The physical and biological doses of methacholine are different for Mefar MB3 and Jaeger APS sidestream nebulizers

Within a study on respiratory symptoms in rural areas, we used the European Community Respiratory Health Survey methacholine challenge protocol. For quicker and more reliable handling, we had to change the nebulizer in the bronchial challenge system from Mefar model MB3 (Bovezzo, Italy) to Jaeger APS Sidestream (similar to Mefar; Würzburg, Germany). Therefore, we compared the physical properties of the two systems, adapted the challenge protocol, and compared the results of both systems in subjects with and without airway hyperresponsiveness to methacholine.

The physical properties of both systems were characterized by the residual method indicating a similar particle size distribution and an average output of 6 muL/s for Mefar MB3 and 1.25 muL/s for APS Sidestream. In the comparison study, 34 subjects were included. Airway responsiveness was quantified by provocative dose of methacholine causing a 20% fall in FEV(1).

A significant difference was found between the two challenge systems (p =0.004, McNemar test). Nine subjects reached a 20% drop in FEV(1) with the APS Sidestream only. The FEV(1) dropped by > 20% using either system in eight subjects. In 17 subjects, none of the two systems caused a 20% decrease in FEV(1).

Even if the physical dose is determined with elaborate methods, the biological dose may vary between two nebulizer systems, causing incomparable outcomes for subjects tested with different systems.