1. World Health Organization2017Chronic obstructive pulmonary disease fact sheet
http://www.who.int/mediacentre/factsheets/fs315/en/
2. Time course and pattern of COPD exacerbation onset
3. Global Initiative for Chronic Obstructive Lung Disease2016Global strategy for the diagnosis, management and prevention of chronic obstructive pulmonary disease
http://goldcopd.org/download/120/
4. Impact of preventing exacerbations on deterioration of health status in COPD