Gas exchange efficiency slopes to assess exercise tolerance in chronic obstructive pulmonary disease

In patients with chronic obstructive pulmonary disease (COPD), the clinical use of the minute ventilation-carbon dioxide production ([Formula: see text] -[Formula: see text] ) slope has been reported as a measure of exercise efficiency, but the oxygen uptake efficiency slope (OUES), i.e., the slope of oxygen uptake ([Formula: see text] ) versus the logarithmically transformed [Formula: see text] , has rarely been reported. We hypothesized that the [Formula: see text] -[Formula: see text] slope is more useful than OUES in clinical use for the pathophysiological evaluation of COPD. Then, we investigated the cardiopulmonary exercise testing parameters affecting each of these slopes in 122 patients with all Global Initiative for Chronic Obstructive Lung Disease (GOLD) COPD grades selected from our database. Compared with the GOLD I-II group (n = 51), peak [Formula: see text] (p