Fig. 1.

Calculation of OUES. a) The relationship between oxygen uptake (_O2: mL ⋅ min⁻¹) and the common logarithm of minute ventilation (_E: L ⋅ min⁻¹) (b) the relationship between _O2 (mL ⋅ min⁻¹) and _E (L ⋅ min⁻¹). _O2 and _E obtained from breath-by-breath gas-exchange measurements in one COPD patient with GOLD I (75 years old, 64.2 kg) were used. OUES was calculated as the slope of the regression line relating _O2 (mL ⋅ min^− 1) to the common logarithm of _E (L ⋅ min^− 1) by the equation: _O2 = slope × log _10E + intercept. where the constant ‘slope’ is the OUES. Basically, to avoid possible irregular breathing patterns, data from the 3-min resting period, from the first minute of exercise, and from a plateau in _O2 were excluded from the calculation of the OUES. Green cross: exercise starting point; blue crosses: period during which OUES was calculated