Measurement characteristics of peak expiratory flow.

STUDY OBJECTIVES To evaluate features of the peak expiratory flow (PEF) test protocol, and to characterize patterns of reproducibility in multiple PEF measurements. DESIGN Cross-sectional study. SETTING University population. PARTICIPANTS Two hundred twenty-three healthy adults. INTERVENTIONS Participants recorded five PEF measurements in each of five sessions per day for 1 week. MEASUREMENTS AND RESULTS Patterns of within-session variability were characterized using a reproducibility criterion based on a large percentage difference between best trials and evidence of a maneuver-induced bronchospasm (MIB) indicated by successive drops of PEF values in a session. Although the maximum PEF value in a session occurred on the fourth or fifth trial 32% of the time, the change in PEF values was small. Supervision was associated with small improvements in level and reproducibility. Using a cutoff of 5% for defining reproducibility, 15% of all sessions were not reproducible. When averaged over each subject, 9% of the cohort had a mean difference > 5%. Overall, MIB was unusual and observed in 8% of all test sessions; however, MIB was more common among asthmatics and subjects with wheeze, atopy, or allergies than subjects without. By contrast, poor reproducibility was more common among smokers and subjects with cough and phlegm. CONCLUSIONS These results illustrate that it may be unnecessary to supervise all sessions or collect more than three efforts. Results also suggest that reproducibility reflects smoking-related abnormalities, whereas MIB may reflect airways hyperresponsiveness.