Structural Changes in Airway Diseases

Structural Changes in Airway DiseasesAsthma and COPD are the most prevalent airway obstructive conditions. Both are complex diseases in which inflammatory and remodeling processes have been depicted. Less is known about remodeling features of other airway diseases, such as reactive airways dysfunction syndrome (RADS), cystic fibrosis (CF), and bronchiectasis. In this review, we will describe briefly the main airway remodeling features observed in obstructive diseases—tentatively defined as a change in the nature, content, and distribution of structural airway elements—their potential functional consequences and clinical relevance, as well as current evidence of pharmacologic modulation of these features in airway diseases,

Airway Structure and Remodeling Features
From a histologic perspective, the human airway can be divided into three layers: the inner wall, the outer wall, and the smooth-muscle layers. The inner wall layer refers to the epithelium, the basement membrane, and the submucosa. The outer wall layer consists of loose connective tissue between the muscle layer and surrounding parenchyma. In comparison to healthy airways, all airway layers have been shown to present some alterations in airway obstructive diseases. Epithelial alterations, goblet-cell and submucosal gland hyperplasia, smooth-muscle cell hyperplasia and hypertrophy, subepithelial fibrosis, microvascular proliferation, cartilage changes, airway wall edema, and inflammatory cell infiltration are the main histologic features of airway diseases. The relative magnitude of the structural changes among the airway diseases is summarized in Table 1. The ideal approach to assess airway remodeling is histopathologic analysis of lung tissue derived from autopsy or lung resection. However, these specimens are rarely available. Most studies use airway tissues obtained by endobronchial biopsies performed under flexible bronchoscopy.

Table 1—Air-way Structural Changes in Airway Diseases

Variables Asthma Irritant-Induced Occupational Asthma COPD Bronchiectasis
Mucus gland hyperplasia + + + + ? + + + + + + +
Subepithelial collagen deposition + + + + + + + + +
Angiogenesis + + + ? + +
Increased smooth muscle + + + + + ? + +
Increased proteoglycan deposition + + + + + +? + +
Increased elastin + + + + ? +
Epithelial damage + + + + + + + + + +
This entry was posted in Pulmonary Function and tagged airway inflammation, airway remodeling, antiasthmatic therapy, asthma, COPD, corticosteroids, cystic fibrosis.