| Exercise-induced asthma | |
|---|---|
| Classification and external resources | |
| ICD-10 | J45.990 |
| ICD-9 | 493.81 |
| DiseasesDB | 31728 |
| eMedicine | sports/155 |
| MeSH | D001250 |
Exercise-induced asthma, or E.I.A., is a medical condition that occurs when the airways narrow as a result of exercise. The preferred term for this condition is exercise-induced bronchoconstriction (EIB); exercise does not cause asthma, but is frequently an asthma trigger.
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While the potential triggering events for E.I.A. are well delineated, the underlying pathogenesis is poorly understood. It usually occurs after at least several minutes of vigorous, "aerobic" activity, which demands that normal nasal breathing be supplemented by mouth-breathing. The resultant inhalation of air that has not been warmed and humidified by the nasal passages seems to generate increased blood flow to the linings of the bronchial tree, resulting in edema. Constriction of these vessels then follows, worsening the degree of obstruction to airflow. This sequence generates symptoms similar to those seen in other forms of asthma, but occurs without the inflammatory changes that underlie them.
During an attack, the E.I.A. victim will likely be short of breath and/or coughing, with an elevated respiratory rate and wheezing, which may be audible even without a stethoscope. Examination will usually reveal the wheezing and a prolonged expiratory phase. In the occasional severe attack, altered level of consciousness and cyanosis due to depressed oxygenation of the blood may occur. Severe attacks are often the result of someone with both allergic and exercise-induced asthma exercising in a high-allergen environment (e.g. walking uphill alongside slowly moving traffic at dusk), and can be fatal.
In most cases, a relative "refractory period" follows resolution of an attack. During this approximately one hour period, resumption of exercise will likely produce either none or mild symptoms. Curiously as well, some 6–10 hours after the initial attack, a rebound attack with milder symptoms often develops without precipitating exertion.
The presence of exercise-induced asthma can be difficult to diagnose clinically given the lack of specific symptoms and frequent misinterpretation as manifestations of vigorous exercise. There are many mimics of EIB that present with similar symptoms, such as vocal cord dysfunction, cardiac arrhythmias, cardiomyopathies, and gastroesophageal reflux disease. Because of the wide differential diagnosis of exertional respiratory complaints, the diagnosis of exercise-induced asthma based on history and self-reported symptoms alone has been shown to be inaccurate.[1][2] If health care providers rely on history alone to make a diagnosis of exercise-induced asthma, evidence shows they will be incorrect > 50% of the time.[3]
Objective testing should begin with spirometry before and after inhaled bronchodilator therapy, which frequently identifies athletes who have abnormal baseline lung function and may warrant maintenance treatment for asthma. However, most individuals who experience exercise-induced asthma will have normal baseline lung function, and spirometry alone is not adequate to diagnose exercise-induced asthma.
Treadmill- or ergometer-based testing in lung function laboratories are effective methods for diagnosing exercise-induced asthma, but may result in false-negatives if the exercise stimulus is not intense enough.
Field-exercise challenge tests that involve the athlete performing the sport in which they are normally involved and assessing [[FEV1]] after exercise have been shown to be less sensitive than eucapnic voluntary hyperventilation.[4] The International Olympic Committee recommends eucapnic voluntary hyperventilation challenge as the test recommended to document exercise-induced asthma in Olympic athletes.
Pharmacological challenge tests, such as the methacholine challenge test, have a lower sensitivity for detection of exercise-induced asthma in athletes and are also not a recommended first-line approach in the evaluation of exercise-induced asthma.[5]
Mannitol inhalation is a promising new method for documenting exercise-induced asthma[6][7] and was recently approved for use in the United States.
As with any asthma, the best treatment is avoidance, when possible, of conditions predisposing to attacks. In athletes who wish to continue their sport or do so at times in adverse conditions, preventive measures that can be taken include altered training techniques and medications.
Some athletes take advantage of the refractory period by precipitating an attack by "warming up," and then timing their competition such that it occurs during the refractory period. Step-wise training works in a similar fashion. An athlete warms up in stages of increasing intensity, using the refractory period generated by each stage to get up to a full workload.
The most common medication approach is to use a beta agonist about twenty minutes before exercise. Some physicians prescribe inhaled anti-inflammatory mists such as corticosteroids or leukotriene antagonists, and mast cell stabilizers have also proven effective. A randomized crossover study compared oral montelukast with inhaled salmeterol, both given two hours before exercise. Both drugs had similar benefit but montelukast lasted 24 hours.[8]
As evidenced by the many professional athletes who have overcome E.I.A. using some combination of the above treatments, the prognosis is usually very good. Olympic swimmers Tom Dolan, Amy Van Dyken, and Nancy Hogshead, Olympic track star Jackie Joyner-Kersee, baseball Hall of Famer Catfish Hunter, and American football player Jerome Bettis are among the many who have done so.
According to International Olympic Committee statistics, during most of Olympic Games in last 20 years from 1/3 to 2/3 of athletes claimed to have asthma. Some medical experts tie such inordinate rates of reported asthma with athletes' desire to use complex medication to help them achieve better results.
Apart from sportsmen, school children are one of the major groups suffering from EIA as exercise programs and sports activities form a big part of most schools. Proactive schools usually set special EIA-friendly guidelines for EIA students so that they can be included in mainstream student exercise programs without feeling left out.[9]
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