Relation of changes in peak expiratory flow (PEF) and forced expiratory volume in 1 s (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 s (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 along with 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 and κ-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 and 0.893 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. 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 metre with a handheld spirometer might improve diagnostic accuracy of home monitoring in asthma.