Peak flow variation in childhood asthma: relationship to symptoms, atopy, airways obstruction and hyperresponsiveness. Dutch CNSLD Study Group.

Although home recording of peak expiratory flow (PEF) is considered useful in managing asthma, little is known about the relationship of PEF variation to other indicators of disease activity. We examined the relationship of PEF variation, expressed in various ways, to symptoms, atopy, level of lung function, and airways hyperresponsiveness in schoolchildren with asthma. One hundred and two asthmatic children (aged 7-14 yrs) recorded symptoms and PEF (twice daily) in a diary for 2 weeks after withdrawal of all anti-inflammatory maintenance medication. PEF variation was expressed as amplitude % mean, as standard deviation and coefficient of variation of all recordings, and as low % best (lowest PEF as percentage of the highest of all values). Atopy and level of forced expiratory volume in one second (FEV1) % predicted were not significantly related to PEF variation. The provocative dose of histamine causing a 20% fall in FEV1 (PD20) and symptom scores were significantly, but weakly, related to PEF variation. The index, low % best, proved easy to calculate and effective in identifying a short-term episode of reduced PEF. We conclude that peak expiratory flow variation in children with stable, moderately severe asthma is significantly, but weakly, related to symptoms and airways hyperresponsiveness. These three phenomena, therefore, all provide different information on the actual disease state. Expressing peak expiratory flow variation as low % best is easy to perform and appears to be clinically relevant.