Exercise-induced bronchoconstriction (EIB), formerly called exercise-induced asthma, refers to transient narrowing of airways occurring during or after vigorous physical activity. It affects approximately 90% of patients with established asthma (where it represents an asthma trigger termed exercise-triggered asthma) and 10% of athletes without underlying asthma diagnosis (where it occurs as isolated EIB without persistent symptoms). The condition disproportionately affects elite athletes (cross-country skiers up to 50%, swimmers, ice rink athletes, distance runners) due to high minute ventilation during training and competition.
Pathophysiology: rapid breathing through the mouth during exercise bypasses nasal warming/humidification, exposing the airway epithelium to cool, dry air. This causes airway surface fluid evaporation and transient hyperosmolarity, triggering mast cell, eosinophil, and epithelial cell activation with release of inflammatory mediators (histamine, leukotrienes—especially LTC4, LTD4, LTE4—prostaglandins, neurokinins). These mediators cause smooth muscle contraction, vascular leakage, and edema, producing 5-20 minute episodes of bronchoconstriction typically peaking 5-15 minutes after exercise cessation, with most resolution by 30-60 minutes. A refractory period of 1-3 hours follows in many patients during which subsequent exercise produces less bronchoconstriction (basis for warm-up protocols).
Diagnosis combines history (cough, wheeze, chest tightness, dyspnea during/after exercise; symptoms reproducible with similar exercise), pre/post exercise spirometry (≥10% drop in FEV1 confirms EIB), exercise challenge in laboratory (treadmill or cycle ergometer reaching 80-90% predicted maximum heart rate for 6-8 minutes) or eucapnic voluntary hyperventilation (EVH—voluntary hyperpnea breathing room air enriched with 5% CO2, gold standard for elite athletes), and methacholine challenge (less specific). Treatment per ATS/GINA guidelines: short-acting β2-agonist (albuterol 2 puffs 15 minutes before exercise—first-line preventive); for those exercising frequently or with persistent symptoms despite SABA, daily inhaled corticosteroid (low-dose budesonide, fluticasone) is preferred over chronic SABA monotherapy (avoids tachyphylaxis); leukotriene receptor antagonists (montelukast 10 mg daily) protective and useful when ICS not used or symptoms not fully controlled; mast cell stabilizers (cromolyn) less effective; warm-up exercise (15 minutes pre-event high-intensity interval) reduces bronchoconstriction via refractory period; environmental modifications (warm humid air via mask, avoid cold/dry environments and irritants like ice rink ammonia, chlorinated pool fumes); long-acting β-agonists not first-line for EIB (regulatory boxed warning); identifying and treating underlying asthma is critical when present. Education on inhaler technique and trigger avoidance important; competitive athletes may need WADA Therapeutic Use Exemption documentation.