Computational Fluid Dynamics Modeling of Hemodynamic Parameters in the Human Diseased Aorta: A Systematic Review.

BACKGROUND: The analysis of the correlation between blood flow and aortic pathology through computational fluid dynamics (CFD) shows promise in predicting disease progression, the effect of operative intervention, and guiding patient treatment. However, to date, there has not been a comprehensive systematic review of the published literature describing CFD in aortic diseases and their treatment. METHODS: This review includes 136 published articles which have investigated the application of CFD in all types of aortic disease (aneurysms, dissections, and coarctation). We took into account case studies of both, treated or untreated pathology, investigated with CFD. We also graded all studies using an author-defined Grading of Recommendations Assessment, Development and Evaluation (GRADE) approach based on the validation method used for the CFD results. RESULTS: There are no randomized controlled trials assessing the efficacy of CFD as applied to aortic pathology, treated or untreated. Although a large number of observational studies are available, those using clinical imaging tools as independent validation of the calculated CFD results exist in far smaller numbers. Only 21% of all studies used clinical imaging as a tool to validate the CFD results and these were graded as high-quality studies. CONCLUSIONS: Contemporary evidence shows that CFD can provide additional hemodynamic parameters such as wall shear stress, vorticity, disturbed laminar flow, and recirculation regions in untreated and treated aortic disease. These have the potential to predict the progression of aortic disease, the effect of operative intervention, and ultimately help guide the choice and timing of treatment to the benefit of patients and clinicians alike.

Ventricular vortex loss analysis due to various tricuspid valve repair techniques: an ex vivo study.

The deteriorating nature of severe functional tricuspid regurgitation (FTR) has led to the heightened interest in this pathology. However, therapies are heterogeneous and an ideal technique is uncertain. The hemodynamic impact on the cardiac chamber following therapeutic repairs has not been well studied, while its analysis could be used to predict the treatment success. In this study, the hemodynamics of the right ventricle (RV) after 1) clover edge-to-edge tricuspid repair, and 2) double orifice tricuspid repair was evaluated in three right heart models using an ex vivo pulsatile platform emulating severe FTR with the aid of stereoscopic particle image velocimetry. Although all repairs substantially reduced tricuspid regurgitant area, they resulted in a more than 50% reduction in diastolic tricuspid valve (TV) opening area. Splitting the TV orifice into multiple smaller orifices by both repairs eliminated the ring-shaped vortical structure inside the RV observed in FTR cases. Postrepair RV domain was mostly occupied with irregular vortical features and isolated vortex residuals. Moreover, vortical features varied among repair samples, indicating enhanced sensitivity of RV flow to postrepair TV morphology. Compared with clover repair, double orifice subjected the RV to enhanced swirling motions and exposed more regions to vortical motions, potentially indicating better rinsing and lower risk of mural thrombus formation. Double orifice repair increased the levels of RV mean kinetic energy and viscous energy loss than those observed in clover repair, although the impact of these on the cardiac efficiency remains unclear. These preliminary insights could be used to improve future treatment design and planning.NEW & NOTEWORTHY While clover and double orifice tricuspid repairs markedly improved leaflet coaptation, they substantially reduced diastolic tricuspid opening area. Postrepair right ventricle (RV) exhibited specific hemodynamic traits, including the loss of ring-shaped vortical structure and the enhanced sensitivity of RV flow to postrepair tricuspid valve morphology. Compared with clover technique, double orifice repair led to higher swirling motions in the RV domain, which could indicate lower risk of mural thrombus formation.

Effects of Microporous Stent Graft on the Descending Aortic Aneurysm: A Patient-Specific Computational Fluid Dynamics Study.

Thoracic endovascular aortic repair (TEVAR) method is an alternative treatment for thoracic aortic aneurysm (TAA) compared to open surgery. It is believed that stent graft implantation can potentially reduce the risk of aneurysm rupture by altering the associated blood flow disturbances within an aneurysm. To investigate the hemodynamics changes of TEVAR intervention to the TAA, three models, namely healthy, aneurysm before treatment, and aneurysm after stent graft implantation models were built. These three models were presented and compared in terms of their flow patterns, time-averaged wall shear stress (TAWSS), oscillating shear index (OSI), and relative residence time (RRT). Reduced TAWSS and OSI with altered flow pattern were found on the aneurysm wall after the deployment of the microporous stent graft. Elevated RRT on the aneurysm sac indicated that red blood cells and platelets tended to stay longer in the aneurysm sac after implantation of the microporous stent graft. The alteration of flow patterns caused by the microporous stent graft revealed its potential to create a beneficial hemodynamic environment, which promotes platelet activation within the aneurysm and elicits localization of thrombus formation that ultimately lead to the recovery of an aortic aneurysm.

Transformative Potential of AI in Healthcare: Definitions, Applications, and Navigating the Ethical Landscape and Public Perspectives.

Artificial intelligence (AI) has emerged as a crucial tool in healthcare with the primary aim of improving patient outcomes and optimizing healthcare delivery. By harnessing machine learning algorithms, natural language processing, and computer vision, AI enables the analysis of complex medical data. The integration of AI into healthcare systems aims to support clinicians, personalize patient care, and enhance population health, all while addressing the challenges posed by rising costs and limited resources. As a subdivision of computer science, AI focuses on the development of advanced algorithms capable of performing complex tasks that were once reliant on human intelligence. The ultimate goal is to achieve human-level performance with improved efficiency and accuracy in problem-solving and task execution, thereby reducing the need for human intervention. Various industries, including engineering, media/entertainment, finance, and education, have already reaped significant benefits by incorporating AI systems into their operations. Notably, the healthcare sector has witnessed rapid growth in the utilization of AI technology. Nevertheless, there remains untapped potential for AI to truly revolutionize the industry. It is important to note that despite concerns about job displacement, AI in healthcare should not be viewed as a threat to human workers. Instead, AI systems are designed to augment and support healthcare professionals, freeing up their time to focus on more complex and critical tasks. By automating routine and repetitive tasks, AI can alleviate the burden on healthcare professionals, allowing them to dedicate more attention to patient care and meaningful interactions. However, legal and ethical challenges must be addressed when embracing AI technology in medicine, alongside comprehensive public education to ensure widespread acceptance.

Study of Power Equivalent Continuous Approximation Based on the Recent Consensus Recommendations for Brain Tumor Imaging with Pulsed Chemical Exchange Saturation Transfer at 3T.

The quantitative analysis of pulsed-chemical exchange saturation transfer (CEST) using a full model-based method is computationally challenging, as it involves dealing with varying RF values in pulsed saturation. A power equivalent continuous approximation of B1 power was usually applied to accelerate the analysis. In line with recent consensus recommendations from the CEST community for pulsed-CEST at 3T, particularly recommending a high RF saturation power (B1 = 2.0 µT) for the clinical application in brain tumors, this technical note investigated the feasibility of using average power (AP) as the continuous approximation. The simulated results revealed excellent performance of the AP continuous approximation in low saturation power scenarios, but discrepancies were observed in the z-spectra for the high saturation power cases. Cautions should be taken, or it may lead to inaccurate fitted parameters, and the difference can be more than 10% in the high saturation power cases.

The Impact of Left Ventricular Assist Device Outflow Graft Positioning on Aortic Hemodynamics: Improving Flow Dynamics to Mitigate Aortic Insufficiency.

Heart failure is a global health concern with significant implications for healthcare systems. Left ventricular assist devices (LVADs) provide mechanical support for patients with severe heart failure. However, the placement of the LVAD outflow graft within the aorta has substantial implications for hemodynamics and can lead to aortic insufficiency during long-term support. This study employs computational fluid dynamics (CFD) simulations to investigate the impact of different LVAD outflow graft locations on aortic hemodynamics. The introduction of valve morphology within the aorta geometry allows for a more detailed analysis of hemodynamics at the aortic root. The results demonstrate that the formation of vortex rings and subsequent vortices during the high-velocity jet flow from the graft interacted with the aortic wall. Time-averaged wall shear stress (TAWSS) and oscillatory shear index (OSI) indicate that modification of the outflow graft location changes mechanical states within the aortic wall and aortic valve. Among the studied geometric factors, both the height and inclination angle of the LVAD outflow graft are important in controlling retrograde flow to the aortic root, while the azimuthal angle primarily determines the rotational direction of blood flow in the aortic arch. Thus, precise positioning of the LVAD outflow graft emerges as a critical factor in optimizing patient outcomes by improving the hemodynamic environment.

Haemodynamic changes in visceral hybrid repairs of type III and type V thoracoabdominal aortic aneurysms.

The visceral hybrid procedure combining retrograde visceral bypass grafting and completion endovascular stent grafting is a feasible alternative to conventional open surgical or wholly endovascular repairs of thoracoabdominal aneurysms (TAAA). However, the wide variability in visceral hybrid configurations means that a priori prediction of surgical outcome based on haemodynamic flow profiles such as velocity pattern and wall shear stress post repair remain challenging. We sought to appraise the clinical relevance of computational fluid dynamics (CFD) analyses in the setting of visceral hybrid TAAA repairs. Two patients, one with a type III and the other with a type V TAAA, underwent successful elective and emergency visceral hybrid repairs, respectively. Flow patterns and haemodynamic parameters were analysed using reconstructed pre- and post-operative CT scans. Both type III and type V TAAAs showed highly disturbed flow patterns with varying helicity values preoperatively within their respective aneurysms. Low time-averaged wall shear stress (TAWSS) and high endothelial cell action potential (ECAP) and relative residence time (RRT) associated with thrombogenic susceptibility was observed in the posterior aspect of both TAAAs preoperatively. Despite differing bypass configurations in the elective and emergency repairs, both treatment options appear to improve haemodynamic performance compared to preoperative study. However, we observed reduced TAWSS in the right iliac artery (portending a theoretical risk of future graft and possibly limb thrombosis), after the elective type III visceral hybrid repair, but not the emergency type V repair. We surmise that this difference may be attributed to the higher neo-bifurcation of the aortic stent graft in the type III as compared to the type V repair. Our results demonstrate that CFD can be used in complicated visceral hybrid repair to yield potentially actionable predictive insights with implications on surveillance and enhanced post-operative management, even in patients with complicated geometrical bypass configurations.

Biventricular biaxial mechanical testing and constitutive modelling of fetal porcine myocardium passive stiffness.

The evaluation of fetal heart mechanical function is becoming increasingly important for determining the prognosis and making subsequent decisions on the treatment and management of congenital heart diseases. Finite Element (FE) modelling can potentially provide detailed information on fetal hearts, and help perform virtual interventions to assist in predicting outcomes and supporting clinical decisions. Previous FE studies have enabled an improved understanding of healthy and diseased fetal heart biomechanics. However, to date, the mechanical properties of the fetal myocardium have not been well characterized which limits the reliability of such modelling. Here, we characterize the passive mechanical properties of late fetal and neonatal porcine hearts via biaxial mechanical testing as a surrogate for human fetal heart mechanical properties. We used samples from both the right and left ventricles over the late gestational period from 85 days of gestation to birth. Constitutive modelling was subsequently performed with a transversely isotropic Fung-type model and a Humphrey-type model, using fiber orientations identified with histology. We found no significant difference in mechanical stiffness across all age groups and between the right and left ventricular samples. This was likely due to the similarity in LV and RV pressures in the fetal heart, and similar gestational maturity across these late gestational ages. We thus recommend using the constitutive model for the average stress-stress behaviour of the tissues in future modelling work. Furthermore, we characterized the variability of the stiffness to inform such work.

A novel coating method to reduce membrane infolding through pre-crimping of covered stents - Computational and experimental evaluation.

A covered stent has been used to treat carotid artery stenosis to reduce the chance of embolization, as it offers improved performance over bare-metal stents. However, membrane infolding of covered stents can affect efficiency and functionality for treating occlusive disease of first-order aortic branches. In order to mitigate the degree of infolding of the stent once it was re-expanded, we proposed a new coating method performed on the pre-crimped stent. A systematic study was carried out to evaluate this new coating technique: a) in vivo animal testing to determine the degree of membrane infolding; b) structural finite element modeling and simulation were used to evaluate the mechanical performance of the covered stent; and c) computational fluid dynamics (CFD) to evaluate hemodynamic behavior of the stents and risk of thrombosis after stent deployment. The degree of infolding was substantially reduced as demonstrated by the in vivo deployment of the pre-crimped stent compared to a conventional dip-coated stent. The structural analysis results demonstrated that the membrane of the covered stent manufactured by conventional dip-coating resulted in a large degree of infolding but this could be minimized by our new pre-crimped coating method. CFD studies showed that the new coating method reduced the risk of thrombosis compared to the conventional coating method. In conclusion, both simulation and in vivo testing demonstrate that our new pre-crimped coating method reduces membrane infolding compared with the conventional dip-coating method and may reduce risk of thrombosis.

Addressing Discrepancies between Experimental and Computational Procedures.

Imaging subject-specific heart valve, a crucial step to its design, has experimental variables that if unaccounted for, may lead to erroneous computational analysis and geometric errors of the resulting model. Preparation methods are developed to mitigate some sources of the geometric error. However, the resulting 3D geometry often does not retain the original dimensions before excision. Inverse fluid-structure interaction analysis is used to analyze the resulting geometry and to assess the valve's closure. Based on the resulting closure, it is determined if the geometry used can yield realistic results. If full closure is not reached, the geometry is adjusted adequately until closure is observed.

Biomechanics of Human Fetal Hearts with Critical Aortic Stenosis.

Critical aortic stenosis (AS) of the fetal heart causes a drastic change in the cardiac biomechanical environment. Consequently, a substantial proportion of such cases will lead to a single-ventricular birth outcome. However, the biomechanics of the disease is not well understood. To address this, we performed Finite Element (FE) modelling of the healthy fetal left ventricle (LV) based on patient-specific 4D ultrasound imaging, and simulated various disease features observed in clinical fetal AS to understand their biomechanical impact. These features included aortic stenosis, mitral regurgitation (MR) and LV hypertrophy, reduced contractility, and increased myocardial stiffness. AS was found to elevate LV pressures and myocardial stresses, and depending on severity, can drastically decrease stroke volume and myocardial strains. These effects are moderated by MR. AS alone did not lead to MR velocities above 3 m/s unless LV hypertrophy was included, suggesting that hypertrophy may be involved in clinical cases with high MR velocities. LV hypertrophy substantially elevated LV pressure, valve flow velocities and stroke volume, while reducing LV contractility resulted in diminished LV pressure, stroke volume and wall strains. Typical extent of hypertrophy during fetal AS in the clinic, however, led to excessive LV pressure and valve velocity in the FE model, suggesting that reduced contractility is typically associated with hypertrophy. Increased LV passive stiffness, which might represent fibroelastosis, was found to have minimal impact on LV pressures, stroke volume, and wall strain. This suggested that fibroelastosis could be a by-product of the disease progression and does not significantly impede cardiac function. Our study demonstrates that FE modelling is a valuable tool for elucidating the biomechanics of congenital heart disease and can calculate parameters which are difficult to measure, such as intraventricular pressure and myocardial stresses.

Experimental Study of Right Ventricular Hemodynamics After Tricuspid Valve Replacement Therapies to Treat Tricuspid Regurgitation.

The increased understanding of right heart diseases has led to more aggressive interventions to manage functional tricuspid regurgitation (FTR). In some cases of FTR, prosthetic valve replacement is typically considered when concomitant organic components or significant geometrical distortions are involved in the pathology of the tricuspid valve. However, little is known of the performance of current devices in the right heart circulation. In this study, a novel in vitro mock circulatory system that incorporated a realistic tricuspid valve apparatus in a patient-specific silicon right ventricle (RV) was designed and fabricated. The system was calibrated to emulate severe FTR, enabling the investigation of RV hemodynamics in pre- and post-implantation of tri-leaflet tissue implant and bi-leaflet mechanical implant. 2D particle imaging velocimetry was performed to visualize flow and quantify relevant hemodynamic parameters. While our results showed all prosthetic implants improved cardiac output, these implants also subjected the RV to increased turbulence level. Our study also revealed that the implants did not create the optimal behavior of fluid transfer in the RV as we expected. Among the implants tested, tissue implant created the most dominant vortices, which persisted throughout diastole; its observed strong negative vortex could lead to increase energy expenditure due to undesired fluid direction. In contrast, both native valve and mechanical implant had both weaker vortex formation as well as more significant vortex dissipation. Interestingly, the vortex dissipation of native valve was associated with streamlined flow pattern that tended towards the pulmonary outlet, while the mechanical implant generated more regions of flow stagnation within the RV. These findings heighten the imperative to improve designs of current heart valves to be used in the right circulation.

Effect of spatial inlet velocity profiles on the vortex formation pattern in a dilated left ventricle.

Despite the advancement of cardiac imaging technologies, these have traditionally been limited to global geometrical measurements. Computational fluid dynamics (CFD) has emerged as a reliable tool that provides flow field information and other variables essential for the assessment of the cardiac function. Extensive studies have shown that vortex formation and propagation during the filling phase acts as a promising indicator for the diagnosis of the cardiac health condition. Proper setting of the boundary conditions is crucial in a CFD study as they are important determinants, that affect the simulation results. In this article, the effect of different transmitral velocity profiles (parabolic and uniform profile) on the vortex formation patterns during diastole was studied in a ventricle with dilated cardiomyopathy (DCM). The resulting vortex evolution pattern using the uniform inlet velocity profile agreed with that reported in the literature, which revealed an increase in thrombus risk in a ventricle with DCM. However the application of a parabolic velocity profile at the inlet yields a deviated vortical flow pattern and overestimates the propagation velocity of the vortex ring towards the apex of the ventricle. This study highlighted that uniform inlet velocity profile should be applied in the study of the filling dynamics in a left ventricle because it produces results closer to that observed experimentally.