Fetal vibroacoustic stimulation test: vibrator response characteristics in pregnant sheep postmortem
Peters, A.J.; Abrams, R.M.
Obstetrics and Gynecology 81(2): 181-184
1993
ISSN/ISBN: 0029-7844 PMID: 8423945 Document Number: 422419
Objective: To determine the effect of small decreases in battery voltage on the sound pressure level and spectral features of sound within the ureterus during vibroacoustic stimulation with a battery-powered electronic artificial larynx. Methods: In eight pregnant, recently sacrificed sheep, the fluid-borne, intra-amniotic sound pressures resulting from vibration of the abdominal wall with an electronic artificial larynx were compared with airborne sound pressures produced by an artificial larynx and measured at 50 cm. Results: At all frequencies, the intrauterine sound pressure was higher than the sound pressure in air. Decreasing battery voltage from 9 to 7 V resulted in a 5-18-dB decrease in intrauterine sound pressure at the electronic artificial larynx fundamental frequency and most overtone, but only a 4-8-dB decrease in airborne signal. The results indicate that for frequencies relevant to fetal hearing, the reduction of sound pressure level caused by inadequate battery voltage may result in a difference in fetal response. Conclusion: Routine verification of the function of a vibroacoustic device by means of a battery voltage check is recommended.