Exercise-induced asthma, also known as exercise-induced bronchoconstriction, is characterized by airway narrowing shortly after rigorous exercise. This condition affects 5-20% of the general population and interestingly is more prevalent in elite aerobic sport athletes. Exercise-induced asthma can occur at any age but most cases are diagnosed by age 20 due to higher levels of activity in childhood.
How does exercise-induced asthma occur?
Vigorous exercise increases the minute ventilation, or amount of air a patient breathes into their lung each minute. A rush of cool, dry air triggers airway inflammation and bronchoconstriction, leading to symptoms such as cough, chest tightness, wheezing, and shortness of breath. Symptoms occur within 3-5 minutes of exercise onset and typically peak by 15 minutes. In most patients, after peak bronchoconstriction, there follows a refractory period where further exercise does not induce further symptom progression.
When patients are not exercising, they are usually asymptomatic without any pulmonary limitations. Some patients, however, may have more severe forms of asthma, where other triggers besides exercise also induce bronchoconstriction symptoms.
How is exercise-induced asthma diagnosed?
In most younger patients, a clinical history alone is enough to suggest a diagnosis of exercise-induced asthma. Formal diagnosis requires demonstration of decreased pulmonary function following simulated exercising done in the pulmonary lab. However, most patients do not require these tests to make a diagnosis. In older patients and those who present with unusual symptoms, formal testing in the pulmonary function lab is recommended. This will help distinguish exercise-induced asthma from other conditions such as cardiac disease, airway obstruction, acid reflux, and laryngeal or vocal cord dysfunction.
How is this condition managed?
One commonly asked question is whether it is safe to exercise with exercise-induced asthma. In the majority of cases, the answer is yes. Regular exercise is an essential aspect of a healthy lifestyle and can be safely incorporated for most patients with exercise-induced asthma. Furthermore, improving cardiovascular fitness decreases the minute ventilation required for exercise thus improving asthma control. A small percentage of patients with exercise-induced asthma actually may have exercise-induced anaphylaxis which is a much more serious condition. Patients with exercise-induced anaphylaxis should have a careful discussion with an allergist regarding how they can safely pursue exercise and triggers to be avoided before exercise. As a reminder, always make sure to consult with your personal physicians before starting a new exercise regimen.
Exercise modifications such as a slower warm-up phase and exercising in warmer and more humid conditions should be considered. The most common therapy is probably the use of short-acting beta-agonist inhalers approximately 5-15 minutes before the start of exercise. This will allow the airways to remain open throughout exercise. For elite athletes who exercise multiple times throughout the day, daily use of an inhaled corticosteroid or oral medication in the leukotriene receptor antagonist class may be necessary. If symptoms remain difficult to control, a consultation with a pulmonologist may be necessary to discuss treatment options for advanced asthma or consider alternative diagnoses.