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Computational Analysis of Flow Structures in Turbulent Ventricular Blood Flow Associated With Mitral Valve
Joel Kronborg1, Frida Svelander1, Samuel Eriksson-Lidbrink1
1Department of Computational Science and Technology, School of Electrical Engineering and Computer Science, KTH Royal Institute of Technology, Stockholm, Sweden.
Insights
Computational models reveal how mitral valve interventions alter heart blood flow, increasing shear stress. This finding is crucial for understanding and preventing thrombosis events in cardiac patients.
Area of Science:
- Cardiovascular dynamics
- Biomedical engineering
- Computational fluid dynamics
Background:
- Cardiac disease and interventions can alter blood flow, increasing thrombosis risk.
- Mechanical forces on blood cells, particularly platelets, influence activation.
- Understanding intraventricular flow mechanics is key to mitigating thrombotic events.
Purpose of the Study:
- To analyze blood flow in the left ventricle using patient-specific data.
- To investigate the impact of mitral valve interventions on intraventricular flow dynamics.
- To differentiate flow structures and their mechanical stimuli on blood cells.
Main Methods:
- Developed a computational model of left ventricular blood flow using Navier-Stokes equations.
- Employed a parameterized model for mitral valve flow and a finite element method for solving equations.
- Utilized triple decomposition of the velocity gradient tensor to analyze flow structures (rotation, strain, shear).
Main Results:
- Mitral valve clip intervention significantly modified intraventricular flow patterns.
- Shear stress increased more in clipped cases compared to untreated cases.
- Reduced valve opening area led to substantial increases in rotation, strain, and particularly shear.
Conclusions:
- Computational analysis provides insights into shear-induced platelet activation.
- The study offers an algorithm to distinguish shear from other flow modalities in the left ventricle.
- Findings can improve models of platelet activation in cardiac conditions and interventions.
Abstract:
Cardiac disease and clinical intervention may both lead to an increased risk for thrombosis events due to a modified blood flow in the heart, and thereby a change in the mechanical stimuli of blood cells passing through the chambers of the heart. Specifically, the degree of platelet activation is influenced by the level and type of mechanical stresses in the blood flow. In this article we analyze the blood flow in the left ventricle of the heart through a computational model constructed from patient-specific data. The blood flow in the ventricle is modelled by the Navier-Stokes equations, and the flow through the mitral valve by a parameterized model which represents the projected opening of the valve. A finite element method is used to solve the equations, from which a simulation of the velocity and pressure of the blood flow is constructed. The intraventricular blood flow is complex, in particular in diastole when the inflow jet from the atrium breaks down into turbulent flow on a range of scales. A triple decomposition of the velocity gradient tensor is then used to distinguish between rigid body rotational flow, irrotational straining flow, and shear flow. The triple decomposition enables the separation of three fundamentally different flow structures, that each generates a distinct type of mechanical stimulus on the blood cells in the flow. We compare the results in a simulation where a mitral valve clip intervention is modelled, which leads to a significant modification of the intraventricular flow. Further, we perform a sensitivity study of the results with respect to the positioning of the clip. It was found that the shear in the simulation cases treated with clips increased more compared to the untreated case than the rotation and strain did. A decrease in valve opening area of 64% in one of the cases led to a 90% increase in rotation and strain, but a 150% increase in shear. The computational analysis opens up for improvements in models of shear-induced platelet activation, by offering an algorithm to distinguish shear from other modalities in intraventricular blood flow.
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