Fig. 4
From: Gas exchange efficiency slopes to assess exercise tolerance in chronic obstructive pulmonary disease
Relationship between oxygen uptake (\(\rm{\dot V}\)O2: mL ⋅ min−1) and minute ventilation (\(\rm{\dot V}\)E: L ⋅ min−1) in (a) GOLD III-IV without exertional desaturation, 3% or less decrease (n = 23) and (b) GOLD III-IV with exertional desaturation, greater than 3% decrease (n = 48). Plots from left to right at rest, at 2 min, and at peak exercise. To see whether it is inappropriate to represent the relationship of \(\rm{\dot V}\)O2 to \(\rm{\dot V}\)E as a line, the dotted line is a straight line connecting the resting and 2-minute plots. GOLD: Global Initiative for Chronic Obstructive Lung Disease. Mean ± standard error. *: p < 0.05 between the non-desaturation and desaturation groups in \(\rm{\dot V}\)E (x-component)