Methacholine Challenge: Comparison of Airway Responsiveness Produced by a Vibrating Mesh Nebulizer Versus a Jet Nebulizer.

BACKGROUND

The latest methacholine challenge testing (MCT) guidelines published by the European Respiratory Society recommend the characterization of nebulizers before their use in clinics and research. Such investigations are necessary for accurately determining the provocative dose of methacholine causing a 20% fall in FEV (PD) delivered by a given device. The standard English Wright (Wright) jet nebulizer recommended in the 1999 guidelines by the American Thoracic Society has become difficult to obtain and possesses some characteristics that complicate the calculation of dose delivery from this device (e.g. evaporation). Our objective was to determine if the Aerogen Solo (Solo) vibrating mesh nebulizer provides similar methacholine challenge test results compared to the currently used Wright jet nebulizer.

METHODS

Sixty mild-to-moderate asthmatics were studied across three research sites in a randomized crossover study. Both methacholine challenges were completed at least 24 hours apart within a 2-week period. Testing with the Wright device was performed as per the 2-minute tidal breathing protocol. The Solo study arm followed the same procedure except for a shorter inhalation time of 1 minute. The provocative concentration of methacholine causing a 20% fall in FEV (PC) and the methacholine PD were calculated following each methacholine challenge.

RESULTS

The geometric mean methacholine PC values for the Solo and the Wright differed statistically (0.65 mg/mL vs. 2.58 mg/mL, respectively, p < 0.00001) and clinically. Between-nebulizer geometric mean methacholine PD results are comparable by clinical standards [81.7 μg (Solo) vs. 64.7 μg (Wright)], although the slight difference in dose was statistically significant (p = 0.018).

CONCLUSIONS

The comparability of PD values between the Solo and the Wright validates the importance of reporting airway responsiveness to methacholine in terms of dose and not concentration, as stressed in the latest testing guidelines. This finding along with several benefits associated with the Solo make it a promising nebulizer for performing MCT.