Methacholine Challenge Testing: A Novel Method for Measuring PD 20 .

BACKGROUND: New guidelines for methacholine challenge testing recommend reporting the test outcome as dose rather than concentration. Jet nebulizers have historically been used for methacholine challenge testing, but much of the weight loss, often (incorrectly) referred to as aerosol output, is actually evaporation. The Wright nebulizer is well characterized and still widely used, but its availability is unclear, and it is nondisposable. We developed a novel method using a vibrating mesh nebulizer (Solo). This method was compared with the standard 2-min tidal breathing method using the Wright nebulizer. Repeatability within and between nebulizers was also tested.

METHODS: Fifteen patients with mild asthma completed four methacholine challenges (two with the Solo vibrating mesh nebulizer and two with the Wright jet nebulizer). Challenges with the same nebulizer were 24 h apart, and challenges between nebulizers were separated by 1 week. Standard 2-min tidal breathing methods were used with the Wright nebulizer. For the Solo nebulizer, the tidal breathing method was modified by nebulizing to completion 0.5 mL of doubling concentrations of methacholine at 5-min intervals.

RESULTS: Geometric mean methacholine doses required to cause a 20% fall in FEV1 were similar (96 vs 110 μg; P > .05); methacholine concentrations that caused a 20% fall in FEV1 were significantly lower with the vibrating mesh nebulizer (0.48 vs 4.4 mg/mL; P < .001). Repeatability of methacholine doses required to cause a 20% fall in FEV1 within and between nebulizers was excellent (intraclass correlation coefficient > 0.92).

CONCLUSIONS: We have developed a novel, simple, repeatable method for conducting methacholine challenges using new nebulizer technology. Importantly, the method meets recommendations set out in the new guidelines.

TRIAL REGISTRY: ClinicalTrials.gov; No.: 02965482; URL: www.clinicaltrials.gov.