EFFECT OF ABDOMINAL VIBROACOUSTIC STIMULATION ON SOUND AND ACCELERATION LEVELS AT THE HEAD OF THE FETAL SHEEP

Objective: To measure the vibratory response of the fetal head and abd ominal wall in sheep during vibroacoustic stimulation. Methods: A piez oresistive accelerometer was attached to the skulls of seven sheep fet uses (128-134 days' gestational age), and a miniature hydrophone was a ttached to the skin overlying the fetal temporal bone. During fetal pr eparation and vibroacoustic stimulation procedures, ewes were anesthet ized and supine. Vibroacoustic stimulation of the maternal abdomen was produced by each of two clinical devices that differed in spectral co ntent, and an electric toothbrush. Results: The approximate fundamenta l frequencies (f(0)) and first overtones (f(1)), as determined by both recordings of intrauterine sound pressure level and fetal head accele ration, were as follows: fetal acoustic stimulator, 75 and 150 Hz; ele ctronic larynx, 150 and 300 Hz; and electric toothbrush, 25 and 50 Hz, respectively. At fundamental frequencies and first overtones, the ran ges of fetal head accelerations (expressed in 1/12-octave bands) were as follows: fetal acoustic stimulator, 10-53 and 25-224 mm/sec(2); ele ctronic larynx, 10-53 and 18-114 mm/sec(2); and electric toothbrush, 3 3-792 and 8-116 mm/sec(2), respectively. Sound pressure levels exceede d 110 dB in all cases. High sound pressure levels in the uterus were p roportional to fetal head vibration levels. Conclusion: Vibroacoustic stimulation of the surface of the abdomen of pregnant sheep is accompa nied by both acoustic and vibratory exposure of the fetus. ((C) 1997 b y The American College of Obstetricians and Gynecologists.)