The influence of O ₂ on exercise capacity (6-minute-walking-distance, 6MWD) in COPD

We investigated the additional effect of supplemental oxygen on 6MWD in severe COPD-patients. The aim of the study was to find out if the response to nasal oxygen during 6-minute-walking-test (6MWT) depends on the level of exercise capacity. To identify characteristics of patients with high oxygen response, we defined patients as “O 2 - Responder” if they increase their 6MWD by ≥ 35m due to oxygen supply. 111 COPD-patients (age: 63,5y±8,7; FEV 1 : 35,9%pred.±11,6; m:f=65:46) took part in a randomized, single-blinded, prospective study. The patients underwent a 6MWT pretest followed by 2 6MWT either on 2L oxygen or on medical air (MA). After 3 week rehabilitation including resistance- and endurance-training both tests were repeated. We measured lung function before and after rehabilitation, SpO 2 , paO 2 , paCO 2 and BORG-scale before and after every 6MWT. The difference between 6MWD O2 and 6MWD MA (O 2 -response) was greater pre (Δ=7,16%) than post rehabilitation (Δ=3,25%). Separating patients in 2 groups, O 2 -response was significantly higher in patients with 6MWD<349m (p<0,05). With increasing 6MWD from pre to post rehabilitation O 2 -Response decreases (r=0,52, p=0,001). “O 2 -Responders” were characterized by: lower FEV 1 % pred. (p<0,01), higher paCO 2 (before and after 6MWT; p<0,01), higher levels of dyspnea (p=0,01) and lower SpO 2 (after 6MWD). We detected a negative relationship between O 2 -response and exercise capacity. “O 2 -Responders” showed lower FEV 1 and higher limitations during exercise. We speculate that training therapy improves muscle oxygen-efficiency and increases exercise capacity even without oxygen supply with the consequence that supplemental oxygen becomes less important.