In chronic bronchitis, considerable damage is caused to the central airways of the lungs, blocking the passage way for air (obstructive) and leading to breathing difficulties. The three main manifestations of chronic bronchitis include:
- Build-up of scar tissue due to damage to airways.
- Peribronchial thickening and fibrosis due to excess inflammation and endothelial damage.
- Mucus gland overmultiplication.
Irritation caused a s a result of smoking leads to injury to the pulmonary endothelial cells and causes release of extracellular matrix, fibroblasts, and inflammatory cells. Goblet cell hyperplasia (a state where the number of columnar epithelial and endothelial cells secrete mucus) leads to altered consistency of mucus (the original imunoprotective water-consistency being lost) and hence makes the airways mucoid. Incomplete wound healing results in scarring of the airways, and infiltration of immune cells increases their purulent nature, which also harbors bacteria at later stages. As a result of this, the airways get clogged and results in cough and sputum production in the patient.
Due to obstructed pathways, the lung is poorly ventilated, causing the heart to beat faster than usual to meet up with the oxygen demands of the lungs. The stress caused due to this results in hypoxia and hypercapnia (a decrease in the amount of Co2 in blood), ultimately leading to pulmonary arterial hypertension and right-heart failure.