Travel Reference
In-Depth Information
CHAPTER 26
COLD INJURIES
James A. Wilkerson, M.D.
Principal Contributor
The common disorders produced by cold are hypothermia and frostbite. Hypothermia is a
decrease inthecoretemperature ofthebodythat impairs intellectual andmuscular function,
including cardiac function. Frostbite is a localized injury characterized by freezing of tis-
sues. Preventing and treating these disorders requires knowledge of the way heat is lost or
gained and the body's responses to cold.
MECHANISMS OF HEAT EXCHANGE
Heat is lost or gained from the environment by four routes:
Radiation
Evaporation
Convection
Conduction
Radiation
Radiation, by far the largest source of heat loss in temperate climates, is a form of direct
energy emission, much of it as infrared radiation. Heat is exchanged directly with the envir-
onment, and heat loss is determined by the difference in temperature between the skin and
the atmosphere or surrounding objects such as rocks, trees, snow, or ice. Radiant heat loss
increases as the environment grows colder.
Inanenvironmentthatiswarmerthantheskinsurfacetemperature(about95°For35°C),
radiant heat is absorbed by the body. The inability to lose heat by radiation in such environ-
ments can contribute to heat illness.
Clothing has little effect on heat loss by radiation. The heat radiates from the body to the
clothing and from there to the atmosphere. Efforts to develop clothing materials that reflect
heat back to the body have met with little success. However, radiant heat loss becomes a
major problem only in extremely cold situations (below −20°to −30°F or −29° to −35°C).
If clothing adequately limits heat loss by other routes, particularly convection, the body can
compensate fortheincreased radiant heatlossencountered inmostcoldwilderness environ-
ments ( Fig. 26-1 ).
Evaporation
 
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