Abstract
Assessment of middle ear impedance using noninvasive electroacoustic measurements
has undergone successive developments since its first clinical application in the
1940s, and gained widespread adoption since the 1970s in the form of 226-Hz tympanometry,
and applications in multifrequency tympanometry. More recently, wideband acoustic
immittance (WAI) is allowing unprecedented assessments of the middle ear acoustic
mechanics thanks to the ability to record responses over a wide range of frequencies.
The purpose of this article is to present fundamental concepts for the assessment
and interpretation of wideband measures, including a review of acoustic impedance
and its relation to the mass, stiffness, and resistance components of the middle ear.
Additionally, an understanding of the middle ear transfer function reveals the relationship
between impedance and middle-ear gain as a function of frequency. Wideband power absorbance,
a WAI measure, quantifies the efficiency of sound conduction through the middle ear
over a wide range of frequencies, and can serve as an analogous clinical measure to
the transfer function. The interpretation of absorbance measures in ears with or without
a conductive condition using absorbance measured at ambient pressure and pressurized
conditions (wideband tympanometry) is described using clinical case examples. This
article serves as an introduction to the fundamental principles of WAI measurements.
Keywords
wideband acoustic immittance - acoustic impedance - wideband power absorbance - middle
ear transfer function - resonance frequency
