Occurrence of a late response to exercise in asthmatic children: multiple regression approach using time-matched baseline and histamine control days

At the present time, there is still controversy concerning the presence of a late asthmatic response (LAR) to exercise challenge in asthma. We have, therefore, investigated the occurrence of a LAR after exercise in asthmatic children visiting an out-patient clinic, using time-matched baseline and histamine control days, and a statistical analysis according to recently published recommendations. After a screening exercise day, 17 children (aged 7-14 yrs) randomly performed, on three subsequent study days, either: a second standardized exercise challenge; or a histamine challenge whilst matching the bronchoconstriction after exercise; or measurement of baseline lung function without any challenge. Measurements of forced expiratory volume in one second (FEV1) were made repeatedly during 8 h. Analysis was performed using multiple regression analysis for each patient, with FEV1 as the dependent, and test day (exercise or control) and clock time as independent variables during the period 2-8 h after exercise. A significant interaction (p <0.05) between test day and clock time was considered to be indicative of a LAR. Fifteen children completed the study. All children showed an early asthmatic reaction to exercise (range 14-62% fall in FEV1). In two children, a significant interaction (p <0.05) was found between test day and clock time. However, the difference in FEV1 between exercise and control days for each clock time did not exceed the 99.6% confidence limits of normal diurnal variation in any of the children. We conclude that, in children with mild-to-moderate asthma, a LAR to exercise does not occur. This suggests that exercise is only a symptomatic trigger of asthma. Whether exercise is capable of inducing inflammation needs to be further investigated