Abstract: Circadian rhythm widely exists in living organism, and it is regulated by the biological clock，which keeps life activities showing a rhythmic oscillation with a period of approximately 24 hours. Growing evidence has shown that circadian rhythms are closely related to the physiological function of the cardiovascular system，and blood pressure，heart rate，hormone secretion，endothelial function，vasoconstriction and vasodilation are regulated by the biological clock. Clinically，syncopal episodes peak in the morning，and abnormal blood pressure circadian pattern exists in most children with orthostatic intolerance（OI）. Simulated microgravity can lead to circadian rhythm disorders in rats’ cardiovascular system. It suggests that circadian rhythms play an important role in the occurrence and development of OI. The paper introduces the relationship between circadian rhythm and OI as well as its possible mechanism.

Key words: biological clock, circadian rhythm, orthostatic intolerance, child

摘要： 昼夜节律普遍存在于生物体中，主要由生物钟控制，使生命活动表现为近似24 h的振荡周期。越来越多研究表明生物钟与心血管生理功能密切相关，血压、心率、自主神经功能、激素分泌、血管内皮功能以及血管收缩和舒张均受生物钟的调节。临床上，晕厥发作是在上午达到高峰，大多数直立不耐受（OI）患儿血压昼夜节律异常，模拟失重大鼠模型提示心血管节律紊乱，提示OI的发生、发展与昼夜节律关系密切。该文介绍了昼夜节律与OI的关系及其可能机制的研究进展。

关键词: 生物钟, 昼夜节律, 直立不耐受, 儿童