title: An animal model for assessment of amniotic fluid clearance from the middle ear.
abstract: OBJECTIVE
  To determine the time needed for clearance of amniotic fluid from the middle ear after birth, an animal model study was performed.
  
  
  BACKGROUND
  Before birth, the middle ear is full of amniotic fluid, and there is controversy about the time it takes for it to clear postnatally. This is of importance because it is suspected that amniotic fluid in the middle ear of the newborn may affect results of screening of hearing when using otoacoustic emissions.
  
  
  METHODS
  Adult and neonatal guinea pigs underwent a right-side cochleotomy followed by baseline otoscopy, tympanometry, and auditory nerve- and brainstem-evoked response (ABR) measurements of the left ear. Subsequently, the animals' left middle ears were filled with saline through a hole drilled in the bulla. Over the next few days, assessment of saline clearance was conducted by repeated left-side otoscopy, tympanometry, and measurement of ABR.
  
  
  RESULTS
  After filling the middle ear with saline, the tympanic membrane was opaque, a type B tympanogram was obtained, and the ABR threshold was elevated. After an average of 6.3 +/- 3.0 days, air bubbles were seen in otoscopy, a type C tympanogram was obtained, and the ABR threshold improved. Finally, after an average of 9.5 +/- 2.7 days, all 3 parameters returned to their baseline values.
  
  
  CONCLUSIONS
  Taking into consideration that this is an animal study, the results suggest that clearance of amniotic fluid from the newborn middle ear takes longer than has been generally thought. In addition, an animal model for assessing the clearance of fluid from the middle ear has been developed.
authors.affiliation: Department of Otolaryngology and Head and Neck Surgery, Shaare Zedek Medical Center, Jerusalem, Israel.
authors.forename: Ronen
authors.initials: R
authors.lastname: Perez
authors.forename: Ronit
authors.initials: R
authors.lastname: Priner
authors.forename: David
authors.initials: D
authors.lastname: Cohen
authors.forename: Sharon
authors.initials: S
authors.lastname: Freeman
authors.forename: Haim
authors.initials: H
authors.lastname: Sohmer
mesh_terms: D000158:Acoustic Impedance Tests; D000653:Amniotic Fluid / Q000378:metabolism*; D000818:Animals; D000831:Animals, Newborn; D001309:Auditory Threshold / Q000502:physiology; D003051:Cochlea / Q000601:surgery; D004432:Ear, Middle / Q000378:metabolism*; D016057:Evoked Potentials, Auditory, Brain Stem / Q000502:physiology; D006168:Guinea Pigs; D008657:Metabolic Clearance Rate / Q000502:physiology; D017084:Otoacoustic Emissions, Spontaneous / Q000502:physiology