生理血压循环不太可能引起早晨的心血管事件


  【24drs.com】研究人员指出,血压(BP)有强烈的生理节律,在晚上9点时达最高峰;这篇新发现认为,内因性血压节律可能和发生于早晨的心血管事件无关。
  
  哈佛医学院的Steven A. Shea博士等人写道,血压在夜间睡眠期间通常会降低、日间活动时增加;至于这种内因性生理控制系统是否造成这个日常血压变化情况,并没有适当地控制型研究加以探讨。
  
  这篇研究在线发表于4月7日的Circulation Research期刊。
  
  为了了解人类是否有「内因性血压生理节律」,Shea博士等人将28名血压正常成年志愿者(包括16名男性)随机分成三个小组,这些都在实验室内进行。
  
  进行研究前,研究对象在家维持规律的睡眠-清醒周期,包括16小时的表订清醒时间以及8小时的睡眠时间,进行2- 3周以稳定生理节律,接著在实验室进行2天2夜的开始期,睡眠与清醒规律则和在家中一样,之后延伸实验室规范,从血压和其它生理变项,区别内在生理影响、行为和环境因素对血压的影响。
  
  这些控制的行为与环境状况变项包括活动、姿势、餐点、睡眠、室温与灯光;研究人员也测量核心体温,相对而言,这个内在生理周期标记比行为更有独立判断意义。
  
  这三种实验方式如下:
  * 38小时「稳定例行」期,连续清醒且固定姿势;
  * 196小时「强迫不同步」期(强制的睡眠/清醒周期,和研究对象的正常模式有冲突),包括28小时睡眠/清醒周期,其中18小时40分清醒、9小时20分睡著;
  * 240小时「强迫不同步」期,进行12次20小时睡眠/清醒循环。
  
  这些研究设计都是在微暗灯光下进行,以避免还需再度设定一个人的身体生理节律。
  
  这篇研究指出,三种方式都发现几乎一样的收缩与舒张心脏节律。收缩压最高值与最低值的差异是3- 6 mm Hg,舒张压是2-3 mm Hg(P < .05),此外,三种方式的6次收缩压与舒张压高峰的生理节律几乎都是在晚上9点时。
  
  血压节律与可体松、儿茶酚胺、心脏迷走冲动、心律或尿量等也会影响心血管事件的其它内因性节律无关。
  
  研究作者写道,我们对于血压的内因性生理高峰期是在晚上这个结果感到意外,而最低的生理周期血压值发生在最可能有心血管事件时,因此,最容易发生心血管事件的清晨时间不是和生理节律相关血压上升有关。
  
  Shea博士在一篇声明中指出,我们现在需要研究不同心血管疾病风险的人,目前,我们研究了没有高血压、没有造成突发心脏事件之动脉血块的健康族群。
  
  资料来源:http://www.24drs.com/professional/list/content.asp?x_idno=6512&x_classno=0&x_chkdelpoint=Y
  

Circadian BP Cycle Unlikely to Cause Morning CV Events

By Fran Lowry
Medscape Medical News

April 28, 2011 — Blood pressure (BP) has a strong circadian rhythm and reaches its highest peak at around 9 pm. This new finding suggests that the endogenous BP rhythm is probably not linked to the well-documented peak in adverse cardiovascular events that occurs in the morning, researchers say.

"Blood pressure usually decreases during nocturnal sleep and increases during daytime activities," write Steven A. Shea, PhD, from Harvard Medical School, Boston, Massachusetts, and colleagues. "Whether the endogenous circadian control system contributes to this daily BP variation has not been determined under appropriately controlled conditions."

The study was published online April 7 in Circulation Research.

To discover whether an endogenous circadian rhythm of BP exists in humans, Dr. Shea and his team randomized 28 normotensive adult volunteers, including 16 men, to 3 multiday protocols, which were performed in the laboratory.

Before the study, the participants maintained a regular sleep-wake schedule at home, which consisted of 16 hours of scheduled wakefulness with 8 hours of scheduled sleep, for 2 to 3 weeks to stabilize circadian rhythms. The participants then underwent 2 baseline days and nights in the laboratory with the same sleep-wake schedule as at home, followed by a prolonged laboratory protocol designed to separate internal circadian effects from behavioral and environmental effects on BP and other physiologic variables.

These controlled behavioral and environmental conditions included activity, posture, meals, sleep, room temperature, and light. The researchers also measured core body temperature, which is an endogenous circadian phase marker that is relatively independent of behavior.

The 3 protocols were as follows:

  • 38-hour "constant routine" with continuous wakefulness and constant body posture;
  • 196-hour "forced desynchrony" (forcing a sleep/wake cycle to conflict with participants' normal pattern), consisting of recurring 28-hour sleep/wake cycles with 18 hours 40 minutes awake and 9 hours 20 minutes asleep; and
  • 240-hour "forced desynchrony," with 12 recurring 20-hour sleep/wake cycles.

All protocols were performed in dim light to avoid resetting any of the body's circadian rhythms.

The study found that all 3 protocols revealed almost identical systolic and diastolic circadian rhythms.

The peak-to-trough amplitudes were 3 to 6 mm Hg for systolic BP and 2 to 3 mm Hg for diastolic BP (P < .05). In addition, all 6 peaks in systolic and diastolic BP in the 3 protocols occurred at a circadian phase corresponding to approximately 9 pm.

The BP rhythm appeared to be unrelated to other internal rhythms known to influence cardiovascular events, such as cortisol, catecholamines, cardiac vagal tone, heart rate, or urine flow.

"Our results are perhaps unexpected because the timing of the endogenous circadian peak in BP occurs in the evening — whereas the lowest circadian BP occurs around the most vulnerable time for adverse cardiovascular events," the study authors write. "Thus, our data suggest that the morning peaks in adverse cardiovascular events are not caused by circadian rhythm-related increases in BP."

In a statement, Dr. Shea added, "We now need to study people with different vulnerabilities and risk factors for cardiovascular disease. So far, we have studied very healthy people who don’t have hypertension or the buildup of arterial plaques that could bring them closer to the theoretical threshold for precipitating an adverse cardiac event."

The study was funded by grants from the National Institutes of Health. Dr. Shea has disclosed no relevant financial relationships.

Circ Res. 2011;108:980-984. Published online April 7, 2011.

    
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