Gaetano Burriesci

Mitral valve dynamics in structural and fluid–structure interaction models

Modelling and simulation of heart valves is a challenging biomechanical problem due to anatomical variability, pulsatile physiological pressure loads and 3D anisotropic material behaviour. Current valvular models based on the finite element method can be divided into: those that do model the interaction between the blood and the valve (fluid–structure interaction or ‘wet’ models) and those that do not (structural models or ‘dry’ models). Here an anatomically sized model of the mitral valve has been used to compare the difference between structural and fluid–structure interaction techniques in two separately simulated scenarios: valve closure and a cardiac cycle. Using fluid–structure interaction, the valve has been modelled separately in a straight tubular volume and in a U-shaped ventricular volume, in order to analyse the difference in the coupled fluid and structural dynamics between the two geometries. The results of the structural and fluid–structure interaction models have shown that the stress distribution in the closure simulation is similar in all the models, but the magnitude and closed configuration differ. In the cardiac cycle simulation significant differences in the valvular dynamics were found between the structural and fluid–structure interaction models due to difference in applied pressure loads. Comparison of the fluid domains of the fluid–structure interaction models have shown that the ventricular geometry generates slower fluid velocity with increased vorticity compared to the tubular geometry. In conclusion, structural heart valve models are suitable for simulation of static configurations (opened or closed valves), but in order to simulate full dynamic behaviour fluid–structure interaction models are required.

Fluid-structure interaction study of the edge-to-edge repair technique on the mitral valve

The effect of functional mitral regurgitation has been investigated in an anatomically sized, fluid-structure interaction mitral valve model, where simulated correction has been performed by applying: (1) edge-to-edge repair with annuloplasty and (2) edge-to-edge repair only. Initially defined in an open unstressed/corrected configuration, fluid-structure interaction simulations of diastole have been performed in a rigid ventricular volume. Comparison of the maximum principal stresses (during diastole) in the normal and repaired models has shown that the magnitude of stress in the repaired scenarios is ~200% greater. The combined edge-to-edge and annuloplasty procedure was found to spread the induced stresses across the free margin of the leaflets, whereas without annuloplasty a localised stress concentration in the region of the suture was observed. Fluid flow downstream of the corrected configurations was able to achieve the same magnitude as in the normal case, although the flow rate was impaired. The maximum flow rate was found to be reduced by 44-50% with the peak flow rate shifted from the end of the diastole in the normal case to the start in the repaired cases.

Adaptation and development of software simulation methodologies for cardiovascular engineering: present and future challenges from an end-user perspective.

This paper describes the use of diverse software tools in cardiovascular applications. These tools were primarily developed in the field of engineering and the applications presented push the boundaries of the software to address events related to venous and arterial valve closure, exploration of dynamic boundary conditions or the inclusion of multi-scale boundary conditions from protein to organ levels. The future of cardiovascular research and the challenges that modellers and clinicians face from validation to clinical uptake are discussed from an end-user perspective.