Capital Region Special Surgery Blog

I turned a recent trip to Hollywood Studios in Orlando with the kids into an educational experience. I was on a ride with my son that involved sitting in a chair and spinning. It was hard keeping the camera steady but this is what happened alex-nystagmus . You can clearly see that his eyes are deviating while he is spinning. Why does this happen?

Each of our inner ears has a set of three balance canals that represent three dimensional space. Each is hardwired to a set of eye muscles so that if one canal is activated it will cause eye deviation to that side. Another example of the reflex is shown here were a patient is wearing infrared goggles and is moving his head. His inner ear senses it and tries to make corrective movements vestibulo-ocular-reflex

This reflex allows us to maintain a steady gaze at an object as we move around. For example as we walk the height of our head goes up and down. The vestibulocular reflex makes subtle corrections so that the world looks steady as we walk. People that have weak inner ears suffer from a disorder called osscilopsia. The world bounces as they walk. They have trouble , for example, driving and reading a traffic sign.

The reflex is also responsible for why we develop vertigo. Vertigo by definition is a hallucination of motion. It is caused by one ear telling our brain that we are moving even if we are not. This can be caused by an inner ear infection or anything that disturbes the delicate balance between the two ears. The ear tells our eyes to move and we see the world as spinning.

When our inner ears and our eyes do not agree as to what is going on we get a different feeling called seasickness. This happens when we are on a boat and looking at the boat. Our poor ears are telling us that we are moving (which we are relative to gravity) but our eyes are telling us that we are stationary (which we are relative to the boat). Our brains cannot resolve this and we feel ill. The best way to cure sea or car sickness is to look out over the horizon or any other place outside of the vessel that we are in.

What do horses, tigers, humans, and bats have in common?

It turns out that all of these animals have a small “hearing” bone in their ears called the stapes bone.

On a recent trip to the Museum of Natural History in New York City my son, upon taking a quick sly scan of a display poster on evolutionary traits, had the audacity to call me an epithere. Before jumping to conclusions (and thereby acknowledging I had no idea what my precocious son was even remotely talking about) I decided to investigate. In my travels through the museum I learned some cool facts about how early mammals developed.

Fact 1: Ages ago, in some mammals, the main artery for the brain went through the stapes.

Fact 2: Hearing bones developed from parts of the jaw bone that “migrated” over millions of years to a more posterior position.

Amazingly, when humans develop as embryos there is a stage where the brain is actually fed by a stapedial artery. As the human embryo continues to develop in the womb this stapedial artery regresses and the carotid artery takes over.

Fact 3: Epitherians (A-HA!) comprise all the eutherian mammals except the Xenarthra. They are primarily characterized by having a stirrup-shaped stapes in the middle ear, which allows for passage of a blood vessel.

If you go to any mall in America you will find a plethora of teenagers wearing the ubiquitous ipod or other personal music player. About a year ago I did a television segment on the dangers of these music players. This issue resurfaced last week in a New York Times article and deserves new discussion.

Using a portable sound meter we tested various earphones and devices such as the ipod, an old Sony Walkman (remember those?), and various other MP3 players. We found that the sound intensity was dependant on two things: the actual player and the earphones. Most of the players could deliver very loud sound. The ipod went up to about 115 dB. The maximal recommended level for earphones is about 80dB. The earphones were just as important. It turned out that the better the earphone, the more sound it could generate. So a more expensive earphone with a heavier magnet could generate more sound than a cheaper pair.

Exposure to any load sound can lead to permanent hearing loss. The loss usually occurs in the very high frequencies at first. The human ear has a resonance at 4000Hz. That means that any multifrequency sound is maximally amplified at that frequency and therefore selectively produces damage in the part of the inner ear responsible for sensing that frequency (see “How The Ear Works”). Very often ear noise or tinnitus accompanies this type of hearing loss.

The Occupational Safety and Health administration publishes the maximal noise exposure guidelines and can be found on their website.

Below are the guidelines. Notice that the allowable levels are time dependant.
|
Duration per day, hours | Sound level dBA slow response
____________________________|_________________________________
|
8………………………| 90
6………………………| 92
4………………………| 95
3………………………| 97
2………………………| 100
1 1/2 ………………….| 102
1………………………| 105
1/2 ……………………| 110
1/4 or less…………….| 115
____________________________|________________________________
Footnote(1) When the daily noise exposure is composed of two or
more periods of noise exposure of different levels, their combined
effect should be considered, rather than the individual effect of
each. If the sum of the following fractions: C(1)/T(1) + C(2)/T(2)
C(n)/T(n) exceeds unity, then, the mixed exposure should be
considered to exceed the limit value. Cn indicates the total time of
exposure at a specified noise level, and Tn indicates the total time
of exposure permitted at that level. Exposure to impulsive or impact
noise should not exceed 140 dB peak sound pressure level.

Moral of the story: turn down the volume and protect those ears!

Think way back to those college days. You went on a long night out with your friends at the local watering hole. You open your eyes at the first ray of light and all of a sudden the whole world is spinnning faster than Dorothy Gale’s house.

It turns out that there is a very real physiologic reason why this happens and it is directly related to a very common nonalchohol related problem called Benign Paraxysmal Positional Vertigo.

In order to understand why this occurs you must understand how your ear helps you maintain balance. Each ear has a set of three balance canals called the semicircular canals.

These three canals are set at right angles to one another corresponding to three dimensional space. They are made up of a hollow tube filled with a fluid. At one end of that tube is a dilated space that houses a pice of jellatenous material called the cupula that literally floats in its surrounding fluid. There is a delicate balance between the density (weight) of the cupula and the fluid. When we move our heads the cupula gets difflected by innertia which in tern triggers nerve endings. This “tells” our ears that our head is moving. This system is designed to be insensitive to gravity and only sense angular acceleration (how quickly you move your head in one plane). Any change in the density of the Cupula or surrounding will cause the jelly to float or sink in resonse to gravity.

Alchohol (ethanol) is lighter than water. During your night of revelry the ethanol that you drink quickly creeps into fluid within the balance canals. This causes a difference in the “weight” of the fluid relative to the cupula and causes the cupula to rise or sink relative to gravity. Over time (as you sleep) this process reverses. The ethanol leaves the fluid and creeps into the cupula. As you wake up the cupula is becoming lighter than it surrounding fluid due to the ethanol getting into it. When you roll over in bed the cupula starts to float up activating the nerve endings telling your brain that you are moving. All of a sudden your head is spinning.

Benign Paroxysmal Positional Vertigo is very similar but in reverse. In this disorder calcium particles get stuck within the semicircular canal disrupting the delicate balance of cupula and fluid. The same thing happens in this disorder as in a hangover, only in reverse. You roll over, the calcium pushes on the nerve endings causing a sensation of spinning.

Lyme disease is prevalent in the Capital Region. I recently saw several patients who came to me for dizziness and disequilibrium. As part of a routine work-up I send these patients for a Lyme titer. A Lyme titer looks for antibodies in the blood. These antibodies can mean that you have a current or past infection. The results can be positive, negative or equivocal, (which means borderline). An equivocal result should be repeated in two to four weeks to see if there is any change. Since antibodies to other infections may look similar to Lyme Disease antibodies a “false positive” result may occur.

Another test used is the Western Blot or Immunoblot. This test looks at the specific parts of the bacteria to which antibodies attach. This test is more specific and less affected by antibiotic treatment. These are also reported as positive, negative or equivocal. An equivocal result should be repeated in two to four weeks. This test is done along with the Lyme titer since to detect a “false positive” result from the titer.

I am not a Lyme / Infectious Disease specialist so I usually send my patients to one when they test positive. These patients I mentioned at the start of this post all had negative tests. One patient in particular went the extra mile and saw several specialists and was finally tested positive for the disease. He is now on long term intravenous therapy and is feeling much better.

Lyme has been called the great masquerader. The disease can manifest in many forms and symptoms. The classic finding is a “bulls-eye” rash that is centered on the tick bite mark. In my experience this finding seems to be not as common as published in the literature. I would not discount the diagnosis if there is no rash. There are several tests available and not all have the greatest sensitivity so I will be sending multiple Western Blott tests from now on.

Here is a link for a new documentary about Lyme Disease “Under Our Skin”
http://www.youtube.com/watch?v=sxWgS0XLVqw

Ahhh……. the good ol’ days. Going out with your buds to a summer rock concert, hanging out all day with some good, although loud, tunes. Maybe standing in front of those monolithic dental filling loosening speakers to get that extra rush. Maybe dancing the night away at that hip new club. Has anybody experienced the temporary decrease in hearing or the tinnitus (head noise) that occurs after that night? Well welcome to the “temporary threshold shift.” Here’s why it occurs (or so we think).

For a primer on this section please see how we hear on our web site

Noise induced hearing loss that is permanent is thought to occur because delicate hair cells within our inner ear have been stressed to breakage.

This is a picture of a pigeon cochlea showing the well ordered rows of hair cells. The white structures are “hair cell fibers”, actually stereocilia which are the pressure receptors that transducer the physical vibrations of sound into an electrical signal that goes to our brains. This particular “pigge” was listening to Mozart at a reasonable level.

This little “pigge” to the right went to see Aerosmith and sat right in front of the speakers for days on end (mixed in with some NASCAR). See the difference?

This type of physical damage is usually permanent and occurs only after many years of abuse.

So how does this temporary stuff happen? The running theory is based on the fact that the inner ear hair cells are very active metabolically. That means that they burn a lot of energy and as a result have a lot of byproducts. Some major byproducts of cellular respiration that have gotten a lot of attention are called free radicals and superoxides. One example of a free radical isozone. An example of a superoxide is hydrogen peroxide. While ozone may be great for keeping you from getting a sunburn and peroxide is great for cleaning boo boo’s (actually not so great) they are not very healthy to ingest. Our bodies constantly make these free radicals and oxides and our bodies are constantly trying to get rid of them.

The idea is that you make the hair cell work so hard that it creates these superoxides and free radicals. If the cell cannot get rid of them the cell can be damaged. 

Recently some researchers have been looking at using antioxidants to help these cells, and other body cells, out. Others don’t care about real research and have just tried to get rich off of the teaming millions that believe everything they hear. Some examples of antioxidant rich foods are: red wine, pomagranite juice, broccoli, red wine, vegetable juices, fruits, berries, and oh…. did I mention red wine. Pomagranite juice has twice the antioxidant value of red wine. I’ll have two glasses of Merlot then.

It turns out that Owls have fascinating ears. People have two ears for several reasons. One main one is that it allows us to detect the direction of sound. When a sound comes at us from one direction, say the right side, our right ear detects it a fraction of a second before the left one does (the time it takes for the sound to travel the foot or so between ears). This is called a phase delay. This is why people who have lost hearing in one ear have trouble detecting the direction of sound and why we recommend bilateral hearing aids, bilateral cochlear implants, etc.

Owls have taken it one step further as discussed bellow and in the web link. Their ears are assymetrically placed so that they can tiangulate the position of their prey not only in the horizontile direction but also where the prey is abobe or bellow them.

Some time ago I learned this while watching a special on owls with my 8 year old son. I had the brilliant idea of why we cannot place our bilateral cochlear implants asymetrically. I came rushing into work like a madman one day to tell our audiologist, Sharon Rende, all about what I learned the night before and how it was going to change how we placed implants into patients from this day foward. After asking me to stop drinking with my son while watching owl programs she thought that it was a stupid idea, and parents would not like it if their kids had only one implant on the top of their heads.

I sent an email about this to Ruth Litovsky PhD. She is a world renowned audiologist and researcher at Washington U. in St. Louis who specializes in the neural pathways for the detection of sound direction. Turns out that do not humans share the same neural pathway as owls. Hence we humans are not able to make sense of these auditory cues. Science marches on.

OWL HEARING

Because Owls are generally active at night, they have a highly developed auditory (hearing) system. The ears are located at the sides of the head, behind the eyes, and are covered by the feathers of the facial disc. The “Ear Tufts” visible on some species are not ears at all, but simply display feathers.
The shape of the ear opening (known as the aperture) depends on the species of Owl - in some species, the opening has a valve, called an operculum covering it . The opening varies from a small, round aperture to an oblong slit with a large operculum. All owls of the family Tytonidae have rounded openings with large opercula, while in Strigidae, the shape of the outer ear is more varied.

An Owl’s range of audible sounds is not unlike that of humans, but an Owl’s hearing is much more acute at certain frequencies enabling it to hear even the slightest movement of their prey in leaves or undergrowth.

Some Owl species have asymmetrically set ear openings (i.e. one ear is higher than the other) - in particular the strictly nocturnal species, such as the Barn Owl or the Tengmalm’s (Boreal) Owl. These species have a very pronounced facial disc, which acts like a “radar dish”, guiding sounds into the ear openings. The shape of the disc can be altered at will, using special facial muscles. Also, an Owl’s bill is pointed downward, increasing the surface area over which the soundwaves are collected by the facial disc. In 4 species (Ural, Great Gray, Boreal/Tengmalm’s & Saw-whet), the ear asymmetry is actually in the temporal parts of the skull, giving it a “lop-sided” appearance.

An owl uses these unique, sensitive ears to locate prey by listening for prey movements through ground cover such as leaves, foliage, or even snow. When a noise is heard, the owl is able to tell its direction because of the minute time difference in which the sound is perceived in the left and right ear. For example, if the sound was to the left of the owl, the left ear would hear it before the right ear. The owl then turns it’s head so the sound arrives at both ears simultaneously - then it knows the prey is right in front of it. Owls can detect a left/right time difference of about 0.00003 seconds (30 millionths of a second!)

An owl can also tell if the sound is higher or lower by using the asymmetrical or uneven Ear openings. In a Barn Owl, the left ear left opening is higher than the right - so a sound coming from below the owl’s line of sight will be louder in the right ear.

The translation of left, right, up and down signals are combined instantly in the owl’s brain, and create a mental image of the space where the sound source is located. Studies of owl brains have revealed that the medulla (the area in the brain associated with hearing) is much more complex than in other birds. A Barn Owl’s medulla is estimated to have at least 95,000 neurons - three times as many as a Crow.

Once the Oowl has determined the direction of its next victim, it will fly toward it, keeping its head in line with the direction of the last sound the prey made. If the prey moves, the owl is able to make corrections mid flight. When about 60 cm (24″) from the prey, the owl will bring its feet forward and spread its talons in an oval pattern, and, just before striking, will thrust it’s legs out in front of it’s face and often close it’s eyes before the kill.

References:
Campbell, Wayne. 1994. “Know Your Owls (CD-ROM)”. Axia Wildlife
Hollands, David. 1991. “Birds of the Night”. Reed Books
König, Weick and Becking. 1999. “Owls: A Guide to the Owls of the World”. Yale University Press
Long, Kim. 1998. “Owls: A Wildlife Handbook”. Johnson Books
Mikkola, Heimo. 1983. “Owls of Europe”. Buteo Books

David Foyt, M.D.
Capital Region Ear Institute
Clinical Associate Professor Surgery(Otolaryngology / Neurosurgery)

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