2
The point on the tympanogram which represents the point of maximum
compliance (admittance) is the compliance peak of the tympanogram.
The air pressure (pressure at the peak) where this compliance peak
occurs approximates the pressure within the middle-ear system, since
maximum mobility is only possible when there is little or no pressure
difference between the ear canal and the middle-ear space. Compliance
is measured with respect to the ability of an equivalent volume of air
to conduct sound and the scientific quantity used is cm
3
. Air pressure
is measured in decapascals (daPa).
NOTE
1.0 daPa = 1.02 mm H
2
O
The presence of a pathological condition which interferes with the mo-
bility of the tympanic membrane, the ossicular chain, or the air pressure
within the middle-ear space can be detected during tympanometry.
For example:
• If the air pressure within the middle-ear space becomes negative
due to a blocked Eustachian tube, tympanometry permits the
measurement of this negative pressure and its effect on middle-
ear compliance.
• If fluid builds up within the middle-ear space, this fluid will restrict
the ability of the ossicular chain to conduct sound to the cochlea.
If small air pockets exist within the fluid, the tympanogram will in-
dicate the negative pressure where the restricted mobility occurs.
With a totally fluid-filled middle-ear space, no mobility will be mea-
sured during tympanometry at any pressure value.
• In the case of a “glue-ear”, the ossicular chain is restricted in mo-
bility but the air pressure within the middle-ear space is at atmo-
spheric pressure. This tympanogram would depict a restricted
compliance peak at or near 0 daPa.
1.2.2 Gradient
Gradient (width) measurements are used to describe the shape of a
tympanogram in the vicinity of the peak. Often, the presence or ab-
sence of fluid in the middle ear is not clearly indicated by otoscopy
and the tympanometric peak alone. This evaluation is especially difficult
when the peak pressure is in the normal range.
The presence of fluid within the middle-ear space alters the shape of
a tympanogram, i.e., makes the tympanogram wider near its peak.
A larger-than-normal gradient can indicate the presence of fluid in the
middle ear when other parameters are within normal limits. In this way,
the gradient acts as an adjunct to the peak and ear canal volume
measurements by helping to differentiate between tympanograms
with similar peak values.
