The Experts below are selected from a list of 164052 Experts worldwide ranked by ideXlab platform
Roberto J. Groszmann - One of the best experts on this subject based on the ideXlab platform.
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tumor necrosis factor α a major contributor to the hyperdynamic circulation in prehepatic portal hypertensive rats
Gastroenterology, 1995Co-Authors: Juan Carlos Lopeztalavera, William W Merrill, Roberto J. GroszmannAbstract:Abstract Background/Aims: Portal hypertension is often accompanied by a hyperdynamic circulatory syndrome. Tumor necrosis factor (TNF) α causes vasodilatation and a hyperdynamic state in mammals by activating nitric oxide synthesis. The aim of this study was to investigate whether TNF-α plays a role in developing the hyperdynamic syndrome in portal hypertension. Methods: Portal-hypertensive rats, induced by partial ligation of the portal vein (PVL), were used. In experiment 1, rats that underwent PVL were treated with polyclonal anti-mouse TNF-α or placebo intravenously the same day of the PVL operation and 24 hours before Hemodynamic studies. Hemodynamic studies were performed 5 days after PVL. In experiment 2, rats that underwent PVL received anti-TNF-α or placebo intravenously 3 days and 24 hours before Hemodynamics as in experiment 1. Hemodynamics were performed 14 days after the PVL operation. TNF-α blood levels were measured using a bioassay. Results: Anti-TNF-α treatment induced a significant increase in mean arterial pressure, heart rate, and systemic vascular resistance and a significant decrease in cardiac index, portal pressure, and TNF-α levels in comparison with placebo animals. No significant effects were observed in sham rats. Conclusions:Anti-TNF-α treatment in rats that underwent PVL significantly blunts the development of the hyperdynamic circulation and reduces portal pressure. TNF-α may play a role in the Hemodynamic abnormalities of portal hypertension.
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liver pancreas and biliary tract tumor necrosis factor a major contributor to the hyperdynamic circulation in prehepatic portal hypertensive rats
1995Co-Authors: Juan Carlos Lopeztalavera, William W Merrill, Roberto J. GroszmannAbstract:Background/Aims: Portal hypertension is often accompanied by a hyperdynamic circulatory syndrome. Tumor necrosis factor (TNF) (~ causes vasodilatation and a hyperdynamic state in mammals by activating nitric oxide synthesis. The aim of this study was to investigate whether TNF-~ plays a role in developing the hyperdynamic syndrome in portal hypertension. Methods: Portal-hypertensive rats, induced by partial ligation of the portal vein (PVL), were used. In experiment 1, rats that underwent PVL were treated with polyclonal anti-mouse TNF-~ or placebo intravenously the same day of the PVL operation and 24 hours before Hemodynamic studies. Hemodynamic studies were performed 5 days after PVL. In experiment 2, rats that underwent PVL received anti-TNF-¢ or placebo intravenously 3 days and 24 hours before Hemodynamics as in experiment 1. Hemodynamics were performed 14 days after the PVL operation. TNF-~ blood levels were measured using a bioassay. Results: Anti-TNF-~ treatment induced a significant increase in mean arterial pressure, heart rate, and systemic vascular resistance and a significant decrease in cardiac index, portal pressure, and TNF-(~ levels in comparison with placebo animals. No significant effects were observed in sham rats. Conclusions: Anti-TNF-~ treatment in rats that underwent PVL significantly blunts the development of the hyperdynamic circulation and reduces portal pressure. TNFmay play a role in the Hemodynamic abnormalities of portal hypertension,
Mattias Villani - One of the best experts on this subject based on the ideXlab platform.
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physiological gaussian process priors for the Hemodynamics in fmri analysis
Journal of Neuroscience Methods, 2020Co-Authors: Josef Wilzen, Anders Eklund, Mattias VillaniAbstract:Abstract Background Inference from fMRI data faces the challenge that the Hemodynamic system that relates neural activity to the observed BOLD fMRI signal is unknown. New method We propose a new Bayesian model for task fMRI data with the following features: (i) joint estimation of brain activity and the underlying Hemodynamics, (ii) the Hemodynamics is modeled nonparametrically with a Gaussian process (GP) prior guided by physiological information and (iii) the predicted BOLD is not necessarily generated by a linear time-invariant (LTI) system. We place a GP prior directly on the predicted BOLD response, rather than on the Hemodynamic response function as in previous literature. This allows us to incorporate physiological information via the GP prior mean in a flexible way, and simultaneously gives us the nonparametric flexibility of the GP. Results Results on simulated data show that the proposed model is able to discriminate between active and non-active voxels also when the GP prior deviates from the true Hemodynamics. Our model finds time varying dynamics when applied to real fMRI data. Comparison with existing method(s) The proposed model is better at detecting activity in simulated data than standard models, without inflating the false positive rate. When applied to real fMRI data, our GP model in several cases finds brain activity where previously proposed LTI models does not. Conclusions We have proposed a new non-linear model for the Hemodynamics in task fMRI, that is able to detect active voxels, and gives the opportunity to ask new kinds of questions related to Hemodynamics.
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physiological gaussian process priors for the Hemodynamics in fmri analysis
bioRxiv, 2017Co-Authors: Josef Wilzen, Anders Eklund, Mattias VillaniAbstract:Inference from fMRI data faces the challenge that the Hemodynamic system, that relates the underlying neural activity to the observed BOLD fMRI signal, is not known. We propose a new Bayesian model for task fMRI data with the following features: (i) joint estimation of brain activity and the underlying Hemodynamics, (ii) the Hemodynamics is modeled nonparametrically with a Gaussian process (GP) prior guided by physiological information and (iii) the predicted BOLD is not necessarily generated by a linear time-invariant (LTI) system. We place a GP prior directly on the predicted BOLD time series, rather than on the Hemodynamic response function as in previous literature. This allows us to incorporate physiological information via the GP prior mean in a flexible way. The prior mean function may be generated from a standard LTI system, based on a canonical Hemodynamic response function, or a more elaborate physiological model such as the Balloon model. This gives us the nonparametric flexibility of the GP, but allows the posterior to fall back on the physiologically based prior when the data are weak. Results on simulated data show that even with an erroneous prior for the GP, the proposed model is still able to discriminate between active and non-active voxels in a satisfactory way. The proposed model is also applied to real fMRI data, where our Gaussian process model in several cases finds brain activity where a baseline model with fixed Hemodynamics does not.
Jian Liu - One of the best experts on this subject based on the ideXlab platform.
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discrimination of intracranial aneurysm rupture status patient specific inflow boundary may not be a must have condition in Hemodynamic simulations
Neuroradiology, 2020Co-Authors: Shengzhang Wang, Zhongbin Tian, Wei Zhu, Yisen Zhang, Ying Zhang, Yang Wang, Kun Wang, Xinjian Yang, Jian LiuAbstract:Computational fluid dynamics (CFD) are important in evaluating the Hemodynamics of intracranial aneurysm rupture, and the setting of inflow boundary conditions is critical. We evaluated intracranial aneurysm Hemodynamics based on generalized versus patient-specific inflow boundary conditions to examine the effect of different Hemodynamic results on the discrimination of intracranial aneurysm rupture status. We enrolled 148 patients with 156 intracranial aneurysms. For each included aneurysm, we performed CFD simulation once based on patient-specific and once based on generalized inflow boundary conditions. First, we compared the Hemodynamics of intracranial aneurysms based on different inflow boundary conditions. Then, we divided the included aneurysms into a ruptured and unruptured group and compared the Hemodynamics between the two groups under patient-specific and generalized inflow boundary conditions. For the Hemodynamic parameters using specific inflow boundary conditions, more complex flow (p = 0.002), larger minimum WSS (p = 0.024), lower maximum low WSS area (LSA) (p = 0.038), and oscillatory shear index (p = 0.002) were found. Furthermore, we compared the Hemodynamics between ruptured and unruptured groups based on different inflow boundary conditions. We found that the significant Hemodynamic parameters associated with rupture status were the same, including the proportion of aneurysms with flow complex and unstable flow and the minimum and maximum of LSA (p = 0.011, p = 0.003, p = 0.001 and p = 0.004, respectively). Patient-specific and generalized inflow boundary conditions of aneurysmal Hemodynamics resulted in significant differences. However, the significant parameters associated with rupture status were the same in both conditions, indicating that patient-specific inflow boundary conditions may not be necessary for predicting rupture risk.
Shengzhang Wang - One of the best experts on this subject based on the ideXlab platform.
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discrimination of intracranial aneurysm rupture status patient specific inflow boundary may not be a must have condition in Hemodynamic simulations
Neuroradiology, 2020Co-Authors: Shengzhang Wang, Zhongbin Tian, Wei Zhu, Yisen Zhang, Ying Zhang, Yang Wang, Kun Wang, Xinjian Yang, Jian LiuAbstract:Computational fluid dynamics (CFD) are important in evaluating the Hemodynamics of intracranial aneurysm rupture, and the setting of inflow boundary conditions is critical. We evaluated intracranial aneurysm Hemodynamics based on generalized versus patient-specific inflow boundary conditions to examine the effect of different Hemodynamic results on the discrimination of intracranial aneurysm rupture status. We enrolled 148 patients with 156 intracranial aneurysms. For each included aneurysm, we performed CFD simulation once based on patient-specific and once based on generalized inflow boundary conditions. First, we compared the Hemodynamics of intracranial aneurysms based on different inflow boundary conditions. Then, we divided the included aneurysms into a ruptured and unruptured group and compared the Hemodynamics between the two groups under patient-specific and generalized inflow boundary conditions. For the Hemodynamic parameters using specific inflow boundary conditions, more complex flow (p = 0.002), larger minimum WSS (p = 0.024), lower maximum low WSS area (LSA) (p = 0.038), and oscillatory shear index (p = 0.002) were found. Furthermore, we compared the Hemodynamics between ruptured and unruptured groups based on different inflow boundary conditions. We found that the significant Hemodynamic parameters associated with rupture status were the same, including the proportion of aneurysms with flow complex and unstable flow and the minimum and maximum of LSA (p = 0.011, p = 0.003, p = 0.001 and p = 0.004, respectively). Patient-specific and generalized inflow boundary conditions of aneurysmal Hemodynamics resulted in significant differences. However, the significant parameters associated with rupture status were the same in both conditions, indicating that patient-specific inflow boundary conditions may not be necessary for predicting rupture risk.
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high shear stress and flow velocity in partially occluded aneurysms prone to recanalization
Stroke, 2011Co-Authors: Bin Luo, Shengzhang Wang, Yisen Zhang, Ying Zhang, Xinjian Yang, Jialiang Chen, Zhicheng Liu, Guanghong DingAbstract:Background and Purpose—Hemodynamic factors are thought to play an important role in the initiation, growth, and rupture of cerebral aneurysms. However, the Hemodynamic features in the residual neck of the partially embolized aneurysms and their influences on recanalization are rarely reported. In this study, we characterized the Hemodynamics of partially occluded aneurysms, which were proven to undergo recanalization during follow-up using computational fluid dynamic analysis. Methods—From May 2007 to June 2009, we identified 11 partial aneurysms during follow-up, including 5 recanalized cases and 6 stable cases with 3-dimensional digital subtraction angiography. We retrospectively characterized the Hemodynamic features around the residual aneurismal pouch using the available postprocedural digital subtraction angiography image data. The occluded part of the aneurysm was regarded as completely separated from the circulation. Results—The overall blood flow patterns before embolization were almost the same ...
Charles B. L. M. Majoie - One of the best experts on this subject based on the ideXlab platform.
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Generalized versus Patient-Specific Inflow Boundary Conditions in Computational Fluid Dynamics Simulations of Cerebral Aneurysmal Hemodynamics
American Journal of Neuroradiology, 2014Co-Authors: Ilaria Jansen, J.j. Schneiders, Wouter V. Potters, P. Van Ooij, R. Van Den Berg, E. Van Bavel, Henk A. Marquering, Charles B. L. M. MajoieAbstract:BACKGROUND AND PURPOSE: Attempts have been made to associate intracranial aneurysmal Hemodynamics with aneurysm growth and rupture status. Hemodynamics in aneurysms is traditionally determined with computational fluid dynamics by using generalized inflow boundary conditions in a parent artery. Recently, patient-specific inflow boundary conditions are being implemented more frequently. Our purpose was to compare intracranial aneurysm Hemodynamics based on generalized versus patient-specific inflow boundary conditions. MATERIALS AND METHODS: For 36 patients, geometric models of aneurysms were determined by using 3D rotational angiography. 2D phase-contrast MR imaging velocity measurements of the parent artery were performed. Computational fluid dynamics simulations were performed twice: once by using patient-specific phase-contrast MR imaging velocity profiles and once by using generalized Womersley profiles as inflow boundary conditions. Resulting mean and maximum wall shear stress and oscillatory shear index values were analyzed, and Hemodynamic characteristics were qualitatively compared. RESULTS: Quantitative analysis showed statistically significant differences for mean and maximum wall shear stress values between both inflow boundary conditions (P CONCLUSIONS: Using generalized and patient-specific inflow boundary conditions for computational fluid dynamics results in different wall shear stress magnitudes and Hemodynamic characteristics. Generalized inflow boundary conditions result in more vortices and inflow jet instabilities. This study emphasizes the necessity of patient-specific inflow boundary conditions for calculation of Hemodynamics in cerebral aneurysms by using computational fluid dynamics techniques.
