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The term exercise-induced asthma is often used to describe intermittent narrowing (bronchoconstriction) of the airways following exercise. The term, however, is potentially misleading as it implies that exercise causes asthma.
Exercise-induced bronchoconstriction (EIB) is the presently preferred term to describe symptoms that occur when the airway narrows because of physical activity. EIB is present in a significant percentage of patients with asthma but may also occur in individuals without asthma.
WHAT ARE THE SYMPTOMS OF EXERCISE-INDUCED BRONCHOCONSTRICTION (EIB)?
The symptoms of EIB are variable and sometimes nonspecific. Symptoms may include shortness of breath, feeling of chest tightness, cough, and wheezing.
These symptoms usually begin in 10 to 15 minutes of intense exercise and often resolve with rest by 30 to 60 minutes. Symptoms may range from mild to severe. Hoarseness, stridor (high-pitched noise during inhalation), and a feeling of throat tightening are not common symptoms of EIB and should raise the possibility of exercise-induced vocal cord dysfunction.
WHAT CAUSES EXERCISE-INDUCED BRONCHOCONSTRICTION?
To meet the body’s oxygen demand, we breathe faster, deeper, and with an open mouth during exercise. Therefore, the air reaching the airways during exercise lacks the warming and humidifying effects that happen when breathing more slowly through the nose.
Drying of the airway lining (mucosa) and cooling the airway during exercise has been proposed as a possible mechanism for airway narrowing during exercise. Environmental exposures during exercise may also contribute to EIB. Such exposures include cold air, dry air, ambient ozone, and airborne particulate matter.
HOW IS EXERCISE-INDUCED BRONCHOCONSTRICTION DIAGNOSED?
The diagnosis of EIB is often made based on self-reported symptoms without objective lung function tests. However, self-reported symptoms have been shown to be poor predictors of EIB, and diagnosis based on symptoms alone would result in a large proportion of patients with these symptoms getting diagnosed with EIB when they do not have one.
Current guidelines (American Thoracic Society, European Respiratory Society) require documentation of lung function changes provoked by exercise to diagnose EIB. A treadmill or bicycle exercise test provides useful information about the presence of EIB.
During an exercise challenge, the inhaled air should be dry, and the exercise needs to be intense enough to trigger symptoms. Therefore, serial lung function tests are done before and after the end of the exercise. A decline in lung function by more than 10% after exercise from the baseline (obtained before exercise) is required for an EIB diagnosis.
Several substitutes for exercise testing have been developed. These include cold-air challenge (having an individual hyperventilate while breathing air that has been cooled to a temperature of between -10°C and -20°C) and inhalation of a 4.5% saline or dry powder mannitol. These substitute tests are not as accurate as exercise challenge tests, but they all have utility for identifying sensitive airways consistent with a diagnosis of EIB. In our practice, we use cold, dry air during exercise to increase the accuracy of the exercise test.
WHAT OTHER CONDITIONS MIMIC EXERCISE-INDUCED BRONCHOCONSTRICTION?
Several conditions could present with symptoms similar to those of exercise-induced bronchoconstriction.
An individual with exercise-Induced vocal cord dysfunction may complain of shortness of breath and throat tightness during exercise. Anxiety may produce a heightened sense of breathlessness and dyspnea during exercise and can result in hyperventilation. Deconditioning and obesity can imitate EIB. In addition, cardiac abnormalities, pulmonary arteriovenous malformations, disease of skeletal muscles (myopathies), and diseases of the lungs could present initially with shortness of breath during exercise.
HOW IS EXERCISE-INDUCED BRONCHOCONSTRICTION TREATED?
Exercise should not be avoided because of EIB. However, several steps can be taken to minimize or prevent bronchoconstriction from happening in the first place and to relieve bronchoconstriction should it occur.
Inhaled short-acting bronchodilators, such as Albuterol, taken before exercise can prevent and control EIB symptoms. If your child continues to have symptoms despite taking albuterol before exercise, you should talk to your child’s pediatrician or pulmonologist about other treatment options. In addition to medications, maneuvers to prewarm and humidify the air during exercise (e.g., wearing a loose scarf or mask over the nose and mouth when exercising outside on very cold days), a warm-up phase before regular exercise and a cool-down period afterward could help prevent EIB.
You should also restrict your child from exercising in the presence of viral upper respiratory infections. In addition, if your child has a pollen allergy, outside exercise should be limited during high pollen days.
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