Baseline characteristics of the study sample, presented as the mean ± s.d. for continuous variable and as the percentage for categorical variables.

#smokers/ex-smokers/nonsmokers.*FEV1: Forced expiratory volume in 1 s.†PaO2: arterial oxygen tension.§LTDOT: Long-term domiciliary oxygen therapy.##Exacerbations requiring either hospitalization or treatment with oral antibiotics or oral steroids.**Associations were tested with t-test and Chi-square.Baseline characteristics of the study sample, presented as the mean ± s.d. for continuous variable and as the percentage for categorical variables.