Diastolic Wall Shear Stress Research Articles

Analysis of diastolic left ventricular wall shear stress in normal people of different age groups.

BackgroundDiastolic wall shear stress (WSS), assessed by using vector flow mapping (VFM), is the result of the interaction between the blood flow and the ventricular wall. This study aimed to evaluate the trend of left ventricular (LV) WSS in normal subjects.Methods and resultsA total of 371 healthy volunteers were recruited and divided into four age groups (group I: 18–30 years; group II: 31–43 years; group III: 44–56 years; group IV: 57–70 years). LV WSS of different age groups was measured at each diastolic phase (P1: isovolumic diastolic period, P2: rapid filling period, P3: slow filling period, and P4:atrial contraction period) to evaluate the change trend of LV WSS. In each age group, LV WSS coincided with a trend of increasing-decreasing-increasing during P1–P4 (P < 0.05). Besides, among groups I, II, III, and IV, WSS of anterolateral, inferoseptal, and anteroseptal in P1 and WSS of inferolateral, inferoseptal, and anteroseptal in P4 all showed an increasing trend with age (P < 0.05). Regarding sex differences, women had greater diastolic WSS compared to men (P < 0.05).ConclusionLV WSS showed a regular variation and had specific age- and sex-related patterns in different diastolic phases.

Cerebral aneurysm rupture status classification using statistical and machine learning methods.

Morphological characterization and fluid dynamics simulations were carried out to classify the rupture status of 71 (36 unruptured, 35 ruptured) patient specific cerebral aneurysms using a machine learning approach together with statistical techniques. Eleven morphological and six hemodynamic parameters were evaluated individually and collectively for significance as rupture status predictors. The performance of each parameter was inspected using hypothesis testing, accuracy, confusion matrix, and the area under the receiver operating characteristic curve. Overall, the size ratio exhibited the best performance, followed by the diastolic wall shear stress, and systolic wall shear stress. The prediction capability of all 17 parameters together was evaluated using eight different machine learning algorithms. The logistic regression achieved the highest accuracy (0.75), whereas the random forest had the highest area under curve value among all the classifiers (0.82), surpassing the performance exhibited by the size ratio. Hence, we propose the random forest model as a tool that can help improve the rupture status prediction of cerebral aneurysms.

Characterization of left ventricular cavity flow, wall stress and energy loss by color doppler vector flow mapping in children and adolescents with cardiomyopathy.

Vector flow mapping is an emerging echocardiographic method allowing for investigation of intracardiac blood flow mechanics, wall shear stress (WSS), and energy loss (EL). We hypothesized that alterations in EL and WSS will differ among subjects with hypertrophic (HCM), dilated (DCM) cardiomyopathy, and normal controls. Echocardiograms were prospectively performed with the ProSound F75CV (Hitachi HealthCare., Tokyo, Japan) on all subjects. 2D color Doppler cine loop images were obtained from apical 5 and the apical long axis views and stored digitally. Measurements were averaged over three cardiac cycles using VFM software to derive flow patterns, WSS, and EL. Standard left ventricular (LV) systolic and diastolic functional parameters were also obtained. A total of 85 subjects, 22 with HCM (age 18±9 yrs.), 18 DCM (age 18±9 yrs.), and 45 age and gender matched controls were included in the study. Diastolic wall shear stress was found significantly different in HCM (0.004±0.185N/m2) compared with DCM (0.397±0.301N/m2, P<0.001), and controls (0.175±0.255N/m2, P=0.027). Furthermore, indexed systolic EL was found to be significantly elevated in HCM (13.91±13.17mW/m2/m3) compared with DCM (8.17±9.77mW/m2/m3, P<0.001), but not controls (6.45±7.47mW/m2/m3). Differences in abnormal ventricular mechanics observed in HCM and DCM are reflected in both EL and WSS, and are suggestive that changes in energetic parameters may represent novel indices of ventricular dysfunction.

A novel in vivo assessment of fluid dynamics on aortic valve leaflet using epi-aortic echocardiogram.

Mechanical stress caused by blood flow, such as wall shear stress (WSS) and its related parameters, is key moderator of endothelial degeneration. However, an in vivo method to measure WSS on heart valves has not been developed. We developed a novel approach, based on vector flow mapping using intraoperative epi-aortic echocardiogram, to measure WSS and oscillatory shear index (OSI) on the aortic valve. We prospectively enrolled 15 patients with normal valves, who underwent coronary artery bypass graft. Systolic WSS on the ventricularis (2.40±0.44Pa [1.45-3.00Pa]) was higher than systolic WSS on the fibrosa (0.33±0.08Pa [0.14-0.47Pa], P<.001) and diastolic WSS on the ventricularis (0.18±0.07Pa [0.04-0.28Pa], P<.001). Oscillatory shear index on the fibrosa was higher than on the ventricularis (0.29±0.04 [0.24-0.36] vs 0.05±0.03 [0.01-0.12], P<.001). A pilot study involving two patients with severe aortic regurgitation showed significantly different values in fluid dynamics. Vector flow mapping method using intraoperative epi-aortic echocardiogram is an effective way of measuring WSS and OSI on normal aortic leaflet in vivo, allowing for better understanding of the pathophysiology of aortic valve diseases.

Elevated diastolic wall shear stress in regurgitant semilunar valvular lesions.

Alterations in wall shear stress (WSS) assessed using 4D flow MRI have been shown to play a role in various vascular pathologies, such as bicuspid aortic valve aortopathy. Most studies have focused on systolic WSS, whereas altered diastolic hemodynamics in regurgitant semilunar valvular lesions have not so far been well characterized. To investigate diastolic WSS in aortic and pulmonary regurgitation. Retrospective data analysis. Thirty tetralogy of Fallot patients, 19 bicuspid aortic valve patients, 11 healthy volunteers. 5 T, 3D time-resolved phase-contrast MRI with 3D velocity encoding. Estimation of WSS and its axial and circumferential vector components along cardiac cycle timeframes in the proximal main pulmonary artery in pulmonary regurgitation (PR) and in the proximal ascending aorta in aortic regurgitation (AR) as well as in healthy volunteers. Wilcoxon matched pairs test was used for intra-group comparisons and Mann-Whitney test for intergroup comparisons. Correlations were assessed using Spearman correlation. WSS along the entire cardiac cycle was higher in PR and AR in comparison with controls (mean WSS 0.381 ± 0.070 vs. 0.220 ± 0.018, P < 0.0001; 0.361 ± 0.099 vs. 0.212 ± 0.030, P < 0.0001; respectively). Peak diastolic WSS was significantly higher than the mean WSS in AR and PR (P < 0.0001-0.005). The severity of PR correlated with the peak diastolic axial WSS (Spearman's r s = 0.454, P = 0.018), whereas the severity of AR correlated with both peak systolic and diastolic tangential WSS (Spearman's r s = 0.458, P = 0.049; r s = 0.539, P = 0.017, respectively). Elevated diastolic WSS is a component of the altered flow hemodynamics in AR and PR. This may give more insight into the pathophysiologic role of WSS in vascular remodeling in AR and PR. 4 Technical Efficacy Stage: 1 J. Magn. Reson. Imaging 2019;50:763-770.

Evidence for non-Newtonian behavior of intracranial blood flow from Doppler ultrasonography measurements.

Computational fluid dynamics (CFD) studies of intracranial hemodynamics often use Newtonian viscosity model to close the shear rate term in the Navier-Stokes equation. This is based on a commonly accepted hypothesis which state that non-Newtonian effects can be neglected in intracranial blood flow. This study aims to examine the validity of such hypothesis to guide future CFD studies of intracranial hemodynamics. Doppler ultrasonography (DUS) measurements of systolic and diastolic vessel diameter and blood velocity were conducted on 16 subjects (mean age 50.6). The measurements were conducted on the internal carotid (ICA), middle cerebral (MCA), and anterior communicating (AComA) arteries. Systolic and diastolic wall shear stress (WSS) values were calculated via the Hagen-Poiseuille exact solution using Newtonian and three different non-Newtonian models: namely Carreau, power-law and Herschel-Bulkley models. The Weissenberg-Rabinowitsch correction for blood shear-thinning viscosity was applied to the non-Newtonian models. The error percentage between the two sets of models was calculated and discussed. The Newtonian hypothesis was tested statistically and discussed using paired t tests. Significant differences (P < 0.0001) were found between the Newtonian and non-Newtonian WSS in ICA. In MCA and AComA, similar differences were found except in the systole and diastole for the Herschel-Bulkley and power-law models (P = 0.0669, P = 0.7298), respectively. The error between the Newtonian and non-Newtonian models ranged from -27 to 30% (0.2 to 2.2Pa). These values could affect the physical interpretation of IA CFD studies. Evidence suggests that the Newtonian assumption may be inappropriate to investigate intracranial hemodynamics. Graphical abstract The WSS estimation error resulting from using the Newtonian assumption compared to three non-Newtonian models for ICA, MCA, and AComA in systole and diastole conditions, based on TCCD measurements of 16 subjects. The error due to the Newtonian assumption ranged from 0.2 to 2.2Pa (- 27 to 30%). These values could affect the physical interpretation of IA CFD studies.

Determining Significant Morphological and Hemodynamic Parameters to Assess the Rupture Risk of Cerebral Aneurysms

Hemodynamics and morphology are recognized as major factors in the rupture risk of cerebral aneurysms, and exploration of their relationship is necessary to establish a method that can be employed by clinicians to assess the likelihood of rupture. In this work, morphological analysis and computational fluid dynamics were carried out to examine a database of 58 lateral cerebral aneurysms (26 ruptured and 32 unruptured) distributed among 49 patients. Eight morphological and six hemodynamic parameters were calculated and evaluated for statistical significance. It was observed that size ratio (SR), systolic wall shear stress (SWSS), diastolic wall shear stress (DWSS) and relative residence time (RRT) were statistically significant. The SR, DWSS, SWSS, and RRT were employed in multivariate logistic regression, obtaining a combined morphological–hemodynamic model, a pure morphological model, and a pure hemodynamic model to evaluate the odds ratio for rupture risk. The combined model had the highest efficiency, but no distinctive difference existed in the predictive capacity of the three models.

Low WSS and High OSI Measured by 3D Cine PC MRI Reflect High Pulmonary Artery Pressures in Suspected Secondary Pulmonary Arterial Hypertension.

Purpose:Institutional Review Board (IRB)-approved prospective study was conducted to test whether objective and quantitative hemodynamic markers wall shear stress (WSS) and oscillatory shear index (OSI) measured by three-dimensional (3D) cine phase-contrast (PC) can reflect pulmonary arterial hypertension (PAH).Patients and Methods:Seventeen consecutive patients of suspected secondary PAH were examined for pulmonary artery pressures (PAPs) with right heart catheterization (RHC) and three-dimensional (3D) cine PC MR. Based on the RHC data, patients were subdivided into two groups of 12 non-PAH (median age of 74.5 years) and 5 PAH (median age of 77 years) patients. Based on 3D cine PC magnetic resonance (MR), hemodynamic parameters including spatially averaged systolic WSS (sWSS), diastolic WSS (dWSS), mean WSS (mWSS), OSI and blood vessel section area (BVSA) at the pulmonary arterial trunk were calculated. Streamline images in the pulmonary arteries were also assessed. All the parameters were compared between non-PAH and PAH groups.Results:sWSS (N/m2) and mWSS (N/m2) of PAH group was lower than that of non-PAH group (0.594 ± 0.067 vs. 0.961 ± 0.590, P = 0.001), (0.365 ± 0.035 vs. 0.489 ± 0.132, P = 0.027). OSI of PAH group was higher than that of non-PAH (0.214 ± 0.026 vs. 0.130 ± 0.046, P = 0.001). sWSS, mWSS, and dWSS were inversely correlated and OSI was positively correlated to mean PAP or systolic PAP with r values of –0.638 (P = 0.005), –0.643 (P = 0.005), –0.485 (P = 0.049), and 0.625 (P = 0.007); or –0.622 (P = 0.008), –0.629 (P = 0.007), –0.484 (P = 0.049), and 0.594 (P = 0.012), respectively. sWSS was also inversely correlated to BVSA with r value of –0.488 (P = 0.049), and OSI was correlated to BVSA with r value of 0.574 (P = 0.016). Vortex or helical flows were observed more frequently in PAH patients.Conclusions:The low sWSS and mWSS as well as high OSI measured with 3D cine PC MR could be potential hemodynamic markers for the increased PAP in suspected secondary PAH patients.

Diastolic Carotid Artery Wall Shear Stress Is Associated With Cerebral Infarcts and Periventricular White Matter Lesions

Low wall shear stress (WSS) is an early marker in the development of vascular lesions. The present study aims to assess the relationship between diastolic and systolic WSS in the internal carotid artery and periventricular (PWML), deep white matter lesions, and cerebral infarcts (CI). Early, mid, and late diastolic and peak systolic WSS were derived from shear rate obtained by gradient echo phase contrast magnetic resonance sequences multiplied by individually modeled viscosity. PWML, deep white matter lesions, and CI were derived from proton density (PD), T2, and fluid attenuated inversion recovery (FLAIR) MRI in 329 participants (70-82 years; PROSPER baseline). Analyses were adjusted, if appropriate, for age, gender, intracranial volume, and multiple cardiovascular risk factors. Mid-diastolic WSS was significantly correlated with the presence of PWML (B=-10.15; P=0.006) and CI (B=-2.06; P=0.044), but not with deep white matter lesions (B=-1.30; P=0.050; adjusted for age, gender, WML, and intracranial volume). After adjustment for cardiovascular risk factors, these correlations weakened but remained significant. Systolic WSS was not correlated with any of the cerebrovascular parameters. This study is the first to our knowledge to present a cross-sectional correlation between carotid artery WSS and cerebrovascular pathology such as PWML and CI in a large population. Furthermore, it shows that diastolic hemodynamics may be more important than systolic or mean hemodynamics. Future studies exploring vascular hemodynamic damage should focus on diastolic WSS.

In vivo three‐dimensional MR wall shear stress estimation in ascending aortic dilatation

To estimate surface-based wall shear stress (WSS) and evaluate flow patterns in ascending aortic dilatation (AscAD) using a high-resolution, time-resolved, three-dimensional (3D), three-directional velocity encoded, radially undersampled phase contrast MR sequence (4D PC-MRI). 4D PC-MRI was performed in 11 patients with AscAD (46.3 ± 22.0 years) and 10 healthy volunteers (32.9 ± 13.4 years) after written informed consent and institutional review board approval. Following manual vessel wall segmentation of the ascending aorta (MATLAB, The Mathworks, Natick, MA), a 3D surface was created using spline interpolation. Spatial WSS variation based on surface division in 12 segments and temporal variation were evaluated in AscAD and normal aortas. Visual analysis of flow patterns was performed based on streamlines and particle traces using EnSight (v9.0, CEI, Apex, NC). AscAD was associated with significantly increased diastolic WSS, decreased systolic to diastolic WSS ratio, and delayed onset of peak WSS (all P < 0.001). Temporally averaged WSS was increased and peak systolic WSS was decreased. The maximum WSS in AscAD was on the anterior wall of the ascending aorta. Vortical flow with highest velocities along the anterior wall and increased helical flow during diastole were observed in AscAD compared with controls. Changes in WSS in the ascending aorta of AscAD correspond to observed alterations in flow patterns compared to controls.

Carotid and Basilar Artery Wall Shear Stress in Alzheimer’s Disease and Mild Cognitive Impairment

Background/Aims: Vascular pathology is increasingly seen as a factor contributing to the development of Alzheimer’s disease (AD). With this in mind we hypothesized that this vascular pathology could be directly detected in the arteries contributing to the cerebral circulation of mild cognitive impairment (MCI) and AD patients by means of wall shear stress (WSS) measurements. Methods: In this study we investigated the mean wall shear stress (MWSS), diastolic wall shear stress (DWSS) and systolic wall shear stress (SWSS) in the carotid and basilar arteries of control subjects (mean age: 72; SD: 8.8), patients suffering from MCI (mean age: 76; SD: 6.7), and patients suffering from AD (mean age: 72; SD: 8.2) that were consecutively referred to our outpatient memory clinic using in-house developed software on gradient echo phase-contrast MRI sequences. Results: We found that all these parameters were significantly lower in the carotid arteries of patients suffering from AD or MCI when compared to control subjects. In the basilar artery only DWSS was lower in MCI or AD patients compared to control subjects. In none of the arteries a difference was found for any WSS parameter between MCI and AD patients. WSS parameters were significantly associated (corrected for age and sex) with the degree of cognitive impairment. Conclusion: Increased vascular pathology, as expressed by lower WSS measures, was found in patients suffering from MCI and AD compared to normal controls. This might point to the involvement of vascular pathology in the development of AD.

Diastolic Wall Shear Stress in the Internal Carotid Artery Is Associated with Different Cardiovascular Risk Factors than Systolic Wall Shear Stress

Background and Purpose: Wall shear stress (WSS) is the frictional force exerted by the circulating blood on the endothelium. Low systolic WSS is identified as an atherosclerotic risk factor. Recently, also the importance of diastolic WSS has been described. Still, it is unknown whether diastolic WSS carries similar cardiovascular risk factors compared to systolic WSS. Methods: Of 379 subjects (70–82 years, 56% male) diastolic and systolic WSS in the internal carotid arteries was determined. Results: After adjustment for age and gender, diastolic blood pressure was associated with systolic WSS (p = 0.02). Body mass index was associated with diastolic WSS (p = 0.04). Smoking was associated with diastolic WSS (p = 0.05). Myocardial infarction was associated with both systolic WSS (p = 0.04) and diastolic WSS (p < 0.01). No associations between cholesterol, HDL, LDL, triglycerides, history of diabetes, hypertension, angina pectoris, claudication, stroke, or any vascular disease were found with systolic or diastolic WSS. Conclusions: Our data indicates different cardiovascular risk factors for diastolic WSS compared to systolic WSS.

Measurement of systolic and diastolic arterial wall shear stress in the ascending aorta

Purpose Wall shear stress (WSS) appears to contribute significantly in the initiation and progression of atherosclerotic disease. The purpose of this work is to present in vivo systolic and diastolic WSS calculations in the human ascending aorta by the application of three straightforward methodologies based on Poiseuille's theory of flow. Materials and methods Blood flow measurements were performed retrospectively in the ascending aorta of 20 non-atherosclerotic patients using phase-contrast MRI. WSS calculations were performed assuming Poiseuille's theory of flow based on average flow volume, average flow velocity and maximum flow velocity. Systolic and diastolic WSS values were calculated and compared with the calculated maximum and minimum values of WSS throughout the cardiac cycle. Results Systolic WSS values calculated by average flow volume, average flow velocity and maximum flow velocity were similar (0.4 ± 0.2 N/m 2, 0.4 ± 0.3 N/m 2and 0.4 ± 0.2 N/m 2, respectively). Diastolic WSS values calculated by maximum flow velocity were significantly higher (11.6 ± 7.0 × 10 −2 N/m 2) compared to values calculated by average flow volume (0.3 ± 0.9 × 10 −2 N/m 2) and average flow velocity (0.3 ± 1.0 × 10 −2 N/m 2). Comparison of systolic and diastolic WSS values with maximum and minimum WSS values showed that time instances of maximum and minimum blood flow velocities do not coincide with time instances of maximum and minimum blood flow volume. Conclusion In vivo calculation of WSS in the ascending aorta is feasible by phase-contrast MRI flow measurements and straightforward methodologies based on Poiseuille's theory of flow. However, measurements based on maximum flow velocity show larger deviations compared to measurements based on mean flow volume or mean flow velocity.

Unsteady wall shear stress in a distensible tube

An asymptotic expression of the wall shear stress (WSS) in an elastic tube is deduced for small values of the Womersley parameter. In the case of a rigid tube this asymptotic expression is shown to compare better with the exact solution than Poiseuille's or Lambossy's approximations. Its integration in a one-dimensional model of the internal carotid artery blood flow predicts more marked systolic and less marked diastolic WSS than those predicted by the commonly used Poiseuille's approximation.