Airway responses to exercise in mild asthmatics

Measurements of flow on maximal and partial expiratory flow-volume (MEFV and PEFV) curves offer a simple, sensitive, and safe method for studying the prevalence, clinical characteristics, and airway changes of exercise-induced bronchospasm (EIB). These methods show that asthmatic individuals with even mild disease clearly differ from nonasthmatic persons in terms of their airway response to exercise. Nineteen asthmatic and fourteen nonasthmatic volunteers underwent graded exercise testing to elicit exercise-induced bronchospasm. Pulmonary function was measured using MEFV and PEFV curves before and after exercise. Exercise-induced bronchospasm was demonstrated in 17 of 19 asthmatic subjects without inducing marked degrees of airway constriction. The most sensitive index of EIB was changes in flow rates measured at low lung volumes, particularly those measured on PEFV curves. Analysis of flow-volume curves suggested two patterns of airway response to exercise among asthmatics, involving, respectively, small and larger airways. No significant changes in pulmonary function were demonstrated in the nonasthmatic subjects. The degree of EIB measured by changes in flow rates on the PEFV curve correlated with airway reactivity to nonspecific irritants such as cold weather, tobacco smoke, and respiratory tract infections, but not with a history of specific allergies. We suggest that EIB is a general feature of asthma, reflecting the increased reactivity of asthmatics to a wide variety of airway irritants.