Exercise-induced pulmonary arterial hypertension: a new addition to the spectrum of pulmonary vascular diseases.

Although the complex molecular mechanisms responsible for the vasculopathy of pulmonary artery hypertension (PAH) have only recently begun to be unraveled, it has been recognized for decades that the most significant determinant of both symptoms and survival in PAH is the degree of cardiac impairment that results from the increased right ventricular afterload.1 Exertional dyspnea, the most frequent presenting symptom of PAH,2,3 results from several physiological impairments that are measurable with cardiopulmonary exercise testing and are indicative of impaired right ventricular output during physical activity: (1) an inability to increase O2 transport to tissues during exercise, measured as a decrease in peak V̇O2 compared with normal; (2) premature lactic acidosis, measured as a decrease in the anaerobic threshold, increasing CO2 output and ventilatory drive; and (3) underperfusion of ventilated lung, measured as a high V̇E/V̇CO2 at the anaerobic threshold.4 Unfortunately, exertional dyspnea is a nonspecific complaint, and a definitive diagnosis of PAH is often delayed until signs and symptoms indicative of more advanced degrees of right heart functional impairment are present.