What is reactive airway?

What is Reactive Airway Disease?

Reactive airway disease (RAD) is a general term describing respiratory conditions characterized by airway hyperresponsiveness and bronchoconstriction triggered by various stimuli, manifesting clinically as wheezing and reversible airflow obstruction. 1

Core Pathophysiology

The fundamental mechanism involves excessive airway narrowing beyond normal physiologic limits, where airways fail to reach a plateau in the dose-response curve to bronchoconstrictive stimuli. 2 This represents both:

• Increased sensitivity (hyperresponsiveness) - airways respond to lower concentrations of triggers than in healthy individuals 3
• Excessive reactivity - the magnitude and rate of airway narrowing is exaggerated 2

The underlying process is driven by chronic airway inflammation involving multiple cell types including mast cells, eosinophils, neutrophils, T lymphocytes, macrophages, and epithelial cells. 3, 4 This inflammation causes structural changes including airway smooth muscle hypertrophy, subepithelial fibrosis, and mucus hypersecretion. 3, 2

Clinical Triggers and Manifestations

RAD symptoms are provoked by diverse environmental and physiologic stimuli:

• Environmental allergens (dust mites, animal proteins, pollens, molds) 4
• Irritants (tobacco smoke, chemical fumes, occupational exposures) 4
• Cold air exposure - causes direct airway vasoconstriction followed by reactive hyperemia 3, 2
• Exercise - particularly in cold, dry air environments 3
• Viral respiratory infections - especially in young children 4
• Hypoxia - can trigger airway constriction 3

Clinical Contexts Where RAD Occurs

The term encompasses multiple distinct clinical entities:

• Asthma - the most common chronic inflammatory airway disease 3
• Exercise-induced bronchoconstriction (EIB) - transient airway narrowing after exercise, which may occur with or without underlying asthma 3
• Chronic lung disease of infancy (CLDI) - premature infants demonstrate persistent airway obstruction and hyperreactivity into childhood and adulthood 3, 2
• Post-infectious states - particularly following severe RSV bronchiolitis in infancy, though causality remains debated 1, 5
• Reactive airways dysfunction syndrome (RADS) - sudden-onset asthma-like symptoms following high-level inhalational exposure to corrosive gases, vapors, or fumes 6

Important Clinical Distinctions

The term "reactive airway disease" is descriptive rather than diagnostic - it describes a pattern of airway behavior rather than a specific disease entity. 1 Key considerations:

• RAD in infants and young children often represents early asthma, viral-induced wheezing, or sequelae of prematurity 3, 5
• Airway hyperresponsiveness exists on a continuum in the general population following a normal distribution 5
• Not all wheezing represents true airway hyperreactivity - acute viral bronchiolitis in infants <12 months typically does not demonstrate persistent hyperresponsiveness 5

Diagnostic Approach

While formal diagnosis requires specialized testing, key features include:

• Reversible airflow obstruction - FEV1 improvement ≥12% and ≥200 mL after bronchodilator administration 2
• Peak flow variability >15% over 2 weeks supports the diagnosis 2
• Bronchoprovocation testing with methacholine, histamine, exercise, or eucapnic voluntary hyperpnea can demonstrate hyperresponsiveness 3

Long-term Implications

Airway hyperresponsiveness often persists despite intensive anti-inflammatory treatment, suggesting irreversible structural airway alterations. 2 In children with CLDI, studies show:

• FEV1 averaging 80% of predicted values persists into adolescence 3
• 40-50% demonstrate ongoing airway hyperreactivity to challenge testing 3
• Obstructive pattern with elevated residual volume to total lung capacity ratio (130% of controls) 3
• These abnormalities can persist into early adult life 3

Treatment Principles

Management addresses both acute bronchoconstriction and underlying inflammation:

• Bronchodilators (beta-2 agonists, anticholinergics) provide acute relief by reversing airway smooth muscle constriction 3, 2
• Inhaled corticosteroids reduce underlying inflammation and hyperresponsiveness 2
• Combination therapy may have synergistic effects, particularly bronchodilators with diuretics in specific populations 3

A critical pitfall: the term "reactive airway disease" should not be used as a substitute for proper diagnosis. When asthma is present, it should be diagnosed as asthma; when exercise-induced bronchoconstriction occurs, that specific term is preferred. 3 The term RAD is most appropriately used when describing the physiologic phenomenon of airway hyperresponsiveness across various clinical contexts or when a more specific diagnosis cannot yet be established.