Pathophysiology of Asthma

Core Inflammatory Process

Asthma is fundamentally a chronic inflammatory disorder of the airways where inflammation drives three interconnected pathophysiologic processes: bronchoconstriction, bronchial hyperresponsiveness, and progressive airway remodeling that together produce the variable and reversible airflow obstruction characteristic of the disease 1
The underlying inflammation involves multiple cellular players working in concert, including mast cells, eosinophils, T lymphocytes, macrophages, and epithelial cells, with neutrophils playing a particularly important role in sudden-onset fatal exacerbations, occupational asthma, and in patients who smoke 1, 2, 3

Bronchial smooth muscle contracts rapidly in response to allergens, irritants, and other stimuli, quickly narrowing the airways, representing the most immediately reversible component of airflow obstruction 1, 4
Airways develop an exaggerated bronchoconstrictor response to stimuli that would not affect normal airways 1
As inflammation becomes more persistent, edema, mucus hypersecretion, and formation of inspissated mucus plugs further limit airflow, with these changes being less immediately reversible than bronchoconstriction alone 1

Persistent inflammation leads to permanent structural changes in the airway architecture, including sub-basement membrane fibrosis, smooth muscle hypertrophy, epithelial cell injury and shedding, angiogenesis, and mucus gland hyperplasia 1, 5
These structural changes explain why airflow limitation may become incompletely reversible in some patients despite aggressive treatment 1

The development of asthma requires both genetic susceptibility and environmental triggers, with a strong genetic component where 80% of children with two asthmatic parents develop asthma 1, 6
Gene-environment interactions are critical, with environmental exposures during immune system development being essential, and in utero exposures such as maternal smoking increasing childhood asthma risk in a dose-dependent pattern 1, 6

Different asthma phenotypes exist with varying patterns of inflammation, cellular mediators, and therapeutic responses, including occupational asthma with prominent neutrophilic inflammation 1, 3
Understanding these phenotypes is increasingly important as treatment approaches may eventually be directed to specific patient phenotypes and genotypes 1, 6

The pathophysiologic changes produce characteristic symptoms, including recurrent episodes of coughing, wheezing, breathlessness, and chest tightness, with variable airflow obstruction that is often reversible either spontaneously or with treatment 1, 3, 5
Symptoms can be triggered by specific stimuli, including allergens, irritants, exercise, cold air, and viral infections, and can be present even in patients with mild asthma when they have few symptoms 1, 5, 6

Asthma causes air trapping due to small airway obstruction, inflammation, and mucus plugging, resulting in a characteristic pathophysiologic feature of the disease 7, 8
Bronchoconstriction and mucus plugging create widespread but variable airflow obstruction, limiting airflow particularly during expiration 7, 8

Hyperinflation on physical examination with or without wheeze in patients with chronic asthma is a key indicator of air trapping 9

Incomplete expiration results from obstructive changes, leading to breath stacking and buildup of positive end-expiratory pressure (auto-PEEP), particularly evident during acute exacerbations 10