Operating Instructions MI 24, MI 24h
2 Description
The MI 24 is an automatic instrument that is designed for tympanometric screening.
Tests done in the tympanometric screening mode measure middle ear mobility and
ipsilateral acoustic reflex. Contralateral acoustic reflex is available as an option. Test
results are displayed on the front panel LCD (liquid crystal display) screen and may be
printed.
The design of the MI 24 allows rapid and reliable measurements. This equipment is
designed for middle ear function screening.
PC-Interface:
A USB interface for data transfer to a connected computer is built in.
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.
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).
hearing
nerve
ear canal
middle
ear
bones
ear drum
middle ear
eustachian tube
cochlea
musculus
stapedius
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