Comparison of airway conductance and FEV1 as measures of airway responsiveness to methacholine - Discrimination of small differences in bronchial responsiveness with Gaw and FEV1

When defining bronchial responsiveness in healthy, non-asthmatic, subjects exposed in different working situations, it is not clear whether different outcome measures yield similar results. Therefore, the concentration and do se of methacholine that caused a 20% decrease in forced expiratory volume i n 1 s (FEV1) (PC20(FEV1) and PD20(FEV1)), the corresponding change in Gaw a nd the relationship between the dose-response slope (DRS) for FEV1 and Gaw was studied in different working populations and healthy control subjects ( n = 1038). The two outcome measures were compared in groups of subjects in whom differences in bronchial responsiveness could be anticipated [atopics (n = 72) and non-atopics (n = 207) and subjects exposed (n = 54) and not ex posed (n = 32) to saw dust]. A bronchial challenge was also made before and after exposure in a swine confinement building, an exposure known to incre ase bronchial responsiveness (n = 37). PD20(FEV1) was 1.7 mg in atopics and 4.9 mg in non-atopics, 7.1 mg in saw dust exposed and >20 mg in non-expose d subjects and 5.3 mg before and 0.79 mg after exposure to organic dust. Th ere was a correlation between DRSFEV1, and DRSGaw, r = 0.87 (P<0.001). In s ubjects who were highly sensitive to methacholine a 20% change in FEV1 corr esponded to <40% change in Gaw, while a 20% decrease in FEV1 corresponded t o none or a minor decrease in Gaw in subjects with less methacholine-sensit ive airways. The ability to detect differences in bronchial responsiveness between groups, or to detect changes in bronchial responsiveness following exposure was approximately the same for FEV1 and Gaw. The reproducibility w as similar for both variables and a second measurement was within one doubl ing of the methacholine concentration of the first provocation in approxima te to 95% of all measurements (n = 41). In conclusion, with our methacholin e provocation method, FEV1 and Gaw had similar sensitivity in detecting sma ll differences in bronchial responsiveness in healthy subjects.