In human blood there is an equilibrium between water and carbon dioxide. Your
body is very sensitive to this equilibrium. When you exercise heavily, you
produce large amounts of CO2. The brain detects the increased CO2
and sends a signal to increase your breathing rate. The faster you breathe, the
more CO2 you exhale, thus lowering the level of CO2 in
your blood. This is an attempt by the body to re-establish the equilibrium
between carbon dioxide and water in your blood. This example demonstrates one
behavior common to all equilibria - the ability to self-regulate.
In certain people, a condition known as hyperventilation occurs in which anxiety
may cause rapid breathing. This also expels CO2, but because there
was no excess of CO2 in the blood, the rapid breathing causes the CO2
in the blood to fall below normal levels. This time, the remedy is to allow CO2
to build up in the blood - by either not exhaling so much or by re-breathing air
which is high in CO2. If something is not done to accomplish this,
like breathing into a paper bag, unconsciousness will result - the person will
faint and while unconscious, the breathing rate will return to normal.
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In certain people, a condition known as hyperventilation occurs in which anxiety
may cause rapid breathing. This also expels CO2, but because there
was no excess of CO2 in the blood, the rapid breathing causes the CO2
in the blood to fall below normal levels. This time, the remedy is to allow CO2
to build up in the blood - by either not exhaling so much or by re-breathing air
which is high in CO2. If something is not done to accomplish this,
like breathing into a paper bag, unconsciousness will result - the person will
faint and while unconscious, the breathing rate will return to normal.