Quantification of hemodynamic irregularity using oscillatory velocity index in the associations with the rupture status of cerebral aneurysms

BackgroundComplex and unstable flow patterns are reported to be associated with the rupture status of cerebral aneurysms, while their evaluation depends on qualitative analysis of streamlines of bloodflow. Oscillatory velocity index (OVI) is a hemodynamic parameter to quantify flow patterns. The aim of this study is to elucidate the associations between OVI and the rupture status of cerebral aneurysms.MethodsOne hundred and twenty-nine ruptured and unruptured cerebral aneurysms were analyzed with computational fluid dynamics under pulsatile flow conditions. With the use of median value of OVI, all aneurysms were divided into high and low OVI groups. Statistical analysis was performed to compare rupture status, and morphological and hemodynamic parameters between the two groups.ResultsThe median value of OVI was 0.006. High OVI was more likely observed in ruptured aneurysms (P=0.028) and associated with irregular shape, complex flow patterns, and unstable flow patterns (P<0.001, respectively). In morphological parameters, maximum size, aspect, projection, size, and volume-to-ostium area ratios were significantly higher in the high OVI group (P<0.001, respectively). In hemodynamic parameters, wall shear stress and wall shear stress gradient were significantly lower, and oscillatory shear index and gradient oscillatory number were significantly higher in the high OVI group (P<0.001, respectively).ConclusionHigh OVI was associated with rupture status, and morphological and hemodynamic characteristics of ruptured aneurysms. These results indicate that OVI may serve as a valuable hemodynamic parameter for diagnosing rupture status and risks of aneurysms.

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STUDY ON THE RELATIONSHIP BETWEEN WALL SHEAR STRESS AND ASPECT RATIO OF CEREBRAL ANEURYSMS WITH DIFFERENT PRESSURE DIFFERENCES USING CFD SIMULATIONS

Journal of Mechanics in Medicine and Biology ◽

10.1142/s0219519418500550 ◽

2018 ◽

Vol 18 (05) ◽

pp. 1850055

Author(s):

ALFREDO ARANDA ◽

ALVARO VALENCIA

Keyword(s):

Shear Stress ◽

Aspect Ratio ◽

Wall Shear Stress ◽

Cerebral Aneurysms ◽

Cfd Simulations ◽

Unruptured Aneurysms ◽

Ruptured Aneurysms ◽

Sphericity Index ◽

Wall Shear ◽

The Relationship

CFD simulations were performed for 60 human cerebral aneurysms (30 previously ruptured and 30 previously unruptured) to study the behavior of the time-averaged wall shear stress (TAWSS) with respect to the aspect ratio (AR), implementing a set of low, normal, and high-pressure differences between the inlet and the outlets of each artery. It is well known that there exists a direct relationship between TAWSS and the rupture. In this investigation, we presented an important result because the condition of the pressure among the branches and the AR may be measured in any patient, then a slope may be associated, and finally a TAWSS may be estimated. We found that when the pressure difference increased, the absolute slopes between TAWSS and AR increased as well. Also, the magnitude of the slope in the previously unruptured aneurysms was 4.7 times the slope in the previously ruptured aneurysms. On the other hand, TAWSS was higher in the previously unruptured aneurysm than previously ruptured aneurysms due to the unruptured aneurysms that have a smaller surface area. Furthermore, we analyzed the relationship between TAWSS and other geometric parameters of the aneurysm, such as bottleneck and non-sphericity index; however, no correlation was found for either cases.

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Analysis of Morphological-Hemodynamic Risk Factors for Aneurysm Rupture Including a Newly Introduced Total Volume Ratio

Journal of Personalized Medicine ◽

10.3390/jpm11080744 ◽

2021 ◽

Vol 11 (8) ◽

pp. 744

Author(s):

Ui Yun Lee ◽

Hyo Sung Kwak

Keyword(s):

Shear Stress ◽

Aspect Ratio ◽

Wall Shear Stress ◽

Volume Ratio ◽

Wall Stress ◽

Aneurysm Rupture ◽

Oscillatory Shear Index ◽

Unstable Flow ◽

Ruptured Aneurysms ◽

Wall Shear

The purpose of this study was to evaluate morphological and hemodynamic factors, including the newly developed total volume ratio (TVR), in evaluating rupture risk of cerebral aneurysms using ≥7 mm sized aneurysms. Twenty-three aneurysms (11 unruptured and 12 ruptured) ≥ 7 mm were analyzed from 3-dimensional rotational cerebral angiography and computational fluid dynamics (CFD). Ten morphological and eleven hemodynamic factors of the aneurysms were qualitatively and quantitatively compared. Correlation analysis between morphological and hemodynamic factors was performed, and the relationship among the hemodynamic factors was analyzed. Morphological factors (ostium diameter, ostium area, aspect ratio, and bottleneck ratio) and hemodynamic factors (TVR, minimal wall shear stress of aneurysms, time-averaged wall shear stress of aneurysms, oscillatory shear index, relative residence time, low wall shear stress area, and ratio of low wall stress area) were statistically different between ruptured and unruptured aneurysms (p < 0.05). By simple regression analysis, the morphological factor aspect ratio and the hemodynamic factor TVR were significantly correlated (r2 = 0.602, p = 0.001). Ruptured aneurysms had complex and unstable flow. In ≥7 mm ruptured aneurysms, high aspect ratio, bottleneck ratio, complex flow, unstable flow, low TVR, wall shear stress at aneurysm, high oscillatory shear index, relative resistance time, low wall shear stress area, and ratio of low wall stress area were significant in determining the risk of aneurysm rupture.

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Decreased wall shear stress at high-pressure areas predicts the rupture point in ruptured intracranial aneurysms

Journal of Neurosurgery ◽

10.3171/2018.12.jns182897 ◽

2020 ◽

Vol 132 (4) ◽

pp. 1116-1122 ◽

Cited By ~ 1

Author(s):

Tomoaki Suzuki ◽

Christopher J. Stapleton ◽

Matthew J. Koch ◽

Kazutoshi Tanaka ◽

Soichiro Fujimura ◽

...

Keyword(s):

Shear Stress ◽

Wall Shear Stress ◽

Dynamic Pressure ◽

Cerebral Aneurysms ◽

Aneurysm Rupture ◽

Maximum Pressure ◽

Parent Artery ◽

Hemodynamic Parameters ◽

Unruptured Aneurysms ◽

Wall Shear

OBJECTIVEDegenerative cerebral aneurysm walls are associated with aneurysm rupture and subarachnoid hemorrhage. Thin-walled regions (TWRs) represent fragile areas that may eventually lead to aneurysm rupture. Previous computational fluid dynamics (CFD) studies reported the correlation of maximum pressure (Pmax) areas and TWRs; however, the correlation with aneurysm rupture has not been established. This study aims to investigate this hemodynamic correlation.METHODSThe aneurysmal wall surface at the Pmax areas was intraoperatively evaluated using a fluid flow formula under pulsatile blood flow conditions in 23 patients with 23 saccular middle cerebral artery (MCA) bifurcation aneurysms (16 unruptured and 7 ruptured). The pressure difference (Pd) at the Pmax areas was calculated by subtracting the average pressure (Pave) from the Pmax and normalized by dividing this by the dynamic pressure at the aneurysm inlet side. The wall shear stress (WSS) was also calculated at the Pmax areas, aneurysm dome, and parent artery. These hemodynamic parameters were used to validate the correlation with TWRs in unruptured MCA aneurysms. The characteristic hemodynamic parameters at the rupture points in ruptured MCA aneurysms were then determined.RESULTSIn 13 of 16 unruptured aneurysms (81.2%), Pmax areas were identified that corresponded to TWRs. In 5 of the 7 ruptured cerebral aneurysms, the Pmax areas coincided with the rupture point. At these areas, the Pd values were not higher than those of the TWRs in unruptured cerebral aneurysms; however, minimum WSS, time-averaged WSS, and normalized WSS at the rupture point were significantly lower than those of the TWRs in unruptured aneurysms (p < 0.01).CONCLUSIONSAt the Pmax area of TWRs, decreased WSS appears to be the crucial hemodynamic parameter that indicates the risk of aneurysm rupture.

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Role of pressure and wall shear stress in initiation and development of cerebral aneurysms

2011 2nd International Conference on Instrumentation, Communications, Information Technology, and Biomedical Engineering ◽

10.1109/icici-bme.2011.6108629 ◽

2011 ◽

Cited By ~ 2

Author(s):

Nedya Utami ◽

Hasballah Zakaria ◽

Tati L. R. Mengko ◽

Oerip S. Santoso

Keyword(s):

Shear Stress ◽

Wall Shear Stress ◽

Cerebral Aneurysms ◽

Wall Shear

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Hemodynamic parameters and vessel tortuosity: an investigation with a mesenterial vascular network

Modeling and Artificial Intelligence in Ophthalmology ◽

10.35119/maio.v1i4.46 ◽

2017 ◽

Vol 1 (4) ◽

pp. 62-68

Author(s):

Roberto Annunziata ◽

Bettina Reglin ◽

Axel Pries ◽

Emanuele Trucco

Keyword(s):

Shear Stress ◽

Wall Shear Stress ◽

Oxygen Saturation ◽

Wall Thickness ◽

Blood Velocity ◽

Vascular Network ◽

Hemodynamic Parameters ◽

Vessel Tortuosity ◽

Wall Shear ◽

Quantitative Definition

Purpose: The effect of hemodynamic parameters on vessel tortuosity remains un-clear. Here we investigate the correlation of tortuosity with a set of hemodynamicparameters in a mesenterial vascular network.Methods: A mesenterial vascular network of 389 vessels (131 arteries, 132 veins, and 126 capillaries) was imaged. Eleven hemodynamic parameters were measured (pressure, wall shear stress, diameter, blood velocity and flow, viscosity, haematocrit, partial oxygen saturation, oxygen saturation, wall thickness, and local vessel density). Tortuosity was assessed quantitatively with a validated algorithm and correlation computed with subsets of hemodynamic parameters selected by a lasso regressor.Results: Results suggest that tortuosity is related to pressure, wall shear stress, diameter, blood velocity, viscosity, partial but not full oxygen saturation, and wall thickness for the arteries; diameter, blood flow, hematocrit, and density for the veins; and viscosity (but not hematocrit), partial and full oxygen saturation, and density for the capillaries. The combination of hemodynamic parameters correlating best with tortuosity is the set of all parameters except density (r = 0.64, p < 0.01), using as tortuosity definition the set of tortuosity features (geometric measures) correlating best with a single hemodynamic factor for the arteries.Conclusion: This pilot suggests two general conclusions. First, the quantitative definition of tortuosity (i.e., the set of geometric features adopted) should be tuned to the specific data and problem considered. Second, tortuosity is caused by a combination of hemodynamic factors, not a single one.

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Flow patterns and wall shear stress in arteries

The Fluid Mechanics of Large Blood Vessels ◽

10.1017/cbo9780511896996.004 ◽

1980 ◽

pp. 126-159 ◽

Cited By ~ 1

Keyword(s):

Shear Stress ◽

Wall Shear Stress ◽

Flow Patterns ◽

Wall Shear

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A Review On the Effect of Temporal Geometric Variations of the Coronary Arteries On the Wall Shear Stress and Pressure Drop

Journal of Biomechanical Engineering ◽

10.1115/1.4051923 ◽

2021 ◽

Author(s):

Navid Freidoonimehr ◽

Rey Chin ◽

Anthony C. Zander ◽

Maziar Arjomandi

Keyword(s):

Shear Stress ◽

Pressure Drop ◽

Wall Shear Stress ◽

Coronary Arteries ◽

Cardiac Cycle ◽

Temporal Variations ◽

Hemodynamic Parameters ◽

Clinical Environment ◽

Cross Sectional ◽

Wall Shear

Abstract Temporal variations of the coronary arteries during a cardiac cycle are defined as the superposition of the changes in the position, curvature, and torsion of the coronary artery axis markers and the variations in the lumen cross-sectional shape due to the distensible wall motion induced by the pulse pressure and contraction of the myocardium in a cardiac cycle. This review discusses whether the modelling the temporal variations of the coronary arteries is needed for the investigation of the hemodynamics specifically in time critical applications such as a clinical environment. The numerical modellings in the literature which model or disregard the temporal variations of the coronary arteries on the hemodynamic parameters are discussed. The results in the literature show that neglecting the effects of temporal geometric variations is expected to result in about 5\% deviation of the time-averaged pressure drop and wall shear stress values and also about 20\% deviation of the temporal variations of hemodynamic parameters, such as time-dependent wall shear stress and oscillatory shear index. This review study can be considered as a guide for the future studies to outline the conditions in which temporal variations of the coronary arteries can be neglected, while providing a reliable estimation of hemodynamic parameters.

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The Effect of Wall Distensibility on Flow in a Two-Dimensional End-to-Side Anastomosis

Journal of Biomechanical Engineering ◽

10.1115/1.2895733 ◽

1994 ◽

Vol 116 (3) ◽

pp. 294-301 ◽

Cited By ~ 55

Author(s):

D. A. Steinman ◽

C. Ross Ethier

Keyword(s):

Shear Stress ◽

Wall Shear Stress ◽

Intimal Hyperplasia ◽

Bypass Graft ◽

Numerical Approach ◽

Flow Patterns ◽

Temporal Variations ◽

Model Studies ◽

Wall Shear ◽

Wall Distensibility

The development of intimal hyperplasia at the distal anastomosis is the major cause of long-term bypass graft failure. To evaluate the suspected role of hemodynamic factors in the pathogenesis of distal intimal hyperplasia, an understanding of anastomotic flow patterns is essential. Due to the complexity of arterial flow, model studies typically make simplifying assumptions, such as treating the artery and graft walls as rigid. In the present study this restriction is relaxed to consider the effects of vessel wall distensibility on anastomotic flow patterns. Flow was simulated in an idealized 2-D distensible end-to-side anastomosis model, using parameters appropriate for the distal circulation and assuming a purely elastic artery wall. A novel numerical approach was developed in which the wall velocities are solved simultaneously with the fluid and pressure fields, while the wall displacements are treated via an iterative update. Both the rigid and distensible cases indicated the presence of elevated temporal variations and low average magnitudes of wall shear stress at sites known to be susceptible to the development of intimal hyperplasia. At these same sites, large spatial gradients of wall shear stress were also noted. Comparison between distensible-walled and corresponding rigid-walled simulations showed moderate changes in wall shear stress at isolated locations, primarily the bed, toe and heel. For example, in the case of a distensible geometry and a physiologic pressure waveform, the heel experienced a 38 percent increase in cycle-averaged shear stress, with a corresponding 15 percent reduction in shear stress variability, both relative to the corresponding values in the rigid-walled case. However, other than at these isolated locations, only minor changes in overall wall shear stress patterns were observed. While the physiological implications of such changes in wall shear stress are not known, it is suspected that the effects of wall distensibility are less pronounced than those brought about by changes in arterial geometry and flow conditions.

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Exploring High Frequency Temporal Fluctuations in the Terminal Aneurysm of the Basilar Bifurcation

Journal of Biomechanical Engineering ◽

10.1115/1.4007279 ◽

2012 ◽

Vol 134 (9) ◽

Cited By ~ 15

Author(s):

Matthew D. Ford ◽

Ugo Piomelli

Keyword(s):

Shear Stress ◽

Wall Shear Stress ◽

High Frequency ◽

Cerebral Aneurysms ◽

Patient Specific ◽

Disturbed Flow ◽

Frequency Fluctuations ◽

Wall Shear ◽

Inflow Jet

Cerebral aneurysms are a common cause of death and disability. Of all the cardiovascular diseases, aneurysms are perhaps the most strongly linked with the local fluid mechanic environment. Aside from early in vivo clinical work that hinted at the possibility of high-frequency intra-aneurysmal velocity oscillations, flow in cerebral aneurysms is most often assumed to be laminar. This work investigates, through the use of numerical simulations, the potential for disturbed flow to exist in the terminal aneurysm of the basilar bifurcation. The nature of the disturbed flow is explored using a series of four idealized basilar tip models, and the results supported by four patient specific terminal basilar tip aneurysms. All four idealized models demonstrated instability in the inflow jet through high frequency fluctuations in the velocity and the pressure at approximately 120 Hz. The instability arises through a breakdown of the inflow jet, which begins to oscillate upon entering the aneurysm. The wall shear stress undergoes similar high-frequency oscillations in both magnitude and direction. The neck and dome regions of the aneurysm present 180 deg changes in the direction of the wall shear stress, due to the formation of small recirculation zones near the shear layer of the jet (at the frequency of the inflow jet oscillation) and the oscillation of the impingement zone on the dome of the aneurysm, respectively. Similar results were observed in the patient-specific models, which showed high frequency fluctuations at approximately 112 Hz in two of the four models and oscillations in the magnitude and direction of the wall shear stress. These results demonstrate that there is potential for disturbed laminar unsteady flow in the terminal aneurysm of the basilar bifurcation. The instabilities appear similar to the first instability mode of a free round jet.

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