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

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