scholarly journals Calibration of an Electrical Analog Model of Liver Hemodynamics in Fontan Patients

2020 ◽  
Vol 143 (3) ◽  
Author(s):  
Elyar Abbasi Bavil ◽  
Matthew G. Doyle ◽  
Charlotte Debbaut ◽  
Rachel M. Wald ◽  
Luc Mertens ◽  
...  
Keyword(s):  
Pressure Gradient ◽  
Venous Pressure ◽  
Portal Pressure ◽  
Lumped Parameter Model ◽  
Patient Specific ◽  
Model Parameters ◽  
Liver Health ◽  
Liver Hemodynamics ◽  
Fontan Patients

Abstract Fontan associated liver disease is a common complication in patients with Fontan circulation, who were born with a single functioning heart ventricle. The hepatic venous pressure gradient (HVPG) is used to assess liver health and is a surrogate measure of the pressure gradient across the entire liver (portal pressure gradient (PPG)). However, it is thought to be inaccurate in Fontan patients. The main objectives of this study were (1) to apply an existing detailed lumped parameter model (LPM) of the liver to Fontan patients using patient-specific clinical data and (2) to determine whether HVPG is a suitable measurement of PPGs in these patients. An existing LPM of the liver blood circulation was applied and tuned to simulate patient-specific liver hemodynamics. Geometries were collected from seven adult Fontan patients and used to evaluate model parameters. The model was solved and tuned using waveform measurements of flows, inlet and outlet pressures. The predicted ratio of portal to hepatic venous pressures is comparable to in vivo measurements. The results confirmed that HVPG is not suitable for Fontan patients, as it would underestimate the portal pressures gradient by a factor of 3 to 4. Our patient-specific liver model provides an estimate of the pressure drop across the liver, which differs from the clinically used metric HVPG. This work represents a first step toward models suitable to assess liver health in Fontan patients and improve its long-term management.

A Three Degree of Freedom Lumped Parameter Model of Whole Body Vibration Along the Spine in the Rat

2013 ◽  
Author(s):  
Nicolas V. Jaumard ◽  
Hassam A. Baig ◽  
Benjamin B. Guarino ◽  
Beth A. Winkelstein
Keyword(s):  
Whole Body Vibration ◽  
Degree Of Freedom ◽  
Lumped Parameter Model ◽  
In Vivo Studies ◽  
Whole Body ◽  
Model Parameters ◽  
Body Vibration ◽  
Lumped Parameter ◽  
Three Degree Of Freedom

Whole body vibration (WBV) can induce a host of pathologies, including muscle fatigue and neck and low back pain [1,2]. A new model of WBV in the rat has been developed to define relationships between WBV exposures, kinematics, and behavioral sensitivity (i.e. pain) [3]. Although in vivo studies provide valuable associations between biomechanics and physiology, they are not able to fully define the mechanical loading of specific spinal regions and/or the tissues that may undergo injurious loading or deformation. Mathematical models of seated humans and primates have been used to estimate spinal loads and design measures that mitigate them during WBV [4–6]. Although such models provide estimates of relative spinal motions, they have limited utility for relating potentially pathological effects of vibration-induced kinematics and kinetics since those models do not enable simultaneous evaluation of relevant spinal tissues with the potential for injury and pain generation. As such, the goal of this work was to develop and validate a three degree of freedom (3DOF) lumped-parameter model of the prone rat undergoing WBV directed along the long-axis of the spine. The model was constructed with dimensions of a generalized rat and model parameters optimized using kinematics over a range of frequencies. It was validated by comparing predicted and measured transmissibility and further used to predict spinal extension and compression, as well as acceleration, during WBV for frequencies known to produce resonance in the seated human and pain in the rat [3,7].

scholarly journals Impact of propofol sedation on the diagnostic accuracy of hepatic venous pressure gradient measurements in patients with cirrhosis

2021 ◽  
Author(s):  
Fahim Ebrahimi ◽  
David Semela ◽  
Markus Heim
Keyword(s):  
Portal Hypertension ◽  
Pressure Gradient ◽  
Hepatic Vein ◽  
Venous Pressure ◽  
Portal Pressure ◽  
Intraclass Correlation ◽  
Hepatic Venous Pressure Gradient ◽  
Propofol Sedation ◽  
Gradient Measurements ◽  
Awake Condition

Abstract Background Measurement of the hepatic venous pressure gradient (HVPG) is the gold standard to evaluate the presence and severity of portal hypertension. The procedure is generally safe and well tolerated, but nevertheless, some patients demand for sedation. However, it is unknown whether propofol sedation would impair the accuracy of portal pressure measurements. Methods This is a prospective observational cohort study including cirrhotic patients with suspected portal hypertension undergoing invasive measurement of HVPG. Measurements of HVPG were performed in awake condition as well as under sedation with propofol infusion. Results In total, 37 patients were included. Mean HVPG in awake condition was 15.9 mmHg (IQR 13–19) and during sedation 14.1 mmHg (IQR 12–17). While measures of free hepatic vein pressure (FHVP) were not altered after propofol sedation (p = 0.34), wedged hepatic vein pressure values (WHVP) decreased in an average by  2.05 mmHg (95% CI − 2.46 to − 1.16; p < 0.001) which was proportional to the magnitude of HVPG. In 31 out of 37 patients (83.8%), portal hypertension with HVPG ≥ 12 mmHg was found. Under sedation with propofol, two patients (5.4%) with borderline values would have been incorrectly classified as < 12 mmHg. After adjustment for the average difference of − 10%, all patients were correctly classified. Intraclass correlation coefficient between HVPG measurement in awake condition and under propofol sedation was 0.927 (95% CI 0.594–0.975). Conclusions Propofol sedation during HVPG measurements is generally safe, however it may lead to relevant alterations of HVPG readings.

scholarly journals Single portal pressure measurement predicts survival in cirrhotic patients with recent bleeding

Gut ◽  
1999 ◽  
Vol 44 (2) ◽  
pp. 264-269 ◽  
Author(s):  
D Patch ◽  
A Armonis ◽  
C Sabin ◽  
K Christopoulou ◽  
L Greenslade ◽  
...  
Keyword(s):  
Pressure Gradient ◽  
Pressure Measurement ◽  
Predictive Value ◽  
Bleeding Episode ◽  
Venous Pressure ◽  
Portal Pressure ◽  
Alcoholic Cirrhosis ◽  
Hepatic Venous Pressure Gradient ◽  
Cox Regression Analysis ◽  
Cirrhotic Patients

BackgroundHeight of portal pressure correlates with severity of alcoholic cirrhosis. Portal pressure indices are not however used routinely as predictors of survival.AimsTo examine the clinical value of a single portal pressure measurement in predicting outcome in cirrhotic patients who have bled.MethodsA series of 105 cirrhotic patients who consecutively underwent hepatic venous pressure measurement were investigated. The main cause of cirrhosis was alcoholic (64.8%) and prior to admission all patients had bled from varices.ResultsDuring the follow up period (median 566 days, range 10–2555), 33 patients died, and 54 developed variceal haemorrhage. Applying Cox regression analysis, hepatic venous pressure gradient, bilirubin, prothrombin time, ascites, and previous long term endoscopic treatment were the only statistically independent predictors of survival, irrespective of cirrhotic aetiology. The predictive value of the pressure gradient was much higher if the measurement was taken within the first or the second week from the bleeding and there was no association after 15 days. A hepatic venous pressure gradient of at least 16 mm Hg appeared to identify patients with a greatly increased risk of dying.ConclusionsIndirectly measured portal pressure is an independent predictor of survival in patients with both alcoholic and non-alcoholic cirrhosis. In patients with a previous variceal bleeding episode this predictive value seems to be better if the measurement is taken within the first two weeks from the bleeding episode. A greater use of this technique is recommended for the prognostic assessment and management of patients with chronic liver disease.

Neonatal Aortic Arch Hemodynamics and Perfusion During Cardiopulmonary Bypass

2008 ◽  
Vol 130 (6) ◽  
Author(s):  
Kerem Pekkan ◽  
Onur Dur ◽  
Kartik Sundareswaran ◽  
Kirk Kanter ◽  
Mark Fogel ◽  
...  
Keyword(s):  
Cardiopulmonary Bypass ◽  
Aortic Arch ◽  
Computer Aided Design ◽  
High Speed ◽  
Animal Experiments ◽  
Lumped Parameter Model ◽  
Patient Specific ◽  
Low Velocity ◽  
Blood Damage

The objective of this study is to quantify the detailed three-dimensional (3D) pulsatile hemodynamics, mechanical loading, and perfusion characteristics of a patient-specific neonatal aortic arch during cardiopulmonary bypass (CPB). The 3D cardiac magnetic resonance imaging (MRI) reconstruction of a pediatric patient with a normal aortic arch is modified based on clinical literature to represent the neonatal morphology and flow conditions. The anatomical dimensions are verified from several literature sources. The CPB is created virtually in the computer by clamping the ascending aorta and inserting the computer-aided design model of the 10 Fr tapered generic cannula. Pulsatile (130 bpm) 3D blood flow velocities and pressures are computed using the commercial computational fluid dynamics (CFD) software. Second order accurate CFD settings are validated against particle image velocimetry experiments in an earlier study with a complex cardiovascular unsteady benchmark. CFD results in this manuscript are further compared with the in vivo physiological CPB pressure waveforms and demonstrated excellent agreement. Cannula inlet flow waveforms are measured from in vivo PC-MRI and 3 kg piglet neonatal animal model physiological experiments, distributed equally between the head-neck vessels and the descending aorta. Neonatal 3D aortic hemodynamics is also compared with that of the pediatric and fetal aortic stages. Detailed 3D flow fields, blood damage, wall shear stress (WSS), pressure drop, perfusion, and hemodynamic parameters describing the pulsatile energetics are calculated for both the physiological neonatal aorta and for the CPB aorta assembly. The primary flow structure is the high-speed canulla jet flow (∼3.0 m/s at peak flow), which eventually stagnates at the anterior aortic arch wall and low velocity flow in the cross-clamp pouch. These structures contributed to the reduced flow pulsatility (85%), increased WSS (50%), power loss (28%), and blood damage (288%), compared with normal neonatal aortic physiology. These drastic hemodynamic differences and associated intense biophysical loading of the pathological CPB configuration necessitate urgent bioengineering improvements—in hardware design, perfusion flow waveform, and configuration. This study serves to document the baseline condition, while the methodology presented can be utilized in preliminary CPB cannula design and in optimization studies reducing animal experiments. Coupled to a lumped-parameter model the 3D hemodynamic characteristics will aid the surgical decision making process of the perfusion strategies in complex congenital heart surgeries.

scholarly journals In Vivo Validation of Patient‐Specific Pressure Gradient Calculations for Iliac Artery Stenosis Severity Assessment

2017 ◽  
Vol 6 (12) ◽  
Author(s):  
Stefan G. H. Heinen ◽  
Daniel A.F. van den Heuvel ◽  
Wouter Huberts ◽  
Sanne W. de Boer ◽  
Frans N. van de Vosse ◽  
...  
Keyword(s):  
Pressure Gradient ◽  
Iliac Artery ◽  
Artery Stenosis ◽  
Patient Specific ◽  
Severity Assessment ◽  
Specific Pressure ◽  
Iliac Artery Stenosis ◽  
Stenosis Severity ◽  
In Vivo Validation

Hemodynamic performance of the Fontan circulation compared with a normal biventricular circulation: a computational model study

2014 ◽  
Vol 307 (7) ◽  
pp. H1056-H1072 ◽  
Author(s):  
Fuyou Liang ◽  
Hideaki Senzaki ◽  
Clara Kurishima ◽  
Koichi Sughimoto ◽  
Ryo Inuzuka ◽  
...  
Keyword(s):  
Central Venous Pressure ◽  
Pulmonary Vascular Resistance ◽  
Vascular Resistance ◽  
Venous Pressure ◽  
Fontan Circulation ◽  
Patient Specific ◽  
Model Parameters ◽  
Ventricular Contractility ◽  
Central Venous ◽  
Hemodynamic Performance

The physiological limitations of the Fontan circulation have been extensively addressed in the literature. Many studies emphasized the importance of pulmonary vascular resistance in determining cardiac output (CO) but gave little attention to other cardiovascular properties that may play considerable roles as well. The present study was aimed to systemically investigate the effects of various cardiovascular properties on clinically relevant hemodynamic variables (e.g., CO and central venous pressure). To this aim, a computational modeling method was employed. The constructed models provided a useful tool for quantifying the hemodynamic effects of any cardiovascular property of interest by varying the corresponding model parameters in model-based simulations. Herein, the Fontan circulation was studied compared with a normal biventricular circulation so as to highlight the unique characteristics of the Fontan circulation. Based on a series of numerical experiments, it was found that 1) pulmonary vascular resistance, ventricular diastolic function, and systemic vascular compliance play a major role, while heart rate, ventricular contractility, and systemic vascular resistance play a secondary role in the regulation of CO in the Fontan circulation; 2) CO is nonlinearly related to any single cardiovascular property, with their relationship being simultaneously influenced by other cardiovascular properties; and 3) the stability of central venous pressure is significantly reduced in the Fontan circulation. The findings suggest that the hemodynamic performance of the Fontan circulation is codetermined by various cardiovascular properties and hence a full understanding of patient-specific cardiovascular conditions is necessary to optimize the treatment of Fontan patients.

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