The Physiological and Altitude Lowering Effects of Different Supplemental Oxygen Flow Rates at Extreme Simulated Altitude: A Pilot Study

Wakeham, Denis J, Andrew R Tomlinson, Giorgio Manferdelli, Matthew M Howrey, Anna K Geib, Murugappan Ramanathan, Marcus Payne, Renie Guilliod, James Berry, Tony G Babb, Peter Hackett, Benjamin D Levine, and Christopher M Hearon. The Physiological and Altitude Lowering Effects of Different Supplemental Oxygen Flow Rates at Extreme Simulated Altitude: A Pilot Study. <i>High Alt Med Biol.</i> 00:00-00, 2025. <b><i>Background:</i></b> Approximately 80% of high-altitude climbers use supplemental oxygen >8,000 meters, yet optimal dosing strategies have not been established. <b><i>Methodology:</i></b> Therefore, in six unacclimatized individuals (34 ± 8 years; 2 F/4 M), we quantified the effects of supplemental oxygen flow rates (6, 4, 2, 1 and 0 L/min) using the SUMMIT Oxygen mask at 282 mmHg (rest and cycle ergometry: 60 and 120 Watts) and 253 mmHg (rest only) barometric pressure in a hypobaric chamber. We measured oxygen saturation (SpO₂) and gas fractions in the mask during 4-minute exposures to each flow rate. <b><i>Results:</i></b> Resting at 282 mmHg, SpO₂ (6 L/min: 99% ± 0%; 0 L/min: 70% ± 8%, <i>p</i> < 0.001) and mean inspired oxygen fraction decreased (6 L/min: 65.87% ± 14.11%; 0 L/min: 21.50% ± 0.44%, <i>p</i> < 0.001) with lowering of supplemental oxygen. Exercise further decreased SpO₂ and oxygen fractions across all flow rates at 282 mmHg. At 253 mmHg, SpO₂ followed a similar trend to data collected at 282 mmHg (6 L/min: 96% ± 2%; 4 L/min: 93% ± 3%; 2 L/min: 87% ± 3%; 1 L/min: 71% ± 0%; 0 L/min: 66% ± 9%). Furthermore, at rest at 253 mmHg, 2 L/min of supplemental oxygen lowered the equivalent altitude to 4,489 meters. <b><i>Conclusion:</i></b> All unacclimatized participants were able to tolerate 253 mmHg at rest on as little as 2 L/min of supplemental oxygen.