Fig. 3
From: Gas exchange efficiency slopes to assess exercise tolerance in chronic obstructive pulmonary disease
In COPD Global Initiative for Chronic Obstructive Lung Disease (GOLD) III and IV stages, the correlations of oxygen uptake efficiency slope (OUES) (upper panel) and the \(\rm{\dot V}\)E/\(\rm{\dot V}\)CO2 slope (bottom panel) with exertional variables during cardiopulmonary exercise testing classified by oxygen (O2) desaturation level. Correlations of OUES with peak \(\rm{\dot V}\)O2 (a), \(\rm{\dot V}\)E at peak exercise (b), O2 pulse at peak exercise (c), and ΔFO2 at peak exercise (d) are shown. Correlations of the \(\rm{\dot V}\)E/\(\rm{\dot V}\)CO2 slope with peak \(\rm{\dot V}\)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: \(\rm{\dot V}\)O2/heart rate; \(\rm{\dot V}\)E: minute ventilation; \(\rm{\dot V}\)O2: oxygen uptake. Closed triangle and solid line: group with O2 desaturation of 3% or less during exercise (n = 23). Open triangle and dotted line: group with O2 desaturation greater than 3% during exercise (n = 48). The shaded area indicates the CI. The correlation coefficient (r) was obtained in the analysis for each group