The acute effect of supplemental oxygen during exercise has been shown to differ largely among patients with COPD. It is unknown what the oxygen response is influenced by.
In a randomized and single-blinded fashion, 124 COPD patients underwent one 6-minute walk test on supplemental oxygen (6MWTO2) and one on compressed room air (6MWTRA) after a practice 6MWT. Both gases wedre delivered via standard nasal prongs (2 liters/min). For analyses, patients were stratified based on PaO2 values: (a) 34 patients with resting hypoxemia (HYX), (b) 43 patients with exercise-induced hypoxemia (EIH) and (c) 31 normoxemic patients (NOX) were compared.
Oxygen supplementation resulted in an increase of 6-minute walk distance (6MWD) in the total cohort (+27±42m, p<0.001) and in the subgroups of HYX (+37±40m, p<0.001) and EIH (+28±44m, p<0.001), but not in NOX patients (+15±43m, p=0.065). 42% of HYX and 47% of EIH patients improved 6MWD to a clinical relevant extent (≥30m) by using oxygen. These oxygen responders were characterized by significantly lower 6MWDRA compared to patients without a relevant response (306±106m vs. 358±113m, p<0.05). Although SpO2 was significantly higher during 6MWTO2 compared to 6MWTRA in all 3 subgroups, it dropped below 88% during 6MWTO2 in 73.5% of HYX patients.
In contrast to NOX patients, HYX and EIH generally benefit from supplemental oxygen by increasing exercise capacity. However, less than half of them reached the threshold of clinical relevant improvements. These oxygen responders were characterized by significantly lower exercise capacity levels.