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Chapter 9 — 4
MIDDLE EAR BAROTRAUMA
OF DESCENT
(
MIDDLE EAR SQUEEZE
,
AEROTITIS MEDIA
)
The main risk of barotrauma to the ears is encountered on descent and the commonest site is the
middle ear. About one quarter of diving trainees experience this, to a variable degree.
Water pressure around the diver increases as he descends. This pressure is transmitted to the
body fluids and tissues surrounding the middle ear space causing compression of the gas space
in the middle ear (Boyle's Law). The diver is aware of this sensation of pressure and voluntarily
compensates for the reduction in middle ear gas volume by "
equalising the ear
" “auto-
inflation” or "
clearing
". In this manoeuvre, air is blown up the Eustachian tube to replace the
volume of gas compressed in the middle ear space. The ways of doing this are described later.
If the diver fails to equalise, water pressure will force the ear drum inwards, stretching it and
escalating the sensation of pressure into one of pain. At the same time, reduced gas volume in
the middle ear is compensated by blood and tissue fluid, swelling of the lining (mucosa) of the
middle ear space. Ultimately, the blood vessels become over distended and rupture, bleeding
into the ear drum and the middle ear space. This tissue damage takes days or weeks to resolve.
Sometimes the ear drum itself will tear or rupture.
The depth at which this damage occurs depends on the size of the middle ear space and the
flexibility of the ear drum. It is normally reached at 1–2 metres and if the diver does not equalise
by the time he has reached this depth, barotrauma of the ear is likely.
The commonest diving problem
!
If the diver can equalise his ears on the surface,
the problem is due to incorrect diving technique
Fig. 9.4