What is aviation medicine?
Aviation Medicine is a medical specialty which combines
aspects of preventive, occupational, environmental and clinical medicine with
the physiology and psychology of man in flight. It is concerned with the health
and safety of those who fly; both crew and passengers;
as well as the selection and performance of those who hold aviation licenses.
Travel by
air:
Air travel; particularly long-distance travel, exposes
passengers to a number of factors that may adversely affect their health and
well-being. Passengers with pre-existing health problems may find that
they are more susceptible to these factors. Health risks associated with air
travel can be minimized if the traveler plans carefully and takes some precautions
before, during and after the flight. An explanation of the various factors that
may affect the health and well-being of air travelers follows:
Cabin air
pressure:
Although aircraft cabins are pressurised,
cabin air pressure at cruising altitude is lower than air pressure at sea
level. At a typical cruising altitude of 11 000 meters (37 feet), air pressure
in the cabin is equivalent to that at an altitude of 1 500 – 2 500 meters (5
000 – 8000 feet) above sea level. As a consequence, the available oxygen is
reduced and gases within the body expand. The effect of
reduced cabin air pressure are usually well tolerated by healthy
passengers.
Oxygen and
hypoxia:
During all stages of flight, cabin air contains ample oxygen
for healthy passengers. However, because cabin air pressure is relatively low,
the oxygen saturation of the blood is slightly reduced, leading to mild hypoxia
(i.e. reduced supply of oxygen to the tissues). Passengers with cardiovascular
or respiratory disease, or certain disorder of the blood such as anaemia or sickle cell disease, may not tolerate hypoxia
well. Moreover, the effect of alcohol on the brain is increased by hypoxia.
Gas
expansion:
Air expands in all air-filled body cavities as a result of
the reduced cabin air pressure. Abdominal gas expansion may cause moderate
discomfort, which may be exacerbated by consumption of carbonated beverages and
certain vegetables. As the aircraft ascends, air escapes from the middle ear
and the sinuses, usually without causing problems. As the aircraft descends air
must be allowed to flow back into the middle ear and sinuses in order to
equalize pressure differences (“clearing the ears”).
Most discomfort can be alleviated by swallowing, chewing or
yawning; if the problem persists, forcefully expiration against a closed nose
and mouth will usually help. For infants, feeding or giving a pacifier to
stimulate swallowing may reduce the symptoms.
People with ear, nose and sinus infection should avoid
flying because pain and injury may result from the inability to equalize
pressure differences. If travel cannot be avoided and problems arise during
flight, decongestant nasal drops may be helpful.
Individuals who have recently undergone certain types of
surgery should not fly for a period of time because of possible damage
resulting from gas expansion.
Cabin
humidity:
The relative humidity in aircraft cabins is low, usually
less than 20%. Low humidity may cause discomfort of the eyes, mouth and nose
but presents little risk to health. Discomfort can be alleviated by maintaining
good fluid intake before and during the flight, using a skin-moisturising lotion, using a saline nasal spray to moisturise the nasal passages and wearing spectacles rather
than contact lenses.
Dehydration:
Measures should be taken to prevent dehydration during long
flights. Fluids intake should consist of non-alcoholic beverages (water and
fruit-juices) both before and throughout the flight. As alcohol contributes to
dehydration, consumption of alcohol should be restricted, and preferably
avoided before and during the flight.
Ozone and
cosmic radiation:
The concentration of ozone (triatomic oxygen, O3) and the
intensity of cosmic radiation both increase with altitude. Ozone is easily
converted to oxygen by heat and various catalytic processes. In modern jet
aircraft, almost all ozone in the ambient air is converted to oxygen in the
compressors that provide pressurized air for the cabin.
During descent, when engine power is low, a build-up of
ozone is prevented by catalytic converters. At usual cruising altitudes, the
concentration of ozone in the cabin air is negligible. Cosmic radiation is the
sum of solar and galactic radiation. At aviation altitudes, the cosmic ray
field consists of high energy-ionizing radiation and neutrons. The atmosphere
and the earth’s magnetic field are natural shields. Because of the orientation
of the magnetic field and the “flattening” of the atmosphere over the North and
South Poles, the cosmic radiation levels are significantly higher at polar than
at equatorial latitudes. The intensity of cosmic radiation levels increases
with altitude and dose rates of 1 – 3 microSv/hour on
short haul and 5microSv/hour on long haul rotes are typical. For comparison,
the natural background radiation from soil, water and building materials is
about 2microSv per year in most countries.
The International Commission on Radiological Protection has
set 1mSv per year as a basic safety standard for the protection of the health
of the general public against the dangers arising from additional ionizing
radiation.
Reference: