The relation between age and time to maximal bronchoconstriction following exercise in children

SummaryBackgroundThe exercise challenge test (ECT) is a common tool for assessment of asthma in children. Many studies suggest that the “time to maximal bronchoconstriction” (Nadir-t) after exercise challenge in asthmatic children may be age-dependent, although this has never been systematically studied. Such findings may influence epidemiological surveys where the schedule of post-exercise measurements is trimmed. This study systematically assesses the relation between age and time to maximal bronchoconstriction post-ECT.MethodsData were collected retrospectively from 131 subjects (87 male; 3–18 years) who were referred for ECT. The routine ECT was performed according to ATS recommendation of a 6-min run. Spirometry was measured at 1, 3, 5, 10, 15, and 20 min post-exercise. The post-exercise nadir of FEV1 (%baseline) (FEV1-nadir) and the time to maximal fall in Nadir-t (minutes) were sought and values were related to age.ResultsBaseline FEV1 values (mean ± SD) were 90.5 ± 13.8% predicted. FEV1-nadir was −23.6 ± 11.7% from baseline values. The Nadir-t was reached at 5.1 ± 2.6 min (range 2–12 min). A positive correlation between children's age and Nadir-t was observed (r2 = 0.542; SD of residuals = 1.79; p < 0.001), regardless of FEV1-nadir, whether the cutoff of point was −10% or −15% of baseline FEV1. Children <10 years of age showed Nadir-t at 3.4 ± 1.7 min post-exercise and older children at 6.6 ± 2.5 min post-exercise (p < 0.0001).ConclusionOur results indicate that the time to maximal bronchoconstriction is age-dependent in children and adolescents, and imply that the schedule of post-exercise FEV1 measurements should be cautiously trimmed.