RT Journal Article SR Electronic T1 Endogenous opioids modify dyspnoea during treadmill exercise in patients with COPD JF European Respiratory Journal JO Eur Respir J FD European Respiratory Society DO 10.1183/09031936.00145208 A1 D.A. Mahler A1 J.A. Murray A1 L.A. Waterman A1 J. Ward A1 W.J. Kraemer A1 X. Zhang A1 J.C. Baird YR 2009 UL http://erj.ersjournals.com/content/early/2009/02/12/09031936.00145208.abstract AB