Comparison of two standardized methods of methacholine inhalation challenge in young adults

In the European Community Respiratory Health Study (ECRHS), airway responsi veness to methacholine was determined using the Mefar dosimeter protocol. E lsewhere, the 2-min tidal breathing method has become the preferred standar dized method. The relationship between measurements of responsiveness by th ese two methods is not well established. This study measured airway responsiveness to methacholine by dosimeter and tidal breathing methods in 47 healthy asthmatic subjects aged 20-44 yrs. Te sts were performed within 1 week and in random order. Baseline forced expiratory volume in one second (FEV1) varied by <10% betwe en tests in 42/47 subjects. There was a close association between responsiv eness determined by the two methods. A provocative concentration of methach oline causing a 20% fall in FEV1 (PC20) value of less than or equal to 8.0 mg.mL(-1) (tidal method) used to categorize airway hyper-responsiveness agr eed most closely with a provocative dose of methacholine causing a 20% fall in FEV1 (PD20) value of less than or equal to 0.5 mg (dosimeter method) (k appa statistic 0.78). Each doubling or halving of PC20 to define a level of hyperresponsiveness agreed closely with a doubling or halving of PD20. Assessment of airway responsiveness as provocative dose of methacholine cau sing a 20% fall in forced expiratory volume in one second by the Mefar dosi meter protocol gave a close and predictable relationship with provocative c oncentration of methacholine causing a 20% fall in expiratory volume in one second assessed using the tidal breathing method. Airway hyperresponsivene ss as determined by the accepted criterion of provocative concentration of methacholine causing a 20% fall in expiratory volume in one second less tha n or equal to 8 mg.mL(-1) was best correlated with provocative dose of meth acholine causing a 20% fall in forced expiratory volume in one second <0.5 mg by Mefar dosimeter.