[Study of dyspnea by the pneumologist: methodology and functional approach].

Dyspnea is presently considered to be related to the sense of effort made by the inspiratory muscles. It may appear under three different sets of clinical circumstances: increase in ventilatory load (obstructive syndrome, restrictive syndrome); increase in minute ventilation (exercise, hyperventilation, disorder of respiratory gas exchanges); muscle weakness (myasthenia, myopathies). The functional approach is based on history and physical examination of the patient, as well as on simple routine tests such as spirometry and blood gases. Exercise test (ergospirometry) represents the most sensitive and reliable tool in differentiating between the numerous etiologies of dyspnea. Respiratory and cardiocirculatory causes of dyspnea can usually be distinguished on the basis of the pulmonary gas exchanges and oxygen consumption at maximal exercise, and on determination of the anaerobic threshold. Thus, dyspnea of unknown origin, i.e. with normal spirometric tests, should be investigated using a maximal exercise test with gas exchanges. Indication for right heart catheterization should be limited to the rare cases of severe pulmonary hypertension.