Heart rate as an indicator of the behavioral state. Studies in the newborn infant and prospects for fetal heart rate monitoring

Earthquake Experience at Different Trimesters during Pregnancy Is Associated with Leukocyte Telomere Length and Long-term Health in Adulthood

Leukocyte telomere length (LTL) is a predictor of age-related diseases, cancer, and even early mortality. Prenatal stress experience has been suggested to associate with short LTL and an increased disease risk in adult life. The present study aimed to evaluate the 39-year effects of prenatal earthquake stress (PES) exposure on LTL and increased age-related disease risk in adulthood. Here, we compared the LTL in the subjects who were exposed to PES to healthy controls (CN) and evaluated whether stress exposure at different times during pregnancy is associated with a shorter LTL and long-term health conditions in adulthood. LTL was measured in 100 adults who experienced the 1976 7.8 Richter scale Tangshan earthquake of the Hebei province in utero and divided them into first, second, and third trimester groups according to the exposure timing during pregnancy. A total of 80 healthy volunteers from Shijiazhuang of the Hebei province were also assessed for their LTL. The telomere-to-single copy gene (T/S) ratio of the PES group (0.78 ± 0.06, p = 0.04) showed a significantly lower LTL than the CN group (0.97 ± 0.08). The results of the LTL analysis indicated that the subjects who experienced PES in the second (0.69 ± 0.09, p = 0.04) or third trimester (0.67 ± 0.76, p = 0.02) showed significantly shorter LTLs compared with those in the first trimester group (0.99 ± 0.12). A fully adjusted regression model indicated the same conclusions. In addition, we found that systolic pressure (SBP; 129.32 ± 14.86 mmHg, p = 0.041), body mass index (BMI; 22.54 ± 2.71, p = 0.046), and low-density lipoprotein (LDL; 3.09 ± 0.98 mmol/L, p = 0.048) in the subjects with PES were significantly higher than those measurements in the CN subjects (SBP; 122.06 ± 10.55 mmHg; BMI; 20.24 ± 2.13; LDL; 2.91 ± 0.76 mmol/L), and there was a significant negative correlation between an increased adult hypertension risk and a shorter LTL.

Aerobic exercise during pregnancy and presence of fetal-maternal heart rate synchronization

It has been shown that short-term direct interaction between maternal and fetal heart rates may take place and that this interaction is affected by the rate of maternal respiration. The aim of this study was to determine the effect of maternal aerobic exercise during pregnancy on the occurrence of fetal-maternal heart rate synchronization.

Heart rate variability: a review

Heart rate variability (HRV) is a reliable reflection of the many physiological factors modulating the normal rhythm of the heart. In fact, they provide a powerful means of observing the interplay between the sympathetic and parasympathetic nervous systems. It shows that the structure generating the signal is not only simply linear, but also involves nonlinear contributions. Heart rate (HR) is a nonstationary signal; its variation may contain indicators of current disease, or warnings about impending cardiac diseases. The indicators may be present at all times or may occur at random-during certain intervals of the day. It is strenuous and time consuming to study and pinpoint abnormalities in voluminous data collected over several hours. Hence, HR variation analysis (instantaneous HR against time axis) has become a popular noninvasive tool for assessing the activities of the autonomic nervous system. Computer based analytical tools for in-depth study of data over daylong intervals can be very useful in diagnostics. Therefore, the HRV signal parameters, extracted and analyzed using computers, are highly useful in diagnostics. In this paper, we have discussed the various applications of HRV and different linear, frequency domain, wavelet domain, nonlinear techniques used for the analysis of the HRV.

Heart rate variability: a review

Heart rate variability (HRV) is a reliable reflection of the many physiological factors modulating the normal rhythm of the heart. In fact, they provide a powerful means of observing the interplay between the sympathetic and parasympathetic nervous systems. It shows that the structure generating the signal is not only simply linear, but also involves nonlinear contributions. Heart rate (HR) is a nonstationary signal; its variation may contain indicators of current disease, or warnings about impending cardiac diseases. The indicators may be present at all times or may occur at random-during certain intervals of the day. It is strenuous and time consuming to study and pinpoint abnormalities in voluminous data collected over several hours. Hence, HR variation analysis (instantaneous HR against time axis) has become a popular noninvasive tool for assessing the activities of the autonomic nervous system. Computer based analytical tools for in-depth study of data over daylong intervals can be very useful in diagnostics. Therefore, the HRV signal parameters, extracted and analyzed using computers, are highly useful in diagnostics. In this paper, we have discussed the various applications of HRV and different linear, frequency domain, wavelet domain, nonlinear techniques used for the analysis of the HRV.

Heart rate variability: a review

Heart rate variability (HRV) is a reliable reflection of the many physiological factors modulating the normal rhythm of the heart. In fact, they provide a powerful means of observing the interplay between the sympathetic and parasympathetic nervous systems. It shows that the structure generating the signal is not only simply linear, but also involves nonlinear contributions. Heart rate (HR) is a nonstationary signal; its variation may contain indicators of current disease, or warnings about impending cardiac diseases. The indicators may be present at all times or may occur at random-during certain intervals of the day. It is strenuous and time consuming to study and pinpoint abnormalities in voluminous data collected over several hours. Hence, HR variation analysis (instantaneous HR against time axis) has become a popular noninvasive tool for assessing the activities of the autonomic nervous system. Computer based analytical tools for in-depth study of data over daylong intervals can be very useful in diagnostics. Therefore, the HRV signal parameters, extracted and analyzed using computers, are highly useful in diagnostics. In this paper, we have discussed the various applications of HRV and different linear, frequency domain, wavelet domain, nonlinear techniques used for the analysis of the HRV.

Arterial blood flow and autonomic function in full-term infants

OBJECTIVES

To investigate variations in the autonomic functions and blood-flow velocity of the arteries supplying to the brainstem in supine and prone positions.

METHODS

Forty-one full-term infants were studied at the age of 24-72 h. Each infant underwent respiratory, cardiac and eye movement analyses in supine and prone positions. In addition, blood-flow velocity of the basilar and vertebral arteries was measured with a 2 MHz probe for 5 min in each position. Two time domain measures of heart rate variability (HRV) (Standard deviation of normal R-R intervals for long-term and pNN50 for short-term variability) were employed.

RESULTS

Significantly decreased short- (P<0.001) and long (P = 0.003)-term variabilities were observed in prone when compared with supine position. Increased short-term variability in active sleep with no interaction with position was observed (P = 0.005). A significant decreased mean (P = 0.001) and peak (P = 0.001-0.003) blood-flow velocity in prone when compared with supine position were measured in all three arteries supplying to the brainstem. No significant correlation between HRV and arterial blood-flow velocity (ABFV) was observed in either position.

COMMENT

The results of the present study in agreement with previous studies reflect the vulnerability of infants in prone position as related to brainstem function. However, it appears that ABFV and autonomic functions as reflected by HRV are independent physiological measures, possibly indicating regulation autonomy of the central nervous system.

Laserspectroscopy in the fetus during labour

The newly available modified laserspectroscopy for fetal physiologic measurements provides information about biochemical parameters and is potentially an additional technique for fetal surveillance.

METHOD

Using laserspectroscopy it was possible to trace changes in absorbances at four different wavelengths and to calculate relative changes of HbO2, desaturated haemoglobin, total haemoglobin, and cytochrome aa3. Using an experimental set-up with fetal lamb during intermittend cord occlusion, we were able to study tissue oxygenation of the fetal brain (tpO2) under defined conditions. Furthermore, the NIR sensor was used during physiologic measurements in the human fetus.

RESULTS

As had been proposed earlier, it is obvious that the tolerance to hypoxia is increased after cord compression is repeated, as is indicated by the shifting of the cytochrome dissociation curve to the left. In the human fetus without fetal distress we observed stable values with only minor fluctuations related to changes of intrauterine pressure. On the other hand, in cases where there was an intrauterine complication the deterioration of oxygenation was detected form a decrease in HbO2 and cytochrome aa3.

DISCUSSION AND CONCLUSION

The routinely used CTG has been criticised for the effect of leading to an unacceptably high number of cesarean sections. Information on biochemical variables leads to better identification of fetal distress. In comparison to fetal blood sampling NIR laserspectroscopy holds the promise of a non-invasive tool providing continues monitoring.

Spectral analysis of heart rate variability in spontaneously breathing very preterm infants

The influence of maturation, sleep state and respiration on heart rate variability was studied in 16 spontaneously breathing preterm infants (< 33 weeks). ECG, respiratory impedance curve and movements were recorded four times a day, during the first three days of life. The power content of selected frequency bands of the R-R interval power spectrum, as well as respiratory frequency and breath amplitude oscillation frequency, were calculated for 3-min periods. An increase in low-frequency heart rate variability with gestational age was found. High-frequency variability increased during early postnatal life. Sleep state influenced very low-frequency heart rate variability. The amount of respiratory sinus arrhythmia and breath amplitude sinus arrhythmia was determined mainly by respiratory rate and breath amplitude oscillation frequency, respectively. The influences of gestational and postnatal age on heart rate variability might be due to an increase in sympathetic tone before birth and a change in parasympathetic-sympathetic balance after birth. Respiration has an important influence on heart rate variability, even in very preterm infants.

Heart rate variation during fetal behavioural states 1 and 2

Fetal heart rate (FHR) variation was numerically assessed in relation to behavioural states in 34 normal near term fetuses, in order to study the normal ranges of FHR variation during state 1F and 2F and to determine possible factors influencing variation in these states. In all individuals 2-h recordings were made of fetal heart rate, and body and eye movements. FHR variation was quantified using the Sonicaid System 8000. During both 1F and 2F there was a large range in variation, with a wide overlap in variation between both states (mean 1-min range in pulse intervals 16-53 ms and 36-97 ms, respectively). In all fetuses variation was higher during 2F than during 1F. The large ranges in variation were mainly caused by differences in basal heart rate and the correlation coefficients between rate (beats/min) and variation were -0.68 and -0.49 for 1F and 2F, respectively. Other reasons for a relatively high FHR variation during 1F included 'pseudo' sinusoidal patterns related to fetal sucking or mouth movements and relatively flat periods sporadically interrupted by an acceleration. With the System 8000, periods of low and high variation are identified using fixed criteria. Because of the large overlap in variation between both states, these episodes poorly correlated with the underlying behavioural states. Objective identification of the heart rate patterns during states 1F and 2F requires incorporation of heart rate itself in the analysis. As yet, 'global' visual identification of heart rate patterns is superior to computer analysis in identifying the underlying fetal behavioural states.

Quantitated fetal heart rhythm at 20, 32 and 38 weeks of gestation and dependence on rest-activity patterns

Quantitative parameters of fetal heart rate (FHR) were automatically analysed at 20, 32 and 38 weeks of pregnancy. FHR was obtained both by the fetal ECG method and by wide range Doppler ultrasound with autocorrelation. At 32 and 38 weeks, FHR was studied in relation to fetal rest-activity according to the fetal behavioural state concept (coincidence 1F and 2F). Basal fetal heart rate was significantly higher at 20 weeks of gestation than at 32 and 38 weeks. The number of accelerations increased significantly from 20 weeks to 32 and 38 weeks for C2F periods. Parameters of FHR variability, i.e. ID, ABB, LTI indices and bandwidth, were higher during periods C2F compared to periods C1F. Lowest values of all four parameters were found at 20 weeks gestation. The ID index, which is a measure of short-term variability increased significantly between 32 to 38 (C2F). The absolute values of ID, ABB and LTI were lower for ultrasound recordings than for the fetal ECG.

Influences on heart rate variability in spontaneously breathing preterm infants

To investigate the influence of maturational and physiological factors on heart rate variability in spontaneously breathing very preterm infants (n = 29) a multiparametric study was performed during the first 3 days of life in infants born at a gestational age below 33 weeks. Four times a day, RR-intervals, respiration curve and rate, transcutaneously measured blood gases and observed body movements were recorded while the infants were asleep. All data were stored simultaneously in a micro-computer. Non-invasively measured blood pressure and patency of the ductus arteriosus were documented as well. Four sets of short- (STV) and long term variability (LTV) indices were calculated. Both STV and LTV appeared to be significantly influenced by conceptional and postnatal age in the appropriate for gestational age infants. LTV was influenced by the behavioural state and body movements. During state coincidence 2 ('active sleep') LTV was influenced by respiratory rate and the variations in transcutaneous PO2. An effect of blood pressure or ductus patency could not be demonstrated.

The influence of respiratory distress syndrome on heart rate variability in very preterm infants

In a multi-parametric study the influence of pathological neonatal conditions on heart rate variability was investigated in 60 preterm infants born at a gestational age below 33 weeks. Measurements were performed during the first 3 days of life. Four times a day, RR-intervals, respiration curve and rate, transcutaneously measured blood gases and observed body movements were recorded while the infants were asleep. All data were stored simultaneously in a micro-computer. Severity of respiratory distress syndrome (RDS), patency of ductus arteriosus and periventricular haemorrhage were documented as well. Four sets of short- (STV) and long-term variability (LTV) indices were calculated. Severe RDS was associated with a significant decrease in LTV. The influence of RDS on LTV persisted after correction for conceptional age, postnatal age, behavioural state and variations in respiratory rate and in transcutaneous PO2. Infants with a symptomatic patent ductus arteriosus had lower LTV than controls with the same severity of RDS. STV was predominantly influenced by postnatal and conceptional age, and tended to be lower in infants with periventricular haemorrhage.

Fetal heart rate response to vibroacoustic stimulation during low and high heart rate variability episodes in late pregnancy

In 52 women in late pregnancy, the mean durations of transient fetal tachycardia after vibroacoustic stimulation during low fetal heart rate variability (4.8 minutes) and high fetal heart rate variability (6.3 minutes) were similar. The fetal heart rate continued with high variability in all cases, suggesting that the fetus did not return to its prestimulation state after vibroacoustic stimulation during quiescence. In 10 women, the duration of high variability after vibroacoustic stimulation during low fetal heart rate variability was significantly shorter (mean, 22 minutes) than the preceding (mean, 36 minutes) or subsequent (mean, 43 minutes) high-variability components of complete rest activity cycles. In another 10 women, the duration of high variability after vibroacoustic stimulation during high fetal heart rate variability was similar to preceding and subsequent high-variability episodes. In these 20 women, the next complete rest-activity cycle after vibroacoustic stimulation was not different in duration to the complete cycle recorded on the previous day.

Longitudinal assessment of behavioural transitions in healthy human fetuses during the third trimester of pregnancy

A longitudinal study was performed on 35 healthy fetuses in order to evaluate the developmental course of behavioural transitions during the last trimester of pregnancy. A progressive decrease in the duration of transitions as a function of gestational age was evidenced for both transitions from 1F to 2F and transitions from 2F to 1F. Concerning the sequence in change of behavioural variables (fetal heart rate, fetal eye movements and fetal gross body movements) a random distribution was found until 30 weeks for 1F to 2F transitions and until 34 weeks for 2F-1F transitions. After these gestational ages fetal heart rate and fetal gross body movements respectively become the first variable to change during 1F-2F and 2F-1F transitions. Reference values for these parameters are calculated in order to provide a basis for the diagnosis of behavioural abnormalities in high risk fetuses.

Coincidence of behavioural state parameters in the human fetus at three gestational ages

The fetal behavioural state concept was used to study fetal rest-activity cycles in normal pregnancies at gestational ages of 32 and 38 weeks. In addition, it was investigated if clustering of fetal movements was already present in recordings obtained at 20 weeks. At 20 weeks, 17 periods lasting longer than 3 min were found in which fetal body movements were absent. The mean duration of these periods was 4.0 +/- 0.8 min. On the basis of random scattering of movements on a time axis, it appeared unlikely that these periods of inactivity occurred by chance alone. At 32 and 38 weeks, data on body movements were combined with data on eye movements and the FHR pattern. At 32 weeks, true fetal behavioural states were not found. The average coincidence of 1F to 4F was 58%, while only 23% was to be expected if state parameters had fulfilled state criteria purely by chance. At 38 weeks, coincidence of 1F to 4F had increased to 80% (P less than 0.001). Expected coincidence purely by chance was 30%. True fetal behavioural states were found in 17 out of 35 recordings. For transitions from 1F into 2F, the FHR changed relatively early, i.e. as first or second parameter, while for the reverse transitions it changed relatively late (P less than 0.05). There was no clearly preferred sequence for body and eye movements within transitions.

SCSB method compared to EEG-based polygraphy in sleep state scoring of newborn infants

Knowledge of the sleep state is important in physiological studies since many physiological variables show different properties in different sleep states. The recently developed static charge sensitive bed (SCSB) method allows long-term recordings of body movements, respiration and ballistocardiogram without electrodes attached to the subject. The recordings are easy to carry out and they do not disturb the subject in any way. The recorded variables are basic characteristics of different sleep states. SCSB-recordings and electroencephalography (EEG) based polygraphy as well as blind sleep state scoring were carried out in 8 newborn infants. The positive correlation between SCSB-scoring and EEG-based polygraphy scored by two clinical neurophysiologists was 68.1 and 64.1%. Only in 2% of all epochs was active sleep scored as quiet sleep or vice versa. The results indicate the usefulness of the SCSB method in sleep state scoring of newborn infants.

The influence of physiological parameters on long term heart rate variability in healthy preterm infants

The instantaneous heart rate shows a variation around the mean heart rate caused by cardioregulatory mechanisms which are mediated through the sympathetic and vagal autonomic nervous system. To gain more insight into the influence of physiological parameters on neonatal heart rate variability a study was performed in four healthy preterm newborns during the first five days of life. Instantaneous heart rate, respiration rate, transcutaneous pO2, blood pressure and behaviour were recorded during 40 minutes four times a day. Long term heart rate variability was calculated as the difference between p95 and p5 of instantaneous heart rate values sampled during three minutes. A clear relationship between long term variability and age (maturity of the autonomic nervous system), respiration rate (respiratory sinus arrhythmia or a tidal volume mediated effect) and behaviour (increase of sympathetic tone during REM sleep) was found. No influence of blood pressure, heart rate, and transcutaneous pO2 within physiological ranges could be detected. The relative influence of the different physiological parameters on heart rate variability has to be established before the value of heart rate variability as a monitoring tool in neonatal intensive care can be investigated.

Fetal heart rhythms during behavioural state 1F

Behavioural state 1F (quiet sleep) of the term fetus is defined on the basis of absence of eye and body movements, and the presence of a specific heart rate pattern (FHRP A), characterized by a stable heart rate with a small oscillation bandwidth. In the present paper the fetal heart rate pattern was studied in 39 enclosed periods with absence of fetal eye and body movements. In 37 periods the heart rate pattern met the criteria of FHRP A. Within FHRP A various distinct types of heart rhythm could be distinguished related to presence of breathing or regular mouthing and complete absence of movements. The bandwidth in the various heart rhythms differed significantly and was largest during breathing movements. During regular mouthing an oscillatory pattern was present with a frequency similar to the frequency of the clusters of mouthing movements. In 2 periods the heart rate deviated from the definition for FHRP A, i.e. a sinusoidal-like rhythm associated with sucking movements. These observations demonstrate the strong association between the fetal heart rate pattern and fetal movements during behavioural state 1F.

Computerized assessment of fetal behavioral states

Fetal heart rate and fetal movements provide information on the fetal condition. In the near term human fetus, four behavioural states have been described based upon heart rate patterns and presence or absence of eye and body movements. For our studies concerning fetal physiology as well as the influence of maternal antiepileptic medication and the effects of intrauterine growth retardation on the fetal condition, we developed a computerized system for acquisition and storage of fetal heart rate signals and observed fetal movements. Fetal heart rate is recorded using a commercially available monitor combined with a home-made computer interface. Fetal movements are observed using two real-time ultrasound units. The observers handle keyboards to mark occurrence and duration of various types of fetal movements, and pedals to mark the visibility of the observed part of the fetal body. Keyboards and pedals are scanned by the computer. Special techniques are used to store heart rate and movement signals in an efficient way. Three experts determine fetal heart rate patterns by application of a Delphi group opinion procedure. Fetal behavioral states are identified by the computer using the results of the Delphi procedure, and performing the so-called extended automatic window procedure. This procedure identifies periods of presence and periods of absence of fetal eye and body movements, and incorporates the loss of visibility of the ultrasound images during the recording session. Fetal heart rate variability indices and distributions of fetal movements can be computed in the context of the fetal behavioral state concept.

Differentiation of healthy newborns and newborns-at-risk by spectral analysis of heart rate fluctuations and respiratory movements

Neonatal heart rate and its interaction with respiration were computerized by spectral and coherence analysis (FFT) to differentiate healthy newborns (n = 9) from newborns with mild neonatal risk (n = 20). An increased mean heart rate and decreased total variability have been found in newborns-at-risk. Respiratory Sinus Arrhythmia is diminished in newborns-at-risk possibly caused by an impairment of autonomic brain stem function. Furthermore, Respiratory Sinus Arrhythmia holds a central position in differentiating healthy newborns and newborns-at-risk with and without neurological abnormalities during the first year of life. Respiratory Sinus Arrhythmia is diminished in newborns-at-risk showing these abnormalities. None of the parameters discriminates between the two groups of risk infants. The final prognostic value of our results must be confirmed in further clinical follow-up examinations.

Maternal perception of fetal movements: the optimal duration of a recording period

A regular count of perceived fetal movements by the mother has been proposed as a screening method for the early recognition of fetal distress. Absence or a strongly decreased number of fetal movements during a particular period is considered as a sign of fetal distress. In the study presented, the optimal duration of a recording period for the maternal perception of fetal movements was examined. 186 pregnant patients at gestational ages of 32 and 38 weeks were asked to mark each perceived fetal movement on a time axis for two continuous hours. From these patients an 'optimal' group of 143 pregnancies was selected to constitute the study group. A window technique was applied to the 2 h recordings, searching for periods in which 0, 1 or 2 fetal movements were noted. 23% of the recordings at 32 weeks and 14% at 38 weeks showed absence of fetal movements for at least 30 min. At both 32 weeks and 38 weeks there was absence of fetal movements for more than 1 h in only 1.5% of the recordings. The findings are in agreement with the fetal behavioural state concept. A recording time of 1 h exceeds the normal duration of a fetal quiet-sleep state and minimizes the risk of unjustified suspicion of fetal distress.

Fetal responses to acoustic stimulation depend on heart rate variability pattern, stimulus intensity and repetition

Fetuses (37-40 wks DA) were exposed to three successive presentations of a 5-s high-pass filtered (800 Hz) pink noise either at 105 dB or at 110 dB SPL. Stimulations were given during high or low variability heart rate (HR) patterns (HV or LV) which presumably correspond mostly to active and quiet sleep episodes, respectively. The proportion of fetuses showing cardiac response (CR) was always greater than the proportion showing leg movement (LM) but the presence of an accompanying leg movement always increased the amplitude of CR, independent of HR pattern, stimulus repetition and intensity. Fetal reactiveness always diminished with stimulus repetition but diminished more on the three examined dimensions (CR ratio, LM ratio and CR amplitude) with LV infants than with HV infants, and more with the 105 dB stimulus than with the 110 dB stimulus. More importantly, stimulus parameters and HR patterns interacted. At 110 dB in HV, neither the median amplitude of the CRs nor the probability of a CR changed over trials but the probability of a concommittant LM decreased. At 110 dB in LV, repetition induced a decrement on all three response dimensions from the second trial onwards. At 105 dB in HV, LM decreased rapidly, as much as at 110 dB in LV. Thus, state, as reflected by HR pattern, plays a significant role in determining the occurrence and the amplitude of the CR and the occurrence of a LM which, in turn, will enhance the CR amplitude.

Classification of fetal and neonatal heart rate patterns in relation to behavioural states

For the assessment of behavioural states in the human fetus, the fetal heart rate (FHR) pattern is one of the state variables. A statistical method is described to classify FHR patterns. FHR recordings were made between 38 and 40 wk gestation. The tachogram was averaged over 3-s intervals. For FHR segments of 3 min duration the parameters of an autoregressive-moving average (ARMA) model were estimated. Simulated FHR patterns, generated by using these estimated ARMA parameters, resembled real recordings. The ARMA parameters were used as features for a retrospective classification of the FHR segments, using a linear discriminant function. The classification by the above method was compared with an independent visual classification of the FHR patterns. The computer/observer classification agreement was 85% (kappa = 0.70). These data were compared with classification results for neonatal heart rate segments. For prospective classification of FHR patterns a moving discriminant function was introduced.

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 with values in the control nonstimulated periods (p less than 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.

Heart rate response related to body movements in healthy and neurologically damaged infants during sleep

Sixteen infants were studied with the static charge sensitive bed (SCSB) method. This method is newly developed for neonatal recordings and it allows recording of body movements, respiration and of the ballistocardiographic signal. Eight healthy newborn infants and eight infants with clear neurological dysfunction were recorded and the heart rate acceleration-deceleration responses to body movements during sleep were studied. Healthy infants had a constant heart rate response to body movements but infants with neurological symptoms had either too weak or hyperactive reactions. This finding can be explained by abnormal function of the autonomic nervous system in infants with disturbance of the central nervous system.

Behavioral states in the human fetus during labor

Behavioral states in the near-term human fetus have been described during pregnancy. The aim of this study was to observe whether these same states are present during labor. Nine patients with uncomplicated singleton pregnancies participated. Fetal heart rate and uterine contractions were recorded. Fetal eye, mouth, rotation, and retroflexion of the head were observed by real-time ultrasound. Fetal movements were recorded with coded event-markers. Behavioral states were identified by the movement pattern. A total of 13 ultrasound observations, varying from 25 to 66 minutes, were obtained. Optimal viewing was present at least 60% and on the average 80% of the time. State 1F (quiet sleep), state 2F (active sleep), and state 3F (quite awake), as well as a total of 10 state changes, were identified during labor in spite of increasing contractions and/or ruptured membranes. These observations demonstrate existence of alternating behavioral states in the healthy term fetus during labor.

Feasibility of prenatal hearing test

Variability in foetal responses to sound stimulations is described and the effect of the different factors involved in this reactivity, in particular the physical characteristics of the stimulus and state of alertness of the foetus, is discussed. Results obtained with a high pass filtered pink noise at a 106, 109 and 113 dB SPL on 37-40 week foetuses are given to illustrate this dependency. For all tested levels, responsiveness was reduced after repetition of the stimulus. This was observed even at 113 dB when stimulation was preceded by a series of lower level stimuli to which foetuses were (or became) unresponsive. Motor responses (lower limb movements) were the first and the most affected by stimulus repetition, followed by cardiac response decrement--but with a lower proportion of non-responses, especially at 113 dB. Consequently, with this specific stimulus, cardiac reactivity seems a more reliable parameter to examine when more than one stimulus is needed to ascertain foetal hearing. It was also demonstrated that foetuses were much less reactive when stimulated during low heart rate variability sequences than during high heart rate variability. Testing of prenatal hearing seems feasible in utero and should be a promising method for detecting gross hearing impairment once the influence of each biophysical parameter has been carefully studied.

External physical stimulation of the human fetus during episodes of low heart rate variation

The effect of shaking the fetus through the maternal abdomen during episodes of low (nonreactive) fetal heart rate variation was studied in 10 healthy nulliparous women near term. Heart rate monitoring from an abdominal electrocardiogram was combined with real-time scanning for body movements and fetal breathing. In each fetus two episodes of low variation were examined, one during which external stimulation was performed and one as a control without stimulation. There were no differences between the groups, with or without stimulation, in the duration of the nonreactive trace or heart rate variation or in the incidence of breathing or body movements. Therefore, shaking the fetus during a nonreactive heart rate episode has no useful purpose. The results are comprehensible in the light of fetal and neonatal behavioral states.

A comparison of episodic heart-rate patterns in the fetus and newborn

Fourier analysis was applied to episodes of high and low heart-rate variation in the near-term fetus. The spectral densities of the variations in pulse intervals from 1 to 7 cycles/min, were almost identical with those found by De Haan et al. (1977) in the newborn infant during both active and quiet sleep. A computer programme, designed to separate low and high heart-rate variation episodes in the fetus, identified seven of the eight quiet sleep episodes in four infants. None of the other neonatal behavioural states had low heart-rate variation. It was concluded that, with other published data, there is increasing, although indirect, evidence that low heart-rate variation episodes indicate quiet sleep in the human fetus near term.

Analysis of heart rate and beat-to-beat variability: Interval difference index

The relationshp between the RR interval length (RR) and the RR interval-to-interval differences (RR differences) was investigated. Data on heart rate were obtained from 11 newborn infants in well-defined behavioral states undergoing polygraphy. It was found that the RR differences were strongly dependent on the RR interval length in all behavioral states. The relationship between the RR differences (y) and the interval length (RR) could be described by the equation y = alpha (RR-320)1.5 for the interval length in the investigated range from 375 to 605 msec. On the basis of this relationship the interval difference index (ID index) was constructed for the quantification of beat-to-beat heart rate variability. The ID index showed good independence from the long-term irregularity index (LTI index). Other statistical parameters proposed for the quantification of beat-to-beat heart rate variability are discussed and compared with the ID index.