title: Time course of the suppression effect on transient evoked otoacoustic emissions by prolonged contralateral acoustic stimulation.
abstract: OBJECTIVE
  Although the suppressive effect of the medial efferent acoustic reflex is well known, the time course of this effect over prolonged periods has yet to be fully evaluated. We assessed time-dependent change in the suppression of transient evoked otoacoustic emissions (TEOAEs) by the medial efferent acoustic reflex over a relatively long period.
  
  
  METHODS
  We measured TEOAEs in the right ear before contralateral acoustic stimulation (CAS), and then measured serial TEOAEs in the right ear at four intervals during a total of 16 minutes of continuous CAS, followed by three more recordings after termination of CAS.
  
  
  RESULTS
  TEOAE amplitudes were reduced with CAS during a certain period (from the immediate period to 10 minutes depending on frequency) and subsequently recovered. TEOAE suppression values in the mean amplitudes for overall frequency were 0.76 dB at the initial recording, 0.35 dB at 5 minutes, 0.44 dB at 10 minutes, and 0.33 dB at 15 minutes during CAS. The initial suppression value was significantly larger than other suppression values of 5, 10, and 15 minutes (p<0.05). In recordings obtained after CAS, TEOAE amplitude exceeded pre-acoustic amplitudes at 1 kHz, 1.5 kHz, and 2 kHz.
  
  
  CONCLUSIONS
  The present results show the existence of the medial efferent acoustic reflex and demonstrate the time course that TEOAE suppressions present initially after CAS, showing fatigue over time. Overshooting of TEOAE was observed in recordings at several frequencies after termination of CAS.
authors.affiliation: Department of Otolaryngology, Eulji Medical Center, Eulji University School of Medicine, Seoul, Korea.
authors.forename: Hyun Woo
authors.initials: HW
authors.lastname: Kang
authors.affiliation: Department of Otolaryngology, Eulji Medical Center, Eulji University School of Medicine, Seoul, Korea.
authors.forename: Hyun Joon
authors.initials: HJ
authors.lastname: Shim
authors.affiliation: Department of Otolaryngology, Eulji Medical Center, Eulji University School of Medicine, Seoul, Korea.
authors.forename: Seong Jun
authors.initials: SJ
authors.lastname: Song
authors.affiliation: Department of Otolaryngology, Eulji Medical Center, Eulji University School of Medicine, Seoul, Korea.
authors.forename: Seong Hee
authors.initials: SH
authors.lastname: Lee
authors.affiliation: Department of Otolaryngology, Eulji Medical Center, Eulji University School of Medicine, Seoul, Korea.
authors.forename: Sang Won
authors.initials: SW
authors.lastname: Yoon
keywords: Acoustic reflex; Acoustic stimulation; Efferent fiber; Otoacoustic emissions