Richard
and John arrived on Andros Island in the Bahamas at noon, and by five
o'clock were in the water on their first deep dive of their weeklong
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Susceptibility
to oxygen ear squeezes will begin when this diver exits the
water.
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vacation. Their
dive was on the wreck of the Holly, located at a depth of 245 fsw (75
mw), with their 25-minute bottom time necessitating two hours of decompression.
Richard was using a mixed gas closed circuit rebreather (CCR), while
John was diving open circuit air (twins), and carrying cylinders containing
EAN36 and oxygen for decompression. Conditions were generally good,
with 82oF (28C) water, no current, 165-foot (50m) visibility, and a
1-2 foot (1-2m) swell running. The dive went off without a hitch, and
they exited the water at 7:30 p.m. An hour later, they were both in
bed, tired from their seven-hour plane rides and the excitement of the
first dive. The next morning, both Richard and John awoke to find their
ears very sore and filled with fluid.
What
happened? Did they pick up an infection on the plane ride? Was there
a pathogen or nasty chemical in the water? Some strange decompression
hit? Maybe a fungus in the hotel room? Was it from the swells that
forced them to equalize every few seconds during the decompression
stops, even though they felt fine during the dive? It seemed unlikely
to be an equipment related problem of some type, as one used a CCR
and the other twin open circuit cylinders. All they knew was they
felt fine the day before, and now the doctor had recommended not diving
for a week, giving the fluid he could see behind their tympanic membranes
time to drain and their ears time to return to normal. So much for
their diving vacation!
In
actuality, both of them had squeezes. Squeezes?! How could they have
an ear squeeze if they had no problems during the dive?! During our
initial dive training we were taught that if we failed to equalize
as we descended, then a pressure imbalance could create a painful
condition known as a squeeze. We were also taught that in some circumstances,
during ascent if the Eustachian tube was blocked we could also get
a squeeze, called a reverse block. Either way, once we returned to
the surface, and dive was over, the threat of ear squeeze was eliminated
as well. This is not true with some forms of technical diving.
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Divers learn that
upon returning to the surface at the end of the dive, the threat
of ear squeeze is eliminated as well. This is not true with
some forms of technical diving.
| TECHNICAL
TIP: Divers using rebreathers should also take into consideration
the risk of middle ear oxygen absorption syndrome. Periodic
manual equalization after surfacing can prevent the syndrome
and should be a regular post-diving procedure. |
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In
open circuit diving while using air, divers descend and equalize with
air. The gas filling their middle ears is the same as the gas they
are breathing on the surface. In technical diving, this may not be
true. For example, in our story above, Richard was using a rebreather.
Typically, in mixed gas CCRs, the oxygen fraction (percentage of oxygen
in the breathing mix) is very high at the beginning of the dive, typically
0.7 (70%) or higher. Thus, the middle ear is filled with gas containing
a high concentration of oxygen.
During
the dive, this presents no problem, as the diver equalizes whenever
a pressure imbalance is felt. However, upon reaching the surface,
divers no longer consider the need to equalize, as they have reached
a stable pressure. But their middle ears may still be filled with
an oxygen-rich gas. Slowly, over time, the oxygen in the middle ear
may be metabolized (used) by the tissues surrounding the area. The
volume of gas slowly decreases, resulting in a net pressure imbalance
between the outer and middle ear. This can result in a squeeze, identical
in effect to that experienced by descending without equalizing.
This
type of squeeze is known as middle ear oxygen absorption syndrome,
or "O2 ear." It is also seen in military aviators as well,
who commonly use oxygen during high altitude operations and experience
the squeeze some time after landing. Because onset is so gradual,
an individual may not notice the pressure imbalance until noticeable
damage has occurred. This is especially true if one goes to sleep
soon after the causative event.
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Illustrations
of Middle Ear Oxygen Absorption Syndrome - Click to Enlarge
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Anatomy of a
Normal Ear
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Diagram
of Middle
Ear Oxygen Absorption Syndrome
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Before
dive. Middle ear filled with air (nitrogen and oxygen)
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Are
you in the risk group for this potential health problem? You may be
if you use: (1) an oxygen rebreather, (2) a semi-closed rebreather
with high-fraction nitrox supply gas, (3) a mixed gas CCR, (4) any
high fraction nitrox during open circuit diving. The risk is generally
less for open circuit divers, as descent (and pressure equalization)
usually occurs on air or whatever bottom mix is being utilized. The
use of oxygen or high fraction nitrox mixes is generally constrained
to use at decompression stops, not during descents. However, if any
event forces you to equalize often while at decompression (for example
swells passing overhead, or depth drift during the stop), then you
may also be at risk. This is what happened to John in our example
above, who filled his middle ear spaces with oxygen while equalizing
every time a swell passed overhead during the final 60-minute deco
stop.
Not
all fliers or divers will experience this problem, only those who
routinely have to make some effort to equalize. Those with "sewer
pipes" for Eustachian tubes and have to make no effort to equalize
will not experience this type of squeeze, as they will generally "auto-equalize"
even after reaching the surface. However, the rest of us must manually
equalize after reaching the surface at periodic intervals to prevent
this type of squeeze. Any maneuver that you typically use to equalize
while descending will work for this purpose. Generally, equalizing
every 15-30 minutes for 2-4 hours after the dive will prevent the
syndrome.
So
add this procedure to your repertoire of technical diving tricks,
and remember that just when you thought you were safe from squeezes,
you might not be….
