Exercise-induced bronchoconstriction

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Exercise-induced bronchoconstriction (EIB) is the acute constriction of the lower airways that manifests during physical exertion. Although EIB most commonly affects individuals with asthma, it can also manifest in those without a history of asthma. The typical presentation includes dyspnea, wheezing, cough, and chest tightness that begins within 15 minutes of initiating intense exercise and resolves within an hour. The initial diagnostic workup comprises of spirometry with bronchial reversibility testing, and depending on results, may be followed by additional studies (e.g., bronchial provocation studies, evaluation of differential diagnoses) or the initiation of treatment. The first step in management is nonpharmacological therapy (e.g., pre-exercise warm-up, reduction of environmental triggers) for all patients and therapeutic optimization in patients with asthma. First-line pharmacological therapy consists of inhaled beta-agonists 15–30 minutes before exercise; usage should be limited to no more than 3 times a week to prevent tachyphylaxis. Patients with refractory symptoms or those who require inhaled beta-agonists ≥ 4 times a week should be started on daily pharmacological therapy (e.g., with inhaled corticosteroids or montelukast); referral to a pulmonologist may be considered.

• 10–15% of the general population ^[2]
• 80–90% of individuals with asthma ^[2]

Epidemiological data refers to the US, unless otherwise specified.

• Symptoms typically start within 15 minutes of initiation of intense exercise, and resolve within 60 minutes. ^[3]
• Common symptoms include: ^[3]
  • Dyspnea
  • Wheezing
  • Cough
  • Chest tightness (or chest pain, in children)
  • Increased mucus production
  • Reduced exercise tolerance

EIB typically develops within 15 minutes of exercise and may continue to worsen despite cessation of exercise; if SOB rapidly resolves with cessation of physical activity, consider differential diagnoses of EIB, e.g., deconditioning. ^[3][4]

Approach ^[3][5][6]

• Perform baseline spirometry with bronchial reversibility testing. ^[7]
• If spirometry is normal but EIB is still suspected, perform a bronchial provocation test.
  • Positive provocation test: EIB confirmed; start treatment.
  • Negative bronchial provocation test: Workup for differential diagnoses of EIB.

Spirometry with reversibility testing ^[3][5][6]

Baseline spirometry should be performed in all patients to assess for asthma and help exclude differential diagnoses of EIB.

Bronchial provocation tests

• Exercise challenge test ^[5][6]
  • Measure spirometry at baseline.
  • Patients exercise to achieve 85–95% of their estimated maximum heart rate for approximately 6 minutes.
  • During the challenge, patients breathe dry air (< 10 mg H2O/L) through the mouth.
  • Spirometry is performed at 5, 10, 15, and 30 minutes after exercise.
  • Airway obstruction is present if an FEV₁ drop of ≥ 10% is recorded in 2 consecutive measurements.
• Surrogate bronchial provocation tests: used as an alternative to exercise to assess bronchial hyperresponsiveness ^[5][6]
  • Eucapnic voluntary hyperpnea (EVH) ^[3]
    • Positive if there is ≥ 10% drop in FEV₁
    • Preferred in professional athletes but not widely available
  • Histamine or methacholine challenge test: positive if ≥ 20% drop in FEV₁
  • Osmotic agents (mannitol, hypertonic saline): positive if there is ≥ 15% drop in FEV₁

Exercise challenge tests can also be performed in the field using portable spirometry; this may be helpful for individuals whose EIB is triggered by particular sports or weather conditions. ^[3]

Exercise-induced bronchoconstriction can coexist with other conditions causing exercise-induced dyspnea, including exercise-induced laryngeal dysfunction, cardiac disorders, and anxiety. ^[6]

The differential diagnoses listed here are not exhaustive.

Approach ^[3][5][6]

• Advise all patients on nonpharmacological therapy.
• Patients with known asthma: optimize asthma treatment, including inhaler technique and medication adherence. ^[4]
• Patients with no history of asthma: Start an inhaled beta-agonist to be used before exercise.
• Reevaluate patients regularly.
• Patients with refractory symptoms may benefit from daily therapy.
• Consider referral to a pulmonologist for patients with atypical or refractory symptoms.

Nonpharmacological therapy ^[3]

• Pre-exercise warm-up and breathing exercises. ^[3][6]
  • Warm-up should be for 10–15 minutes at 50–80% of the maximum heart rate.
  • May create a refractory period for up to 3 hours in which symptoms are not experienced ^[6]
• Reduction of environmental triggers, e.g.: ^[3]
  • Cold weather
    • Advise patients to exercise indoors during the winter months.
    • For outdoor exercise, patients should cover the mouth with a mask or scarf and/or breathe through the nose.
  • Allergens
    • Avoid exercising near high-traffic roads or during peak travel hours.
    • Train indoors if the pollen count is high; avoid exercising outdoors early in the morning and late in the day, and shower immediately afterward. ^[3]
    • Patients who react to chlorine should avoid indoor pools and consider swimming in water disinfected using other methods. ^[3]
• Recommend smoking cessation. ^[10]
• There is some weak evidence to support a low sodium diet, and fish oil and ascorbic acid supplementation. ^[3][5]

Pharmacological therapy ^[3][4][5]

First-line: beta-agonist therapy

• Options (see also “Antiasthmatic medications”) ^[3][4][5]
  • SABA, e.g., albuterol
  • LABA, e.g., salmeterol
  • Patients with known asthma: inhaled corticosteroid/LABA combination, e.g., budesonide/formoterol (off label)
• Use: ^[6]
  • 10–15 minutes prior to exercise
  • Maximum ≤ 3 times/week ^[5]
• If response is insufficient and/or beta-agonist is needed ≥ 4 times/week, manage as refractory EIB.

Refractory symptoms

• Consider the addition of any of the following: ^[6]
  • Daily inhaled corticosteroid, especially in patients with asthma (for recommendations and dosages see “Antiasthmatic medications”) ^[4]
  • LTRA, e.g., montelukast daily or 2 hours pre-exercise ^[3][6]
• Specialists may suggest anticholinergic agents, mast cell stabilizers, or methylxanthines, but their efficacy in EIB is unclear.

Elite athletes require both specific confirmatory testing and therapeutic use exemptions for some medications in order to compete; check with the relevant sporting bodies (e.g., World Anti-Doping Agency) before prescribing medications. ^[3]

Patients should not use an inhaled SABA or LABA ≥ 4 times/week, as chronic use can result in tolerance. ^[6]