Exercise-induced asthma. Physiologic and clinical considerations

Exercise-induced asthma is one feature of the generalized increase in non-specific airways reactivity found in asthma. It represents an important symptom complex since it may be a major disabling manifestation of asthma or may be an unrecognized cause of exercise-induced dyspnea. While exercise-induced asthma appears to be produced by cooling and drying of the respiratory tract, the precise mechanism by which airway cooling produces bronchospasm is unknown. Various hypotheses include vagal and sympathetic neural mechanisms, the release of mediators of immediate hypersensitivity, and alterations in the properties of airway secretions. In spite of these controversies, the physiologic manifestations of post-exertional asthma are well characterized. Within 10 minutes after cessation of exercise, bronchospasm develops. It lasts for 30 to 60 minutes and its severity is accentuated by higher levels of pulmonary ventilation and breathing cold dry air. Exercise challenge testing or the assessment of airways reactivity to pharmacologic agents may be useful in evaluating this syndrome in some clinical situations. Fortunately, in most asthmatics, exercise-induced bronchospasm can be prevented or reversed with routine pharmacologic therapy.