A Patient-Specific Computational Fluid Dynamic Model for Hemodynamic Analysis of Left Ventricle Diastolic Dysfunctions

Fluid-Structure Interaction Model for Predicting Surgical Result of Total Anomalous Pulmonary Venous Connection and Estimating Pulmonary Venous Properties

OBJECTIVES

To build a fluid-structure interaction model of pulmonary veins with total anomalous pulmonary venous connection, which can be used to predict the result of surgical treatment and at the same time to estimate the elastic properties of pulmonary veins based on patient-specific data and clinic postoperative results.

METHODS

The fluid-structure interaction (FSI) model was used to simulate the anastomosis on pulmonary veins based on computed tomography angiography data collected from three children with total anomalous pulmonary venous connection (TAPVC), supra-cardiac type. The deformation and the stress of anastomosis, and also the velocity of blood flow were calculated in fluid-structure coupling algorithm. During the simulation the variable boundary conditions were applied, including the thickness of vessel wall and the vessel elasticity for which was selected a range of values. The calculation results were finally compared to postoperative results of same patients and discussed. The corresponding outcomes are given in the conclusions section.

RESULTS

The blood flow velocity through the outlet will vary depending on the properties of vessels, including physical properties and thickness of vessel wall. The stress on vessel is lower for smaller values of Young's modulus. The calculated blood flow velocity correlates well with the postoperative results for the Young's modulus of vessels ranging from 0.5 to 1.0 MPa.

CONCLUSIONS

The FSI model has high potential to predict the result of surgery for TAPVC and to estimate the physical properties of pulmonary vein. This model also has potential to guide the strategy for surgical treatment.

Investigation of left heart flow using a numerical correlation to model heart wall motion

A three-dimensional computational fluid dynamics (CFD) method has been developed to model the flow in the left heart including atrium and ventricle. Since time resolution of the medical scans does not fit the requirements of the CFD calculations, the main challenge in a numerical simulation of heart chambers is wall motion modeling. This study employs a novel three-dimensional approximation scheme to correlate the wall boundary and grid movement in systole and diastole. It uses a geometry extracted from medical images in the literature and deformed based on the reported flow rates. The opening and closing of the mitral (MV) and the aortic valve (AV) considered as simultaneous events. Unstructured tetragonal grids were used for the meshing of the domain. The calculation was performed by a Navier-Stokes solver using the arbitrary Lagrange-Euler (ALE) formulation. Results show that the proposed correlation for the wall motion could predict the main features of heart flows.

The effect of chordae tendineae on systolic flow

When using Computational Fluid Dynamics to simulate ventricular blood flow in the heart, it has been common practice to neglect the effect of the sub-valvular apparatus and the trabeculae on the flow conditions. In this study, we analyze the effect of neglecting the chordae tendineae on the fluid flow and pressure drop. To test the assumption we use a previously developed dynamic 3D model of the left ventricle, aorta and valves that is based on 3D echocardiographic recordings. To this model we add the chordae tendineae as a sub-grid model. The previously developed 3D model for the left ventricle during systole is based on real-time three-dimensional echocardiography (RT3DE) recordings of a 30 years old female volunteer. The segmented ventricular wall does not include details of the aorta and the mitral valve, so these were reconstructed. The subgrid model for the flow across the chordae tendineae is based on the Actuator Line Method, which means that they are represented by drag coefficients. The analysis shows that the effect of the chordae tendineae on the pressure drop and work efficiency of the normal heart during systole is minor, and it seems that for simulating ventricular fluid flow and pressure drop during systole, one can follow the current practice and ignore the chordae. However, there can be local effects such as small vortices behind the chordae. Whether such effects are important for a particular application must be evaluated for the given case.

Heart function and hemodynamic analysis for zebrafish embryos

The Zebrafish has emerged to become a powerful vertebrate animal model for cardiovascular research in recent years. Its advantages include easy genetic manipulation, transparency, small size, low cost, and the ability to survive without active circulation at early stages of development. Sequencing the whole genome and identifying ortholog genes with human genome made it possible to induce clinically relevant cardiovascular defects via genetic approaches. Heart function and disturbed hemodynamics need to be assessed in a reliable manner for these disease models in order to reveal the mechanobiology of induced defects. This effort requires precise determination of blood flow patterns as well as hemodynamic stress (i.e., wall shear stress and pressure) levels within the developing heart. While traditional approach involves time-lapse brightfield microscopy to track cell and tissue movements, in more recent studies fast light-sheet fluorescent microscopes are utilized for that purpose. Integration of more complicated techniques like particle image velocimetry and computational fluid dynamics modeling for hemodynamic analysis holds a great promise to the advancement of the Zebrafish studies. Here, we discuss the latest developments in heart function and hemodynamic analysis for Zebrafish embryos and conclude with our future perspective on dynamic analysis of the Zebrafish cardiovascular system. Developmental Dynamics 246:868-880, 2017. © 2017 Wiley Periodicals, Inc.

Physiological mechanisms of pulmonary hypertension

Pulmonary hypertension is usually related to obstruction of pulmonary blood flow at the level of the pulmonary arteries (eg, pulmonary embolus), pulmonary arterioles (idiopathic pulmonary hypertension), pulmonary veins (pulmonary venoocclusive disease) or mitral valve (mitral stenosis and regurgitation). Pulmonary hypertension is also observed in heart failure due to left ventricle myocardial diseases regardless of the ejection fraction. Pulmonary hypertension is often regarded as a passive response to the obstruction to pulmonary flow. We review established fluid dynamics and physiology and discuss the mechanisms underlying pulmonary hypertension. The important role that the right ventricle plays in the development and maintenance of pulmonary hypertension is discussed. We use principles of thermodynamics and discuss a potential common mechanism for a number of disease states, including pulmonary edema, through adding pressure energy to the pulmonary circulation.

Patient-Specific MRI-Based Right Ventricle Models Using Different Zero-Load Diastole and Systole Geometries for Better Cardiac Stress and Strain Calculations and Pulmonary Valve Replacement Surgical Outcome Predictions

Background

Accurate calculation of ventricular stress and strain is critical for cardiovascular investigations. Sarcomere shortening in active contraction leads to change of ventricular zero-stress configurations during the cardiac cycle. A new model using different zero-load diastole and systole geometries was introduced to provide more accurate cardiac stress/strain calculations with potential to predict post pulmonary valve replacement (PVR) surgical outcome.

Methods

Cardiac magnetic resonance (CMR) data were obtained from 16 patients with repaired tetralogy of Fallot prior to and 6 months after pulmonary valve replacement (8 male, 8 female, mean age 34.5 years). Patients were divided into Group 1 (n = 8) with better post PVR outcome and Group 2 (n = 8) with worse post PVR outcome based on their change in RV ejection fraction (EF). CMR-based patient-specific computational RV/LV models using one zero-load geometry (1G model) and two zero-load geometries (diastole and systole, 2G model) were constructed and RV wall thickness, volume, circumferential and longitudinal curvatures, mechanical stress and strain were obtained for analysis. Pairwise T-test and Linear Mixed Effect (LME) model were used to determine if the differences from the 1G and 2G models were statistically significant, with the dependence of the pair-wise observations and the patient-slice clustering effects being taken into consideration. For group comparisons, continuous variables (RV volumes, WT, C- and L- curvatures, and stress and strain values) were summarized as mean ± SD and compared between the outcome groups by using an unpaired Student t-test. Logistic regression analysis was used to identify potential morphological and mechanical predictors for post PVR surgical outcome.

Results

Based on results from the 16 patients, mean begin-ejection stress and strain from the 2G model were 28% and 40% higher than that from the 1G model, respectively. Using the 2G model results, RV EF changes correlated negatively with stress (r = -0.609, P = 0.012) and with pre-PVR RV end-diastole volume (r = -0.60, P = 0.015), but did not correlate with WT, C-curvature, L-curvature, or strain. At begin-ejection, mean RV stress of Group 2 was 57.4% higher than that of Group 1 (130.1±60.7 vs. 82.7±38.8 kPa, P = 0.0042). Stress was the only parameter that showed significant differences between the two groups. The combination of circumferential curvature, RV volume and the difference between begin-ejection stress and end-ejection stress was the best predictor for post PVR outcome with an area under the ROC curve of 0.855. The begin-ejection stress was the best single predictor among the 8 individual parameters with an area under the ROC curve of 0.782.

Conclusion

The new 2G model may be able to provide more accurate ventricular stress and strain calculations for potential clinical applications. Combining morphological and mechanical parameters may provide better predictions for post PVR outcome.

Heart blood flow simulation: a perspective review

Cardiovascular disease (CVD), the leading cause of death today, incorporates a wide range of cardiovascular system malfunctions that affect heart functionality. It is believed that the hemodynamic loads exerted on the cardiovascular system, the left ventricle (LV) in particular, are the leading cause of CVD initiation and propagation. Moreover, it is believed that the diagnosis and prognosis of CVD at an early stage could reduce its high mortality and morbidity rate. Therefore, a set of robust clinical cardiovascular assessment tools has been introduced to compute the cardiovascular hemodynamics in order to provide useful insights to physicians to recognize indicators leading to CVD and also to aid the diagnosis of CVD. Recently, a combination of computational fluid dynamics (CFD) and different medical imaging tools, image-based CFD (IB-CFD), has been widely employed for cardiovascular functional assessment by providing reliable hemodynamic parameters. Even though the capability of CFD to provide reliable flow dynamics in general fluid mechanics problems has been widely demonstrated for many years, up to now, the clinical implications of the IB-CFD patient-specific LVs have not been applicable due to its limitations and complications. In this paper, we review investigations conducted to numerically simulate patient-specific human LV over the past 15 years using IB-CFD methods. Firstly, we divide different studies according to the different LV types (physiological and different pathological conditions) that have been chosen to reconstruct the geometry, and then discuss their contributions, methodologies, limitations, and findings. In this regard, we have studied CFD simulations of intraventricular flows and related cardiology insights, for (i) Physiological patient-specific LV models, (ii) Pathological heart patient-specific models, including myocardial infarction, dilated cardiomyopathy, hypertrophic cardiomyopathy and hypoplastic left heart syndrome. Finally, we discuss the current stage of the IB-CFD LV simulations in order to mimic realistic hemodynamics of patient-specific LVs. We can conclude that heart flow simulation is on the right track for developing into a useful clinical tool for heart function assessment, by (i) incorporating most of heart structures' (such as heart valves) operations, and (ii) providing useful diagnostic indices based hemodynamic parameters, for routine adoption in clinical usage.