Modeling the Fontan circulation: a computer simulation of the effects of respiration

"Fontan" is a generic term applied to numerous surgical procedures that separate the systemic and pulmonary circuits in patients with only one functional ventricle. Two options are the total cavopulmonary repair (TCP=the inferior and superior vena cava connected directly to the pulmonary arteries) and an atriopulmonary shunt (AP=the right atrium connected to the main pulmonary artery via an anastomosis or an extracardiac shunt). The advantage of the AP repair is thought to be the pumping power of the right atrium. The advantage of the TCP repair is the exclusion of chambers that set up areas of flow recirculation and stagnation. To study the global effects of these alterations, computer simulations of the entire cardiovascular system of a one-year old child under normal, TCP and AP flow conditions have been performed. This report focuses on the effects of respiration parameters: rate, baseline pressure, average pressure, inspiratory time, mean pressure, and inspiratory and expiratory time constants. Results are consistent with those observed in animal models. Fontan circulations are more sensitive to parameter changes and demonstrate different optimal values.