Objective -To assess whether mini flow meters used to measure peak expiratory flow can track changes in lung function and indicate clinically important changes.
Design -Comparison of measurements with a spirometer and different brands of mini flow meter; the meters were allocated to subjects haphazardly.
Subjects -12 boys with asthma aged 11 to 17 attending boarding school.
Main outcome measures -Peak expiratory flow measured twice daily for three months with a spirometer and at least one of four brands of mini flow meter.
Results -The relation between changes in lung function measured with the spirometer and those measured with the mini flow meters was generally poor. In all, 26 episodes (range 1-3 in an individual child) of clinically important deterioration in lung function were detected from the records obtained with the spirometer. One mini flow meter detected six of 19 episodes, one detected six of 15, one detected six of 18, and one detected three of 21.
Conclusions -Not only are the absolute values of peak expiratory flow obtained with mini flow meters inaccurate but the clinical message may also be incorrect. These findings do not imply that home monitoring of peak expiratory flow has no place in the management of childhood asthma but that the values obtained should be interpreted cautiously.