The relation between age and time to maximal bronchoconstriction following exercise in children - 07/08/11

The 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.

Data 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 20min 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.

Baseline 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±2.6min (range 2–12min). 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±1.7min post-exercise and older children at 6.6±2.5min post-exercise (p<0.0001).

Our 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.