Exercise-induced bronchoconstriction is defined as acute, reversible airway narrowing that occurs during or after strenuous exercise. It is a very common problem, especially in physically active people, and can occur with or without underlying asthma. It is estimated that 10%-20% of the general population and up to 90% of people previously diagnosed with asthma have exercise-induced bronchoconstriction. Some studies suggest that exercise-induced bronchoconstriction can occur in as many as 30-70% of Olympic or elite-level athletes.
The following evidence-based guidelines were developed by the American Thoracic Society (ATS) to provide clinicians with practical guidance for the diagnosis and treatment of exercise-induced bronchoconstriction (EIB).
Diagnosis
Diagnosing EIB can be difficult as symptoms tend to be nonspecific and variable. Further, the presence or absence of common respiratory symptoms (such as chest tightness, cough, wheezing, and dyspnea) has very poor predictive value for the confirmation of EIB. Symptom severity ranges from mild to moderate – defined as causing impairment of athletic performance but rarely significant respiratory distress – and can be provoked by exercise or specific environments such as snowy mountains, ice rinks, or indoor swimming pools. An official EIB diagnosis should be established by monitoring changes in lung function provoked by exercise, not simply on the basis of symptoms.
Testing
To determine if EIB is present and to quantify the severity of the disorder, providers should conduct serial lung function measurements after a specific exercise or hyperpnea challenge. An example of an exercise challenge protocol is 5-8 minutes of exercise at 85% of maximum heart rate or 80% of maximal oxygen uptake (80% VO2 max). The type, duration, and intensity of exercise and the temperature and water content of the air are variables that should be considered. According to ATS and the European Respiratory Society guidelines, at least two reproducible FEV1 (forced expiratory volume in 1 second) values should be measured after the exercise challenge, with the highest value recorded at each interval – usually 5, 10, 15, and 30 minutes after exercise. Experts prefer measuring FEV1 because it is more discriminating and has better repeatability than peak expiratory flow rate.
There are a number of alternatives for testing, described in detail in ATS’s online supplement, which may be easier to implement than exercise challenges. These alternatives include eucapnic voluntary hyperpnea of dry air and inhalation of hyperosmolar aerosols of 4.5% saline or dry powder mannitol.
Interpreting results
Airway response is first calculated by finding the difference between the pre-exercise FEV1 value and the lowest FEV1 value recorded within 30 minutes after exercise. The percent fall in FEV1 from the baseline value is used to diagnose EIB, requiring a percentage fall of greater than 10% for official diagnosis. The severity of EIB can be graded as mild (more than 10% but less than 25% fall in FEV1), moderate (more than 25% but less than 50%), or severe (more than 50%).
Treatment
To prevent EIB, ATS recommends that patients use an inhaled short-acting beta2-agonist (SABA) 15 minutes prior to exercise and perform "interval or combination warm-up exercises" when possible. Use of a SABA prior to exercise provides 2-4 hours of attenuation of exercise-induced bronchospasm. Because of the potential for environmental triggers, ATS also recommends routine use of an air-warming and humidifying mask during exercise in cold weather. Daily use of a SABA may result in the development of tolerance, with reduction in the amount and duration of protection from EIB. This is thought to be due to desensitization of the beta2-receptors on mast cells.
For patients who have an inadequate response to an inhaled SABA before exercise and/or patients who require an inhaled SABA daily or more frequently, a controller agent such as an inhaled corticosteroid or a leukotriene receptor antagonist is recommended. Patients should be informed that maximal therapeutic benefit may take 2-4 treatment weeks.
In addition to the daily regime, ATS suggests the addition of a mast cell stabilizing agent or an inhaled anticholinergic agent before exercise if needed (both are relatively weaker recommendations). And finally, they recommend against daily use of an inhaled long-acting beta2-agonist (LABA) as a single therapy because of the strong concern for adverse side effects.
Special provisions
ATS recommends antihistamine use for patients with EIB and allergies who continue to be symptomatic despite daily or more frequent inhaled SABA use. They recommend against using antihistamines for patients who have EIB but who do not have allergies.
ATS also provides some weaker recommendations for those who want to control EIB symptoms with dietary modification. A low-salt diet supplemented with fish oils and ascorbic acid may increase symptom control.