title: Cochlear microphonics recorded from fetal and newborn sheep.
abstract: OBJECTIVE
  Sounds present within the uterus stimulate the fetal inner ear and central auditory pathway. This study was undertaken to determine the efficiency of transmission of exogenous airborne stimuli to the fetal inner ear. In this way, we may quantify the extent to which the fetal auditory system is isolated from sounds produced outside the mother.
  
  
  METHODS
  Cochlear microphonics were recorded from fetal and newborn sheep to evaluate the extent to which the fetus is isolated from sounds exogenous to the ewe. Electrodes were surgically placed in contact with the round window membrane in nine near-term fetal sheep. Cochlear microphonics were recorded in response to 1/3 octave-band noises (0.125 to 2.0 kHz) delivered through a loudspeaker 1.8 m from one side of the pregnant ewe. Sound pressure levels generated by the noises were simultaneously recorded ex utero with a microphone and in utero with a hydrophone previously sutured to the fetal neck. After cochlear microphonic amplitudes were recorded, the fetus was delivered through an abdominal incision. Recordings were repeated from the newborn lamb. Fetal sound isolation was calculated as the difference between the sound pressure levels that were necessary to evoke equal cochlear microphonic amplitudes from the fetus and from the newborn lamb.
  
  
  RESULTS
  The sound attenuation observed was variable for all frequencies. The fetus was isolated from external sounds by 11.1 dB for 0.125 kHz, 19.8 dB for 0.25 kHz, 35.3 dB for 0.5 kHz, 38.2 dB for 1.0 kHz, and 45.0 dB for 2.0 kHz.
  
  
  CONCLUSIONS
  Other investigators have demonstrated that the immature auditory system is more susceptible to damage produced by noise exposure than is the mature auditory system. Low-frequency noise produces damaged cells that later in life code higher frequencies. A possibility of fetal hearing loss produced by intense noise exposure needs more careful evaluation.
authors.affiliation: Department of Communication Processes and Disorders, University of Florida, Gainesville 32611.
authors.forename: K J
authors.initials: KJ
authors.lastname: Gerhardt
authors.forename: R
authors.initials: R
authors.lastname: Otto
authors.forename: R M
authors.initials: RM
authors.lastname: Abrams
authors.forename: J J
authors.initials: JJ
authors.lastname: Colle
authors.forename: D J
authors.initials: DJ
authors.lastname: Burchfield
authors.forename: A J
authors.initials: AJ
authors.lastname: Peters
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D003055:Cochlear Microphonic Potentials / Q000502:physiology*; D007758:Ear, Inner / Q000196:embryology* / Q000502:physiology; D005314:Embryonic and Fetal Development / Q000502:physiology; D012756:Sheep; D013016:Sound