Low-Dose CO2 Inhalation to Improve Oxygenation and Exercise Capacity at High Altitude: A Double-Blind Pilot Study.

BACKGROUND AND

OBJECTIVES

Inhalation of CO2 might improve hypoxia and exercise performance at high altitude by increasing respiratory drive and offsetting hypocapnia. We developed a novel device with minimized dead space and respiratory resistance to deliver CO2 at precise concentrations at high altitude.

METHODS

Twenty-eight healthy lowlanders (aged 38 ± 13 years, male/female: 13/15) were recruited and taken from an altitude lower than 500 m to 4505 m in Tibet by airplane. A randomized double-blind study was performed to compare blood gases and endurance shuttle walk test (ESWT) during inhalation of ambient air and 2.5% CO2 using the device. Arterial blood gases were measured within 4 h of arrival at high altitude, and the ESWT was performed on the morning of the second day after arrival.

RESULTS

Both PaCO2 and PaO2 during CO2 inhalation were significantly higher than during ambient air breathing (PaCO2: 33.5 ± 4.0 vs. 31.4 ± 3.5 mmHg; PaO2: 42.3 ± 5.8 vs. 34.9 ± 5.1 mmHg; all p < 0.001) at high altitude. Compared with ambient air, CO2 inhalation was also associated with a lower heart rate. There was no difference in pH and respiratory rate during inhalation of 2.5% CO2 and ambient air. ESWT distance during inhaling 2.5% CO2 was significantly longer than that during inhalation of ambient air at high altitude (960.0 (713.2-1464.8) m vs. 677.0 (554.2-1026.9) m, p < 0.001).

CONCLUSIONS

Our results suggest that inhalation of 2.5% CO2 increases both PaO2 and exercise performance at 4505 m.

TRIAL REGISTRATION: ClinicalTrials. gov identifier: NCT05798416.