Note: If volume exceeds 2.0 cc the
MicroTymp
will not record a
tympanogram. Above 2.0 cc a LEAK
(
=:)
symbol will appear;
above 2.5 cc, an OPEN
(
;I
) symbol will appear.
HIGH ADMITTANCE PATHOLOGIES
Tympanic
membrane abnormalities.
The tympanic membrane is normally a stiff, conically-shaped struc-
ture that derives its stiff characteristic from the lamina propria, a
layer of connective tissue that is situated between the outer layer
of squamous epithelium (skin) and the inner layer of mucous mem-
brane. When the eardrum heals after a relatively large perforation,
the lamina propria may be absent or thin in the region of the scar.
This
neomembrane
can be set into vibration with greater ease than
the normally-stiff tympanic membrane. The result is a high static
admittance. Although the tympanogram is abnormal, the condition
rarely affects hearing sensitivity or requires further medical treatment.
Ossicular disruption.
Disruption of the ossicular chain ranges from partial interruption
with fibrous attachments between ossicular remnants, to complete
absence of the ossicles. These conditions result from the erosive
effects of chronic infection, trauma, and congenital defect. Ossicular
disruption is usually associated with a substantial conductive hearing
loss. Because the ossicles normally “load” the eardrum, con-
tributing to its tension, the eardrum in an ear with ossicular dis-
ruption can be more easily set into vibration than the normal
eardrum. This results in high static admittance.
FRESSIIRE
-
d&c.
.31
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