Diurnal variation of peak expiratory flow rate in asthmatic children.

A diurnal variation in peak expiratory flow rate (PEFR) has been described in normal and asthmatic adults. This variation has been apparent in data reported from children, but the rhythm has not been characterized. Sixty-eight asthmatic children recorded PEFR three times a day for 4 weeks at home. Data were analyzed using paired t-tests, cosinor analysis, and spectral analysis. Fifty subjects (73.5%) had significant diurnal variations in PEFR on paired t-tests. Mean amplitude, derived from cosinor analysis, was 22.6% (SD = 13.2%) of mean PEFR. The trough of the PEFR rhythm occurred at 0345 hours for the group. Spectral analysis confirmed that the major component of the variation in PEFR was due to a rhythm with a period of 24 hours. The amplitude of the diurnal variation was not related to the subjects' age, sex, or medications taken but was inversely related to mean lung function (expressed as percentage predicted).