Keeping children with exercise-induced asthma active.

Abstract

Exercise-induced bronchospasm, exercise-induced bronchoconstriction, and exercise-induced asthma (EIA) are all terms used to describe the phenomenon of transient airflow obstruction associated with physical exertion. It is a prominent finding in children and young adults because of their greater participation in vigorous activities. The symptoms shortness of breath, cough, chest tightness, and wheezing normally follow the brief period of bronchodilation present early in the course of exercise. Bronchospasm typically arises within 10 to 15 minutes of beginning exercise, peaks 8 to 15 minutes after the exertion is concluded, and resolves about 60 minutes later, but it also may appear during sustained exertion. EIA occurs in up to 90% of asthmatics and 40% of patients with allergic rhinitis; among athletes and in the general population its prevalence is between 6% and 13%. EIA frequently goes undiagnosed. Approximately 9% of individuals with EIA have no history of asthma or allergy. Fifty percent of children with asthma who gave a negative history for EIA had a positive response to exercise challenge.6 Among high school athletes, 12% of subjects not considered to be at risk by history or baseline spirometry tested positive. Before the 1984 Olympic games, of 597 members of the US team, 67 (11%) were found to have EIA. Remarkably, only 26 had been previously identified, emphasizing the importance of screening for EIA even in well-conditioned individuals who appear to be in excellent health. The severity of bronchospasm in EIA is related to the level of ventilation, to heat and water loss from the respiratory tree, and also to the rate of airway rewarming and rehydration after the challenge. Postexercise decrease in the peak expiratory flow rate of normal children may be as much as 15%; therefore, only a decrease in excess of 15% should be viewed as diagnostic. EIA is usually provoked by a workload sufficient to produce 80% of maximum oxygen consumption; however, in severe asthmatics even minimal exertion may be enough to produce symptoms. Patients with normal lung function at rest may have severe air flow limitation induced by exercise,10 and as many as 50% of patients who are well-controlled with inhaled corticosteroids still exhibit EIA. A challenge of sufficient magnitude will provoke EIA in all patients with asthma. PHARMACOLOGIC THERAPY: Exercise, unlike exposure to allergens, does not produce a long-term increase in airway reactivity. Accordingly, patients whose symptoms manifest only after strenuous activity may be treated prophylactically and do not require continuous therapy. Most asthma medications, even some unconventional ones such as heparin, furosemide, calcium channel blockers, and terfenadine, given before exercise, suppress EIA. McFadden accounts for the efficacy of these disparate classes of drugs by their potential effect on the bronchial vasculature that modulates the cooling and/or rewarming phases of the reaction. Short-acting -agonists provide protection in 80% to 95% of affected individuals with insignificant side effects and have been regarded for many years as first-line therapy. Two long-acting bronchodilators, salmeterol and formoterol, have been found effective in the prevention of EIA.18-21 A single 50-microg dose of salmeterol protects against EIA for 9 hours; its duration appears to wane in the course of daily therapy. Cromolyn sodium is highly effective in 70% to 87% of those diagnosed with EIA and has minimal side effects. Nedocromil sodium provides protection equal to that of cromolyn in children. Children commonly engage in unplanned physical activity and sometimes are not allowed to carry their own medication. Thus, a simple long-acting regimen given at home is likely to be more effective than short-acting drugs that must be administered in a timely manner. Although the 12-hour protection by salmeterol reported by Bronsky et al may not persist with continued use, the 9-hour duration of action is