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).
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Inhalation of 2.5% CO2 increases arterial oxygen partial pressure and exercise performance at high altitude in healthy lowlanders The current body of evidence comprises 1 study, including 1 randomized controlled trial. EvidenceHub rates the overall confidence at 42/100 (low).
The Claim
Inhalation of 2.5% CO2 increases arterial oxygen partial pressure and exercise performance at high altitude in healthy lowlanders
This conclusion is most relevant to: 28 healthy lowlanders (aged 38 ± 13 years, 13 male/15 female) transported from <500 m to 4505 m in Tibet.
What the Research Shows
The conclusion draws on 1 linked study. Highlights from the cited literature:
- ▸Low-Dose CO2 Inhalation to Improve Oxygenation and Exercise Capacity at High Altitude: A Double-Blind Pilot Study. (Respirology (Carlton, Vic.), 2026) —
How It Works
The proposed biological pathway:
- ▸Inhalation of CO2 increases respiratory drive
- ▸Offsetting hypocapnia at high altitude
- ▸Increased PaCO2 and PaO2
- ▸Improved exercise performance
Who Might Benefit
Evidence fit by population:
- ▸28 healthy lowlanders (aged 38 ± 13 years, 13 male/15 female) transported from <500 m to 4505 m in Tibet
Recommended Dose
2.5% CO2 in inhaled air
Limitations & Caveats
Important context when interpreting this evidence:
- ▸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.
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