Chronic obstructive pulmonary disease (COPD) includes respiratory tract disorders that cause obstruction to airflow. These are chronic bronchitis, emphysema and small airway disease. The main cause of COPD is long-term exposure to substances (cigarette smoke, second-hand smoke) that irritate the lungs. Feelings of anxiety and depression are common in patients with COPD. However, physical activity among patients with COPD can reduce risk of developing anxiety and reduce risk of becoming depressed.