Wideband acoustic immittance: Concepts and clinical utility

Measurements of middle ear (ME) acoustic power flow and related measures (e.g., reflectance, absorbance, impedance, resistance, and reactance) have several important advantages over other measures of acoustic impedance, such as the clinical “gold standard” measure, tympanometry. In addition to its wide bandwidth and ease of use, the absorbance curve, on a dB scale, has a shape that is similar to the ME transfer function, and is easily codified by three audiologically relevant parameters. Wideband acoustic impedance measures (resistance and reactance) can provide additional important information about ME status. Alone, or together with other audiological tests such as otoacoustic emission tests and audiometry, acoustical tympanic membrane (TM) measurements can help identify many abnormal conditions, including degrees of otitis media, TM perforations, otosclerosis and ossicular disarticulation. In addition, the problem of ear canal standing waves may be solved by the introduction of the Forward Pressure level (FPL) calibration. Reference Equivalent Forward Pressure Level (RETFPL) is an alternative to the the present “gold standard” Reference Equivalent Sound Pressure Level (RETSPL). Reflectance and absorbance also provide new ways of measuring the middle-ear reflex (MER) that may be more sensitive, allowing lower stimulus levels. Normative data from several studies are summarized. Abbreviations: DPOAE = distortion product otoacoustic emission; HL = hearing level; ME = middle ear; MER = middle ear reflex; OME = otitis media with effusion; RETSPL = Reference equivalent sound pressure level; RETFPL = Reference equivalent forward pressure level; SPL = sound pressure level; FPL = Forward pressure level; Tympanic membrane = TM.