Cardiopulmonary response to exercise in patients with the Fontan circulation

The Fontan circuit is characterized by a pulmonary circulation dependent on central venous pressure in the absence of a subpulmonary ventricle. Patients with this circulation usually exhibit a low cardiac output. In addition to their abnormal cardiac state, recent studies have demonstrated impaired cardiac autonomic nervous activity, elevated neurohormonal factors, and impaired endothelial function, findings also encountered in adults with chronic heart failure. One major component of these impairments is the abnormal cardiorespiratory response during exercise. Despite some pathophysiologic similarities to adults with cardiac disease, those with the Fontan circulation usually have a congenitally malformed heart underscoring abnormal haemodynamics, with further compromise from multiple surgical procedures. It differs in many aspects from the situation in the adults with impaired systolic ventricular function in the setting of chronic cardiac failure. In this review, I will focus on the cardiorespiratory response during exercise, seeking to clarify the characteristics in these particular patients with the Fontan circulation.