The Importance of the Muscle and Ventilatory Blood Pumps During Exercise in Patients Without a Subpulmonary Ventricle (Fontan Operation)

Abstract

The aim of this study was to determine the relative contribution of the muscle and ventilatory pumps to stroke volume in patients without a subpulmonic ventricle. In patients with Fontan circulation, it is unclear how venous return is augmented to increase stroke volume and cardiac output during exercise. Cardiac output (acetylene rebreathing), heart rate (electrocardiography), oxygen uptake (Douglas bag technique), and ventilation were measured in 9 patients age 15.8 ± 6 years at 6.1 ± 1.8 years after Fontan operation and 8 matched controls. Data were obtained at rest, after 3 min of steady-state exercise (Ex) on a cycle ergometer at 50% of individual working capacity, during unloaded cycling at 0 W (muscle pump alone), during unloaded cycling with isocapnic hyperpnea (muscle and ventilatory pump), during Ex plus an inspiratory load of 12.8 ± 1.5 cm water, and during Ex plus an expiratory load of 12.8 ± 1.6 cm water. In Fontan patients, the largest increases in stroke volume and stroke volume index were during zero-resistance cycling. An additional increase with submaximal exercise occurred in controls only. During Ex plus expiratory load, stroke volume indexes were reduced to baseline, non-exercise levels in Fontan patients, without significant changes in controls. With Fontan circulation increases in cardiac output and stroke volume during Ex were due to the muscle pump, with a small additional contribution by the ventilatory pump. An increase in intrathoracic pressure played a deleterious role in Fontan circulation by decreasing systemic venous return and stroke volume.