ACCELERATION OF FETAL HEAD INDUCED BY VIBRATION OF MATERNAL ABDOMINAL-WALL IN SHEEP

OBJECTIVE: The human body is often exposed to significant vibration st ress in the workplace, at home, and during recreational activities, Th e current study was designed to evaluate whether low- to midfrequency vibrations present at the extraabdominal wail would be attenuated acro ss this wall and what the levels of exposure would be once these vibra tions reached the fetal head. STUDY DESIGN: Four pregnant sheep were i nstrumented with acceleration transducers to obtain acceleration level s at the extraabdominal and intraabdominal walls and at the fetal head . Sine-wave vibration stimulation was applied over a frequency range o f 3 to 150 Hz at a constant acceleration level of 2.5 m/sec(2) (root-m ean-square). RESULTS: Vibration of the extraabdominal wall resulted in a frequency-dependent rise in vibration levels at the intraabdominal wall, from 4% to 140% of the input level. At the fetal head a broad pe ak in response was noted between 6 and 12 Hz, but the overall levels n ever exceeded 4% oi the input level. CONCLUSION: Fetal exposure to loc alized vibratory stimulation of the maternal abdomen is maximal in the range of 6 to 12 Hz.