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 vessels to swell and tissues to press on the sensitive membrane 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 cerebral 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 ascend to 11,000 feet, HACE is a rare disorder. Characterized by mental confusion, hallucinations, and a drunken stagger, HACE is almost always fatal if descent is not immediate.

 

　　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。