MULTI-SCALE MODELING OF THE FONTAN CIRCULATION USING A MOCK CIRCULATORY SYSTEM

The Fontan circulation is the result of a series of operations performed to save the lives of children born with univentricular circulations. The Fontan procedure achieves venous return to the pulmonary circulation without a ventricular power source. The load on the heart is reduced to normal, and these patients can lead a normal life into adulthood, although late complications continue to prevent normal lifespan. A unique feature of the Fontan circulation is the dependency of inferior vena cava flow on respiration. The Fontan circulation has been modeled experimentally using an adjustable mock circulatory system, which for the first time includes the influence of respiration. A multi-scale model based on a realistic, 3D patient-specific test section coupled with a lumped parameter model tuned to patient-specific parameters is used to simulate the pressure and flow found in the Fontan circulation. For the first time, the clinically observed respiratory effects in TCPC venous physiology were successfully simulated in an experimental model, where venous flow increased during inspiration and decreased during expiration. Clinically observed hepatic vein flow reversal was also seen in the model. This reverse flow was accentuated when the pulmonary vascular resistance was increased on the venous side

Mock Circulatory System of the Fontan Circulation to Study Respiration Effects on Venous Flow Behavior

We describe an in vitro model of the Fontan circulation with respiration to study subdiaphragmatic venous flow behavior. The venous and arterial connections of a total cavopulmonary connection (TCPC) test section were coupled with a physical lumped parameter (LP) model of the circulation. Intrathoracic and subdiaphragmatic pressure changes associated with normal breathing were applied. This system was tuned for two patients (5 years, 0.67 m2; 10 years, 1.2 m2) to physiological values. System function was verified by comparison to the analytical model on which it was based and by consistency with published clinical measurements. Overall, subdiaphragmatic venous flow was influenced by respiration. Flow within the arteries and veins increased during inspiration but decreased during expiration, with retrograde flow in the inferior venous territories. System pressures and flows showed close agreement with the analytical LP model (p < 0.05). The ratio of the flow rates occurring during inspiration to expiration were within the clinical range of values reported elsewhere. The approach used to set up and control the model was effective and provided reasonable comparisons with clinical dat