曝光台 注意防骗
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membrane, grade 3 gross haemorrhage and retraction of the membrane, grade 4 free blood or fluid in the
middle ear, and grade 5 perforation of the tympanic membrane. In the 5-level classification grade 2 and 3 has
merged. An exact description of the findings is of importance when determining the prognosis. Also other
findings should be taken into account (pain, hearing loss, vertigo). Signs and symptoms of aerotitis media are
not compatible with active flying.
Because of fairly rapid changes in atmospheric pressure during flight, it is essential that there be a ready
interchange of air between the middle ear and the environment, in order to maintain equal pressure on the
inside and outside of the tympanic membrane. Under normal conditions this equilibrium is maintained through
the Eustachian tube3. The pharyngeal end of the tube is slit-like in shape and acts as a one-way flutter valve.
The lumen is closed except during the acts of swallowing, yawning, chewing, etc.
During ascent, the air in the middle ear expands. The Eustachian tube is forced open by excess pressure in the
tympanic cavity, middle ear pressure equalizes and the tympanic membrane snaps or "clicks" into its normal
position. During descent from altitude, when the atmospheric pressure increases, a totally different effect is
produced. The collapsed pharyngeal end of the Eustachian tube then acts as a flutter valve preventing entry of
air. The flight crew member must remember to swallow, yawn or perform Valsalva manoeuvres4 while
descending. While swallowing, the lips of the tubal opening are pulled apart and air rushes into the middle ear,
equalizing pressure.
When an applicant is unable to equalize the pressure, if necessary by conscious effort during descent, there is
a rapid onset of deafness, tinnitus and pain in the ear. In exceptional cases, severe vertigo may occur due to
inner ear barotrauma. A rupture of the fenestral membrane at the round or oval window may take place. If the
differential pressure reaches 200-500 mm Hg, the tympanic membrane might rupture. It should be noted that
aerotitis media may occur at low altitudes, even in the pressurized cabins of modern jets. Relevant altitude
pressure values are indicated in Table 12-1.
Altitude in metres Altitude in feet Pressure (mm
Hg)
0 0 760
600 2 000 706
1 200 4 000 656
1 850 6 000 609
2 450 8 000 564
3 050 10 000 522
3 960 13 000 460
Table 12-1. Altitude-pressure relationship
In 85 per cent or more of the cases, failure to equalize the pressure (and the injury that follows) is all secondary
to disease of the upper respiratory tract. Obstruction of the Eustachian tube, as by congestion of the mucous
2After R.W.Teed, American otologist (20th century)
3 Eustachian tube: pharyngotympanic (auditory) tube or tuba auditiva. After Bartolommeo Eustachio, Italian
anatomist (1524-1574).
4 Valsalva manoeuvre: Forced expiratory effort with closed lips and nostrils. After Antonio Valsalva, Italian anatomist
(1666-1723).
ICAO Preliminary Unedited Version — October 2008 III-12-5
membranes when suffering from common cold, is followed by absorption of the air in the middle ear. The
symptoms are stuffiness in the ear, loss of hearing (conductive type) and sometimes pain. If not treated at this
stage, transudation of fluid into the middle ear follows - acute serous otitis media. The entire tympanic
membrane may be amber coloured, or the lower half may be amber coloured and the upper half normal in
appearance due to the presence of the transudate in the middle ear. Often a fine black line will be seen across
the tympanic membrane - the meniscus of a fluid level. Sometimes air bubbles can be seen through the
tympanic membrane.
Many cases of serous otitis media recover spontaneously or after inflation of the Eustachian tube. If the
condition is neglected and the fluid remains in the middle ear for weeks or months, it may thicken and organize
to cause permanent hearing loss. These cases should be referred to ear, nose and throat (ENT) specialists for
evaluation and treatment. If infection follows, the middle ear cavity may fill with pus - acute or chronic
suppurative otitis media. If untreated, the tympanic membrane commonly ruptures and pus drains into the
external canal. Suppurative otitis media must still be considered a form of abscess and surgical drainage
(myringotomy) may be indicated, especially when one considers the aspects of future hearing. Once drainage
is established, resolution may proceed rapidly.
Aerotitis media Otitis media External otitis
Due to barometric
pressure changes
Inflammatory
Inflammatory
Retraction of tympanic
membrane
Bulging of tympanic membrane View of tympanic
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Manual of Civil Aviation Medicine 2(73)
