The medical community defines hypothermia as the loss of heat in the human body greater than the heat replenishment, causing the temperature of the core area of the human body to decrease, and producing a series of symptoms such as chills and cardiopulmonary failure, and eventually possible death. It does not necessarily occur in a cold and freezing environment, as long as external factors such as wind and rain quickly take away the body's heat, it may be hypothermia.
More than 50% of the energy obtained by the human body through the three major thermogenic nutrients is directly converted into heat energy to maintain body temperature, and the rest is transmitted to the body adenosine diphosphate into adenosine triphosphate, which is stored in the form of chemical energy to supply muscle contraction, nerve conduction, gland secretion, etc. Maintaining body temperature is very energy-intensive, and ectothermic animals (except birds and mammals) do not need to maintain a high body temperature, and they can survive for a long time after a full meal.
As a thermostatic animal, body temperature is one of the basic vital signs. Body temperature in physiology or clinical medicine usually refers to the average temperature of the core area of the human body (referred to as core temperature), generally 37.5-38 °C. The range of the core area of the human body changes at different ambient temperatures. In cold environments, the core area is concentrated in the head and chest and abdomen; In hot environments, the core area can be extended to the extremities. Core temperature is not easy to measure, clinically it is usually measured rectal temperature, oral temperature, armpit temperature to represent core temperature. The opposite of the core temperature is the body surface temperature, generally 27-37 °C, which is easily affected by the ambient temperature.
Under normal circumstances, the human body temperature is relatively stable, and when the body temperature is abnormally increased or lowered for some reason, it will be life-threatening. When the body temperature exceeds 42 ° C, brain function will be severely impaired, and brain waves will be weakened or disappeared; When the body temperature exceeds 44-45 °C, it can be fatal due to irreversible denaturation of proteins. Conversely, the nervous system function decreases when the body temperature is low, and consciousness disorders can occur below 34 °C, nerve reflexes can disappear below 30 °C, cardiac autonomic disorders occur, and heart activity stops below 28 °C.
The body's maintenance of relatively constant body temperature depends on the body's thermoregulatory ability, which is manifested in the dynamic balance of the two physiological response processes of heat production and heat dissipation. Thermogenesis involves converting energy from muscle contraction into heat energy during chills and using the body's brown adipose tissue for oxidation and energy. Brown adipose tissue differs from white adipose tissue in that it is located above the neck and collarbone, which quickly activates at low temperatures and releases a lot of heat. Heat dissipation involves heat dissipation through the evaporation of sweat, increasing blood flow to the skin so that heat is brought from the body to the surface. The thermoregulatory center of the hypothalamus senses the temperature of the blood and body surface through temperature-sensitive free nerve endings distributed in the skin, mucous membranes, and internal organs, thereby performing negative feedback regulation of heat production or heat dissipation, so that the body temperature remains constant.
The ability to regulate body temperature combined with the protection of heating or cooling measures allows humans to survive in Siberia at minus 32°C or Libya at minus 58°C. However, thermoregulation has a certain limit and takes time to complete, and if the temperature changes too drastically or rapidly, the thermoregulation will fail, which is why a strong geological surveyor can suddenly lose his life in a rain and wind.
How to avoid hypothermia? The best way to do this is to prevent problems before they happen. Warm hats, gloves, neck bibs, windbreakers, thick socks, wind masks, and even goggles are essential items for traveling in windy and cold weather. Participate in outdoor sports should prepare a set of quick-drying underwear, once the clothes are wet by sweat, rain, river water will be changed in time, wearing wet underwear can easily lead to hypothermia. Don't let yourself be physically overdrawn during exercise, and use food and hot drinks to replenish body calories in time. Once hypothermia occurs, try to find a place to shelter from the wind and rain, find a way to drink warm sugar water and supplement food, healthy companions can be close to the hypothermia person with body temperature to help him recover; If you participate in a marathon or other race, you must fully understand the local climate, race equipment, supply station location, medical rescue, emergency equipment, etc., and then rationally choose whether to participate according to your own situation.