Sensitivity of peak expiratory flow rate for diagnosing bronchial obstruction on methacholine inhalation challenge in school-aged asthmatic children.

To study whether forced expiratory volume in 1 s (FEV1) for the diagnosis of bronchial reactivity by means of the methacholine inhalation challenge test could be appropriately replaced by simple measurements of peak expiratory flow rate (PEFR), 75 consecutively referred asthmatic children aged 6-15 y were examined during a symptom-free period. Their baseline FEV1 and PEFR values ranged from 70 to 130% (mean 99.1) and from 77 to 122% (mean 101.4) of those predicted, respectively. The methacholine inhalation challenge was performed with stepwise doubled cumulative doses and both FEV and PEFR were measured at each step. Of the 67 children who had a 20% reduction in either test, the fall in FEV was achieved after a lower dose of methacholine than the 20% fall in PEFR in 49 cases, after a higher dose in 15 and after the same dose in 3. There was a significant correlation (r = 0.56, p < 0.001) between the changes in FEV1 and PEFR, although considerable scatter was found in the results. The 64 children who had a reduction of 20% in FEV showed a corresponding drop in PEFR that varied from 1.8 to 28.8% (mean 15.3), including 9 children for whom this drop was less than 10%. The results indicate that if the challenge test were based on PEFR measurements, the reference values for the test would have to be different.