Introduction to Tympanometry
Aural acoustic immittance
measurements have become an
integral component of audiologic and otologic evaluation. One class
of aural acoustic immittance measurement,
tympanometty,
has
become routine in the assessment of ear disease. Since the original
report of Terkildsen and Thomsen
(1959)
tympanometry has been
used widely by physicians and audiologists as a research tool for
studying the effects of ear disease on middle ear function and as a
clinical test for detecting medically significant pathology. Recent
technological advances provide the capability for the MicroTymp, a
low-cost, portable, precision instrument that can be of significant
value for determining the need for medical referral, for diagnosis of
ear disease, and for monitoring the course of medical/surgical
intervention.
The Welch
Allyn
MicroTymp is a single-component aural
acoustic
admittance
meter that records a
tympanogram
with a 226-Hz
probe tone. In
order, to
properly use the MicroTymp and to interpret
the results correctly, the user should be familiar with the basic
principles of tympanometry!
Acoustic admittance is the ease with which acoustic energy is
transferred from one system to another*. If the air in the ear canal
is easily set into vibration, the admittance is high. If the air is difficult
to set into vibration the admittance of the system is low. The ease or
difficulty of setting the air in the ear canal into vibration is determined
by the volume of air and the admittance of the middle ear.
Tympano-
metry
provides a method of evaluating the physical characteristics
of the middle ear by measuring the admittance of the air trapped in
the ear canal.
‘For more in depth information see:
Margolis, 1981; Margolis and Shanks, 1985; Van Camp et al., 1988.
2Mathematically:
Ya = v
P
where Ya is acoustic admittance, v is volume velocity, and p is sound pressure. The unit
of acoustic admittance is the acoustic millimho
(mmho).
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