HOT DAYS AND HOT HEADS: UNDERSTANDING HEAT
ILLNESS
by Buck Tilton
Across the thundering heat of an African savanna, a million
years ago, give or take a few hundred centuries, runs something
you would recognize instantly as almost human. It runs to live.
Not fast, and not quick, it will run, with short breaks, for
nearly 24 hours. In the end it will catch and kill a prehistoric
antelope, using its bare hands as weapons.
In order to survive as a species, humans adapted in their own
special ways, with virtually hairless skin filled with abundant
sweat glands and powered by a cardiovascular system of marvelous
endurance. Those same additions allow you spring and summer.
You are not however, a foolproof design. Oveheating can ruin
your day, and your life.
To understand heat illness, let's start with the fundamentals
of human thermal dynamics, body heat production vs. body heat
loss. There are two major internal sources of heat. Even as you
sit quietly reading these words, you are making heat via basal
metabolism, the energy necessary to sustain your life at complete
rest. When you leave the house and start exercising, a second
heat source kicks in, exercise metabolism. Strenuous exercise
metabolism may produce 15 to 18 times the amount of heat of basal
metabolism, depending on your level of fitness. From external
sources, the human body can absorb heat, from things such as
the sun, a fire, and the ingestion of hot drinks. You end up
with far more heat than you need and, if you couldn't shed the
excess, you would literally cook in your own juices.
Human heat is lost in four ways: conduction, radiation, convection,
and evaporation. Conduction, heat loss through direct contact
with something cooler than you, does not help much on a hot day.
On a desert-like afternoon, you may actually take in heat from
a hot environment. Radiation is energy lost directly from your
skin's surface and, as the air warms up around you, it may effectively
stop on a sunny summer day. Convection is heat loss through the
movement of air around your body. Without wind, convective heat
loss practically stops when you're not moving, and it stops when
the air temperature reaches approximately 92 degrees F.
That leaves evaporation, the vaporization of sweat from your
skin, the primary source of heat loss for the human. As your
skin heats up, pores dilate and sweat floods out. Evaporation
of the sweat cools your skin, heat is drawn from your blood near
the surface of your body, and the cooler blood circulates to
keep your insides maintained at an acceptable temperature. In
other words, if you don't sweat, you ain't gonna make it.
Sweat comes from your circulatory system, and it's not uncommon
to sweat out a liter of water in an hour during periods of exercise
in a hot environment. This water loss may reach two-and-a-half
liters per hour with prolonged exercise. And sweat contains salt,
a critical component of normal body function. It is this combined
water and electrolyte depletion that forms the basis of a spectrum
of problems with one general name: heat illness.
Although you are unique in the animal world in your ability to
shed excess heat, if body heat production gets a jump on body
heat loss, you are heading toward heat illness. On the minor
end of the problem are heat cramps, a painful spasm of major
muscles that are being exercised. Those most often cramped are
people unacclimatized to heat who are sweating profusely. Heat
cramps are poorly understood, but probably result not only from
the water lost in sweat, but also the salt lost in sweat. Gentle
massage and stretching of the affected muscles usually provides
relief. Drinking water, preferably with a pinch of salt per liter
added, is advisable. Heat cramps do not often occur in someone
who is adequately hydrated. Once the pain is gone, exercise may
be continued if necessary, but a day of rest is better.
Prolonged sweating may move you along the spectrum to heat exhaustion,
characterized by headache, dizziness, nausea, rapid breathing,
and, of course, exhaustion. Sufferers are so sweaty they often
feel cool, grow goose bumps and complain of chills. Treatment
should include moving the exhausted person to a shady spot and
oral rehydration with cool, very slightly salty water. Some experts
prefer using an electrolyte-balanced drink such as Gatorade,
but the drink should be watered-down three or four times for
more rapid absorption in a resting person. Maximum absorption
ranges from 150 to 250 ml per 15 minutes, so it takes about an
hour to get a liter back into circulation. Heat exhaustion is
not physiologically damaging, but it should be treated aggressively
before it progresses to a more serious condition.
On the serious end of the spectrum lies heat stroke, a problem
that kills approximately 4000 people in the United States every
year. There are two varieties of heat stroke. In classic heat
stroke, the patient is usually elderly or sick, or both. Temperature
and humidity have been high for several days, and the patient
has dehydrated to the point where his or her heat loss mechanisms
are overwhelmed. You might say they simply run out of sweat.
Skin gets hot, red, and dry. They lapse into a coma and, if untreated,
die.
But more and more people are being killed of the second variety,
exertional heat stroke. The victim is usually young, fit, and
unaccustomed to heat, sweating but producing heat faster than
it can be shed. Signs include, primarily, a sudden and very noticeable
alteration in normal mental function: disorientation, irritability,
combativeness, bizarre delusions, incoherent speech. Skin is
hot and red, but wet with sweat. Rapid breathing and rapid heart
rates are almost universal. Collapse is imminent.
Quick cooling may be required to saver this victim's life, and
the best method includes removal of clothing, covering with wet
cotton, and vigorously fanning, all of which increases evaporative
heat loss. Massaging of arms and legs and ice packs at the neck,
groin, and armpits increase heat loss. Throwing patients into
cold water is less effective and often dangerous since they are
difficult to manage and may drown. Heat stroke victims should
be seen by a physician as soon as possible, even if they seem
to have recovered. Too much internal heat can cause breakdowns
in some body systems that show up later.
ACCLIMATIZATION TO HEAT
Acclimatization usually takes 2 to 3 weeks.
Exercise in the early morning and late evening for the first
week.
Work your way gradually toward midday exercise.
On spectacularly hot days, only exercise early and late.
Drink one-fourth liter of cold water every 15 minutes during
intense exercise.
Drink at least three liters of water every day.
