SAMPLE-SIZE ESTIMATION IN STUDIES MONITORING EXERCISE-INDUCED BRONCHOCONSTRICTION IN ASTHMATIC-CHILDREN

Background - The repeatability of the response to standardised treadmi ll exercise testing using dry air and monitoring of heart rate in asth matic children suffering from exercise-induced bronchoconstriction (EI B) has not been well established. Methods - Twenty seven asthmatic chi ldren with known EIB performed standardised exercise testing twice wit hin a period of three weeks. The tests were performed on a treadmill w hile breathing dry air. During both tests heart rate had to reach 90% of the predicted maximum. Response to exercise was expressed as % fall in forced expiratory volume in one second (FEV1) from baseline and as area under the curve (AUG) of the time-response curve. Results - The intra-class correlation coefficients for % fall and AUC (log-transform ed) were 0.57 and 0.67, respectively. From these data, power curves we re constructed that allowed estimations to be made of sample sizes req uired for studies of EIB in children. These indicated that, ifa drug i s expected to reduce EIB by 50%, as few as 12 patients would be suffic ient to demonstrate this effect (90% power) using a parallel design st udy. Conclusions - Standardised exercise testing for EIB using dry air and monitoring of heart rate is adequately repeatable for use in rese arch and clinical practice in children with asthma.