Cold-Related Injuries #7 – Hypothermia


Hypothermia is a lowering of body’s core temperature to level where normal brain & muscle function are impaired.
It is the one of the most common threats and causes of wilderness emergencies.
We are a hairless mammal, designed for the hot tropics, not the cold environs.
We have little or no defense against the cold, other than behavior, i.e., wear warm clothing.

Balance of heat production & heat loss.
Thermoequilibrium is monitored & controlled by the brain.
Thermoregulation is performed by the skin, via the vasculature.

Heat Production: 
Internal sources:
Basal metabolism – burning of glucose to produce heat
Nutrition/digestion – “logs on the fire”
Exercise/shivering – muscle contraction to produce heat (as byproduct)
External sources:
Fire, stoves, sun, other people

Heat Loss:         
Conduction – heat transfer from one solid object to another
Convection – heat transfer from solid object to air
Radiation – infrared energy given off by warm objects      
Evaporation – heat transfer to water during liquid to gas change

Body’s defensive reaction to cooling off: 

Peripheral vasoconstriction
– skin’s attempt to decrease heat loss.
Involuntary shivering – muscles’ attempt to produce heat.
Increased basal metabolism – may increase to 5 times its normal rate.

For more detailed information on Hypothermia see the Jan/Feb 2004 issue, When Jack Frost Bites, and the Nov/Dec 2004 issue, Frozen Mythbusters, of the Wilderness Medicine Newsletter. Click on this link to learn more about or subscribe to the Wilderness Medicine Newsletter.

This blog is powered by the Wilderness Medicine Newsletter, now celebrating 20 years of publication. The WMN is published and distributed online six times each year by TMC Books, and subscriptions cost as little as $10 per year. To find out more, or to subscribe online, click here.


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