RT Journal Article SR Electronic T1 The heterogeneity of chronic obstructive pulmonary disease JF Thorax JO Thorax FD BMJ Publishing Group Ltd and British Thoracic Society SP 631 OP 632 DO 10.1136/thorax.55.8.631 VO 55 IS 8 A1 J A WEDZICHA YR 2000 UL http://thorax.bmj.com/content/55/8/631.abstract AB