Complementary and non-coincident increases in heart rate variability and irregularity during fetal development

Exploring the Influence of Fetal Sex on Heart Rate Dynamics Using Fetal Magnetocardiographic Recordings

Fetal sex has been associated with different development trajectories that cause structural and functional differences between the sexes throughout gestation. Fetal magnetocardiography (fMCG) recordings from 123 participants (64 females and 59 males; one recording/participant) from a database consisting of low-risk pregnant women were analyzed to explore and compare fetal development trajectories of both sexes. The gestational age of the recordings ranged from 28 to 38 weeks. Linear metrics in both the time and frequency domains were applied to study fetal heart rate variability (fHRV) measures that reveal the dynamics of short- and long-term variability. Rates of linear change with GA in these metrics were analyzed using general linear model regressions with assessments for significantly different variances and GA regression slopes between the sexes. The fetal sexes were well balanced for GA and sleep state. None of the fHRV measures analyzed exhibited significant variance heterogeneity between the sexes, and none of them exhibited a significant sex-by-GA interaction. The absence of a statistically significant sex-by-GA interaction on all parameters resulted in none of the regression slope estimates being significantly different between the sexes. With high-precision fMCG recordings, we were able to explore the variation in fHRV parameters as it relates to fetal sex. The fMCG-based fHRV parameters did not show any significant difference in rates of change with gestational age between sexes. This study provides a framework for understanding normal development of the fetal autonomic nervous system, especially in the context of fetal sex.

Sex differences in heart: from basics to clinics

Sex differences exist in the structure and function of human heart. The patterns of ventricular repolarization in normal electrocardiograms (ECG) differ in men and women: men ECG pattern displays higher T-wave amplitude and increased ST angle. Generally, women have longer QT duration because of reduced repolarization reserve, and thus, women are more susceptible for the occurrence of torsades de pointes associated with drugs prolonging ventricular repolarization. Sex differences are also observed in the prevalence, penetrance and symptom severity, and also in the prognosis of cardiovascular disease. Generally, women live longer, have less clinical symptoms of cardiac diseases, and later onset of symptoms than men. Sex hormones also play an important role in regulating ventricular repolarization, suggesting that hormones directly influence various cellular functions and adrenergic regulation. From the clinical perspective, sex-based differences in heart physiology are widely recognized, but in daily practice, cardiac diseases are often underdiagnosed and untreated in the women. The underlying mechanisms of sex differences are, however, poorly understood. Here, we summarize sex-dependent differences in normal cardiac physiology, role of sex hormones, and differences in drug responses. Furthermore, we also discuss the importance of human induced pluripotent stem cell-derived cardiomyocytes in further understanding the mechanism of differences in women and men.

Fetal heart rate, heart rate variability, and heart rate/movement coupling in the Safe Passage Study

OBJECTIVE

To determine normative values for heart rate patterns in healthy fetuses.

METHODS

This research is from the Safe Passage Study conducted by the Prenatal Alcohol and SIDS and Stillbirth (PASS) Network. A standardized protocol assessed fetal heart rate (FHR), heart rate variability (HRV), and movement from 1655 fetuses at three-time points during gestation (20-24 weeks, 28-32 weeks, 34-38 weeks gestation).

RESULTS

FHR decreased while HRV increased over gestation. At the latter two ages, males had significantly lower FHR than females while there were no sex differences in FHR at 20-24 weeks. When accounting for the fetal state during late gestation (34-28 weeks), we found that males had significantly lower FHR than females in the active fetal state only.

CONCLUSION

Results demonstrate significant state, gestational age, and sex-related changes in cardiac activity, somatic activity, and autonomic function as the fetus approaches birth.

Entropy Measures in Analysis of Head up Tilt Test Outcome for Diagnosing Vasovagal Syncope

The paper presents possible applications of entropy measures in analysis of biosignals recorded during head up tilt testing (HUTT) in patients with suspected vasovagal syndrome. The study group comprised 80 patients who developed syncope during HUTT (57 in the passive phase of the test (HUTT(+) group) and 23 who had negative result of passive phase and developed syncope after provocation with nitroglycerine (HUTT(−) group)). The paper focuses on assessment of monitored signals’ complexity (heart rate expressed as R-R intervals (RRI), blood pressure (sBP, dBP) and stroke volume (SV)) using various types of entropy measures (Sample Entropy (SE), Fuzzy Entropy (FE), Shannon Entropy (Sh), Conditional Entropy (CE), Permutation Entropy (PE)). Assessment of the complexity of signals in supine position indicated presence of significant differences between HUTT(+) versus HUTT(−) patients only for Conditional Entropy (CE(RRI)). Values of CE(RRI) higher than 0.7 indicate likelihood of a positive result of HUTT already at the passive phase. During tilting, in the pre-syncope phase, significant differences were found for: (SE(sBP), SE(dBP), FE(RRI), FE(sBP), FE(dBP), FE(SV), Sh(sBP), Sh(SV), CE(sBP), CE(dBP)). HUTT(+) patients demonstrated significant changes in signals’ complexity more frequently than HUTT(−) patients. When comparing entropy measurements done in the supine position with those during tilting, SV assessed in HUTT(+) patients was the only parameter for which all tested measures of entropy (SE(SV), FE(SV), Sh(SV), CE(SV), PE(SV)) showed significant differences.

The complexity of hemodynamic response to the tilt test with and without nitroglycerine provocation in patients with vasovagal syncope

The paper presents a comparison of vasovagal syndrome occurrence in a head up tilt table test between patients with a positive result of passive tilt test and those with a positive result after pharmacological provocation. The study group consisted of 80 patients: 57 patients who experienced syncope in the passive phase of the test (43 women (aged: 35.6 ± 16.2) and 14 men (aged: 41.7 ± 15.6) and 23 patients who experienced syncope after pharmacological provocation (17 women (age: 32.3 ± 12) and 6 men (age: 43 ± 15). The main investigation was based on the assessment of monitored signals complexity: heart rate, blood pressure and stroke volume. The analysis of complexity in chosen measurement phases was performed with Sample Entropy. The investigation showed that the reactions of autonomic nervous system during tilt test and before syncope are similar for positive result of passive tilt test and positive result of tilt test with provocation. The differences in supine position occurred only in analysis based on impedance measurement (SV: p = 0.01). Significant differences were denoted for all signals just before the syncope (RRI, sBP, dBP: p = 0,00001 and SV: p = 0.01). In analysis of signals complexity the significant differences occurred just before the syncope for Sample Entropy of blood pressure (SampEn (sBP): p = 0.0008, SampEn (dBP): p = 0,0001).

Information Theory and Atrial Fibrillation (AF): A Review

Atrial Fibrillation (AF) is the most common cardiac rhythm disorder seen in hospitals and in general practice, accounting for up to a third of arrhythmia related hospitalizations. Unfortunately, AF treatment is in practice complicated by the lack of understanding of the fundamental mechanisms underlying the arrhythmia, which makes detection of effective ablation targets particularly difficult. Various approaches to AF mapping have been explored in the hopes of better pinpointing these effective targets, such as Dominant Frequency (DF) analysis, complex fractionated electrograms (CFAE) and unipolar reconstruction (FIRM), but many of these methods have produced conflicting results or require further investigation. Exploration of AF using information theoretic-based approaches may have the potential to provide new insights into the complex system dynamics of AF, whilst also providing the benefit of being less reliant on empirically derived definitions in comparison to alternate mapping approaches. This work provides an overview of information theory and reviews its applications in AF analysis, with particular focus on AF mapping. The works discussed in this review demonstrate how understanding AF from a signal property perspective can provide new insights into the arrhythmic phenomena, which may have valuable clinical implications for AF mapping and ablation in the future.

Comparison of diurnal variations, gestational age and gender related differences in fetal heart rate (FHR) parameters between appropriate-for-gestational-age (AGA) and small-for-gestational-age (SGA) fetuses in the home environment

Objective

To assess the influence of gender, time of the day and gestational age on fetal heart rate (FHR) parameters between appropriate-for-gestational-age (AGA) and small-for-gestational age (SGA) fetuses using a portable fetal ECG monitor employed in the home setting.

Methods

We analysed and compared the antenatal FHR data collected in the home setting on 61 healthy pregnant women with singleton pregnancies from 24 weeks gestation. Of the 61 women, 31 had SGA fetuses (estimated fetal weight below the tenth gestational centile) and 30 were pregnant with AGA fetuses. FHR recordings were collected for up to 20 h. Two 90 min intervals were deliberately chosen retrospectively with respect to signal recording quality, one during day-time and one at night-time for comparison.

Results

Overall, success rate of the fetal abdominal ECG in the AGA fetuses was 75.7% compared to 48.6% in the SGA group. Based on randomly selected episodes of heart rate traces where recording quality exceeded 80% we were able to show a marginal difference between day and night-time recordings in AGA vs. SGA fetuses beyond 32 weeks of gestation. A selection bias in terms of covering different representation periods of fetal behavioural states cannot be excluded. In contrast to previous studies, we neither controlled maternal diet and activity nor measured maternal blood hormone and heart rate as all mothers were monitored in the home environment.

Conclusion

Based on clinically unremarkable, but statistically significant differences in the FHR parameters between the AGA and SGA group we suggest that further studies with large sample size are required to assess the clinical value of antenatal fetal ECG monitoring.

Linear and nonlinear features of fetal heart rate on the assessment of fetal development in the course of pregnancy and the impact of fetal gender

OBJECTIVE

This work aims to investigate the impact of gestational age and fetal gender on fetal heart rate (FHR) tracings.

APPROACH

Different linear and nonlinear parameters indicating correlation or complexity were used to study the influence of fetal age and gender on FHR tracings. The signals were recorded from 99 normal pregnant women in a singleton pregnancy at gestational ages from 28 to 40 weeks, before the onset of labor. There were 56 female fetuses and 43 male.

MAIN RESULTS

Analysis of FHR shows that the means as well as measures of irregularity of FHR, such as approximate entropy and algorithmic complexity, decrease as gestation progresses. There were also indications that mutual information and multiscale entropy were lower in male fetuses in early pregnancy.

SIGNIFICANCE

Fetal age and gender seem to influence FHR tracings. Taking this into consideration would improve the interpretation of FHR monitoring.

Evolution of linear and nonlinear fetal heart rate indices throughout pregnancy in appropriate, small for gestational age and preterm fetuses: A cohort study

BACKGROUND AND OBJECTIVES

To assess the evolution of linear and nonlinear fetal heart rate (FHR) analysis throughout pregnancy in appropriate (AGA), small for gestational age (SGA) and preterm (PTB) fetuses.

METHODS

A prospective cohort study was carried out in 171 singleton pregnancies divided in three groups: AGA (n = 147), SGA (n = 13) fetuses and spontaneous PTB (n = 11). FHR was recorded with an external sensor from the 24th to the 40th week of gestation. Linear time- and frequency-domain and nonlinear FHR indices were computed on 10-min segments. Longitudinal analysis of indices throughout pregnancy was performed with generalized estimating equations, and receiver operating characteristic (ROC) curves were calculated for the prediction of SGA and PTB fetuses.

RESULTS

Increasing gestational age significantly affected most FHR indices, with a general increase in variability and entropy indices, and a decrease in mean FHR. The PTB group exhibited a significantly lower short-term variation, and no monotonic increase in the sympatho-vagal balance as observed in the AGA group. The SGA group exhibited higher long-term irregularity and lower short-term irregularity than the AGA group throughout gestation. In prediction of SGA and PTB, the largest areas under the ROC curves obtained were 0.76 and 0.78, respectively.

CONCLUSIONS

Linear and nonlinear FHR analysis provides useful information on the evolution of fetal autonomic nervous and complexity control systems throughout pregnancy, in relation with AGA, SGA and PTB fetuses, which may be helpful in clinical practice.

Gender-specific evolution of fetal heart rate variability throughout gestation: A study of 8823 cases

BACKGROUND

Fetal heart rate (FHR) variability throughout gestation reflects aspects of fetal development, and its analysis has been used for the assessment of fetal well-being.

AIM

The objective of this study was to provide a gender-specific analysis of the evolution of FHR variability indices throughout gestation, using linear time-domain, spectral and nonlinear FHR indices.

STUDY DESIGN

A large retrospective study was carried out using antepartum FHR recordings obtained from 4713 male and 4110 female fetuses, with normal pregnancy outcome, between 2004 and 2013, with gestational ages ranging between 25 and 40weeks.

OUTCOME MEASURES

FHR variability was analysed through linear time-domain methods, as well as using spectral analysis and entropy indices. Evolution of FHR indices throughout gestation was analysed through Spearman correlation coefficient. Comparison between male and female fetuses was performed using nonparametric bootstrap 95% confidence intervals for the median.

RESULTS

Mean FHR decreased significantly throughout gestation, whereas most variability indices increased. Sympatho-vagal balance measured by spectral analysis exhibited two local maxima at 29-30 and 34-35weeks and decreased afterwards. Entropy indices increased until around the 34th week, slightly decreasing after the 37th week. Female fetuses presented higher mean FHR and entropy from the 34th week afterwards, and lower short-term variability and sympatho-vagal balance in the same period.

CONCLUSIONS

Spectral and entropy analysis should be considered as a complement to conventional FHR variability analysis, aiming at a better characterization and follow-up of fetal development/maturation throughout gestation. Additionally, gestational age needs to be considered when defining reference ranges for FHR indices in systems of computerized analysis.

Simultaneous monitoring of maternal and fetal heart rate variability during labor in relation with fetal gender

Male gender is considered a risk factor for several adverse perinatal outcomes. Fetal gender effect on fetal heart rate (FHR) has been subject of several studies with contradictory results. The importance of maternal heart rate (MHR) monitoring during labor has also been investigated, but less is known about the effect of fetal gender on MHR. The aim of this study is to simultaneously assess maternal and FHR variability during labor in relation with fetal gender. Simultaneous MHR and FHR recordings were obtained from 44 singleton term pregnancies during the last 2 hr of labor (H_1, H₂ ). Heart rate tracings were analyzed using linear (time- and frequency-domain) and nonlinear indices. Both linear and nonlinear components were considered in assessing FHR and MHR interaction, including cross-sample entropy (cross-SampEn). Mothers carrying male fetuses (n = 22) had significantly higher values for linear indices related with MHR average and variability and sympatho-vagal balance, while the opposite occurred in the high-frequency component and most nonlinear indices. Significant differences in FHR were only observed in H₁ with higher entropy values in female fetuses. Assessing the differences between FHR and MHR, statistically significant differences were obtained in most nonlinear indices between genders. A significantly higher cross-SampEn was observed in mothers carrying female fetuses (n = 22), denoting lower synchrony or similarity between MHR and FHR. The variability of MHR and the synchrony/similarity between MHR and FHR vary with respect to fetal gender during labor. These findings suggest that fetal gender needs to be taken into account when simultaneously monitoring MHR and FHR.

Maternal abuse history and reduced fetal heart rate variability: Abuse-related sleep disturbance is a mediator

The consequences of childhood maltreatment are profound and long lasting. Not only does the victim of abuse suffer as a child, but there is mounting evidence that a history of maltreatment places the next generation at risk for significant psychopathology. Research identifies postnatal factors as affecting this intergenerational transmission of trauma. However, emerging evidence suggests that part of this risk may be transmitted before birth, passed on via abuse-related alterations in the in utero environment that are as yet largely unidentified. To date, no study has directly assessed the influence of pregnant women's abuse history on fetal neurobehavioral development, nor considered trauma-associated poor sleep quality as a mediator reflecting established physiological dysregulation. Using data from 262 pregnant adolescents (ages 14-19), a population at elevated risk for childhood maltreatment, the current study examined maternal emotional abuse history and sleep quality in relation to third-trimester fetal resting heart rate variability, an index of parasympathetic nervous system functioning. The results indicate that maternal emotional abuse history is indirectly associated with lower fetal heart rate variability via abuse-related sleep disturbances. These data demonstrate an association between maternal abuse histories and fetal development, showing that at least part of the intergenerational transmission of risk occurs during pregnancy.

Circadian changes and sex-related differences in fetal heart rate parameters

BACKGROUND

Previous researchers have studied circadian changes in the fetal heart rate (FHR) on small sample sizes and in a strictly controlled environment. This study was undertaken to investigate these changes during the late second and third trimesters, using a portable fetal electrocardiogram recording device (Monica AN24) in pregnant women in home and hospital environments with unrestricted mobility.

METHODS

This was a prospective cohort study of 54 pregnant women with uncomplicated singleton pregnancies between 25 and 40 weeks gestation. FHR recordings were made up to 16 h at home or in the hospital setting in the United Kingdom. FHR data over 90 min periods were averaged and the day (7:00 am-11:00 pm) and night (11:00 pm-7:00 am) data from the same individual were compared. Data were examined for evidence of sex-related differences.

RESULTS

During the night, there was a significant reduction in basal heart rate (bFHR) and a significant increase in short term variation (STV) and long term variation (LTV) (P < 0.05). Basal FHR decreased (P < 0.002), whereas LTV increased (P = 0.014) with advancing gestation. Male fetuses showed greater day: night variation than females regardless of gestation (P = 0.014). There was a higher bFHR in fetuses monitored during the day in hospital (P = 0.04).

CONCLUSION

This study demonstrates that there are sex-, environment and time-related differences in the FHR parameters measured. These differences may need to be considered taken when interpreting FHR data.

Sex-related differences in the development of fetal heart rate dynamics

BACKGROUND

Despite previous efforts to explain the general advantages of female fetuses over males regarding health, sex-related differences in the dynamics or complexity of fetal heart rate (FHR) variability and FHR maturation patterns have not yet been identified.

AIM

To make linear and nonlinear comparisons of antepartum FHR indices, dynamics, complexity, and reactivity to the non-stress test (NST) and vibroacoustic-stimulation test (VAST) in male and female fetuses.

STUDY DESIGN

A total of 3835 singleton term deliveries without maternal and fetal complications were divided into female (n=1849) and male (n=1986) groups, and subjected to comparison and analyses.

SUBJECTS

Linear FHR indices, approximate entropy (ApEn), sample entropy (SampEn), short-term/long-term exponents (α1/α2), correlation dimension (CD), NST and VAST criteria, and modified nonlinear reactive criteria (MNRC) were used to evaluate outcomes.

RESULTS

ApEn was consistently higher in female fetuses than in male ones. ApEn in female fetuses was maximal at 29-30 gestational weeks, while the increase in ApEn was delayed in male fetuses but more rapid, reaching its peak at 31-32 gestational weeks. In both sexes, CD increased up to term, and α2 rapidly decreased up to 31-32weeks in an analogous manner. The two sexes differed significantly in response to VAST at <31 gestational weeks and there was a structural difference in reactive patterns under MNRC.

CONCLUSIONS

Female fetuses exhibit greater heart rate dynamics in early gestational periods, suggesting that their cardiovascular system matures earlier than that of males. Male fetuses undergo a compensatory period of rapid change to catch up with females at term.

STUDIES IN FETAL BEHAVIOR: REVISITED, RENEWED, AND REIMAGINED

Among the earliest volumes of this monograph series was a report by Lester Sontag and colleagues, of the esteemed Fels Institute, on the heart rate of the human fetus as an expression of the developing nervous system. Here, some 75 years later, we commemorate this work and provide historical and contemporary context on knowledge regarding fetal development, as well as results from our own research. These are based on synchronized monitoring of maternal and fetal parameters assessed between 24 and 36 weeks gestation on 740 maternal-fetal pairs compiled from eight separate longitudinal studies, which commenced in the early 1990s. Data include maternal heart rate, respiratory sinus arrhythmia, and electrodrmal activity and fetal heartrate, motor activity, and their integration. Hierarchical linear modeling of developmental trajectories reveals that the fetus develops in predictable ways consistent with advancing parasympathetic regulation. Findings also include:within-fetus stability (i.e., preservation of rank ordering over time) for heart rate, motor, and coupling measures; a transitional period of decelerating development near 30 weeks gestation; sex differences in fetal heart rate measures but not in most fetal motor activity measures; modest correspondence in fetal neurodevelopment among siblings as compared to unrelated fetuses; and deviations from normative fetal development in fetuses affected by intrauterine growth restriction and other conditions. Maternal parameters also change during this period of gestation and there is evidence that fetal sex and individual variation in fetal neurobehavior influence maternal physio-logical processes and the local intrauterine context. Results are discussed within the framework of neuromaturation, the emergence of individual differences, and the bidirectional nature of the maternal-fetal relationship.We pose a number of open questions for future research. Although the human fetus remains just out of reach, new technologies portend an era of accelerated discovery of the earliest period of development

Sex differences in the fetal heart rate variability indices of twins

AIMS

To evaluate the differences in linear and complex heart rate dynamics in twin pairs according to fetal sex combination [male-female (MF), male-male (MM), and female-female (FF)].

METHODS

Fourteen twin pairs (6 MF, 3 MM, and 5 FF) were monitored between 31 and 36.4 weeks of gestation. Twenty-six fetal heart rate (FHR) recordings of both twins were simultaneously acquired and analyzed with a system for computerized analysis of cardiotocograms. Linear and nonlinear FHR indices were calculated.

RESULTS

Overall, MM twins presented higher intrapair average in linear indices than the other pairs, whereas FF twins showed higher sympathetic-vagal balance. MF twins exhibited higher intrapair average in entropy indices and MM twins presented lower entropy values than FF twins considering the (automatically selected) threshold rLu. MM twin pairs showed higher intrapair differences in linear heart rate indices than MF and FF twins, whereas FF twins exhibited lower intrapair differences in entropy indices.

CONCLUSIONS

The results of this exploratory study suggest that twins have sex-specific differences in linear and nonlinear indices of FHR. MM twins expressed signs of a more active autonomic nervous system and MF twins showed the most active complexity control system. These results suggest that fetal sex combination should be taken into consideration when performing detailed evaluation of the FHR in twins.

A critical care monitoring system for depth of anaesthesia analysis based on entropy analysis and physiological information database

Diagnosis of depth of anaesthesia (DoA) plays an important role in treatment and drug usage in the operating theatre and intensive care unit. With the flourishing development of analysis methods and monitoring devices for DoA, a small amount of physiological data had been stored and shared for further researches. In this paper, a critical care monitoring (CCM) system for DoA monitoring and analysis was designed and developed, which includes two main components: a physiologic information database (PID) and a DoA analysis subsystem. The PID, including biologic data and clinical information was constructed through a browser and server model so as to provide a safe and open platform for storage, sharing and further study of clinical anaesthesia information. In the analysis of DoA, according to our previous studies on approximate entropy, sample entropy (SampEn) and multi-scale entropy (MSE), the SampEn and MSE were integrated into the subsystem for indicating the state of patients underwent surgeries in real time because of their stability. Therefore, this CCM system not only supplies the original biological data and information collected from the operating room, but also shares our studies for improvement and innovation in the research of DoA.

Change of Spectral Analysis of Fetal Heart Rate During Clinical Hypnosis: a Prospective Randomised Trial from the 20th Week of Gestation Till Term

Objective: To investigate the functional adaptive process of the fetal autonomic nervous system during hypnosis from the 20th week of gestation till term. Are there changes in the power spectrum analysis of fetal heart rate when the mother is having a clinical hypnosis or control period? Study Design: Fourty-nine FHR recordings were analysed. Included recordings were from singletons and abdominal fetal ECG-monitored pregnancies. All women were randomised to receive clinical hypnosis followed by a period with no intervention or vice versa. Statistical analyses were performed with the Wilcoxon signed ranks and Spearman rho correlation tests. Results: There was a significant difference found between fetal heart rate at baseline (144.3 ± 6.0) and hypnosis (142.1 ± 6.4). A difference was also detected between the standard deviation of the heart rate between baseline (6.7 ± 1.9) and hypnosis (6.8 ± 3.5). LFnu was smaller during baseline (80.2 ± 5.3) than during hypnosis (82.1 ± 5.7), whereas HFnu was significantly larger (19.8 ± 5.3 vs. 17.9 ± 5.7). There was no correlation between the gestation age and the change in LFnu, HFnu or ratio LF/HF due to the hypnosis intervention. Conclusion: The functional adaptive process of the fetal autonomic system during hypnosis is reflected by a sympathovagal shift towards increased sympathetic modulation.

Sex differences in linear and complex fetal heart rate dynamics of normal and acidemic fetuses in the minutes preceding delivery

AIM

To assess linear and complex heart rate dynamics in relation to fetal gender in normal and acidemic fetuses during the minutes preceding delivery.

METHODS

Linear and non-linear fetal heart rate indices, namely mean FHR, long-term irregularity index, short-term variability, low and high frequency spectral indices, approximate and sample entropy, were assessed in 36 female and 30 male fetuses, adjusted for gestational age and weight, during the minutes preceding delivery. Analysis was performed in the initial and final minutes of each tracing in fetuses with umbilical artery blood pH at delivery >or=7.20, 7.11-7.19 and <or=7.10.

RESULTS

Progression of labor was associated with a significant decrease in non-linear indices and an increase in almost all linear indices, both in female and male fetuses, but changes were more marked in female fetuses. Non-acidemic females showed higher mean FHR in the final minutes of labor, compared with males. Acidemic females had higher linear indices when compared to similar male fetuses.

CONCLUSIONS

During the minutes preceding delivery, female fetuses express higher linear indices than male fetuses, suggesting greater activation of the autonomic nervous system, while maintaining similar complexity indices, which suggests different reaction and adaptation capabilities to stress and distress.

Nonlinear properties of vagal and sympathetic modulations of heart rate variability in ovine fetus near term

Fetal heart rate (FHR) monitoring is commonly used although clinical studies questioned its diagnostic value. Sophisticated FHR variability (fHRV) measures such as fHRV complexity may improve the sensitivity and specificity of FHR monitoring. A more detailed understanding of the physiology underlying fHRV complexity is essential to harness its use for monitoring fetal health. To examine the specific effects of vagal and sympathetic modulations on fHRV complexity, we blocked vagal activity with atropine and sympathetic activity with propranolol in near-term fetal sheep ( n = 7, 0.85 gestation). Under these conditions, we analyzed the linear and nonlinear parts of fHRV complexity from autonomic information flow. Overall fHRV complexity decreased with both drugs compared with nonrapid eye movement sleep baseline ( P < 0.05). With atropine, this was because of a decrease of the linear part of fHRV complexity on the long-term time scale ( P < 0.05), suggesting that vagal modulation of fHRV is adequately described by linear fHRV measures. With propranolol, the nonlinear part of fHRV complexity decreased on the short-term time scale ( P < 0.05), suggesting that sympathetic influences on fHRV can be detected by the nonlinear part of fHRV complexity. Thus the complex interplay of vagal and sympathetic modulations of fHRV is reflected differently and specifically in the linear and nonlinear properties of fHRV complexity, and on different time scales. Analysis of linear and nonlinear properties of fHRV may improve sensitivity and specificity of FHR monitoring.

Linear and complex heart rate dynamics vary with sex in relation to fetal behavioural states

BACKGROUND

A better understanding of gender influences on fetal heart rate can help to improve analysis of the latter and perhaps elucidate the increased risk of perinatal death that occurs in males.

AIM

To assess differences in linear and complex heart rate dynamics according to fetal sex, in the antepartum period of normal term pregnancies, for patterns associated with fetal behavioural states.

STUDY DESIGN AND SUBJECTS

One hundred and eighty seven fetal heart rate segments of 10-minute duration, acquired with a system for computerized analysis of cardiotocograms and classified into fetal behavioural patterns A, B, C or D were analysed. They had been acquired from 24 female and 23 male term fetuses, with uneventful perinatal outcomes. Four different comparative studies between female and male fetuses were conducted, considering different adjustments for gestational age, weight and FHR pattern.

OUTCOME MEASURES

Indices of linear and nonlinear fetal heart rate variability, namely, long-term irregularity index, very low, low and high frequency spectral indices, approximate entropy and sample entropy.

RESULTS

Pattern B was the most frequent, both in female and male fetuses. Pattern A was more likely to be associated to female than male fetuses, whereas the opposite occurred with patterns C and D. Linear indices were significantly higher in male than in female fetuses, whereas the opposite occurred with nonlinear indices.

CONCLUSIONS

Male fetuses exhibited significantly more linear and significantly less complex fetal heart rate activity than female fetuses, expressing signs of a more active autonomous nervous system and of less active complexity control systems. These aspects may need to be considered when interpreting FHR tracings.

Fetal heart rate and variability: stability and prediction to developmental outcomes in early childhood

Stability in cardiac indicators before birth and their utility in predicting variation in postnatal development were examined. Fetal heart rate and variability were measured longitudinally from 20 through 38 weeks gestation (n = 137) and again at age 2 (n = 79). Significant within-individual stability during the prenatal period and into childhood was demonstrated. Fetal heart rate variability at or after 28 weeks gestation and steeper developmental trajectories were significantly associated with mental and psychomotor development at 2 years (n = 82) and language ability at 2.5 years (n = 61). These data suggest that the foundations of individual differences in autonomic control originate during gestation and the developmental momentum of the fetal period continues after birth.

Quantification of fetal heart rate regularity using symbolic dynamics

Fetal heart rate complexity was examined on the basis of RR interval time series obtained in the second and third trimester of pregnancy. In each fetal RR interval time series, short term beat-to-beat heart rate changes were coded in 8 bit binary sequences. Redundancies of the 2(8) different binary patterns were reduced by two different procedures. The complexity of these sequences was quantified using the approximate entropy (ApEn), resulting in discrete ApEn values which were used for classifying the sequences into 17 pattern sets. Also, the sequences were grouped into 20 pattern classes with respect to identity after rotation or inversion of the binary value. There was a specific, nonuniform distribution of the sequences in the pattern sets and this differed from the distribution found in surrogate data. In the course of gestation, the number of sequences increased in seven pattern sets, decreased in four and remained unchanged in six. Sequences that occurred less often over time, both regular and irregular, were characterized by patterns reflecting frequent beat-to-beat reversals in heart rate. They were also predominant in the surrogate data, suggesting that these patterns are associated with stochastic heart beat trains. Sequences that occurred more frequently over time were relatively rare in the surrogate data. Some of these sequences had a high degree of regularity and corresponded to prolonged heart rate accelerations or decelerations which may be associated with directed fetal activity or movement or baroreflex activity. Application of the pattern classes revealed that those sequences with a high degree of irregularity correspond to heart rate patterns resulting from complex physiological activity such as fetal breathing movements. The results suggest that the development of the autonomic nervous system and the emergence of fetal behavioral states lead to increases in not only irregular but also regular heart rate patterns. Using symbolic dynamics to examine the cardiovascular system may thus lead to new insight with respect to fetal development.

Increase in regularity of fetal heart rate variability with age

It is generally assumed that fetal heart rate variability increases with gestation, reflecting prenatal development of the autonomic nervous system. We examined standard measures quantifying fetal heart rate variability, as well as a complexity measure, approximate entropy, in 66 fetal magnetocardiograms recorded from 22 healthy pregnant women between the 16th and 42nd week of gestation. In particular, regularity in the fetal RR interval time series was assessed on the basis of symbolic dynamics. The results showed that, beside an overall increase in fetal heart rate variability and complexity during pregnancy, there was also an increase in specific sets of binary patterns with low approximate entropy, i.e., a high degree of regularity. These sets were characterized by short epochs of heart rate acceleration and deceleration, and comparison with surrogate data confirmed that their random occurrence is rare. The results most likely reflect the influence of increasingly differentiated fetal behavioral states and transitions between them in association with fetal development.

V(D)J recombinase-mediated processing of coding junctions at cryptic recombination signal sequences in peripheral T cells during human development

V(D)J recombinase mediates rearrangements at immune loci and cryptic recombination signal sequences (cRSS), resulting in a variety of genomic rearrangements in normal lymphocytes and leukemic cells from children and adults. The frequency at which these rearrangements occur and their potential pathologic consequences are developmentally dependent. To gain insight into V(D)J recombinase-mediated events during human development, we investigated 265 coding junctions associated with cRSS sites at the hypoxanthine-guanine phosphoribosyltransferase (HPRT) locus in peripheral T cells from 111 children during the late stages of fetal development through early adolescence. We observed a number of specific V(D)J recombinase processing features that were both age and gender dependent. In particular, TdT-mediated nucleotide insertions varied depending on age and gender, including percentage of coding junctions containing N-nucleotide inserts, predominance of GC nucleotides, and presence of inverted repeats (Pr-nucleotides) at processed coding ends. In addition, the extent of exonucleolytic processing of coding ends was inversely related to age. We also observed a coding-partner-dependent difference in exonucleolytic processing and an age-specific difference in the subtypes of V(D)J-mediated events. We investigated these age- and gender-specific differences with recombination signal information content analysis of the cRSS sites in the human HPRT locus to gain insight into the mechanisms mediating these developmentally specific V(D)J recombinase-mediated rearrangements in humans.

Impaired parasympathetic response to feeding in ventilated preterm babies

BACKGROUND

Premature very low birthweight (VLBW) infants are born with an underdeveloped parasympathetic nervous system (PNS) which may limit their ability to respond adequately to feeding and may limit their capacities for extrauterine growth and development.

OBJECTIVES

To describe the patterns of autonomic response to feeding and identify relationships between change in heart period variability measures over time with selected infant characteristics.

METHODS

Individual growth curve analysis techniques were used to describe the patterns of change over time in sympathetic and parasympathetic tone as measured by low and high frequency heart period power.

RESULTS

Sixteen mechanically ventilated VLBW infants with a mean corrected gestational age of 30.4 weeks participated in the study. The low frequency (LF) power slope was -17.67 (p = 0.0002) and the high frequency (HF) power slope was -0.92 (0.0003). There was a significant relationship between HF slope and birth gestational age (r = -0.49, p = 0.05).

CONCLUSIONS

HF power, representing primarily parasympathetic activity, did not increase with enteral feeding as anticipated. LF power, an indicator of sympathetic tone, decreased during and after feeding suggesting the anticipated effect of inhibition of the sympathetic nervous system in response to the gut stimulus. Critically ill VLBW infants possess an overriding sympathetic response, but may not have adequate PNS tone development.

Neurobehavioral assessment before birth

The complexities of neurobehavioral assessment of the fetus, which can be neither directly viewed nor manipulated, cannot be understated. Impetus to develop methods for measuring fetal neurobehavioral development has been provided by the recognition that individual differences in neurobehavioral functioning do not originate with birth and acceptance of the key contribution of the antenatal period to postnatal life. Research has centered around four aspects of fetal functioning: heart rate, motor activity, behavioral state, and responsivity to stimulation. Longitudinal studies have revealed that the developmental trajectories of these characteristics parallel the developing nervous system, detected a transitional period between 28 and 32 weeks gestation, and established within-fetal stability during the second half of gestation. Despite the promise of fetal stimulation and habituation paradigms as measures of neural functioning, significant safety and ethical concerns exist. Construction of a unified fetal neurobehavioral scale is premature until a sufficient degree of normative data is available and the predictive validity of specific aspects of fetal neurobehavior to child developmental outcomes is better established.

Spectral Analysis of Heart Rate Variability: An Emerging Tool for Assessing Stability During Transition to Extrauterine Life

Transition from fetal to neonatal life is likely the most physiologically demanding time of life. Complex changes in major organ system functioning and reorganization of metabolic processes must occur rapidly to achieve postnatal homeostasis. Identifying the neonate with subtle signs of unsuccessful transition is a challenge to the perinatal health care provider. Alterations in fetal or neonatal heart rate and heart rate variability may serve as an indicator of the neural control influencing cardiac function and a sensitive indicator of compromised health. Evaluation of the neural control of the heart can be done noninvasively and provides a discriminating measure of the level of stress vulnerability the fetus or newborn may be experiencing. This article reviews the origins of physiological variability of the fetal and neonatal heart rate in the transition to extrauterine life. The technique of spectral analysis as a new tool for surveillance of the at-risk fetus and neonate is then introduced, and implications for clinical practice and future research avenues are discussed.

Fetal Neurobehavioral Development: A Tale of Two Cities

Longitudinal neurobehavioral development was examined in 237 fetuses of low-risk pregnancies from 2 distinct populations--Baltimore, Maryland, and Lima. Peru--at 20, 24, 28, 32, 36, and 38 weeks gestation. Data were based on digitized Doppler-based fetal heart rate (FHR) and fetal movement (FM). In both groups. FHR declined while variability, episodic accelerations, and FM-FHR coupling increased, with discontinuities evident between 28 and 32 weeks gestation. Fetuses in Lima had higher FHR and lower variability, accelerations, and FM-FHR coupling. Declines in trajectories were typically observed 1 month sooner in Lima, which magnified these disparities. Motor activity differences were less consistent. No sex differences in fetal neurobehaviors were detected. It is concluded that population factors can influence the developmental niche of the fetus.

Mutational spectral analysis at the HPRT locus in healthy children

There is growing evidence linking somatic mutational events during fetal development and childhood to an increasing number of multifactorial human diseases. Despite this, little is known about the relationship between endogenous and environmentally induced exogenous mutations during human development. Here we describe a comparative spectral analysis of somatic mutations at the hypoxanthine-guanine phosphoribosyltransferase (HPRT) reporter gene locus in healthy children. We observed an age-specific decrease in the proportion of large alterations and a corresponding increase in the proportion of small alterations with increasing age following birth (P<0.001). The age specific decrease in the proportion of large alterations (67-30%) was mainly due to a decrease in the proportion of aberrant variable (V), diversity (D) and joining (J) (V(D)J) recombinase mediated HPRT deletions (P<0.001). The increase in the proportion of small alterations with age (28-64%) was associated with an increase in transversions from 8% in children at the late stages of fetal development to 31% in children 12-16 years old (P=0.003). Transitions decreased with age, especially at CpG dinucleotides (P=0.010), as transversions increased (P=0.009). These patterns of mutations provide insight into important spontaneous, genotoxic, and site-specific recombinational somatic mutational events associated with the age-specific development of human disease in children as well as adults.

Assessing serial irregularity and its implications for health

Approximate entropy (ApEn) is a recently formulated family of parameters and statistics quantifying regularity (orderliness) in serial data, with developments within theoretical mathematics as well as numerous applications to multiple biological contexts. We discuss the motivation for ApEn development, from the study of inappropriate application of dynamical systems (complexity) algorithms to general time-series settings. ApEn is scale invariant and model independent, evaluates both dominant and subordinant patterns in data, and discriminates series for which clear feature recognition is difficult. ApEn is applicable to systems with at least 50 data points and to broad classes of models: it can be applied to discriminate both general classes of correlated stochastic processes, as well as noisy deterministic systems. Moreover, ApEn is complementary to spectral and autocorrelation analyses, providing effective discriminatory capability in instances in which the aforementioned measures exhibit minimal distinctions. Representative ApEn applications to human aging studies, based on both heart rate and endocrinologic (hormonal secretory) time series, are featured. Heart rate (HR) studies include gender- and age-related changes in HR dynamics in older subjects, and analyses of "near-SIDS" infants. Endocrinologic applications establish clear quantitative changes in joint LH-testosterone secretory dynamics in older versus younger men (a "partial male menopause"), via cross-ApEn, a related two-variable asynchrony formulation; a disruption in LH-FSH-NPT (penile tumescence) synchrony in older subjects; and changes in LH-FSH secretory dynamics across menopause. The capability of ApEn to assess relatively subtle disruptions, typically found earlier in the history of a subject than mean and variance changes, holds the potential for enhanced preventative and earlier interventionist strategies.

Gender-related heart rate differences in human neonates

The aim of the present study was to examine gender-related differences in heart rate of human neonates controlled for their behavior. Previous studies could not find any difference in male and female fetuses and newborns, although this gender-dependent difference clearly exists in children and adults. The heart rate of 99 newborns (47 girls and 52 boys) was measured with simultaneous video recording of their behavior. Results proved that alert newborns showed the same difference as adults: boys had a significantly lower baseline heart rate than girls. This suggests that heart rate is gender-dependent from birth onward.

Physiological time-series analysis using approximate entropy and sample entropy

Entropy, as it relates to dynamical systems, is the rate of information production. Methods for estimation of the entropy of a system represented by a time series are not, however, well suited to analysis of the short and noisy data sets encountered in cardiovascular and other biological studies. Pincus introduced approximate entropy (ApEn), a set of measures of system complexity closely related to entropy, which is easily applied to clinical cardiovascular and other time series. ApEn statistics, however, lead to inconsistent results. We have developed a new and related complexity measure, sample entropy (SampEn), and have compared ApEn and SampEn by using them to analyze sets of random numbers with known probabilistic character. We have also evaluated cross-ApEn and cross-SampEn, which use cardiovascular data sets to measure the similarity of two distinct time series. SampEn agreed with theory much more closely than ApEn over a broad range of conditions. The improved accuracy of SampEn statistics should make them useful in the study of experimental clinical cardiovascular and other biological time series.

Fetal heart rate variability and complexity in the course of pregnancy

Aim of this study was the examination of fetal heart rate variability and complexity measures during pregnancy using fetal magnetocardiography. We registered 80 fetal magnetocardiograms in 19 healthy fetuses between the 16th and 41st week of gestation. On the basis of beat to beat intervals, mean RR interval (mRR), its standard deviation (SD), root mean square of successive differences (RMSSD), as well as complexity variables such as dimension (ApD1), entropy (ApEn), Lyapunov exponent (ApML) and trajectory divergence rate (p) were calculated for each recording. Dependency of these variables on gestational age was evaluated with correlation analysis. All variables changed consistently over time. RMSSD showed the strongest dependency on gestational age, followed closely by ApEn, SD and p. ApD1 and mRR showed only weak dependency. We conclude that magnetocardiography is well suited to register fetal cardiac activity with sufficient accuracy to permit detailed analysis of various heart rate variables during the second and third trimester of pregnancy. The observed increases in heart rate variability and complexity of fetuses most likely reflect differing but overlapping aspects of fetal development. They may be linked to the maturation of the autonomic nervous system and could aid in the timely identification of pathological conditions.

Gender-specific frequency of background somatic mutations at the hypoxanthine phosphoribosyltransferase locus in cord blood T lymphocytes from preterm newborns

Limited information is available regarding the frequency, spectrum, and clinical relevance of somatic mutations in the developing fetus. The goal of this study was to determine somatic mutant frequencies (Mfs) at the hypoxanthine phosphoribosyltransferase (HPRT) reporter gene in cord blood T lymphocytes from preterm infants to gain insight into in utero mutational events. Mf determinations were made by using the HPRT T cell cloning assay on cord blood samples from 52 preterm infants. Natural logarithm Mfs (lnMfs) from preterm infants were compared with results from our database for full-term infants. Our analysis revealed higher lnMfs in cord blood T lymphocytes from preterm compared with full-term infants (P = 0.008). In addition, preterm females had significantly higher lnMfs compared with full-term females (P < 0.001), whereas preterm males were found to have significantly lower lnMfs than preterm females (P = 0.005). Regression analyses also demonstrate a significant relationship between lnMf and gestational age for preterm females that does not exist for preterm males. These results demonstrate the gender-specific association between Mf and age in humans.

Assessing sequential irregularity of both endocrine and heart rate rhythms

The quantification of subtle patterns in sequential data, and their changes, has considerable potential utility both in analysis of hormonal secretory dynamics, and of fetal heart rate rhythms. Approximate entropy, a recently developed statistic quantifying serial irregularity, has been applied in both these settings, and has yielded a number of new findings. Among endocrine applications, approximate entropy increases with increasing age for luteinizing hormone and follicle stimulating hormone, for both women and men, indicating greater irregularity (more apparently random dynamics) in the older groups; for the luteinizing hormone-testosterone axis, both irregularity and asynchrony increases accompany advancing age for men. These findings produce a means to potentially predict time until menopause onset, the efficacy of infertility drugs, and also provide firm quantitative support of a partial male menopause. In fetal monitoring, antepartum, and postnatal heart rate studies, approximate entropy consistently detected subtle shifts in heart rate rhythmicity, with greater regularity clinically corresponding to compromised physiology in all settings. Both the capability of approximate entropy to quantify rhythm changes undiscernible by auscultation, and a continuum interpretation linking per-individual antepartum, perinatal, and postnatal heart rate analyses provide considerable potential enhancement to the present clinical utility of fetal monitoring.

Preliminary evidence for the evolution in complexity of heart rate dynamics during autonomic maturation in neonatal swine

Previous studies suggest that the autonomic nervous system plays an important role in the generation of complex heart rate dynamics. Therefore, we hypothesized that the complexity (irregularity) of cardiac interbeat intervals would evolve with the maturation of autonomic innervation to the heart. Twelve healthy newborn piglets were implanted with ECG transmitters and studied at one or more different ages up to 33 days of age, the period during which pigs develop functional sympathetic innervation of the heart from the stellate ganglia. Three animals underwent right stellate ganglionectomy, two a left stellate ganglionectomy, two a right cardiac vagotomy and five a sham procedure. The statistic, approximate entropy (ApEn), was used to quantify the regularity of interbeat interval fluctuations. Sham-operated animals showed an increase in the standard deviation (SD) and irregularity (ApEn) of cardiac interval fluctuations with increasing age. Right stellate ganglionectomized piglets had lower interbeat interval ApEn values, but similar SD's by 26-27 days of age compared to sham-operated animals. Left stellate ganglionectomy, which affects cardiac inotropy rather than chronotropy, had no effect on cardiac interval irregularity, while vagotomy had an indeterminant effect. The increasing irregularity of interbeat interval dynamics during autonomic maturation and the apparent attenuation of heartbeat irregularity when right stellate ganglion innervation is interrupted, provides empirical support for the notion that complex heartbeat dynamics in the mature animal are the result of a network of autonomic neural pathways that enables an organism to adapt to stress.