Fig. 1
From: Gas exchange efficiency slopes to assess exercise tolerance in chronic obstructive pulmonary disease
Calculation of OUES. a) The relationship between oxygen uptake (\(\rm{\dot V}\)O2: mL ⋅ min−1) and the common logarithm of minute ventilation (\(\rm{\dot V}\)E: L ⋅ min−1) (b) the relationship between \(\rm{\dot V}\)O2 (mL ⋅ min−1) and \(\rm{\dot V}\)E (L ⋅ min−1). \(\rm{\dot V}\)O2 and \(\rm{\dot V}\)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 \(\rm{\dot V}\)O2 (mL ⋅ min− 1) to the common logarithm of \(\rm{\dot V}\)E (L ⋅ min− 1) by the equation: \(\rm{\dot V}\)O2 = slope × log 10\(\rm{\dot V}\)E + 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 \(\rm{\dot V}\)O2 were excluded from the calculation of the OUES. Green cross: exercise starting point; blue crosses: period during which OUES was calculated