Pathogenetic mechanisms of exercise-induced asthma and the refractory period

Exercise is a powerful stimulus to the development of asthma. In most asthmatic subjects the airways obstruction recovers spontaneously within 60 minutes, but in some subjects there is more prolonged airflow obstruction which requires bronchodilator treatment. Approximately 40-50% of subjects with EIA will show a refractory period of two to four hours after an initial exercise task, during which time an identical exercise task will evoke significantly less (less than 50%) bronchoconstriction. In some patients, particularly children, EIA will be followed three to nine hours later by a further episode of bronchospasm, termed the late asthmatic response. There remains considerable debate about the pathogenesis of EIA the refractory period and the late asthmatic response.