RT Journal Article SR Electronic T1 Lighter than air: heliox breathing improves exercise tolerance in COPD JF European Respiratory Review JO EUROPEAN RESPIRATORY REVIEW FD European Respiratory Society SP 1 OP 3 DO 10.1183/09059180.00000210 VO 19 IS 115 A1 P. Palange YR 2010 UL http://err.ersjournals.com/content/19/115/1.abstract AB