by Cody Lundin
Fluctuations in core body temperature, high or low, of even a few degrees can severely compromise your ability to survive. To control its inner temperature, the body must be able to sense a change in environmental temperature and respond accordingly. To do so, in part, the body is equipped with warm and cold receptors located in the skin, spinal cord, muscles, and brain that begin physiological changes to quickly deal with temperature extremes. Many variables contribute to the development and severity of hypothermia and hyperthermia including a person's age, sex, health, nutrition, body size, hydration, physical exercise, exhaustion, duration of exposure to wind and temperature, wetness, medications, intoxicants, and prior adaptation to heat or cold. The core body temperature is thermoregulated by the physiological responses and reflexes of vasoconstriction, vasodilation, shivering, and sweating. Aside from basic physical necessities such as an unobstructed airway, breathing, and circulation, thermoregulation is of prime importance for your short- and long-term survival.
Temperature regulation in humans represents the balance between heat production from metabolic sources such as digesting a pizza and exercise, and heat loss from respiration and evaporation (sweating) and the physics of radiation, convection, and conduction. Once hypothermia develops, the heat deficit is shared by two body compartments, the shell and the core. Your outer skin or "shell" consists of .065 inches of skin and has an average area of 2.2 square yards. This means that on average your shell accounts for only 10 percent of your total body mass. The rest of it is considered "the core." In other words, when your body senses a drop in core temperature, it burns through an enormous amount of calories and puts a dent in your stored food supply.
Human beings suck in their ability to physiologically adapt to cold environments. Temperature regulatory mechanisms act through the autonomic nervous system and are largely controlled by the hypothalamus. The hypothalamus responds to stimuli from nerve receptors in your skin, which is the largest organ in your body. In a cold environment, body heat is conserved first by the constriction of blood vessels near the body's surface (vasoconstriction), keeping the majority of blood (heat) in the core. The body thus uses the skin and underlying fatty layer as insulation. The one area of skin that doesn't constrict blood flow when the outside temperature gets cold is the scalp, which likes to remain at a fairly constant temperature regardless of outside extremes. This is one reason why the head and neck area loses (and gains in hot temperatures) a tremendous amount of heat.
In its attempt to regulate temperature, the body changes blood flow to the skin. When blood vessels are dilated wide open in hot weather, the body can circulate more than four quarts of blood every minute—in the skin alone. In cold weather, blood vessels constrict the skin's blood flow to an amazing 99 percent of the former, a mere 0.02 quarts per minute! Ironically, when temperatures continue to drop, blood vessels in the skin dilate (vasodilation), and if temperatures drop further, the blood vessels alternate back and forth between dilation and constriction in the body's attempt to ensure that the skin remains undamaged from the cold. The result is your red nose, ears, hands, and other appendages in the wintertime. If outside temperatures continue to plummet, however, surface blood vessels constrict continuously to protect the core.
Second in the body's response to cold are uncoordinated waves of muscle contractions more commonly referred to as shivering. Shivering utilizes small parts of the skeletal muscles called motor units, which contract at around ten to twenty times per second and can increase your metabolism fivefold! The energy needed for shivering comes from fats and simple sugars (carbohydrates) and can be used up quickly if not replaced with extra food. Shivering decreases when carbon dioxide levels raise (as in a poorly ventilated home or emergency shelter), when the oxygen in the air becomes thinner (extremes in altitude), and through the use of alcohol, which impairs the shivering response.
Since blood vessels are essentially the pipes your body uses to heat itself by forcing warmed blood throughout your body, ingesting substances that dilate surface blood vessels is stupid. Purposely constricting blood vessels is also a bad move whether through nicotine use, dehydration, or tight clothing. Dehydration slowly turns your blood into ketchup, making it that much harder for the heart to circulate the sludge around in order to keep inner temperatures stable. Low temperatures also change the composition of blood, making it thicker by up to 21 percent, by increasing the number of particles such as platelets, red blood cells, and cholesterol.
When it's hot outside, heat must be lost by the body to maintain a proper core temperature. Brain cells are particularly sensitive to high temperatures. Increased surface blood flow through dilated vessels, especially in the arms and legs, works at dissipating extra heat by exploiting the major surface areas of the body as well as avoiding the insulating properties of subcutaneous fat. Once again, if your blood turns to ketchup because of dehydration, this activity is severely compromised. The increased surface blood flow and the wonders of evaporative heat loss through increased sweating are the main tools your body uses to stabilize its inner core when outside temperatures soar.
Cellular Chaos
Your body's 50 billion cells have permeable membranes, or "walls," consisting of lipids or fats. Through these membranes cells make and break bonds at precise rates, maintaining such levels as our sodium and potassium balance. These membranes, being composed of fats, are very sensitive to changes in temperature.
When your core body temperature drops, proteins within the cells start to clump, causing holes, while water in and around the cells freeze to form jagged ice crystals that shred the delicate membranes. Conversely, as the core overheats, cell membranes begin to lose their elasticity and can actually melt. With cell membranes damaged, precision rates are altered and once-pristine body systems fall into a state of unregulated pandemonium. Fluctuations in core body temperature literally cause chaos on a cellular level, chaos you can see in the uncoordinated signs and symptoms of hypo- and hyperthermia.
In summary, living in cold temperatures without insulated clothing and footwear, lying on uninsulated ground (conduction), or wearing weather-dampened or sweated-out cotton clothing (evaporation) in the wind (convection) while being unable to improvise a heat source (radiation) can all cause death by hypothermia.
Conversely, in hot temperatures, radiation from the sun (directly and reflected from the ground and particulate matter in the air) can heat up conductive ground surfaces in excess of 150 degrees F (65.5 degrees C). This in turn helps produce heated convective winds capable of evaporating sweat obscenely fast with little cooling effect for the body. Add in the effects of metabolic heat produced by digging a sanitation trench in the backyard at noon, and you have a serious setup for dehydration, hyperthermia, and death.
Knowing the Signs and Symptoms of Hypothermia and Hyperthermia
A "sign" is a behavior you see in someone else while a "symptom" is a behavior someone else sees in you. Notice that the psychological signs and symptoms of hypothermia and hyperthermia are very similar, involving disorientation and poor coordination. These similarities are no accident and offer vital clues into a person's physiology at the time. In city or country, recognizing the signs and symptoms of hypothermia and hyperthermia in yourself and others is critical as they are the body's warning signals that things are getting out of whack on a cellular level. The majority of people dead from exposure had ample early warnings that were ignored. These warning signs are your second chance to immediately manipulate your internal and external environment in whatever way you can to prevent further heat loss or gain.
Heinous Hypothermia: The Signs and Symptoms
Early Signs and Symptoms
Core temperature 95–96 degrees F (35–35.5 degrees C)
Shivering
Decreased awareness
Unable to think or solve problems
Apathy
Confusion
Skin pale and cool to the touch
Numbness (stinging pain)
Loss of dexterity
Advancing Signs and Symptoms
Core temperature 93–94 degrees F (33.9–34.5 degrees C)
Obvious shivering
Stumbling
Deterioration of fine and complex motor skills
Little or no effort to protect oneself
Unaware of present situation
Advanced Signs and Symptoms
Core temperature 91–92 degrees F (32.8–33.4 degrees C)
Intense shivering
Difficulty walking
Thick or slurred speech
No effort to protect oneself
Skin appears ashen gray and cold
Possible hallucinations
The Death Zone
Core temperature 87–90 degrees F (30.6–32.2 degrees C)
Shivering comes in waves
Unable to walk
Speech very difficult to understand
If the core temperature continues to drop, shivering will cease, breathing and pulse will appear absent, and the skin will become blue in color. Death will quickly follow.
Hideous Hyperthermia: The Signs and Symptoms
There are three levels of environmental heat illness recognized by the medical profession. Listed in order of severity, from bad to worse, they are heat cramps, heat exhaustion, and heatstroke. There are two types of heatstroke, classical heatstroke and exertional heatstroke. Classical heatstroke generally occurs in out-of-shape, sedentary older folks who decide to weed the garden or mow the lawn at noon in July. Exertional heatstroke happens after intense physical activity in a hot environment, especially during periods of high humidity, which prevent the cooling power of evaporation. During this type of heatstroke, despite earlier beliefs, the victim may still be sweating heavily, as the sweat glands are usually still active at the time of collapse. Heatstroke is extremely serious and can be avoided by paying attention to the signs and symptoms of heat cramps and heat exhaustion.
Signs and Symptoms of Heat Cramps
Core temperature 99–100 degrees F (37.3–37.8 degrees C)
Thirst
Irritability
Profuse sweating
Headache
Dizziness
Nausea, vomiting
Decreased appetite
Generalized weakness
Spasms of the voluntary muscles and abdomen after exercise and exertion in a hot environment
Signs and Symptoms of Heat Exhaustion
Core temperature 101–102 degrees F (38.4–38.9 degrees C)
Excessive thirst
Profuse sweating
Headache
Dizziness
Nausea, vomiting
Generalized weakness
Decreased appetite
Disorientation
Confusion
Cramps
Weak, rapid pulse with shallow, rapid breathing
Cool, pale, moist skin
Decreased awareness or unconsciousness
Signs and Symptoms of Heatstroke
Core temperature 103–106 degrees F (39.5–41.1 degrees C)
Disorientation
Confusion
Hot, flushed, potentially dry skin (classical heatstroke) or hot, flushed, sweaty skin (exertional heatstroke)
Signs and symptoms of shock
Rapid, bounding pulse or rapid, weak pulse
Initial deep breathing, rapidly progressing to shallow breathing, followed ultimately by no breathing
Dilated, sluggish pupils
Delirium
Little or no effort to protect oneself
Unaware of present situation
Seizures
Stroke
Coma
If elevated core temperatures remain constant or continue to rise, the Grim Reaper will take you out to lunch.
How Your Body Loses and Gains Heat
Humans are incredibly vulnerable to temperature extremes. Like a motor vehicle, the body has very limited temperature parameters in which it will "run." If these limits are breached, the vehicle runs worse and worse until it finally stops running altogether. Regardless of where you live on this planet, you are susceptible to certain physical laws that dictate how your body loses and gains heat from the environment. It matters not if your environment is the deep woods of Alaska or an apartment in downtown Tokyo, the laws of nature described below will be enacted. By recognizing and understanding the following general physics involved in heat loss and gain, the survivor can intelligently assess virtually any situation placed before them and, one by one, manage the problems. Knowing these simple laws in advance allows the wise person to prepare accordingly and mitigate potential breaches to thermoregulation before they happen.
Conduction
Conduction is the transfer of heat (energy) through direct contact with an object, including hot or cold air against the skin. The direction of heat flow is always from a warmer to a cooler temperature. If you touch a surface that's less than 92 degrees F (33 degrees C), you will lose heat through conduction. If the object touched is warmer than 92 degrees F, your body gains heat. Substances vary in their thermal conductivity quite radically. Water has twenty-five times the conductivity of air while muscles possess nearly twice the tissue conductivity of fat. Under normal conditions, conduction accounts for approximately 2 percent of the body's heat loss for a standing person.
Convection
Convection is the transfer of heat (energy) through currents in air and liquids and can be either forced or natural. Convection has within it many variables including density, surface shape and temperature profiles, flow dynamics, conductivity, and specific heat. An example of forced convection would be rolling down the windows of a moving car or sitting in front of a fan. Natural convection happens when density changes in heating or cooling molecules next to the body cause them to move away from the body itself. This "boundary layer" effect is caused by slower-moving molecules directly against the skin produced by radiant heat given off by the body. This layer is only a few millimeters thick and is the equivalent of a constant, three-mile-per-hour wind.
Classic convection experienced by everyone is the "wind chill factor," which causes existing outside air temperatures to feel much colder then they actually are. The effects of wind chill are directly responsible for thousands of deaths all over the world. In contrast, hot desert winds can feel like a hair dryer on the skin, and suck away evaporating sweat so quickly you might not think it's hot because you're "not sweating." Sweat evaporating from the skin at such an accelerated rate does little to help cool the body.
Researchers have found that under neutral conditions as much as 40 percent of the heat loss from a naked human body stems from convection! Add wet clothing and/or strong winds to the scenario and the percentage climbs dramatically.
Radiation
Radiation is the act of losing or gaining heat (energy) through, well, radiation. There are two types of radiation we're concerned with. Terrestrial, or long-wave radiation, emanates from fire, a human body, or just about anything else on the planet having a temperature greater than absolute zero or minus 460 degrees F (minus 273 degrees C). Radiated body heat is truly the emission of electromagnetic energy in infrared wavelengths of which the body is both emitting and receiving. Curling up in the fetal position reduces your radiant heat loss by 35 percent when compared to a person standing with arms away from their sides. Radiant heat loss is a force to be reckoned with as it accounts for around 45 percent of the total heat loss from a nude body in neutral conditions. Surfaces that are good at absorbing radiation are also good at giving it off.
Shortwave radiation emanates from the sun and varies in its intensity according to the time of day, altitude, latitude, surface reflection, atmospheric pollution, ozone levels, and season. Most ultraviolet radiation bathes the Earth at midday, 80 percent between the hours of 9 a.m. and 3 p.m. and 65 percent between 10 a.m. and 2 p.m. Radiation from sunlight can heat a person in three ways, directly on the skin, reflected off particulate mat
ter in the atmosphere, and reflected off the ground, and, unlike long-wave radiation, it is absorbed to a greater extent by darker-colored clothing and skin pigmentation. In hot climates, all can lead to dehydration and hyperthermia if not properly managed.
HOW Your Body GAINS Heat
DESTITUTE DON BODY TYPE: Larger surface-area-to-volume ratio superior at eliminating excess heat
A: Direct Solar Gain [Radiation]
B: Breathing through Nose Limits Water Loss [Respiration]
C: Hot Wind [Convection]
D: Reflected Particulate Matter Solar Gain [Radiation]
E: Nicotine: Diuretic, Constricts Blood Vessels, Increases BMR
F: Insulation from Hot ground [Conduction]
G: Ground Reflected Solar Gain [Radiation]
H: Alcohol: Diuretic, Impaired Judgment, Increased Blood Viscosity
Destitute Don loses heat through: I: Increased Heat Loss through Wet Clothing [Evaporation]
HOW Your Body LOSES Heat
TED THE TRANSIENT BODY TYPE: Larger volume-to-surface-area ratio superior at minimizing heat loss
