Fig. 2.
In all COPD stages, correlations of the oxygen uptake efficiency slope (OUES) (upper panel) and the 
E/
CO2 slope (bottom panel) with exertional variables during cardiopulmonary exercise testing. Correlations of OUES with peak 
O2 (a), 
E at peak exercise (b), O2 pulse at peak exercise (c), and ΔFO2 at peak exercise (d) are shown. Correlations of the 
E/
CO2 slope with peak 
O2 (e), ΔFO2 at peak exercise (f), and ΔFO2 max. during exercise (g) are shown. ΔFO2: difference between inspired and expired mean oxygen concentrations; ΔFO2 max.: highest ΔFO2 value during exercise; O2 pulse: 
O2/heart rate; 
E: minute ventilation; 
O2: oxygen uptake. Closed circle: Global Initiative for Chronic Obstructive Lung Disease (GOLD) I-II group (n = 51). Open circle: GOLD III-IV group (n = 71). The shaded area indicates the CI. The correlation coefficient (r) was obtained in the analysis of all COPD stages