Hyperreactivity of Pulmonary Vasculature in Children With Pulmonary Hypertension at Altitude and the Importance of the Prolonged Hyperoxia Test (O 2 Test)

Pulmonary hypertension (PH) is defined hemodynamically, but pulmonary vascular reversibility may provide additional prognostic information, particularly in children exposed to chronic hypobaric hypoxia. We retrospectively analyzed 85 patients diagnosed with PH during childhood at high altitude in Bogotá, Colombia (2,640 m). Seventy‐seven underwent cardiac catheterization and 78 underwent a prolonged hyperoxia test (O 2 Test), consisting of supplemental oxygen at FiO 2 > 0.80 for 4–24 h with echocardiographic assessment of pulmonary artery systolic pressure (PASP). A > 20% reduction in baseline PASP was considered a positive response. Seventy‐two patients (84.7%) had severe PH. Among the 78 patients undergoing O 2 Testing, 49 (62.8%) had a positive response. Patients with a positive O 2 Test were younger at diagnosis than nonresponders (median, 2 vs. 7 years; p = 0.0061), had lower mean pulmonary artery pressure (55 vs. 83 mmHg; p = 0.0047), and were more frequently in World Health Organization functional class I–II. A negative O 2 Test was substantially more frequent among patients who died than among survivors (74.1% vs. 17.6%; p < 0.001). Patients with the longest follow‐up were predominantly diagnosed before 3 years of age and demonstrated preserved pulmonary vascular reactivity. These findings suggest that pulmonary vascular reactivity to prolonged hyperoxia is associated with age at diagnosis, hemodynamic severity, functional status, and long‐term outcome in children with PH living at high altitude. The O 2 Test may provide complementary information to conventional acute vasoreactivity testing in this population.