Cold shock response
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Cold shock response is a series of cardio-respiratory responses caused by sudden immersion in cold water.
In cold water immersions, cold shock response is perhaps the most common cause of death,[1] such as by falling through thin ice. The immediate shock of the cold causes involuntary inhalation, which, if underwater, can result in drowning. The cold water can also cause heart attack due to vasoconstriction,[2] where the heart has to work harder to pump the same volume of blood throughout the body. For people with existing cardiovascular disease, the additional workload can result in cardiac arrest. Inhalation of water (and thus drowning) may result from hyperventilation. Some people are much better able to survive swimming in very cold water due to body or mental conditioning.[1]