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Section 1—Introduction
1.1 INSTRUMENT DESCRIPTION
The TM 262
TM
Auto Tymp
TM
is a versatile combination instrument which
provides testing capability for tympanometry alone, tympanometry
combined with screening acoustic reflex measurements, and manual
audiometry. Two different versions are available to meet your individ-
ual testing needs. The basic version provides two modes of operation,
tympanometry alone and tympanometry plus screening ipsilateral
acoustic reflex testing. The second version adds manual audiometry. It
is possible to field retrofit the manual audiometer to the basic version
after the time of original purchase.
An RS-232 port is also available as an option. This allows the transfer
of data from the instrument to a computer.
A soft-sided carrying case, a dust cover, patient handswitch, patch
cords, and earphone sound enclosures may also be purchased as
optional accessories (see page 60).
1.2 TYMPANOMETRY AND GRADIENT
1.2.1 Tympanometry
Tympanometry is an objective technique used since the late 1960’s
to measure the middle-ear function. During tympanometry, a low
frequency tone (226 Hz) is presented to the ear canal via the probe.
The probe tone is used to measure the compliance (admittance)
changes within the middle-ear system while air pressure within the
hermetically-sealed ear canal is changed from positive to negative. In
the normal ear, positive pressure introduced into the ear canal space
causes the middle-ear system to stiffen up or become less mobile.
Because the pressure difference between the sealed ear canal space
and the middle-ear space forces the tympanic membrane to stretch
inward, this stiffened middle-ear system displays little or no compliance.
As the pressure within the ear canal is brought back toward atmospheric
(ambient or 0 daPa) pressure, the pressure difference between the ear
canal space and the middle-ear space is reduced in normal ears. At or
near atmospheric pressure (0 daPa), the greatest amount of sound
(probe tone) enters the middle-ear system. In other words, this is the
air pressure value where the middle-ear system displays the maximum
amount of compliance (admittance).
As negative pressure is introduced, a pressure difference is once again
established and the middle-ear system becomes less compliant. Thus,
by varying the pressure within the ear canal, it is possible to make a
series of compliance measurements by means of the probe tone.
The tracing which depicts these compliance changes is referred to
as a tympanogram.
