The impact of peak expiratory flow variability on FEV1 repeatability

Background This study evaluated the impact of Peak Expiratory Flow (PEF) variability on Forced Expiratory Volume in one second (FEV 1 ) repeatability during spirometry and assessed the validity of the current Association for Respiratory Technology and Physiology (ARTP) repeatability threshold (40 L min −1 ). Methods A retrospective observational study was performed at Royal Papworth Hospital NHS Foundation Trust using spirometry data from 4,913 patients (22,071 manoeuvres) in 2023. The manoeuvre with the highest PEF was used as the reference; PEF and FEV 1 differences were calculated for all remaining manoeuvres. Patients were stratified by obstruction status (FEV 1 /FVC < LLN vs. ≥ LLN). PEF variability was grouped into bands (< 40 to ≥ 200 L min −1 ). FEV 1 differences were compared across PEF groups using Mann-Whitney U and Friedman tests. Receiver Operating Characteristic (ROC) analysis was used to identify the PEF threshold predictive of clinically significant FEV 1 differences ( > ± 150 mL). We used multivariable logistic regression analysis to investigate the association of the derived threshold with having an FEV 1 difference > ± 150 mL. Results Airflow obstruction was present in 31% of patients. Across all manoeuvres, the median PEF difference was 25 L min −1 and the median FEV 1 difference was 50 mL. 30% of manoeuvres exceeded the ARTP threshold, and these showed significantly greater FEV 1 variability (80 vs. 40 mL, p < 0.001). A progressive increase in FEV 1 difference occurred with rising PEF variability, most notably in obstructed patients. ROC analysis identified an optimal threshold of 44 L min −1 , with values above this conferring nearly threefold higher odds of an FEV 1 difference > ± 150 mL (OR 2.85; 95% CI 2.61–3.11). Conclusion PEF variability is strongly associated with FEV 1 repeatability, particularly in obstructed patients. The optimal threshold identified (44 L min −1 ) closely aligns with the current ARTP criterion, supporting its validity. Larger PEF variability substantially increases the likelihood of clinically meaningful FEV 1 differences. Further work should examine implications for disease grading and clinical decisions.