[Optimal time of the day for measuring peak expiratory flow rates in patients with asthma].

Regular measurement of peak expiratory flow rate (PEF) has been recommended as an aid in the management of asthma, but the time of the day when PEF should be measured remains unclear. We therefore sought to determine the optimal time for measuring PEF in untreated patients with mild to moderate asthma. PEF was measured in 11 patients four times daily: on waking, around noon, in the evening, and at bedtime. Significant (p < 0.05) rhythms were detected by single cosinor analysis in all patients. Analysis by the population mean cosinor method showed that the mesor was 381 +/- 120 l/m, the amplitude was 52 +/- 21 l/m, and the acrophase was at 16:28 +/- 0:55. These data indicate that, in general, PEF is lowest at 4:30 a.m. and highest at 4:30 p.m. in patients with mild to moderate asthma. We conclude that PEF should be measured early in the morning and at 4:30 p.m. in such patients.