The human body is somewhat like that perfect bowl of porridge in "Goldilocks and the Three Bears." It's not too hot, not too cold, but just right.
Our bodies maintain internal body temperatures that allow our insides to keep on cooking without burning up or slowing down -- usually around 98.6 degrees Fahrenheit (37 degrees Celsius). There's even a part of our brain called the hypothalamus that regulates this internal heat to keep everything running smoothly.
But when that core temperature of major organs drops down to 95 degrees or lower, it is called hypothermia. Just like when you have a high fever, hypothermia can slow your body and possibly lead to death.
When it comes to our bodies, a lot depends on heat. Heat is the byproduct of biochemical reactions within our bodies. The food and beverages we consume are just like the wood and kindling that make a fire. Our bodies gain energy from food, and that energy pumps our hearts, grows our hair and helps our digestive system break that food down into usable units. This process is called metabolism.
Think about all of the internal processes that take place when you run. It requires energy to move so many parts of your body at the same time. When all those parts crank up, we burn up energy, producing heat.
In the cold, our bodies strive to retain as much heat, or energy, as possible. In many parts of the body, blood vessels in our skin tissue constrict, or tighten up. This tightening helps keeps blood away from the cold outer layer of the body and helps circulate warmer blood to our core areas. This tightening is also why you may feel stiff after being in the cold for a long time.
However, areas with large blood vessels, particularly around the head, neck, chest and groin, are more susceptible to heat loss because those blood vessels don't constrict as effectively as the smaller ones near the skin. That's why proper winter attire includes a hat, scarf and coat.
With all of these internal actions and reactions taking place within the body, what can we do to protect our core temperature and defend ourselves from hypothermia? We'll answer those questions, and explain how hypothermia develops on the next page.
How Hypothermia Happens
While it is important to keep our bodies properly warm, it is equally important for us to be able to cool down. But in certain environmental conditions our bodies cool down too much. Our temperatures drop too far when they dip into hypothermic internal temperatures of 95 degrees and lower.
There are four main ways that our bodies give off heat and cool themselves: conduction, convection, radiation and evaporation. Each of these processes helps us sustain healthy internal temperatures. They also give us a better understanding of how hypothermia happens.
We constantly release heat in the form of radiation. In the same way the sun emits heat down on us as we bask on a beach, our bodies exude heat as a natural by-product of our metabolism.
When you hold a chocolate chip in your hand for a few minutes, it will likely begin to melt. This process is called conduction. It occurs when our bodies come into contact with something that has a lower temperature. The body gives away heat to that other object.
If we give away heat to something in motion, however, convection takes place. When wind puts air particles in motion, they take away heat as they hit our bodies and move away. That's why a wind chill can make it feel colder outside than the true temperature.
Our blood vessels also play an integral role in heating and cooling. They expand or constrict to free or restrict blood flow to our skin tissue. When our metabolism heats up our insides, it warms our blood as well. To control that building heat, blood vessels at our skin dilate -- like our pupils in low light -- to circulate more of that warmed blood toward the skin's surface and allow the body to release heat. This opening of the blood vessels is called vasodilatation. Alcohol and tobacco both cause vasodilatation, which is why both substances can give you the sensation of warmth, even though your core temperature is colder.
Since our bodies naturally give away heat to colder, active particles, air particles in wind and water particles can accelerate that effect. Water is denser than air, so it absorbs more heat. That's why water can steal up to 32 times more heat from our bodies than air can [source: U.S. Search & Rescue Task Force]. Even when we get caught in a rain shower, it can lead to hypothermia because of how quickly water cools us.
To combat this rapid cooling, we shiver. Think about being outside on a winter day and how, as the cold hits, you instinctively bring in your arms and legs and tighten those muscles. Shivering is our bodies' way of generating heat by exciting our muscles. Our blood vessels also constrict to limit the amount of blood travelling toward our skin.
When someone's re-warming reactions, like shivering, aren't enough to overcome the cooling process, hypothermia can set in. Look for several important signs indicating the different stages of hypothermia.
- Mild Hypothermia: shivering, goose bumps, difficulty with complex motor skills
- Moderate Hypothermia: violent shivering, sluggish, speech problems, difficulty with fine motor skills
- Severe Hypothermia: rigid muscles, dazed, shivering has stopped, blue skin, erratic heart beat, unconscious
If severe hypothermia sets in, complications can include coma and even death. Other cold weather injuries are also associated with hypothermia, such as frostbite, chilblains (ulcers on the toes) and trench foot (a foot infection). For more information on protecting yourself from the cold, read How to Survive the Freezing Cold.
Now that we understand how our bodies can cool too rapidly and cause hypothermia, we'll learn ways to prevent that from happening.
How to Avoid Hypothermia
Although many cases of hypothermia arise from being outdoors in cold weather or water, it can happen at home as well. During the winter, stay aware of how cold your house is. People have become hypothermic in houses that were around 60 degrees Fahrenheit (15.5 degrees Celsius). Power outages in the winter can also send temperatures plunging, making it essential to wrap up and keep warm.
People are most susceptible to hypothermia outdoors. Whether you get stranded in a snowy field or fall into a chilly lake, you can become hypothermic quickly. So you should be prepared.
First, properly fuel yourself. Remember that the body requires food and nutrients to make heat, so going out without eating enough or being dehydrated can put you at risk. Carbohydrates, proteins and fats are the prime food groups to munch on since they provide both short- and long-term energy supplies.
Sweet, non-caffeinated beverages are also appropriate, since the sugar will boost energy quickly. Caffeinated drinks hinder your body from absorbing water, promoting dehydration. Alcohol and smoking should also be completely avoided. Both of these make your blood vessels expand, which is called vasodilatation, and your body lets off heat faster.
In wintery weather, it is also essential that you dress for the C.O.L.D.:
- Cover: Since we lose so much heat from our head, we should wear scarves and hats over head, neck and face. Mittens are also better protectors than gloves because they trap more heat.
- Overexertion: Be careful to not overwork yourself in the cold. If you deplete your body's energy reserves, you will have a harder time warming back up when you get cold.
- Layer: Wear loose clothing in multiple layers. To prevent yourself from sweating and cooling down too much, remove a layer if you get hot. Looser clothing retains heat well, but your sleeves should fit snugly at the wrists. Thermal underwear can also be an effective base layer to keep heat close to your body.
- Dry: Choose insulating fabrics such as wool, silk and polypropylene, rather than absorbent cotton. If your clothes get wet, remove them as soon as possible since water cools the body much faster than cold air.
[source: Mayo Clinic]
Even in warmer weather, water-related accidents can lead to hypothermia. For that reason, wear a lifejacket while on boats and do not drink alcohol while on boats or around water.
If you fall into cold water, it can cool your body up to 32 times faster than air [source: U.S. Search & Rescue Task Force]. Freezing cold water can also render someone unconscious in less than 15 minutes. It's critical to preserve body heat. People who have fallen in cold water should resist the automatic urge to flail or tread water. And unless the shore is less than 200 yards away, people also shouldn't try to swim to land [source: Piantadosi]. Doing so only drains precious energy stores. Instead, if alone in the water, you should pull your knees into your chest with your hands at your sides. If a group of people are in the water, they should huddle together to share body heat.
In the next section, we'll learn what to do if someone exhibits signs of hypothermia. Can you help restore that person to their normal temperature?
How to Avoid Death from Hypothermia
Nearly 700 people in the United States die each year from hypothermia [source: Mayo Clinic]. Hypothermia is a silent killer because once your body temperature drops below 95 degrees, you lose awareness of the cold and become disoriented because less oxygen reaches the brain. For that reason, take special precautions if you're alone in the cold. You may not be aware that your body is in peril.
Groups of people should look after each other for the signs of hypothermia discussed in the previous section. If someone does appear hypothermic, there are a number of things that you can do to prevent that person from dying. In mild to moderate cases, the body can re-warm at a rate of 3.6 degrees per hour.
To start that warming process, first move into shelter. If there is nowhere to go indoors, at least move the person out of the wind, since wind can speed up hypothermia. Remove any wet clothing and replace them with dry blankets or even newspaper.
For people with mild or moderate hypothermia, some food and beverages may be helpful. Warm, sweet liquids, such as diluted gelatin mix or hot chocolate will give the body quick energy boosts to help it produce heat. Proteins, fats and carbohydrates in the form of trail mix and granola can also stimulate the metabolism. Do not give them alcohol or caffeine.
In more severe cases, getting a person out of any wet clothes and into a hypothermic wrap is essential. There should be several layers of insulation between the wrap and the cold ground. A hypothermic wrap covers every part of the body with as few open spaces as possible. A sleeping bag or multiple blankets can serve as hypothermic wraps, as long as the person is completely protected from the cold.
Additionally, extra clothing or blankets should be applied to the neck, groin, armpits and chest to protect major arteries. Sharing body heat by removing your clothes and getting into the wrap with the person may also prove beneficial, except in very severe cases. Also, do not apply heat directly to the skin or give the person a massage because it can circulate the colder blood near the skin to the core, shocking the body.
CPR is another option if a hypothermic person's skin has turned blue, and you can't feel a pulse. But only do this if you are properly trained. If you stimulate the body too much with CPR, it can overexcite the heart and lead to cardiac arrest.
If possible, call 911 to get someone with severe hypothermia to a hospital. A doctor may hook up a person with hypothermia to an IV to put warming fluids directly into the body. He or she may also perform a procedure called hemodialysis, which takes the patient's blood out of the body, runs it through a warming mechanism, and returns it.
For more information on protecting against cold weather calamity, go to the links on the next page.
More Great Links
- Brown, Stanley P.; Miller, Wayne C.; and Eason, Jane M. "Exercise Physiology: Basis of Human Movement in Health and Disease." Lippincott Williams & Wilkins. 2006. (March 13, 2008) http://books.google.com/books?id=T-s3OAZdlhsC
- Centers for Disease Control and Prevention. "Winter Weather: Hypothermia." Updated Dec. 7, 2007. (March 12, 2008) http://www.emergency.cdc.gov/disasters/winter/staysafe/hypothermia.asp
- Curtis, Rick. "Outdoor Action Guide to Hypothermia and Cold Weather Injuries." Princeton University. (March 12, 2008) http://www.princeton.edu/~oa/safety/hypocold.shtml
- Discovery Channel. "Out in the Cold? Avoiding Hypothermia." (March 12, 2008) http://dsc.discovery.com/convergence/survival/ guide/10things/hypothermia.html
- Mayo Clinic. "Hypothermia." Updated June 8, 2007. (March 12, 2008) http://www.mayoclinic.com/print/hypothermia/ DS00333/DSECTION=all&METHOD=print
- MedlinePlus Medical Encyclopedia. "Hypothermia." Update Jan. 16, 2007. (March 12, 2008) http://www.nlm.nih.gov/medlineplus/ency/article/000038.htm
- Piantadosi, Claude A. "The Biology of Human Survival: Life and Death in Extreme Environments." Oxford University Press US. 2003. (March 12, 2008) http://books.google.com/books?id=aG4EbXctp6IC