Operating instructions

A-36
Tympanic Membrane Abnormalities
“Floppy” Tympanic Membrane
The tympanic membrane is normally a stiff, conically-shaped structure 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 membrane. 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. See Figure 31. Although the tympanogram is abnormal, this con-
dition rarely affects hearing sensitivity or requires further medical treatment.
Ossicular Disruption
Disruption of the ossicular chain can range from partial interruption 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, contributing to its tension, the eardrum
in an ear with ossicular disruption can be more easily set into vibration than
the normal eardrum, resulting in high static admittance. See Figure 31.
Figure 31 – High Static Admittance
NOTE: When peak admittance exceeds 1.5 mmho, data
points will be plotted at baseline (0.0 mmho). See Figure 31.