The development of cardiovascular and cerebral vascular control in preterm infants

Cardiovascular and cerebrovascular effects of caffeine maintenance in preterm infants during the transitional period

BACKGROUND AND AIM

Caffeine is routinely used for the prophylaxis of prematurity-related apnoeas. We aimed to evaluate the effect of caffeine maintenance on cardiovascular and cerebrovascular haemodynamics using a non-invasive multimodal monitoring in preterm infants during the transitional period.

METHODS

Infants <32 weeks' gestational age (GA) were enrolled in this observational prospective study. The following parameters were recorded before and after the administration of caffeine citrate 5 mg/kg using near-infrared spectroscopy, pulse oximetry and electrical velocimetry: heart rate, cardiac output, stroke volume, cardiac contractility, systemic vascular resistance (SVR), perfusion index, peripheral and cerebral oxygenation, cerebral fractional oxygen extraction, correlation index between cerebral oxygenation and heart rate (TOHRx, marker of cerebrovascular reactivity). Multilevel mixed-effects linear models were used to assess the impact of caffeine and of relevant clinical covariates on each parameter.

RESULTS

Seventy-seven infants (mean GA 29.3 ± 2.5 weeks, mean birthweight 1148 ± 353 g) were included. Caffeine administration was associated with increased SVR (B = 0.623, p = 0.004) and more negative TOHRx values (B = -0.036, p = 0.022), which suggest improved cerebrovascular reactivity.

CONCLUSIONS

Caffeine administration at maintenance dosage during postnatal transition is associated with increased systemic vascular tone and improved cerebrovascular reactivity. A possible role for caffeine-mediated inhibition of adenosine receptors may be hypothesized.

IMPACT

This study provides a thorough and comprehensive overview of multiple cerebrovascular and cardiovascular parameters, monitored non-invasively by combining near-infrared spectroscopy, electrical velocimetry and pulse oximetry, before and after the administration of caffeine at maintenance dosage in preterm infants during postnatal transition. Caffeine was associated with an improvement in cerebrovascular reactivity and with a slight but significant increase in systemic vascular resistance, with no additional effects on other cardiovascular and cerebrovascular parameters. Our results support the safety of caffeine treatment even during a phase at risk for haemodynamic instability such as postnatal transition and suggest potential beneficial effects on cerebral haemodynamics.

Central Autonomic Network and heart rate variability in premature neonates

INTRODUCTION

The Central Autonomic Network (CAN) is a hierarchy of brain structures that collectively influence cardiac autonomic input, mediating the majority of brain-heart interactions, but has never been studied in premature neonates. In this study, we use heart rate variability (HRV), which has been described as the "primary output" of the CAN, and resting state functional MRI to characterize brain-heart relationships in premature neonates.

METHODS

We studied premature neonates who underwent resting state functional MRI (rsfMRI) at term, (37-weeks postmenstrual age [PMA] or above) and had HRV data recorded during the same week of their MRI. HRV was derived from continuous electrocardiogram data during the week of the rsfMRI scan. For rsfMRI, a seed-based approach was used to define regions of interest (ROI) pertinent to the CAN, and blood oxygen level-dependent signal was correlated between each ROI as a measure of functional connectivity. HRV was correlated with CAN connectivity (CANconn) for each region, and sub-group analysis was performed based on sex and clinical comorbidities.

RESULTS

Forty-seven premature neonates were included in this study, with a mean gestational age at birth of 28.1 +/- 2.6 weeks. Term CANconn was found to be significantly correlated with HRV in approximately one-fifth of CAN connections. Two distinct patterns emerged among these HRV-CANconn relationships. In the first, increased HRV was associated with stronger CANconn of limbic regions. In the second pattern, stronger CANconn at the precuneus was associated with impaired HRV maturation. These patterns were especially pronounced in male premature neonates.

CONCLUSION

We report for the first time evidence of brain-heart relationships in premature neonates and an emerging CAN, most striking in male neonates, suggesting that the brain-heart axis may be more vulnerable in male premature neonates. Signatures in the heart rate may eventually become an important non-invasive tool to identify premature males at highest risk for neurodevelopmental impairment.

Variable Association of Physiologic Changes With Electrographic Seizure-Like Events in Infants Born Preterm

OBJECTIVES

To determine the incidence of seizure-like events in a cohort of infants born preterm as well as the prevalence of associated vital sign changes (heart rate [HR], respiratory rate, and pulse oximetry [SpO2]).

STUDY DESIGN

We performed prospective conventional video electroencephalogram monitoring on infants born at 23-30 weeks of gestational age during the first 4 postnatal days. For detected seizure-like events, simultaneously captured vital sign data were analyzed during the pre-event baseline and during the event. Significant vital sign changes were defined as HR or respiratory rate >±2 SD from the infant's own baseline physiologic mean, derived from a 10-minute interval before the seizure-like event. Significant change in SpO2 was defined as oxygen desaturation during the event with a mean SpO2 <88%.

RESULTS

Our sample included 48 infants with median gestational age of 28 weeks (IQR 26-29) and birth weight of 1125 g (IQR 963-1265). Twelve (25%) infants had seizure-like discharges with a total of 201 events; 83% (10/12) of infants had vital sign changes during these events, and 50% (6/12) had significant vital sign changes during the majority of the seizure-like events. Concurrent HR changes occurred the most frequently.

CONCLUSIONS

Individual infant variability was observed in the prevalence of concurrent vital sign changes with electroencephalographic seizure-like events. Physiologic changes associated with preterm electrographic seizure-like events should be investigated further as a potential biomarker to assess the clinical significance of such events in the preterm population.

Cerebral blood flow patterns in preterm and term neonates assessed with pseudo-continuous arterial spin labeling perfusion MRI

In preterm (PT) infants, regional cerebral blood flow (CBF) disturbances may predispose to abnormal brain maturation even without overt brain injury. Therefore, it would be informative to determine the spatial distribution of grey matter (GM) CBF in PT and full-term (FT) newborns at term-equivalent age (TEA) and to assess the relationship between the features of the CBF pattern and both prematurity and prematurity-related brain lesions. In this prospective study, we obtained measures of CBF in 66 PT (51 without and 15 with prematurity-related brain lesions) and 38 FT newborns through pseudo-continuous arterial spin labeling (pCASL) MRI acquired at TEA. The pattern of GM CBF was characterized by combining an atlas-based automated segmentation of structural MRI with spatial normalization and hierarchical clustering. The effects of gestational age (GA) at birth and brain injury on the CBF pattern were investigated. We identified 4 physiologically-derived clusters of brain regions that were labeled Fronto-Temporal, Parieto-Occipital, Insular-Deep GM (DGM) and Sensorimotor, from the least to the most perfused. We demonstrated that GM perfusion was associated with GA at birth in the Fronto-Temporal and Sensorimotor clusters, positively and negatively, respectively. Moreover, the presence of periventricular leukomalacia was associated with significantly increased Fronto-Temporal GM perfusion and decreased Insular-DGM perfusion, while the presence of germinal matrix hemorrhage appeared to mildly decrease the Insular-DGM perfusion. Prematurity and prematurity-related brain injury heterogeneously affect brain perfusion. ASL MRI may, therefore, have strong potential as a noninvasive tool for the accurate stratification of individuals at risk of domain-specific impairment.

Heart rate surge at respiratory event termination in preterm and term born children with sleep disordered breathing

BACKGROUND

Repetitive surges in heart rate (HR) at respiratory event termination underpin the altered autonomic HR control associated with sleep disordered breathing (SDB). As children born preterm are at greater risk of adverse cardiovascular outcomes, we aimed to determine whether the HR response to obstructive respiratory events was elevated compared to term-born children.

METHODS

Fifty children (3-12 years) born preterm, were matched for SDB severity, age and gender with term born children. Multilevel modelling determined the effect of preterm birth and arousal on HR changes between a 10s baseline to the latter half of respiratory events and 15s post event during NREM and REM.

RESULTS

1203 events were analysed (NREM: term 380; preterm 383; REM: term 207; preterm 233). During NREM fewer events terminated in arousal in the preterm compared with term group (preterm 68%; term 84%; χ² = 27.2, p < 0.001). There were no differences in REM. During NREM, HR was lower in the preterm group at all event phases, with and without associated arousals (P < 0.01 for all). % change in HR from baseline to post event was higher in the preterm compared with term group (preterm: median 23% IQR (12%,34%); term: 18% (10%,29%); p < 0.01) and late event to post event (preterm: 30% (21%, 32%); term 28% (20%,39%); p < 0.01) in events associated with arousals.

CONCLUSION

The greater magnitude of surges in HR following respiratory events terminating with arousal in preterm born children, although small, occur repeatedly throughout the night and may contribute to adverse cardiovascular outcomes, although further studies are required.

Gentle as a mother's touch: C-tactile touch promotes autonomic regulation in preterm infants

Preterm infants are challenged to adapt to an extrauterine milieu, while their interoceptive system and autonomic regulation capacity is still immature. Caressing parental touch is known to foster parasympathetic regulation in infants by stimulating C-tactile (CT) afferents and in preterm infants, slow stroking stimulation also leads to a heart rate decrease. The particular impact of maternal stroking has not yet been investigated and factors influencing the maturation of the CT system in preterm infants remain unclear. We therefore analysed 53 standardized events in which preterm infants (24 to 36 weeks gestational age at birth) were stroked by their mothers. Video analysis revealed that mothers use CT optimal velocities to stroke their preterm child. Analysis of pulse oximetric data showed no effect of stroking on infantile blood oxygenation, but a significant decrease of the heart rate. Compared to term-born children, this decrease was delayed by about two minutes. Furthermore, our data suggested that more immature preterm infants benefited less from stroking than more mature ones. We conclude that maternal stroking touch targets CT afferents in preterm infants and that the preterm CT system is not yet mature.

In infants with congenital heart disease autonomic dysfunction is associated with pre-operative brain injury

BACKGROUND

Brain injury is a serious and common complication of critical congenital heart disease (CHD). Impaired autonomic development (assessed by heart rate variability (HRV)) is associated with brain injury in other high-risk neonatal populations.

OBJECTIVE

To determine whether impaired early neonatal HRV is associated with pre-operative brain injury in CHD.

METHODS

In infants with critical CHD, we evaluated HRV during the first 24 h of cardiac ICU (CICU) admission using time-domain (RMS 1, RMS 2, and alpha 1) and frequency-domain metrics (LF, nLF, HF, nHF). Pre-operative brain magnetic resonance imaging (MRI) was scored for injury using an established system. Spearman's correlation coefficient was used to determine the association between HRV and pre-operative brain injury.

RESULTS

We enrolled 34 infants with median birth gestational age of 38.8 weeks (IQR 38.1-39.1). Median postnatal age at pre-operative brain MRI was 2 days (IQR 1-3 days). Thirteen infants had MRI evidence of brain injury. RMS 1 and RMS 2 were inversely correlated with pre-operative brain injury.

CONCLUSIONS

Time-domain metrics of autonomic function measured within the first 24 h of admission to the CICU are associated with pre-operative brain injury, and may perform better than frequency-domain metrics under non-stationary conditions such as critical illness.

IMPACT

Autonomic dysfunction, measured by heart rate variability (HRV), in early transition is associated with pre-operative brain injury in neonates with critical congenital heart disease. These data extend our earlier findings by providing further evidence for (i) autonomic dysfunction in infants with CHD, and (ii) an association between autonomic dysfunction and brain injury in critically ill neonates. These data support the notion that further investigation of HRV as a biomarker for brain injury risk is warranted in infants with critical CHD.

Effect of Kangaroo Position on microcirculation of preterm newborns: a controlled randomized clinical trial

OBJECTIVE

The objective of this study was to evaluate the effect of Kangaroo Position (KP) in microcirculation (MC) of the flexor muscles of preterm newborns.

METHOD

A controlled clinical trial was conducted in the city of Recife, Brazil, with 26 preterm children randomized in the Kangaroo Group (13) and in the Control Group (13). Assessments of blood flow, temperature, and tissue oxygen saturation (SO₂) were made at two different times and in the biceps brachii muscle and hamstrings muscle group: before the KP and after 24 h of KP. In the Control Group, the registrations were performed at the times corresponding to those of the Kangaroo Group. The mean values among the times were analyzed by paired t-test for repeated measures. The clinical trial was recorded in Clinical Trials (NCT03611088).

RESULTS

In the Kangaroo Group there was an increase in tissue temperature and blood flow at the time evaluation periods (p < 0.05). In the control group, there was no statistical difference between the recording moments hamstring muscles group, but in the biceps brachii, there was a reduction in mean blood flow (p = 0.023).

CONCLUSION

In conclusion, the KP has effects on the microcirculation of the flexor muscles of preterm newborns.

Pulmonary Resilience: Moderating the Association between Oxygen Exposure and Pulmonary Outcomes in Extremely Preterm Newborns

Bronchopulmonary dysplasia (BPD) is a chronic lung disease of infancy associated with high morbidity and mortality. Although most prevalent following extremely preterm birth, BPD is diagnosed at 36 weeks post-menstrual age, when the disease trajectory is underway, and long-term physiological implications may be irreversible. There is an urgent and unmet need to identify how early exposures can be modified to decrease the risk of developing BPD before disease progression becomes irreversible. Extremely preterm newborns encounter a paradox at birth: oxygen is a life-sustaining component of ex utero life yet is undeniably toxic. Attempts at minimizing supplemental oxygen exposure by targeting lower oxygen saturations appear to decrease BPD but may increase mortality. Given the potential association between lower oxygen saturations and increased mortality, practice guidelines favor targeting higher saturations. This uniformly increases oxygen exposure, prompting a cascade of pathogenic mechanisms implicated in BPD development. In this review, we introduce the concept of pulmonary resilience: a homeostatic process driven by the autonomic nervous system (ANS) as a moderator of physiologic stress that when functional, could inform successful environmental adaptation following extremely preterm birth. We hypothesize that infants with early-life ANS dysfunction require a higher oxygen dose for survival; conversely, oxygen exposure could be safely limited in infants with more robust early-life ANS function, an indicator of pulmonary resilience. Characterizing the pulmonary resilience continuum to guide individualized supplemental oxygen dosing may reduce morbidity and mortality in this growing population of extremely preterm infants at risk for BPD.

Correlation between arterial blood pressures and regional cerebral oxygen saturation in preterm neonates during postnatal transition-an observational study

OBJECTIVE

To assess whether blood pressure (systolic (SABP), diastolic (DABP), and mean arterial blood pressure (MABP) and cerebral-regional-oxygen-saturation (crSO2) and cerebral-fractional-tissue-oxygen-extraction (cFTOE) are associated after immediate fetal-to-neonatal transition in preterm neonates with and without respiratory support.

STUDY DESIGN

Post-hoc analyses of secondary outcome parameters of prospective observational studies were performed. We included moderate and late preterm neonates with and without respiratory support with cerebral NIRS monitoring (INVOS 5100c) and an oscillometric blood pressure measurement at minute 15 after birth. Heart rate (HR) and arterial oxygen saturation (SpO2) were monitored routinely. Blood pressure values were correlated with crSO2 and cFTOE.

RESULTS

47 preterm neonates with NIRS measurements and blood pressure measurement during immediate transition after birth were included. Twenty-five preterm neonates (gestational age: 34.4±1.6 weeks) received respiratory support. In these neonates crSO2 correlated significantly positively with systolic blood pressure (SABP; r = 0.46, p = 0.021), diastolic blood pressure (DABP; r = 0.51, p = 0.009) and, mean arterial pressure (MABP; r = 0.48, p = 0.015). cFTOE correlated significantly negatively with SABP (r = -0.44, p = 0.027), DABP (r = -0.49, p = 0.013) and mean MABP (r = -0.44, p = 0.029). Twenty-two preterm neonates (gestational age: 34.5 ± 1.5 weeks) did not receive respiratory support. In those neonates, neither crSO2 nor cFTOE correlated with blood pressure.

CONCLUSION

In compromised moderate and late preterm neonates with respiratory support, both, crSO2 and cFTOE correlated with blood pressure. These findings suggest that passive pressure-dependent cerebral perfusion was present in preterm neonates with respiratory support, indicating an impaired cerebral autoregulation in those compromised preterm neonates.

Plasma Leak From the Circulation Contributes to Poor Outcomes for Preterm Infants: A Working Hypothesis

Preterm infants are at high risk of death and disability resulting from brain injury. Impaired cardiovascular function leading to poor cerebral oxygenation is a significant contributor to these adverse outcomes, but current therapeutic approaches have failed to improve outcome. We have re-examined existing evidence regarding hypovolemia and have concluded that in the preterm infant loss of plasma from the circulation results in hypovolemia; and that this is a significant driver of cardiovascular instability and thus poor cerebral oxygenation. High capillary permeability, altered hydrostatic and oncotic pressure gradients, and reduced lymphatic return all combine to increase net loss of plasma from the circulation at the capillary. Evidence is presented that early hypovolemia occurs in preterm infants, and that capillary permeability and pressure gradients all change in a way that promotes rapid plasma loss at the capillary. Impaired lymph flow, inflammation and some current treatment strategies may further exacerbate this plasma loss. A framework for testing this hypothesis is presented. Understanding these mechanisms opens the way to novel treatment strategies to support cardiovascular function and cerebral oxygenation, to replace current therapies, which have been shown not to change outcomes.

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.

Arterial spin labeling perfusion in neonates

Abnormal brain perfusion is a key mechanism underlying neonatal brain injury. Understanding the mechanisms leading to brain perfusion changes in high-risk neonates and how these alterations may influence brain development is key to improve therapeutic strategies preventing brain injury and the neurodevelopmental outcome of these infants. To date, several studies demonstrated that Arterial Spin Labeling is a reliable tool to accurately and non-invasively analyze brain perfusion, facilitating the understanding of normal and pathological mechanisms underlying neonatal brain maturation and injury. This paper provides an overview of the normal pattern of brain perfusion on Arterial Spin Labeling in term and preterm neonates, and reviews perfusion abnormalities associated with common neonatal neurological disorders.

Cerebral Autoregulation in Sick Infants: Current Insights

Cerebrovascular autoregulation is the ability to maintain stable cerebral blood flow within a range of cerebral perfusion pressures. When cerebral perfusion pressure is outside the limits of effective autoregulation, the brain is subjected to hypoperfusion or hyperperfusion, which may cause vascular injury, hemorrhage, and/or hypoxic white matter injury. Infants born preterm, after fetal growth restriction, with congenital heart disease, or with hypoxic-ischemic encephalopathy are susceptible to a failure of cerebral autoregulation. Bedside assessment of cerebrovascular autoregulation would offer the opportunity to prevent brain injury. Clinicians need to know which patient populations and circumstances are associated with impaired/absent cerebral autoregulation.

Electrocardiographic features at rest and during exercise in young adults born preterm below 30 weeks of gestation

BACKGROUND

Preterm birth has adverse consequences on the cardiovascular system. Whether premature birth is associated with conduction and repolarisation abnormalities past childhood and into adulthood still needs to be demonstrated.

METHODS

We analyzed the ECG of young adults (23.9 ± 3.1 years) born term (≥37 weeks, n = 53) and preterm (<30 weeks, n = 49) at rest, peak exercise and 3 min into recovery during an exercise test on a cycle ergometer. We measured PR, QRS and QT intervals, calculated the corrected QT (QTc), and determined blood calcium, magnesium, potassium and fasting glucose.

RESULTS

Mean gestational age was 39.7 ± 1.1 and 27.3 ± 1.3 weeks for the term and the preterm groups, respectively. Apart from an increased heart rate at rest in individuals born preterm, no significant difference was found between both groups for any other ECG parameters at rest. None of the participants had a severely prolonged QTc (>500 ms) at rest; exercise revealed severely prolonged QTc in two participants including one in the preterm group. The use of QT-prolonging medications did not influence ECG parameters in either groups.

CONCLUSIONS

We observed no significant difference in electrocardiographic measurements between young adults born preterm and term. Current results do not support avoidance of QT-prolonging medications in individuals born preterm.

IMPACT

Preterm birth is associated with adverse cardiovascular consequences in early adulthood, but controversial evidence exists regarding differences in electrocardiographic features between young individuals born term and preterm.This study aims to assess the differences in electrocardiographic features between young adults born term and preterm, at rest and during exercise training.In contrast with previously published data, we observed no significant difference in electrocardiographic measurements between young adults born preterm and term.Our study does not support that preterm birth itself exposes young adults to a higher risk of QT prolongation.Current results do not support avoidance of QT-prolonging medications in individuals born preterm.

SIDS, prone sleep position and infection: An overlooked epidemiological link in current SIDS research? Key evidence for the "Infection Hypothesis"

Mainstream researchers explain the etiology of SIDS with the cardiorespiratory paradigm. This has been the focus of intense study for many decades without providing consistent supporting data to link CNS findings to epidemiological risk factors or to the usual clinicopathological findings. Despite this, and the apparent oversight of the link between prone sleep position and respiratory infection, papers citing CNS, cardiac and sleep arousal findings continue to be published. Discovery of the prone sleep position risk factor provided tangential support for the cardiorespiratory control hypothesis which defines the mainstream approach. Despite many decades of research and huge expenditure, no aetiological answer has been forthcoming. In asking why?This paper exposes some of the shortcomings regarding this apparent oversight by mainstream SIDS researchers and examines the role of respiratory infection and puts the case for the “Infection Hypothesis.” In addition, the paper provides encouragement to neuropathologists to examine the potential link between CNS findings and cardiac function (as opposed to respiratory function) in relation to infection and to examine possible correlates between CNS findings and established risk factors such as recent infection, contaminated sleeping surfaces, maternal/obstetric/higher birth, ethnicity, non-breast-feeding, male gender, etc. or with the usual gross pathological findings of SIDS (intrathoracic petechial hemorrhages, liquid blood, congested lungs). The shortcomings exposed through this review invite questions over current research directions and hopefully encourage research into other more plausible hypotheses, such as the infection paradigm.•

Mainstream SIDS researchers appear to have overlooked the key relationship between prone sleep position and infection.

•

This omission has major implications for current and future SIDS research.

Autonomic nervous system maturation in the premature extrauterine milieu

BACKGROUND

In premature infants, we investigated whether the duration of extrauterine development influenced autonomic nervous system (ANS) maturation.

METHODS

We performed a longitudinal cohort study of ANS maturation in preterm infants. Eligibility included birth gestational age (GA) < 37 weeks, NICU admission, and expected survival. The cohort was divided into three birth GA groups: Group 1 (≤29 weeks), Group 2 (30-33 weeks), and Group 3 (≥34 weeks). ECG data were recorded weekly and analyzed for sympathetic and parasympathetic tone using heart rate variability (HRV). Quantile regression modeled the slope of ANS maturation among the groups by postnatal age to term-equivalent age (TEA) (≥37 weeks).

RESULTS

One hundred infants, median (Q1-Q3) birth GA of 31.9 (28.7-33.9) weeks, were enrolled: Group 1 (n = 35); Group 2 (n = 40); and Group 3 (n = 25). Earlier birth GA was associated with lower sympathetic and parasympathetic tone. However, the rate of autonomic maturation was similar, and at TEA there was no difference in HRV metrics across the three groups. The majority of infants (91%) did not experience significant neonatal morbidities.

CONCLUSION

Premature infants with low prematurity-related systemic morbidity have maturational trajectories of ANS development that are comparable across a wide range of ex-utero durations regardless of birth GA.

IMPACT

Heart rate variability can evaluate the maturation of the autonomic nervous system. Metrics of both the sympathetic and parasympathetic nervous system show maturation in the premature extrauterine milieu. The autonomic nervous system in preterm infants shows comparable maturation across a wide range of birth gestational ages. Preterm newborns with low medical morbidity have maturation of their autonomic nervous system while in the NICU. Modern NICU advances appear to support autonomic development in the preterm infant.

Getting an Early Start in Understanding Perinatal Asphyxia Impact on the Cardiovascular System

Perinatal asphyxia (PA) is a burdening pathology with high short-term mortality and severe long-term consequences. Its incidence, reaching as high as 10 cases per 1000 live births in the less developed countries, prompts the need for better awareness and prevention of cases at risk, together with management by easily applicable protocols. PA acts first and foremost on the nervous tissue, but also on the heart, by hypoxia and subsequent ischemia-reperfusion injury. Myocardial development at birth is still incomplete and cannot adequately respond to this aggression. Cardiac dysfunction, including low ventricular output, bradycardia, and pulmonary hypertension, complicates the already compromised circulatory status of the newborn with PA. Multiorgan and especially cardiovascular failure seem to play a crucial role in the secondary phase of hypoxic-ischemic encephalopathy (HIE) and its high mortality rate. Hypothermia is an acceptable solution for HIE, but there is a fragile equilibrium between therapeutic gain and cardiovascular instability. A profound understanding of the underlying mechanisms of the nervous and cardiovascular systems and a close collaboration between the bench and bedside specialists in these domains is compulsory. More resources need to be directed toward the prevention of PA and the consecutive decrease of cardiovascular dysfunction. Not much can be done in case of an unexpected acute event that produces PA, where recognition and prompt delivery are the key factors for a positive clinical result. However, the situation is different for high-risk pregnancies or circumstances that make the fetus more vulnerable to asphyxia. Improving the outcome in these cases is possible through careful monitoring, identifying the high-risk pregnancies, and the implementation of novel prenatal strategies. Also, apart from adequately supporting the heart through the acute episode, there is a need for protocols for long-term cardiovascular follow-up. This will increase our recognition of any lasting myocardial damage and will enhance our perspective on the real impact of PA. The goal of this article is to review data on the cardiovascular consequences of PA, in the context of an immature cardiovascular system, discuss the potential contribution of cardiovascular impairment on short and long-term outcomes, and propose further directions of research in this field.

The impact of preterm adversity on cardiorespiratory function

NEW FINDINGS

What is the topic of this review? We review the influence of prematurity on the cardiorespiratory system and examine the common sequel of alterations in oxygen tension, and immune activation in preterm infants. What advances does it highlight? The review highlights neonatal animal models of intermittent hypoxia, hyperoxia and infection that contribute to our understanding of the effect of stress on neurodevelopment and cardiorespiratory homeostasis. We also focus on some of the important physiological pathways that have a modulatory role on the cardiorespiratory system in early life.

ABSTRACT

Preterm birth is one of the leading causes of neonatal mortality. Babies that survive early-life stress associated with immaturity have significant prevailing short- and long-term morbidities. Oxygen dysregulation in the first few days and weeks after birth is a primary concern as the cardiorespiratory system slowly adjusts to extrauterine life. Infants exposed to rapid alterations in oxygen tension, including exposures to hypoxia and hyperoxia, have altered redox balance and active immune signalling, leading to altered stress responses that impinge on neurodevelopment and cardiorespiratory homeostasis. In this review, we explore the clinical challenges posed by preterm birth, followed by an examination of the literature on animal models of oxygen dysregulation and immune activation in the context of early-life stress.

Heart rate variability is depressed in the early transitional period for newborns with complex congenital heart disease

PURPOSE

To compare early changes in autonomic nervous system (ANS) tone between newborns with complex congenital heart disease (CHD) and newborns without CHD.

METHODS

We performed a case-control study of heart rate variability (HRV) in newborns with complex CHD [transposition of the great arteries (TGA) or hypoplastic left heart syndrome (HLHS)] and low-risk control newborns without CHD. Cases with CHD were admitted following birth to a pediatric cardiac intensive care unit and had archived continuous ECG data. Control infants were prospectively enrolled at birth. ECG data in cases and controls were analyzed for HRV in the time and frequency domains at 24 h of age. We analyzed the following HRV metrics: alpha short (α_s), alpha long (α_L), root mean square short and long (RMS_s and RMS_L), low-frequency (LF) power, normalized LF (nLF), high-frequency (HF) power, and normalized HF (nHF). We used ANOVA to compare HRV metrics between groups and to control for medication exposures.

RESULTS

HRV data from 57 infants with CHD (TGA, n = 33 and HLHS, n = 24) and from 29 controls were analyzed. The HRV metrics α_S, RMS_L, LF, and nLF were significantly lower in infants with CHD than in the controls. Due to the effect of normalization, nHF was higher in CHD infants (P < 0.0001), although absolute HF was lower (P = 0.0461). After adjusting for medications, α_S and nLF remained lower and nHF higher in newborns with CHD (P  < 0.0005).

CONCLUSIONS

Infants with complex CHD have depressed autonomic balance in the early postnatal period, which may complicate the fetal-neonatal transition.

The Potential of Stem Cell Therapy to Repair White Matter Injury in Preterm Infants: Lessons Learned From Experimental Models

Diffuse white matter injury (dWMI) is a major cause of morbidity in the extremely preterm born infant leading to life-long neurological impairments, including deficits in cognitive, motor, sensory, psychological, and behavioral functioning. At present, no treatment options are clinically available to combat dWMI and therefore exploration of novel strategies is urgently needed. In recent years, the pathophysiology underlying dWMI has slowly started to be unraveled, pointing towards the disturbed maturation of oligodendrocytes (OLs) as a key mechanism. Immature OL precursor cells in the developing brain are believed to be highly sensitive to perinatal inflammation and cerebral oxygen fluctuations, leading to impaired OL differentiation and eventually myelination failure. OL lineage development under normal and pathological circumstances and the process of (re)myelination have been studied extensively over the years, often in the context of other adult and pediatric white matter pathologies such as stroke and multiple sclerosis (MS). Various studies have proposed stem cell-based therapeutic strategies to boost white matter regeneration as a potential strategy against a wide range of neurological diseases. In this review we will discuss experimental studies focusing on mesenchymal stem cell (MSC) therapy to reduce white matter injury (WMI) in multiple adult and neonatal neurological diseases. What lessons have been learned from these previous studies and how can we translate this knowledge to application of MSCs for the injured white matter in the preterm infant? A perspective on the current state of stem cell therapy will be given and we will discuss different important considerations of MSCs including cellular sources, timing of treatment and administration routes. Furthermore, we reflect on optimization strategies that could potentially reinforce stem cell therapy, including preconditioning and genetic engineering of stem cells or using cell-free stem cell products, to optimize cell-based strategy for vulnerable preterm infants in the near future.

Cardiac Autonomic Function in Adults Born Preterm

OBJECTIVE

To evaluate cardiac autonomic function in adults born preterm.

STUDY DESIGN

We studied the association between prematurity and cardiac autonomic function using heart rate variability measurements in 600 adults (mean age of 23.3 years) from a geographically based cohort in Northern Finland. There were 117 young adults born early preterm (<34 weeks), 207 born late preterm (34-36 weeks), and 276 born at term (≥37 weeks, controls). Autonomic function was analyzed by calculating time and frequency domain heart rate variability measurements using linear regression.

RESULTS

Compared with controls, the mean difference in root mean square of successive differences (indicating cardiac vagal activity) was -12.0% (95% CI -22.2%, -0.5%, adjusted for sex, age, source cohort, and season P = .04) for the early preterm group and -7.8% (-16.8%, 2.0%, P = .12) for the late preterm group. Mean differences with controls in low frequency power (indicating cardiac vagal activity, including some sympathetic- and baroreflex-mediated effects) were -13.6% (-26.7%, 1.8%, P = .08) for the early preterm group and -16.4% (-27.0%, -4.3%, P = .01) for the late preterm group. Mean differences in high frequency power (quantifying cardiac vagal modulation in respiratory frequency) were -19.2% (-36.6%, 2.9%, P = .09) for the early preterm group and -13.8% (-29.4%, 5.3%, P = .15) for the late preterm group. Differences were attenuated when controlled for body mass index and physical activity.

CONCLUSIONS

Our results suggest altered autonomic regulatory control in adults born preterm, including those born late preterm. Altered autonomic regulatory control may contribute to increased cardiovascular risk in adults born preterm.

Altered grey matter volume, perfusion and white matter integrity in very low birthweight adults

This study examined the long-term effects of being born very-low-birth-weight (VLBW, <1500 g) on adult cerebral structural development using a multi-method neuroimaging approach. The New Zealand VLBW study cohort comprised 413 individuals born VLBW in 1986. Of the 338 who survived to discharge, 229 were assessed at age 27–29 years. Of these, 150 had a 3 T MRI scan alongside 50 healthy term-born controls. The VLBW group included 53/57 participants born <28 weeks gestation. MRI analyses included: a) structural MRI to assess grey matter (GM) volume and cortical thickness; b) arterial spin labelling (ASL) to quantify GM perfusion; and c) diffusion tensor imaging (DTI) to measure white matter (WM) integrity. Compared to controls, VLBW adults had smaller GM volumes within frontal, temporal, parietal and occipital cortices, bilateral cingulate gyri and left caudate, as well as greater GM volumes in frontal, temporal and occipital areas. Thinner cortex was observed within frontal, temporal and parietal cortices. VLBW adults also had less GM perfusion within limited temporal areas, bilateral hippocampi and thalami. Finally, lower fractional anisotropy (FA) and axial diffusivity (AD) within principal WM tracts was observed in VLBW subjects. Within the VLBW group, birthweight was positively correlated with GM volume and perfusion in cortical and subcortical regions, as well as FA and AD across numerous principal WM tracts. Between group differences within temporal cortices were evident across all imaging modalities, suggesting that the temporal lobe may be particularly susceptible to disruption in development following preterm birth. Overall, findings reveal enduring and pervasive effects of preterm birth on brain structural development, with individuals born at lower birthweights having greater long-term neuropathology.

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Very-low-birth-weight adults had smaller GM volumes and thinner cortex than controls.

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VLBW adults also showed regions of larger grey matter volumes and thicker cortex.

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Several small regions showed lower cerebral perfusion in VLBW adults than in controls.

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Diffusion tensor MRI suggested poorer WM integrity in VLBW adults than in controls.

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Within VLBW adults, all MRI measures showed positive associations with birthweight.

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.

Bradycardias are associated with more severe effects on cerebral oxygenation in very preterm infants than in late preterm infants

BACKGROUND

Commonly the magnitude and frequency of bradycardia is underestimated in the neonatal unit due to the long averaging time used in bedside oximeters. We aimed to assess the frequency and severity of bradycardia in preterm infants using the lowest averaging time (2 s) available on a clinical oximeter, compared with bradycardia detected using electrocardiogram (ECG), and whether bradycardia severity and postmenstrual age affected cerebral oxygenation.

METHODS

Preterm infants (10 M/9F) were studied longitudinally at 26-31 (very preterm) and 32-38 weeks (late preterm) postmenstrual age. Heart rate falls calculated from ECG were used to determine mild or moderate/severe (MS) bradycardias. Cerebral tissue oxygenation index (TOI, %) was recorded and fractional tissue oxygen extraction (FTOE) calculated.

RESULTS

Of the 615 bradycardias scored using ECG criteria, 10% were not detected by oximetry. TOI falls associated with bradycardias were greater for MS bradycardias compared with Mild for both groups (p < 0.001 for both). The FTOE associated with MS bradycardias was higher for the very preterm compared with the late preterm group (p < 0.001). In very preterm infants 61% of MS and 35% Mild bradycardias were associated with TOI nadirs below 55%.

CONCLUSION

Even the most sensitive oximeter setting underestimates bradycardias. The cerebral effect from bradycardias in very preterm infants is more severe than in late preterm infants. Even the mild bradycardias are associated with falls in cerebral oxygenation. Routine NIRS monitoring of cerebral oxygenation in NICUs may increase staff awareness for interventions to reduce the repetitive falls in cerebral oxygenation in preterm infants.

The Critical Role of the Central Autonomic Nervous System in Fetal-Neonatal Transition

The objective of this article is to understand the complex role of the central autonomic nervous system in normal and complicated fetal-neonatal transition and how autonomic nervous system dysfunction can lead to brain injury. The central autonomic nervous system supports coordinated fetal transitional cardiovascular, respiratory, and endocrine responses to provide safe transition of the fetus at delivery. Fetal and maternal medical and environmental exposures can disrupt normal maturation of the autonomic nervous system in utero, cause dysfunction, and complicate fetal-neonatal transition. Brain injury may both be caused by autonomic nervous system failure and contribute directly to autonomic nervous system dysfunction in the fetus and newborn. The central autonomic nervous system has multiple roles in supporting transition of the fetus. Future studies should aim to improve real-time monitoring of fetal autonomic nervous system function and in supporting typical autonomic nervous system development even under complicated conditions.

Supporting preterm cardiovascular function

Preterm infants are at higher risk of adverse neurodevelopmental outcomes. Inadequate cerebral oxygen delivery resulting from poor cardiovascular function is likely to be a significant contributor to preterm brain injury. In this context, improved support of cardiovascular function is integral to improving preterm outcomes. Many of the treatments used to support preterm cardiovascular function are based on adult physiology and may not be appropriate for the unique physiology of the preterm infant. The preterm heart is structurally immature with reduced contractility and low cardiac output. However, there is limited evidence that inotropic support with dopamine and/or dobutamine is effective in preterm babies. Hypovolemia may also contribute to poor preterm cardiovascular function; there is evidence that capillary leakage results in considerable loss of plasma from the circulation of newborn preterm babies. In addition, the vasoconstrictor response to acute stimuli does not develop until quite late in gestation and is limited in the preterm infant. This may lead to inappropriate vasodilatation adding to functional hypovolemia. The first line treatment for hypotension in preterm infants is volume expansion with crystalloid solutions, but this has limited efficacy in the preterm infant. More effective methods of volume expansion are required. Effective support of preterm cardiovascular function requires better understanding of preterm cardiovascular physiology so that treatments can target mechanisms that are sufficiently mature to respond.

Synchronized Oscillations of Arterial Oxygen Saturation, Cerebral Tissue Oxygenation and Heart Rate in Preterm Neonates: Investigation of Long-Term Measurements with Multiple Einstein's Cross Wavelet Analysis

BACKGROUND

In preterm neonates, the cardiovascular and cerebral vascular control is immature, making the brain vulnerable to an increased incidence of hypoxic and hyperoxic episodes.

AIM

The aim of the study was to apply the recently developed multiple Einstein's cross wavelet analysis (MECWA) to quantify the coupling of fluctuations of peripherally measured arterial oxygen saturation (SpO₂), cerebral tissue oxygen saturation (StO₂) and heart rate (HR).

METHODS

Two long-term measurements on preterm neonates with a gestational age at birth of 26.4 and 26.8 weeks and a postnatal age of 2.1 and 3.9 weeks were analyzed. MECWA was applied to SpO₂, StO₂ and HR.

RESULTS

MECWA showed that the fluctuations of SpO₂, StO₂ and HR were synchronized in the low-frequency range with periods of ~1 h and ~0.5 h. The amplitudes of the synchronization frequencies were dependent on the individual neonate.

DISCUSSION

MECWA is a useful novel tool to assess the coupling of physiological signals. The parameters determined by MECWA seem to be related to the chronobiological processes, as well as constant regulations of the cardiovascular and cerebral perfusion state.

CONCLUSION

MECWA was able to identify long-term synchronization of the cardiovascular and cerebral perfusion state in preterm neonates with periods of ~1 h and ~0.5 h.

Autonomic nervous system depression at term in neurologically normal premature infants

BACKGROUND

Premature infants are vulnerable to destructive brain injury and disturbed neurological development. Prematurity may alter maturation of the central autonomic nervous system (ANS).

AIMS

To compare ANS function (using heart rate variability; HRV) between preterm infants with normal neuroimaging at term equivalent age and low-risk term controls. Study design, subjects. We performed a case-control study of preterm infants born ≤28 weeks gestational age that had normal brain imaging and archived continuous EKG data at term equivalent age. We documented other factors thought to influence ANS maturation (e.g. infection, ventilation days, and postnatal steroids). Controls were low-risk term gestational age newborns from uncomplicated pregnancies/deliveries. We characterized HRV metrics using frequency-(Welch periodogram) and time-domain (detrended fluctuation) analyses. Sympathetic tone was characterized by α1, root mean square analysis (RMS1 and RMS2), low-frequency (LF) power, and normalized LF (nLF) and parasympathetic tone was characterized by high-frequency (HF) power and normalized HF (nHF). α2 characterized ultraslow changes in heart rate. We used ANCOVA to compare HRV metrics between groups. Outcome measures, results. HRV from 26 preterm infants were compared to 55 controls. Analyzed HRV data for preterm infants were recorded at median (range) gestational age of 39 (36-39) weeks and for controls at 39 (37-41) weeks gestational age. α1, RMS2, LF and HF were significantly higher in control infants and remained significant after controlling for infection, ventilator days, and postnatal steroids (P < .005).

CONCLUSIONS

Autonomic maturation is impaired in a premature extrauterine environment. In the absence of destructive brain injury, our data suggest an important role for disturbed programming in this impaired autonomic development.

Reduced blood volume decreases cerebral blood flow in preterm piglets

KEY POINTS

Preterm infants often have poor cardiovascular function that is associated with adverse neurodevelopmental outcomes. Preterm infants may be vulnerable to hypovolaemia due to excessive vasodilatation and leaky capillaries. Following reduction in blood volume, cardiac output and mean arterial pressure were reduced to the same extent in term and preterm piglets. Cerebral blood flow was maintained following blood volume reduction in term but not in preterm piglets. Effective detection and treatment of functional hypovolaemia may reduce the risk of brain injury in preterm infants.

ABSTRACT

Preterm infants often have impaired cardiovascular function that may contribute to poor neurodevelopmental outcomes. The study aimed to determine the effects of reduced blood volume on cardiovascular function, including cerebral blood flow, in preterm and term piglets. In preterm (97/115 days) and term piglets, up to 10% of the estimated blood volume was removed. Removal of blood was stopped if MAP dropped below 20 mmHg. Heart rate, cardiac contractility and relaxation, cardiac output, mean arterial pressure (MAP), and cerebral blood flow were measured at baseline and again after blood volume reduction. The volume of blood removed was less in preterm piglets than in term piglets (5.1 ± 1.8 vs. 7.7 ± 0.9 mL kg^-1 , mean ± SD, P < 0.001). Cardiac output and MAP decreased to the same extent in term and preterm piglets. Cerebral blood flow decreased in preterm but not term piglets and cerebral vascular conductance increased in term piglets only. Compensatory responses to maintain cerebral blood flow after blood volume reduction are active in term piglets but not in preterm piglets. As a result, even a small reduction in blood volume, or an increase in the capacity of the circulatory system leading to functional hypovolaemia, may lead to a significant reduction in cerebral blood flow and contribute to brain injury in preterm neonates.

Cerebral Perfusion Is Perturbed by Preterm Birth and Brain Injury

BACKGROUND AND PURPOSE

Early disturbances in systemic and cerebral hemodynamics are thought to mediate prematurity-related brain injury. However, the extent to which CBF is perturbed by preterm birth is unknown. Our aim was to compare global and regional CBF in preterm infants with and without brain injury on conventional MR imaging using arterial spin-labeling during the third trimester of ex utero life and to examine the relationship between clinical risk factors and CBF.

MATERIALS AND METHODS

We prospectively enrolled preterm infants younger than 32 weeks' gestational age and <1500 g and performed arterial spin-labeling MR imaging studies. Global and regional CBF in the cerebral cortex, thalami, pons, and cerebellum was quantified. Preterm infants were stratified into those with and without structural brain injury. We further categorized preterm infants by brain injury severity: moderate-severe and mild.

RESULTS

We studied 78 preterm infants: 31 without brain injury and 47 with brain injury (29 with mild and 18 with moderate-severe injury). Global CBF showed a borderline significant increase with increasing gestational age at birth (P = .05) and trended lower in preterm infants with brain injury (P = .07). Similarly, regional CBF was significantly lower in the right thalamus and midpons (P < .05) and trended lower in the midtemporal, left thalamus, and anterior vermis regions (P < .1) in preterm infants with brain injury. Regional CBF in preterm infants with moderate-severe brain injury trended lower in the midpons, right cerebellar hemisphere, and dentate nuclei compared with mild brain injury (P < .1). In addition, a significant, lower regional CBF was associated with ventilation, sepsis, and cesarean delivery (P < .05).

CONCLUSIONS

We report early disturbances in global and regional CBF in preterm infants following brain injury. Regional cerebral perfusion alterations were evident in the thalamus and pons, suggesting regional vulnerability of the developing cerebro-cerebellar circuitry.

Autonomic Dysfunction in Neonates with Hypoxic Ischemic Encephalopathy Undergoing Therapeutic Hypothermia Impairs Physiological Responses to Routine Care Events

OBJECTIVE

To evaluate whether infants with hypoxic-ischemic encephalopathy and evidence of autonomic dysfunction have aberrant physiological responses to care events that could contribute to evolving brain injury.

STUDY DESIGN

Continuous tracings of heart rate (HR), blood pressure (BP), cerebral near infrared spectroscopy, and video electroencephalogram data were recorded from newborn infants with hypoxic-ischemic encephalopathy who were treated with hypothermia. Videos between 16 and 24 hours of age identified 99 distinct care events, including stimulating events (diaper changes, painful procedures), and vagal stimuli (endotracheal tube manipulations, pupil examinations). Pre-event HR variability was used to stratify patients into groups with impaired versus intact autonomic nervous system (ANS) function. Postevent physiological responses were compared between groups with the nearest mean classification approach.

RESULTS

Infants with intact ANS had increases in HR/BP after stimulating events, whereas those with impaired ANS showed no change or decreased HR/BP. With vagal stimuli, the HR decreased in infants with intact ANS but changed minimally in those with impaired ANS. A pupil examination in infants with an intact ANS led to a stable or increased BP, whereas the BP decreased in the group with an impaired ANS. Near infrared spectroscopy measures of cerebral blood flow/blood volume increased after diaper changes in infants with an impaired ANS, but were stable or decreased in those with an intact ANS.

CONCLUSION

HR variability metrics identified infants with impaired ANS function at risk for maladaptive responses to care events. These data support the potential use of HR variability as a real-time, continuous physiological biomarker to guide neuroprotective care in high-risk newborns.

Regional microstructural organization of the cerebral cortex is affected by preterm birth

Objectives

To compare regional cerebral cortical microstructural organization between preterm infants at term-equivalent age (TEA) and healthy full-term newborns, and to examine the impact of clinical risk factors on cerebral cortical micro-organization in the preterm cohort.

Study design

We prospectively enrolled very preterm infants (gestational age (GA) at birth<32 weeks; birthweight<1500 g) and healthy full-term controls. Using non-invasive 3T diffusion tensor imaging (DTI) metrics, we quantified regional micro-organization in ten cerebral cortical areas: medial/dorsolateral prefrontal cortex, anterior/posterior cingulate cortex, insula, posterior parietal cortex, motor/somatosensory/auditory/visual cortex. ANCOVA analyses were performed controlling for sex and postmenstrual age at MRI.

Results

We studied 91 preterm infants at TEA and 69 full-term controls. Preterm infants demonstrated significantly higher diffusivity in the prefrontal, parietal, motor, somatosensory, and visual cortices suggesting delayed maturation of these cortical areas. Additionally, postnatal hydrocortisone treatment was related to accelerated microstructural organization in the prefrontal and somatosensory cortices.

Conclusions

Preterm birth alters regional microstructural organization of the cerebral cortex in both neurocognitive brain regions and areas with primary sensory/motor functions. We also report for the first time a potential protective effect of postnatal hydrocortisone administration on cerebral cortical development in preterm infants.

Altered Cerebral Perfusion in Infants Born Preterm Compared with Infants Born Full Term

OBJECTIVES

To compare regional cerebral cortical blood flow (CBF) in infants born very preterm at term-equivalent age (TEA) and healthy newborns born full term and to examine the impact of clinical risk factors on CBF in the cohort born preterm.

STUDY DESIGN

This prospective, cross-sectional study included infants born very preterm (gestational age at birth <32 weeks; birth weight <1500 g) and healthy infants born full term. Using noninvasive 3T arterial spin labeling magnetic resonance imaging, we quantified regional CBF in the cerebral cortex: sensorimotor/auditory/visual cortex, superior medial/dorsolateral prefrontal cortex, anterior cingulate cortex (ACC)/posterior cingulate cortex, insula, and lateral posterior parietal cortex, as well as in the brainstem, and deep gray matter. Analyses were performed controlling for sex, gestational age, and age at magnetic resonance imaging.

RESULTS

We studied 202 infants: 98 born preterm and 104 born full term at TEA. Infants born preterm demonstrated greater global CBF (β = 9.03; P < .0001) and greater absolute regional CBF in all brain regions except the insula. Relative CBF in the insula, ACC and auditory cortex were decreased significantly in infants born preterm compared with their peers born at full term (P < .0001; P = .026; P = .036, respectively). In addition, the presence of parenchymal brain injury correlated with lower global and regional CBF (insula, ACC, sensorimotor, auditory, and visual cortices) whereas the need for cardiac vasopressor support correlated with lower regional CBF in the insula and visual cortex.

CONCLUSIONS

Altered regional cortical CBF in infants born very preterm at TEA may reflect early brain dysmaturation despite the absence of cerebral cortical injury. Furthermore, specific cerebral cortical areas may be vulnerable to early hemodynamic instability and parenchymal brain injury.

Cardiovascular autonomic dysfunction in sudden infant death syndrome

A failure of cardiorespiratory control mechanisms, together with an impaired arousal response from sleep, are believed to play an important role in the final event of sudden infant death syndrome (SIDS). The 'triple risk model' describes SIDS as an event that results from the intersection of three overlapping factors: (1) a vulnerable infant, (2) a critical developmental period in homeostatic control and (3) an exogenous stressor. In an attempt to understand how the triple risk hypothesis is related to infant cardiorespiratory physiology, many researchers have examined how the known risk and protective factors for SIDS alter infant cardiovascular control during sleep. This review discusses the association between the three components of the triple risk hypothesis and major risk factors for SIDS, such as prone sleeping, maternal smoking, together with three "protective" factors, and cardiovascular control during sleep in infants, and discusses their potential involvement in SIDS.

Heart rate variability and salivary cortisol in very preterm children during school age

The autonomic nervous system (ANS) plays a major role in the human stress response and reflects physical and psychological adaptability to a changing environment. Long-term exposure to early life stressors may alter the function of the ANS. The present study examines differences in the ANS between children born very preterm and full-term as well as the association between the ANS and the hypothalamic-pituitary-adrenal (HPA) axis, the other main branch of the human stress system. Fifty-four healthy children born very preterm (<32nd gestational week) and 67 full-term children aged 7-12 years provided data for the present study. Polysomnography (PSG) assessments were obtained during a night at the children's home in lying position at rest (wake) and during different sleep stages (stage 2 sleep, slow wave sleep, rapid-eye-movement sleep). Autonomic function was assessed by use of heart rate variability, specifically low frequency power (LF), high frequency power (HF), total spectral power (Tot Pow), and the LF/HF ratio. HPA axis activity was measured using salivary cortisol the next morning at awakening, 10, 20, and 30min later. Children born very preterm had lower LF/HF ratio during wake and stage 2 sleep compared to full-term children. Moreover, higher LF, Tot Pow, and LF/HF ratio during wake, stage 2 sleep, and REM sleep were related to more post-awakening cortisol secretion. The present study provides evidence on long-term ANS alterations after very preterm birth. Moreover, findings suggest a relation between the ANS and the HPA axis and therefore support the notion of mutual feedback between the two human stress systems.

Role of Perinatal Inflammation in Neonatal Arterial Ischemic Stroke

Based on the review of the literature, perinatal inflammation often induced by infection is the only consistent independent risk factor of neonatal arterial ischemic stroke (NAIS). Preclinical studies show that acute inflammatory processes take place in placenta, cerebral arterial wall of NAIS-susceptible arteries and neonatal brain. A top research priority in NAIS is to further characterize the nature and spatiotemporal features of the inflammatory processes involved in multiple levels of the pathophysiology of NAIS, to adequately design randomized control trials using targeted anti-inflammatory vasculo- and neuroprotective agents.

Origin and dynamics of oligodendrocytes in the developing brain: Implications for perinatal white matter injury

Infants born prematurely are at high risk to develop white matter injury (WMI), due to exposure to hypoxic and/or inflammatory insults. Such perinatal insults negatively impact the maturation of oligodendrocytes (OLs), thereby causing deficits in myelination. To elucidate the precise pathophysiology underlying perinatal WMI, it is essential to fully understand the cellular mechanisms contributing to healthy/normal white matter development. OLs are responsible for myelination of axons. During brain development, OLs are generally derived from neuroepithelial zones, where neural stem cells committed to the OL lineage differentiate into OL precursor cells (OPCs). OPCs, in turn, develop into premyelinating OLs and finally mature into myelinating OLs. Recent studies revealed that OPCs develop in multiple waves and form potentially heterogeneous populations. Furthermore, it has been shown that myelination is a dynamic and plastic process with an excess of OPCs being generated and then abolished if not integrated into neural circuits. Myelination patterns between rodents and humans show high spatial and temporal similarity. Therefore, experimental studies on OL biology may provide novel insights into the pathophysiology of WMI in the preterm infant and offers new perspectives on potential treatments for these patients.

Fetal-growth-restricted preterm infants display compromised autonomic cardiovascular control on the first postnatal day but not during infancy

BackgroundFetal growth restriction (FGR) is associated with increased perinatal mortality and long-term cardiovascular and neurodevelopmental sequelae. We hypothesized that FGR impacts on the development of autonomic heart rate and blood pressure control, contributing to unfavorable short- and long-term outcomes following FGR.MethodsWe studied 25 preterm FGR and 22 preterm and 19 term appropriate for gestational age (AGA) infants. Preterm neonates were studied on postnatal day 1, and all infants were studied at 1 and 6 months post-term age. To investigate autonomic cardiovascular control, we examined heart rate variability (HRV) and baroreflex sensitivity using spectral power and transfer-function analyses.ResultsPreterm FGR neonates exhibited higher heart rates and reduced HRV compared with preterm AGA controls on postnatal day 1. No significant differences were found between the three groups at 1 or 6 months post-term age.ConclusionPreterm FGR neonates display compromised HRV on postnatal day 1, which may suggest increased vulnerability to circulatory instability. This may predispose these neonates to systemic and cerebral hypoperfusion and increase the risk of long-term neurodevelopmental sequelae. Differences were no longer found at 1 and 6 months post-term age, suggesting that the maturation of autonomic cardiovascular control may be preserved following FGR.

Baroreflex Sensitivity in Premature Infants – Relation to the Parameters Characterizing Intrauterine and Postnatal Condition

At present, there are insufficient information about baroreflex sensitivity (BRS) and factors that determine BRS in premature newborns. The objective of this study was to determine the relationship between BRS and the characteristics that reflecting the intrauterine development (gestational age and birth weight), as well as postnatal development (postconception age and the actual weight of the child at the time of measurement). We examined 57 premature infants, who were divided into groups according to gestational age and postconception age as well as birth weight, and weight at the time of measurement. Continuous and noninvasive registration of peripheral blood pressure (BP) was performed in every child within 2-5 min under standard conditions using a Portapres (FMS) device. The results showed a close correlation of baroreflex sensitivity, heart rate and respiratory rate with gestational age, postconception age, birth weight and actual weight at the time of measurement premature newborns. An increase in the characteristics (ages and weights) resulted in increased BRS and diastolic arterial pressure (DAP), and in decreased heart and respiratory rates. Baroreflex sensitivity in the first week was in the group of very premature newborns the lowest (4.11 ms/mmHg) and in the light premature newborns was almost double (8.12 ms/mmHg). BRS increases gradually in relation to postnatal (chronological) and to postconception age as well as to birth and actual weight. The multifactor analysis of BRS identified birth weight and postconception age as the best BRS predictors. The two independent variables together explained 40 % of interindividual BRS variability.

Heart Rate Variability in Newborns

Heart rate (HR) and heart rate variability (HRV) in newborns is influenced by genetic determinants, gestational and postnatal age, and other variables. Premature infants have a reduced HRV. In neonatal HRV evaluated by spectral analysis, a dominant activity can be found in low frequency (LF) band (combined parasympathetic and sympathetic component). During the first postnatal days the activity in the high frequency (HF) band (parasympathetic component) rises, together with an increase in LF band and total HRV. Hypotrophy in newborn can cause less mature autonomic cardiac control with a higher contribution of sympathetic activity to HRV as demonstrated by sequence plot analysis. During quiet sleep (QS) in newborns HF oscillations increase – a phenomenon less expressed or missing in premature infants. In active sleep (AS), HRV is enhanced in contrast to reduced activity in HF band due to the rise of spectral activity in LF band. Comparison of the HR and HRV in newborns born by physiological vaginal delivery, without (VD) and with epidural anesthesia (EDA) and via sectio cesarea (SC) showed no significant differences in HR and in HRV time domain parameters. Analysis in the frequency domain revealed, that the lowest sympathetic activity in chronotropic cardiac chronotropic regulation is in the VD group. Different neonatal pathological states can be associated with a reduction of HRV and an improvement in the health conditions is followed by changes in HRV what can be use as a possible prognostic marker. Examination of heart rate variability in neonatology can provide information on the maturity of the cardiac chronotropic regulation in early postnatal life, on postnatal adaptation and in pathological conditions about the potential dysregulation of cardiac function in newborns, especially in preterm infants.

Malignant Cerebral Swelling After Cranioplasty due to Ipsilateral Intracranial Vasculopathy: Case Report and Literature Review

BACKGROUND

Cranioplasty is a well-established surgical operation that is used worldwide for patients with skull defects following decompressive craniectomy (DC). However, in some cases, potentially fatal complications may occur, such as malignant cerebral swelling after uneventful cranioplasty.

CASE DESCRIPTION

We present a rare case of massive malignant ipsilateral cerebral swelling following uneventful titanium mesh cranioplasty due to rare ipsilateral intracranial vasculopathy confirmed by magnetic resonance angiography (MRA) and magnetic resonance venography (MRV). Fortunately, we performed titanium mesh explantation and extended DC in time, and the patient survived. Malignant cerebral swelling after uneventful cranioplasty is an unpredictable but fatal complication. Most reported cases have had an unfavorable prognosis. To the best of our knowledge, the mechanism was first confirmed by MRA and MRV, which demonstrated that the cerebral swelling was due to unilateral intracranial vasculopathy, including a rare ipsilateral intracranial internal carotid artery occlusion, as well as extremely thin lateral and sigmoid sinuses.

CONCLUSIONS

Our case demonstrates for the first time that ipsilateral intracranial vasculopathy is a risk factor for malignant cerebral swelling after cranioplasty. Patients with traumatic brain injury with suspected intracranial vasculopathy should undergo a comprehensive vascular evaluation before cranioplasty to help prevent malignant cerebral swelling.

Population-based reference curve for umbilical cord arterial pH in infants born at 28 to 42 weeks

OBJECTIVE

The objective of the study was to examine normal variations of umbilical cord arterial pH by gestational age (GA).

STUDY DESIGN

Population-based cohort study of 46 199 infants born from 2008 to 2014 in Stockholm, Sweden, with GA 28 to 42 weeks, Apgar score ⩾7 at 5 min, non-instrumental vaginal delivery, and birth weight for GA⩾3rd and ⩽97th percentile. Quantile regression was used to investigate the associations between GA and infant sex, and pH.

RESULTS

The mean umbilical cord arterial pH (s.d.) was 7.29 (0.10), 7.27 (0.07), 7.25 (0.07) and 7.23 (0.07) among infants born at 28 to 31, 32 to 36, 37 to 41 and 42 weeks, respectively. Arterial pH decreased linearly with increasing GA, and female infants had higher pH than male infants (P<0.001).

CONCLUSION

Umbilical cord arterial pH varied in a linear fashion by GA and was influenced by infant sex. The provided reference curve taking GA into account may yield a more accurate definition of acidosis at birth.

Proteomic and transcriptomic study of brain microvessels in neonatal and adult mice

Infants born before 29 weeks gestation incur a major risk of preterm encephalopathy and subependymal/intracerebral/intraventricular haemorrhage. In mice, an ontogenic window of haemorrhage risk was recorded up to 5 days after birth in serpine1 knock-out animals. Using proteome and transcriptome approaches in mouse forebrain microvessels, we previously described the remodelling of extracellular matrix and integrins likely strengthening the vascular wall between postnatal day 5 (P5) and P10. Haemorrhage is the ultimate outcome of vessel damage (i.e., during ischaemia), although discreet vessel insults may be involved in the aetiology of preterm encephalopathy. In this study, we examined proteins identified by mass spectrometry and segregating in gene ontology pathways in forebrain microvessels in P5, P10, and adult wild type mice. In parallel, comparative transcript levels were obtained using RNA hybridization microarrays and enriched biological pathways were extracted from genes exhibiting at least a two-fold change in expression. Five major biological functions were observed in those genes detected both as proteins and mRNA expression undergoing at least a two-fold change in expression in one or more age comparisons: energy metabolism, protein metabolism, antioxidant function, ion exchanges, and transport. Adult microvessels exhibited the highest protein and mRNA expression levels for a majority of genes. Energy metabolism-enriched gene ontology pathways pointed to the preferential occurrence of glycolysis in P5 microvessels cells versus P10 and adult preparations enriched in aerobic oxidative enzymes. Age-dependent levels of RNA coding transport proteins at the plasma membrane and mitochondria strengthened our findings based on protein data. The data suggest that immature microvessels have fewer energy supply alternatives to glycolysis than mature structures. In the context of high energy demand, this constraint might account for vascular damage and maintenance of the high bleeding occurrence in specific areas in immature brain.

Myocardial function during bradycardia events in preterm infants

BACKGROUND

Transient bradycardia episodes are common in preterm infants and often secondary to apnea. Decreased ventilation with resultant hypoxemia is believed to be the predominant mechanism. Sudden bradycardias without apnea are also reported, possibly due to vagal stimulation. Point of care ultrasound is used to diagnose and follow cardiovascular complications in preterm infants. Inadvertently, the operator would sometimes capture bradycardia events. This study reports on left ventricular function during such events.

METHODS

We retrospectively reviewed our cardiac ultrasound database for bradycardia events. Apical four or three chamber images before, during and after a bradycardia event were analysed with speckle tracking software which provides systolic and diastolic parameters of myocardial motion, deformation and volume.

RESULTS

Over a 2year period, 15 bradycardia events were noted in 14 patients with a median gestational age of 26weeks (range 23 to 29). Heart rate decreased by an average of 43% (171/min to 98/min). Myocardial velocity and longitudinal strain rate during the atrial component of diastole were reduced during bradycardia. Longitudinal strain during systole was increased and radial deformation was unchanged. Ventricular volumes and ejection fraction did not change. Most parameters returned to baseline values after the event. Longitudinal systolic strain rate remained lower and stroke volume was 12% higher compared to baseline.

CONCLUSION

Parameters of systolic contractility and stroke volume were maintained and parameters of atrial contractility were reduced during mild to moderate bradycardia in preterm infants. Bradycardia reduces total cardiac output with a compensatory increase detected following the event.