RT Journal Article SR Electronic T1 COPD exacerbations ยท 2: Aetiology JF Thorax JO Thorax FD BMJ Publishing Group Ltd and British Thoracic Society SP 250 OP 258 DO 10.1136/thx.2005.041822 VO 61 IS 3 A1 Sapey, E A1 Stockley, R A YR 2006 UL http://thorax.bmj.com/content/61/3/250.abstract AB Exacerbations of COPD are thought to be caused by complex interactions between the host, bacteria, viruses, and environmental pollution. These factors increase the inflammatory burden in the lower airways, overwhelming the protective anti-inflammatory defences leading to tissue damage. Frequent exacerbations are associated with increased morbidity and mortality, a faster decline in lung function, and poorer health status, so prevention or optimal treatment of exacerbations is a global priority. In order to evolve new treatment strategies there has been great interest in the aetiology and pathophysiology of exacerbations, but progress has been hindered by the heterogeneous nature of these episodes, vague definitions of an exacerbation, and poor stratification of known confounding factors when interpreting results. We review how an exacerbation should be defined, its inflammatory basis, and the importance of exacerbations on disease progression. Important aetiologies, with their potential underlying mechanisms, are discussed and the significance of each aetiology is considered.