Table 1 Asthma Definitions

Asthma

Inflammatory disease of the airways characterized by:

   • Infiltration by eosinophils, lymphocytes and neutrophils

   • Mast cell activation

   • Epithelial loss

Associated reversible airway obstruction, recurrent symptoms and bronchial hyper-responsiveness

Gene-by-environment interactions are important

Inflammation

Plays central role in asthma pathophysiology

Mediated by T cells, lymphocytes, mast cells, eosinophils and epithelium. Other resident cells such as fibroblasts and smooth muscle play a role

Airway remodeling

As inflammation proceeds, other changes evolve leading to reparative or remodeling changes and include:

   • Sub-basement membrane thickening

   • Subepithelial fibrosis

   • Smooth muscle hypertrophy

   • Angiogenesis

Mucus gland hyperplasia and hypersecretion

Bronchoconstriction

Airway narrowing resulting in wheezing

Probably acutely due to release of mast cell mediators such as histamine, leukotrienes, and tryptase

Obstruction could be mediated by multiple factors:

   • Smooth muscle contraction

   • Airway edema

   • Airway remodeling and fibrosis

Bronchial Hyperresponsiveness

Exaggerated bronchoconstrictive response to a wide variety of stimuli; best measured clinically by methacholine challenge testing; mediated by inflammation, remodeling and other airway changes that occur in asthma