Operating Instructions
3
The SPL and frequencies of the test tones and the averaging time used to process the signals can be
determined by the tester through adjustable settings maintained in static memory within the
ERO•SCAN
Pro instrument.
What Frequency Range of Hearing is Estimated?
DPOAEs: Approximately 1.5 kHz to 12 kHz (depending on the frequency range selected). Since the
health of the hair cells in the region of the f
2
test frequency are estimated, and a) the 2f
1
-f
2
emission
frequency is at about six-tenths of the f
2
frequency, b) emissions tend to be weak below 600 Hz or so,
and c) the ambient noise tends to be highest at low frequencies, the lowest f
2
test frequency that can
be routinely measured is about 1 kHz. TEOAEs: Roughly 500 Hz to 4 kHz. TEOAEs can be reliably
recorded at lower frequencies than DPOAEs, but cannot be measured reliably above 4 kHz.
1.3 Tympanometry
What is tympanometry?
Tympanometry is the objective measurement of middle ear mobility (compliance) and pressure within
the middle ear system. During the test, a probe tone (226 or 1,000 Hz) is presented to the ear canal by
means of the
Tymp•OAE P
robe. This tone is used to measure the change in compliance in the middle
ear system while the air pressure is varied automatically from a positive value (+200 daPa) to a negative
value (-400 daPa max.).
How is compliance measured?
Maximum compliance of the middle ear system occurs when the pressure in the middle ear cavity is
equal to the pressure in the external auditory canal. This is the highest peak of the curve as it is recorded
on the chart. The position of the peak on the horizontal axis and on the vertical axis of the chart will
provide diagnostic information regarding the function of the middle ear system. Examples of normal
and abnormal tympanograms can be found in a later section of this manual.
What other measurements are calculated?
Gradient calculations are reported as the tympanogram
width at half of peak compliance expressed in daPa. A
“limits” box is available on both the display and printout
to aid in diagnosis. Compliance is measured with respect
to an equivalent volume of air, with the scientific quantity
milliliter (ml). Air pressure is measured in deca-Pascals
(daPa).
What does tympanometry tell us?
The impedance measurement assists in diagnosing of the
condition of the middle ear and can therefore not be
compared directly with other audiometric tests such as
sound or speech audiometry which assists in the
measurement of hearing. Furthermore, the impedance
measurement is an objective measuring method which
does not depend on the cooperation of the test person and can therefore not be falsified by the
patient.
The impedance measurement examines the acoustic resistance of the middle ear. If the eardrum is hit by
a sound, part of the sound is absorbed and sent via middle ear to the inner ear while the other part of
the sound is reflected. The stiffer the eardrum is the more sound is reflected and the less sound reaches
the inner ear. Inside the probe of the impedance measuring instrument a small loudspeaker is installed
which emits a low frequency sound through a tube (Figure 3) into the auditory canal before the
eardrum. Another tube is connected to the microphone inside the probe which receives the sound.
Together with a third tube, all three are inserted deeply into the ear canal and are made airtight against
Содержание Ero Scan Pro
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