The Experts below are selected from a list of 46818 Experts worldwide ranked by ideXlab platform
Tomoaki Suzuki - One of the best experts on this subject based on the ideXlab platform.
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decreased wall shear stress at high pressure areas predicts the rupture point in ruptured intracranial aneurysms
Journal of Neurosurgery, 2020Co-Authors: Tomoaki Suzuki, Christopher J Stapleton, Matthew J Koch, Kazutoshi Tanaka, Soichiro Fujimura, Takashi Suzuki, Takeshi YanagisawaAbstract: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.
Won Young Kim - One of the best experts on this subject based on the ideXlab platform.
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optimal Hemodynamic Parameter to predict the neurological outcome in out of hospital cardiac arrest survivors treated with target temperature management
Therapeutic hypothermia and temperature management, 2020Co-Authors: Younjung Kim, Sang Hun Lee, Seung Mok Ryoo, Won Young KimAbstract:Current guidelines suggest the maintenance of systolic blood pressure (SBP) at >90 mmHg and mean arterial pressure (MAP) at >65 mmHg in postcardiac arrest patients. There remains a lack of clarity ...
Yi Qian - One of the best experts on this subject based on the ideXlab platform.
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identification of a Hemodynamic Parameter for assessing treatment outcome of edas in moyamoya disease
Journal of Biomechanics, 2015Co-Authors: Kaavya Karunanithi, Cong Han, Chang Joon Lee, Wanchao Shi, Lian Duan, Yi QianAbstract:This work is a novel attempt to incorporate computational fluid dynamics (CFD) techniques in the analysis of Hemodynamic Parameters of Moyamoya disease (MMD). Highly prevalent in Asian countries, MMD is characterised by progressive occlusion of the intracranial Internal Carotid Arteries (ICA). We intend to identify a reliable Hemodynamic Parameter that can be used to gauge treatment outcome. This will aid surgeons in the perioperative management of MMD patients. We carried out CFD analysis on eight patients (5 female, 3 male) with MMD treated by EDAS (encephalo-duro-arterio-synangiosis) between 2011 and 2012. All the eight patients presented with haemorrhage, with subsequent 4–12 month follow-up done using Magnetic Resonance Angiography (MRA) to capture auto-remodelling. We calculated percentage change in flow rate and pressure drop indicator (ΡDI) across the Left and Right ICA. Pressure drop indicator (PDI) is defined as the difference of pressure reduction within the carotid arteries, measured at post-op and follow up, using patient specific inflow rates. The measured percentage flow change and pressure reduction showed an increase at follow up for improved patients (characterised by angiography according to the method of Matsushima), who did not develop any complications after surgery. The inverse was observed in patients who were clinically classified as no change and retrogressed (according to the method of Matsushima) cases post-operation. This elucidates that our findings have instituted a new Parameter that may well play a critical role as an assistive clinical decision making tool in MMD.
Clement Kleinstreuer - One of the best experts on this subject based on the ideXlab platform.
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Effect of carotid artery geometry on the magnitude and distribution of wall shear stress gradients
Journal of vascular surgery, 1996Co-Authors: Don R. Wells, Joseph P. Archie, Clement KleinstreuerAbstract:Purpose: Recent informatioin indicates that large, sustained wall shear stress gradients are a dominant Hemodynamic Parameter associated with the location and severity of atherosclerosis and myointimal hyperplasia. This study computes the spatial values of wall shear stresses and their gradients for three carotid artery bifurcation geometries. Methods: A computational fluid dynamics program was used to solve the transient two-dimensional partial differential equations that describe fluid flow. Blood was treated as both a Newtonian and a non-Newtonian incompressible fluid. Solutions for the velocities, wall shear stresses, and wall shear-stress gradients were obtained for three carotid bifurcation geometries: a normal carotid bifurcation (similar to a primarily carotid bifurcation geometries: a normal carotid bifurcation (similar to a primarily reconstructed carotid endarterectomy), a patch-reconstructed carotid endarterectomy, and a gradually tapered, low-angle carotid bifurcation (no carotid bulb). Results: Computed velocity profiles closely match published experimental ones. Disturbed flow velocities are largest in the bulb segment of the normal carotid bifurcation. Peak and minimum wall shear stresses and peak shear stress gradients occurred in the lateral internal carotid artery wall. These were binodal in the normal or primarily reconstructed carotid artery, localized at the distal end of the patch-reconstructed carotid bifurcation, and minimal in the smooth, tapered carotid bifurcation. Wall shear stresses and their gradients were slightly higher for non-Newtonian than Newtonian fluids in the normal carotid artery but were similar in the other two geometric configurations. Conclusion: These results indicate that flow disturbances in general and wall shear stress gradients in particular are markedly reduced in carotid artery bifurcations that are smooth and gradually tapered and do not have a bulb. Abrupt geometric wall changes such as those occurring in the normal carotid blub and at the distal end of a patch-reconstruction after carotid endarterectomy are harbingers of disturbed flow and high wall shear stress gradients. These results suggest that carotid endarterectomy reconstruction geometry characterized by a gradually tapered internal carotid artery may minimize the Hemodynamically induced component of early myointimal hyperplasia and thrombosis and late atherosclerotic restenosis
Bernhard Maisch - One of the best experts on this subject based on the ideXlab platform.
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1075 Assessment and relevance of ventricular wall stress in dilated cardiomyopathy
Journal of Cardiovascular Magnetic Resonance, 2008Co-Authors: Peter Alter, Heinz Rupp, Klaus J. Klose, Marga B. Rominger, Bernhard MaischAbstract:enddiastolic and endsystolic volume (r = 0.73, P < 0.001; r = 0.70, P < 0.001), patients with DCM exhibited increased LV wall stress. Both enddiastolic and endsystolic LV wall stress were correlated with the enddiastolic LV volume (r = 0.54, P < 0.001; r = 0.81, P < 0.001). LV enddiastolic wall stress was correlated with pulmonary pressure (capillary: r = 0.69, P < 0.001; artery: r = 0.67, P 8 kPa: 587 ± 648 pg/ml, P 12 kPa: 715 ± 661 pg/ml, P < 0.001; normal = 4 kPa: 124 ± 203 pg/ml). Analysis of variance revealed LV enddiastolic wall stress as the only independent Hemodynamic Parameter influencing BNP (P < 0.01). When compared with the CMR based wall stress analysis, the echocardiography based method underestimated LV wall stress systematically.
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B-type natriuretic peptide and wall stress in dilated human heart.
Molecular and Cellular Biochemistry, 2008Co-Authors: Peter Alter, Heinz Rupp, Klaus J. Klose, Marga B. Rominger, A Vollrath, F Czerny, J H Figiel, P Adams, F Stoll, Bernhard MaischAbstract:Background Although B-type natriuretic peptide (BNP) is used as complimentary diagnostic tool in patients with unknown thoracic disorders, many other factors appear to trigger its release. In particular, it remains unresolved to what extent cellular stretch or wall stress of the whole heart contributes to enhanced serum BNP concentration. Wall stress cannot be determined directly, but has to be calculated from wall volume, cavity volume and intraventricular pressure of the heart. The hypothesis was, therefore, addressed that wall stress as determined by cardiac magnetic resonance imaging (CMR) is the major determinant of serum BNP in patients with a varying degree of left ventricular dilatation or dysfunction (LVD). Methods A thick-walled sphere model based on volumetric analysis of the LV using CMR was compared with an echocardiography-based approach to calculate LV wall stress in 39 patients with LVD and 21 controls. Serum BNP was used as in vivo marker of a putatively raised wall stress. Nomograms of isostress lines were established to assess the extent of load reduction that is necessary to restore normal wall stress and related biochemical events. Results Both enddiastolic and endsystolic LV wall stress were correlated with the enddiastolic LV volume (r = 0.54, P < 0.001; r = 0.81, P < 0.001). LV enddiastolic wall stress was related to pulmonary pressure (capillary: r = 0.69, P < 0.001; artery: r = 0.67, P < 0.001). Although LV growth was correlated with the enddiastolic and endsystolic volume (r = 0.73, P < 0.001; r = 0.70, P < 0.001), patients with LVD exhibited increased LV wall stress indicating an inadequately enhanced LV growth. Both enddiastolic (P < 0.05) and endsystolic (P < 0.01) wall stress were increased in patients with increased BNP. In turn, BNP concentration was elevated in individuals with increased enddiastolic wall stress (>8 kPa: 587 +/- 648 pg/ml, P < 0.05; >12 kPa: 715 +/- 661 pg/ml, P < 0.001; normal < or =4 kPa: 124 +/- 203 pg/ml). Analysis of variance revealed LV enddiastolic wall stress as the only independent Hemodynamic Parameter influencing BNP (P < 0.01). Using nomograms with "isostress" curves, the extent of load reduction required for restoring normal LV wall stress was assessed. Compared with the CMR-based volumetric analysis for wall stress calculation, the echocardiography based approach underestimated LV wall stress particularly of dilated hearts. Conclusions In patients with LVD, serum BNP was increased over the whole range of stress values which were the only Hemodynamic predictors. Cellular stretch appears to be a major trigger for BNP release. Biochemical mechanisms need to be explored which appear to operate over this wide range of wall stress values. It is concluded that the diagnostic use of BNP should primarily be directed to assess ventricular wall stress rather than the extent of functional ventricular impairment in LVD.