Detection of otoacoustic emissions in chinchilla when the middle ear contains amniotic fluid.

OBJECTIVES/HYPOTHESIS Otoacoustic emissions have frequently been used for newborn hearing screening. However, they have low specificities and high referral rates. The presence of amniotic fluid in the middle ear is one reason for these problems. The aim of this study was to determine the effects of human amniotic fluid on otoacoustic emissions and on middle-ear function. METHODS Forty-six chinchillas were randomly divided into eight groups based on the type (amniotic fluid or normal saline) and volume (0.5, 1, 1.5, 2 ml) of liquid introduced into the middle ear. Distortion product otoacoustic emission (DPOAE) and wideband reflectance (WBR) measurements were taken under inhalational anaesthesia before and after introduction of middle-ear liquid. The differences in these measurements were subjected to statistical analyses. STUDY DESIGN Prospective controlled animal study. RESULTS Significant reductions of DPOAE levels and increases in WBR occurred across all frequencies when there was liquid in the middle ear, and the changes became greater for increased volumes of liquid. Changes in the noise level had important effects on the otoacoustic-emission signal-to-noise ratio at the three lowest frequencies. CONCLUSION Both human amniotic fluid and saline in the chinchilla middle ear resulted in changes in otoacoustic-emission detection patterns and WBR that may be relevant to newborn hearing screening.