the gas in the
In an un-pressurised
aircraft climbing to higher and higher altitudes, your body is exposed
to less and less pressure upon its outer surfaces. Because the pressure
inside your body is still the same as it was on the ground, strange
things begin to happen. Gases trapped in the body cavities start
expanding in an effort to equalize the pressure with that of the
environmental gas (that is, air). This phenomenon can cause you some
discomfort. Trapped in such places as the sinuses, behind the ear drum,
and in the stomach the expanding gas may lead to a headache, ear pain,
or a feeling of abdominal fullness.
At 8,000 feet, the gases
in your body expand to a volume of about 20% greater than that at ground
level. If your rate of climb is gradual and your physical condition is
good, you can usually adjust to this change easily and comfortably. At
18,000 feet, the wet gas bubbles more than double their normal size and
the expansion continues as the un-pressurised aircraft gains altitude. A
very rapid change of altitude is naturally more hazardous and
uncomfortable than a slow change.
You can usually reduce
the discomforts resulting from the expansion of trapped gases by slowing
your rate of ascent. If they persist, descend to a lower altitude where
the atmosphere is denser. Most of the gas in the intestines is swallowed
air, but some is formed by the digestive process. The amount of gas
varies with the individual and with the type of food eaten. If you
expect to fly at high altitude, the following "Diet Don'ts" may help to
minimize abdominal gas;
1. Don't eat too
quickly before a flight.
2. Don't eat too much. (Swallowed air increases with each bite)
3. Avoid large quantities of fluid, especially cokes, pop, and
4. Don't eat gas-forming foods. (Beans, cabbage, onions, raw
apples, cucumbers, melons, or any greasy foods)
5. Avoid chewing gum on the way up - it may result in your
swallowing a great deal of air.
In addition to gases
trapped in the body cavities, a considerable volume of gas (primarily
nitrogen) exists within the body, not in its normal state, but in
solution. That is, it is dissolved in the blood and other body tissues,
especially fat. When the outside pressure falls, these gases tend to
come out of solution, forming gas bubbles - just as carbonated beverages
release bubbles when you remove the cap and let the pressure escape.
These bubble can produce severe pain. Pain caused by bubble formation
around the joints or muscles is called "bends." The same bubble
formation in the lung tissue is called the "chokes" and is recognized by
a burning sensation or stabbing pain the chest area, a cough, and
difficulty in breathing. Needless to say, the effects upon your ability
to operate the aircraft can be disastrous.
difficulties are seldom experienced below 25.000 feet so the
low-altitude pilots need not be too concerned. If you should be
operating a high-performance aircraft at higher flight levels and
suspect that you might have the bends or chokes, the quickest relief can
be obtained by lowering your altitude.