文章来源:未知 文章作者:meng 发布时间:2010-04-23 01:33 字体: [ ]  进入论坛

The standard practice of cooling and then rewarming a patient to prevent organ damage during cardiac(心脏的) bypass surgery(心脏搭桥手术) may impair1 the body's mechanism2 that controls blood flow to the brain, potentially increasing the patient's risk of stroke, new research from Johns Hopkins suggests. "For reasons we don't yet understand, it appears that during rewarming, an autoregulation(自动调整) mechanism that protects the brain from fluctuations3(起伏现象,变动) in the body's blood pressure can malfunction4(故障,失灵) ," says Brijen Joshi, M.D., the study's leader and a research fellow in anesthesiology(麻醉学) and critical care medicine at the Johns Hopkins University School of Medicine. "This could increase the chances that the brain won't get enough blood flow and oxygen and increase the risk of brain injury."

As many as five percent of cardiac bypass patients, the study finds, wake up from surgery with significant loss of controlled movement or speech caused by an interruption of blood flow to the brain — a stroke — but physicians have been unable to explain why. In a report on the observational study, published in the journal Anesthesia & Analgesia5, the scientists suggest that the culprit(犯人,罪犯) could be a breakdown6 of this blood-flow regulation mechanism.

That mechanism seems to fail, they say, as doctors work to restore body temperature to its normal 36 degrees Celsius7(摄氏度) after cooling it to protect organs and facilitate(促进,帮助) heart bypass. If the autoregulation mechanism stops working, blood flow in the brain becomes entirely8 dependent upon blood pressure and can allow too much or too little blood to flow into the brain — a dangerous result.

"You come in with a heart problem and now you can't move a limb or you can't speak and you have a neurological problem," says Joshi. "We have to figure out why this is happening."

As part of the study, Joshi and his colleagues monitored the blood pressure and brain blood flow of 127 patients undergoing standard, lengthy9 cardiac bypass surgery during which they spent two hours on a heart-lung machine that circulated their blood for them. Their bodies were cooled to below 34 degrees Celsius and then rewarmed. Eleven patients undergoing shorter bypass operations were kept at normal body temperature throughout and served as a control group.

After surgery, none of the control patients had experienced any neurological problems, while seven of the standard group had strokes and one experienced a transient(短暂的,路过的) ischemic(缺血性的) attack, or TIA, a brief interruption of blood flow that's considered a harbinger(先驱,前兆) for future stroke.

The study notes that while cooling and rewarming to protect organs during bypass surgery may impair autoregulation and increase the risk of stroke, there is little evidence that this practice is necessary.

Joshi and his colleagues say more research is necessary into the precise causes of the malfunction in the brain's blood-flow regulation mechanism. Currently, there is no good monitor to alert doctors in real time that blood flow in the brain is too low or too high, says Charles W. Hogue Jr., M.D., associate professor of anesthesiology and critical care medicine at the Johns Hopkins University School of Medicine and the study's principal investigator10.

"We measure the heart, blood pressure, kidney function and more during surgery," Hogue says. "But there's a huge need for a better monitor for the brain."

To that end, the team has been developing a monitoring device that, during bypass surgery, would measure blood flow to the brain using near infrared11 spectroscopy(光谱学) , along with software that tracks changes in individual patients as they happen. When the body gets to the point where it isn't properly regulating blood flow in the brain, doctors don't know it in real time. If a monitoring device could alert doctors that blood flow to the brain had declined, they could quickly adjust blood pressure, restoring adequate flow and potentially avoid a stroke.

"Once we find the point at which this mechanism fails, we might be able to keep blood pressure above that threshold(极限,门槛) and prevent brain injury," Joshi says.


1 impair Ia4x2     
  • Loud noise can impair your hearing.巨大的噪音有损听觉。
  • It can not impair the intellectual vigor of the young.这不能磨灭青年人思想活力。
2 mechanism zCWxr     
  • The bones and muscles are parts of the mechanism of the body.骨骼和肌肉是人体的组成部件。
  • The mechanism of the machine is very complicated.这台机器的结构是非常复杂的。
3 fluctuations 5ffd9bfff797526ec241b97cfb872d61     
波动,涨落,起伏( fluctuation的名词复数 )
  • He showed the price fluctuations in a statistical table. 他用统计表显示价格的波动。
  • There were so many unpredictable fluctuations on the Stock Exchange. 股票市场瞬息万变。
4 malfunction 1ASxT     
  • There must have been a computer malfunction.一定是出了电脑故障。
  • Results have been delayed owing to a malfunction in the computer.由于电脑发生故障,计算结果推迟了。
5 analgesia yLyyP     
  • Acupuncture anesthesia and acupuncture analgesia has promoted the acupuncture therapy.针灸麻醉和针灸止痛促进了针灸疗法的发展。
  • Scientists believe swearing elicits an emotional response which leads to what is known as "stress-induced analgesia."科学家们认为,咒骂引发情绪反应,该反应引起被称作“压力诱发止痛”的现象。
6 breakdown cS0yx     
  • She suffered a nervous breakdown.她患神经衰弱。
  • The plane had a breakdown in the air,but it was fortunately removed by the ace pilot.飞机在空中发生了故障,但幸运的是被王牌驾驶员排除了。
7 Celsius AXRzl     
  • The temperature tonight will fall to seven degrees Celsius.今晚气温将下降到七摄氏度。
  • The maximum temperature in July may be 36 degrees Celsius.七月份最高温度可能达到36摄氏度。
8 entirely entirely     
  • The fire was entirely caused by their neglect of duty. 那场火灾完全是由于他们失职而引起的。
  • His life was entirely given up to the educational work. 他的一生统统献给了教育工作。
9 lengthy f36yA     
  • We devoted a lengthy and full discussion to this topic.我们对这个题目进行了长时间的充分讨论。
  • The professor wrote a lengthy book on Napoleon.教授写了一部有关拿破仑的巨著。
10 investigator zRQzo     
  • He was a special investigator for the FBI.他是联邦调查局的特别调查员。
  • The investigator was able to deduce the crime and find the criminal.调查者能够推出犯罪过程并锁定罪犯。
11 infrared dx0yp     
  • Infrared is widely used in industry and medical science.红外线广泛应用于工业和医学科学。
  • Infrared radiation has wavelengths longer than those of visible light.红外辐射的波长比可见光的波长长。
TAG标签: patient brain blood stroke