30 Seconds tidal breathing method with AeroEclipse II nebulizer (AE) versus aerosol provocation system (APS) in methacholine challenge testing

Introduction: Methacholine challenge tests (MCT) are often used to rule out asthma. Recently it has been recommended that for a high sensitive test the methacholine should be inhaled without deep inhalations. Aim: Our objective was to compare the methacholine PD20 performed with an AE, with the standard APS method. Methods: From Nov to Dec 2013, 100 patients (mean age 54 ± 17), 30 m, performed a MCT using a 30 sec tidal breathing (TB) method with an AE. From Nov to Dec 2012, 100 patients (mean age 50 ± 16), 34 m, used a dosimeter method on APS. The nebulizers were calibrated and outputs were calculated to administer the same cumulative dose (2.27 mg). A maximum of 9 doubling concentrations of methacholine was used. FEV1 was measured by spirometry after each dose. The PD20 is a calculated value of the dosage of methacholine required to cause a 20% fall in the subject9s FEV1. The number of patients with a positive tests (PD20 Results: In the 30 sec TB group we found positive tests in 65% (mean PD20 0.360 mg) whereas only 40% in the group of APS (mean PD20 0.673 mg) had a positive test. This difference of 25% between the two groups was statistically significant (P=0.0004, chi square test). Conclusion: This study found a clinically relevant and statistically significant difference in outcome of the number of positive MCT between the 30 sec TB group using AE and the group using APS method. The APS method resulted in higher PD20 values, possibly due to a bronchodilator effect from the deep inhalations. The 30 sec TB resulted in lower PD20 values and appears to be a more sensitive test.