Bronchiectasis pathophysiology
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Saarah T. Alkhairy, M.D.
Overview
Bronchiectasis involves bronchi that are permanently dilated, inflamed, and easily collapsible. This results in airflow obstruction and impaired clearance of secretions.
Pathophysiology
- Dilation of the bronchial walls results in airflow obstruction and impaired clearance of secretions because the dilated areas interrupt normal air pressure of the bronchial tubes, causing sputum to pool inside the dilated areas instead of being pushed upward.[1]
- The pooled sputum provides an environment conducive to the growth of infectious pathogens. Therefore, that particular area is vulnerable to infections.
- The more infections that the lungs experience, the more damaged the alveoli in the lung become.
- With more damage to the lung tissue, the bronchial tubes become more inelastic and dilated. This creates a perpetual, destructive cycle within this disease.
- The most widely known model of the development of bronchiectasis is Cole’s “vicious cycle hypothesis”. In this model, Cole proposed that an environmental insult often on a background of genetic susceptibility impaired muco-ciliary clearance resulting in persistence of microbes in the sinobronchial tree and microbial colonization. The microbial infection caused chronic inflammation resulting in tissue damage and impaired mucociliary motility. In turn this led to more infection with a cycle of progressive inflammation causing lung damage. The current view is that the two factors required for the development of this condition are persistent infection and a defect in host defense.[2]
- The biopsies indicate that the infiltrate contains neutrophils, T lymphocytes and macrophages. The sputum contains elastase, interleukin-8, tumor necrosis factor a (TNF-a), and prostanoids.
Immune Response
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Schematic representation of a vicious circle of events which occurs during chronic bronchial infection. IL: interleukin; TNF: tumour necrosis factor; LT: leukotriene; MMP: matrix metalloproteinase
European Respiratory Journal
