BMJ 2013 Dec 9;347:f7358. Epub 2013 Dec 9.
British Thoracic Society Chronic Obstructive Pulmonary Disease Specialist Advisory Group, National Heart and Lung Institute, Imperial College, London SW3 6NP, UK.
Thorax 2013 Sep;68 Suppl 2:ii1-30
Nottingham Respiratory Research Unit, University of Nottingham, City Hospital campus, Nottingham, UK.