The conductive mechanism plays an important role in our hearing: the first stage of signal processing in the auditory system. While it consists of the ear canal, the crucial portion is the middle ear system, which transforms airborne sound into mechanical vibration and helps improve sound transmission into the fluid-filled inner ear. Hearing loss due to dysfunction of the middle ear system may be threatening to the quality of life for humans. For example, conductive hearing loss may significantly impact normal speech and language development of children. Assessment of middle ear dysfunction is essential for audiological diagnosis of hearing loss and differential diagnosis of ear diseases. For instance, middle ear dysfunction may cloud outcomes of newborn hearing screening. Acoustic immittance is the current clinical technique for assessment of middle ear dysfunction. The major procedures include tympanometry and acoustic reflex test. In these procedures, a single-frequency probe tone (e.g., 226 Hz and 1000 Hz) is used to estimate the acoustic impudence/admittance of the middle ear. Although they have been a clinical routine in audiology since 1970s, value of these procedures in assessment of conductive dysfunction has been limited. Wideband Acoustic Immittance (WAI) is the most recently developed technique for evaluating middle ear transfer function. Compared with the conventional acoustic immittance technique, WAI uses a different calibration technique with the sound pressure in the ear canal measured in the presence of a probe single. On the basis, several measures could be derived such as acoustic impedance/admittance and pressure reflectance. Energy reflectance (defined as the squared pressure reflectance, sometimes called power reflectance) has been investigated the most. It represents the proportion of energy that is reflected back from the middle ear, which varies from 0 to 1. Its complement is referred to as energy absorbance. One advantage of WAI is that the outcome is minimally influenced by the position of probe in the ear canal if the reflectance measure is used. In other words, the reflectance measured at the canal is a good approximation of the reflectance at the eardrum. Another advantage of this technique is utilization of wideband probe signals, e.g. clicks and tone chirps. Thus, the middle ear transfer function is evaluated in a wide frequency range (e.g. from 226 to 8000 Hz).
Citation: Sun XM (2014) Assessment of Conductive Dysfunction: Wideband Acoustic Immittance. Commun Disord Deaf Stud Hearing Aids 2:e115. doi: 10.4172/2375-4427.1000e115