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Impulse Noise Exposures: Characterization and Effects on Fetal Sheep in Utero

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Twenty fetal sheep were exposed to impulses with peak levels of 169 dB SPL pSPL. Auditory evoked potentials and behavioral state were recorded from the fetuses before and after impulse exposures. In the uterus of pregnant sheep, the pSPL varied as a function of fetal head location. When the fetal head was against the abdominal wall, peak levels were within 2 dB of airborne levels. When the fetal head was deep within the uterus, the peak amplitude decreased by more than 20 dB. Data from ten fetuses exposed at 117 days gestational age dGA and from 10 fetuses exposed at 127 dGA revealed slight elevations in post-exposure auditory brainstem response thresholds for low-frequency eliciting stimuli. Scanning electron microscopy revealed damage to inner and outer hair cells located in the middle and apical turns of the cochlea. Cochleae of fetuses exposed at 117 dGA showed greater damage than cochleae of fetuses exposed at 127 dGA. Recordings of behavioral state indicated disruption of normal cycling during and shortly after the exposure, however, individual variation was noted. The major finding is that impulse noise exposure produced significant damage to sensory hair cells located in the apical region of the inner ear in fetal sheep.

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  • Biology
  • Medicine and Medical Research
  • Stress Physiology

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