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App. 1.2
Tympanometry
In tympanometry you can measure the acoustic admittance of the middle ear system as a function of ear canal air pressure.
The resulting tympanogram is predominantly determined by the ear cavity volumes, the mobility of the eardrum and the
ossicular chain, and the middle ear air pressure. Admittance values are shown on the vertical axis of the tympanogram, and
the ear canal air pressure is shown on the horizontal axis.
Tympanometry is used to indicate or, in conjunction with other audiological tests, confirm disorders such as ossicular dis-
continuity, otosclerosis, flaccid (hypermobile) eardrum, eardrum perforation, obstruction of the ear canal, middle ear effu-
sion, or Eustachian tube malfunctions.
The tympanometry tests are controlled by a number of default settings, which you can either leave as they are, or cus-
tomize to your requirements.
App. 1.2.1
Tympanometry testing on infants
It is strongly recommended that the 1000 Hz probe tone is used for infant tympanometry up to 4 - 6 months of age. The
1000 Hz probe tone is recommended for a number of reasons; one of them is to avoid the very low resonance frequency
that is characteristic for infant ears.
A number of developmental aspects through the first few months of life are believed to significantly alter the acoustic
response properties of the infant's middle ear, thus also influencing tympanometry, e.g.
•
size increase of the external ear, middle ear cavity and mastoid
•
a change in the orientation of the tympanic membrane
•
fusion of the tympanic ring
•
a decrease in the overall mass of the middle ear due to changes in bone density
•
loss of mesenchyme (connective tissue of the embryo)
•
tightening of the ossicular joints
•
closer coupling of the stapes to the annular ligament
•
the formation of the bony ear canal wall
The infant ear anatomy differs in many ways when compared with the adult ear. Because of these differences, a higher fre-
quency probe tone is needed to collect tympanograms that will be useful in identifying middle ear effusion. Infants below
4 months may demonstrate what appears to be a normal 226 Hz tympanogram even with confirmed middle ear effusion. It
is also possible to obtain what appears to be abnormal 226 Hz tympanograms in normal ears. The 1000 Hz probe tone has
proven to be the best choice for immittance measurements in infants.
App. 1.2.2
Tympanometric features
Tympanometric Peak Pressure, TPP
Tympanometric Peak Pressure, TPP, denotes the air pressure value on the horizontal axis, where the admittance peak is
registered. This value may be taken to approximate the current middle ear pressure.
Static Admittance, SA
Static Admittance, SA, is a measure of the middle ear admittance calculated as the difference between the admittance at
the peak of the tympanogram (including both the middle ear and ear canal components) and the baseline admittance meas-
Otometrics - MADSEN Zodiac
App. 1 MADSEN Zodiac immittance methodology and features
141
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