Regarding Audiological Evaluation
For most people, the words “hearing test” bring up memories of marching to the nurse’s office in elementary school and being told to put on a set of headphones and raise a hand at the beeping sound—but these memories describe nothing more than a simple screening.
There’s much more to a full hearing test than you may realize, just like the mechanism and process involved in normal, everyday hearing is more complex than most of us believe. We probably hardly think about—and perhaps even take for granted—how acoustic energy (sound) is transferred by and from our ears. In reality, sound is directed from the outer ear, through the middle and inner ear, and finally to the brain via mechanical and electrical processes involving both the circulatory and nervous systems.
A comprehensive hearing evaluation involves a battery, or series, of tests. One such test is called tympanometry, which measures the function of the middle ear, a critical section of our hearing pathway. This procedure was initially developed by K. Terkildsen and his colleague K.A. Thompsen in 1959 and more recently advanced by three main researchers on the principles of tympanometry: Robert H. Margolis, Ph.D., Janet E. Shanks, Ph.D., and Richard H. Wilson, Ph.D. (1986).
What Is Tympanometry?
By definition, tympanometry is “the measurement of the acoustic immittance of the ear as a function of ear canal air pressure.” In basic terms, this means that a tympanometry evaluation measures air pressure against the tympanic membrane (eardrum) and the ease with which sound flows through the eardrum as well as the tiny bones of the middle ear.
The equipment used to perform this test is called an acoustic immittance device, or tympanometer. This device creates a tympanogram, which is a chart that provides a pictured curve of how the middle ear moves as function of the air pressure placed against the eardrum.
A Brief Introduction to Ear Anatomy
The middle ear is an air-filled space that begins at the tympanic membrane (eardrum). This membrane is connected within the middle ear space to three small ossicles (bones) that create what’s called an ossicular chain: the hammer (malleus), anvil (incus), and stirrup (stapes).
Related Audiological Definitions
- Audiologist: The primary health-care professional who evaluates, diagnoses, treats, and manages hearing loss and balance disorders in individuals of all ages, from infants, to teens, to the elderly.
- Otoscopy: Direct visualization of the external auditory canal and tympanic membrane through an otoscope.
- Tympanic Membrane: The eardrum.
- Parts of the Middle Ear
- Ossicular Chain
- Hammer: The malleus bone.
- Anvil: The incus bone.
- Stirrup: The stapes bone (the smallest bone in the body).
- Eustachian Tube: The airway connecting the middle ear to the back of the throat.
- Ossicular Chain
- Acoustic Immittance: The process of sound waves flowing through the ear drum and middle ear.
- Acoustic Impedance: The total opposition of the flow of sound waves through the ear drum and middle ear.
- Tympanometry: A procedure that measures how easily sound flows through the middle ear at different air pressure levels.
- Tympanometer: The instrument audiologists use to perform the tympanometry test.
- Tympanogram: The graph (plotted curve) created by the tympanometer that illustrates how the ear drum and ossicles move in response to air pressure.
How Is Tympanometry Performed?
Typically, either an audiologist, a hearing health-care professional, or a physician (typically an E.N.T. or otologist) will perform the tympanometry exam in conjunction with a full evaluation. Sometimes, the test might be run outside of the full evaluation with the intention of determining middle ear function.
Before the test, your clinician will visually inspect your ear using a lighted otoscope to ensure your ear canal is clear and to take a look at the eardrum itself. Then, they’ll insert the tympanometer instrument’s probe—which has a disposable, soft, and flexible tip—into the ear canal. This probe sends a small amount of pressure into the ear canal, in turn causing the eardrum and middle ear bones to move. As it measures this movement, the device creates the tympanogram, which provides information on eardrum and ossicle function.
If this is tough to visualize, think about what it feels like when you take off or land in an airplane. As you quickly change altitude, air pressure is introduced and/or changed in the ear, causing the eardrum and ossicles to move in response. The tympanometry test simply measures whether or not that movement is within normal limits, and in some cases, it detects no movement at all.
Another related aspect of the middle ear is its connection to the back of the throat by the eustachian tube, an anatomical airway that is typically open. When you swallow, your middle ear pressure equalizes, causing the eustachian tube to close and open again. When this tube is inflamed—such as when you have a cold—the inflamed airway cannot efficiently close and open to equalize the pressure in the middle ear, causing your ears to feel “plugged.”
Why Is Tympanometry Performed?
Tympanometry is used to ensure that the eardrum and middle ear are functioning normally. You can tell quite a bit from the appearance of your tympanogram:
- A single, smooth “mountain” peak on the tympanogram indicates normal function.
- A flat tympanogram may indicate abnormal influence by fluid in the middle ear and behind the eardrum. This could signify a middle ear infection, abnormal Eustachian tube function, or stiffness of the middle ear bones.
- A high-peaked or discontinuous curve may indicate a perforation (hole) in the eardrum or a separation of the ossicle bones.
Hearing loss conditions that occur within the outer or middle ear are classified as conductive hearing loss. Usually, these are treatable, and they must always be ruled out before considering a hearing aid.
Some hearing loss is temporary, and conductive hearing loss can at times go away on its own. It can also sometimes be cured with medical intervention or repaired with surgery. Regardless of where it came from or how it might be treated, any and all indication of a conductive issue should be medically addressed. If you think you are experiencing conductive hearing loss, reach out to your M.D. or E.N.T.
The Remarkable Auditory Pathway
Tympanometry is just one of the many tests performed during the comprehensive hearing evaluation, and it measures just one aspect of the complex auditory pathway.
So how does sound actually travel through the ears?
The pinna and outer ear acoustically collect sound waves and send them through the ear canal until they hit and mechanically vibrate the eardrum. This induces the middle ear bones—the malleus, incus, and stapes—to move together. As the footplate of the last bone in the chain—the stapes—moves in and out of the ovular window of the cochlea (the snail-like sensory organ in the inner ear), fluid is hydraulically displaced inside the membrane and across the thousands of tiny stereocilia cells, which are all tuned to specific frequencies and spaced from low to high. As these cells are stimulated by the fluid, they create an electrical impulse at the base of the cell that reaches across the synapse to the auditory nerve ending, which in turn receives and sends the impulse to the auditory cortex in the brain. There, this impulse is interpreted as a sound!