Circadian rhythm in peak expiratory flow: Alteration with nocturnal asthmaand theophylline chronotherapy

We investigated changes in the circadian rhythm of peak expiratory flow (PE F) in seven persons with nocturnal asthma for a 24h span when (1) they were symptom free and their disease was stable, (2) their asthma deteriorated a nd nocturnal symptoms were frequent, and (3) they were treated with theophy lline chronotherapy. Subjects recorded their PEF every 4h between 07:00 and 23:00 one day each period. Circadian rhythms in PEF were assessed using th e group-mean cosinor method. The circadian rhythm in PEF varied according t o asthma severity. Significant circadian rhythms in PEF were detected durin g the period when asthma was stable and when it was unstable and nocturnal symptoms were frequent. When nocturnal symptoms were present, the bathyphas e (trough time) of the PEF rhythm narrowed to around 04:00; during this tim e of unstable asthma, the amplitude of the PEF pattern increased 3.9-fold c ompared to the symptom-free period. No significant group circadian rhythm w as detected during theophylline chronotherapy. Evening theophylline chronot herapy proved to be prophylactic for persons whose symptoms before treatmen t had occurred between midnight and early morning. Changes in the character istics of the circadian rhythm of PEF particularly amplitude and time of ba thyphase, proved useful in determining when to institute theophylline chron otherapy to avert nocturnal asthma symptoms.