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 Cole's Cycle describes how infections and a defect in the host defense are factors for this disease. An immune response also plays a role in the pathogenesis.

Pathophysiology

• Dilation of the bronchial walls results in airflow obstruction and impaired clearance of secretions
• The dilated areas interrupt normal air pressure of the bronchial tubes, causing sputum to pool inside the dilated areas instead of being pushed upward
• The pooled sputum provides an environment favorable to the growth of infectious pathogens
• 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
• 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

Cole's Cycle

• Also known as Cole's "vicious cycle hypothesis"
• The most widely known model of the development of bronchiectasis
• Impaired muco-ciliary clearance due to genetic susceptibility causes environmental insult
• Results in persistence of microbes in the sinobronchial tree
• The microbial infection causes chronic inflammation
• This results in tissue damage and impaired mucociliary motility
• This leads to more infection with a cycle of inflammation causing lung damage
• Two factors required for the development of this condition are persistent infection and a defect in host defense

Immune Response

• 

  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

References

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