Definition and etiology Chronic bronchitis is defined by the presence of chronic bronchial secretions sufficient to cause expectoration occurring on most days for a minimum of 3 months for 2 consecutive years. It became recognized as a distinct disease in the late 1950s associated with the great British Smog. It develops in response to long-term irritants on the bronchial mucosa. Important irritants include cigarette smoke, dust, smoke, and fumes; other causes include respiratory infection, particularly in infancy, and exposure to dampness, sudden changes in temperature, and fog. In the United Kingdom, it affects 10% of older people, and it is more common in industrial countries. Chronic bronchitis is a slowly progressive disorder unless the precipitating factors are avoided and it is treated.
Clinical features Symptoms include productive cough and frequent and recurrent chest infections. The disease progresses over many years from a troublesome cough producing a little clear sputum to marked wheezing, severe breathlessness leading to poor exercise tolerance, and copious and purulent sputum. It may cause right heart failure (i.e., cor pulmonale), such as oedema and cyanosis.
Pathology There is hypertrophy of the mucus-secreting glands. The structural changes described in the airways include atrophy, focal squamous metaplasia, ciliary abnormalities, variable amounts of airway smooth muscle hyperplasia, inflammation, and bronchial wall thickening. The respiratory bronchioles display a mononuclear inflammatory process, lumen occlusion by mucus plugging, goblet cell metaplasia, smooth muscle hyperplasia, and distortion due to fibrosis. These changes combined with loss of supporting alveolar attachments cause airflow limitation by allowing airway walls to deform and narrow the airway lumen.
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