Exercise-Induced Pulmonary Hypertension Translating Pathophysiological Concepts into Clinical Practice

Exercise stress testing of the pulmonary circulation for the diagnosis of latent or early stage pulmonary hypertension is gaining acceptance. There is emerging consensus to define exercise-induced pulmonary hypertension by a mean pulmonary artery pressure higher than 30 mmHg at a cardiac output of less than 10 L/min and a total pulmonary vascular resistance higher than 3 Wood units at maximum exercise, in the absence of pulmonary hypertension at rest. Exercise-induced pulmonary hypertension has been reported in association with a bone morphogenetic receptor-2 gene mutation, in systemic sclerosis, in left heart conditions, in chronic lung diseases and in chronic pulmonary thrombo-embolism. Exercise-induced pulmonary hypertension is a cause of decreased exercise capacity, may precede the development of manifest pulmonary hypertension in a proportion of patients, and is associated with a decreased life expectancy. Exercise stress testing of the pulmonary circulation has to be dynamic and rely on measurements of the components of the pulmonary vascular equation during, not after exercise. Noninvasive imaging measurements may be sufficiently accurate in experienced hands, but suffer from lack of precision, so that invasive measurements are required for individual decision making. Exercise-induced pulmonary hypertension is caused either by pulmonary vasoconstriction, pulmonary vascular remodeling or by increased upstream transmission of pulmonary venous pressure. This differential diagnosis is clinical. Left heart disease as a cause of exercise-induced pulmonary hypertension can be further ascertained by a pulmonary artery wedge pressure above or below 20 mmHg at a cardiac output below 10 L/min or a pulmonary artery wedge pressure-flow relationship above or below 2 mmHg/L/min during exercise.