What is chronic bronchitis?
Chronic bronchitis is diagnosed on a clinical basis:
It is defined as the presence of a persistent productive cough for at least 3 consecutive months in at least 2 consecutive years.
- The cough is caused by mucus over secretion.
- Quite frequently, chronic bronchitis is associated with emphysema and is termed chronic obstructive pulmonary disease(COPD).
- Common among urban dwellers and cigarette smokers in smog-ridden cities.
- The distinctive feature of chronic bronchitis is; Mucus hypersecretion beginning in large airways.
- The most important etiologic factors for the majority of cases of chronic bronchitis are cigarette smoking and atmospheric pollution.
- Other contributory factors such as occupation, infection, familial and genetic factors.
The most important cause is cigarette smoking
- Prolonged cigarette smoking impairs ciliary movement.
- It inhibits the alveolar macrophage functions.
- It leads to hypertrophy and mucus-secreting glands hyperplasia.
- It causes considerable obstruction of small airways & stimulates the vagus causing bronchoconstriction.
Environmental irritants induce:
- Mucous glands hypertrophy in the trachea and bronchi.
- Increase in mucin-secreting goblet cells in smaller airways.
- Cause inflammation
- Some of the atmospheric pollutants that increase the risk of developing chronic bronchitis are sulfur dioxide, nitrogen dioxide, particulate dust, and toxic fumes.
- Workers engaged in certain occupations such as in cotton mills (byssinosis), plastic factories, etc are exposed to various organic or inorganic dust which contributes to disabling chronic bronchitis in such individuals.
- Bacterial, viral, and mycoplasmal infections do bronchitis. Cigarette smoke, however, predisposes to infection responsible for acute exacerbation in chronic bronchitis.
Familial and genetic factors:
- There are some poorly defined familial tendencies and genetic predispositions to developing chronic bronchitis.
- However, it is more likely in nonsmoker family members who are exposed to air pollution and hence have increased blood levels of carbon monoxide.
Airflow obstruction in chronic bronchitis results from:
- Small airway disease, induced by mucous plugging, inflammation, and bronchiolar wall fibrosis
- Coexistent emphysema
Small airway disease (chronic bronchiolitis)
- Early, mild airflow obstruction
With significant airflow obstruction:
- Almost always is complicated by emphysema in later stage
Effects of environmental irritants:
- Release of cytokines IL-13 from T cells
- Mucin production
- Production of neutrophil elastase
- Often present but has a secondary role.
Morphology of Chronic bronchitis
- The mucosal lining of the larger airways:
- The bronchial wall is thickened, Hyperemic and oedematous
- Covered by mucinous or mucopurulent secretions
- Smaller airways: filled with secretions.
- Diagnostic feature in larger airways:
- Enlargement of the mucus-secreting glands
- The magnitude of increase in size is appraised by:
- Increased Reid Index: The ratio of the submucosal gland thickness layer to that of the bronchial wall (Reid index— normally 0.4).
- The thickness increased can be quantitatively assessed by micrometer lens or by morphometry.
- Inflammatory cells: Neutrophils, macrophages
- The bronchial epithelium may show dysplasia and squamous metaplasia.
- Chronic bronchiolitis:
- Mucous plugging, Goblet cell metaplasia, inflammation, and fibrosis.
- In severe cases:
- Complete obliteration of lumen by fibrosis seen (bronchiolitis obliterans).
- Emphysematous changes often coexist.
- Variable features
- In some patients, cough and sputum production persist indefinitely without ventilatory dysfunction, initially beginning in a heavy smoker with ‘morning catarrh’ or ‘throat clearing’ which worsens in winter.
- Recurrent respiratory infections.
- Features of right heart failure (corpulmonale) are common.
- Chest X-ray shows an enlarged heart with prominent vessels.
- Dyspnoea is normally not prominent at rest but is more on exertion.
- Progressive disease:
- Pulmonary hypertension, sometimes leading to cardiac failure
- Absence of increased respiratory drive the patient retains carbon dioxide, becoming hypoxic and often cyanotic/ edematous so-called “blue bloaters”.