Operating Instructions MI 34 / MI 34 H
GEBAmi34e.11a.docx
6
850 232/14 08/11
Figure 1 the middle ear
hearing
nerve
ear canal
middle
ear
bones
ear drum
middle ear
eustachian tube
cochle
musculus
stapedius
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 is measured in deca-
Pascals (daPa).
NOTE:
1.02 mmH
2
O = 1.0 daPa.
2.3 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.
