Abstract

Bronchial methacholine challenge is well established in asthma diagnostics and research. ATS guidelines propose a five step standard dosimeter (SDM) protocol with incremental concentrations of methacholine to calculate the concentration causing a 20% drop in FEV1 in an individual (PC20FEV1). In contrast, the aerosol provocation system (APS) by Viasys automatically determines the administered dose of methacholine by measuring the effective nebulisation time and referring it to drug concentration and nebuliser power. Therefore, it offers a feasible and less time-consuming provocation procedure by applying incremental doses (PD20) of methacholine using a single concentration (16 mg/mL methacholine, APS-SC). In this study
we compared these two methods in 52 young adults (25+/- 5.8 years). Following a screening visit, subjects were randomly assigned to undergo either SDM or APS-SC followed by the other method within 1 week. A close correlation between concentration and dosage causing a 20% fall of FEV1 was found (r=0.69, p<0.001). Using the ATS categorisation of bronchial responsiveness we interpreted the results of the APSSC method as follows: PD20 methacholine <0.3 mg as ‘‘moderate to severe BHR’’, 0.3-0.6 mg as
‘‘mild BHR’’, 0.6-1.0 mg as ‘‘borderline BHR’’, and >1.0 mg as ‘‘normal bronchial response’’.
We conclude that the five-step APS-SC is a suitable method, providing reliable results. In clinical practice the APS-SC is a timesaving procedure and less prone to errors since only one dilution of methacholine is necessary compared to the SDM.

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