Relation of changes in PEF and FEV1 during bronchoconstriction

Diagnosis of asthma can be confirmed based on variability in peak expiratory flow (PEF) or changes in forced expiratory volume in 1 second (FEV1) measured with spirometry. Our aim was to use methacholine challenge as a model of induced airway obstruction to assess how well relative changes in PEF reflect airway obstruction in comparison to relative changes in FEV1. We retrospectively studied 878 patients who completed a methacholine challenge test. To assess congruency as well as differences between relative changes in FEV1 and PEF during airway obstruction, a regression analysis was performed, and a Bland & Altman plot was constructed. ROC analysis, sensitivity, specificity, positive and negative predictive values (PPV and NPV) and kappa-coefficient were used to analyze how decrease in PEF predicts decrease of 10% or 15% in FEV1. The relative change in PEF was on average less than the relative change in FEV1. In the ROC analysis areas under the curve were 0.844 (p<0.001) and 0.893 (p<0.001) for PEF decrease to predict a 10% and 15% decrease in FEV1, respectively. The agreement between changes in PEF and FEV1 varied from fair to moderate (kappa values of 0.325 – 0.558) depending on the cut-points. Airway obstruction detected by change in PEF was false in about 40% of cases when compared to change in FEV1. Change in PEF is not a very accurate measure of airway obstruction when compared to change in FEV1. Replacing peak flow meter with a handheld spirometer might improve diagnostic accuracy of home monitoring in asthma.