Hot Days and Hot Heads: Understanding
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. Overheating
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.
at least three liters of water every day.
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