Tympanometry
Encyclopedia
Tympanometry is an examination used to test the condition of the middle ear
and mobility of the eardrum
(tympanic membrane) and the conduction bones by creating variations of air pressure in the ear canal.
Tympanometry is an objective test of middle-ear function. It is not a hearing test
, but rather a measure of energy transmission through the middle ear. The test should not be used to assess the sensitivity of hearing and the results of this test should always be viewed in conjunction with pure tone audiometry
.
Tympanometry is a valuable component of the audiometric evaluation. In evaluating hearing loss, tympanometry permits a distinction between sensorinueural and conductive hearing loss, when evaluation is not apparent via Weber
and Rinne
testing. Furthermore, in a primary care setting, tympanometry can be helpful in making the diagnosis of otitis media by demonstrating the presence of a middle ear effusion.
The general term used to describe how energy is transmitted through the middle ear is admittance. The instrument measures the reflected sound and expresses it as an admittance or compliance, plotting the results on a chart known as a tympanogram.
Normally, the air pressure in the ear canal is the same as ambient pressure. Also, under normal conditions, the air pressure in the middle ear is approximately the same as ambient pressure since the eustachian tube
opens periodically to ventilate the middle ear and to equalize pressure. In a healthy individual, the maximum sound is transmitted through the middle ear when the ambient air pressure in the ear canal is equal to the pressure in the middle ear.
Tympanograms are categorized according to the shape of the plot. A normal tympanogram (left) is labelled Type A. There is a normal pressure in the middle ear with normal mobility of the eardrum and the conduction bones. Type B and C tympanograms may reveal fluid in the middle ear, perforation of the tympanic membrane, scarring of the tympanic membrane, lack of contact between the conduction bones of the middle ear or a tumor in the middle ear.
The categorising of tympanometric data should not be used as a diagnostic indicator. It is merely a description of shape. There is no clear distinction between the three types, nor the two subtypes of type A, namely A
and A
. Only measures of static acoustic admittance, ear canal volume, and tympanometric width/gradient compared to gender, age, and race specific normative data can be used to somewhat accurately diagnose middle ear pathology along with the use of other audiometric data (e.g. air and bone conduction thresholds, otoscopic examination, normal word recognition at elevated presentation levels, etc.).
Middle ear
The middle ear is the portion of the ear internal to the eardrum, and external to the oval window of the cochlea. The mammalian middle ear contains three ossicles, which couple vibration of the eardrum into waves in the fluid and membranes of the inner ear. The hollow space of the middle ear has...
and mobility of the eardrum
Eardrum
The eardrum, or tympanic membrane, is a thin membrane that separates the external ear from the middle ear in humans and other tetrapods. Its function is to transmit sound from the air to the ossicles inside the middle ear. The malleus bone bridges the gap between the eardrum and the other ossicles...
(tympanic membrane) and the conduction bones by creating variations of air pressure in the ear canal.
Tympanometry is an objective test of middle-ear function. It is not a hearing test
Hearing test
A hearing test provides an evaluation of the sensitivity of a person's sense of hearing and is most often performed by an audiologist using an audiometer. An audiometer is used to determine a person's hearing sensitivity at different frequencies. There are other hearing tests as well, e.g...
, but rather a measure of energy transmission through the middle ear. The test should not be used to assess the sensitivity of hearing and the results of this test should always be viewed in conjunction with pure tone audiometry
Audiometry
Audiometry is the testing of hearing ability, involving thresholds and differing frequencies. Typically, audiometric tests determine a subject's hearing levels with the help of an audiometer, but may also measure ability to discriminate between different sound intensities, recognize pitch, or...
.
Tympanometry is a valuable component of the audiometric evaluation. In evaluating hearing loss, tympanometry permits a distinction between sensorinueural and conductive hearing loss, when evaluation is not apparent via Weber
Weber test
The Weber test is a quick screening test for hearing. It can detect unilateral conductive hearing loss and unilateral sensorineural hearing loss...
and Rinne
Rinne test
The Rinne test is a hearing test. It compares perception of sounds transmitted by air conduction to those transmitted by bone conduction through the mastoid...
testing. Furthermore, in a primary care setting, tympanometry can be helpful in making the diagnosis of otitis media by demonstrating the presence of a middle ear effusion.
Operation
A tone of 226Hz is generated by the tympanometer into the ear canal, where the sound strikes the tympanic membrane, causing vibration of the middle ear, which in turn results in the conscious perception of hearing. Some of this sound is reflected back and picked up by the instrument. Most middle ear problems result in stiffening of the middle ear, which causes more of the sound to be reflected back.The general term used to describe how energy is transmitted through the middle ear is admittance. The instrument measures the reflected sound and expresses it as an admittance or compliance, plotting the results on a chart known as a tympanogram.
Normally, the air pressure in the ear canal is the same as ambient pressure. Also, under normal conditions, the air pressure in the middle ear is approximately the same as ambient pressure since the eustachian tube
Eustachian tube
The Eustachian tube is a tube that links the nasopharynx to the middle ear. It is a part of the middle ear. In adult humans the Eustachian tube is approximately 35 mm long. It is named after the sixteenth-century anatomist Bartolomeo Eustachi...
opens periodically to ventilate the middle ear and to equalize pressure. In a healthy individual, the maximum sound is transmitted through the middle ear when the ambient air pressure in the ear canal is equal to the pressure in the middle ear.
Procedure
After an otoscopy (examination of the ear with an otoscope) to ensure that the path to the eardrum is clear and that there is no perforation, the test is performed by inserting the tympanometer probe in the ear canal. The instrument changes the pressure in the ear, generates a pure tone, and measures the eardrum responses to the sound at different pressures. This produces a series of data measuring how admittance varies with pressure, which is plotted as a tympanogram.Tympanograms are categorized according to the shape of the plot. A normal tympanogram (left) is labelled Type A. There is a normal pressure in the middle ear with normal mobility of the eardrum and the conduction bones. Type B and C tympanograms may reveal fluid in the middle ear, perforation of the tympanic membrane, scarring of the tympanic membrane, lack of contact between the conduction bones of the middle ear or a tumor in the middle ear.
The categorising of tympanometric data should not be used as a diagnostic indicator. It is merely a description of shape. There is no clear distinction between the three types, nor the two subtypes of type A, namely A
and A. Only measures of static acoustic admittance, ear canal volume, and tympanometric width/gradient compared to gender, age, and race specific normative data can be used to somewhat accurately diagnose middle ear pathology along with the use of other audiometric data (e.g. air and bone conduction thresholds, otoscopic examination, normal word recognition at elevated presentation levels, etc.).External links
- Impedance audiometry at Otolaryngology Online by drtbalu
- Basic Multifrequency Tympanometry: The Physical Background