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Exercising outside can be one of the great pleasures of summer. But a sweaty body and racing pulse may be signaling more than your performance -- it could be a sign of life-threatening heatstroke.
Heatstroke can strike with scant warning, even after as little as a half hour if you are exercising hard, doctors say. Although drinking plenty of water can help, you can still get heatstroke even if you aren't dehydrated, particularly while exercising. Complicating matters, experts have sharply divergent guidelines on how to treat a person suffering from the condition.
Heatstroke hits when exertion or external heat, or both, overwhelm the body's ability to regulate its temperature. As internal temperatures climb, cells of the body can be damaged -- causing organ failure, brain dysfunction and, potentially, coma or death.
'It's like you are in an oven and your cells are being roasted,' says Douglas J. Casa, a professor of kinesiology at the University of Connecticut and a co-author of the American College of Sports Medicine's guidelines for treating heatstroke.
Athletes are at special risk, and the bulk of heatstroke deaths in high-school and college sports are in football, where heavy gear and sometimes insufficient breaks during practice contribute to overheating, researchers say.
The American College of Sports Medicine advocates cooling athletes first and transporting them to a hospital later. In its 2007 guidelines, the group recommends immersion in a cold or ice-water bath to cool the body as fast as possible. Survival 'comes down to the number of minutes that you are above the critical threshold for cell damage, which is around 105 degrees Fahrenheit,' says Dr. Casa. Most people survive if you can adequately cool them in 30 minutes, he says.
The next best options are dousing with a garden hose, putting the person in a cold shower and applying ice packs to the groin, head and neck, says William Roberts, a professor of family medicine at the University of Minnesota in Minneapolis and a co-author of the 2007 guidelines.
By contrast, the American Heart Association favors slower, gentler cooling of heatstroke victims. The AHA's First Aid guidelines for heatstroke recommend calling 911 and then fanning and sponge-bathing the person, or misting with cool, not cold, water.
'If you use ice water such as plunging into ice cold bath, you may induce shivering, which causes muscles to produce more heat,' says Monica Kleinman, chairman of the AHA's Emergency Cardiac Care committee.
A 2005 article in the British Journal of Sports Medicine reviewed 17 studies on cooling methods used in heatstroke and concluded that the current evidence suggests that ice water is the 'most effective' cooling method.
The article acknowledged methodological flaws with the underlying work that could have skewed the results: Many of the studies either used just one cooling method, or if they did compare one method to another, did not randomly assign patients to a specific group.
Spotting heatstroke as fast as possible is key. In adults, confusion or irrational speech or behavior is often the most obvious sign, Dr. Kleinman says.
Other symptoms can include red, hot and dry skin, rapid strong pulse, throbbing headache, dizziness, nausea and unconsciousness, according to the Centers for Disease Control and Prevention. Sometimes a person stops sweating when heatstroke hits.
Infants and children may exhibit lethargy and reduced interaction with others, says Dr. Kleinman. Context is important -- a half hour in a hot car could be a bigger risk than a day at the beach with good hydration, she adds.
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戶外運動可能是夏季最愜意的事情之一。但是大汗淋漓的身體和猛烈的心跳可能在給你傳遞這樣的信號：你已經(jīng)運動過量了──可能發(fā)生中暑，進而危及你的生命。
醫(yī)生們說，中暑的發(fā)生，有時候很少有征兆，甚至可能在你劇烈運動半小時后就會發(fā)生。雖然大量喝水可能會起到一定作用，但即使在不脫水的情況下也可能發(fā)生中暑，尤其是你在運動的時候。復(fù)雜的是，對于怎樣對待中暑患者，專家們的意見大不相同。
中暑發(fā)生在過量運動、氣溫過高，或者二者皆備的情況下。這時候，人體溫度高得超過了人體所能調(diào)整的范圍。隨著體溫的上升，人體的細(xì)胞就會被破壞──造成器官功能衰竭、大腦機能障礙，進而可能導(dǎo)致昏迷或死亡。
康涅狄格大學(xué)（University of Connecticut）的運動機能學(xué)教授道格拉斯•卡薩（Douglas J. Casa）說，“這就像是置身于一個烤箱內(nèi)，你全身的細(xì)胞都在高溫中被炙烤著。”卡薩是美國運動醫(yī)學(xué)學(xué)會（American College of Sports Medicine）編纂的中暑治療指導(dǎo)手冊的作者之一。
研究人員認(rèn)為，運動員中暑的風(fēng)險尤其高。中學(xué)和大學(xué)運動項目中的大多數(shù)中暑死亡者都是橄欖球運動員，因為厚重的防護服，或過短的運動間隙休息都可能導(dǎo)致體溫過高。
美國運動醫(yī)學(xué)學(xué)會主張，運動員發(fā)生中暑之后，應(yīng)首先采取降溫措施，然后將患者送到醫(yī)院。在該學(xué)會2007年的指導(dǎo)手冊中，各位作者建議將患者的身體浸在冷水或冰水里，盡快給患者降溫。卡薩醫(yī)生說，搶救生命的關(guān)鍵是“體溫超過損壞細(xì)胞的臨界門檻（即華氏105度，攝氏40.5度）的幾分鐘。”他說，如果能在30分鐘內(nèi)實施科學(xué)的降溫措施，大多數(shù)人都能轉(zhuǎn)危為安。
2007年指導(dǎo)手冊的作者之一、明尼阿波利斯市明尼蘇達大學(xué)（University of Minnesota）的家庭醫(yī)學(xué)教授威廉•羅伯茨（William Roberts）說，其次的最佳措施是，用給花園澆水的橡膠水管給患者身上澆水，給患者做冷水浴。同時，在患者的腹股溝、頭部和頸部部位放置冰塊。
但美國心臟協(xié)會（American Heart Association）的建議卻是，對中暑患者應(yīng)采取緩慢溫和的降溫措施。該協(xié)會編寫的中暑急救手冊建議，首先撥打911電話，然后用扇子給患者扇風(fēng)，并用蘸水的海綿擦拭患者身體，或者給患者身上慢慢地噴灑涼水，而不是溫度過低的冷水。
美國心臟協(xié)會心臟緊急護理委員會（Emergency Cardiac Care committee）的主席莫妮卡•克雷曼（Monica Kleinman）說，“如果使用冰水的話，比如把患者直接放到冰水里，可能會導(dǎo)致患者顫栗發(fā)抖，從而讓肌肉產(chǎn)生更多的熱量。”
2005年，《英國運動醫(yī)學(xué)雜志》（British Journal of Sports Medicine）的一篇文章分析了關(guān)于中暑降溫的17項研究，其結(jié)論是，到當(dāng)時為止，證據(jù)顯示，冰水是“最有效的”降溫措施。
文章承認(rèn)，該研究工作也存在方法上的缺陷，這些缺陷可能影響結(jié)論的全面性：很多研究項目只采用了一種降溫方法，即使有的研究項目對兩種方法進行了比較，也沒有對病人進行隨機分組。
提早發(fā)現(xiàn)是關(guān)鍵。克雷曼醫(yī)生說，對于成年人，思維混亂、言語不清、行為怪異往往是最明顯的中暑征兆。
美國疾病預(yù)防與控制中心（Centers for Disease Control and Prevention）表示，中暑還有一些其他癥狀，比如皮膚發(fā)紅、發(fā)熱或發(fā)干、脈搏又快又猛、一陣陣的頭痛，以及頭暈、惡心、意識不清。有時候，發(fā)生中暑時，患者會停止出汗。
克雷曼醫(yī)生說，嬰幼兒中暑時會表現(xiàn)出無精打采、寡言少語的癥狀。她說，環(huán)境很重要──在炎熱的汽車?yán)锎舭雮�小時的風(fēng)險可能比在飲用水充足的情況下在海邊呆一天還要大。
