Circadian and circannual patterns of stroke

Abstract

Background: Cerebrovascular event peaks occur in the morning (≈ 9:00 am) with another one peak in the evening (≈ 8:00 pm) and a trough at night. Knowledge about circadian influences on mechanisms involved in cerebrovascular events is important for optimising the timing of therapy, preventing behavioural triggers at potentially risky circadian phases and selecting the timing of diagnostic procedures. This work aims to evaluate circadian and circannual patterns of stroke onset, and variation in pattern of stroke onset in the month of Ramadan. Patients and methods: The study was conducted on 98 stroke patients and 98 age-and sex-matched normal subjects. All patients had a documented time of stroke symptom onset. End-tidal carbon dioxide and core body temperature were served as measures of endogenous circadian phase. Cerebral blood flow velocity was measured using transcranial colour-coded duplex. Circadian rhythm of blood pressure and heart rate variability were also assessed. Results: Both ischaemic and haemorrhagic stroke showed a circadian variation regarding their onset, with the peak in the morning and the nadir during night-time. We found a pathologically reduced or abolished circadian blood pressure variation after stroke. Conclusion: Stroke was more frequent in the morning; also, it was less likely to occur during the summer and autumn than the winter or spring. Stroke prevention with therapies that target the morning rise in risk factors could be advantageous in reducing the overall risk of stroke.