The relationships of ΔFVC and PC ₂₀ on the dose-response curve to methacholine with peak expiratory flow variability in children with mild asthma

Background : In asthmatic subjects, not only airway sensitivity but maximal airway response are increased on the dose-response curve to methacholine. The percentage decrease in forced vital capacity (ΔFVC) at the methacholine PC 20 (provocative concentration causing a 20% fall in FEV 1 ) has been proposed as a surrogate marker of maximal airway response. Another hallmark of asthma is increased spontaneous variation in airway caliber, which is commonly measured by peak expiratory flow (PEF) variability. Aims : The aim of this study was to compare airway sensitivity and ΔFVC with regard to their relationships with PEF variability in children with mild asthma. Methods : Fifty-five children with mild asthma underwent methacholine challenge testing, and ΔFVC and PC 20 were measured. Subjects recorded PEF each morning and each evening for 14 consecutive days. PEF variability was expressed as amplitude percentage mean (amp%mean), averaged over 14 days, and as the lowest percentage highest (low%high), recorded over the period. Results : Methacholine PC 20 did not correlate with both indices of PEF variability (amp%mean r=-0.220, P=0.106 ; low%high r=0.189, P=0.166). However, there was a significant and strong correlation between ΔFVC and both amp%mean (r=0.444, P=0.001) and low%high (r=-0.352, P=0.008). Conclusions : The close relationship between PEF variability and ΔFVC, but not methacholine PC 20 , suggests that PEF variability may be better refracted by maximal airway response than by airway hypersensitivity.