Design of a cardiovascular simulation circuit driven by time varying elastance

Abstract

Chronic Heart Failure (CHF) is a major cause of death for which only known non-palliative treatment is Heart Transplantation (HTx). Due to donor shortage, only a small cohort of people can be treated. Left Ventricular Assist Devices (LVADs) are widely used to sustain patients on the HTx waiting lists. LVADs are pumps that are implanted between the ventricular apex and ascending aorta, unloading the left ventricle. Before clinical use, LVADs must be thoroughly tested in-vitro, commonly with CardiovascularMockCircuits(CVMCs), forsafetyandefficacy. Thefirststeptodesign a CVMC is mathematical modeling, and validation of its efficacy, stability, robustness and limitations. In this thesis, a zero-dimensional lumped model of the cardiovascular system, consisting of left and right hearts, and systemic, pulmonary and coronary circulations, was established. A novel time-varying elastance generation method, originating from biomechanical characteristics of the myocardium, was created based on previouslypublishedexperimentaldata,andauniqueauxotoniclength-tension-velocity relationship for the myocardial sarcomere was derived. Tension values were converted into ventricular pressures, and controlled with a binary activation signal to introduce myocardial active state. The resulting time course of state variables, load-dependent and -independent performance indexes were observed to be in accordance with the literature. The system showed stability and robustness against external disturbances and parameter variations under various physiological conditions (normal/disease and rest/exercise). In conclusion, the model constituted a very promising simulation platform to test LVAD performance.|Keywords : Cardiovascular mock circuit, Mathematical modeling, Myocardial mechanics, Time-varying elastance, Feedback control.