Serial lung function variability using four portable logging meters.

OBJECTIVE Portable lung function logging meters that allow measurement of peak expiratory flow (PEF) and forced expiratory volume in 1 second (FEV(1)) are useful for the diagnosis and exclusion of asthma. The aim of this study was to investigate the within and between-session variability of PEF and FEV(1) for four logging meters and to determine the sensitivity of meters to detect FEV(1) and PEF diurnal changes. METHODS Thirteen assessors (all hospital staff members) were asked to record 1 week of 2-hour PEF and FEV(1) measurements using four portable lung function meters. Within-session variability of PEF and FEV(1) were compared for each meter using a coefficient of variation (COV). Between-session variability was quantified using parameter estimates from a cosinor analysis which modeled diurnal change for both lung function measures and also allowed for variation between days for individual sessions. RESULTS The mean within-session COV for FEV(1) was consistently lower than that for PEF (p <0.001). PEF showed a higher but not significantly different (p = 0.068) sensitivity for detecting diurnal variation than FEV(1). PEF was also slightly more variable between days, but not significantly different than FEV(1) (p = 0.409). PEF and FEV(1) diurnal variability did not differ between the 4 meters (p = 0.154 and 0.882 respectively), but within-session FEV(1) COV differed between meters (p = 0.009). CONCLUSION PEF was marginally more sensitive to within-day variability than FEV(1) but was less repeatable. Overall, differences between the 4 meters were small, suggesting that all meters are clinically useful.