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 suummer. 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 necesssary 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 throught 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 bunps 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 GatoradeX, 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.