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Operation Manual touchTymp MI 26 and MI 36 Version
8511780 Rev. 4
7
30/06/2021
the air pressure is varied automatically from a positive value (i.e. +200 daPa) to a
negative value (i.e. -400 daPa max).
Figure 1
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. Gradient calculations are reported as
the Tympanogram width at half of peak compliance expressed in daPa. A normative
box is available on both the display and printout to aid in diagnosis.
NOTE
: 1 mmho
≙
1 ml for 226 Hz probe tone
1.5.3 Acoustic Reflex
An
Acoustic Reflex
, or contraction of the stapedial muscle, occurs under normal
conditions when a sufficiently intense sound is presented to the auditory pathway. This
contraction of the muscle causes a stiffening of the ossicular chain which changes the
compliance of the middle ear system. As in
Tympanometry
, a probe tone is used to
measure this change in compliance.
When the stimulus presentation and measurement are made in the same ear by means
of the probe, this acoustical reflex is referred to as an
Ipsilateral
Acoustic Reflex
.
When the stimulus presentation is made in the opposite ear of where the measurement
is made, this acoustical reflex is referred to as a
Contralateral Acoustic Reflex
.
For best results, this reflex measurement is automatically conducted at the air pressure
value where the compliance peak occurred during the
Tympanometric
test. Stimulus
tones of varying intensities at 500 Hz, 1000 Hz, 2000 Hz or 4000 Hz are presented as
short bursts. If a change in compliance greater than the selected value is detected, a
reflex is considered present. Because this is an extremely small compliance change,
any movement of the probe during the test may produce an artifact (false response).
The test result is recorded as
Pass/No Response (NR
), and in graphical form.
If the
Tympanometric
results display any abnormal findings, the results of the
Acoustic Reflex
testing may be inconclusive and should be interpreted with care.
Theoretically, a compliance peak is necessary to observe a reflex at peak pressure.
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