Comparison of intermittent and continuous inhalation provocation tests

To improve standardization of inhalation provocation tests, two tests utilizing intermittent and continuous inhalation of methacholine aerosol were compared in five normal and ten asthmatic patients. During the intermittent inhalation test, methacholine aerosols with stepwise incremental concentrations were inhaled during tidal breathing for two minutes with a following 5-minute pause interval. Specific airway conductase (SGaw) and respiratory resistance (Rrs) were measured one-half, one and one-half, and five minutes after the end of each inhalation period. Specific airway conductance and Rrs were measured with the panting and forced oscillation methods, respectively. During the continuous inhalation test, the same stepwise incremental concentrations of methacholine aerosol were inhaled during tidal breathing for two minutes without a pause while Rrs was continuously measured. The cumulative dose of methacholine required to reduce SGaw by 35% of the baseline value (PD₃₅ SGaw) during the intermittent inhalation test was significantly correlated with the cumulative methacholine dose required to reduce Grs (= 1/Rrs) by 35% of the baseline value during the continuous inhalation test (PD₃₅ Grs) (r = .98). There was also a significant correlation between the slopes of the intermittent inhalation test and continuous inhalation test curves (r = .80). The results indicate that methacholine provocation can be measured as reliably using a simple continuous inhalation method as by a more complex intermittent one.