3
The TM 262TM Auto TympTM determines tympanometric width (gradient)
by measuring the pressure interval at one-half of the peak height. Differ-
ing peak widths can point to different middle-ear conditions, even when
peak height and pressure are within normal range. For example, middle-
ear effusion brought on by secretory otitis media might result in an
increased tympanogram width and, therefore, an increased gradient
value. This would occur because the ossicular chain cannot react to the
change in pressure introduced during the tympanogram in the same
way that it would if the middle ear were properly aerated. The contin-
ued presence of effusion, leading eventually to a completely fluid-filled
middle-ear cavity, will reduce the magnitude of the tympanogram to the
point where no change in compliance is detectable across the pressure
range. Under this condition, no gradient measurement is possible.
1.3 SCREENING ACOUSTIC REFLEX
An acoustic reflex occurs when a very loud sound (stimulus) is present-
ed to the auditory pathway. During ipsilateral acoustic reflex testing, the
stimulus is presented to the ear canal through the probe. This stimulus
then travels through the middle ear to the cochlea. From the cochlea,
frequency and intensity information are transmitted via the 8th nerve to
the brain stem. If the intensity of the stimulus is high enough to elicit the
reflex response, a bilateral response occurs, i.e., the right and left 7th
nerves innervate their respective middle-ear muscles (stapedial mus-
cles) causing them to contract. As these muscles contract, they stiffen
their respective ossicular chains. This stiffening of the ossicular chain
reduces the compliance of each middle-ear system. As in tympano-
metry, a probe tone is used to measure this decrease in compliance.
During ipsilateral acoustic reflex testing, both the stimulus and the probe
tone are presented via the hand-held probe.
Acoustic reflex measurements are useful in determining the integrity of
the neuronal pathway involving the 8th nerve, brainstem, and the 7th
nerve. Since the acoustic reflex test is performed at high intensity levels
and since it involves a measurement of middle-ear mobility, acoustic
reflex testing is not a test of hearing.
The acoustic reflex test also serves as a good validation of tympano-
metric results, since an acoustic reflex cannot be measured in the
absence of a compliance peak. In other words, if the tympanometric
results indicate no mobility over the pressure range available with
the TM 262, no reflex can be measured. If the test results indicate a
reflex response in the absence of a compliance peak, one has cause
to question the validity of the tympanometric test results. This indi-
cates that the tympanogram should be repeated.
Clinical middle-ear instruments allow the measurement of the acoustic
reflex threshold, since they provide the ability to manually change the
intensity of the stimulus to a level where a reflex response is just barely
