Effect of an Overnight Stay at 2,500 Meters on Nocturnal Hypoxemia and Sleep-Disordered Breathing in Patients with Pulmonary Vascular Disease: A Randomized Clinical Trial

<b>Rational:</b> Patients with pulmonary vascular disease often reveal nocturnal hypoxemia and sleep apnea. We investigated whether exposure to high altitude worsens those conditions. <b>Methods and Objectives:</b> In a randomized controlled crossover trial, stable patients with pulmonary arterial hypertension or chronic thromboembolic pulmonary hypertension without resting hypoxemia (arterial oxygen pressure, >8 kPa at low altitude) underwent respiratory polygraphy at 470 meters and during an overnight stay at 2,500 meters. Patients with severe hypoxemia (oxygen saturation as measured by pulse oximetry [Sp_O₂], <80% for >30 min) at 2,500 meters received supplemental oxygen therapy (SOT) according to safety criteria. The main outcomes were the number of patients who did not require SOT, the effect of high altitude on nocturnal Sp_O₂, oxygen desaturation index (ΔSp_O₂, ⩾3%), apnea-hypopnea index, and the effect of SOT. <b>Results:</b> Of 27 patients (44% women; 20/7 pulmonary arterial hypertension/chronic thromboembolic pulmonary hypertension; mean ± standard deviation age, 62 ± 14 y), 10 (37%) required SOT during the course of the night (<i>P</i> = 0.008 vs. low altitude). At 2,500 meters versus 470 meters, mean nocturnal Sp_O₂ on ambient air decreased from 91 ± 2% to 83 ± 4% (mean change [95% confidence interval], -8% [-9 to -6]; <i>P</i> < 0.001), time with Sp_O₂ <90% increased from 29 ± 27% to 92 ± 15% (+63% [30 to 92]; <i>P</i> < 0.001), and the oxygen desaturation index increased from 17 ± 14 events/h to 42 ± 26 events/h (+24.8 events/h [12.8 to 36.5]; <i>P</i> < 0.001), but the apnea-hypopnea index remained unchanged. With SOT, Sp_O₂ was restored to values at 470 meters. <b>Conclusions:</b> In stable, low-risk patients with pulmonary vascular disease, altitude worsened nocturnal hypoxemia but not sleep-disordered breathing. The majority of patients did not require SOT according to predefined safety criteria. When needed, SOT restored low-altitude indices of oxygenation. Clinical trial registered with www.clinicaltrials.gov (NCT05089487).