Cold shock response is the physiological response of organism

Organism

In biology, an organism is any contiguous living system . In at least some form, all organisms are capable of response to stimuli, reproduction, growth and development, and maintenance of homoeostasis as a stable whole.An organism may either be unicellular or, as in the case of humans, comprise...

s to sudden cold, especially cold water.

Myth of sudden hypothermia

In humans, cold shock response is perhaps the most common cause of death from immersion in very cold water, such as by falling through thin ice. The cold water can cause heart attack (as cold blood from the extremities reaches the heart) and inhalation of water (and thus drowning) from hyperventilation

Hyperventilation

Hyperventilation or overbreathing is the state of breathing faster or deeper than normal, causing excessive expulsion of circulating carbon dioxide. It can result from a psychological state such as a panic attack, from a physiological condition such as metabolic acidosis, can be brought about by...

. Some people, due to body type or mental conditioning, are much better able to survive swimming in very cold water.

Hypothermia

Hypothermia

Hypothermia is a condition in which core temperature drops below the required temperature for normal metabolism and body functions which is defined as . Body temperature is usually maintained near a constant level of through biologic homeostasis or thermoregulation...

from exposure to cold water is not as sudden as is often believed. A person who survives the initial minute of trauma (after falling into icy water), can survive for at least thirty minutes provided they don't drown. However, the ability to perform useful work (for example to save oneself) declines substantially after 10 minutes (as the body protectively cuts off blood flow to "non-essential" muscles).

Winter swimmers

It is possible to undergo physiological conditioning to reduce the cold shock response, and some people are naturally better suited to swimming in very cold water. Adaptations include the following: (1) having an insulating layer of body fat covering the limbs and torso without being overweight; (2) ability to experience immersion without involuntary physical shock or mental panic; (3) ability to resist shivering; (4) ability to raise metabolism (and, in some cases, increase blood temperature slightly above normal levels); (5) a slight but significant ability to mentally control blood flow to the muscles: and (6) a generalized delaying of metabolic shutdown (including slipping into unconsciousness) as central and peripheral body temperatures fall. In these ways, winter swimmers can survive both the initial shock and prolonged exposure. Nevertheless, the human organism is limited by its thermal design: in freezing water, the struggle to maintain blood temperature (by swimming or conditioned metabolic response) produces great fatigue after 30 minutes or less.

Sources

• A physiological trip through cold water exposure. The Science of Sport. Sourced 2008-05-17.
• Introduction to Frozen Mythbusters and Myth #1. Wilderness Medicine Newsletter. Sourced 2008-05-17.