听力文摘：为什么高海拔会引起头痛？

Why Does Altitude Cause Headache?

为什么高海拔会引起头痛？

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.

当勇敢面对冷风，冰坡和参差不齐的悬崖时，登山运动员面临着很多危险。但是其中一个他们面临最严峻的危险就是他们的头。

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.

为什111么高海拔会引起头痛？随着大气越来越薄，血液中的氧气越来越少，因此流到大脑中的血液就会增多。多余的血会使血管膨胀，挤压敏感的在大脑周围细胞膜，导致头痛。

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.

但并不是每个人都会在适度的高海拔感到头痛，部分是由于大气中低氧引起攀登者常常喘不过气，驱使二氧化碳离开血液。

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.

血液中的二氧化碳少了，身体中流入大脑中的血液就会减少。一个个体对于海拔降低引起头痛的敏感性和头痛的严重性，取决于全面流入大脑中的血液是增多了还是减少了。

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.

在高海拔，常常超过3000米，一种不相关的高海拔脑水肿情况出现。当大脑的部分浸满水的时候脑水肿就会出现。

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.

当海拔超过3300米，90%的人会出现海拔降低的头痛，与此不同的是，脑水肿是一种罕见的混乱。其特征是精神混乱，幻觉和酒醉后的蹒跚。如果下降的不够及时，那么脑水肿几乎是致命的。

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。