore associations between ascending aortic hemodynamics, assessed using four-dimensional flow cardiovascular magnetic resonance imaging (4D Flow CMR), and circulating biomarkers in aortic dilation. Forty-seven cases with aortic dilation (diameter ≥40 mm) and 50 sex-and age-matched controls (diameter <40 mm), all with tricuspid aortic valves, underwent 4D flow CMR and venous blood sampling. Associations between flow displacement, wall shear stress (WSS), and oscillatory shear index in the ascending aorta derived from 4D Flow CMR, and biomarkers including interleukin-6, collagen type I α1 chain, metalloproteinases (MMPs), and inhibitors of MMPs derived from blood plasma, were investigated. Cases with dilation exhibited lower peak systolic WSS, higher flow displacement, and higher mean oscillatory shear index compared to controls without dilation. No significant differences in biomarkers were observed between the groups. Correlations between hemodynamics and biomarkers were observed, particularly between maximum time-averaged WSS and interleukin-6 (r = 0.539, p < 0.001), and maximum oscillatory shear index and collagen type I α1 chain (r = -0.575, p < 0.001 in cases). Significant associations were discovered between 4D flow CMR derived whole-cardiac cycle WSS and circulating biomarkers representing inflammation and collagen synthesis, suggesting an intricate interplay between hemodynamics and the processes of inflammation and collagen synthesis in patients with early aortic dilation and tricuspid aortic valves.

Assessing the influence of aneurysm dimensions on hemodynamic patterns and wall deformation dynamics for predicting rupture risk

Cerebral aneurysms are among the most dangerous cardiovascular diseases which display no symptoms prior to reaching critical conditions. As cerebral aneurysms are deadly diseases with a very small treatment window after reaching the critical stage, numerical investigations of this phenomenon are commonly used to assess the risk of rupture. In this study, the fluid-structure interaction (FSI) method is used to analyze the effects of aneurysm size on hemodynamic factors predicting rupture in three aneurysms of different geometries, at the same location, and using the same boundary conditions. In the present study, the aneurysms experience TAWSS at values under 2 Pa in incremented areas as the aneurysmal sizes increase, this is while the relatively larger distribution of high TAWSS (as high as 20 Pa) regions are perceived in smaller aneurysms. Furthermore, the maximum OSI stands at below 0.05 in the smaller cases while the larger case experiences a maximum OSI as high as 0.2, which is considered a predictive parameter for rupture. The vortex core lines experience discontinuities with increased aneurysmal size, which is in agreement with the development of flow complexities with size. The hemodynamics factors such as the time-averaged wall shear stress (TAWSS), oscillatory shear index (OSI), and vortex core line investigated in this study, suggest that greater size can be considered a major risk factor for rupture. In addition to that, we have found that the displacement trend of the aneurysm changes as size increases; developing more in the dome rather than the aneurysmal sac. This change in trend might also present a potential to be used as a predictive parameter.

Deformed Popliteal Artery Due to Highly Flexed Knee Position Can Cause Kinks, Creating an Unfavorable Hemodynamic State.

Endovascular treatment devices of the femoropopliteal artery have evolved, improving clinical results. However, the effects of dynamic changes in the popliteal artery during knee flexion have not been sufficiently investigated. In this study we performed a 3-dimensional analysis to clarify the dynamic changes in the popliteal artery during knee flexion and their effects on hemodynamics.Methods and Results: To analyze dynamic changes in the popliteal artery in the knee flexion position, a computed tomography protocol was developed in the right-angled and maximum flexion knee positions. Thirty patients with lower extremity artery disease were recruited. V-Modeler software was used for anatomical and hemodynamic analyses. Various types of deformations of the popliteal artery were revealed, including hinge points and accessory flexions. Kinks can occur in the maximum flexion position; however, they rarely occur in the right-angled flexion position. In addition, hemodynamic analysis revealed a tendency for lower minimum wall shear stress and a higher maximum oscillatory shear index at the maximum curvature of the popliteal artery. Kinks in the maximum flexion position suggested that the outcome of endovascular treatment may change in areas such as Japan, where knee flexion is customary. Hemodynamics at the maximum curvature of the popliteal artery indicated that the luminal condition was unfavorable for endovascular treatment.

Assessing the impact of aneurysm morphology on the risk of internal carotid artery aneurysm rupture: A statistical and computational analysis of endovascular coiling

Computational modeling and investigation have become increasingly useful in assessing the hemodynamic and structural factors that contribute to aneurysm rupture, particularly when conventional clinical tools are inadequate. To this end, we conduct a study of a realistic internal carotid artery (ICA) under various working conditions using computational fluid dynamics. We analyze nine specific real ICA geometries in terms of coiling porosity and blood hematocrit, using a response surface model to evaluate 25 runs across selected geometrical parameters and treatment factors. The computational domain is created using computed tomography data from an actual patient, and we apply proposed boundary conditions to solve three-dimensional transient Navier–Stokes equations. By analyzing these cases, we try to understand how the sac section area, mean radius of the parent vessel, hematocrit, and coiling porosity interact and affect the risk of ICA rupture. We conduct an extensive study of the effects of sac section area and mean radius of the parent vessel on blood hemodynamics, examining several factors and comparing them at the peak systolic time instant, including wall shear stress (WSS), oscillatory shear index (OSI), pressure distributions, and velocity. Our results show that a 12% increase in the mean radius of the parent vessel reduced the maximum OSI value by approximately 50%, while a 120% increase in the sac section area decreases WSS on the aneurysm wall by up to 300%. These findings demonstrate the potential of computational modeling to provide valuable insight into the complex factors that influence aneurysm rupture, especially in cases where traditional clinical tools may be insufficient.

Ascending aortic volume: A feasible indicator for ascending aortic aneurysm elective surgery?

Diameter-based criterion have been widely adopted for preventive surgery of ascending thoracic aortic aneurysm (ATAA). However, recent and growing evidence has shown that diameter-based methods may not be sufficient for identifying patients who are at risk of an ATAA. In this study, fluid-structure interaction (FSI) analysis was performed on one-hundred ATAA geometries reconstructed from clinical data to examine the relationship between hemodynamic conditions, ascending aortic volume (AAV), ascending aortic curvature, and aortic ratios measured from the reconstructed 3D models. The simulated hemodynamic and biomechanical parameters were compared among different groups of ATAA geometries classified based on AAV. The ATAAs with enlarged AAV showed significantly compromised hemodynamic conditions and higher mechanical wall stress. The maximum oscillatory shear index (OSI), particle residence time (PRT) and wall stress (WS) were significantly higher in enlarged ATAAs compared with controls (0.498 [0.497, 0.499] vs 0.499 [0.498, 0.499], p = 0.002, 312.847 [207.445, 519.391] vs 996.047 [640.644, 1573.140], p < 0.001, 769.680 [668.745, 879.795] vs 1072.000 [873.060, 1280.000] kPa, p < 0.001, respectively). Values were reported as median with interquartile range (IQR). AAV was also found to be more strongly correlated with these parameters compared to maximum diameter. The correlation coefficient between AAV and average WS was as high as 0.92 (p < 0.004), suggesting that AAV might be a feasible risk identifier for ATAAs. Statement of SignificanceAscending thoracic aortic aneurysm is associated with the risk of dissection or rupture, creating life-threatening conditions. Current surgical intervention guidelines are mostly diameter based. Recently, many studies proposed to incorporate other morphological parameters into the current clinical guidelines to better prevent severe adverse aortic events like rupture or dissection. The purpose of this study is to gain a better understanding of the relationship between morphological parameters and hemodynamic parameters in ascending aortic aneurysms using fluid-solid-interaction analysis on patient-specific geometries. Our results suggest that ascending aortic volume may be a better indicator for surgical intervention as it shows a stronger association with pathogenic hemodynamic conditions.

Distribution and regional variation of wall shear stress in the curved middle cerebral artery using four-dimensional flow magnetic resonance imaging.

To investigate the distribution and regional variation of wall shear stress (WSS) in the curved middle cerebral artery (MCA) in healthy individuals using four-dimensional (4D) flow magnetic resonance imaging (MRI). A total of 44 healthy participants (18 males; mean ages: 27.16±5.69 years) were included in this cross-sectional study. The WSS parameters of mean, minimum, and maximum values, the coefficient of variation of time-averaged WSS (TAWSSCV), and the maximum values of the oscillatory shear index (OSI) were calculated and compared in the curved proximal (M1) segments. Three cross-sectional planes were selected: the location perpendicular to the beginning of the long axis of the curved M1 segment of the MCA (proximal section), the most curved M1 location (curved M1 section), and the location before the insular (M2) segment bifurcation (distal section). The WSS and OSI parameters of the proximal, curved, and distal sections of the curved M1 segment were compared, including the inner and outer curvatures of the curved M1 section. Of the curved M1 segments, the curved M1 section had significantly lower minimum TAWSS values than the proximal (P=0.031) and distal sections (P=0.002), and the curved M1 section had significantly higher maximum OSI values than the distal section (P=0.001). The TAWSSCV values at the curved M1 section were significantly higher than the proximal (P=0.001) and distal sections (P<0.001). At the curved M1 section, the inner curvature showed a significantly lower minimum TAWSS (P=0.013) and higher maximum OSI values (P=0.002) than the outer curvature. There are distribution variation of WSS and OSI parameters at the curved M1 section of the curved MCA, and the inner curvature of the curved M1 section has the lowest WSS and highest OSI distribution. The local hemodynamic features of the curved MCA may be related to the predilection for atherosclerotic plaque development.

Computational analysis of the blood hemodynamic inside internal cerebral aneurysm in the existence of endovascular coiling

The precise evaluations of intracranial aneurysms (IAs) are highly prominent for the treatment and control of aneurysm rupture. Computational fluid dynamic (CFD) simulations based on angiography image is a reliable tool for the recognition of high-risk region and aneurysm status in recent years. In our study, the CFD is used to investigate the impacts of blood hematocrit and coiling techniques on the risk of aneurysm rupture. To do this, wall shear stress (WSS), oscillatory shear index (OSI) and pressure distribution on the wall of an aneurysm are comprehensively evaluated in various coding porosities and blood viscosities. One-way Fluid Solid Interaction (FSI) technique is applied to investigate the non-Newtonian, pulsatile blood stream inside the sac of the aneurysm. Impacts of two coiling porosities and blood hematocrits of 0.3 and 0.5 on blood features inside the sac are also analyzed. The influence of the blood mass flow rate in four different time instants of blood cycles on the size of the high-risk region on the aneurysm wall is demonstrated. Our results show that more than 40% reduction is noticed when the hematocrit (HCT) of blood is reduced from 0.5 to 0.3 in different time instants. Our findings also reveal that decreasing the porosity from 0.96 to 0.74 in the peak systolic stage results in a 28% reduction in the maximum OSI at specific HCT = 0.4.

Risk factors for the rupture of mirror middle cerebral artery aneurysm using computer-assisted semiautomated measurement and hemodynamic analysis

ObjectivesTo identify the morphologic and hemodynamic risk factor of mirror middle cerebral artery (MCA) aneurysms. MethodsWe conducted a retrospective analysis of 40 paired mirror MCA aneurysms. Aneurysms were divided into ruptured and unruptured groups. Seventeen morphological and nine hemodynamic parameters were measured using computer-assisted semiautomated measurement (CASAM) and computer flow dynamic (CFD) simulation. We performed a paired t-test (for normally distributed data) or a paired Wilcoxon rank-sum (for non-normally distributed data) to analyze all parameters between the groups. Multivariate conditional logistic regression analysis identified independent risk factors. The receiver operating characteristic curve was analyzed to acquire the area under the curve (AUC) and the cutoff values of the independent risk factors. ResultsThere were significant differences in morphological and hemodynamic parameters between the ruptured and unruptured mirror aneurysms. The multivariate logistic analysis showed that the greater size (odds ratio [OR] = 9.807, p = 0.003), smaller neck diameter (OR = 0.285, p = 0.018) and maximum oscillatory shear index (OSI) (OR = 0.000001, p = 0.046) were independently correlated with aneurysm rupture. AUCs for size, N. and maximum OSI were 0.794, 0.695, and 0.701, respectively. The cutoff values of the size, neck diameter, and maximum OSI were 6.30, 5.07, and 0.356437, respectively. ConclusionsMorphology and hemodynamics can help predict aneurysm rupture risks. The more significant size, smaller neck diameter and maximum OSI were independent risk factors for the rupture of MCA aneurysms. The variables could aid practical risk evaluation.

Should the Proximal Part of a Bifurcated Aortic Graft be Kept as Short as Possible? A Computational Study Elucidates on Aortic Graft Hemodynamics for Various Main Body Lengths

It is accepted that surgically placed bifurcated aortic grafts should be shaped as a short proximal main tube with two long distal limbs. We aim to investigate the hemodynamic effect of different main body lengths in bifurcated aortic grafts using 3D computer models. Five different idealized models are generated to represent an aorto-bifemoral graft. Distance from renal to femoral arteries is set at 25cm and distance between the femoral arteries is set at 14cm. Values of the main body length taken into account to build the idealized models are 3cm, 6cm, 9cm, 12cm and 15cm. Blood flow resistance, Time Average Wall Shear Stress (TAWSS), Oscillatory Shear Index (OSI) and Relative Residence Time (RRT) are estimated using the constructed 3D models. The total resistance decreased monotonically by as far as 40% as the main body length increased. Appropriate hemodynamic simulations show a maximum TAWSS decrease and a corresponding maximum OSI and RRT increase with elongated main body configurations, indicating a hemodynamic benefit of the "Short" main body configuration. Nevertheless, the differences in these later variables are small, affecting a limited portion of the geometries. A long main body of a bifurcated aortic graft results in significantly reduced total resistance in idealized models designed to represent an aorto-bifemoral surgical graft, while the differences observed in TAWSS, OSI and RRT between models are small.

The Association Between Time-Varying Wall Shear Stress and the Development of Plaque Ulcerations in Carotid Arteries From the Plaque at Risk Study.

Background and Purpose: Shear stress (WSS) is involved in the pathophysiology of atherosclerotic disease and might affect plaque ulceration. In this case-control study, we compared carotid plaques that developed a new ulcer during follow-up and plaques that remained silent for their exposure to time-dependent oscillatory shear stress parameters at baseline.Materials and Methods: Eighteen patients who underwent CTA and MRI of their carotid arteries at baseline and 2 years follow-up were included. These 18 patients consisted of six patients who demonstrated a new ulcer and 12 control patients selected from a larger cohort with similar MRI-based plaque characteristics as the ulcer group. (Oscillatory) WSS parameters [time average WSS, oscillatory shear index (OSI), and relative residence time (RRT)] were calculated using computational fluid dynamics applying the MRI-based geometry of the carotid arteries and compared among plaques (wall thickness>2 mm) with and without ulceration (Mann–Whitney U test) and ulcer-site vs. non-ulcer-site within the plaque (Wilcoxon signed rank test). More detailed analysis on ulcer cases was performed and the predictive value of oscillatory WSS parameters was calculated using linear and logistic mixed-effect regression models.Results: The ulcer group demonstrated no difference in maximum WSS [9.9 (6.6–18.5) vs. 13.6 (9.7–17.7) Pa, p = 0.349], a lower maximum OSI [0.04 (0.01–0.10) vs. 0.12 (0.06–0.20) p = 0.019] and lower maximum RRT [1.25 (0.78–2.03) Pa−1 vs. 2.93 (2.03–5.28) Pa−1, p = 0.011] compared to controls. The location of the ulcer (ulcer-site) within the plaque was not always at the maximal WSS, but demonstrated higher average WSS, lower average RRT and OSI at the ulcer-site compared to the non-ulcer-sites. High WSS (WSS>4.3 Pa) and low RRT (RRT < 0.25 Pa) were associated with ulceration with an odds ratio of 3.6 [CI 2.1–6.3] and 2.6 [CI 1.54–4.44] respectively, which remained significant after adjustment for wall thickness.Conclusion: In this explorative study, ulcers were not exclusively located at plaque regions exposed to the highest WSS, OSI, or RRT, but high WSS and low RRT regions had a significantly higher odds to present ulceration within the plaque even after adjustment for wall thickness.

Study on the association of wall shear stress and vessel structural stress with atherosclerosis: An experimental animal study

Background and aimsArtery is subject to wall shear stress (WSS) and vessel structural stress (VSS) simultaneously. This study is designed to explore the role of VSS in development of atherosclerosis. MethodsSilastic collars were deployed on the carotid to create two constrictions on 13 rabbits for a distinct mechanical environment at the constriction. MRI was performed to visualize arteries’ configuration. Animals with high fat (n = 9; Model-group) and normal diet (n = 4; Control-group) were sacrificed after 16 weeks. 3D fluid-structure interaction analysis was performed to quantify WSS and VSS simultaneously. ResultsTwenty plaques were found in Model-group and 3 in Control-group. In Model-group, 8 plaques located proximally to the first constriction (Region-1, close to the heart) and 7 distally to the second (Region-2, close to the head) and 5 plaques were found on the contralateral side of 3 rabbits. Plaques at Region-1 tended to be bigger than those at Region-2 and the macrophage density at these locations was comparable. Minimum time-averaged WSS (TAWSS) in Region-1 was significantly higher than that in Region-2, and both maximum oscillatory shear index (OSI) and particle relative residence time (RRT) were significantly lower. Peak and mean VSS in Region-1 were significantly higher than those in Region-2. Correlation analyses indicated that low TAWSS, high OSI and RRT were only associated with plaque in Region-2, while lesions in Region-1 were only associated with high VSS. Moreover, only VSS was associated with wall thickness of plaque-free regions in both regions. ConclusionsVSS might contribute to the initialization and development of atherosclerosis solely or in combination with WSS.

Effects of waveform shape of pulsatile blood flow on hemodynamics in an artery bifurcation model

Pulsatile non-Newtonian fluid flow was simulated in an artery bifurcation model, with three different inlet flow waveform shapes and an identical inlet mean velocity steady-state condition, to quantify the impact of three different waveform shapes on hemodynamics such as flow patterns, wall shear stress, and oscillatory shear index during a cardiac cycle. It was found that the degree of flow separation is insensitive to changes in flow waveform shape. There is remarkable similarity in the position and magnitude of the maximum wall shear stress at peak systole and the maximum time-averaged wall shear stress for all examined cases. The oscillatory shear index distributions are broadly similar except that the local maximum oscillatory shear index increases proportionally with the pulsatility index of the waveform shape. The maximum oscillatory shear index values on the planar branch are within 8.7% in all examined cases, while these oscillatory shear index values on the nonplanar branch are identical due to the effects of its curvature. The negligible hemodynamic differences between simplified and characteristic waveform cases suggest that changes in waveform shape play a minimal role in the progression and development of atherosclerosis. Although the computed hemodynamics is almost consistent for the three different waveform shapes, several slight differences were observed.

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.

Computational Fluid Dynamics Analysis of Carotid–Ophthalmic Aneurysms with Concomitant Ophthalmic Artery Infundibulum in a Patient-Specific Model

Although previous studies have reported cases of coexistence of carotid-ophthalmic aneurysm and ophthalmic artery (OA) infundibulum, the hemodynamic characteristics of this complicated structure and its damaging effects on vision remain to be elucidated. The aim of the present study was to analyze this artery structure using computational fluid dynamics (CFD) techniques. We have presented the case of a patient with a diagnosis of carotid-ophthalmic aneurysm, who had been experiencing blurred vision. A transient analysis was performed to investigate the blood flowing in the parent artery. Hemodynamic parameters such as streamline, wall shear stress (WSS), oscillatory shear index (OSI), and relative residence time were obtained. When the inlet velocity of the parent artery was at the second peak, the flow rate and intensity of the vortex reached their maximum. In the aneurysm neck, a region of high time-averaged WSS (TAWSS) and a region of low TAWSS with a high OSI coexisted. In addition, a relaxation area was found. In the aneurysm dome, the minimum TAWSS was 2.5 Pa, the maximum OSI was 0.48, and the 2 regions did not overlap. In the OA infundibulum, the maximum OSI and relative residence time were 0.47 and 39.2, respectively; the minimum TAWSS was 0.59 Pa. We detected aneurysm regions that were susceptible to further expansion and assessed the rupture risk of each region. The relaxation area could promote aneurysm progression. In addition, the location of the vortex shear force center varied with time. Finally, double vortex streamlines influenced the blood supply through the OA, impairing the vision. Infundibulum might promote thrombus formation and, hence, retard OA blood flow.

Development and internal validation of an aneurysm rupture probability model based on patient characteristics and aneurysm location, morphology, and hemodynamics

Unruptured cerebral aneurysms pose a dilemma for physicians who need to weigh the risk of a devastating subarachnoid hemorrhage against the risk of surgery or endovascular treatment and their complications when deciding on a treatment strategy. A prediction model could potentially support such treatment decisions. The aim of this study was to develop and internally validate a model for aneurysm rupture based on hemodynamic and geometric parameters, aneurysm location, and patient gender and age. Cross-sectional data from 1061 patients were used for image-based computational fluid dynamics and shape characterization of 1631 aneurysms for training an aneurysm rupture probability model using logistic group Lasso regression. The model's discrimination and calibration were internally validated based on the area under the curve (AUC) of the receiver operating characteristic and calibration plots. The final model retained 11 hemodynamic and 12 morphological variables, aneurysm location, as well as patient age and gender. An adverse hemodynamic environment characterized by a higher maximum oscillatory shear index, higher kinetic energy and smaller low shear area as well as a more complex aneurysm shape, male gender and younger age were associated with an increased rupture risk. The corresponding AUC of the model was 0.86 (95% CI [0.85, 0.86], after correction for optimism 0.84). The model combining variables from various domains was able to discriminate between ruptured and unruptured aneurysms with an AUC of 86%. Internal validation indicated potential for the application of this model in clinical practice after evaluation with longitudinal data.

An approach to quantitative assessment of hemodynamic differences between unruptured and ruptured ophthalmic artery aneurysms

Background and purpose: Hemodynamic parameters are important in the pathogenesis, evolution and rupture of intracranial aneurysm. Energy loss (EL) has been applied for the rupture risk prediction of artery aneurysms recently. We proposed a new EL and further investigate its effects on the rupture of aneurysms. Materials and methods: Sixty-four patient-specific ophthalmic aneurysm datasets were divided into ruptured and unruptured groups based on their clinical history. Based on patient-specific 3D-DSA data, realistic models were retrospectively reconstructed and then analyzed by using computational fluid dynamic method. Results: The flow field feature EL in ruptured cases was significantly higher than that in unruptured cases. The average wall shear stress (WSS) and the maximum WSS in ruptured cases were higher than those in unruptured cases. Modified pressure loss coefficient (PLCM) in ruptured cases was slight higher than that in unruptured cases but the difference has no statistical significance. Multivariate logistic regression analysis demonstrated flow field feature EL (p < 0.05) and the maximum WSS (p < 0.05) were the only independently significant variables to predict rupture of ophthalmic aneurysm. There were no differences in PLCM, the maximum oscillatory shear index (OSI), the average OSI and AR between the two groups. Conclusion: Flow field feature EL may be a reliable factor to predict the rupture risk of aneurysms.

The hemodynamic alterations induced by the vascular angular deformation in stent-assisted coiling of bifurcation aneurysms

The hemodynamic changes induced by stent deployment and vascular remodeling in bifurcation aneurysms were investigated using computational fluid dynamics. The stent deployment reduced the intra-aneurysmal flow activity by decreasing the mean velocity, mean kinetic energy, mean wall shear stress, and mean vorticity. These hemodynamic parameters increased with an increase in the branching angle because of the vessel deformation caused by stent straightening. The maximum wall shear stress and its spatial gradient occurred near the neck of the aneurysm in the stented left daughter vessel, whereas a maximum oscillatory shear index was detected near the neck of the right aneurysm of the right daughter vessel. Theses parameters, which might be related to the recurrence of aneurysms, were also increased by stent-induced vessel deformation.

Impact of competitive flow on wall shear stress in coronary surgery: computational fluid dynamics of a LIMA–LAD model

Competitive flow from native coronary vessels is considered a major factor in the failure of coronary bypass grafts. However, the pathophysiological effects are not fully understood. Low and oscillatory wall shear stress (WSS) is known to induce endothelial dysfunction and vascular disease, like atherosclerosis and intimal hyperplasia. The aim was to investigate the impact of competitive flow on WSS in mammary artery bypass grafts. Using computational fluid dynamics, WSS was calculated in a left internal mammary artery (LIMA) graft to the left anterior descending artery in a three-dimensional in vivo porcine coronary artery bypass graft model. The following conditions were investigated: high competitive flow (non-significant coronary lesion), partial competitive flow (significant coronary lesion), and no competitive flow (totally occluded coronary vessel). Time-averaged WSS of LIMA at high, partial, and no competitive flow were 0.3-0.6, 0.6-3.0, and 0.9-3.0 Pa, respectively. Further, oscillatory WSS quantified as the oscillatory shear index (OSI) ranged from (maximum OSI = 0.5 equals zero net WSS) 0.15 to 0.35, <0.05, and <0.05, respectively. Thus, high competitive flow resulted in substantial oscillatory and low WSS. Moderate competitive flow resulted in WSS and OSI similar to the no competitive flow condition. Graft flow is highly dependent on the degree of competitive flow. High competitive flow was found to produce unfavourable WSS consistent with endothelial dysfunction and subsequent graft narrowing and failure. Partial competitive flow, however, may be better tolerated as it was found to be similar to the ideal condition of no competitive flow.

Computational analysis of effects of external carotid artery flow and occlusion on adverse carotid bifurcation hemodynamics.

This is a computational analysis of the effects of external carotid artery (ECA) flow, waveform, and occlusion geometry on two hemodynamic wall parameters associated with intimal hyperplasia and atherosclerosis. Study design Transient three-dimensional fluid mechanics analysis was applied to a standard carotid artery bifurcation. Mean internal carotid artery (ICA) flow was maintained at 236 mL/min with a normal waveform. ECA flow was increased from zero to 151 mL/min (64% of ICA flow) with both a normal biphasic waveform and a damped waveform. Geometry of five ECA occlusions was studied: distal, proximal stump, smooth, smooth without carotid sinus, and optimal reconstruction.Primary outcome measures Two time-averaged and area-averaged hemodynamic wall parameters were computed from the velocity and wall shear stress (WSS) solutions, ie, wall shear stress angle gradient (WSSAG) and oscillatory shear index (OSI). Both local and area-averaged hemodynamic wall parameters were computed for the distal common carotid artery (CCA) and the proximal ICA. When ECA flow with a normal waveform is increased from zero to 151 mL/min, area-averaged WSS values increase in the CCA, from 3.0 to 4.4 dynes/cm(2) (46%), and in the ICA, from 16.5 to 17.1 dynes/cm(2) (4%); minimum local WSS values in the carotid sinus remain less than 1 dyne/cm(2); maximum local values of WSSAG and OSI are observed in the carotid sinus and increase from 3.5 to 9.1 radian/cm (160%) and 0.23 to 0.46 (100%), respectively; CCA plus ICA area-averaged WSSAG increases by 52%, and OSI increases by 144%; and damping of the ECA waveform has little effect on local or area-averaged WSSAG but reduces OSI to 68%. When the ECA is occluded, the minimum local WSS in the carotid sinus is less than 1 dyne/cm(2). However, if the carotid sinus is removed or the CCA-ICA geometry hemodynamically optimized, the minimum WSS is approximately 4 dynes/cm(2). Similarly, eliminating the carotid sinus markedly reduces local maximum WSSAG, from 3.0-3.5 radian/cm to 0.3 radian/cm, and reduces local maximum OSI from 0.22-0.49 to 0.04. Area-averaged WSSAG and OSI over the CCA and ICA are reduced by approximately 50% with elimination of the carotid sinus. The degree of adverse carotid bifurcation hemodynamics as measured with WSSAG and OSI is directly proportional to ECA flow. The marked difference in normal ICA and ECA flow waveforms does not contribute to adverse wall hemodynamics. Location of an ECA occlusion (distal, proximal, stump, smooth) does not affect adverse carotid hemodynamics; however, marked improvement is obtained with elimination of the carotid sinus.