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

摘要

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 3.7 dB of airborne levels. When the fetal head was deep within the uterus, the peak amplitude decreased by 18.5 dB. Data from ten fetuses exposed at 117 days gestational age (dGA) and from 10 fetuses exposed at 127 dGA revealed significant 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 dGOA showed similar amounts of damage when compared to cochleae of fetuses exposed at 127 dGA. Recordings of behavioral state indicated disruption of normal cycling during and shortly after the exposure. Significant changes occurred for fetal heart rate, and spectral power in the electrocorticogram for Alpha, Delta and Theta bands. The major finding was that exposure to 20 impulses at 169 dB peak sound pressure level produced significant damage to primarily the inner row of hair cells located in the apical region of the cochlea in fetal sheep.