Impact Of Nocturnal Oxygen Enrichment On High Elevation Acclimatization

To offset sleep disturbances at terrestrial altitude during acclimatization, those operating at high elevations occasionally use nocturnal oxygen enrichment. However, deliberately dampening the hypoxic stimulus for acclimatization may limit adaptations. PURPOSE: Determine the impact of nocturnal oxygen enrichment on altitude acclimatization. METHODS: 22 males were assigned to sleep with (O2+, 32.3 ± 2.5% O2) or without (O2-, 20.8 ± 0.1% O2) nocturnal oxygen enrichment. An 8-day acclimatization protocol occurred at a field-based research site with access to sea level (0 m), sleeping dormitories (2800 m), and a hikeable route to 4200 m. Participants were housed at 2800 m and completed 5 daily hikes of 10.4 ± 1.2 km with 1371.5 ± 145.1 m of gain. To assess acclimatization, testing occurred on Day 0 at 0 m and Days 1, 4, and 7 at 2800 m to evaluate vastus lateralis muscle oxygenation (oxygenated hemoglobin, O2Hb; deoxygenated hemoglobin, HHb), arterial oxygen saturation (SPO2), heart rate (HR), and expired gases at rest and during a 5-min cycling bout (1.75 W·kg-1). RESULTS: Total sleep was longer in the O2+ (452 ± 63 min) than the O2- group (427 ± 63, p = 0.028). Accordingly, the O2+ group had a higher overnight SPO2 (96 ± 1, 91 ± 2%, p < 0.001) and lower overnight heart rate (48 ± 5, 57 ± 10 beat·min-1, p < 0.001) than the O2- group. However, no other group differences were noted at rest, while cycling, or on any acclimatization day. ∆O2Hb did not differ between the O2+ (-2.2 ± 2.4 A.U.) and O2- groups (-1.6 ± 2.6 A.U., p = 0.426). ∆HHb did not differ between the O2+ (4.2 ± 4.8 A.U.) and O2- groups (3.4 ± 3.8 A.U., p = 0.643). SPO2 did not differ between the O2+ (91 ± 5%) and O2- groups (91 ± 5%, p = 0.416). HR did not differ between the O2+ (86 ± 29 beats·min-1) and O2- groups (91 ± 31 beats·min-1, p = 0.744). Respiratory exchange ratio did not differ between the O2+ (0.74 ± 0.27) and O2- groups (0.84 ± 0.08, p = 0.360). CONCLUSION: Nocturnal oxygen enrichment during terrestrial altitude acclimatization promoted longer total sleep but did not hinder short-term acclimatization when partaking in daily prolonged exercise at high elevation. Supported by a U.S. Air Force Research Laboratory grant (FA8650-19-C6124). Supported by a U.S. Air Force Research Laboratory grant (FA8650-19-C6124).