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The reproducibility and sample size requirements of exercise-induced bronchoconstriction measurements

¹ Division of Respiratory Medicine, Dept of Medicine at Karolinska Hospital, Karolinska Institute, Stokholm, Sweden. ² Asthma Research Group, McMaster University, Hamilton, Ontario, Canada

CORRESPONDENCE: M.D. Inman, Dept of Medicine, McMaster University, St Joseph's Hospital, Hamilton, Ontario, Canada. Fax: 19055406510

Keywords: asthma, exercise-induced bronchoconstriction, intraclass correlation coefficient, power, study design

Received: December 31, 1999
Accepted October 9, 2000

Dry air exercise challenges are frequently used to screen medications that have potential utility in the management of exercise–induced bronchoconstriction (EIB). The purpose of this study was to determine the reproducibility of three outcome measurements made using such challenges, and sample size requirements for drug evaluation studies based on these outcomes.

Forty adult subjects with asthma, who tested positively on a screening exercise challenge, were subjected to two further identical challenges, separated by 1 to >35 days. Outcome measurements included the maximum per cent fall in forced expiratory volume in one second (FEV₁), after exercise (% fall_max), and the area under the per cent fall in FEV₁/time curve for 30 min (AUC₃₀) and 60 min (AUC₆₀) after exercise.

The reproducibility of these outcomes, as assessed by intraclass correlation coefficients was 0.72, 0.53 and 0.35 for % fall_max, AUC₃₀ and AUC₆₀ measurements, respectively. The sample size requirements to demonstrate an attenuation of EIB equivalent to a 50% reduction in % fall_max was 9, 14 and 19 subjects for the % fall_max, AUC₃₀ and AUC₆₀ responses, respectively (90% power).

It is concluded that the maximum percentage fall in forced expiratory volume in one second has greater reproducibility and results in greater power in clinical trials than area under the curve measurements. Sample size calculation curves are provided which may be used in study design and interpretation of published studies.