Differences in serial lung function recorded on four data-logging meters

Lung function measurements performed several times daily are useful for the diagnosis of occupational asthma. Patient fabrication of hand-recorded charts can limit confidence in the results; this is overcome using electronic meters that log time and measurement. We have compared individual and meter differences in FEV1 and PEF recorded by hand and from meter logs using expert subjects on four data-logging spirometers with different methods of measurement and different quality control software.

Eight workers in a respiratory physiology department were asked to record FEV1 and PEF 2-hourly from waking for 7 days using four electronic meters (Easyone, Micro DL, Vitalograph Diary card 2110 and Piko-1) in random order. Subjects hand-recorded the best FEV1 and PEF from each session, this was compared with the logged data.

Discordant measurements from individuals were lower for FEV1 than PEF and differed from 4.4-19.1% for FEV1 (mean 9.4%, p < 0.0001) and 6-23.3% for PEF (mean 12.6, p < 0.0001). There were also significant differences between meters for both variables (p < 0.0001). The magnitude of the differences in PEF was highest for the Easyone (34l/min) and lowest for the Vitalograph Diary card 2110 (14l/min) and varied significantly between meters (mean 22l/min, p = 0.002).

Differences between hand-recorded and logged measurements are unlikely to be due solely to patient fabrication and can be due to quality criteria or other unclear software requirements applied after the results are shown on the meter screen; they differ between meters. Whether the differences shown affect clinical outcome will require further investigation.