Winter’s science lessons: Cold can be deadly
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.
For more related SurvivalCommonSense.com tips and stories, click on the highlighted words:
- STOP: Use this exercise to reduce stress and focus your thoughts.
- Write a note to let people know where you went, before you left.
- Take your Ten Essentials on every outing.
- Dress with the right fabrics.
- Have a plan to make a tarp shelter.
- Carry lightweight, compact firestarter.
- Find the most effective fire ignition system.
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- Use charcloth as an effective method of catching a spark to make a fire.
Hi Leon,
Great web site and the blog is a great idea to share the wealth of experience out there. As you know, I was an EMT for 22 years and an alpine patroller with the National Ski Patrol for 20 years. I’ve seen a lot of varying degrees of temperature related injuries.
Here are a couple of important points your readers should keep in mind concerning heat related injuries. The first is that more cases of hypothermia occur when temperatures are in the 40s and 50s than below freezing. This condition deals with core body temperature issues not frost bite etc. My personal belief is that you are more on the lookout for hypothermia at lower temperatures and it kind of sneaks up on you at warmer temperatures because you don’t expect it and are not thinking in those terms.
Those persons most susceptible are usually tired and wet, and often not thinking straight. Getting wet can come from the environment on outside, or sweat on the inside. In really cold environments the motto is: you sweat you die! Monitoring layering of clothing to match the level of energy output is critical.
Not thinking straight is the second big point and can result from a couple of sources. Alcohol, which is often involved, not only has its effect on judgment, but is also a vasodilator and increases the speed of heat loss by increasing the blood flow in the skin. Continued consumption produces a spiraling effect of greater impaired judgment and increased heat loss.
Impaired judgment can result from a body core temperature drop as little as one or two degrees. (That would be Fahrenheit. I like to keep things in the real world.) Your situation becomes a lot more perilous when you start doing stupid things.
For those desiring more information on this phenomenon, PBS had a show on it. (I can’t remember the name, but I think it might have been on NOVA. I’m sure the PBS store can help those interested.) Several mountain climbers each swallowed a capsule that transmitted their body core temperature during their climb on Mount Everest. A decrease in thinking speed, comprehension, and judgment was noted with a one to two degree change body core temperature. This was also true for an equal increase in body core temperature. FYI: for those considering hiking Death Valley.
Leon you should continue this with a bit on insulation: like, maybe the time we went camping in the pine forest and you tried to make it through a -10oF night with an old cotton sleeping bag and old cotton insulated coveralls. You could also provide some instruction on “How to get into a sleeping bag while wearing insulated coveralls”.
Well, happy trails to all. Keep your head about you, and you’ll keep your ass out of trouble.
It’s a good thing we all don’t have the same skill sets – life would be really weird if we did! Thanks for your comments!
I am not going to be original this time, so all I am going to say that your blog rocks, sad that I don’t have suck a writing skills