Vibratory acoustic stimulation and the flow velocity waveform in the fetal internal carotid artery

Eleven healthy fetuses between 36 and 39 weeks of gestation were studied during the active sleep state to examine effects of a 5-s vibratory acoustic stimulus on the baseline fetal heart rate and flow velocity waveform in the fetal internal carotid artery. There was an immediate marked rise in baseline fetal heart rate with concomitant drop in pulsatility index in the flow velocity waveform of the fetal internal carotid artery, which persisted for at least 15 min after the stimulus. However, when the pulsatility index was standardized for a fetal heart rate of 140 beats/min this index remained virtually unaltered. These data suggest that in the healthy term fetus during active sleep state, a vibratory acoustic stimulus has no measurable effect on cerebral vascular resistance. Since virtually all reported studies on vibratory acoustic stimulation of the fetus were carried-out during the quiet sleep state, the data from the present study do not provide any information on the safety of this device when employed as a means of assessing of fetal well-being.