What is exercise-induced asthma?

Exercise-Induced Asthma: Definition, Diagnosis, and Management

Exercise-induced asthma (EIA), more accurately termed exercise-induced bronchoconstriction (EIB), is defined as transient airway narrowing that occurs as a result of exercise, characterized by symptoms such as wheezing, cough, chest tightness, and dyspnea that typically occur after strenuous exertion. 1

Definition and Pathophysiology

• EIB describes acute airway narrowing that occurs after exercise and can affect both individuals with and without underlying asthma 1
• The term "exercise-induced bronchoconstriction" is preferred over "exercise-induced asthma" as it does not imply that exercise causes asthma or that the patient necessarily has underlying chronic asthma 1
• EIB is triggered by a period of high-intensity exercise or increased minute ventilation, causing a prototypical bronchoconstriction response that occurs predominantly after exercise cessation 1
• The pathophysiologic mechanism involves cooling and drying of airways during exercise followed by rapid rewarming, leading to:
  • Loss of heat and water from bronchial mucosa 2
  • Increased osmolarity stimulating mast cell degranulation 1
  • Release of inflammatory mediators (histamine, tryptase, leukotrienes) from eosinophils and mast cells 1
  • Vascular congestion, increased permeability, and edema during airway rewarming 2

Epidemiology

• EIB occurs in up to 90% of patients with asthma 3
• Prevalence in the general population is approximately 10-13% 4, 3
• Elite athletes have a higher prevalence (30-70%) than the general population 1
• Specific sports carry higher risk due to environmental exposures:
  • Ice rink athletes: ~30% prevalence due to cold dry air and pollutants from ice resurfacing machines 1
  • Nordic skiers: High prevalence due to inhalation of cold, dry air 1
  • Competitive swimmers: 11-29% prevalence associated with trichloramine exposure 1

Clinical Presentation

• Symptoms typically develop 5-10 minutes after exercise, peak 8-15 minutes post-exercise, and resolve within 30-90 minutes without treatment 1, 2
• Common symptoms include:
  • Chest tightness
  • Cough
  • Wheezing
  • Dyspnea 1
• Symptoms are often mild to moderate but can impair athletic performance 1
• Severe episodes can occur rarely, potentially leading to respiratory failure 1
• A refractory period of up to 3 hours may occur after recovery, during which repeat exercise causes less bronchospasm 2

Diagnosis

• Diagnosis is established by changes in lung function after exercise, not based on symptoms alone 1
• Symptoms are neither sensitive nor specific for identifying EIB 1
• Initial spirometry should be performed to evaluate for underlying chronic asthma 4
• A positive diagnosis requires:
  • A decrease in FEV1 of ≥10% after exercise 2
  • Symptoms consistent with bronchospasm during or after exercise 4
• If spirometry is normal but EIB is suspected, additional testing is needed:
  • Exercise challenge test (achieving 80-95% of maximum heart rate for 6-8 minutes) 1
  • Surrogate tests like eucapnic voluntary hyperpnea (EVH) or inhaled mannitol challenge 1

Management

Pharmacologic Treatment

• First-line treatment: Short-acting β2-agonists (SABAs) 15 minutes before exercise 5

  • Provides protection in 80-95% of affected individuals 6
  • Should be used less than daily on average (ideally <4 times per week) to prevent tolerance 5

• For patients with persistent symptoms despite pre-exercise SABA:

  • Add daily inhaled corticosteroids (ICS) 5
  • Consider leukotriene receptor antagonists (LTRAs) like montelukast 5, 7
  • Mast cell stabilizing agents before exercise 1, 5
  • Consider inhaled anticholinergic agents before exercise 1

• For patients with EIB and allergies who continue to have symptoms:

  • Consider antihistamines (not recommended for non-allergic patients) 1

• Important caution: Avoid daily use of long-acting β2-agonists (LABAs) as monotherapy due to risk of serious side effects and development of tolerance 5

Non-Pharmacologic Approaches

• Warm-up exercise before planned activity (interval or combination warm-up) 1, 5
• Use of a face mask or scarf to warm and humidify air during cold weather exercise 1, 5
• Dietary modifications that may help:
  • Low-salt diet 1
  • Fish oil supplementation 1
  • Ascorbic acid (vitamin C) supplementation 1
• Avoid known triggers and high-pollution environments 1
• Choose sports with lower minute ventilation when possible 5

Special Considerations

• EIB is frequently undiagnosed, even in well-conditioned athletes 6

• With proper management, individuals with EIB can participate in physical activity at all levels, including elite competition 3

• Alternative diagnoses should be considered if symptoms persist despite appropriate treatment:

  • Vocal cord dysfunction
  • Cardiac conditions
  • Other pulmonary disorders
  • Anxiety 4

• Environmental factors significantly influence EIB risk and severity:

  • Cold, dry air increases risk 1
  • Indoor swimming pools (chlorine exposure) 1
  • High allergen or pollution environments 1

With appropriate diagnosis and management, EIB should not limit physical activity or athletic performance for most individuals.