Dysbarisms and Altitude Sickness
We have already commented on the decrease in atmospheric pressure which occurs with altitude.
Boyle’s Law states that, at constant temperature, the volume of a gas varies inversely with the pressure. If
the pressure of gas is halved, its volume is doubled. Application of this simple law to the closed body
cavities quickly indicates where problems are likely to occur.
Barotitis
By far the most common problems are with the middle ear. It resembles a box, closed by a flexible
diaphram at one end and drained by the Eustachian tube narrow tube at the other. The eustachian tube
however is not rigid or symmetrical throughout its length and becomes slit-like at its outlet in the
nasopharnyx. On ascent expanding trapped air usually escapes easily and the only thing noticed is a
periodic “popping” due to movements of the drum as pressure equalizes. On descent however equalization
of pressure through the slit-like outlet is much more difficult and a negative pressure can build up in the
middle ear. This leads to a decrease in hearing and to pain. The ear can be cleared by opening and closing
the mouth, thus activating the tensor tympani muscle and dilating the tube, or by inflation by a Valsalva
maneuver. In an U.R.I. or other pathology of the nasopharynx, congestion of the outlet makes clearing
more difficult or even impossible. The pressure in the middle ear on descent may then become so low
relative to the outside pressure that exudation and
hemorrhage may take place and ultimately the eardrum may burst. Excessive valsalva maneuvers
however may force bacteria into the middle ear, leading to infection.
When an ear blocks and cannot be cleared by the usual maneuvers, the best way to deal with the
situation is to reascend and start a slower descent. This is not always possible. During World War II the
pilots of vertical diving Stukas had constant ear problems and their flight surgeons solved these by
periodically incising the drums! Nowadays this is not
recommended! A particular problem occurs when pilots flying at high altitude on oxygen retire to sleep
soon after landing. The middle ear is full of soluble oxygen (rather than inert introgen) which is absorbed
during sleep. On awakening they have earache due to the indrawn drums. This is called “oxygen ear”.
Other Barotraumas
Other air spaces are equally affected. The nasal sinuses are a common source of pain as may be
poorly filled teeth if the filling has not been carefully inserted and a gas space remains below it. These
various symptoms are referred to as “barotraumas” and toothache of this type is known as
“barodontalgia”. The best approach to these conditions is knowledge and prevention. Fortunately
most professional pilots are well aware of the problems and avoid flying when they are congested.
Intestinal Gas
A common irritating, embarrassing and potentially serious problem is gas in the bowel. This expands
rapidly as might be expected and, if it cannot be passed, may lead to severe pain. Chewing gum, air
swallowing, carbonated drinks and beer (in the passenger) all add to the gas, as do various gas
producing foods. Passengers with ostomy bags or various types of bowel obstruction are particularly
likely to have problems.
Inflatable Medical Aids
Boyle’s Law must be kept in mind if you are involved in the transport by air of patients requiring cuffed
tubes of any type or if casts or pneumatic dressings are being used. Cuffs should be inflated with saline
(or water) rather than air before the trip.
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