Bronchodilator response in asthmatic children is significantly reduced when measured immediately after methacholine challenge.

Aim: Airway responses to a bronchodilator (BDR) and to methacholine are frequently measured in the assessment of childhood asthma and in pulmonary research. For practical reasons, we wondered whether it would be possible to obtain a reliable BDR immediately after completion of a methacholine challenge test. To this end, we compared BDR with and without a preceding methacholine challenge.

Methods: The BDR was measured twice in random order on consecutive days in 24 asthmatic children with methacholine hyperresponsiveness. It was calculated as the change in forced expiratory volume in one second (FEV1) before and 20 min after inhaling 800 microg of salbutamol (metered dose inhaler with a spacer), expressed as a percentage of the predicted value (deltaFEV1%pred). On one day BDR was measured immediately after completing a methacholine challenge, on the other day without any preceding challenge.

Results: Mean(SD) baseline FEV1%pred was not significantly different between test days [98.6(14.2)% and 98.1(13.8)%, respectively, p=0.53]. The geometric mean provocative dose of methacholine producing a 20% fall in FEV1 (PD20) was 56.2 microg (range 10.3-306.2 microg). The mean (SEM) BDR without preceding methacholine challenge was 10.8(1.4)%, while after preceding methacholine challenge it was 5.2(1.5)% (mean difference 5.6%, 95% CI 3.0%-8.1%, p<0.001). Mean(SEM) postbronchodilator FEV1%pred was 109.4(3.0)% without and 103.4(2.7)% with preceding methacholine challenge (mean difference 6.0%, 95% CI 3.5%-8.6%, p<0.001).

Conclusion: A preceding methacholine challenge significantly reduces BDR in asthmatic children. Therefore, a BDR, measured immediately after completing a methacholine challenge, cannot be used as a substitute for a separate bronchodilator test.