Definition
The aural acoustic immittance test battery
(tympanometry and acoustic reflex measurements) reflects the
physical and physiological status of the eardrum, middle ear,
cochlea, seventh and eighth cranial nerves and the auditory pathway
in the brainstem. This
test battery is not a test of hearing.
Clarification
In 1988, the American Speech Language and Hearing
Association (ASHA) Working Group on Aural Acoustic Immittance
Measurements, Committee on Audiologic Evaluation states: "Although
tympanometry is a powerful addition to the audiologic test battery,
the measures must be interpreted with the following two limitations
in mind....caution must be exercised in correlating tympanometric
findings with hearing sensitivity. Tympanometry is a measurement
of the input impedance or admittance of the middle-ear transmission
system. The acoustic energy that flows into the system can
be measured but not how much energy is transmitted through the
system. For example, an eardrum pathology such as tympanosclerotic
plaques or neomembrane typically is associated with an abnormally
flaccid tympanometric pattern, but hearing sensitivity remains
relatively unaffected. Conversely, otosclerosis produces
a marked hearing loss in conjunction with a relatively normal
tympanometric pattern."
Normal tympanograms can be obtained from people
with normal hearing, conductive hearing loss (e.g. otosclerosis),
cochlear hearing loss of any degree and cadavers. Thus, it
is clearly shown that tympanometry does not measure presence, degree
or configuration of hearing loss, and as such is not a test of
human hearing. Likewise, tympanometry does not predict
the presence or absence of an air/bone gap and cannot be used
as a substitute for bone conduction threshold testing.
The acoustic reflex is the reflexive contraction
of middle ear muscles in response to auditory stimuli. Attempts
have been made to predict hearing sensitivity by the acoustic reflex
thresholds. While the acoustic reflex can reflect the presence
of peripheral hearing loss, it is not accurate in quantifying the
hearing loss. The use of acoustic reflexes to predict hearing
levels is not an accepted part of clinical audiologic practice
today and is not substantiated by the professional literature.
Use of the acoustic reflex to predict Loudness
Discomfort Levels (LDL) has been repeatedly shown to be unreliable. The
acoustic reflex is a physiologic event; LDLs are a psychoacoustic
phenomena. Greenfield, et al. (1985) summarized the published
literature on acoustic reflex measures and loudness discomfort
levels (LDL) and concluded "the use of acoustic-reflex measure
in the estimation of an individual's LDL is unwarranted."
The aural acoustic immittance test battery
has one purpose: to assess auditory function by indicating the
physical and physiological status of the eardrum, middle ear,
cochlea, seventh and eighth cranial nerves and the auditory pathway
in the brainstem. It is not a test of hearing. Therefore aural
acoustic immittance measures should only be performed by professionally-trained
audiologists. They are clearly under the scope of practice
of the licensed audiologist.
ASHA working Group on Aural Acoustic-Immittance Measurements,
Committee of Audiologic Evaluation, (1988). Tutorial Tympanometry,
Journal of Speech and Hearing Disorders, 53, 354-377.
Hall, J. and Bleakney, M. (1981). Hearing loss prediction by the
acoustic reflex: comparison of seven methods. Ear and Hearing,
2,4, 156-169.
Greenfield, D., Wiley, T. and Block, M. (1985). Acoustic-reflex
dynamics and the loudness-discomfort level. Journal of
Speech and Hearing Disorders. 50, 14-20.
