By Donna Healy

Published in the Billings Gazette, Jan.17, 2010

Cold weather and icy conditions can lead to hypothermia, no matter if you're in the wilderness or some urban setting.

Winter’s cold can kill, but the precise body temperature at which a person dies from hypothermia remains elusive.

The lowest recorded core-body temperature of an adult who survived accidental hypothermia is 56.8 degrees Fahrenheit, according to the medical text “Wilderness Medicine.” A core temperature is the temperature of the body’s vital organs, normally about 99.6 degrees F. in humans.

Because humans are warm-blooded, we need to maintain a fairly constant core temperature. Here’s a description of what typically happens when we don’t:

Outdoors, in winter, the first danger sign may be achingly cold fingers because your body lets your fingers chill to preserve warmth in the vital organs.

“The body doesn’t think the hands are as important as the vital organs, but, unfortunately, if you’re trying to get out of trouble, your hands can be very important,” said Dr. Warren Bowman, a retired  Billings doctor who spent 30 years as the medical adviser to the National Ski Patrol.

Bowman wrote a chapter in “Wilderness Medicine” on the “Essentials of Wilderness Survival.” At age 80, he’s reworking a sixth edition of the chapter’s text.

Initial fumbles may become stumbles and mumbles as a person suffers from the biting cold.

By the time your core temperature sinks to 95 degrees, you’re likely to be shivering uncontrollably as your body tries to generate additional heat. Two degrees lower, and cold clouds your judgment and your behavior.

At 91.4 you’re apathetic; at 89.6 you’re in a stupor and your oxygen consumption has decreased by 25 percent.

At 86 degrees, your heart pumps at two-thirds of its normal output. Like a cold-blooded animal, your body loses control of its own temperature, a medical condition known as poikilothermia.

“Once you’re at 86, nothing that you can do will warm you,” Bowman said. “Your temperature will coincide with the environment you’re in.”

A degree lower, and you might suddenly feel hot and start stripping off layers of clothing, a behavior described as “paradoxical undressing.”

At 82.4 degrees, you’ve entered a state of severe hypothermia. Your oxygen consumption and pulse are half the normal rate.

“Your heart loses the rhythm of the heartbeat,” Bowman said.

Instead, it writhes.

At around 80 degrees, you lose the ability to move. At 77, the brain’s blood flow is one-third of normal.

What’s labeled “profound hypothermia’’ occurs when the body’s core temperature sinks to 68 degrees. At 66 degrees, an electroencephalogram, or EEG, a tool used to measure the brain’s electrical activity, ceases to chart brain waves.

“It sort of straight lines,” Bowman said.

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