Chronic bronchitis is the recurrent or persistent inflammation of the bronchial tree (bronchi and bronchioles) characterized by coughing and sputum production for at least 3 months in two consecutive years. It is very common in long term smokers and is on the rise even among non-smokers who live in polluted cities (smog). Chronic bronchitis should be differentiated from acute bronchitis which is almost always due to an infection. Acute exacerbations in chronic bronchitis however, may be due to secondary infections that are often bacterial in nature.
Chronic Bronchitis COPD
Apart from a productive cough, there is narrowing of the airways which eventually becomes permanent, especially if the causative factor is not removed – for example, continuing to smoke cigarettes or inhale smog-laden air.It is important to note that while long term smoking is still the most significant cause of chronic bronchitis, this disease is also seen in industrial workers exposed to pollutants like sulfur dioxide gas and dust from silica, grain and cotton.
In the early years of the disease, most chronic bronchitis patients will report a persistent bronchitis that follows a bout of seasonal influenza (flu) and then resolves after two months or so. The patient is then almost symptom-free for months afterwards, apart from the odd transient cough. It is only once the productive cough persists and varying degrees of dyspnea sets in do patients seek specialist medical attention and consider quitting cigarette smoking. The clinical presentation is discussed further under chronic bronchitis symptoms.
How does Chronic Bronchitis Occur?
Tobacco smoke irritates the lining of the airways. This in turn causes mucus hypersecretion and coughing. In the chronic setting there is hypertrophy (enlargement) of the mucus secreting submucosal glands in the trachea and bronchi which is perpetuated by the secretion of proteases by the accumulation of neutrophils in these areas. Over time, the number of goblet cells in the lining increases substantially that contributes to excessive mucus hypersecretion.
Partial blockage of the airways then sets in as result of the swelling of the inflamed bronchi and bronchioles and further accompanied by the accumulation of excessive mucus. Secondary infections may lead to acute exacerbations of bronchitis but it is not the primary pathogenesis responsible for chronic bronchitis. As the disease progresses, especially if cigarette smoking continues, the airways may narrow significantly and emphysema may also set in. The condition may progress from simple chronic bronchitis, to chronic mucopurulent bronchitis and then chronic bronchitis with obstruction.