Effects of impulse noise on the hearing of fetal sheep in utero

Abstract

Knowledge of the transmission of exogenous sounds to the fetal head and the effects that these sounds have on fetal hearing is incomplete. The purposes of this study were to measure the transmission of impulse noise into the uterus and to evaluate the effects of impulse noise delivered to pregnant sheep on the hearing of the fetus in utero. A shock tube produced impulses that averaged 169.7 dB peak sound pressure level (pSPL) in air. In the uterus, 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 and the stimulus resembled a Friedlander wave. When the fetal head was deep within the uterus, the duration of the impulse increased and the peak amplitude decreased. In some instances the decrease in pSPL exceeded 10 dB. Slight elevations of evoked potential thresholds were noted but only for low-frequency stimuli. The integrity of hair cells from these animals was assessed using scanning electron microscopy.