RT Journal Article SR Electronic T1 Concomitant use of β-blockers and β2-agonists JF European Respiratory Journal JO Eur Respir J FD European Respiratory Society SP 905 OP 906 DO 10.1183/09031936.00153707 VO 31 IS 4 A1 Y. Ling A1 W. Saleem A1 C. D. Shee YR 2008 UL http://erj.ersjournals.com/content/31/4/905.abstract AB