Chronicle obstructive pulmonary disease is a worldwide cause of mortality and morbidity. This systemic disease progressively leads to dyspnea, muscle wasting and exercise capacity impairment.

Pulmonary rehabilitation is a cornerstone in the management of these systemic effects. Unfortunately, access to pulmonary rehabilitation is limited for many people who would benefit from it, primarily because of a lack of pulmonary rehabilitation and assessment centers. Optimal assessment should include an incremental cardiopulmonary exercise testing. This test allows to evaluate the factors contributing to exercise intolerance by linking performance and physiological parameters to the underlying metabolism. Moreover, it is the standard test to determine both the optimal training settings as well as any cardiopulmonary contraindications to pulmonary rehabilitation. However, this test is not available in most centers and when it is, consultations are limited. Therefore, pulmonary rehabilitation is often delayed for several weeks and patients can lose motivation.

In order to promote pulmonary rehabilitation, the incremental cardiopulmonary exercise testing could be replaced by field tests to individualize pulmonary rehabilitation prescription.

The six-minute stepper test is a new field tool. Its sensitivity and reproducibility have previously been reported in patients with chronicle obstructive pulmonary disease. It is easy to set up in the clinical setting and could be used to individualize pulmonary rehabilitation.

The main drawback when using field test is that they only provide a non specific assessement of the functional capacity because cardiopulmonary parameters and gaz exchanges are not monitored.

Although the performance during the 6-minute stepper test is moderately related with the maximal oxygen consumption during the incremental cardiopulmonary exercise testing performed on a cycloergometer, a direct comprehensive comparison of cardiopulmonary parameters and gaz exchanges during these two tests have never been performed.

Moreover, stepping is more closely related with activities of daily life (requiring a repetitive transition from rest to submaximal exercise intensity) than the maximal incremental exercise on cycloergometer and could provide further insight on the disability of patients during their usual activities, such as stair climbing (which is frequently avoided). Additionally, on-transient phase two oxygen consumption kinetic is particularly relevant because it evaluation is independent of the patient's motivation or criteria used to terminate exercise.

Therefore, the aim of this study is to compare the cardiorespiratory parameters, the gaz exchanges and the maximality between the six-minute stepper test and the incremental cardiopulmonary exercise testing performed on a cycloergometer.

The secondary objective was to compare the on-transient oxygen consumption phase two kinetic parameters (time constant, span and steady state) according to the severity of the disease.

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.

Inclusion Criteria:

• Age > 18 ans ;
• Chronicle obstructive pulmonary disease stage I/IV ;
• Weight ≤ 90kg ;
• Eligible for pulmonary rehabilitation.

Exclusion Criteria:

• Require during exercise oxygen ;
• Pregnant woman or likely to be ;
• Patient under guardianship ;
• Contraindication to cardiopulmonary exercise testing ;
• Patient medically treated with heart rate modulator (excluding oral B2-agonist) ;
• Patient treated with pacemaker or defibrillator ;
• History of lower limb impairment (i.e. peripheral artery disease, orthopedic disorder etc.).

Patients with chronicle obstructive pulmonary disease reffered for pulmonary rehabilitation.