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

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Annual rept. 1 Sep 96-31 Aug 97

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Progress has been made in addressing each of the three primary objectives 1 characterization of the transmission of impulse noises into the uterus 2 evaluation of the effects of impulse noise exposures on the hearing of the fetus in utero and 3 evaluation of the effects of impulse noise exposures on the behavioral state of the fetus. The shock tube produced impulses in air that averaged 169.7 dB, peak sound pressure level pSPL. 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 morphology of the waveform resembled a Freidlander wave. When the fetal head was deep within the uterus, the duration of the impulse waveform increased and the peak amplitude decreased. In some instances the decrease in pSPL exceeded 10 dB. Data from six fetuses exposed at 117 days gestational age dGA and from six fetuses exposed at 127 dGA revealed slight post-exposure threshold elevations for low-frequency auditory brainstem response eliciting stimuli. Cochleae from these animals are currently being evaluated using scantling electron microscopy. Behavioral state rapid eye-movement sleep and heart rate data from eight fetuses taken before, during and after exposure to impulses are under evaluation.

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  • Anatomy and Physiology
  • Medicine and Medical Research
  • Stress Physiology

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