Search

The paper presents a multi-physics and multi-scale modeling approach on the closure dynamics of a bileaflet prosthetic heart valve. The modeling methodology consists of coupling a multi-scale model of the left ventricle contraction to a 3D CFD-FSI model, in order to investigate the closure of a cavity pivot bileaflet valve. The rebound motion of the valve is also modeled. The potential of the valve to generate thrombogenic and cavitation effects are assessed on the basis of the duration for which the blood flow is exposed to elevated wall shear stress, large negative pressure transients and increased flow vorticity. A special attention is given to the flow field in the hinge region of the valve.

Primary percutaneous coronary intervention is effective in opening the infarct-related artery in patients with myocardial infarction with ST-segment elevation. However, the embolization of athero-thrombotic debris induces micro vascular obstruction and diminishes myocardial reperfusion. The aspiration catheter’s design, the coronary anatomy and the physical properties of the thrombi are key factors in ensuring a successful interventional procedure.

Coronary artery diseases are at present commonly treated by minimally invasive treatment such as intravascular stents. However, such treatment is compromised by in-stent restenosis, a re-narrowing of the artery related to the injury of the vessel wall as a result of the local stress caused by the stent struts. The aim of this study is to develop a computational model to represent this tissue growth in a finite element model of a stented coronary artery.

In this study numerical simulation is carried out to investigate cardiovascular response under the support of a displacement pump type ventricular assist device (VAD). The native cardiovascular system model employed in this study is a simplified version of a published system model, and the VAD is characterized by prescribed flow-rate changes in the VAD inlet and outlet. The CellML markup language is used for the description of the numerical model, and the resulting model is executed in the PCEnv simulation environment for the calculation of cardiac responses. Simulation results show that the VAD provides satisfactory support to the diseased heart. CellML, combined with PCEnv, provides a flexible and cohesive environment for the description of models represented by systems of ordinary differential equations, and thus facilitates the study of the dynamics of the circulation.

Patterns in normal abdominal movement captured with medical imaging can be recognised by a trained radiologist but the process is time consuming. Abdominal adhesions present a diagnostic problem in which the radiologist is asked to detect abnormal movement that may be indicative of pathology. This paper postulates that the use of image analysis can augment the diagnostic abilities of the radiologist in respect of adhesions. Proof of concept experiments were conducted in-silico to explore the effectiveness of the technique. The results indicate that trained participants are accurate in their assessment of abnormalities when supplied with additional information from image analysis techniques. However without the additional information, participants made incorrect diagnoses on many occasions. ROC methods were used to quantify the outcomes of the in-silico experiment.

To better understand the flow pattern and the mechanical environment induced by the single leaflet mechanical heart valves, both experimental and theoretical studies have been conducted. A pulse duplicator was used for driving two mechanical heart valves (Medtronic Hall and Omniscience) and a high speed video camera (500 frames per second) tracked their motion. Several tests, at different heart rates and cardiac outputs (stroke volumes) have been performed. Using a 2D image segmentation tool, developed in Matlab, the information about the instantaneous position of the valve was extracted from each frame of the video data. The pressure drop across the valve and the transvalvular flow has also been measured. The experimental results were in good agreement with the theoretical ones, previously obtained and reported by the authors.

A newly developed lumped parameter model of the left ventricle contraction and a computational fluid dynamics (CFD) representation of the fluid structure interaction (FSI) of a single leaflet mechanical heart valve are coupled to investigate the cavitation potential of a single leaflet prosthetic heart valve. The left ventricle model gives a “more-realistic” representation of the cardiac muscle contraction, from the level of the contractile proteins, up to the hemodynamics of the whole ventricle. A commercial finite volume CFD code (ANSYS-CFX) is coupled to the lumped parameter ventricle model through the inlet and outlet boundary conditions. Cavitation potential is evaluated from the negative pressure gradients occurring on the surface of the occluder and vortex formations adjacent to its atrial aspect.

Computer simulations play an increasingly important role in the area of Medical Physics, from fundamental research to patient specific treatment planning. One particular application we address in this paper is the simulation of blood flow and clotting, in both synthetic model geometries and domains created from medical images (in particular, magnetic resonance imaging — MRI and computed tomography — CT). Our focus is on the efficient implementation of the lattice Boltzmann method for this type of medical application, particularly the clotting process.

This work encompasses together a number of diverse disciplines (physiology, biomechanics, fluid mechanics and simulation) in order to develop a predictive model of the behaviour of a prosthetic heart valve in vivo. The application of simulation, for the study of other cardiovascular problems, such as blood clotting is also discussed. A commercial, finite volume, computational fluid dynamics (CFD) code (ANSYS/CFX) is used for the 3D component of the model. This software provides technical options for advanced users which allow user-specific variables to be defined that will interact with the flow solver. User-defined functions and junction boxes offer appropriate options to facilitate multi-physics and multi-scale complex applications. Our main goal is to present a 3D model using the internal features available in ANSYS/CFX coupled to a multiscale model of the left ventricle to address complex cardiovascular problems.