IMPROVING THE MODELLING OF POSITIVE DISPLACEMENT HEARTS USING A FLUID-STRUCTURE INTERACTION APPROACH

For those suffering from biventricular heart failure, where a heart transplant is not viable, a total artificial heart is a feasible alternative. The Realheart®, developed by Scandinavian Real Heart, mimics the mechanics of the native heart by vertical translation of an atrioventricular (AV) plane. Previous numerical models of the Realheart® were not flow-driven but relied on prescribed motion of AV and semilunar (SL) valves. This tended to overestimate device output and limited the operating conditions that could be simulated. This study's objective was to develop a new modelling strategy, combining computational fluid dynamics and fluid-structure interactions, that generalised the pumping mechanics of the Realheart®. Initially, only the essential and most challenging features will be modelled before proceeding to whole device simulation.
Fluent (Ansys Inc, Canonsburg Pennsylvania, USA, Version 2020 R2) was used to model a fluid cylinder containing two bileaflet mechanical heart valves aligned in series, representing the AV (upstream) and SL (downstream) valves. Constant pressures of 15 and 70 mmHg were applied on the inlet and outlet respectively, and the Navier-Stokes equations were solved assuming Newtonian rheology. The resistance of the downstream vasculature was represented using a 5 mm diameter restriction, placed upstream of the outlet. Overset meshing was used, allowing for a refined mesh around the boundary of the leaflet valves. The 6 degrees of freedom solver computed the leaflet rotation using the forces and moments exerted by the fluid. A vertical sinusoidal translation was applied to the AV overset mesh zone, achieving both rotational and translational motion of the AV valve.
The modelling strategy successfully achieved flow-driven valve motion, with the SL valve opening upon downward translation of the AV plane, and closing upon upward translation of the AV plane, due to backflow through the domain. The restriction caused accurate pressure build-up within the model, but backflow caused a fluid jet that was not physiologically realistic. Future work will implement a Windkessel model, replacing the restriction, to better capture physiological flow conditions. The generalised nature of the model will allow efficient investigations into the interplay between different stroke parameters, efficiency, and valve leakage.