Peter Andriessen

Baroreceptor reflex sensitivity in human neonates: the effect of postmenstrual age

We performed a cross‐sectional study in human infants to determine if indices of R–R interval variability, systolic blood pressure (SBP) variability, and baroreceptor reflex sensitivity change with postmenstrual age (PMA: gestational age + postnatal age). The electrocardiogram, arterial SBP and respiration were recorded in clinically stable infants (PMA, 28–42 weeks) in the quiet sleep state in the first days after birth. (Cross‐)spectral analyses of R–R interval series and SBP series were performed to calculate the power of low‐frequency (LF, indicating baroreceptor reflex activity, 0.04–0.15 Hz) and high‐frequency (HF, indicating parasympathetic activity, individualized between the p‐10 and p‐90 values of respiratory frequency) fluctuations, and transfer function phase and gain. The mean R–R interval, and LF and HF spectral powers of R–R interval series increased with PMA. The mean SBP increased with PMA, but not the LF and HF spectral powers of SBP series. In the LF range, cross‐spectral analysis showed high coherence values (> 0.5) with a consistent negative phase shift between R–R interval and SBP, indicating a ∼3 s lag in R–R interval changes in relation to SBP. Baroreceptor reflex sensitivity, calculated from LF transfer gain, increased significantly with PMA, from 5 (preterm) to 15 ms mmHg−1 (term). Baroreceptor reflex sensitivity correlated significantly with the (LF and) HF spectral powers of R–R interval series, but not with the LF and HF spectral powers of SBP series. The principal conclusions are that baroreceptor reflex sensitivity and spectral power in R–R interval series increase in parallel with PMA, suggesting a progressive vagal maturation with PMA.

Mesenchymal stem cells induce T-cell tolerance and protect the preterm brain after global hypoxia-ischemia.

Hypoxic-ischemic encephalopathy (HIE) in preterm infants is a severe disease for which no curative treatment is available. Cerebral inflammation and invasion of activated peripheral immune cells have been shown to play a pivotal role in the etiology of white matter injury, which is the clinical hallmark of HIE in preterm infants. The objective of this study was to assess the neuroprotective and anti-inflammatory effects of intravenously delivered mesenchymal stem cells (MSC) in an ovine model of HIE. In this translational animal model, global hypoxia-ischemia (HI) was induced in instrumented preterm sheep by transient umbilical cord occlusion, which closely mimics the clinical insult. Intravenous administration of 2 x 106 MSC/kg reduced microglial proliferation, diminished loss of oligodendrocytes and reduced demyelination, as determined by histology and Diffusion Tensor Imaging (DTI), in the preterm brain after global HI. These anti-inflammatory and neuroprotective effects of MSC were paralleled by reduced electrographic seizure activity in the ischemic preterm brain. Furthermore, we showed that MSC induced persistent peripheral T-cell tolerance in vivo and reduced invasion of T-cells into the preterm brain following global HI. These findings show in a preclinical animal model that intravenously administered MSC reduced cerebral inflammation, protected against white matter injury and established functional improvement in the preterm brain following global HI. Moreover, we provide evidence that induction of T-cell tolerance by MSC might play an important role in the neuroprotective effects of MSC in HIE. This is the first study to describe a marked neuroprotective effect of MSC in a translational animal model of HIE.

Cardiovascular fluctuations and transfer function analysis in stable preterm infants.

To examine the baroreceptor reflex function, a beat-to-beat analysis between systolic blood pressure (SBP) and R-R interval fluctuations was studied in 10 stable appropriate-for-gestational age preterm infants (range, 27.2–33.7 wk) in the first postnatal week during quiet sleep. Spectral power analysis, using fast Fourier transform, and transfer functions (gain and phase difference) between SBP and R-R fluctuations were estimated in a low-frequency band (LF, 0.03–0.2 Hz) and high-frequency band (HF defined as the frequency band between the 10th and 90th centiles of the individual respiratory frequency). The LF/HF ratio reflects the sympathovagal balance. The mean frequency (±SD) of LF peaks was centered at 0.07 ± 0.02 Hz. The mean frequency (±SD) of the individual HF band was 0.82 ± 0.21 Hz. The LF/HF ratio in the R-R interval series [median, 29; interquartile range (IQR), 16–40] was higher than in the SBP series (median, 8; IQR, 4–14). The gain between R-R interval and SBP fluctuations (median, 4.2 ms/mm Hg; IQR, 2.4–5.0) in the LF band was higher than in the HF band (median, 1.7 ms/mm Hg; IQR, 1.4–3.0). SBP fluctuations lead R-R interval fluctuations in the LF band with a median phase difference of +96° (IQR, 67–132). At LF the fluctuations in SBP precede changes in R-R interval with a time delay of 3.8 s. These observations indicate a dominant role of the sympathetic system in stable preterm infants in comparison with published adult values. Cross-spectral analysis allows a test for tracking the development of the sympathetic system in neonates.

Epidemiology of pyridoxine-dependent seizures in The Netherlands

Background: Pyridoxine dependent epilepsy is a rare cause of seizures in childhood. The diagnosis is made on clinical criteria, that in many cases are never met. Therefore, epidemiological data on pyridoxine dependency are scarce. Aims: To study the epidemiology of pyridoxine dependent epilepsy in the Netherlands, and to determine whether the diagnosis is based on the appropriate criteria. Methods: Nationwide all departments of paediatrics (n = 113) and of paediatric or neonatal neurology (n = 17) were asked to report cases of pyridoxine dependent seizures. Birth incidences were calculated using national data on live births from 1991 to 2003. Results: Response was received from 67% of paediatric departments, including all university hospitals and 94% of child neurology departments. Thirteen patients were reported. Four definite (31%), three probable (23%), and four possible cases (31%) were identified. Two cases (15%) did not meet criteria for either of these groups. The birth incidence was 1:396 000 for definite and probable cases and 1:252 000 when possible cases are included. Conclusions: Thus far, epidemiological data on pyridoxine dependent seizures were only available from the UK and Ireland. A higher incidence was found in the Netherlands, in accordance with earlier suggestions of a regional difference. The study shows that the diagnosis is often made without performance of a formal trial of withdrawal. The importance of confirming the diagnosis, concerning the consequences as for individual prognosis, the potential side effects of prolonged pyridoxine substitution, and the possibility of treating the mother in case of future pregnancies are emphasised.

Cerebral inflammation and mobilization of the peripheral immune system following global hypoxia-ischemia in preterm sheep

BackgroundHypoxic-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.MethodsPreterm 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.ResultsGlobal 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.ConclusionsOur 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.

Beat-to-beat detection of fetal heart rate: Doppler ultrasound cardiotocography compared to direct ECG cardiotocography in time and frequency domain.

In order to obtain power spectral information on the fetal heart rate in stages of pregnancy earlier than labor an algorithm has been developed to calculate the fetal heart rate on a beat-to-beat basis from Doppler ultrasound cardiotocographic signals. The algorithm was evaluated by comparing the calculated fetal heart rate with the heart rate determined from direct ECG signals measured with a scalp electrode. Heart rates were compared both in time and frequency domain. In the time domain the results achieved by both methods correlate well (correlation coefficient = 0.977 (p < 0.001)), in the frequency domain the results correlate even better (correlation coefficient = 0.991 (p < 0.001)). Based on these findings, it can be concluded that the developed algorithm provides a valuable tool for obtaining power spectral information on the fetal heart rate in stages of pregnancy earlier than labor.

Mesenchymal Stromal Cell-Derived Extracellular Vesicles Protect the Fetal Brain After Hypoxia-Ischemia

Preterm neonates are susceptible to perinatal hypoxic‐ischemic brain injury, for which no treatment is available. In a preclinical animal model of hypoxic‐ischemic brain injury in ovine fetuses, we have demonstrated the neuroprotective potential of systemically administered mesenchymal stromal cells (MSCs). The mechanism of MSC treatment is unclear but suggested to be paracrine, through secretion of extracellular vesicles (EVs). Therefore, we investigated in this study the protective effects of mesenchymal stromal cell‐derived extracellular vesicles (MSC‐EVs) in a preclinical model of preterm hypoxic‐ischemic brain injury. Ovine fetuses were subjected to global hypoxia‐ischemia by transient umbilical cord occlusion, followed by in utero intravenous administration of MSC‐EVs. The therapeutic effects of MSC‐EV administration were assessed by analysis of electrophysiological parameters and histology of the brain. Systemic administration of MSC‐EVs improved brain function by reducing the total number and duration of seizures, and by preserving baroreceptor reflex sensitivity. These functional protections were accompanied by a tendency to prevent hypomyelination. Cerebral inflammation remained unaffected by the MSC‐EV treatment. Our data demonstrate that MSC‐EV treatment might provide a novel strategy to reduce the neurological sequelae following hypoxic‐ischemic injury of the preterm brain. Our study results suggest that a cell‐free preparation comprising neuroprotective MSC‐EVs could substitute MSCs in the treatment of preterm neonates with hypoxic‐ischemic brain injury, thereby circumventing the potential risks of systemic administration of living cells.

Maturational Changes in Automated EEG Spectral Power Analysis in Preterm Infants

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.

Quantitative Analysis of Amplitude-Integrated Electroencephalogram Patterns in Stable Preterm Infants, with Normal Neurological Development at One Year

Background: The amplitude-integrated EEG (aEEG) is feasible for monitoring cerebral activity in preterm infants. However, quantitative data on normal patterns in these infants are limited. Objective: To study maturational aEEG changes in a cohort of stable preterm infants by automated quantification. Methods: In a cohort of stable preterm infants with gestational age (GA) <32 weeks and normal neurological follow-up at 1 year, weekly 4 h EEG recordings were performed. aEEG traces were obtained from channel C3-C4. The upper margin amplitude (UMA), lower margin amplitude (LMA) and bandwidth (BW) were quantitatively calculated using an expert software system. In addition, the relative duration of discontinuous background pattern (discontinuous background defined as activity with LMA <5 µV, expressed as DC-%) was calculated. Results: 79 aEEG recordings (4–6 recordings/infant) were obtained in 18 infants. Analysis of the first week recordings demonstrated a strong positive correlation between GA and LMA, while DC-% decreased significantly. Longitudinally, all infants showed increase of LMA. Multivariate analysis showed that GA and postnatal age (PA) both contributed independently and equally to LMA and DC-%. We found a strong correlation between postmenstrual age (GA + PA) and LMA and DC-%, respectively. Conclusion: To our knowledge, this is the first study where aEEG development was studied by automated quantification of aEEG characteristics in a cohort of stable preterm infants with a normal neurological development at 1 year of age. LMA and DC-% are simple quantitative measures of neurophysiologic development and may be used to evaluate neurodevelopment in infants.

Rhythm of Life Aid (ROLA): An Integrated Sensor System for Supporting Medical Staff During Cardiopulmonary Resuscitation (CPR) of Newborn Infants

During the stress of cardiopulmonary resuscitation (CPR), it is difficult to maintain the right rhythm and correct ratio of insufflations to chest compressions and to exert the compressions at a constant pressure. In this paper, we propose and demonstrate an integrated sensor system-the “Rhythm of Life Aid” (ROLA) to support medical staff during CPR of newborn infants. The design concept is based on interactive audio and visual feedback with consideration of functionalities and user friendliness. A prototype ROLA device is built, consisting of a transparent foil integrated with pressure sensor and electroluminescent foil actuators for indication of the exerted chest compression pressure, as well as an audio box to generate distinctive sounds as audio guidance for insufflations and compressions. To evaluate the performance of the ROLA device, a sensory mannequin and a dedicated software interface are implemented to give immediate feedback and record data for further processing. Tests of the ROLA prototype on the sensory mannequin by ten pairs of a doctor and a nurse at Máxima Medical Centre in Veldhoven, The Netherlands show that the use of ROLA device achieves a more constant rhythm and pressure of chest compressions during CPR of newborn infants.