Oxygen Uptake Efficiency Slope in Coronary Artery Disease: Clinical Use and Response to Training

Abstract The Oxygen Uptake Efficiency Slope (OUES), a new parameter derived from respiratory gas analysis, has been suggested as a submaximal index of cardiopulmonary functional reserve. We evaluated the clinical application and the effect of physical training on the OUES in patients with coronary artery disease (CAD). Maximal cycle-ergometer testing with respiratory gas analysis (breath-by-breath) was performed in 590 patients with CAD and again after three months of physical training in 425 patients. OUES was determined from the linear relation of oxygen uptake (V·O 2 ) vs. the logarithm of pulmonary ventilation (V E ) during exercise, i.e. V·O 2 = a log 10 V E + b, where a is the OUES. The ventilatory anaerobic threshold (VAT) and the slope of the relation of V E ν carbon dioxide production (V·CO 2 ) (V E -V·CO 2 slope) were also determined. Correlation coefficients of the relation from which OUES was derived in individuals averaged 0.975 ± 0.024 (mean ± SD) when calculated from data up to a respiratory gas exchange ratio of 1.0. Submaximal OUES was marginally lower (5.4 ± 7.9 %, p < 0.05) than the OUES calculated from 100 % of respiratory exercise data. Of all submaximal parameters, submaximal OUES (r = 0.837, p < 0.001) and VAT (r = 0.860, p < 0.001) correlated best with peak V·O 2 , followed by V E -V·CO 2 slope (r = - 0.469, p < 0.001). OUES was lower in patients who underwent coronary artery bypass grafting as compared with patients after coronary angioplasty (p < 0.05). Peak V·O 2 and OUES increased significantly (p < 0.001) after training with 24 ± 19.2 % and 20.9 ± 19.3 %, respectively. Changes in peak V·O 2 correlated better with changes in OUES and in VAT (r = 0.61 and r = 0.55, p < 0.001, respectively) than with changes in V E -V·CO 2 slope (r = - 0.171, p < 0.001). The submaximal OUES is clinically useful for the quantification of exercise performance and is sensitive to physical training in patients with CAD.