BACKGROUND:Term and near-term infants are at high risk of developing brain injury and life-long disability if they have suffered from severe perinatal asphyxia. We hypothesized that propofol administration to the maternal-fetal unit can diminish cerebral injury in term and near-term infant fetuses in states of progressive severe asphyxia.METHODS:Forty-four late preterm lambs underwent total umbilical cord occlusion (UCO) or sham treatment in utero. UCO resulted in global asphyxia and cardiac arrest. After emergency cesarean section under either maternal propofol or isoflurane anesthesia, the fetuses were resuscitated and subsequently anesthetized the same way as their mothers.RESULTS:Asphyctic lambs receiving isoflurane showed a significant increase of total and low-frequency spectral power in bursts indicating seizure activity and more burst-suppression with a marked increase of interburst interval length during UCO. Asphyctic lambs receiving propofol showed less EEG changes. Propofol increased levels of anti-apoptotic B-cell lymphoma-extra large (Bcl-xL) and phosphorylated STAT-3 and reduced the release of cytochrome c from the mitochondria and the protein levels of activated cysteinyl aspartate-specific protease (caspase)-3, -9, and N-methyl-d-aspartate (NMDA) receptor.CONCLUSIONS:Improvement of fetal EEG during and after severe asphyxia could be achieved by propofol treatment of the ovine maternal-fetal unit. The underlying mechanism is probably the reduction of glutamate-induced cytotoxicity by down-regulation of NMDA receptors and an inhibition of the mitochondrial apoptotic pathway.

OBJECTIVE:To quantify the neuronal connectivity in preterm infants between homologous channels of both hemispheres. METHODS:EEG coherence analysis was performed on serial EEG recordings collected from preterm infants with normal neurological follow-up. The coherence spectrum was divided in frequency bands: δnewborn(0-2 Hz), θnewborn(2-6 Hz), αnewborn(6-13 Hz), βnewborn(13-30 Hz). Coherence values were evaluated as a function of gestational age (GA) and postnatal maturation. RESULTS:All spectra show two clear peaks in the δnewborn and θnewborn-band, corresponding to the delta and theta EEG waves observed in preterm infants. In the δnewborn-band the peak magnitude coherence decreases with GA and postnatal maturation for all channels. In the θnewborn-band, the peak magnitude coherence decreases with GA for all channels, but increases with postnatal maturation for the frontal polar channels. In the βnewborn-band a modest magnitude coherence peak was observed in the occipital channels, which decreases with GA. CONCLUSIONS:Interhemispherical connectivity develops analogously with electrocortical maturation: signal intensities at low frequencies decrease with GA and postnatal maturation, but increase at high frequencies with postnatal maturation. In addition, peak magnitude coherence is a clear trend indicator for brain maturation. SIGNIFICANCE:Coherence analysis can aid in the clinical assessment of the functional connectivity of the infant brain with maturation.

BACKGROUND: The understanding of hypoxemia-induced changes in baroreflex function is limited and may be studied in a fetal sheep experiment before, during, and after standardized hypoxic conditions.METHODS: Preterm fetal lambs were instrumented at 102 d gestation (term: 146 d). At 106 d, intrauterine hypoxia ischemia was induced by 25 min of umbilical cord occlusion (UCO). Baroreflex-related fluctuations were calculated at 30-min intervals during the first week after UCO by transfer function (cross-spectral) analysis between systolic blood pressure (SBP) and R R interval fluctuations, estimated in the low-frequency (LF, 0.04-0.15 Hz) band. LF transfer gain (baroreflex sensitivity) and delay (s) reflect the baroreflex function.RESULTS: Baseline did not differ in LF transfer gain and delay between controls and the UCO group. In controls, LF gain showed postnatal increase. By contrast, LF gain gradually decreased in the UCO group, resulting in significantly lower values 4-7 d after UCO. In the UCO group, LF delay increased and differed significantly from controls.CONCLUSION: Our results show that intrauterine hypoxia ischemia results in reduced baroreflex sensitivity over a period of 7 d, indicating limited efficacy to buffer BP changes by adapting heart rate. Cardiovascular dysregulation may augment already present cerebral damage after systemic hypoxia ischemia in the reperfusion period.

The aim of this study was to evaluate EEG source localization by standardized weighted low-resolution brain electromagnetic tomography (swLORETA) for monitoring of full-term newborns with hypoxic-ischemic encephalopathy, using a standard anatomic head model. Three representative examples of neonatal hypoxic-ischemia were included. The method was validated with MRI data. Hypoxic-ischemic areas, visible on MRI, correlated well with swLORETA current density distributions. In addition, neonatal seizure activity may be localized. The calculated current density distributions provide easy-to-interpret localized information about neonatal brain function, which may enable detailed longitudinal monitoring and potential assessment of treatment efficacy.

BACKGROUND:Hypoxic-ischemic encephalopathy (HIE) is one of the most important causes of brain injury in preterm infants. Preterm HIE is predominantly caused by global hypoxia-ischemia (HI). In contrast, focal ischemia is most common in the adult brain and known to result in cerebral inflammation and activation of the peripheral immune system. These inflammatory responses are considered to play an important role in the adverse outcomes following brain ischemia. In this study, we hypothesize that cerebral and peripheral immune activation is also involved in preterm brain injury after global HI.METHODS:Preterm instrumented fetal sheep were exposed to 25 minutes of umbilical cord occlusion (UCO) (n = 8) at 0.7 gestation. Sham-treated animals (n = 8) were used as a control group. Brain sections were stained for ionized calcium binding adaptor molecule 1 (IBA-1) to investigate microglial proliferation and activation. The peripheral immune system was studied by assessment of circulating white blood cell counts, cellular changes of the spleen and influx of peripheral immune cells (MPO-positive neutrophils) into the brain. Pre-oligodendrocytes (preOLs) and myelin basic protein (MBP) were detected to determine white matter injury. Electro-encephalography (EEG) was recorded to assess functional impairment by interburst interval (IBI) length analysis.RESULTS:Global HI resulted in profound activation and proliferation of microglia in the hippocampus, periventricular and subcortical white matter. In addition, non-preferential mobilization of white blood cells into the circulation was observed within 1 day after global HI and a significant influx of neutrophils into the brain was detected 7 days after the global HI insult. Furthermore, global HI resulted in marked involution of the spleen, which could not be explained by increased splenic apoptosis. In concordance with cerebral inflammation, global HI induced severe brain atrophy, region-specific preOL vulnerability, hypomyelination and persistent suppressed brain function.CONCLUSIONS:Our data provided evidence that global HI in preterm ovine fetuses resulted in profound cerebral inflammation and mobilization of the peripheral innate immune system. These inflammatory responses were paralleled by marked injury and functional loss of the preterm brain. Further understanding of the interplay between preterm brain inflammation and activation of the peripheral immune system following global HI will contribute to the development of future therapeutic interventions in preterm HIE.

OBJECTIVE:To quantify the electroencephalography (EEG) burst frequency spectrum of preterm infants by automated analysis and to describe the topography of maturational change in spectral parameters. METHODS:Eighteen preterm infants <32weeks gestation and normal neurological follow-up at 2years underwent weekly 4-h EEG recordings (10-20 system). The recordings (n=77) represent a large variability in postmenstrual age (PMA, 28-36weeks). We applied an automated burst detection algorithm and performed spectral analysis. The frequency spectrum was divided into δ1 (0.5-1Hz), δ2 (1-4Hz), θ (4-8Hz), α (8-13Hz) and β (13-30Hz) bands. Spectral parameters were evaluated as a function of PMA by regression analysis. Results were interpolated and topographically visualised. RESULTS:The majority of spectral parameters show significant change with PMA. Highest correlation is found for δ and θ band. Absolute band powers decrease with increasing PMA, while relative α and β powers increase. Maturational change is largest in frontal and temporal region. CONCLUSIONS:Topographic distribution of maturational changes in spectral parameters corresponds with studies showing ongoing gyration and postnatal white matter maturation in frontal and temporal lobes. SIGNIFICANCE:Computer analysis of EEG may allow objective and reproducible analysis for long-term prognosis and/or stratification of clinical treatment.

Assessment of the neonatal EEG may be hampered by drug-specific changes in electrocortical activity. To quantify effects of a loading dose of midazolam and lidocaine on the EEG frequency spectrum of full-term neonates with perinatal arterial ischemic stroke (PAIS), 11 full-term infants underwent multi-channel amplitude-integrated EEG (aEEG) and EEG recordings. During recording, midazolam and/or lidocaine were administered as anti-epileptic drug. Retrospectively, we performed spectral analysis on 4-h EEG segments around the loading dose. The frequency spectrum was divided in δ (1-4 Hz), θ (4-8 Hz), α (8-13 Hz) and β (13-30 Hz) bands. Midazolam induced immediate suppression of the aEEG background pattern for 30-60 min. Spectral EEG analysis showed decreased total and absolute frequency band powers. Relative δ power decreased, θ power increased while α and β powers remained constant. Lidocaine induced no aEEG background pattern suppression. Total and absolute EEG band powers were unchanged. Relative δ power decreased, θ and α power increased and β power remained constant. Effects of lidocaine were more pronounced in the stroke-affected hemisphere. In conclusions, both drugs induced a shift from low to higher frequency electrocortical activity. Additionally, midazolam reduced total EEG power. These spectral changes differ from those seen in adult studies.

Electroencephalographic characteristics are useful in assessment of the functional status of specific neuronal connections relative to postmenstrual age. Interhemispheric burst synchrony (IBS) is a measure of the functional connectivity between the hemispheres in the maturing preterm brain. An algorithm was developed to assess IBS and was used in a prospective, longitudinal EEG study on 18 very preterm infants (< 32 weeks gestational age) with normal follow-up at 2 years of age. The preterm infants underwent weekly 4-hour multi-channel EEG recordings, resulting in n = 77 EEGs. After automated detection of bursts, the algorithm defines the start and end of interhemispheric synchronous burst activity, based on selection criteria found in literature. The algorithm was designed to emulate visual inspection, providing objective results in an automated manner. This approach may be applied in clinical use and open novel avenues to automated analysis in EEG monitoring and, moreover, it may facilitate assessment of the functional status of interhemispheric connections. As such, assessment of low interhemispheric synchrony may be associated with brain injury.

Background and aims: Preterm and term-born infants suffering from severe perinatal asphyxia resulting in cardiac arrest are at high risk to develop brain injury and life-long disability. Until now, there is no therapy available to reduce severe cerebral injury in preterm infants. We hypothesized that propofol administration to the maternal-fetal-unit can diminish injury in preterm fetuses in states of progressive severe asphyxia. Methods: 44 late preterm lambs underwent standardized total umbilical cord occlusion (UCO) or sham-treatment in utero. UCO resulted in global asphyxia and cardiac arrest. After emergency Caesarean section under either propofol or isoflurane maternal anaesthesia the fetuses were resuscitated and anaesthetized the same way as their mothers. EEG measurements were performed in utero, during UCO and postnatally during 8 hours of ventilation. Occurrence of apoptosis, reactive oxygen species (ROS) formation, and protein levels of GABA- and NMDA receptors were determined in fetal cerebral frontal cortex. Results: Lambs receiving isoflurane anaesthesia showed a profound increase of total spectral power in burst epochs (estimate for seizure activity) and marked increase of interburst intervals during UCO (more suppression), whilst lambs receiving propofol anaesthesia showed less EEG changes. Propofol treatment reduced cerebral ROS formation and protein levels of activated caspase-3, GABA- and NMDA-R after severe asphyxia. Conclusions: Perinatal neuroprotection in the ovine maternal-fetal-unit can be achieved by pre- and postconditioning with propofol. The underlying mechanism is probably an avoidance of lipid peroxidation by ROS scavenging and the reduction of glutamate induced cytotoxicity by downregulation of NMDA receptors.

In this paper we present an autonomic cardiovascular model of a preterm infant of 28 weeks of gestation with a birth weight of 1000 g and a closed ductus arteriosus by the end of the first week, that is capable of describing the complex interactions between heart rate, blood pressure and respiration. The hemodynamic model consists of a pulsatile heart and several vascular compartments, and is regulated by a baroreflex control system. The model is relatively simple to allow for a mathematical analysis of the dynamics but sufficiently complex to provide a realistic representation of the underlying physiology. The model provides (beat-to-beat) values of R-R interval and blood pressure that resemble realistic signals of preterm infants. The model is validated with experimental data obtained in preterm infants.

Aim: To analyze quantitatively multi-channel amplitude-integrated EEG (aEEG) characteristics and assess regional differences.Methods: We investigated 40 preterm infants (postmenstrual age, PMA: range 27-37 weeks) with normal follow-up at 24 months of age, at a median postnatal age of 8 days using 4-h EEG recordings according to the international 10-20 system reduced montage. Nine (3 transverse and 6 longitudinal) channels were selected and converted to aEEG registrations. For each aEEG registration, lower margin amplitude (LMA), upper margin amplitude (UMA) and bandwidth (UMA-LMA) were calculated.Results: In all channels PMA and LMA showed strong positive correlations. Below 32 weeks of PMA. LMA was <= 5 mu V. Linear regression analysis showed a maximum LMA difference between channels of approximately 2 and 11 mu V at 27 and 37 weeks of PMA, respectively. The lowest are LMA values in the occipital channel and the highest values are in centro-occipital channels. In the frontal, centro-temporal and centro-occipital channels, UMA and bandwidth changed with PMA. No differences in LMA, UMA and bandwidth were found between hemispheres. Skewness of LMA values strongly correlated with PMA, positive skewness indicating an immature brain (PMA <= 32 weeks) and negative skewness a maturing (PMA>32 weeks) brain.Conclusions: We detected symmetric increase of aEEG characteristics, indicating symmetric brain maturation of the left and right hemispheres. Our findings demonstrate the clinical potential of computer-assisted analyses of aEEG recordings in detecting maturational features which are not readily identified visually. This may provide an objective and reproducible method for assessing brain maturation and long-term prognosis. (C) 2011 Elsevier Ireland Ltd. All rights reserved.

To aid with prognosis and stratification of clinical treatment for preterm infants, a method for automated detection of bursts, interburst-intervals (IBIs) and continuous patterns in the electroencephalogram (EEG) is developed. Results are evaluated for preterm infants with normal neurological follow-up at 2 years. The detection algorithm (MATLAB®) for burst, IBI and continuous pattern is based on selection by amplitude, time span, number of channels and numbers of active electrodes. Annotations of two neurophysiologists were used to determine threshold values. The training set consisted of EEG recordings of four preterm infants with postmenstrual age (PMA, gestational age + postnatal age) of 29-34 weeks. Optimal threshold values were based on overall highest sensitivity. For evaluation, both observers verified detections in an independent dataset of four EEG recordings with comparable PMA. Algorithm performance was assessed by calculation of sensitivity and positive predictive value. The results of algorithm evaluation are as follows: sensitivity values of 90% ± 6%, 80% ± 9% and 97% ± 5% for burst, IBI and continuous patterns, respectively. Corresponding positive predictive values were 88% ± 8%, 96% ± 3% and 85% ± 15%, respectively. In conclusion, the algorithm showed high sensitivity and positive predictive values for bursts, IBIs and continuous patterns in preterm EEG. Computer-assisted analysis of EEG may allow objective and reproducible analysis for clinical treatment.

Our study aimed at automated power spectral analysis of the EEG in preterm infants to identify changes of spectral measures with maturation. Weekly (10–20 montage) 4-h EEG recordings were performed in 18 preterm infants with GA <32 wk and normal neurological follow-up at 2 y, resulting in 79 recordings studied from 27+4 to 36+3 wk of postmenstrual age (PMA, GA + postnatal age). Automated spectral analysis was performed on 4-h EEG recordings. The frequency spectrum was divided in delta 1 (0.5–1 Hz), delta 2 (1–4 Hz), theta (4–8 Hz), alpha (8–13 Hz), and beta (13–30 Hz) band. Absolute and relative power of each frequency band and spectral edge frequency were calculated. Maturational changes in spectral measures were observed most clearly in the centrotemporal channels. With advancing PMA, absolute powers of delta 1 to 2 and theta decreased. With advancing PMA, relative power of delta 1 decreased and relative powers of alpha and beta increased, respectively. In conclusion, with maturation, spectral analysis of the EEG showed a significant shift from the lower to the higher frequencies. Computer analysis of EEG will allow an objective and reproducible analysis for long-term prognosis and/or stratification of clinical treatment.

This study consisted of continuous EEG monitoring of neonates at risk of hypoxia ischemia ( HI), alternated by MRI examinations on predefined time points. It is hypothesized that combining EEG with MRI could give more information about the development of possible brain damage. Included were 8 term newborns with suspected neonatal encephalopathy caused by perinatal HI. The EEG was intermittently measured between day 1 and 8 after birth. MRI data was acquired between day 1 and 9, within 24 hrs from an observed EEG event. Preliminary results indicate an agreement between abnormalities in diffusion weighted MR images and signal fluctuations at corresponding electrode locations.

Introduction Premature neonates have a high incidence of hypoxia-ischemia (HI), which can lead to permanent neurophysiologic deficits. Therefore, these newborns are frequently monitored by means of EEG. However, clinical intervention strategies are mostly based upon MRI examinations. The time points of these studies usually depend on MRI availability. The aim of this study is to develop protocols for the indication of MRI examinations based on EEG monitoring. To aid in the development of these protocols, knowledge of the correlation of EEG and MRI is important. In order to investigate this correlation following a hypoxic-ischemic insult under carefully controlled experimental conditions, simultaneous EEG and MRI measurements in an experimental neonatal cerebral ischemia model were conducted. It is known that the developmental stage of the brain of neonatal rats with an age between 10 and 15 days closely resembles that of premature to term human neonates [1], the clinically relevant target group for this study. The MRI measurements include DTI, known for early detection of HI [2]. DTI based fiber tracking is sensitive to cellular changes, which are hypothesized to correlate to changes in neuronal functioning, as measured by EEG. Challenges in this setup are, amongst others, reduction of artifacts in the EEG signal due to MRI sequences, and artifacts in MRI images resulting from the EEG electrodes and leads.

Diffusion‐weighted imaging (DWI) is frequently used to diagnose stroke. However, the origin of the observed reduction in the apparent diffusion coefficient (ADC) in the acute phase following ischemia is not well understood. Although cell swelling is considered to play an important role, it is unclear whether this can completely explain the large ADC decrease. We developed a method to induce in neonatal rat hippocampal slices both osmotic perturbations, which lead to cell swelling, and oxygen/glucose deprivation (OGD), which simulates ischemia. A perfusion system was used to provide the hippocampal slices with nutrients and oxygen to maintain slice viability, which was verified with the use of fluorescent dyes (live/dead staining). Upon induction of OGD, the ADC decreased to ∼57% of the initial value within 2 hr. The ADC reduction cannot fully be explained by changes due to cell swelling, since these led only to a maximum decrease of ∼83%. Therefore, in addition to cell swelling, other changes must contribute significantly to the ADC reduction. Magn Reson Med 53:348–355, 2005. © 2005 Wiley‐Liss, Inc.