Madsen zodiac, Reference Manual

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Infant testing
Acoustic reflex testing may also be used for infant screening purposes. The main objective is to confirm general middle ear
function. For this purpose, a test protocol using a 1000 Hz probe tone, ipsilateral stimulation and broad band noise stim-
ulus is recommended.
App. 1.3.2 Acoustic reflex threshold
The reflex threshold is the lowest stimulus level at which a measurable reflex is elicited. The acoustic reflex is typically con-
sidered present when deflections are 0.02 mmho or greater, and a reflex growth can be confirmed (larger deflections
observable with increasing stimulus intensities).
The reflex threshold is highly stimulus dependent, for instance broad band noise has proven to elicit the reflex at stimulus
levels about 15-20 dB lower than pure tone stimuli. There may also be differences in detectability depending on the pure
tone signal frequency that is used.
Acoustic reflex testing involves high stimulus levels, which are used to elicit the reflex. These high sound levels may be
unacceptable to some patients.
App. 1.3.3 Acoustic reflex decay
The acoustic reflex decay adaptation test is used to investigate whether the stapedius muscle contraction can be sustained
during prolonged stimulation. A pure tone stimulus at 500 Hz or 1000 Hz is presented 10 dB above the acoustic reflex
threshold for 10 seconds. A 226 Hz probe tone is used. Adaptation is considered present if the deflection is decreased by
≥
50% of the initial magnitude. The point in time after stimulus onset when the 50% criterion is reached is referred to as
half-life time
and is reported as the test result.
A half-life time less than either 5 seconds or 10 seconds are typically taken to indicate retrocochlear pathology. The two
different time criteria have been used by different researchers. The acoustic reflex is more prone to adaptation with
higher stimulus frequencies. Accordingly, adaptation to the 500 Hz stimulus is considered a stronger indicator of abnor-
mality than adaptation to the 1000 Hz stimulus.
App. 1.3.4 Admittance Recording
The default stimulus level is automatically set to
Off
when no reflex thresholds have been established. This facilitates
admittance monitoring done in order to evaluate baseline fluctuations resulting from for instance tensor tympani muscle
contractions or interference from vascular flow or eustachian tube dysfunction. The stimulus can of course also be set to
Off
manually, if this type of admittance monitoring is to be done after the reflex thresholds have already been measured.
App. 1.4 ETF-P (Eustachian Tube Function - Perforated)
ETF-P can be performed on ears with eardrum perforations prior to reconstructive surgery to evaluate whether the middle
ear could be ventilated through the Eustachian tube following tympanoplasty. Air must be able to pass through the Eus-
tachian tube in order to equalize the middle ear pressure following reconstructive surgery.
For testing the Eustachian tube function in ears with perforated eardrums (ETF-P), a method different from immittance
measurements is used. In ETF-P, the ear air pressure is monitored continuously to detect any airflow through the Eus-
tachian tube.
An initial positive or negative air pressure is applied to the ear through the probe. Due to the eardrum perforation, the
pressure will be applied to both the ear canal and middle ear cavities. The patient is then instructed to swallow some
water, which typically causes a functioning Eustachian tube to open. Any pressure equalization through the tube will show
Otometrics - MADSEN Zodiac 145
App. 1 MADSEN Zodiac immittance methodology and features