One day you notice your ears feel plugged, perhaps after a viral illness, a cold or a trip through the mountains. You clear your ears by blowing your nose vigorously or by doing this nifty stunt called a Toynbee Maneuver, where you exhale forcefully from your nose against tightly-closed nostrils squeezed with your fingers. You feel a “pop” and your hearing improves along with the plugging and muffled sensation.
“How cool!” you say aloud, and then naturally, “Gee, I
wonder what’s the pathophysiology behind this truly gratifying phenomenon?” Or maybe not.
The problem could be the eustachian tube. The eustachian tube (abbreviated ET)
is a collapsible tube that travels from the back of your nose (nasopharynx) to
the middle ear (ME). The ME is a
space, or chamber, found behind the ear drum (tympanic membrane,
abbreviated as TM). This allows free
passage of air to and from the ME during changes in atmospheric pressure, such
as changing altitudes during a plane flight or a trip through the mountains.
The atmosphere, or more simply the air around us, is not
empty space. Air is comprised of densely
packed molecules. These molecules apply
force on the objects, including the human body and ear. Since we are literally bathed all around by
these air molecules, there is pressure exerted on us continuously, only we’re
accustomed to this having lived our entire lives in earth’s atmosphere. Higher up in the earth’s atmosphere, the air
becomes less dense, meaning there are fewer molecules packed in a given
volume.
During the ascent of a plane flight or travel up into higher
elevations, say into the mountains, the atmospheric pressure, the pressure
around us, decreases. Once we descend
back down, the atmospheric increases again. Usually the ET remains open to equalize the
pressure within the ME. On the contrary,
diving into deep water creates greater pressure outside of the ear and
ascending back up to the surface decreases it back again.
If the eustachian tube does not function properly, meaning
it does not remain open when it ought to, a relative negative pressure
is created in the ME. This is called Eustachian
Tube Dysfunction. When I say
“relative,” this means compared to the atmospheric pressure outside of the
ear. So a negative ME pressure means the
pressure is less inside the ME compared to outside of it. How does this happen?
During a viral illness such as a cold or upper respiratory
infection (URI), the ET can become swollen and then close off. ET closure can also occur during landing on
an air flight, where the outside pressure increases as the plane descends. If the cabin is not depressurized properly or
the plane descends too quickly, or if by some misfortune you have a weaker ET,
the pressure inside the ME remains unchanged as the outside pressure
increases. This creates a relative
negative ME pressure, which acts as a vacuum and causes the cartilaginous part
of the ET to shut closed. Air inside the
ME is then absorbed by the cells of the mucosa lining the ME space, causing further
negative pressure. The TM, comprised of
a very thin membrane, then gets sucked inward.
This worsens hearing but also can cause a bit of pain. If the negative pressure persists, fluid is
sucked from the mucosa and into the ME.
And since the ET is still closed, the fluid is trapped in the ME. This is known as a middle ear effusion,
or otitis media with effusion. If
bacterial accumulate in the fluid, pus is created, the ME mucosa and the TM
become inflamed and unpleasant things such as pain and fever and worsening
hearing result. This is acute
suppurative otitis media. For more
on otitis media, check out Ear
Tubes and Otitis Media.
Popping the ears by means of the Toynbee maneuver helps by
forcing air up the ET and into the ME.
This improves hearing as pressure is restored. The problem resolves when the ET regains
function and opens up again. The fluid
drains, normal ME pressure is restored, the TM reverts back to normal and all
is hunky-dory.
Yet people continue with the Toynbee maneuver. Despite things coming back to normal, they
still notice brief improvement in hearing long after the ET opens up and the ME
pressure is equalized. This is true in
some respects. As they blow air through
a normal ET and ME, the middle ear pressure increases. This increases air density in the ME, which in
turn causes the TM to bulge out.
This change in TM shape can improve hearing but is short lived. Also sound conducts better through denser
air, as there are more molecules to pass sound waves from one to another (see Hearing
and the Physics of Sound Mechanics) However, this persistent positive
pressure cannot, and should not persist.
They must cease doing this as the repeated bulging out of
the TM can lead to problems such as thinning the TM out or blowing a hole through
it, which is not a very desirable condition.
If there truly is a persistent problem with the ET, then a
tube can be placed across the TM if things don’t recover properly in a timely
fashion. The tube is referred to by a
variety of names: ventilation tube , tympanostomy tube, PE (pressure
equalizing) tube… They’re all
synonymous, referring to the same little device.
The purpose of the tube is to maintain normal ME pressure
which then allows the TM, ME mucosa and ET to recover and return back to
normal. Particularly for the ET, this
takes a considerable amount of time for it to regain its function and starting
opening again. This also is the reason
folks without a tube and have a dysfunctional ET still feel fullness even
months afterwards.
Now some patients have a sense of ear fullness that persists
and is not related to a problem with the ET or ME at all. This is another topic altogether and will
cover this in another post, but I’ll go into a brief digression here, since
some people who present with this problem feel that if I just popped a hole
into their ear drum or place a tube through it, the pressure will release and
all will be well. On the contrary, I try
to explain that such procedures merely equalize ME pressure; air crossing to
and from the opening in the TM will naturally keep the ME pressure normal at
all times. And if he/she would do a
Toynbee maneuver to blow air from the nose into the ear there will be no effect
on the TM or hearing since the air forced from the ET passes through ME and out
the opening in the TM. They’re literally
“blowing it out of their ear” and will notice no change in hearing.
As the title alludes, there is more on this topic of the
eustachian tube, so I’ll try to keep posting stuff to keep you entertained and
informed. Hang tight!
©Randall S. Fong, M.D.
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