Conditions
artificial/y
flatten
the
tympanogram.
In order to measure the mechanical properties of the middle ear,
the MicroTymp must be capable of changing the pressure differential
across the eardrum. Two conditions can prevent this from happening
and artificially flatten the tympanogram:
1. Ear canal occlusion:
If the ear canal is occluded by impacted
cerumen, foreign body, tumor, stenosis, or atresia, the volume of
air in front of the probe will be very small. This small volume may
be manifest in two ways with the Welch Allyn MicroTymp:
l
The BLOCK
symbol may be displayed, indicating that the
equivalent volume in front of the probe is less than 0.2 cc
l
A flat tympanogram may occur with a small equivalent volume
for children or <
for adults)
2. Tympanic membrane perforation or patent tympanostomy
tube:
In these cases the air pressure produced by the MicroTymp
escapes through the perforation or tube so that a pressure dif-
ference across the eardrum does not occur. Because the air
pressure changes have no effect on the tension of the eardrum, the
tympanogram is flat. In cases in which the middle ear mucosa is
relatively normal, the flat tympanogram will be accompanied by a
large equivalent volume
1.5 cc for adults and 1.0 cc for
preschool-aged children). Many patients with tympanic membrane
perforations have a flat tympanogram but do not show a large
equivalent volume due to inflammation of the middle ear.
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