A randomized double-blind crossover pilot study evaluated inhalation of 2.5% CO₂ (via a novel low-dead-space device) vs. ambient air in 28 healthy lowlanders acutely exposed to 4505 m altitude in Tibet, measuring arterial blood gases and endurance shuttle walk test (ESWT) distance.
CO₂ inhalation significantly raised PaO₂ (42.3 vs. 34.9 mmHg, p<0.001) and PaCO₂ (33.5 vs. 31.4 mmHg, p<0.001), and increased ESWT distance (960 m vs. 677 m, p<0.001) compared with ambient air, with no change in pH or respiratory rate.
Small pilot sample (n=28); results apply only to acute high-altitude exposure (within ~24–48 h), not prolonged stays; all participants were healthy lowlanders, limiting generalizability to patients with cardiopulmonary disease or acclimatized individuals.
Low-dose CO₂ inhalation (2.5%) via a purpose-built device may offer a simple, drug-free way to acutely improve oxygenation and physical capacity at very high altitude, but larger trials are needed before clinical adoption.
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