Bond Graph Modeling of Mechanical Circulatory Support Device - Cardiovascular System Interactions

Though mechanical circulatory support (MCS) devices, such as ventricular assist devices and total artificial hearts (TAH), provide heart failure patients with bridges to heart transplantation or are alternatives to transplantation, device performance, and corresponding control strategies are often difficult to evaluate. Difficulties arise due to the complex interaction of multiple domains - i.e., biological, hydraulic, hemodynamics, electromechanical, system dynamics, and controls. In an attempt to organize, integrate and clarify these interactions, a technique often used in hydraulic pump design and robotics, called "bond graph modeling," is applied to describe the performance and functionality of MCS devices and the interaction between the cardiovascular (CV) system and the MCS device. This technical brief demonstrates the advantages of this tool in formulating a model for the systemic circulation interacting with the left side of a TAH, adopting the fundamental structure of either a hydraulic mechanism (i.e., AbioCor/Carmat) or a pneumatic mechanism (i.e., SynCardia), combined with a systemic circulation loop. The model captures the dynamics of the membrane, the hydraulic source or pneumatic source, and the systemic circulation. This multidisciplinary cross-pollination of an analytical tool from the field of dynamic systems may provide important insight to further aid and improve the design and control of future MCS systems.