Exercise Testing and Training in Children With Congenital Heart Disease

Abstract

The primary function of the cardiopulmonary system is to provide blood flow (and oxygen) in quantities sufficient to support the metabolic needs of the body. The capacity of the cardiopulmonary system to fulfill this function is maximally stressed when an individual's metabolic rate is increased, a condition that occurs most commonly during physical activity/exercise. A number of physiological changes accompany and facilitate the accommodation of the circulatory system to the hemodynamic demands of exercise (Figure 1). In normal individuals, these changes (which during upright exercise include a tripling of the resting heart rate, a >60% reduction in systemic and pulmonary vascular resistance, and a >50% increase in stroke volume) can ultimately produce a >5-fold increase in cardiac output. The increase in cardiac output is accompanied by enhanced ventricular preload (as the ventricles move up their Starling curves to accommodate the increased workload), a doubling of systolic and mean pulmonary artery pressures (most of the increase in pulmonary artery pressures is due to the concomitant rise in left-sided filling pressures; the increase in transpulmonary pressure gradient is relatively small), and a more modest increase in systemic arterial pressures.1,–,4 Figure 1. Some of the physiological changes that accompany and facilitate the accommodation of the circulatory system to the hemodynamic demands of exercise. RAp indicates right atrial pressure; LAp, left atrial pressure; PVR, pulmonary vascular resistance; SVR, systemic vascular resistance; PAp, pulmonary artery pressure; and AOp, aortic pressure. Congenital heart disease (CHD) may, in a variety of ways and to a variable extent, adversely affect these hemodynamic adaptations. For instance, patients with a Fontan procedure lack a pulmonary ventricle. They therefore cannot increase their pulmonary blood flow and pressures normally (and consequently cannot maintain their ventricular preload and systemic blood flow) during exercise.5 Patients with tetralogy of Fallot and …