Experimental design:
This study is a pre-specified ancillary study to two other studies (with exactly the same design but a different population) aimed to assess the usability of the six-minute stepper test to prescribe endurance training in patients with mild to moderate (NCT02842463) and severe to very severe (NCT04004689) chronicle obstructive pulmonary disease respectively.
Patients already participating in one of these studies will be approached and offered to participate in an additional testing session (on a different day) using exactly the same procedure but monitoring cardiopulmonary parameters and gaz exchanges using a face mask, a pneumotachograph and a gaz analyser (indirect calorimetry).
Data from these additional two six-minute stepper tests will be compared with those obtained from the previously performed incremental cardiopulmonary exercise testing.
According to the American Thoracic Society and American College of Chest Physicians statement on cardiopulmonary exercise testing, maximality will be considered if either one or more of the following criteria occured:
1. The patient achieves predicted peak oxygen uptake and/or a plateau is observed.
2. Predicted maximal heart rate is achieved (\>90%)
3. There is evidence of ventilatory limitation (breathing reserve \<11liters or \< 15%)
4. Respiratory exchange ratio \> 1.15
5. Patient exhaustion/Borg Scale rating of 9-10 on a 0-to-10 scale.
Phase II oxygen consumption kinetics will be modelized by averaging the breath by breath measurement over consecutive periods of 5s for using the following monoexponential equation :
VO2 (τ) = VO2rest + VO2ss - VO2rest))\*(1-e-t/τ). with " VO2rest " representing the baseline level of VO2 at rest, " VO2ss " representing the steady state of VO2 during exertion and τ (time constant) representing the time course of the monoexponential VO2 curve. The amplitude of the VO2 (VO2span) corresponds to the difference between VO2ss and VO2rest.
A curve by curve analysis will be performed across participants and parameters (time constant, span and steady state oxygen consumption) will be compared according to the stage of severity.
