Cold shock response
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.[1] 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 that can take part. The cold water can cause heart attack due to severe vasoconstriction,[2] 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 and/or acute heart failure, which ultimately may lead to a cardiac arrest. A vagal response to an extreme stimulus as this one, 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.[3]
Some people are much better prepared to survive sudden exposure to very cold water due to body and mental characteristics and due to conditioning.[1] In fact, cold water swimming (also known as ice swimming or winter swimming) is a sport and an activity that reportedly can lead to several health benefits when done regularly.[4]
Physiological response[edit]
Cold water immersion syndrome — four-stage model[edit]
The physiological response to a sudden immersion in cold water may be divided in three or four discrete stages, with different risks and physiological changes, all being part of an entity labelled as Cold Water Immersion Syndrome. Although this process is a continuum, the 4 phases was initially described in the 1980s as follows:[3][4]
Cold water immersion tactics are often employed by athletes to speed up muscle recovery and reduce inflammation and soreness after intense exercise or after trauma.[5]
There are several reported benefits from regular ice swimming, namely:[4]
Cold water swimming still poses a significant health risk for inexperienced and untrained swimmers. It is recommended that in order to fully benefit from the metabolic and thermogenic effects of cold water swimming, a grade and progressive acclimatization program is required and preferably done under supervisor.
Cold shock response in other organisms[edit]
Cold shock in mammals[edit]
Cold shock has been described in several species and at least part of the physiology is similar, as described above in the Diving Reflex.
Cold shock in bacteria[edit]
A cold shock is when bacteria undergo a significant reduction in temperature, likely due to their environment dropping in temperature. To constitute as a cold shock the temperature reduction needs to be both significant, for example dropping from 37 °C to 20 °C, and it needs to happen over a short period of time, traditionally in under 24 hours.[6] Both prokaryotic and eukaryotic cells are capable of undergoing a cold shock response.[7] The effects of a cold shock in bacteria include:[8]