Occupational Asthma Reference

Bright P, Burge PS, Repeatability of home measurements of peak expiratory flow (PEF) and FEV1, Thorax, 1996;51 Suppl 3:A70,

Keywords: Oasys, PEF, FEV1, quality control, Micromed

Known Authors

Sherwood Burge, Oasys Sherwood Burge

Phil Bright, Oasys Phil Bright

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Serial measurements of PEF and increasingly FEV1 are used in the diagnosis of occupational asthma. Repeatability criteria for these indices are well established for measurements made in the clinical setting. We have investigated the repeatability of PEF and FEV1 from records of subjects performing home lung function monitoring. Subjects were asked to perform 3 maximal 2-second exhalations every 2 hours fro waking to sleeping for a minimum of 21 days. The 2 second exhalations were self-timed. Subjects (n=24) used portable turbine spirometers (Micromed) which stored the PEF and FEV1 for all blows for later downloading to a computer. For each session the repeatability (absolute difference between the best and next best reading) and as a % of the best) for PEF and FEV1 was found. We report the median repeatabilities (95% CI) for PEF and FEV1 for whole records and correlation between reading number (first to fortieth) and median repeatabilities.
For PEF the median absolute repeatabilities were 31.8 L/min (25.2, 36.0). Repeatability % best was 9.0 (7.0, 12.0). For FEV1 the median absolute repeatabilities were 0.16L (0.12, 0.24) and 8.0 (5.2, 13.8) respectively. For PEF 21 subjects had median repeatabilities (% best) >5%. Below are the correlations with repeatability and reading number.
Comparison r p (t test)
PEF (absolute) 0.15 0.47
PEF (% best) 0.02 0.53
FEV1 (absolute) 0.02 0.91
FEV1 (% best) 0.13 0.51

There is only an insignificant correlation between repeatability and reading number suggesting that the quality has not deteriorated during the duration of the record. Most subjects when performing home monitoring of PEF and FEV1 fail to meet standard limits of repeatability. This supports the use of meters with inbuilt quality control to improve the standard of data collected.

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