Table 1.

Asthma Definitions

Manifestation	Definition
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