Summary of: Sun, X. M., & Shaver, M. D. (2009). Effects of negative middle ear pressure on distortion product otoacoustic emissions and application of a compensation procedure in humans. Ear and hearing, 30(2), 191–202. https://doi.org/10.1097/AUD.0b013e31819769e1
Evoked otoacoustic emissions (OAE) refer to the acoustic energy recorded in the ear canal generated from the cochlea in response to an evoking stimulus. The evoking stimulus is typically a transient signal or a pair of tones, which produce transient OAEs (TEOAEs) or distortion-product OAEs (DPOAEs), respectively. OAE generation indicates function of the outer hair cells within the cochlea. In addition to the health of cochlear hair cells, the measurement of OAEs depends upon the forward transmission of the evoking acoustic energy from ear canal to the cochlea, and reverse transmission of the cochlear response from the cochlea back to the ear canal. Because the middle-ear is positioned between the ear canal and the cochlea, any dysfunction within the middle ear cavity can alter the OAE. One such common example is negative middle-ear pressure caused by Eustachian tube dysfunction. The objective of this study is to examine the effect of middle-ear pressure on DPOAEs and to validate the effect of compensating for negative middle-ear pressure on DPOAEs. Within a sample of 36 adults with no hearing loss or otologic disease, negative-middle ear pressure reduces DPOAEs for an f2 of 1000 Hz and below. Specifically, negative-middle between -40 and -65 daPa reduces DPOAEs by 4-6 dB, and further reduces DPOAEs down to -12 dB as middle-ear pressure decreases down to -420 daPa. Further, the f2 frequency of 3000 Hz shows a similar reduction in DPOAEs as the magnitude of negative pressure is increased. DPOAEs do not show a significant change for f2 frequencies of 2000, 4000, and 6000 Hz. However, DPOAEs tend to increase for f2 frequencies of 8000 Hz for negative middle ear pressure below -160 daPa, albeit the change is not significant. When pressure applied to the ear canal matches the pressure at peak compliance of the middle ear, the DPOAE response is corrected and resembles the DPOAE response with no negative middle-ear pressure. Finally, the peak and notch of the DPOAE response increases as negative middle-ear pressure decreases, which suggests a change in the resonant attributes of the middle-ear cavity. This study suggests that compensation for deviant middle-ear pressure improves the level of the DPOAE.