什麼是「動暈症」? (難度:4)

暈動病
暈機病、暈船病通稱暈動病或運動病，主要是人乘坐飛機、船時因飛機、船發動機產生的轟轟隆隆的低頻噪聲或次聲引起的一種病。例如，（1）火車、卡車、摩托車、拖拉機的次聲非常小，人在乘坐這類車時不管怎麼運動也不會發生運動病。（2）各種艦船中，快艇的噪聲最大，暈船發病率也最高。（3）各種飛機中，噴氣飛機的噪聲最大，暈機發病率也最高。其癥狀表現為噁心、嘔吐、食慾減退等。
由於運動不是暈動病的直接原因，因此，有關暈動病或運動病的病名是不科學的。如，美國早期的兩次太空活動中，同樣處在失重的太空中，第一次因噪聲小，太空人沒有發生暈動病，第二次因噪聲大，太空人就發生了暈動病(軍事醫學，上海科學技術出版社，1995年11月，838頁）。


Motion sickness or kinetosis is a poison response provoked by motion. Nausea is the most common symptom of motion sickness; in fact, nausea in Greek means seasickness (naus means ship). If the motion causing nausea is not resolved, the sufferer will frequently vomit. Unlike ordinary sickness, vomiting in motion sickness tends not to relieve the nausea. Another part of motion sickness is an accompanying stress response. The sufferer feels stressed, and stress hormones are secreted into the blood.
Motion sickness on the sea can result from being in the berth of a rolling boat without being able to see the horizon. Sudden jerky movements tend to be worse for provoking motion sickness than slower smooth ones, because they disrupt the fluid balance more. A "corkscrewing" boat will upset more people than one that is gliding smoothly across the oncoming waves. Cars driving rapidly around winding roads or up and down a series of hills will upset more people than cars that are moving over smooth, straight roads. Looking down into one's lap to consult a map or attempting to read a book while a passenger in a car may also cause motion sickness.
Motion sickness can also occur when playing certain video games for exactly the opposite reason -- one can see motion but cannot feel it. This is most likely to occur when the screen takes up much of one's field of vision; using a smaller screen, or sitting farther away from it, can relieve motion sickness by making one's stationary surroundings more visible.
Humans have developed motion sickness as a defence mechanism. The area postrema in the brain is responsible for inducing vomiting when poisons are detected, and for resolving conflicts between vision and balance. When feeling motion but not seeing it (for example, in a ship with no windows), the inner ear transmits to the brain that it senses motion, but the eyes tell the brain that everything is still. The brain seems to conlude that it has been poisoned and the response is nausea, vomiting, and stress. Half of the astronauts in the U.S. space program have suffered from space sickness,[citation needed] including Senator Jake Garn, who made it his study project while a passenger on the Space Shuttle in 1985. The specially-designed zero-gravity toilet aboard the Space Shuttle has two settings: one for ordinary waste and another for vomit.

動暈症誘發的原因很多，可分內在因素，如疲倦、感冒、飲酒、睡眠不足或腸胃不適等，或外在因素，如：交通工具過度動搖，刺激半規管和耳石器；視覺刺激引起的「知覺衝突」，如船上看波浪狀的海面、搭火車看窗外景物；五官刺激，如聞到油味、看到人嘔吐、聽到引擎聲等。上述這些原因都可能引發了自律神經失調，產生噁心、嘔吐、胃部不舒服、冒冷汗、步態不穩、心跳加快、血壓升高、頭暈頭痛的症狀，而形成動暈症。




葉大偉主任說動暈症是可預防的，也可經後天訓練而獲得改善。要預防動暈症當然首先要避開前面提到的內因和外因，必要時可於上路前30分服用抗組織胺或輕量鎮定止暈劑，若等到動暈發作才服用則全無效果。

案例：一位40歲女性因頭暈嘔心、心跳加快、步態不穩而至門診就醫，她表示前二天她參加旅行，一上遊覽車沒多久她就開始頭暈想吐，下車後仍然很不舒服，休息了一、二天仍然沒改善，她以為自己有眩暈，後來，經耳鼻喉科醫師診斷為「動暈症」。




台灣署立新竹醫院耳鼻喉科葉大偉主任表示，「眩暈」是平衡系統發生左右不平衡引起的，而動暈症則是一種反射性眩暈，是由陸、海、空各種可能的交通工具動搖震盪引起半規管、耳石器異常衝動所導致眩暈、噁吐等症狀。