Inhalation of 2.5% CO2 increases arterial oxygen partial pressure and exercise performance at high altitude in healthy lowlanders
In a double-blind pilot study at 4505 m, inhalation of 2.5% CO2 significantly increased PaO2 (42.3 vs. 34.9 mmHg) and PaCO2 (33.5 vs. 31.4 mmHg) compared to ambient air. Endurance shuttle walk test distance was also significantly longer with CO2 inhalation (960.0 m vs. 677.0 m).
Evidence Score
Study Evidence
Study 1. Low-Dose CO2 Inhalation to Improve Oxygenation and Exercise Capacity at High Altitude: A Double-Blind Pilot Study.
observationalLiang S, Catcheside P, Wellman A, Wu L, Wang L, Steier J, He B, Schwartz AR, Eckert DJ, Luo Y · Respirology (Carlton, Vic.) (2026)
Result:
Mechanism Graph
Limitations
- ⚠Small sample size (n=28) limits generalizability
- ⚠Pilot study design with no long-term follow-up or safety data
Frequently Asked Questions
Does inhaling CO2 at high altitude improve oxygen levels?▼
Yes, the study found that inhaling 2.5% CO2 significantly increased PaO2 from 34.9 to 42.3 mmHg at 4505 m.
What was the effect on exercise performance?▼
Endurance shuttle walk test distance increased from 677.0 m with ambient air to 960.0 m with 2.5% CO2 inhalation.
Was there any change in heart rate or breathing rate?▼
Heart rate was lower with CO2 inhalation, but there was no significant difference in respiratory rate or pH.
Is this a safe intervention for high altitude?▼
The study was a short-term pilot with no reported adverse events, but larger studies are needed to confirm safety.
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References
- 1.Liang S, Catcheside P, Wellman A, Wu L, Wang L, Steier J, He B, Schwartz AR, Eckert DJ, Luo Y. "Low-Dose CO2 Inhalation to Improve Oxygenation and Exercise Capacity at High Altitude: A Double-Blind Pilot Study.." Respirology (Carlton, Vic.), 2026. PMID: 42429551 DOI: 10.1002/resp.70278