Impedance Measurements; Tympanometry; Acoustic Reflex - Maico easyTymp Operating Manual

easyTymp® Operating Manual

2 Impedance measurements

2.1 Tympanometry

Tympanometry is the objective measurement of middle ear mobility (compliance) and pressure
within the middle ear system. During the test, a low-pitched probe tone (226 Hz) is presented
to the ear canal by means of the hand-held probe. 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.).
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.
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.

2.2 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 and measurement are made in opposite ears, the reflex is referred to as a contra
lateral 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, 1000, 2000 or 4000 Hz are presented as short bursts. If a change in
compliance greater than 0.05 ml 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 level at which a reflex occurs is recorded as a number, as
PASS/FAIL and in graph 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. If a "flat" tympanogram is
observed, showing a non-mobile middle ear system, the easyTymp® will not perform an
acoustic reflex test. Theoretically, a compliance peak is necessary to observe a reflex at peak
pressure.
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