Assessment of mid flow rate measurements in patients undergoing methacholine challenge
Abstract:The objective of this study is to assess the FEF25–75 and FEF25–75/FVC in relation to the FEV1 in patients who have had a methacholine inhalation challenge study for a variety of clinical indications. The study is a retrospective review of methacholine challenge results at the university medical center. One hundred twenty-one consecutive patients who had a methacholine challenge performed for clinical indications were included in the study with no intervention. Methacholine was administered in successively increasing twofold concentrations in doses from 0.62 mg to a final concentration of 10 mg. A 20% drop in FEV1compared to the prechallenge value was considered a positive test. We considered ≥25% decrease in FEF25–75 as a significant change. The ≥25% decrease in FEF25–75 occurred sooner than the 20% drop in FEV1 with a positive response occurring at least one full dose sooner in 23 of the 55 subjects. Thirty two subjects reacted at the same dose. The dose at which the FEF25–75 decreased by ≥25% was significantly different from the corresponding dose causing a 20% decrease in FEV1. The FEF25–75 decreases more per mg methacholine. There were no subjects in whom there was ≥20% decrease in FEV1 without a ≥25% decrease in FEF25–75. The mean FEF25–75/FVC after diluent inhalation = 0.87 ± 0.27 standard deviation with a range of 0.23 to 1.67. The doses at which the FEF25–75/FVC decreased by ≥20% and by ≥30% was significantly lower than the corresponding doses causing a 20% decrease in FEV1. FEF25–75 and the FEF25–75/FVC are more sensitive but less specific than the FEV1 as indicators of a positive response to a methacholine challenge. The FEF25–75/FVC does not provide additional information to that provided by the FEF25–75.
Document Type: Research Article
Publication date: 2006-07-01
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