Approximately 1 billion people travel each year by air on the many
domestic and international airlines. On U.S. air carriers alone, it has been
predicted that in the coming two decades, the number of passengers will double.
A global increase in air travel, as well as a growing aged population in many
countries, makes it reasonable to assume that there will be a significant increase
in older passengers and passengers with illness.
Because of a growing interest by the public of health issues associated
with commercial flying, the Aerospace Medical Association prepared this
monograph for interested air travelers. It is informational only and should not be
interpreted by the reader as prescriptive. If the traveler has any questions about
fitness to fly, it is recommended that he or she consult a physician. The authors
sincerely hope that this publication will educate the traveler and contribute to safe
and comfortable flight for passengers.
Stresses of Flight
Modern commercial aircraft are very safe and, in most cases, reasonably
comfortable. However, all flights, short and long haul, impose stresses on all
passengers. Preflight, these include airport tumult (e.g., carrying baggage,
walking long distances, and flight delays). Inflight stresses include lowered
barometric and oxygen pressure, noise and vibration (including turbulence),
cigarette smoking (banned on most airlines today), erratic temperatures, low
humidity, jet lag, and cramped seating. Nevertheless, healthy passengers endure
these stresses which, for the most part, are quickly forgotten once the destination
is reached. In general, passengers with stable medical conditions usually
arrive at the destination airport none the worse. However, there is always the
potential that some passengers, particularly those with unstable illness, may
become ill during or postflight due to these stresses. A brief review of these
stresses follows.
The primary difference between the aircraft environment and the ground
environment relates to the atmosphere. Contrary to popular belief, modern
aircraft are not pressurized to sea level pressure. Indeed, on most flights the
cabin altitude will be between 6,000 and 8,000 ft. (1,828m and 2,438m) even
though the aircraft is flying at much higher altitudes. In other words, on most
flights, it is as if you are on top of a hill or small mountain. This imposes two
stresses on the body: less oxygen; and, expansion of gases in the body cavities.
First, with a reduced barometric pressure, there is a decrease in oxygen
pressure. However, because of the characteristics of hemoglobin, the chemical in
the blood that carries oxygen throughout the body, it remains 90% saturated with
oxygen even at the cruising cabin altitude. (At sea level it is about 97%
saturated.) Although most passengers can normally compensate for this small
3
decrease in saturation, this may not be true for individuals with heart, lung, or
certain blood diseases.
Furthermore, an increase in cabin altitude will cause gases in our body
cavities (abdomen, middle ear behind the ear drum, sinuses) to expand as much
as 25%. This can cause problems in the abdomen (bloating or stomach cramps),
ears (a crackling sensation or ear block), and respiratory tract/sinuses that will be
described later.
Although there is always some degree of vibration and aircraft turbulence,
it is usually very mild. Nevertheless, passengers are always well advised to keep
their seat belts secured because there is always the chance of moderate or
severe turbulence that could cause injury. Severe turbulence is sometimes
unpredictable and may be encountered even on clear days in excellent weather.
The hazards of cigarette smoking, active and passive, are well known and
need not be recounted here. Unfortunately, some airlines still permit it although
the trend is in the opposite direction. There is a worldwide movement to ban
inflight smoking with the International Civil Aviation Organization (ICAO) asking
all member states to comply. On U.S. air carriers, smoking is prohibited on all
flights. As a result, there has been a vast improvement in cabin air quality and
thus passenger comfort.
Today’s airplanes have very low cabin humidity, usually ranging from 5-
15%. This is unavoidable because air is drawn into the cabin from the outside
and at high altitude it is completely devoid of moisture. As a result, there can be a
drying effect on airway passages, the eyes (particularly under contact lenses),
and the skin. However, the body’s protective mechanisms prevent dehydration
and there is no harm to health.
Jet lag occurs when crossing multiple time zones. Our body clock, which
controls hormone levels, is synchronized to the day/night cycle where we started.
When we travel long distances in a matter of hours, we will arrive in another time
zone, yet our body is still functioning as if it were in the time zone at the point of
origin. This results in symptoms, such as fatigue and sleep disturbances that are
well known to travelers. Crossing time zones may not only be an annoyance for
well passengers, but it can also complicate the timing of medication dosages
such as insulin (See Jet Lag and Diabetes sections).
On most flights, regardless of aircraft type, some passengers may be
seated in a small, cramped space. This can be uncomfortable and it also reduces
the opportunity to get up, stretch, and walk about the cabin. Sitting for long
periods is tolerable for most passengers, but for some there is the potential for
ankle swelling, cramps, and other circulatory problems. Of particular concern is
blood clot formation causing deep venous thrombosis, although there is no
4
evidence that this condition is caused by cramped seating. (See Deep Venous
Thrombosis section.)