Chronic bronchitis is differentiated from other COPD conditions as it involves significant changes to the bronchi. It is caused by constant irritation of the bronchi from cigarette smoke or exposure to industrial pollutants with the effects being irreversible and progressive. Chronic bronchitis is characterised by inflammation with swelling and excess mucous in the bronchi (Figure 3).
Figure 3: Effects of Chronic Bronchitis
Chronic bronchitis is a progressive disease which manifests through the following processes:
- The mucosa becomes inflamed and swollen due to irritation from cigarette smoke or other air pollutants
- Hypertrophy (enlargement) and hyperplasia (accelerated production of cells) of the mucous glands occur causing increased secretions
- Many cells that line the airways lose their cilia affecting their ability to move particles and fluid (especially mucous). Over time the ciliated cells will often be replaced by so-called goblet cells
- The goblet cells secrete mucous into the airways and the warm moist environment along with the nutrients in the mucous creates an excellent medium for growing bacteria which leads to large amount of infections causing irritation and inflammation to the airways and a productive cough.
- The chronic irritation and inflammation leads to fibrosis and thickening of the bronchial wall and further obstruction occurs.
Secretions pool distal to obstructions and are difficult to remove causing mucous plugs to develop. This coupled with the inflammation, swelling, and increased mucous significantly inhibits the airflow to and from the lung alveoli by narrowing and partially obstructing the bronchi and bronchioles.
- Chronic coughing develops as the body attempts to open and clear the bronchial airways of particles and mucus or as an overreaction to the ongoing inflammation.
- All of the above leads to reduced oxygen levels reaching the alveoli, causing chronic hypoxia and hypercapnia (as deoxygenated blood passes alveoli without gas exchange occurring).
- Severe dyspnoea and fatigue interfere with nutrition, communication and daily activities leading to general debilitation.
Hypoxia causes pulmonary vasoconstriction leading to peripheral oedema and pulmonary hypertension. As with emphysema cor pulmonale is common in the later stages.