睡眠促成缺血性中风但不会造成出血性中风

　　August 18, 2006 -- 一个最大型的研究检视中风型态的全天候变项的影响，显示睡眠促成缺血性中风，但不会造成出血性中风。
　　
　　日本Iwate医学大学的研究者研究不同的全天候变项对三种主要中风型态—栓塞性脑中风(CIF)、脑内出血(ICH)、蛛网膜下腔出血(SAH) —的影响，发现CIF较常在睡眠或刚入睡时发生。
　　
　　该研究刊登于8月17日的Journal of Neurology, Neurosurgery, and Psychiatry期刊线上版。
　　
　　【检测三种主要型态】
　　已知中风的全天候变项会影响中风的时间，本研究作者指出，尚不清楚的是各种型态之中风发生的时间。
　　
　　根据作者所述，之前的大多研究并未同时着眼于对这三种型态，而这些研究的ICH和SAH案例数都太少，无法准确研究全天候变项。
　　
　　为了更了解中风发生的触发和风险因子，研究者采取大族群基础之研究，包括12,957例经MRI或CT诊断之首次中风案例，资料来源是日本Honshu岛北部的Iwate Stroke Registry。
　　
　　【早晨高峰】
　　整个研究群中，有7575位有CIF、3852位有 ICH、1530位有SAH，为了确定中风发生的时间，将整天分成12时辰，研究者再加以观察不同中风型态之间和发生时间的相关模式。
　　
　　这三种型态在一天之中都有两个高峰 — 一次在06:00 - 07:59、一次在18:00 -19:59，而睡眠时发生中风的数目则显著下降，详细的分析显示CIF相较于其他两型，在早晨有较高的高峰、在下午则较低。
　　
　　在睡眠时发生CIF的比率约20%，发生ICH和SAH 的比率约10%，作者报告指出在睡眠时发生CIF的大多数病患，发生在醒来前一刻。
　　
　　睡眠时发生缺血性中风之风险 (06:00-07:59)

中风型态	相对危险比 (95% CI)
CIF	426 (353.1-515.5)

　　病患醒着时发生CIF的案例有两个高峰— 一次在10:00 -11:59 、一次在18:00 - 19:59，中午时分较低，晚上最低。
　　
　　相对来说，ICH和 SAH在清晨属较低峰、在下午则较高峰。
　　
　　【血压下降】
　　所有中风型态中，男性平均比女性年轻五岁，不过作者报告指出，两性之间各类型中风的百分比无显著差异。
　　
　　根据作者所述，睡眠时血压降低可能和增加CIF风险、降低ICH和SAH风险有关。
　　
　　至于在之前的研究中占有一席之地的其他风险因子，如清晨时增加血比容值、血小板凝集力、和高凝血状态也同时降低出血风险和增加缺血性中风风险。
　　
　　中风发作之触发似乎有两类因子组成— 一类是血压、通常造成缺血性和出血性中风且有两种模式，另一类是血液功能、造成缺血性中风但可预防清晨之出血性中风。
　　
　　J Neurol Neurosurg Psychiatry。发表于August 17, 2006线上版。

Sleep Promotes Ischemic but Not Hemorrhagic Stroke

By Caroline Cassels
Medscape Medical News

August 18, 2006 — One of the largest-ever studies to examine the influence of circadian variations in stroke subtypes shows sleep promotes ischemic stroke but suppresses hemorrhagic stroke.

Researchers at Iwate Medical University in Japan investigated the influence of differences in circadian variations among 3 major stroke subtypes — cerebral infarction (CIF), intracerebral hemorrhage (ICH), and subarachnoid hemorrhage (SAH) — and found CIF was much more likely to occur during or just after sleep.

The study is published online August 17 in the Journal of Neurology, Neurosurgery, and Psychiatry.

Three major subtypes examined

While it is known that stroke circadian variations influence the timing of stroke, the study authors point out that it is not well understood how the timing of stroke onset may differ among the various subtypes.

According to the authors, most previous studies have not looked at the 3 major subtypes simultaneously, and of those that have, the numbers of cases of ICH and SAH were too small to accurately investigate circadian variation.

To better understand triggers and risk factors for stroke onset, the investigators undertook the large population-based study, which included 12,957 cases of first-ever stroke diagnosed by magnetic resonance imaging (MRI) or by computed tomography (CT). The data source was the Iwate Stroke Registry, a large stroke registry in the northern part of Honshu Island in Japan.

Morning Peak

Of the total study group, 7575 had CIF, 3852 had ICH, and 1530 had SAH. To determine the time of stroke onset, the day was divided into 12 two-hour intervals. Researchers then looked for any obvious patterns between different stroke types and the time of day they occurred.

All 3 stroke subtypes registered 2 peaks during the day — one between 06:00 and 07:59 and the other between 18:00 and 19:59, with a significant dip in the number of strokes occurring during sleep. Closer analysis revealed that CIF had a higher peak in the morning and lower peak in the afternoon compared with the other 2 subtypes.

The percentage of CIF, ICH, and SAH that occurred while subjects were asleep was about 20% in CIF compared with about 10% of the other 2 stroke subtypes. The authors report that among CIF cases that occurred during sleep, most patients experienced onset immediately before waking.

Risk of Ischemic Stroke Onset During Sleep (06:00 to 07:59)

Stroke Type	Relative Risk (95% CI)
CIF	426 (353.1-515.5)

Onset of CIF cases when patients were awake showed 2 peaks — one from 10:00 to 11:59 and the other from 18:00 to 19:59, with a dip around noon and a nadir during the night.

In contrast, ICH and SAH were more likely to have lower peaks in the morning and higher peaks in the afternoon.

Blood Pressure Drop

In all stroke subtypes, men were about 5 years younger than women on average. However, the authors report, percentages of cases were not markedly different between the sexes in any subtype.

According to the authors, it is likely the drop in blood pressure that occurs during sleep is simultaneously responsible for increasing the risk of CIF and decreasing the risk of ICH and SAH.

In addition, other factors, which have been shown in previous research to play a role, including morning increases in levels of hematocrit, platelet aggregability, and hypercoagulability, also simultaneously reduce hemorrhagic stroke risk and increase ischemic stroke risk.

"The triggers for stroke onset seem to consist of 2 types of factors — that is, blood pressure, which is common to both ischemic and hemorrhagic stroke and shows a bimodal pattern, and hemostatic functions, which promote ischemic stroke and prevent hemorrhagic stroke in the morning," they write.

J Neurol Neurosurg Psychiatry. Published online August 17, 2006.