Clinical relevance of autonomic nervous system disturbances in pulmonary arterial hypertension.

In their editorial, R. Naeije and P. van de Borne discuss the cause of exercise hyperventilation in PAH, as well as in patients with congestive heart failure, and attribute it mainly to an increased chemosensitivity on the basis of some previous inert gases studies. In fact, three factors determine the ventilatory response to exercise, 1) the CO2 production, 2) the ratio of physiological dead space (VD) to tidal volume (VT), VD/VT, 3) the arterial CO2 tension or set point. By analysing each factor in quantitative terms, it is possible to determine the role of each in the high ventilatory response observed in patients during exercise without the help of a costly technique.