Exercise-induced bronchospasm in children: comparison of FEV1 and FEF25-75% responses

The response of asthmatic children to exercise has usually been evaluated by forced expiratory volume in 1 sec (FEV(1)). We reasoned that other respiratory indexes derived from the forced vital capacity maneuver such as forced expiratory flow between 25-75% of vital capacity (FEF(25-75%)) would add significant information in the evaluation of the relationship between asthma severity and response to exercise. We studied 164 children with intermittent (n = 63), mild persistent (n = 30), moderate persistent (n = 40), and severe persistent asthma (n = 31). Subjects exercised for 6 min on a cycle ergometer at 80% of their maximum heart rate, and spirometry was performed before and 5, 10, and 20 min after exercise. There was good correlation between changes in FEV(1) and FEF(25-75%) after exercise (r = 0.60, P < 0.001 for intermittent asthma and r = 0.80, P < 0.001 for severe persistent asthma). The presence of a fall in both FEV(1) (>/=10%) and in FEF(25-75%) (>/=26%) when compared to a decrease in only one of these two indexes was significantly greater in children with more severe asthma (60.0% for intermittent asthma and 94.4% for severe persistent asthma, P = 0.022). FEF(25-75%) can decrease in response to exercise without changes in FEV(1), mainly in children with mild asthma. In the evaluation of the response to exercise in children with different asthma severities, more than one maximum expiratory flow-volume parameter should be used.