Chronobiological aspects of acute cerebrovascular diseases

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Abstract
The study was aimed at further investigating the circadian and circannual patterns of stroke onset. Study design and type of participants: 977 strokes (475 in men and 502 in women) concerning 926 subjects (457 men and 469 women) admitted to Ferrara Hospital in two calendar years (1990–1991), were prospectively investigated. The strokes were classified as based on cerebral infarction (CI), transient ischemic attack (TIA) and cerebral hemorrhage (CH: subarachnoid and intracerebral hemorrhage). Two statistical models of analysis were used. The assessment of circadian and circannual periodicity was performed utilizing the single cosinor method. A separate analysis was performed after distribution of events into 6-hour intervals, and chi-square test for fit was applied to the number of observed versus expected cases. The majority of strokes occurred in the morning between 7 a.m. and noon (35% of cases) and the hypothesis of a uniform distribution of the time onset was rejected on the basis of the chi-square for all subtypes of stroke. A circadian rhythm was found for CI and TIA with acrophase at the 11.56 and 12.41 respectively. Also a circannual periodicity was found for CI with a prevalent peak in October. The spectral analysis detected a circadian cycle for CH having a period of 4 h, and a circannual cycle for TIA with a period of 4 months. This study confirms that stroke is a high-chronorisk disease, with specific circadian and circannual rhythms. This is very important for a better understanding and control of the underlying factors and in terms of prevention.