Hearing Loss and Deafness 171Acoustic Impedance Audiometry and Middle Ear Testing
According to Martin and Clark (2003), the common use of the term impedance audiometry
is technically incorrect: “ Because audiometry per se is involved only with re spect to the acoustic
ref lex, this term is not strictly accurate” (p. 144). They also note that referencing this type of testing
to the middle ear is misleading because it primarily involves the tympanic membrane, not direct
testing of the entire middle ear. However, because of their widespread ac cep tance by clinicians
from a variety of disciplines, the terms acoustic impedance audiometry and middle ear testing are
used rather than more technically accurate terms such as acoustic immittance metering. Typically,
acoustic impedance audiometry provides three mea sure ments of middle ear functioning: compli-
ance, stapedial ref lex, and tympanometry.
In audiometry, compliance is the ease with which the middle ear structures function.
Technically, static acoustic compliance indicates the f lexibility and mobility of the middle ear
structures, particularly the tympanic membrane. Stapedial ref lex refers to the protective action
of the stapedius muscle (and tensor tympani) in response to loud sounds. The stapes, the smallest
bone of the ossicular chain, is in contact with the oval win dow of the cochlea. The contraction
of this muscle protects the ear by increasing the impedance of the middle ear and thus reducing
the potential damage caused by loud sounds. Tympanometry mea sures the middle ear pressure
changes and the compliance of the tympanic membrane in response to pressure changes due to
the testing device. The presence or absence of the stapedial ref lex, positive and negative pressures,
and increased or reduced compliance provides diagnostic information about the functioning of the
tympanic membrane, eustachian tubes, and ossicular chain.
Speech Audiometry
According to Martin and Clark (2003), the terminology for speech audiometry has been incon-
sistent. In general, speech audiometry consists of mea sur ing a patient’s ability to hear and under-
stand syllables and words. The stimuli control for stress and use phonetically balanced words,
monosyllables with the same distribution of phonemes occurring in connected speech. Specific
Figure 9-3. Binaural sensorineural hearing loss.