Population characteristics: age 66.8 ± 9.3, male 91.7%, BMI 20.6 ± 3.6 kg / m2, current smoking 31.2%, number of pack. year 47 ± 16, mMRC > 1 point 89.6%, group B and D 89.6%, post-bronchodilator FEV1 (% predicted) 51 ± 18.4%, awake SpO2 94 ± 3%.