Clinical and demographic information of the study participants

		Patients with COPD (GOLD classification)
Stage	Control subjects	I	II	III	IV
No.	103	46	55	41	13
Age (y), mean ± SD	51 ± 7	57 ± 11	62 ± 8	65 ± 9	62 ± 7
Male sex, no.	32	29	48	35	10
Lung function
FEV1 (%) ± SD	95 ± 12	82 ± 13	57 ± 11∗	37 ± 10∗	24 ± 4∗
Dlco (%) ± SD	67 ± 13	59 ± 13	50 ± 11∗	36 ± 10∗	27 ± 7∗
Smoking status, no.
Current	56	34	28	14	5
Former	22	12	27	27	8
Never	25	0	0	0	0
PPY, mean ± SD	28 ± 26	47 ± 32	69 ± 40	65 ± 32	72 ± 47
Quitting (y), mean ± SD	14 ± 11	14 ± 12	11 ± 11	10 ± 9	6 ± 5

Dlco, Diffusing capacity of the lung for carbon monoxide; PPY, pack per year (number of packs smoked × number of years).