Respiratory Determinants of Exercise Limitation: Focus on Phrenic Afferents and the Lung Vasculature.

We examine 2 means by which the healthy respiratory system contributes to exercise limitation. These include the activation of respiratory and locomotor muscle afferent reflexes, which constrain blood flow and hasten fatigue in both sets of muscles, and the excessive increases in pulmonary vascular pressures at high cardiac outputs, which constrain O2 transport and precipitate maladaptive right ventricular remodeling in endurance-trained subjects.