A lot of cardiovascular events tend to  happen more frequently in the early morning between 4 am and 10 am. This is   related to the defensive mechanisms of the body to prepare for the difficulties of daily life hence producing more catecholamines which raise the blood pressure， increasing blood flow to the brain and the heart to get it ready; but at the same time they can cause arrhythmias， increase in blood pressure and can cause plaque ruptures. During sleep， we know from our ambulatory blood pressure monitoring， that pressure is low and most of the patients have lower pressure while asleep than when awake. These are the so-called “dippers”. These patients have less risk of cardiovascular events. Those that do not drop their pressure during sleep are at higher risk. At the same time， those who have an excessive increase in blood pressure in the early hours， after four or five o浙lock， are at increased risk of developing cardiovascular events.

    很多心血管事件出现在早晨4~10点。这种现象与人体的防御机制有关，防御机制为应对日间困难提供了必要准备，通过产生更多的儿茶酚胺（可升高血压）增加脑和心脏的血流使它们对应激有所准备，但同时高浓度的儿茶酚胺也可导致心律失常、血压升高以及斑块破裂。由动态血压监测可知，血压在睡眠时较低，大多数人睡眠血压均低于清醒血压，即所谓的勺型血压。勺型血压者心血管疾病危险较低，而睡眠血压不下降或清晨4点或5点左右血压极度升高者，心血管事件发生风险较高。

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