RT Journal Article SR Electronic T1 Interpretation of treatment changes in six-minute walk distance in patients with COPD JF European Respiratory Journal JO Eur Respir J FD European Respiratory Society DO 10.1183/09031936.00140507 A1 M.A. Puhan A1 M.J. Mador A1 U. Held A1 R. Goldstein A1 G.H. Guyatt A1 H.J. Schünemann YR 2008 UL http://erj.ersjournals.com/content/early/2008/06/11/09031936.00140507.abstract AB