Abstract 14379: The Importance of the Muscle and Ventilatory Blood Pumps During Exercise, in Patients Without a Sub-pulmonary Ventricle (Fontan Operation)
Purpose: To better understand the mechanism of stroke volume and cardiac output (Qc) change during exercise in patients with passive total systemic venous blood flow into the pulmonary circulation (Fontan circulation).
Methods: We measured cardiac output (Qc, C2, H2 re-breathing), HR (ECG), oxygen uptake (VO2 by Douglas Bag technique) and ventilation (VE) in 9 patients aged 15.8±6 yrs at 6.1±1.8 yrs after Fontan surgery and 8 individually age and sex matched controls. Data were obtained at 1) rest, 2) after 3 minutes of steady state exercise (Ex) on a cycle ergometer at 50% of individual working capacity, 3) during unloaded cycling at 0 watts (0W: muscle pump alone), 4) during unloaded cycling with isocapnic hyperpnea matching respiratory rate and VE obtained during Ex (0W+H: muscle and ventilatory pump), 5) during Ex plus an inspiratory load (IL) of -12.8+1.5 cm H2O and 6) during Ex plus an expiratory load (EL) of +12.8+ 1.6 cm H2O.
Results: Stroke volume index (SVI) and cardiac index (CI) increased in both groups during submaximal exercise (p<0.04, p<0.001). SVI increased 17% with 0W and an additional 5% with 0W+H in Fontan patients achieving that observed during exercise. In controls, SVI increased 5% with 0W and an additional 8% with 0W+H. With an expiratory load during exercise, SVI was reduced by 13% in Fontan patients without significant change in controls.
Conclusion: In patients with a Fontan circulation, cardiac index and stroke volume increased with exercise primarily as a result of the muscle pump with additional contribution by the ventilatory pump. Increased intrathoracic pressure may play a deleterious role in Fontan circulation by decreasing venous return and stroke volume.
- © 2011 by American Heart Association, Inc.