scholarly journals Translesional Pressure Gradient Alters Relationship Between Blood Pressure and Recurrent Stroke in Intracranial Stenosis

Stroke ◽  
2020 ◽  
Vol 51 (6) ◽  
pp. 1862-1864
Author(s):  
Xueyan Feng ◽  
Ka Lung Chan ◽  
Linfang Lan ◽  
Jill Abrigo ◽  
Vincent H.L. Ip ◽  
...  
Keyword(s):  
Fluid Dynamics ◽  
Computed Tomography ◽  
Blood Pressure ◽  
Computational Fluid Dynamics ◽  
Pressure Gradient ◽  
Primary Outcome ◽  
Recurrent Stroke ◽  
Pressure Ratio ◽  
Increased Risk ◽  
Dynamics Models

Background and Purpose— There is debate over an optimal systolic blood pressure (SBP) in secondary stroke prevention of patients with symptomatic intracranial atherosclerotic stenosis (sICAS). We investigated whether translesional pressure gradient across sICAS would alter the relationship between SBP and risk of recurrent stroke in such patients. Methods— We recruited patients with sICAS (50%–99% stenosis) confirmed in computed tomography angiography. We simulated blood flow across sICAS with computed tomography angiography-based computational fluid dynamics models. Translesional pressure ratio (PR=Pressure post-stenotic /Pressure pre-stenotic ) was calculated in each case. Pressure ratio (PR) ≤ median was defined as low PR, indicating larger translesional pressure gradient across sICAS. All patients received optimal medical treatment. We investigated the interaction of translesional PR and mean SBP during follow-up (SBP FU ) in determining the risk of the primary outcome, recurrent ischemic stroke in the same territory within 1 year. Results— Among 157 patients with sICAS, the median PR was 0.93. Multivariate Cox regression revealed significant PR-SBP FU interaction on the primary outcome ( P =0.008): in patients with normal PR, risk of primary outcome significantly decreased with lower SBP FU (hazard ratio for 10 mm Hg decrement =0.46; P =0.018); however, in those with low PR, SBP FU ≤130 mm Hg was associated with significantly increased risk of primary outcome, compared with 130<SBP FU <150 mm Hg (hazard ratio=5.08; P =0.043). Conclusions— Low SBP level may be associated with increased risk of stroke recurrence in patients with sICAS with a large translesional pressure gradient. Translesional PR by computational fluid dynamics models may yield a promising indicator to guide more individualized blood pressure management in patients with sICAS, warranting future studies.

Abstract WP121: An Evaluation of Hemodynamics Across Intracranial Steno-occlusive Lesions by Computational Fluid Dynamics

Stroke ◽  
2016 ◽  
Vol 47 (suppl_1) ◽  
Author(s):  
Florence SY Fan ◽  
Vincent HL Ip ◽  
Alexander YL Lau ◽  
Anne YY Chan ◽  
Lisa WC Au ◽  
...  
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Pressure Gradient ◽  
Pressure Difference ◽  
Pressure Ratio ◽  
Velocity Ratio ◽  
Strongly Correlated ◽  
Hemodynamic Parameters ◽  
Moderate Correlation ◽  
Anterior Circulation

Introduction: Intracranial atherosclerotic steno-occlusive disease (ICAS) is a major cause of stroke worldwide and portends a high risk of recurrence. Computational fluid dynamics (CFD) is a novel technique developed to solve and analyze the dynamic effects of fluid flow. We aimed to analyse hemodynamics across ICAS using CFD on processed CTA images and explore the correlation between the degree of arterial stenosis and hemodynamic flow status. Methods: We recruited patients with symptomatic ICAS from Acute Stroke Unit, Prince of Wales Hospital. All patients received CTA and DSA as vascular workup. Using CFD analysis of processed CTA images, we first defined the hemodynamic parameters, including pressure difference, pressure ratio, pressure gradient, shear strain rate ratio (SSR), wall shear stress (WSS) ratio and velocity ratio, across the stenosed vessels, and then we correlated the severity of stenosis as defined by DSA, with these parameters. Results: Among the 53 recruited patients (mean age 62.9 years, 69.8% males), 45 (85%) had lesions in the anterior circulation. The severity of stenosis showed a weak-to-moderate correlation with pressure difference (rs=0.392, p=0.004), pressure ratio (rs=-0.429, p=0.001) and pressure gradient (rs=0.419, p=0.002). There was no significant correlation between the severity of stenosis with SSR ratio, WSS ratio and velocity ratio. Among patients with anterior circulation stroke or TIA, the severity of stenosis showed a weak to moderate correlation with pressure difference (rs=0.381, p=0.01), pressure ratio (rs=-0.426, p=0.004) and pressure gradient (rs=0.407, p=0.005). For patients with posterior circulation stroke or TIA, the severity of stenosis was strongly correlated with pressure difference (rs=0.714, p=0.047) and pressure ratio (rs=-0.714, p=0.047); and very strongly correlated with velocity ratio (rs=0.833, p=0.01). Conclusions: The severity of ICAS showed only weak-to-moderate correlation with hemodynamic parameters across the culprit lesion. Thus, risk stratification and treatment based solely on stenotic severity may be inadequate. Our findings may guide further research in estimating stroke risks and selection of high-risk patients who may benefit from adjunctive treatments.

scholarly journals Agreement between rhinomanometry and computed tomography-based computational fluid dynamics

2021 ◽  
Author(s):  
Manuel Berger ◽  
Aris I. Giotakis ◽  
Martin Pillei ◽  
Andreas Mehrle ◽  
Michael Kraxner ◽  
...  
Keyword(s):  
Fluid Dynamics ◽  
Computed Tomography ◽  
Computational Fluid Dynamics ◽  
Lattice Boltzmann ◽  
Univariate Analysis ◽  
Error Rates ◽  
Bland Altman Method ◽  
Nasal Side ◽  
Computational Fluid Dynamics Cfd ◽  
Side Error

Abstract Purpose Active anterior rhinomanometry (AAR) and computed tomography (CT) are standardized methods for the evaluation of nasal obstruction. Recent attempts to correlate AAR with CT-based computational fluid dynamics (CFD) have been controversial. We aimed to investigate this correlation and agreement based on an in-house developed procedure. Methods In a pilot study, we retrospectively examined five subjects scheduled for septoplasty, along with preoperative digital volume tomography and AAR. The simulation was performed with Sailfish CFD, a lattice Boltzmann code. We examined the correlation and agreement of pressure derived from AAR (RhinoPress) and simulation (SimPress) and these of resistance during inspiration by 150 Pa pressure drop derived from AAR (RhinoRes150) and simulation (SimRes150). For investigation of correlation between pressures and between resistances, a univariate analysis of variance and a Pearson’s correlation were performed, respectively. For investigation of agreement, the Bland–Altman method was used. Results The correlation coefficient between RhinoPress and SimPress was r = 0.93 (p < 0.001). RhinoPress was similar to SimPress in the less obstructed nasal side and two times greater than SimPress in the more obstructed nasal side. A moderate correlation was found between RhinoRes150 and SimRes150 (r = 0.65; p = 0.041). Conclusion The simulation of rhinomanometry pressure by CT-based CFD seems more feasible with the lattice Boltzmann code in the less obstructed nasal side. In the more obstructed nasal side, error rates of up to 100% were encountered. Our results imply that the pressure and resistance derived from CT-based CFD and AAR were similar, yet not same.

The Application of Non-Axisymmetric Endwall Contouring in a Single Stage, Rotating Turbine

2009 ◽  
Author(s):  
Glen Snedden ◽  
Dwain Dunn ◽  
Grant Ingram ◽  
David Gregory-Smith
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Pressure Gradient ◽  
Full Scale ◽  
Secondary Flows ◽  
Tip Clearance ◽  
Detailed Understanding ◽  
Low Speed ◽  
Endwall Contouring ◽  
Probe Measurements

As turbine manufacturers strive to develop machines that are more efficient, one area of focus has been the control of secondary flows. To a large extent these methods have been developed through the use of computational fluid dynamics and detailed measurements in linear and annular cascades and proven in full scale engine tests. This study utilises 5-hole probe measurements in a low speed, model turbine in conjunction with computational fluid dynamics to gain a more detailed understanding of the influence of a generic endwall design on the structure of secondary flows within the rotor. This work is aimed at understanding the influence of such endwalls on the structure of secondary flows in the presence of inlet skew, unsteadiness and rotational forces. Results indicate a 0.4% improvement in rotor efficiency as a result of the application of the generic non-axisymmetric endwall contouring. CFD results indicate a clear weakening of the cross passage pressure gradient, but there are also indications that custom endwalls could further improve the gains. Evidence of the influence of endwall contouring on tip clearance flows is also presented.

scholarly journals Sex differences in the association of abdominal adipose tissue measurements by using quantitative computed tomography (QCT) with untreated hypertension in a Chinese population

2020 ◽  
Author(s):  
Youzhou Chen ◽  
Zhuoli Zhang ◽  
Jihong Wang ◽  
Huayi Sun ◽  
Xingshan Zhao ◽  
...  
Keyword(s):  
Computed Tomography ◽  
Blood Pressure ◽  
Adipose Tissue ◽  
Chinese Population ◽  
Quantitative Computed Tomography ◽  
Hip Circumference ◽  
Hypertension Status ◽  
Increased Risk ◽  
Visceral Adipose ◽  
Subcutaneous Adipose

Abstract Background: There are inconsistent results regarding the relationships of adiposity anthropometric indices and blood pressure (BP) and hypertension, and whether these relationships differ by sex is unclear. We aimed to elucidate the associations of adiposity indices measured using quantitative computed tomography (QCT) with BP and hypertension and to determine the effect of sex on the relationships in a Chinese population. Methods: Abdominal adipose fat, including visceral adipose tissue (VAT) area and subcutaneous adipose tissue (SAT) area, was measured by QCT in 1488 participants. Body mass index (BMI), waist circumference (WC), hip circumference (HC) and systolic (SBP) and diastolic BP (DBP) were measured. Results: Compared to women, men had significantly greater VAT but less SAT regardless of hypertension status. VAT, SAT and WC correlated more with SBP in men than in women. After controlling for body weight, height and age, VAT area and WC in women and VAT area in men were positively associated with SBP and DBP level. VAT area correlated more with the increased risk of hypertension in men than in women [men: odds ratio (OR) = 1.013, women: OR = 1.011]. WC had a significant correlation with an increased risk of hypertension in women but a borderline association in men (P = 0.059) when adjusted for VAT area and SAT area. Conclusions: The association of abdominal adiposity with blood pressure components and hypertension differs qualitatively by sex. WC may be an important determinant of hypertension and may be used for risk stratification for hypertension among Chinese individuals.

scholarly journals A Rapid and Computationally Inexpensive Method to Virtually Implant Current and Next-Generation Stents into Subject-Specific Computational Fluid Dynamics Models

2011 ◽  
Vol 39 (5) ◽  
pp. 1423-1437 ◽  
Author(s):  
Timothy J. Gundert ◽  
Shawn C. Shadden ◽  
Andrew R. Williams ◽  
Bon-Kwon Koo ◽  
Jeffrey A. Feinstein ◽  
...  
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Next Generation ◽  
Inexpensive Method ◽  
Subject Specific ◽  
Dynamics Models

Effect of Cavities in Suddenly Expanded Flow at Supersonic Mach Number

CFD letters ◽  
2021 ◽  
Vol 13 (9) ◽  
pp. 57-71
Author(s):  
Atifatul Ismah Ismail
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Mach Number ◽  
Pressure Ratio ◽  
Area Ratio ◽  
Base Pressure ◽  
Sudden Expansion ◽  
Expansion Level ◽  
Computational Fluid Dynamics Cfd ◽  
Base Drag

The contribution from the base drag due to the sub-atmospheric pressure is significant. It can be more than two-thirds of the net drag. There is a need to increase the base pressure and hence decrease the base drag. This research examines the effect of Mach Number on base pressure. To accomplish this objective, it controls the efficacy in an enlarged duct computed by the numerical approach using Computational Fluid Dynamics (CFD) Analysis. This experiment was carried out by considering the expansion level and the aspect cavity ratio. The computational fluid dynamics method is used to model supersonic motion with the sudden expansion, and a convergent-divergent nozzle is used. The Mach number is 1.74 for the present study, and the area ratio is 2.56. The L/D ratio varied from 2, 4, 6, 8, and 10, and the simulated nozzle pressure ratio ranged from 3 to 11. The two-dimensional planar design used commercial software from ANSYS. The airflow from a Mach 1.74 convergent-divergent axi-symmetric nozzle expanded suddenly into circular ducts of diameters 17 and 24.5 mm with and without annular rectangular cavities. The diameter of the duct is taken D=17mm and D=24.5mm. The C-D nozzle was developed and modeled in the present study: K-ε standard wall function turbulence model was used with the commercial computational fluid dynamics (CFD) and validated. The result indicates that the base pressure is impacted by the expansion level, the enlarged duct size, and the passage’s area ratio.

Abstract 81: Translesional Pressure Gradient Alters the Relationship Between Blood Pressure and Stroke Recurrence in Symptomatic Intracranial Atherosclerotic Disease

Stroke ◽  
2020 ◽  
Vol 51 (Suppl_1) ◽  
Author(s):  
Xueyan Feng ◽  
Ka Lung Chan ◽  
Jill Abrigo ◽  
Linda Lan ◽  
Yannie Soo ◽  
...  
Keyword(s):  
Blood Pressure ◽  
Pressure Gradient ◽  
Stroke Prevention ◽  
Primary Outcome ◽  
Stroke Recurrence ◽  
Secondary Stroke Prevention ◽  
Cfd Models ◽  
Intracranial Atherosclerotic Disease ◽  
The Relationship

Objective: Patients with symptomatic intracranial atherosclerotic stenosis (sICAS) have a high risk of stroke recurrence. There is debate over an optimal blood pressure (BP) lowering target in secondary stroke prevention in such patients, when some factors (e.g., impaired cerebral perfusion) may alter the relationship between BP and risk of stroke recurrence. In this study, we investigated whether translesional pressure gradient across sICAS lesions would also alter such relationship. Methods: We recruited patients with sICAS (50-99% stenosis) confirmed in CT angiography (CTA). Computational fluid dynamics (CFD) models were built based on CTA to simulate blood flow across sICAS and calculate the translesional pressure ratio (PR, the ratio of pressures distal and proximal to a lesion). PR ≤ median was defined as low PR, indicating larger translesional pressure gradient and hence restricted downstream perfusion. The primary outcome was recurrent ischemic stroke in the same territory in 1 year. We investigated the interaction of PR and mean systolic BP (SBP) during follow-up in determining the risk of the primary outcome. Results: Among 157 patients, the median PR was 0.93. Multivariate Cox regression revealed significant PR-SBP interaction on the primary outcome (p=0.025): in patients with normal PR, the risk of primary outcome significantly decreased with lower SBP during follow-up (for 10 mmHg decrement: HR 0.46; p=0.018); however, in those with low PR, mean SBP ≤130 mmHg was associated with significantly increased risk of primary outcome, compared with 130<SBP<150mmHg (HR 5.08; p=0.043) (Figure). Conclusion: Intensive BP lowering may increase the risk of stroke recurrence in sICAS patients with a large translesional pressure gradient, warranting further investigation. PR by CFD models may yield a promising indicator to differentiate sICAS patients for different BP management strategies for better secondary stroke prevention.

Sign in / Sign up

Export Citation Format

Share Document