Chronic Bronchitis: Pathophysiology

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In chronic bronchitis exposure to an irritant over many years causes inflammation in the lungs which leads to the following changes:

  • Continual irritants (smoking, infection, pollution) to the lungs cause the airways to become swollen and inflamed.
    • Constant irritants lead to hypertrophy (enlargement) of the mucus-secreting glands of the bronchial tree, an increase in the number of goblet cells, which results in increased mucus secretion.
    • The smooth muscle in the airways becomes thicker and narrows the bronchioles.
  • Extra mucus is produced to trap any irritants and prevent them entering the lungs.
    • The cilia become unable to cope with excessive secretions and therefore the mucus blocks the airways. This is known as Reversible Airways Obstruction.
    • The mucus goes deeper into the lungs and becomes harder to clear.
  • Excessive secretions are liable to infection.
    • The walls of the bronchioles become inflamed, continual inflammation causes gradual destruction of the bronchioles, resulting in fibrosis - Irreversible Airways Obstruction.
  • Disease progression can also affect the pulmonary blood vessels
    • If the inflammation spreads to the blood vessels this will lead to capillary bed wall atrophy (wasting).  This increases the pressure of the pulmonary circulation. Pulmonary arteries may become distended (stretched) and blood may back track into the right side of the heart resulting in right sided hypertrophy (enlargement) and heart failure. This is known as Cor Pulmonale.