Vibratory Acoustic Stimulation Research Articles

The effects of vibratory acoustic stimulation on baseline fetal heart rate in term pregnancy

Fetal heart rate responses to vibratory acoustic stimulation have been studied in normal and complicated pregnancies. To determine the precise nature of these responses, we studied 50 normal term fetuses with 60 minutes of electronic antepartum fetal heart rate monitoring divided in two 30-minute segments separated by 3 seconds of vibratory acoustic stimulation. All tracings were analyzed by a programmed microcomputer. Comparison of grouped mean 30-minute values before and after vibratory acoustic stimulation showed significant increases in baseline fetal heart rate, fetal heart rate variation, frequency of accelerations exceeding 10 and 15 beats/min, duration of accelerations exceeding 15 beats/min, and frequency of decelerations after vibratory acoustic stimulation. Mean baseline fetal heart rate elevation >10 beats/min occurred within 7.6 ± 4.4 seconds in 42 of 50 fetuses and lasted for 596 ± 531 seconds. Reactive tests increased from 35 (70%) to 47 (94%) after vibratory acoustic stimulation. Most healthy term fetuses exhibit fetal heart rate responses after differing in frequency or magnitude from spontaneous fetal heart rate changes. Vibratory acoustic stimulation may be a valid fetal assessment tool but cannot be considered the physiologic equivalent of nonstress testing. (AM J OesTET GYNECOL 1989;160:1086-90.) Key words: Vibratory acoustic stimulation, fetus, fetal heart rate

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.

Vibratory acoustic stimulation in 26- to 32-week, small-for-gestational-age fetus

Seven pregnant women with early-onset (less than 32 weeks' gestation) intrauterine growth retardation were studied to examine fetal heart rate and fetal activity patterns after vibratory acoustic stimulation. All studies were done between 26 and 32 weeks' gestation. All fetuses but one were not acidotic at birth. There was a reduced time during which accelerations (50% less), long-term fetal heart rate variability (25% less), and body movements (60% less) occurred in small-for-gestational-age fetuses compared with these times in age-matched normally grown fetuses. Fetal heart rate and fetal activity patterns were not significantly altered after stimulation with the electronic artificial larynx. We hypothesized that severe, early-onset (less than 32 weeks' gestation), chronic nutritional deprivation of human fetuses is associated with a delay in the functional maturation of fetal sensory receptors.

Fetal heart rate and activity patterns in growth-retarded fetuses: Changes after vibratory acoustic stimulation

Seventeen pregnant women who subsequently were delivered of infants with birth weights less than the third percentile were studied for examination of fetal heart rate and fetal activity patterns before and after a 5-second external vibratory acoustic stimulation. None of the fetuses was acidotic at birth. A reduced time was noted during which accelerations in heart rate occurred (50% less) and long-term fetal heart rate variability (25% less) in small for gestational age fetuses compared with age-matched, normally grown fetuses. The incidence of gross fetal body movements was significantly lower (40% less) in small for gestational age fetuses than in those who were appropriate for gestational age. Fetal heart rate and fetal activity patterns after stimulation with the electronic artificial larynx in small for gestational age fetuses were similar to those of appropriate for gestational age fetuses.

Auscultated fetal heart rate accelerations: III. Use of vibratory acoustic stimulation

The auscultated acceleration test has been proposed as a simple, inexpensive screening test for fetal health; previous studies of the auscultated acceleration test used external stimulation to elicit fetal movement. This study was conducted to explore the ability of the auscultated acceleration test to predict nonstress test results when vibratory acoustic stimulation is used to elicit fetal reactivity. After antepartum nonstress testing on 100 gravid women between 28 and 43 weeks' gestation, a 6-minute auscultated acceleration test protocol was performed with two vibratory acoustic stimulations to the maternal abdomen if no spontaneous fetal heart rate acceleration occurred. The ability of the auscultated acceleration test to predict nonstress test results after selected variables were controlled for was as follows: sensitivity, 75%; specificity, 97.6%; false-positive results, 14.3%; and false-negative results, 4.7%. Logistic regression analysis indicated that, in addition to the auscultated acceleration test, gestational age and race contributed significantly to the prediction of nonstress test results. Although specificity and the false-positive rate were improved, the use of vibratory acoustic stimulations to elicit fetal movement did not improve the validity of the auscultated acceleration test in terms of sensitivity and false-negative results over previous studies. However, the auscultated acceleration test continues to show potential as an initial screening test for fetal assessment. In addition to recommendations for further research, methodologic issues related to sampling techniques are identified.

Auscultated fetal heart rate accelerations

Abstract The auscultated acceleration test has been proposed as a simple, inexpensive screening test for fetal health; previous studies of the auscultated acceleration test used external stimulation to elicit fetal movement. This study was conducted to explore the ability of the auscultated acceleration test to predict nonstress test results when vibratory acoustic stimulation is used to elicit fetal reactivity. After antepartum nonstress testing on 100 gravid women between 28 and 43 weeks' gestation, a 6-minute auscultated acceleration test protocol was performed with two vibratory acoustic stimulations to the maternal abdomen if no spontaneous fetal heart rate acceleration occurred. The ability of the auscultated acceleration test to predict nonstress test results after selected variables were controlled for was as follows: sensitivity, 75%; specificity, 97.6%; false-positive results, 14.3%; and false-negative results, 4.7%. Logistic regression analysis indicated that, in addition to the auscultated acceleration test, gestational age and race contributed significantly to the prediction of nonstress test results. Although specificity and the false-positive rate were improved, the use of vibratory acoustic stimulations to elicit fetal movement did not improve the validity of the auscultated acceleration test in terms of sensitivity and false-negative results over previous studies. However, the auscultated acceleration test continues to show potential as an initial screening test for fetal assessment. In addition to recommendations for further research, methodologic issues related to sampling techniques are identified.

Fetal responses to vibratory acoustic stimulation: Influence of basal heart rate

Forty-three healthy pregnant women between 26 and 40 weeks' gestation were studied to determine the influence of prestimulation basal heart rate on the maximum amplitude of the first fetal heart rate acceleration after external vibratory acoustic stimulation. A significant negative correlation was found between the maximum amplitude of the first fetal heart rate acceleration and the prestimulation basal fetal heart rate from 30 weeks to term. In the presence of fetal tachycardia (basal fetal heart rate greater than 160 beats/min), more than 50% of fetal heart rate accelerations after stimulus were less than 15 beats/min amplitude. There was also a significant maturational process in the immediate fetal heart rate response to vibratory acoustic stimulation that occurred between 26 to 28 and 30 to 32 weeks characterized by a prolonged increase in basal fetal heart rate and an increase in the maximum amplitude of the first acceleration after stimulation.

Umbilical and uterine artery blood flow velocities after vibratory acoustic stimulation

Twelve healthy pregnant women between 37 and 41 weeks' gestational age were studied to determine the effects of external vibratory acoustic stimulation on the blood flow velocity waveform in the umbilical and uterine arteries. There was a significant decrease in umbilical peak-systolic/end-diastolic ratio during the first 5 minutes after stimulus after comparison with control ratios. Analysis of the frequency distribution of instantaneous fetal heart rate values during Doppler measurements suggested that the decrease in umbilical peak-systolic/end-diastolic ratio was due to fetal tachycardia rather than a change in the placental vascular resistance. The uterine artery peak-systolic/end-diastolic ratio was not altered after vibratory acoustic stimulation.

Severe fetal bradycardia caused by external vibratory acoustic stimulation

A case is presented in which external vibratory acoustic stimulation performed on a term fetus produced severe prolonged bradycardia, necessitating emergency cesarean section delivery. The possible pathogenesis is discussed.

Ultrasonic Imaging of Normal Fetal Response to External Vibratory Acoustic Stimulation

Ultrasonic Imaging of Normal Fetal Response to External Vibratory Acoustic Stimulation

Fetal heart rate and fetal activity patterns after vibratory acoustic stimulation at thirty to thirty-two weeks' gestational age

Twenty pregnant women between 30 and 32 weeks' gestational age were studied to examine the effects of a 5-second external vibratory acoustic stimulus on the fetal heart rate, fetal heart rate variability, and fetal activity patterns. There was an immediate significant increase in the basal fetal heart rate for 10 minutes compared with controls. There was also a significant increase in the mean duration of fetal heart rate accelerations without any change in the number of fetal heart rate accelerations. There were no changes in long-term fetal heart rate variability, fetal breathing, and gross fetal body movements.

Ultrasonic imaging of normal fetal response to external vibratory acoustic stimulation

Fetal facial reactions and response decrement patterns to external noise stimulation were studied to characterize normal fetal neurobehavior in the third trimester. Response decrement, or habituation, is thought to reflect higher central nervous system function. Two hundred women with uncomplicated pregnancies, who were subsequently delivered of healthy infants at term, were studied between 26 and 41 weeks' gestation. After ultrasound views of the fetal face were obtained, a vibratory acoustic stimulus was applied repetitively to the maternal abdomen near the fetal head. Response decrement was defined as cessation of all components of the facial reaction, except eye blinking, over two sequential stimuli. Three response patterns were scored: (1) no startle, (2) startle without response decrement, and (3) response decrement by 12 stimuli. Whereas only 53% of fetuses between 26 and 27 weeks displayed startle reaction, all fetuses displayed startle responses by 28 weeks. As gestational age advances, an increasing number of fetuses exhibit response decrement, from no decrement at 26 to 27 weeks to 100% decrement at 40 to 41 weeks. A maturation of neurobehavioral response patterns takes place in normal third-trimester pregnancies. Response decrement testing may be a useful tool for in utero neurologic evaluation.

Fetal heart rate response to vibratory acoustic stimulation predicts fetal pH in labor

Vibratory acoustic stimulation was performed during labor in 188 instances 60 seconds before fetal scalp puncture was done to determine fetal scalp blood pH. The fetal heart rate response was recorded for both vibratory acoustic stimulation and fetal scalp puncture. No instance of fetal acidosis occurred in the presence of an acceleration to either vibratory acoustic stimulation or fetal scalp puncture. Vibratory acoustic stimulation was more likely to elicit an acceleration than fetal scalp puncture in the nonacidotic fetus. Vibratory acoustic stimulation is less invasive and may be used in some instances in which fetal scalp blood puncture for pH determination is technically impossible.

Intrapartum vibrator acoustic stimulation of the human fetus during episodes of decreased heart rate variability

The effects of intrapartum vibratory acoustic stimulation during periods of decreased fetal heart rate variability were studied in 25 healthy term fetuses. Fetal monitoring and real-time ultrasound scanning were used simultaneously to detect fetal response. Vibratory acoustic stimulation was provided by an artificial larynx generating a signal at 85 dB and 85 Hz. This stimulus was applied for 5 seconds on the maternal abdomen over the fetal head after a 20-minute period of decreased fetal heart rate variability. All fetuses reacted with an immediate fetal heart rate acceleration of at least 10 bpm (range: 10 to 35 bpm, mean +/- SD = 18.4 +/- 7.0), and 19 fetuses also had sudden fetal body movement. A deceleration of the fetal heart rate after the initial acceleration was observed in nine fetuses (range: 15 to 70 bpm, mean +/- SD = 45.5 +/- 16.5). The implications of these findings are discussed in relation to the possible use of fetal vibratory acoustic stimulation for intrapartum surveillance.

Human fetal responses to vibrator acoustic stimulation from twenty-six weeks to term

Eighty-three healthy pregnant women between 26 and 40 weeks' gestational age were studied to examine effects of a 5-second external vibratory acoustic stimulus on the fetal heart rate, fetal breathing, and gross fetal body movement patterns. There was an immediate fetal heart rate response, following stimulus, characterized by an increase in duration of fetal heart rate accelerations from 26 weeks to term with an increase in basal fetal heart rate after 30 weeks. There was also a delayed response after 33 weeks' gestation, which consisted of an increase in the number of fetal heart rate accelerations and the incidence of gross fetal body movements for up to 1 hour after a 5-second stimulus with the electronic artificial larynx. Term (36 to 40 weeks) fetuses made breathing movements more irregularly after vibratory acoustic stimulation. We suggest that human fetal responses to stimulation with the electronic artificial larynx may reflect a functional maturation of the fetal central nervous system.

Neonatal auditory acuity following in utero vibratory acoustic stimulation

The fetal heart rate response to externally applied vibratory acoustic stimulation is currently being evaluated as a test of fetal well-being. We have examined the safety of this procedure by subsequent testing of the auditory nerve and brain stem evoked responses in the neonates. The results demonstrated no differences in auditory acuity when control infants were compared with infants previously exposed to antenatal vibratory acoustic stimulation.

External vibratory acoustic stimulation near term: Fetal heart rate and heart rate variability responses

Twenty-five pregnant women between 36 and 40 weeks' gestational age were studied to examine effects of a 5-second external vibratory acoustic stimulus on the fetal heart rate and fetal heart rate variability. Where was an immediate significant increase in the basal heart rate, which persisted for 1 hour after the stimulus, compared to that of the control subjects. There was also a significant increase in the total time during which accelerations occurred for the first 20 minutes after the stimulus. There were no changes in computer-derived indices of fetal heart rate variability. Maternal blood pressure and heart rate were not altered following vibratory acoustic stimulus. We hypothesize that external vibratory acoustic stimulus causes a change from a state of sleep to a state of wakefulness in near term healthy fetuses.

Effects of vibratory acoustic stimulation on human fetal breathing and gross fetal body movements near term

Twenty-five pregnant women between 36 and 40 weeks' gestational age were studied to examine effects of a 5-second external vibratory acoustic stimulus on fetal breathing and gross fetal body movement patterns. When the study period was compared with the control period, there was an immediate significant decrease in the incidence of fetal breathing movements that persisted for 1 hour after the stimulus. Moreover the fetal breathing pattern was more irregular for the hour after the stimulus. There was also a significant but delayed increase in the incidence of gross fetal body movements that persisted for 1 hour after the stimulus. We hypothesize that an external vibratory acoustic stimulus causes a change from a state of sleep to a state of wakefulness in near-term healthy fetuses.

Fetal response to vibratory acoustic stimulation in periods of low heart rate reactivity and low activity

The fetal response to vibratory acoustic stimulation during periods of low fetal activity and low fetal heart rate reactivity was studied in 10 healthy pregnant women at term. In each case, two periods of low reactivity were studied. Consecutive cases alternated: The vibratory acoustic stimulus was applied 10 minutes after the first nonreactive period in half of the cases; the remainder were stimulated during the second nonreactive period. The unstimulated period served as a control. After vibratory acoustic stimulation the baseline fetal heart rate, the mean number of fetal heart rate accelerations, and, the number of fetal movements were significantly increased compared with values in the control nonstimulated periods (p < 0.0001). This consistent response to vibratory acoustic stimulation may prove to be clinically useful in altering periods of low reactivity observed during nonstress testing of normal fetuses.