Background Many patients with the obstructive sleep apnoea syndrome (OSA) travel to the mountains for recreational and professional activities while temporarily discontinuing continuous positive airway pressure (CPAP) treatment. A study was undertaken to evaluate the hypothesis that altitude would aggravate their hypoxaemia, sleep-related breathing disturbances and impair daytime performance. Methods Thirty-four patients with OSA of median age 62 years (IQR 57e65), median apnoea/hypopnoea index (AHI) 47.5 events/h (IQR 32.4e72.8), residing at <600 m were enrolled. A crossover trial randomised for the sequence of altitude exposure was carried out: patients spent 1 day in Zurich (490 m) and 4 days in the Swiss Alps at 1860 m and 2590 m (2 days each) during which continuous positive airway pressure was discontinued. Daily evaluations included polysomnography, symptom questionnaires, physical examination and driving simulator tests. Results Polysomnography revealed median oxygen saturations at 490 m and in the first and second nights at 1860 and 2590 m, respectively, of 94%, 90%, 90%, 86% and 87% (p<0.01 between altitudes). Corresponding median AHI were 47.5, 85.1, 74.6, 90.0 and 90.9 events/h (p<0.01 between altitudes) with ratios of central to obstructive events of 0.1, 0.8, 1.0, 1.9 and 1.9 (p<0.01 between altitudes). Tracking performance during simulated driving was significantly impaired at 2590 m compared with 490 m. Systolic blood pressure and cardiac arrhythmias were increased at altitude. Conclusions Altitude exposure in untreated patients with OSA aggravates hypoxaemia, increases sleeprelated breathing disturbances due to frequent central apnoeas/hypopnoeas, impairs driving simulator performance and induces cardiovascular stress. These findings have implications for counselling and treating patients with OSA planning to travel to high altitude. ClinicalTrials.gov identifier NCT00514826.

AIMS: Data on sleep at altitude are scant due to the limited availability of polysomnography. Therefore, we investigated whether actigraphy might serve as a simple tool for monitoring sleep during altitude field studies. METHODS: Fourteen mountaineers participating in studies on dexamethasone prophylaxis of high altitude pulmonary edema were monitored by actigraphy and polysomnography during 1 night at Zurich (490 m) and 4 nights at the Regina Margherita hut (4559 m). Total sleep time (TST) estimated by actigraphy was compared to polysomnography and subjective sleep quality. RE-SULTS: In 64 comparisons, mean differences±2SD (bias±limits of agreement) between actigraphy and polysomnography were 5±35 min for TST and 1±7% for sleep efficiency. Correlations between subjective and polysomnographic estimates of sleep efficiency and sleep latency were nonsignificant. Medians of nocturnal oxygen saturation were 96% at 490 m and 74%-81% during nights 1 to 4 at 4459 m (p<0.05 vs. 490 m). Medians of polysomnographic TST were similar at 490 m (451 min) and 4559 m (377-456 min during nights 1 to 4, p=NS) but the proportions of slow wave and REM sleep were reduced and arousals were more common (p<0.05 all instances). CONCLUSION: Actigraphy accurately estimates sleep efficiency and duration. Due to its portability and simple use and the potential application over several weeks, it is a convenient tool for investigating altitude effects on sleep during field studies. Methods: Fourteen mountaineers participating in studies on dexamethasone prophylaxis of high altitude pulmonary edema were monitored by actigraphy and polysomnography during 1 night at Zurich (490 m) and 4 nights at the Regina Margherita hut (4559 m). Total sleep time (TST) estimated by actigraphy was compared to polysomnography and subjective sleep quality. Results: In 64 comparisons, mean differences -2SD (bias -limits of agreement) between actigraphy and polysomnography were 5 -35 min for TST and 1 -7% for sleep efficiency.Correlations between subjective and polysomnographic estimates of sleep efficiency and sleep latency were nonsignificant. Medians of nocturnal oxygen saturation were 96% at 490 m and 74%-81% during nights 1 to 4 at 4459 m (p < 0.05 vs. 490 m). Medians of polysomnographic TST were similar at 490 m (451 min) and 4559 m (377-456 min during nights 1 to 4, p = NS) but the proportions of slow wave and REM sleep were reduced and arousals were more common (p < 0.05 all instances). Conclusion: Actigraphy accurately estimates sleep efficiency and duration. Due to its portability and simple use and the potential application over several weeks, it is a convenient tool for investigating altitude effects on sleep during field studies.