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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.
参考译文：
户外运动可能是夏季最惬意的事情之一。但是大汗淋漓的身体和猛烈的心跳可能在给你传递这样的信号：你已经运动过量了──可能发生中暑，进而危及你的生命。
医生们说，中暑的发生，有时候很少有征兆，甚至可能在你剧烈运动半小时后就会发生。虽然大量喝水可能会起到一定作用，但即使在不脱水的情况下也可能发生中暑，尤其是你在运动的时候。复杂的是，对于怎样对待中暑患者，专家们的意见大不相同。
中暑发生在过量运动、气温过高，或者二者皆备的情况下。这时候，人体温度高得超过了人体所能调整的范围。随着体温的上升，人体的细胞就会被破坏──造成器官功能衰竭、大脑机能障碍，进而可能导致昏迷或死亡。
康涅狄格大学（University of Connecticut）的运动机能学教授道格拉斯?卡萨（Douglas J. Casa）说，“这就像是置身于一个烤箱内，你全身的细胞都在高温中被炙烤着。”卡萨是美国运动医学学会（American College of Sports Medicine）编纂的中暑治疗指导手册的作者之一。
研究人员认为，运动员中暑的风险尤其高。中学和大学运动项目中的大多数中暑死亡者都是橄榄球运动员，因为厚重的防护服，或过短的运动间隙休息都可能导致体温过高。
美国运动医学学会主张，运动员发生中暑之后，应首先采取降温措施，然后将患者送到医院。在该学会2007年的指导手册中，各位作者建议将患者的身体浸在冷水或冰水里，尽快给患者降温。卡萨医生说，抢救生命的关键是“体温超过损坏细胞的临界门槛（即华氏105度，摄氏40.5度）的几分钟。”他说，如果能在30分钟内实施科学的降温措施，大多数人都能转危为安。
2007年指导手册的作者之一、明尼阿波利斯市明尼苏达大学（University of Minnesota）的家庭医学教授威廉?罗伯茨（William Roberts）说，其次的最佳措施是，用给花园浇水的橡胶水管给患者身上浇水，给患者做冷水浴。同时，在患者的腹股沟、头部和颈部部位放置冰块。
但美国心脏协会（American Heart Association）的建议却是，对中暑患者应采取缓慢温和的降温措施。该协会编写的中暑急救手册建议，首先拨打911电话，然后用扇子给患者扇风，并用蘸水的海绵擦拭患者身体，或者给患者身上慢慢地喷洒凉水，而不是温度过低的冷水。
美国心脏协会心脏紧急护理委员会（Emergency Cardiac Care committee）的主席莫妮卡?克雷曼（Monica Kleinman）说，“如果使用冰水的话，比如把患者直接放到冰水里，可能会导致患者颤栗发抖，从而让肌肉产生更多的热量。”
2005年，《英国运动医学杂志》（British Journal of Sports Medicine）的一篇文章分析了关于中暑降温的17项研究，其结论是，到当时为止，证据显示，冰水是“最有效的”降温措施。
文章承认，该研究工作也存在方法上的缺陷，这些缺陷可能影响结论的全面性：很多研究项目只采用了一种降温方法，即使有的研究项目对两种方法进行了比较，也没有对病人进行随机分组。
提早发现是关键。克雷曼医生说，对于成年人，思维混乱、言语不清、行为怪异往往是最明显的中暑征兆。
美国疾病预防与控制中心（Centers for Disease Control and Prevention）表示，中暑还有一些其他症状，比如皮肤发红、发热或发干、脉搏又快又猛、一阵阵的头痛，以及头晕、恶心、意识不清。有时候，发生中暑时，患者会停止出汗。
克雷曼医生说，婴幼儿中暑时会表现出无精打采、寡言少语的症状。她说，环境很重要──在炎热的汽车里呆半个小时的风险可能比在饮用水充足的情况下在海边呆一天还要大。
