Cited Passage
3-24 U.S. Navy Diving Manual — Volume 1
n There must be a change in ambient pressure.
3-6.2 Middle Ear Squeeze. Middle ear squeeze is the most common type of barotrauma.
The anatomy of the ear is illustrated in
Figure 3 7 . The eardrum completely seals off
the outer ear canal from the middle ear space. As a diver descends, water pressure
increases on the external surface of the drum. To counterbalance this pressure, the
air pressure must reach the inner surface of the eardrum. This is accomplished by
the passage of air through the narrow eustachian tube that leads from the nasal
passages to the middle ear space. When the eustachian tube is blocked by mucous,
the middle ear meets four of the requirements for barotrauma to occur (gas filled
space, rigid walls, enclosed space, penetrating blood vessels).
As the diver continues his descent, the fifth requirement (change in ambient pres -
sure) is attained. As the pressure increases, the eardrum bows inward and initially
equalizes the pressure by compressing the middle ear gas. There is a limit to this
stretching capability and soon the middle ear pressure becomes lower than the
external water pressure, creating a relative vacuum in the middle ear space. This
negative pressure causes the blood vessels of the eardrum and lining of the middle
ear to first expand, then leak and finally burst. If descent continues, either the
eardrum ruptures, allowing air or water to enter the middle ear and equalize the
pressure, or blood vessels rupture and cause sufficient bleeding into the middle ear
to equalize the pressure. The latter usually happens.
The hallmark of middle ear squeeze is sharp pain caused by stretching of the
eardrum. The pain produced before rupture of the eardrum often becomes intense
enough to prevent further descent. Simply stopping the descent and ascending a
few feet usually brings about immediate relief.
If descent continues in spite of the pain, the eardrum may rupture. When rupture
occurs, this pain will diminish rapidly. Unless the diver is in hard hat diving dress,
the middle ear cavity may be exposed to water when the ear drum ruptures. This
exposes the diver to a possible middle ear infection and, in any case, prevents
the diver from diving until the damage is healed. If eardrum rupture occurs, the
dive shall be aborted. At the time of the rupture, the diver may experience the
sudden onset of a brief but violent episode of vertigo (a sensation of spinning). This
can completely disorient the diver and cause nausea and vomiting. This vertigo is
caused by violent disturbance of the malleus, incus, and stapes, or by cold water
stimulating the balance mechanism of the inner ear. The latter situation is referred
to as caloric vertigo and may occur from simply having cold or warm water enter
one ear and not the other. The eardrum does not have to rupture for caloric vertigo
to occur. It can occur as the result of having water enter one ear canal when swim
ming or diving in cold water. Fortunately, these symptoms quickly pass when the
water reaching the middle ear is warmed by the body. Suspected cases of eardrum
rupture shall be referred to medical personnel.
3‑6.2.1 Preventing Middle Ear Squeeze. Diving with a partially blocked eustachian tube
increases the likelihood of middle ear squeeze. Divers who cannot clear their ears
on the surface should not dive. Medical personnel shall examine divers who have
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