Vibration of the abdominal segment in pregnant sheep

Mechanical vibration of the abdominal wall results in a frequency-related distribution of intra-abdominal sound pressure levels. A greater attenuation of applied signals of equal dynamic force occurs as frequency increases. A broad resonance peak exists between 6 and 18 Hz. Transducers fixed to the fetal head show clear increases in acceleration levels during stimulation of the abdominal surface with the artificial electronic larynx. Sine-wave stimulation results in a frequency-dependent increase in vibration levels of the abdominal wall of 4% to 140% of the input levels. At the fetal head, a broad peak in response was noted between 6 and 12 Hz, but the overall levels never exceeded 4% of the input level.