In patients with severe COPD who are hypoxemic, use of an automatically titrating O2-system (ATOS) yielded clinical improvements in walking endurance time, SpO2, PO2, and dyspnea, with no impact on PCO2, according to research findings recently published in Thorax.

In the current randomized controlled, crossover clinical trial ( Identifier: NCT03803384), researchers had 50 participants engage in 2 shuttle walking tests (at 85% of maximum pace) on consecutive days in randomized order: 1 with exercise-titrated constant-flow oxygen system; and the other with ATOS aimed at an SpO2 of 92%. The primary outcome was change in endurance exercise capacity as measured by the endurance shuttle walking test.

The investigators found that SpO2 was significantly higher (+3%, P <.001) with ATOS, whereas transcutaneous-PCO2, respiratory rate, and heart rate were similar. Exercise outcomes, PO2 (+8.85 mm Hg), and dyspnea (−0.5 points) were all ameliorated by ATOS (all P <.001), whereas PCO2 was similar.

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Results of the current study build on findings of previous studies that bolster utilization of an ATOS vs a constant flow oxygen system in walking exercise. Compared with other studies, the current study offers methodological robustness with comprehensive sample size calculation and a more realistic SpO2 target for ATOS (ie, 92% SpO2 in this study vs 94% SpO2 in others).  In concordance with clinical guidelines, the investigators used constant flow titration during exercise in lieu of resting titration/standardized constant O2-flow.

The higher walking distance in those with ATOS was similar or more than that of participants in previous studies with resting-titrated/standardized CFOS. The authors suggest that this difference could be due to the larger sample size of the current study or more participants being hypoxemic at rest, thus yielding more consistent effects of the supplemental oxygen administration. The researchers noted no differences in lung function in ATOS responders vs non-responders.

“As exercise-induced changes in PCO2 are highly dependent on several pathophysiological mechanisms in COPD the ability to predict the PCO2 post walking may help clinicians better select patients for ATOS,” state the authors.

Limitations of the current study include a shorter exercise limit, with several participants attaining maximal duration. Other limitations include study of only the immediate vs long-term effects of O2-therapy during walking exercise and not other exercises, as well as limitations with ATOS instrumentation.


Schneeberger T, Jarosch I, Leitl D, et al. Automatic oxygen titration versus constant oxygen flow rates during walking in COPD: a randomised controlled, double-blind, crossover trial. Thorax. 2021;0:1–9. doi:10.1136/thoraxjnl-2020-216509