Bronchitis: Introduction. Bronchitis is a general term for two diseases that cause swelling and irritation (inflammation) of the lower airways of the lungs called the bronchi and the bronchioles. Types of bronchitis include chronic bronchitis and acute bronchitis.ronchitis: Introduction. Bronchitis is a general term for two diseases that cause swelling and irritation (inflammation) of the lower airways of the lungs called the bronchi and the bronchioles. Types of bronchitis include chronic bronchitis and acute bronchitis.