英语听力文摘 English Digest 545、为什么高海拔会引起头痛？

 　　Why Does Altitude Cause Headache?

 

　　Mountain climbers face many dangers as they brave the cold winds and icy slopes and jagged cliffs of the peaks they climb. But one of the most serious dangers they face is all in their heads–literally.

 

　　Why does altitude cause headache? Since the air is thinner, there is less oxygen in the blood, so blood flow to the brain increases. The extra blood can cause blood vessels¹ to swell² and tissues to press on the sensitive membrane³ that surrounds the brain, resulting in a headache.

 

　　But not everyone develops a headache at moderately high altitudes, partly because the low oxygen content of the air causes the climber to breath more often, forcing carbon dioxide out of the blood.

 

　　The body reacts to the lowered carbon dioxide content of the blood by decreasing blood flow to the brain. An individual’s susceptibility to altitude-induced headache, as well as the severity of the headache, depends on whether the overall blood flow to the brain increases or decreases.

 

　　At high altitudes, usually over 10,000 feet, an unrelated condition known as high-altitude cerebral⁴ edema, or HACE, can develop. HACE occurs when parts of the brain become waterlogged.

 

　　Unlike altitude-induced headache, which occurs in over ninety percent of the people who ascend⁵ to 11,000 feet, HACE is a rare disorder⁶. Characterized by mental confusion, hallucinations, and a drunken stagger, HACE is almost always fatal if descent is not immediate⁷.

 

　　为什么高海拔会引起头痛？

 

　　攀山者面临很多危险，他们勇于直面凛冽的寒风、冰封的斜坡和所要攀登的山峰上犬牙交错的悬崖。但毫不夸张地说，他们面临的最大危险之一就是头部疾病！

 

　　为什么高海拔会引起头痛？由于空气变得更稀薄，血液中的氧气更少，流入大脑的血液会增多。额外的血液会导致血管膨胀，细胞组织压迫环绕大脑的敏感薄膜，从而导致头痛。

 

　　但在中度海拔地区，并不是每个人都会头痛，这一定程度上是因为空气的低氧含量会使攀登者呼吸频率增加，从而迫使血液中的二氧化碳排出。

 

　　人体通过减少流入大脑的血液量来应对血液中二氧化碳含量的降低。某一个体对高海拔头痛的敏感程度和头痛的严重程度取决于流入大脑的血液总量是增加还是减少。

 

　　在高海拔地区，通常在1万英尺以上，一种与供血无关的名为高海拔脑水肿也叫高原脑水肿（HACE）的病症会出现。当部分大脑出现积水时会引发HACE。

 

　　攀登至1万1千英尺的人中有90%以上会得高海拔头痛，而HACE与之不同，它是一种罕见的人体失调症。HACE的症状为精神混乱、出现幻觉以及肢体行动失调，如果不立即转移至较低海拔地区，患者就会有生命危险。

1 vessels   

n.血管( vessel的名词复数 )；船；容器；（具有特殊品质或接受特殊品质的）人

参考例句：

• The river is navigable by vessels of up to 90 tons. 90 吨以下的船只可以从这条河通过。 来自《简明英汉词典》
• All modern vessels of any size are fitted with radar installations. 所有现代化船只都有雷达装置。 来自《现代汉英综合大词典》

2 swell   

vi.膨胀，肿胀；增长，增强

参考例句：

• The waves had taken on a deep swell.海浪汹涌。
• His injured wrist began to swell.他那受伤的手腕开始肿了。

3 membrane   

n.薄膜，膜皮，羊皮纸

参考例句：

• A vibrating membrane in the ear helps to convey sounds to the brain.耳膜的振动帮助声音传送到大脑。
• A plastic membrane serves as selective diffusion barrier.一层塑料薄膜起着选择性渗透屏障的作用。

4 cerebral   

adj.脑的，大脑的；有智力的，理智型的

参考例句：

• Your left cerebral hemisphere controls the right-hand side of your body.你的左半脑控制身体的右半身。
• He is a precise,methodical,cerebral man who carefully chooses his words.他是一个一丝不苟、有条理和理智的人，措辞谨慎。

5 ascend   

vi.渐渐上升，升高；vt.攀登，登上

参考例句：

• We watched the airplane ascend higher and higher.我们看着飞机逐渐升高。
• We ascend in the order of time and of development.我们按时间和发展顺序向上溯。

6 disorder   

n.紊乱，混乱；骚动，骚乱；疾病，失调

参考例句：

• When returning back,he discovered the room to be in disorder.回家后，他发现屋子里乱七八糟。
• It contained a vast number of letters in great disorder.里面七零八落地装着许多信件。

7 immediate   

adj.立即的；直接的，最接近的；紧靠的

参考例句：

• His immediate neighbours felt it their duty to call.他的近邻认为他们有责任去拜访。
• We declared ourselves for the immediate convocation of the meeting.我们主张立即召开这个会议。