A new analysis of heart rate variability in the assessment of fetal parasympathetic activity: An experimental study in a fetal sheep model

[Fetal monitoring: Current limitations and new approaches based on analysis of the fetal autonomic nervous system]

OBJECTIVE

Currently, fetal monitoring during labor is based on visual analysis of the fetal heart rate (FHR). This test is imperfect, with high intra- and inter-observer variability and a moderate to poor prediction of the occurrence of neonatal acidosis or anoxic-ischaemic encephalopathy. In situations where there is an intermediate risk of acidosis, it is possible to use second-line tests such as blood scalp sampling (with pH or lactate measurement) or ST segment analysis of the fetal ECG. However, these invasive tests have many limitations and their place is debated. Some authors suggest a more physiological approach to FHR assessment. The main actor in maintaining fetal homeostasis is the autonomic nervous system (ANS). Its activity can be assessed by analysing heart rate variability (HRV). The aim is to assess whether HRV can be used to identify situations at risk of acidosis.

MATERIALS AND METHODS

Our team has developed an index, the Fetal Stress Index, to measure HRV. To test it in a situation of acidosis, we used a pregnant ewe model. We also developed in parallel a human fetal ECG recording system.

RESULTS

In our experimental model, we have shown that this index reflects variations in the parasympathetic system and correlates with the onset of acidosis. As its use in clinical practice requires the acquisition of a beat-to-beat FHR signal, we have also developed an abdominal patch that allows highly accurate analysis of the fetal ECG.

CONCLUSION

The future is therefore to validate the FSI as a marker of acidosis in a prospective cohort using the signal obtained from our patch. This could be a new tool for fetal monitoring during labor.

Early heart rate variability changes during acute fetal inflammatory response syndrome: An experimental study in a fetal sheep model

INTRODUCTION

Fetal infection during labor with fetal inflammatory response syndrome (FIRS) is associated with neurodevelopmental disabilities, cerebral palsy, neonatal sepsis, and mortality. Current methods to diagnose FIRS are inadequate. Thus, the study aim was to explore whether fetal heart rate variability (HRV) analysis can be used to detect FIRS.

MATERIAL AND METHODS

In chronically instrumented near-term fetal sheep, lipopolysaccharide (LPS) was injected intravenously to model FIRS. A control group received saline solution injection. Hemodynamic, blood gas analysis, interleukin-6 (IL-6), and 14 HRV indices were recorded for 6 h. In both groups, comparisons were made between the stability phase and the 6 h following injection (H1-H6, respectively) and between LPS and control groups.

RESULTS

Fifteen lambs were instrumented. In the LPS group (n = 8), IL-6 increased significantly after LPS injection (p < 0.001), confirming the FIRS model. Fetal heart rate increased significantly after H5 (p < 0.01). In our FIRS model without shock or cardiovascular decompensation, five HRV measures changed significantly after H2 until H4 in comparison to baseline. Moreover, significant differences between LPS and control groups were observed in HRV measures between H2 and H4. These changes appear to be mediated by an increase of global variability and a loss of signal complexity.

CONCLUSION

As significant HRV changes were detected before FHR increase, these indices may be valuable for early detection of acute FIRS.

Validation of a new smart textiles biotechnology for heart rate variability monitoring in sheep

Robust Animal-Based Measures (ABMs) are fundamental in order to assess animal welfare, however in semi-extensive sheep farming systems is not easy to collect ABMs without inducing additional stress in the animals. Heart rate variability (HRV) is a non-invasive technique of assessing stress levels related to animal welfare. It is considered a sensitive indicator of the functional regulatory characteristics of the autonomic nervous system. Several studies investigated the use of HRV for welfare assessment in dairy cows while research on sheep is scarce. Moreover, assessing HRV in small ruminants at pasture is critical because of the lack of a solution adoptable for field conditions. This study aimed to evaluate if a smart textiles technology is comparable to a Standard base-apex electrocardiogram (ECG) for measuring HRV in small ruminants. Eight healthy Massese dairy sheep were recruited. Standard base-apex ECG and smart textiles technology (Smartex ECG) were simultaneously acquired for 5 min in the standing, unsedated, unclipped sheep. The ECG tracings were recorded when animals were standing quietly. The Bland-Altman test and the linear regression analysis were applied after parameter extraction in time, frequency, and non-linear methods to compare Smartex against standard base-apex ECG systems. The Bland-Altman test was applied to all HRV extracted parameters (Mean RR, pNN50, RMSSD, LF/HF, SampEn, SD1, SD2, stdRR) to evaluate the agreement between the two different instruments, and a linear regression analysis was performed to evaluate the relationship between the two methods. The smart textiles biotechnology was simple to wear and clean. It can be worn without using glue and without shaving the sheep's wool, limiting animal handling and stress. Bland Altman test reported a robust agreement between the two systems. In fact, the regression analysis of HRV parameters showed that half of the parameters recorded had an R2 coefficient &gt;0.75. Results also showed a very small reproducibility coefficient that indicated that the two methods were really close to each other. Smartex textiles technology can be used for HRV evaluation in sheep species as a potential ABM for animal welfare assessment.

Increased variability of fetal heart rate during labour: a review of preclinical and clinical studies

Increased fetal heart rate variability (FHRV) in intrapartum cardiotocographic recording has been variably defined and poorly understood, limiting its clinical utility. Both preclinical (animal) and clinical (human) evidence support that increased FHRV is observed in the early stage of intrapartum fetal hypoxaemia but can also be observed in a subset of fetuses during the preterminal stage of repeated hypoxaemia. This review of available evidence provides data and expert opinion on the pathophysiology of increased FHRV, its clinical significance and a stepwise approach regarding the management of this pattern, and propose recommendations for standardisation of related terminology.

Associations between fetal heart rate variability and umbilical cord occlusions-induced neural injury: An experimental study in a fetal sheep model

INTRODUCTION

This study evaluated the association between fetal heart rate variability (HRV) and the occurrence of hypoxic-ischemic encephalopathy in a fetal sheep model.

MATERIAL AND METHODS

The experimental protocol created a hypoxic condition with repeated cord occlusions in three phases (A, B, C) to achieve acidosis to pH <7.00. Hemodynamic, gasometric and HRV parameters were analyzed during the protocol, and the fetal brain, brainstem and spinal cord were assessed histopathologically 48 h later. Associations between the various parameters and neural injury were compared between phases A, B and C using Spearman's rho test.

RESULTS

Acute anoxic-ischemic brain lesions in all regions was present in 7/9 fetuses, and specific neural injury was observed in 3/9 fetuses. The number of brainstem lesions correlated significantly and inversely with the HRV fetal stress index (r = -0.784; p = 0.021) in phase C and with HRV long-term variability (r = -0.677; p = 0.045) and short-term variability (r = -0.837; p = 0.005) in phase B. The number of neurological lesions did not correlate significantly with other markers of HRV.

CONCLUSIONS

Neural injury caused by severe hypoxia was associated with HRV changes; in particular, brainstem damage was associated with changes in fetal-specific HRV markers.

Entropy Analysis of Neonatal Electrodermal Activity during the First Three Days after Birth

The entropy-based parameters determined from the electrodermal activity (EDA) biosignal evaluate the complexity within the activity of the sympathetic cholinergic system. We focused on the evaluation of the complex sympathetic cholinergic regulation by assessing EDA using conventional indices (skin conductance level (SCL), non-specific skin conductance responses, spectral EDA indices), and entropy-based parameters (approximate, sample, fuzzy, permutation, Shannon, and symbolic information entropies) in newborns during the first three days of postnatal life. The studied group consisted of 50 healthy newborns (21 boys, average gestational age: 39.0 ± 0.2 weeks). EDA was recorded continuously from the feet at rest for three periods (the first day—2 h after birth, the second day—24 h after birth, and the third day—72 h after birth). Our results revealed higher SCL, spectral EDA index in a very-low frequency band, approximate, sample, fuzzy, and permutation entropy during the first compared to second and third days, while Shannon and symbolic information entropies were lower during the first day compared to other periods. In conclusion, EDA parameters seem to be sensitive in the detection of the sympathetic regulation changes in early postnatal life and which can represent an important step towards a non-invasive early diagnosis of the pathological states linked to autonomic dysmaturation in newborns.

Physiological control of fetal heart rate variability during labour: Implications and controversies

The interpretation of fetal heart rate (FHR) patterns is the only available method to continuously monitor fetal wellbeing during labour. One of the most important yet contentious aspects of the FHR pattern is changes in FHR variability (FHRV). Some clinical studies suggest that loss of FHRV during labour is a sign of fetal compromise so this is reflected in practice guidelines. Surprisingly, there is little systematic evidence to support this observation. In this review we methodically dissect the potential pathways controlling FHRV during labour-like hypoxaemia. Before labour, FHRV is controlled by the combined activity of the parasympathetic and sympathetic nervous systems, in part regulated by a complex interplay between fetal sleep state and behaviour. By contrast, preclinical studies using multiple autonomic blockades have now shown that sympathetic neural control of FHRV was potently suppressed between periods of labour-like hypoxaemia, and thus, that the parasympathetic system is the sole neural regulator of FHRV once FHR decelerations are present during labour. We further discuss the pattern of changes in FHRV during progressive fetal compromise and highlight potential biochemical, behavioural and clinical factors that may regulate parasympathetic-mediated FHRV during labour. Further studies are needed to investigate the regulators of parasympathetic activity to better understand the dynamic changes in FHRV and their true utility during labour. This article is protected by copyright. All rights reserved.

Roles of parasympathetic outflow and sympathetic outflow in the cardiovascular response to brief umbilical cord occlusion in fetal sheep

Fetal heart rate (FHR) deceleration is the most common change seen during labor. The role of the autonomic nervous system in regulating the fetal cardiovascular response during multiple uterine contractions has been well-established. However, the mechanism underlying the hemodynamic response remains unclear and the specific reflex that mediates the cardiovascular modifications is still controversial. This study aimed to determine the role of the sympathetic and parasympathetic systems on fetal hemodynamics in complete cord occlusion. Chronically instrumented fetal sheep were randomized to receive an intravenous injection of atropine 2.5 mg (n = 8), propranolol 5 mg (n = 7), atropine and propranolol (n = 7), or a control protocol (n = 9), followed by three episodes of 1-minute umbilical cord occlusion repeated every 5 minutes. Cord compression induces a rapid decrease in the FHR and a rapid increase in MAP. The decrease in FHR is caused by an increase in parasympathetic activity, (atropine and atropine-propranolol abolish the FHR response to the occlusion). The change in FHR during occlusion was not modified by propranolol injection, showing no effect of sympathetic tone. The increase in MAP during occlusion was similar in the four protocols. After releasing occlusion, the FHR was still lower than that at baseline due to a sustained parasympathetic tone. Suppression of the parasympathetic output to the cardiovascular system unmasks an increase in the FHR above baseline values. The lower FHR with the propranolol protocol further supports an increase in myocardial β-adrenoceptor stimulation after cord release. The increase in MAP after cord release was similar in the four protocols, except after the early stage of interocclusion period in atropine protocol. Four minutes after cord release, the FHR returned to baseline irrespective of the drugs that were infused, thereby showing recovery of ANS control. Blood gases (pH, PaCO2, PaO2) and plasma lactate concentrations was similar between the four protocols at the end of three applications of UCO. Complete cord compression-induced deceleration is likely due to acute activation of parasympathetic output. β-adrenoceptor activity is involved in the increase in FHR after cord release. Understanding the reflexes involved in FHR deceleration may help us understand the mechanisms underlying fetal autonomic adaptation during cord occlusion.

Evaluation and impact of fetal physiology training on fetal heart rate analysis

INTRODUCTION

Evaluation of fetal well-being during labor is based on fetal heart rate (FHR) analysis, which requires physiology expertise. The aim of the present study was to assess medical residents' fetal physiology training in terms of theoretical knowledge, FHR interpretation, and use of second-line examinations.

METHODS

This single-center, prospective study of obstetrics and gynecology residents (N = 34) at CHU de Lille Hospital (Lille, France) was conducted from November 2017 to November 2018. Evaluation and training were conducted in three stages. First, residents' pre-training knowledge of FHR interpretation and use of fetal scalp blood sampling (FBS) was assessed using clinical cases. Second, a didactic training session on fetal physiology was delivered. Finally, post-training knowledge was evaluated using the same cases presented during pre-training. I: Pre-training, 3%, 11.8%, and 14.7% of residents considered their training on fetal physiology, FHR analysis, and second-line examinations, respectively, to be sufficient. Training significantly improved their theoretical knowledge, which was assessed using multiple-choice questions (median [interquartile range]: 1.5 [1.0-2.0] vs. 4.0 [3.0-4.5], p<0.001), and reduced the number of FBS requested (36.3% vs. 29.5%, p = 0.002). Krippendorff's alpha coefficient for the reproducibility of residents' responses improved significantly, reflecting greater homogenization of clinical practice decisions (alpha [95% confidence interval]: 0.60 [0.55-0.65] vs. 0.72 [0.67-0.76]).

CONCLUSION

Improved fetal physiology knowledge promotes more accurate FHR interpretation, better indications for second-line examinations, and greater homogenization of clinical practice decisions. Future studies should evaluate the impact of fetal physiology training on clinical practice.

Heart rate variability in Dorper sheep in the fetal and neonatal periods until 120 days of age: Use of the technique in the field

The evaluation of the autonomic cardiac functions may be performed through the analysis of the heart rate variability. Heart rate variability is defined as the fluctuations in the heart rhythm or rate, and represents a useful tool in the evaluation of the autonomic nervous system through the sympathetic and parasympathetic components, as well as its balance and its reflexes on the cardiorespiratory control system. Fetal electrocardiography provides important information regarding the well-being of the fetus since, in human fetuses, there are changes in the behavior of the fetal heart rate during the second and third trimesters of pregnancy due to an increase in parasympathetic activity. Therefore, considering the importance of evaluating fetal viability, this study aims at evaluating the behavior of fetal heart rate and heart rate variability in Dorper sheep, as well as the activity of the autonomic nervous system during fetal life and in newborn lambs. The species is often used in experimental studies and autonomic nervous system activity is a prognostic index, therefore, the diagnosis of modifications in the sympathovagal balance may represent an early index for fetal viability and well-being in lambs. The analyses were performed in 10 Dorper sheep during pregnancy and in 10 lambs after birth until 120 days of age. There was a decrease in the fetal heart rate and heart rate variability indexes during the fifth month of pregnancy, but without statistical significance for the period evaluated. The heart rate of the lambs decreased gradually until they were 21 days old. The indexes SDNN (standard deviation of RR intervals) and RMSSD (square root of the mean of successive differences between adjacent RR intervals) diverged according to age, being high at day 60. Fetal viability is relevant in sheep fetuses to avoid losses during pregnancy and risks to the health of the mother. In the species, there seems to be a predominance of parasympathetic activity starting from the 21st day of age. Heart rate variability may be employed as a tool in the evaluation of the fetus and development of lambs, since changes in its behavior may represent an adverse effect to fetal and neonatal health.

Opioid effect on the autonomic nervous system in a fetal sheep model

PURPOSE

Opioid use during labour can interfere with cardiotocography patterns. Heart rate variability indirectly reflects a fluctuation in the autonomic nervous system and can be monitored through time and spectral analyses. This experimental study aimed to evaluate the impact of nalbuphine administration on the gasometric, cardiovascular, and autonomic nervous system responses in fetal sheep.

METHODS

This was an experimental study on chronically instrumented sheep fetuses (surgery at 128 ± 2 days of gestational age, term = 145 days). The model was based on a maternal intravenous bolus injection of nalbuphine, a semisynthetic opioid used as an analgesic during delivery. Fetal gasometric parameters (pH, pO₂, pCO₂, and lactates), hemodynamic parameters (fetal heart rate and mean arterial pressure), and autonomic nervous system tone (short-term and long-term variation, low-frequency domain, high-frequency domain, and fetal stress index) were recorded. Data obtained at 30-60 min after nalbuphine injection were compared to those recorded at baseline.

RESULTS

Eleven experiments were performed. Fetal heart rate, mean arterial pressure, and activities at low and high frequencies were stable after injection. Short-term variation decreased at T30 min (P = 0.02), and long-term variation decreased at T60 min (P = 0.02). Fetal stress index gradually increased and reached significance at T60 min (P = 0.02). Fetal gasometric parameters and lactate levels remained stable.

CONCLUSION

Maternal nalbuphine use during labour may lead to fetal heart changes that are caused by the effect of opioid on the autonomic nervous system; these fluctuations do not reflect acidosis.

Fetal sheep cerebral electrical activity: A new technique to record EEG

BACKGROUND

Sheep models are commonly used to study fetal cortical activity, including response to hypoxia. The standard technique consists of recording electrocorticogram (ECOG) in utero using electrodes placed on the dura mater.

NEW METHOD

We propose a new method for recording the electroencephalogram (EEG) of fetal sheep, using electrodes placed above the skull bone and fixed to the cranial periosteum.

RESULTS

Twelve animals were instrumented with this new technique. The EEG signal recorded in utero was of sufficient quality for visual and quantitative analysis of the fetal cortical activity.

COMPARISON WITH EXISTING METHOD

This new method is less invasive than the standard method commonly used to record cerebral activity in fetal sheep, because it avoids drilling the skull by hand. The EEG signal recorded in utero had visual and quantitative characteristics comparable to ECOG.

CONCLUSIONS

We present a new method of EEG recording that appears to be an acceptable alternative to the standard ECOG recording method. Fetal sheep EEG can be used to better understand the physiological mechanisms involved in the cerebral response to hypoxia.

Influence of averaged fetal heart rate in heart rate variability analysis

In high-income countries, fetal hypoxia affects 3 to 8 newborns per 1000 live births with subsequent moderate or severe Hypoxic-Ischemic Encephalopathy (HIE) in 0.5 to 1 per 1000 live births. Visual interpretation of FHR signal issued from a Doppler ultrasound cardiotocography is the gold standard to monitor fetal condition. Unfortunately, its analysis presents a high rate of inter-observer variability and a low specificity to predict poor neonatal outcomes. Under hypoxia, the fetus develops several adaptive mechanisms regulated by the autonomic nervous system inducing changes in the fetal heart rate variability. Though fetal heart rate variability methods demonstrated abilities to predict perinatal asphyxia, most of the Doppler ultrasound technologies used in clinical practice do not provide sufficiently accurate fetal heart rate signals for heart rate variability analysis. Indeed, Doppler ultrasound cardiotocography usually provides fetal heart rate values averaged over 2 or 3 beats which can constitute a limitation for spectral analysis. We developed a fetal heart rate variability analysis method: the Fetal Stress Index (FSI). The objective of this study was to investigate the influence of averaged fetal heart rate on this new index in order to check the feasibility of computing the FSI from the signal issued from Doppler ultrasound cardiotocography.

Fetal heart rate variability analysis for neonatal acidosis prediction

Fetal well-being during labor is usually assessed by visual analysis of a fetal heart rate (FHR) tracing. Our primary objective was to evaluate the ability of automated heart rate variability (HRV) analysis methods, including our new fetal stress index (FSI), to predict neonatal acidosis. 552 intrapartum recordings were analyzed. The analysis occurred in the last 90 min before birth and was conducted during two 5-min intervals: (i) a stable period of FHR and (ii) the period corresponding to the maximum FSI value. For each period, we computed the mean FHR, FSI, short-term variability (STV), and long-term variability (LTV). Visual FHR interpretation was performed using the FIGO classification. The population was separated into two groups: (i) an acidotic group with an arterial pH at birth ≤ 7.10 and a control group. Prediction of a neonatal pH ≤ 7.10 was assessed by computing the receiver-operating characteristic area under the curve (AUC). FHR, FSI, STV, and LTV did not differ significantly between groups during the stable period. During the FSI max peak period, LTV and STV correlated significantly in the acidotic group (- 5.85 ± 2.19, p = 0.010 and - 0.62 ± 0.29, p = 0.037, respectively). The AUC values were 0.569 for FIGO classification, 0.595 for STV, and 0.622 for LTV. The multivariate model (FIGO, FSI, FC, STV, LTV) had the greatest accuracy for predicting acidosis (AUC = 0.719). FSI was not predictive of neonatal acidosis probably because of the low quality of the FHR signal in cardiotocography. When used separately, HRV indexes and visual FHR analysis were poor predictors of neonatal acidosis. Including all indexes in a multivariate model increased the predictive ability.

Autonomic response to fetal acidosis using an experimental sheep model

BACKGROUND

The autonomic nervous system has a major role in fetal adaptation to hypoxia. Its activity might be assessed using heart rate variability and heart rate deceleration analyses.

OBJECTIVE

To evaluate the ability of different heart rate variability and morphological deceleration analyses to predict fetal acidosis during labor in an experimental fetal sheep model.

STUDY DESIGN

Repeated 1-minute total umbilical cord occlusions were performed at mild (1minute every 5 min), moderate (1 min every 3 min), and severe (1 min every 2 min) umbilical cord occlusion periodicities until arterial pH reached 7.10. Hemodynamic,blood gas analysis, morphological analysis of decelerations (magnitude, slope, and area ofdecelerations), and heart rate variability parameters were recorded throughout the experiment.Heart rate variability analysis included temporal analysis (root mean square of successivedifferences between adjacent RR intervals, standard deviation of normal to normal RR intervals, short term variability), spectral analysis (low frequencies, high frequencies,normalized high frequencies), and a new index developed by our team, the Fetal Stress Index.We defined and compared three pH groups: >7.20, 7.10-7.20, and <7.10.

RESULTS

Eleven experiments were performed. Repetitive umbilical cord occlusions resulted in progressive fetal acidosis. Fetal Stress Index was correlated with pH and lactate (p < 0.05) and increased with acidosis. There were no significant correlations between pH, lactate, and other indices (spectral analysis, temporal analysis, or morphological analysis of decelerations).

CONCLUSION

This protocol allowed us to identify the progressive onset of fetal acidosis in an experimental model close to labor. Fetal Stress Index is a heart rate variability method that varies with acidosis and indicates an increase in parasympathetic nervous system activity in response to fetal acidosis.

A novel modular fetal ECG STAN and HRV analysis: Towards robust hypoxia detection

This paper introduces a comprehensive fetal Electrocardiogram (fECG) Signal Extraction and Analysis Virtual Instrument that integrates various methods for detecting the R-R Intervals (RRIs) as a means to determine the fetal Heart Rate (fHR) and therefore facilitates fetal Heart Rate Variability (HRV) signal analysis. Moreover, it offers the capability to perform advanced morphological fECG signal analysis called ST segment Analysis (STAN) as it seamlessly allows the determination of the T-wave to QRS complex ratio (also called T/QRS) in the fECG signal. The integration of these signal processing and analytical modules could help clinical researchers and practitioners to noninvasively monitor and detect the life threatening hypoxic conditions that may arise in different stages of pregnancy and more importantly during delivery and could therefore lead to the reduction of unnecessary C-sections. In our experiments we used real recordings from a Fetal Scalp Electrode (FSE) as well as maternal abdominal electrodes. This Virtual Instrument (Toolbox) not only serves as a desirable platform for comparing various fECG extraction signal processing methods, it also provides an effective means to perform STAN and HRV signal analysis based on proven ECG morphological as well as Autonomic Nervous System (ANS) indices to detect hypoxic conditions.

Parasympathetic nervous system response to acidosis: Evaluation in an experimental fetal sheep model

INTRODUCTION

Heart rate variability and fetal heart rate decelerations are impacted by parasympathetic function and reflect acid-base status. Our team developed a new heart rate variability index, the fetal stress index (FSI), which has lower interindividual variability and higher sensitivity for detecting fluctuations in parasympathetic nervous system activity. The aim of this study was to explore the ability of the FSI to predict fetal acidosis in a fetal sheep model.

MATERIAL AND METHODS

Repeated 1-minute total umbilical cord occlusions (UCOs) were performed every 2.5 minutes over 3 hours to generate fetal acidosis mimicking that which occurs during labor and contractions. Fetal hemodynamic parameters, blood gas, the FSI and the magnitude (from the beginning to the nadir) of the fetal heart rate deceleration were recorded at regular intervals. The data were analyzed over three time intervals because of variation in the duration of the experiments: period A (first 12 UCOs), period B (middle 12 UCOs) and period C (last 12 UCOs).

RESULTS

Nine experiments were performed. Acidosis was progressive with a significant difference between the pH, lactate levels and base deficit values for the three periods of occlusion (P < 0.05). Both FSI and the magnitude of fetal heart rate decelerations gradually increased during the UCOs and both differed significantly between periods A and C (P = 0.0008 for FSI and P = 0.003 for deceleration).

CONCLUSION

This experimental protocol allowed the development of progressive acidosis in a good model of the physiology of labor. Parasympathetic nervous system activity increased during acidosis and could be measured using our index, the FSI, and the magnitude of fetal heart rate decelerations.

Autonomic nervous system development and its impact on neuropsychiatric outcome

The central autonomic nervous system (ANS) is essential for maintaining cardiovascular and respiratory homeostasis in the newborn and has a critical role in supporting higher cortical functions. At birth, the central ANS is maturing and is vulnerable to adverse environmental and physiologic influences. Critical connections are formed early in development between the ANS and limbic system to integrate psychological and body responses. The Polyvagal Theory, developed by Stephen Porges, describes how modulation of the autonomic vagal impulse controls social responses and that a broad range of neuropsychiatric disorders may be due to impaired vagal balance, with either deficient vagal tone or excessive vagal reactivity. Under additional circumstances of prematurity, growth restriction, and environmental stress in the fetus and newborn, the immature ANS may undergo "dysmaturation". Maternal stress and health as well as the intrauterine environment are also quite important and have been implicated in causing ANS changes in the infant and neuropsychiatric diseases in children. This review will cover the aspects of ANS development and maturation that have been associated with neuropsychiatric disorders in children.

Heart rate variability: implications for perioperative anesthesia care

PURPOSE OF REVIEW

Heart rate variability (HRV) is a measure of the balance between both the parasympathetic and sympathetic nervous system and may provide useful information for anesthesia care providers. HRV may offer predictive information about critically ill and operative patients. Further, HRV collection provides real-time information of patient autonomic nervous system status and may allow tailoring of the analgesia for patients in the ICU and operating room.

RECENT FINDINGS

Reduced and abnormal resting HRV predict sudden and nonsudden cardiac death. Recent evidence shows that decreased HRV correlates with worsened outcomes in both trauma patients and patients with sepsis, as well as the risk of developing hypotension after induction of general anesthesia and placement of intrathecal local anesthesia. In addition, HRV appears to provide an accurate assessment of the nociception-analgesia balance in deeply sedated ICU patients and those under general anesthesia.

SUMMARY

No study has assessed the prognostic value of preoperative HRV in patients presenting for surgery. Use of HRV for patient risk stratification and intraoperative analgesia management may allow tailored perioperative care and improved outcomes. If intraoperative HRV data leads to decreased perioperative opioid use, opioid-related adverse events, a serious perioperative issue, may be decreased.

CLINICAL TRIALS REGISTRATION

Not applicable.

Exploring fetal response to acidosis in ewes: Choosing an adequate experimental model

INTRODUCTION

Knowledge of fetal physiology during labor has been largely generated from animal models. Our team recently developed a new index to assess parasympathetic activity using different experimental protocols to obtain acidosis. The objective of the present study was to discuss the different protocols and to review other models proposed in the literature.

MATERIAL AND METHODS

Pregnant ewes underwent a surgical procedure at the 123±2 days gestational age (term=145 days). Three experimental protocols were used: protocol A consisted of 25%, 50% and 75% umbilical cord occlusion (UCO) for 20min. Protocol B consisted of partial 75% UCO until reaching a pH<7.10. Protocol C consisted of brief, repetitive complete occlusion until severe acidosis occurred. Hemodynamic and blood gas parameters were compared to those of the stability period before UCO.

RESULTS

Protocol A led to a progressive response depending on the degree of occlusion (decrease in fetal heart rate, arterial hypertension and pH). Protocol B led to severe acidosis, although the duration of UCO varied per animal. Protocol C also progressively led to acidosis. We observed high inter individual variability in the acidosis response.

CONCLUSION

Pregnant ewes are a relevant model for exploring fetal response to acidosis. The frequency of UCO and partial or complete occlusion should be adapted to the expected effects. Knowledge of these protocols is important to respect ethical guidelines and to reduce the required number of animals. Moreover, it is important to consider the high individual variability of the acidosis response in the interpretation of the results.

Correlation of a new index reflecting the fluctuation of parasympathetic tone and fetal acidosis in an experimental study in a sheep model

The autonomic nervous system plays a leading role in the control of fetal homeostasis. Fetal heart rate variability (HRV) analysis is a reflection of its activity. We developed a new index (the Fetal Stress Index, FSI) reflecting parasympathetic tone. The objective of this study was to evaluate this index as a predictor of fetal acid-base status. This was an experimental study on chronically instrumented fetal lambs (n = 11, surgery at 128 +/- 2 days gestational age, term = 145 days). The model was based on 75% occlusion of the umbilical cord for a maximum of 120 minutes or until an arterial pH ≤ 7.20 was reached. Hemodynamic, gasometric and FSI parameters were recorded throughout the experimentation. We studied the FSI during the 10 minutes prior to pH samplings and compared values for pH>7.20 and pH≤ 7.20. In order to analyze the FSI evolution during the 10 minutes periods, we analyzed the minimum, maximum and mean values of the FSI (respectively FSImin, FSImax and FSImean) over the periods. 11 experimentations were performed. During occlusion, the heart rate dropped with an increase in blood pressure (respectively 160(155-182) vs 106(101-120) bpm and 42(41-45) vs 58(55-62) mmHg after occlusion). The FSImin was 38.6 (35.2-43.3) in the group pH>7.20 and was higher in the group pH less than 7.20 (46.5 (43.3-52.0), p = 0.012). The correlation of FSImin was significant for arterial pH (coefficient of -0.671; p = 0.004) and for base excess (coefficient of -0.632; p = 0.009). The correlations were not significant for the other parameters. In conclusion, our new index seems well correlated with the fetal acid-base status. Other studies must be carried out in a situation close to the physiology of labor by sequential occlusion of the cord.