Cold shock response

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Cold shock response is a series of neurogenic cardio-respiratory responses caused by sudden immersion in cold water. In cold water immersions, such as by falling through thin ice, cold shock response is perhaps the most common cause of death. Also, the abrupt contact with very cold water may cause involuntary inhalation, which, if underwater, can result in fatal drowning. Death which occurs in such scenarios is complex to investigate, and there are several possible causes and phenomena involved. The cold water can cause heart attack due to severe vasoconstriction, where the heart has to work harder to pump the same volume of blood throughout the arteries. For people with pre-existing cardiovascular disease, the additional workload can result in myocardial infarction or acute heart failure, which ultimately may lead to a cardiac arrest. A vagal response to an extreme stimulus may, in very rare cases, render per se a cardiac arrest. Hypothermia and extreme stress can both precipitate fatal tachyarrhythmias. A more modern view suggests that an autonomic conflict – sympathetic (due to stress) and parasympathetic (due to the diving reflex) coactivation – may be responsible for some cold water immersion deaths. Gasp reflex and uncontrollable tachypnea can severely increase the risk of water inhalation and drowning, as the ability to hold one's breath decreases from the normal 60-90 seconds to just a few seconds at a water temperature lower than ~15 °C (59 °F). Some people are much better prepared to survive sudden exposure to very cold water because of bodily and mental characteristics and conditioning. In fact, cold water swimming (also known as ice swimming or winter swimming) is a sport and an activity that reportedly has several health benefits when done regularly.