RT Journal Article SR Electronic T1 Review: long acting β2 adrenoceptor agonists are effective in poorly reversible chronic obstructive pulmonary disease JF Evidence Based Medicine JO Evid Based Med FD BMJ Publishing Group Ltd SP 12 OP 12 DO 10.1136/ebm.12.1.12 VO 12 IS 1 YR 2007 UL http://ebm.bmj.com/content/12/1/12.abstract AB