22nd February 2024

Background

Bronchiectasis is defined as dilatation of the terminal bronchioles of more than 2mm, leading to inflammation and partial or complete obstruction by secretions. Inflammation consists of a combination of immune deficiency and persistent infection. This process is continuous and leads to a cycle of worsening pulmonary damage. The prevalence of bronchiectasis in the United Kingdom is approximately 210,000 to 300,000 cases. It is more commonly found amongst females compared to males, with 60% of diagnoses in patients above the age of 70. 

Pathophysiology 

The pathophysiology of bronchiectasis stems from two main processes: infectious insult and subsequent impaired drainage leading to airway obstruction.

The host immune response, led mainly through immune modulator cells (neutrophils) and elastases, in addition to oxidation radicals and inflammatory cytokines, leads to ulceration, inflammation and neovascularisation of airways. Other contributing factors include:

Neutrophil/Neutrophil elastase

The excess presence of neutrophil/neutrophil elastase has been noted in patients with features of bronchiectasis. Unopposed apoptosis, increased release of myeloperoxidase and phagocytosis have been characterised with stable bronchiectasis. Pregnancy-associated zone proteins (PZP) and intracellular neutrophil proteins are associated with infective exacerbation of bronchiectasis and indicate the presence of Pseudomonas aeruginosa. 

Vitamin D deficiency

Vitamin D has been correlated with exacerbation of bronchiectasis. Patients with Vitamin D deficiency are more likely to have Pseudomonas colonisation, worse exacerbations requiring hospitalisation and increased sputum expectancy.

References

• Chan SC, Leung VO, Ip MS, Shum DK. Shed syndecan-1 restricts neutrophil elastase from alpha1-antitrypsin in neutrophilic airway inflammation. Am J Respir Cell Mol Biol 2009; 41:620
• Chalmers JD, McHugh BJ, Docherty C, et al. Vitamin-D deficiency is associated with chronic bacterial colonisation and disease severity in bronchiectasis. Thorax 2013; 68:39.
• Pillarisetti N, Williamson E, Linnane B, et al. Infection, inflammation, and lung function decline in infants with cystic fibrosis. Am J Respir Crit Care Med 2011; 184:75