A computational model-based study on the exchangeability of hepatic venous pressure gradients measured in multiple hepatic veins

The Balloon Catheter Method and the End-hole Catheter Method in the Measurement of Hepatic Venous Pressure Gradient: a Comparative Study

OBJECTIVE

This study aims to evaluate the differences between The balloon catheter method and End-hole Catheter Method in measuring hepatic venous pressure gradient (HVPG) among cirrhosis patients.

METHODS

From October 2017 to January 2024, patients who underwent HVPG measurements using both methods were consecutively included. HVPGs obtained from both methods were compared with the portal vein pressure gradient (PPG) obtained via transjugular intrahepatic portosystemic shunt (TIPS) using paired comparisons. Additionally, the consistency and predictive ability for bleeding risk of the two methods, as well as the impact of intrahepatic veno-venous shunt (IHVS), were analyzed.

RESULTS

The study enrolled 145 patients, each of whom had HVPG measured by both methods. PPG was measured in 61 patients. There was a statistically significant difference between the PPGs and HVPGs measured by both the balloon catheter method and the end-hole catheter method (P < 0.001), with the HVPG mean values obtained by the end-hole catheter method being closer to the PPGs. In the non-IHVS group, no significant statistical difference was found between the two methods (P = 0.071). In contrast, the IHVS group showed a significant difference (P < 0.001), with a mean difference of 2.98 ± 4.03 mmHg. When IHVS was absent, the measurement results from the end-hole catheter method and the balloon catheter method were found to be highly correlated. The end-hole catheter method has a higher screening capability for patients at risk of bleeding compared to the balloon catheter method (75.90% vs. 72.86%).

CONCLUSION

HVPG measurements using either the balloon catheter method or end-hole catheter method showed significant difference with the PPG. The end-hole catheter method has a higher screening capability for patients at risk of bleeding, and IHVS could lead to lower HVPG measurements with The balloon catheter method.

A new computational fluid dynamics based noninvasive assessment of portacaval pressure gradient

Accurate assessment of portacaval pressure gradient (PCG) in patients with portal hypertension (PH) is of great significance both for diagnosis and treatment. This study aims to develop a noninvasive method for assessing PCG in PH patients and evaluate its accuracy and effectiveness. This study recruited 37 PH patients treated with transjugular intrahepatic portosystemic shunt (TIPS). computed tomography angiography was used to create three dimension (3D) models of each patient before and after TIPS. Doppler ultrasound examinations were conducted to obtain the patient's portal vein flow (or splenic vein and superior mesenteric vein). Using computational fluid dynamics (CFD) simulation, the patient's pre-TIPS and post-TIPS PCG was determined by the 3D models and ultrasound measurements. The accuracy of these noninvasive results was then compared to clinical invasive measurements. The results showed a strong linear correlation between the PCG simulated by CFD and the clinical invasive measurements both before and after TIPS (R2 = 0.998, P < 0.001 and R2 = 0.959, P < 0.001). The evaluation accuracy of this noninvasive method reached 94 %, and the influence of ultrasound result errors on the numerical accuracy was found to be marginal if the error was less than 20 %. Furthermore, the information about the hemodynamic environment in the portal system was obtained by this numerical method. Spiral flow patterns were observed in the portal vein of some patients. In a conclusion, this study proposes a noninvasive numerical method for assessing PCG in PH patients before and after TIPS. This method can assist doctors in accurately diagnosing patients and selecting appropriate treatment plans. Additionally, it can be used to further investigate potential biomechanical causes of complications related to TIPS in the future.

A computational model-based study on the feasibility of predicting post-splenectomy thrombosis using hemodynamic metrics

For portal hypertensive patients with splenomegaly and hypersplenism, splenectomy is an effective surgery to relieve the complications. However, patients who have undergone splenectomy often suffer from portal venous system thrombosis, a sequela that requires prophylaxis and timely treatment to avoid deterioration and death. The aim of this study is to investigate the feasibility of predicting post-splenectomy thrombosis using hemodynamic metrics based on computational models. First, 15 portal hypertensive patients who had undergone splenectomy were enrolled, and their preoperative clinical data and postoperative follow-up results were collected. Next, computational models of the portal venous system were constructed based on the preoperative computed tomography angiography images and ultrasound-measured flow velocities. On this basis, splenectomy was mimicked and the postoperative area of low wall shear stress (ALWSS) was simulated for each patient-specific model. Finally, model-simulated ALWSS was statistically compared with the patient follow-up results to investigate the feasibility of predicting post-splenectomy thrombosis using hemodynamic metrics. Results showed that ALWSS could predict the occurrence of post-splenectomy thrombosis with the area under the receiver operating characteristic curve (AUC) equal to 0.75. Moreover, statistical analysis implied that the diameter of the splenic vein is positively correlated with ALWSS (r = 0.883, p < 0.0001), and the anatomical structures of the portal venous system also influence the ALWSS. These findings demonstrated that the computational model-based hemodynamic metric ALWSS, which is associated with the anatomorphological features of the portal venous system, is capable of predicting the occurrence of post-splenectomy thrombosis, promoting better prophylaxis and postoperative management for portal hypertensive patients receiving splenectomy.

A 0D-3D multi-scale model of the portal venous system coupled with the entire cardiovascular system applied to predict postsplenectomy hemodynamic metrics

Splenectomy is a common surgery for portal hypertensive patients with splenomegaly. Although splenectomy is able to effectively relieve the complications of portal hypertension, it also increases the risk of portal venous system thrombosis remarkably. Previous studies demonstrated that the hemodynamic metrics of the portal venous system could be employed in predicting the risk of postsplenectomy thrombosis, and 3D models were utilized to simulate the blood flow in the portal venous system. Aiming to reflect the global effect of splenectomy and better simulate the hemodynamic metrics, in this study, a 0D-3D multi-scale model of the portal venous system coupled with the entire cardiovascular system was constructed based on population-averaged data in combination with patient-specific preoperative clinical measurements. The pre- and postoperative global blood flows as well as the variations were calculated successfully, and the flow field and time-averaged wall shear stress of the portal venous system were simulated. The model-simulated spatial distributions of the hemodynamic metrics in the portal venous system were comparable with the regions suffering from thrombosis after splenectomy. These results imply that the present model could reflect the reallocation of the blood flow in the splanchnic circulation after splenectomy and simulate the hemodynamic metrics of the portal venous system, which would promote the more accurate risk stratification of postsplenectomy thrombosis and improve the patient-specific postoperative management.Clinical Relevance- The computational model developed by the present study provides a feasible scheme for simulating postsplenectomy hemodynamic metrics of the portal venous system more accurately, which would benefit the risk prediction and prophylaxis of portal venous system thrombosis for portal hypertensive patients receiving splenectomy.

Modelling the liver region as porous media to noninvasively measure portal vein pressure gradient (PPG) with numerical methods

Portal hypertension is the initial and main consequence of liver cirrhosis. Currently the diagnosis relies on invasive and complex operation. This study proposed a new computational method in computational fluid dynamics (CFD) analysis to noninvasively measure the portal pressure gradient (PPG) by considering the liver region as porous media to account for the patient-specific liver resistance. Patient-specific computational models based on the CT scan images and the ultrasound (US) velocity measurement was established. The results show that the PPG derived from CFD analysis is in great agreement with clinical measured data (23.93 mmHg vs 23 mmHg). Validation of the numerical method and was performed by post-TIPS PPG measurement (10.69 mmHg vs 11 mmHg). Then the range of porous media parameters is investigated in a validation group of three patients. The computational method proposed in this study is promising in more accurately measuring the PPG noninvasively.

In silico modeling for the hepatic circulation and transport: From the liver organ to lobules

The function of the liver depends critically on its blood supply. Numerous in silico models have been developed to study various aspects of the hepatic circulation, including not only the macro-hemodynamics at the organ level, but also the microcirculation at the lobular level. In addition, computational models of blood flow and bile flow have been used to study the transport, metabolism, and clearance of drugs in pharmacokinetic studies. These in silico models aim to provide insights into the liver organ function under both healthy and diseased states, and to assist quantitative analysis for surgical planning and postsurgery treatment. The purpose of this review is to provide an update on state-of-the-art in silico models of the hepatic circulation and transport processes. We introduce the numerical methods and the physiological background of these models. We also discuss multiscale frameworks that have been proposed for the liver, and their linkage with the large context of systems biology, systems pharmacology, and the Physiome project. This article is categorized under: Metabolic Diseases > Computational Models Metabolic Diseases > Biomedical Engineering Cardiovascular Diseases > Computational Models.

Predicting the risk of postsplenectomy thrombosis in patients with portal hypertension using computational hemodynamics models: A proof-of-concept study

BACKGROUND

The high incidence of thrombosis in the portal venous system following splenectomy (a frequently adopted surgery for treating portal hypertension in patients with splenomegaly and hypersplenism) is a critical clinical issue. The aim of this study was to address whether quantification of postsplenectomy hemodynamics has potential value for assessing the risk of postsplenectomy thrombosis.

METHODS

Computational models were constructed for three portal hypertensive patients treated with splenectomy based on their preoperative clinical data to quantify hemodynamics in the portal venous system before and after splenectomy, respectively. Each patient was followed up for three or five months after surgery and examined with CT to screen potential thrombosis.

FINDINGS

The area ratio of wall regions exposed to low wall shear stress was small before splenectomy in all patients, which increased markedly after splenectomy and exhibited enlarged inter-patient differences. The largest area ratio of low wall shear stress and most severe flow stagnation after splenectomy were predicted for the patient suffering from postsplenectomy thrombosis, with the wall regions exposed to low wall shear stress corresponding well with the CT-detected distribution of thrombus. Further analyses revealed that postoperative hemodynamic characteristics were considerably influenced by the anatomorphological features of the portal venous system.

INTERPRETATION

Postoperative hemodynamic conditions in the portal venous system are highly patient-specific and have a potential link to postsplenectomy thrombosis, which indicates that patient-specific hemodynamic studies may serve as a complement to routine clinical assessments for refining risk stratification and postoperative patient management.

Machine Learning-Based Pulse Wave Analysis for Early Detection of Abdominal Aortic Aneurysms Using In Silico Pulse Waves

An abdominal aortic aneurysm (AAA) is usually asymptomatic until rupture, which is associated with extremely high mortality. Consequently, the early detection of AAAs is of paramount importance in reducing mortality; however, most AAAs are detected by medical imaging only incidentally. The aim of this study was to investigate the feasibility of machine learning-based pulse wave (PW) analysis for the early detection of AAAs using a database of in silico PWs. PWs in the large systemic arteries were simulated using one-dimensional blood flow modelling. A database of in silico PWs representative of subjects (aged 55, 65 and 75 years) with different AAA sizes was created by varying the AAA-related parameters with major impacts on PWs—identified by parameter sensitivity analysis—in an existing database of in silico PWs representative of subjects without AAAs. Then, a machine learning architecture for AAA detection was trained and tested using the new in silico PW database. The parameter sensitivity analysis revealed that the AAA maximum diameter and stiffness of the large systemic arteries were the dominant AAA-related biophysical properties considerably influencing the PWs. However, AAA detection by PW indexes was compromised by other non-AAA related cardiovascular parameters. The proposed machine learning model produced a sensitivity of 86.8 % and a specificity of 86.3 % in early detection of AAA from the photoplethysmogram PW signal measured in the digital artery with added random noise. The number of false positive and negative results increased with increasing age and decreasing AAA size, respectively. These findings suggest that machine learning-based PW analysis is a promising approach for AAA screening using PW signals acquired by wearable devices.

Influences of Anatomorphological Features of the Portal Venous System on Postsplenectomy Hemodynamic Characteristics in Patients With Portal Hypertension: A Computational Model-Based Study

Splenectomy, as an effective surgery for relieving complications caused by portal hypertension, is often accompanied by a significantly increased incidence of postoperative thrombosis in the portal venous system (PVS). While the underlying mechanisms remain insufficiently understood, the marked changes in hemodynamic conditions in the PVS following splenectomy have been suggested to be a potential contributing factor. The aim of this study was to investigate the influences of the anatomorphological features of the PVS on hemodynamic characteristics before and after splenectomy, with emphasis on identifying the specific anatomorphological features that make postoperative hemodynamic conditions more clot-promoting. For this purpose, idealized computational hemodynamics models of the PVS were constructed based on general anatomical structures and population-averaged geometrical parameters of the PVS. In the models, we incorporated various anatomorphological variations to represent inter-patient variability. The analyses of hemodynamic data were focused on the spatial distribution of wall shear stress (WSS) and the area ratio of wall regions exposed to low WSS (ALS). Obtained results showed that preoperative hemodynamic conditions were comparable among different models in terms of space-averaged WSS and ALS (all were small) irrespective of the considerable differences in spatial distribution of WSS, whereas, the inter-model differences in ALS were significantly augmented after splenectomy, with the value of ALS reaching up to over 30% in some models, while being smaller than 15% in some other models. Postoperative ALS was mainly determined by the anatomical structure of the PVS, followed by some morphogeometrical parameters, such as the diameter and curvature of the splenic vein, and the distance between the inferior mesenteric vein and splenoportal junction. Relatively, the angles between tributary veins and trunk veins only had mild influences on ALS. In addition, a marked increase in blood viscosity was predicted after splenectomy, especially in regions with low WSS, which may play an additive role to low WSS in initiating thrombosis. These findings suggest that the anatomical structure and some morphogeometrical features of the PVS are important determinants of hemodynamic conditions following splenectomy, which may provide useful clues to assessing the risk of postsplenectomy thrombosis based on medical imaging data.