Procedures for ambient-pressure and tympanometric tests of aural acoustic reflectance and admittance in human infants and adults

Abstract

Procedures are described to measure acoustic reflectance and admittance in human adult and infant ears at frequencies from 0.2 to 8 kHz. Transfer functions were measured at ambient pressure in the ear canal, and as down- or up-swept tympanograms. Acoustically estimated ear-canal area was used to calculate ear reflectance, which was parameterized by absorbance and group delay over all frequencies (and pressures), with substantial data reduction for tympanograms. Admittance measured at the probe tip in adults was transformed into an equivalent admittance at the eardrum using a transmission-line model for an ear canal with specified area and ear-canal length. Ear-canal length was estimated from group delay around the frequency above 2 kHz of minimum absorbance. Illustrative measurements in ears with normal function are described for an adult, and two infants at 1 month of age with normal hearing and a conductive hearing loss. The sensitivity of this equivalent eardrum admittance was calculated for varying estimates of area and length. Infant-ear patterns of absorbance peaks aligned in frequency with dips in group delay were explained by a model of resonant canal-wall mobility. Procedures will be applied in a large study of wideband clinical diagnosis and monitoring of middle-ear and cochlear function.

Comparisons of transient evoked otoacoustic emissions using chirp and click stimuli

“…An additional port exiting the probe tip transmitted air-pressure changes generated by the pump in the tympanometer (AT235, Interacoustics, with modified firmware). Wideband ambient-pressure and tympanometric reflectance tests were first performed in each ear using procedures described in Keefe et al (2015) prior to TEOAE testing. All tests used the same probe insertion whenever possible.…”

Comparing otoacoustic emissions evoked by chirp transients with constant absorbed sound power and constant incident pressure magnitude

“…As described in Keefe et al (2015), the area S e of the ear-canal at the probe tip was acoustically estimated from Y, and the length x between the probe and a mid-TM region was acoustically estimated from R. With the assumption that the ear canal had a constant cross-sectional area along its length, the real-ear incident pressure Q e was estimated using Eq. (15) in terms of S e and the real-ear pressure P me at the TM was estimated using Eq.…”

“…Ambient-pressure and tympanometric reflectance/admittance tests were first performed in the test ear using procedures described in Keefe et al (2015) prior to TEOAE testing. Whenever possible, all tests used the same probe insertion.…”

“…The sum of the magnitudes of the forward and reverse pressures at the probe tip equals the sum of the magnitudes of the forward and reverse pressures at the TM, but this latter sum is not equal to the magnitude of the pressure at the TM. This is because the pressure reflectance R m of the middle ear at the TM has a non-zero phase, or equivalently, a non-zero group delay (Keefe et al, 2015;Feeney et al, 2016). Souza et al (2014) concluded that forward pressure was advantageous because it quantified stimulus phase and had a smaller dependence on insertion depth in the canal compared to absorbed sound power and incident sound pressure.…”

“…(14) and (16) may be used to calculate L TM ½k and L TMe ½k; respectively, once the distance x between the probe and TM is measured, e.g., using procedures in Keefe et al (2015).…”