Retrospective Analyses of Methacholine Inhalation Challenges

Abstract

We retrospectively analyzed 198 methacholine inhalation challenges (MICs) of symptomatic patients with normal results of lung examinations, spirometry, and chest radiographs. During MIC, five parameters (FEV1, FEF25-75%, FVC, sGaw, TGV) were measured. Using established changes in these parameters at < or = 8 mg/ml methacholine, there were 175 positive tests (no false positives) and 23 negative tests (15 true negatives, 5 false negatives, and 3 unavailable for follow-up). The MIC sensitivity determined by FEV1 responses was significantly lower than the sensitivity using responses in either three (FEV1, FEF25-75%, and FVC; p < 0.001) or five (FEV1, FEF25-75%, FVC, sGaw, and TGV; p < 0.001) parameter sets. Sensitivities were 60.6 percent, 91.1 percent, and 97.2 percent, respectively. All positive MICs (100 percent) were identified by examining changes in the five-parameter set vs 97.3 percent in the three-parameter set; it was a significant difference at p < 0.01. We conclude that the measurement and analysis of non-FEV1 parameters in addition to FEV1 significantly increases the sensitivity of the MIC.