Barotrauma of the Ear
Barotrauma in divers is physical damage to body tissues caused by a difference in pressure between a gas space inside the body,
and the surrounding fluid.
Barotrauma typically occurs when the diver is exposed to a
significant change in ambient pressure, such as during ascents or descents, or
during uncontrolled decompression of a pressure
vessel, (i.e. Chamber).
There are several types of barotraumas that affect divers, today
we will look at Middle Ear Barotrauma or M.E.B.T. Understanding M.E.B.T. will
give your good insight to the other types of barotraumas.
Divers may first incur the symptom of an “ear squeeze” prior to
the actual barotraumas. Pain is never a good thing during diving… or really any
other time.
Ear Function & Anatomy
It will be useful in understanding the subject to have an understanding
of the basic function and anatomy of your ear.
On the side of your head you have a substantial bit of cartilage and skin commonly identified as “an ear”. This is actually the Auricle
and can be fun to nibble on. The passage way going from the Auricle into your
head is the External Auditory Meatus or ear canal. Next you run into the Tympanic
Membrane or ear drum. On the inside of the Tympanic Membrane is the middle ear.
The middle ear is an air space with three bones (Malleus, Incus & Stapes)
connecting the Tympanic Membrane to the inner ear, and the opening to the Eustachian
Tube. Next is the inner ear made up of the Cochlea and Semicircular Canals. (I
left the Semicircular Canals off the diagram for simplicity.) These structures
are filled with a liquid made up of nearly all water, and therefore uncompressible.
There are two very important features on the Cochlea: The Round Window and the
Oval Window. These windows are a flexible connective tissue.
Sound waves enter via the Auricle, pass through the Canal and strike the Tympanic Membrane. The Membrane turns the waves into vibrations which are transmitted via the three bones into the liquid of the Cochlea via the Oval Window. The Auditor Nerve has sensors in the Semicircular Canals which transmit signals to your brain and you interpret the meaning of it all! But what happens to the vibrations in the Cochlea fluid? That energy must be dissipated somehow; the structural material making the Cochlea is very hard, un-giving skull bone. That is where the Round Window comes in. It absorbs the vibrations like a trampoline. The Round Window actually vibrates out into the middle ear space, transferring the energy into the air and displacing air and energy down the Eustachian Tube. There you have it. So simple I am sure it is an accident of nature.
If we simplify the whole thing, and straighten it out it would look something like this:
The “U” shape is filled with water, the center island and
area surrounding the top, bottom and right side are bone. The missing
Semicircular Canals would be represented attached to the top right section.
Barotrauma can affect the external, middle or inner ear. It is
most common in the middle ear and is experienced by 10% - 30% of divers.
Causes
There is really only one mechanism of injury for the diver
to consider: breathing gas in the middle ear or gases in the external ear
becomes trapped and expands causing damage. This can occur on descent or ascent
(reverse squeeze). The gas may become trapped a few different ways:
· The Eustachian Tube is blocked. We see this most
commonly when the diver has a cold or allergies. It can happen if the diver has
used a sinus medicine or nasal spray to clear up his sinuses and the affects of
the medicine wear off during the dive. This is one reason not to use such medicines.
(Another reason is; some of these medicines are in the class of drugs known as Oxygen
Exciters. Oxygen Exciters when used with ambient pressures somewhere more than
1 ATM can impede normal cognitive functions.): Yes, that is a sad face
experience.
· Middle ear infections can cause the middle ear
space to fill with fluid and the exit to the Eustachian Tube to be blocked.
· The Eustachian Tube can be compromised by
infection or trauma.
· A wetsuit hood or similar piece of SCUBA gear worn
over the ear can cause an external Barotrauma rupturing the Tympanic Membrane.
(Ouch!) Wax can also cause a similar
situation. There are those divers who use “ear beer” to clean out their ears
before and after diving. I have never used it and have no recommendation. Except,
don’t drink the concoction: 1/3 rubbing alcohol, 1/3 hydrogen peroxide, 1/3
white vinegar. It’s up to you!
The Pathology
The pathology (a cool word for injury in this case) is normally tearing
or rupturing of the Tympanic Membrane. Less often it is a similar trauma to the
Round Window. It is almost never, or maybe even never, damage to the Oval
Window. Even as pressure builds on the outside of the Tympanic Membrane pushing
the three bones into the Oval Window, hydraulically transferring pressure via
the Cochlea fluids onto the Round Window, causing it to tear or rupture before
the Oval Window will. Which is a good thing; because it is a lot easier for the
Round Window to heal vs. the Oval Window which would likely have the Stapes
bone in the way now. Yes, another accident of nature.
Bottom Line
Be sure to dive only when your ears and sinuses are clear.
If you have a chronic problem or are experiencing seasonally allergies, see a
M.D. who is a diver him/herself and is well acquainted with dive medicine.
While performing descents or ascents if you feel some pressure or
discomfort in your ears: Stop, reverse direction until the pressure or discomfort
goes away, begin your equalization process and then continue on.
Be smart and live to dive another day my friends.
