Analysis of mechanical parameters on the thromboembolism using a patient-specific computational model

Investigation of cardiopulmonary bypass parameters on embolus transport in a patient-specific aorta

Neurological complexities resulting from surgery requiring cardiopulmonary bypass (CPB) remain a major concern, encompassing a spectrum of complications including thromboembolic stroke and various cognitive impairments. Surgical manipulation during CPB is considered the primary cause of these neurological complications. This study addresses the overall lack of knowledge concerning CPB hemodynamics within the aorta, employing a combined experimental-computational modeling approach, featuring computational fluid dynamics simulations validated with an in vitro CPB flow loop under steady conditions. Parametric studies were systematically performed, varying parameters associated with CPB techniques (pump flow rate and hemodiluted blood viscosity) and properties related to formed emboli (size and density). This represents the first comprehensive investigation into the individual and combined effects of these factors. Our findings reveal critical insights into the operating conditions of CPB, indicating a positive correlation between pump flow rate and emboli transport into the aortic branches, potentially increasing the risk of stroke. It was also found that larger emboli were more often transported into the aortic branches at higher pump flow rates, while smaller emboli preferred lower flow rates. Further, as blood is commonly diluted during CPB to decrease its viscosity, more emboli were found to enter the aortic branches with greater hemodilution. The combined effects of these parameters are captured using the non-dimensional Stokes number, which was found to positively correlate with emboli transport into the aortic branches. These findings contribute to our understanding of embolic stroke risk factors during CPB and shed light on the complex interplay between CPB parameters.

In silico analysis of embolism in cerebral arteries using fluid-structure interaction method

Ischemic stroke, particularly embolic stroke, stands as a significant global contributor to mortality and long-term disabilities. This paper presents a comprehensive simulation of emboli motion through the middle cerebral artery (MCA), a prevalent site for embolic stroke. Our patient-specific computational model integrates major branches of the middle cerebral artery reconstructed from magnetic resonance angiography images, pulsatile flow dynamics, and emboli of varying geometries, sizes, and material properties. The fluid-structure interactions method is employed to simulate deformable emboli motion through the middle cerebral artery, allowing observation of hemodynamic changes in artery branches upon embolus entry. We investigated the impact of embolus presence on shear stress magnitude on artery walls, analyzed the effects of embolus material properties and geometries on embolus trajectory and motion dynamics within the middle cerebral artery. Additionally, we evaluated the non-Newtonian behavior of blood, comparing it with Newtonian blood behavior. Our findings highlight that embolus geometry significantly influences trajectory, motion patterns, and hemodynamics within middle cerebral artery branches. Emboli with visco-hyperelastic material properties experienced higher stresses upon collision with artery walls compared to those with hyperelastic properties. Furthermore, considering blood as a non-Newtonian fluid had notable effects on emboli stresses and trajectories within the artery, particularly during collisions. Notably, the maximum von Mises stress experienced in our study was 21.83 kPa, suggesting a very low probability of emboli breaking during movement, impact, and after coming to a stop. However, in certain situations, the magnitude of shear stress on them exceeded 1 kPa, increasing the likelihood of cracking and disintegration. These results serve as an initial step in anticipating critical clinical conditions arising from arterial embolism in the middle cerebral artery. They provide insights into the biomechanical parameters influencing embolism, contributing to improved clinical decision-making for stroke management.

A Fluid-Structure Interaction Analysis of Blood Clot Motion in a Branch of Pulmonary Arteries

INTRODUCTION

Pulmonary embolism (PE) is one of the most prevalent diseases amid hospitalized patients taking many people's lives annually. This phenomenon, however, has not been investigated via numerical simulations.

METHODS

In this study, an image-based model of pulmonary arteries has been constructed from a 44-year-old man's computed tomography images. The fluid-structure interaction method was used to simulate the motion of the blood clot. In this regard, Navier-Stokes equations, as the governing equations, have been solved in an arbitrary Lagrangian-Eulerian (ALE) formulation.

RESULTS

According to our results, the velocity of visco-hyperelastic model of the emboli was relatively higher than the emboli with hyperelastic model, despite their similar behavioral pattern. The stresses on the clot were also investigated and showed that the blood clot continuously sustained stresses greater than 165 Pa over an about 0.01 s period, which can cause platelets to leak and make the clot grow or tear apart.

CONCLUSIONS

It could be concluded that in silico analysis of the cardiovascular diseases initiated from clot motion in blood flow is a valuable tool for a better understanding of these phenomena.

Hyper-viscoelastic damage modeling of whole blood clot under large deformation

Blood clots play a diametric role in our bodies as they are both vital as a wound sealant, as well as the source for many devastating diseases. In blood clots' physiological and pathological roles, their mechanics play a critical part. These mechanics are non-trivial owing to blood clots' complex nonlinear, viscoelastic behavior. Casting this behavior into mathematical form is a fundamental step toward a better basic scientific understanding of blood clots, as well as toward diagnostic and prognostic computational models. Here, we identify a hyper-viscoelastic damage model that we fit to original data on the nonlinear, viscoelastic behavior of blood clots. Our model combines the classic Ogden hyperelastic constitutive law, a finite viscoelastic model for large deformations, and a non-local, gradient-enhanced damage formulation. By fitting our model to cyclic tensile test data and extension-to-failure data, we inform the model's nine unknown material parameters. We demonstrate the predictability of our model by validating it against unseen cyclic tensile test and stress-relaxation data. Our original data, model formulation, and the identified constitutive parameters of this model are openly available for others to use, which will aid in developing accurate, quantitative simulations of blood clot mechanics.

Study protocol of validating a numerical model to assess the blood flow in the circle of Willis

INTRODUCTION

We developed a zero-dimensional (0D) model to assess the patient-specific haemodynamics in the circle of Willis (CoW). Similar numerical models for simulating the cerebral blood flow (CBF) had only been validated qualitatively in healthy volunteers by magnetic resonance (MR) angiography and transcranial Doppler (TCD). This study aims to validate whether a numerical model can simulate patient-specific blood flow in the CoW under pathological conditions.

METHODS AND ANALYSIS

This study is a diagnostic accuracy study. We aim to collect data from a previously performed prospective study that involved patients with aneurysmal subarachnoid haemorrhage (aSAH) receiving both TCD and brain Computerd Tomography angiography (CTA) at the same day. The cerebral flow velocities are calculated by the 0D model, based on the vessel diameters measured on the CTA of each patient. In this study, TCD is considered the gold standard for measuring flow velocity in the CoW. The agreement will be analysed using Pearson correlation coefficients.

ETHICS AND DISSEMINATION

This study protocol has been approved by the Medical Ethics Review Board of the University Medical Center Groningen: METc2019/103. The results will be submitted to an international scientific journal for peer-reviewed publication.

TRIAL REGISTRATION NUMBER

NL8114.

Embolus Analog Trajectory Paths Under Physiological Flowrates Through Patient-Specific Aortic Arch Models

Atrial fibrillation (AF) is the most common irregular heartbeat among the world's population and is a major contributor to cardiogenic embolisms and acute ischemic stroke (AIS). However, the role AF flow plays in the trajectory paths of cardiogenic emboli has not been experimentally investigated. A physiological simulation system was designed to analyze the trajectory patterns of bovine embolus analogs (EAs) (n = 720) through four patient-specific models, under three flow conditions: steady flow, normal pulsatile flow, and AF pulsatile flow. It was seen that EA trajectory paths were proportional to the percentage flowrate split of 25–31% along the branching vessels. Overall, AF flow conditions increased trajectories through the left- (LCCA) and right (RCCA)-common carotid artery by 25% with respect to normal pulsatile flow. There was no statistical difference in the distribution of clot trajectories when the clot was released from the right, left, or anterior positions. Significantly, more EAs traveled through the brachiocephalic trunk (BCT) than through the LCCA or the left subclavian. Yet of the EAs that traveled through the common carotid arteries, there was a greater affiliation toward the LCCA compared to the RCCA (p < 0.05).

Multivessel Occlusion in Patients Subjected to Thrombectomy: Prevalence, Associated Factors, and Clinical Implications

BACKGROUND AND PURPOSE

Patients with embolic large-vessel occlusion may present with additional coincidental acute occlusions within or distant from the involved territory, referred to as multivessel occlusion (MVO). Purpose of this study was to assess prevalence of MVO, associated factors, and clinical relevance in patients undergoing endovascular stroke treatment.

METHODS

Image data of consecutive endovascular candidates (n=720) with direct access to angiography were extracted from a prospective registry. Prevalence of MVO was assessed with multimodal magnetic resonance imaging/computed tomography and confirmed by intra-arterial angiography. Explorative analysis of associated factors and clinical relevance was evaluated using multivariable logistic regression including variables with P<0.15 in univariate comparison. Good functional outcome was defined as modified Rankin Scale score ≤2 at day 90.

RESULTS

MVO was present in 10.7% of patients (95% confidence interval [CI], 6.4%-13.0%). Two, 3, and 4 concomitant occlusions were found in 80.5%, 16.9%, and 2.6% of MVO cases, respectively. Detection rate on initial radiological report was 54.5%. Downstream MVO was present in around one third of MVO (n=27/77, 35.1%), whereas all other MVO (n=50/77, 64.9%) occurred in different territories. Independent factors related to MVO were statin treatment (adjusted odds ratio [aOR], 0.477; 95% CI, 0.276-0.827), higher systolic blood pressure (aOR per mm Hg increase, 1.014; 95% CI, 1.005-1.023), and primary occlusion site M2 (aOR, 1.870; 95% CI, 1.103-3.170). MVO was related to lower rates of successful reperfusion (aOR, 0.549; 95% CI, 0.316-0.953) and lower rates of good functional outcome (aOR, 0.437; 95% CI, 0.207-0.923).

CONCLUSIONS

Every tenth patient subjected to angiography for endovascular stroke treatment experienced MVO in our series, and only half were prospectively identified on preinterventional diagnostic imaging. Patients with MVO had higher baseline systolic blood pressure and were less often medicated with statins, an observation that warrants external validation and evaluation regarding causality. Occurrence of MVO has implication for treatment decisions, negatively affects endovascular treatment success, and is predictive of worse clinical outcome.