Hemodynamics of the cerebral arteries of infants with periventricular leukomalacia

Cerebral Blood Flow, Brain Injury, and Aortic-Pulmonary Collateral Flow After the Fontan Operation

Patients with a single ventricle develop aortopulmonary collaterals (APCs) whose flow has been shown to be inversely proportional to cerebral blood flow (CBF) in a previous cross-sectional study. Longitudinal CBF and APC flow in patients with Fontan physiology adjusting for brain injury (BI) has never been reported. Decreased CBF and BI may adversely impact neurodevelopment. A prospective longitudinal cohort of 27 patients with Fontan physiology (aged 10 ± 1.9 years, 74% male) underwent cardiac and brain magnetic resonance imaging 3 to 9 months and 6.0 ± 1.86 years after Fontan operation to measure the CBF and APC flow and to reassess the BI (focal BI, generalized insult, and hemorrhage). CBF was measured using jugular venous flow and APC flow was measured by the difference between aortic flow and caval return. Multivariate modeling was used to assess the relation between the change in APC flow and BI. A strong inverse relation was found between CBF/aortic flow change and APC flow/aortic flow and APC flow/body surface area change (R2 = 0.70 and 0.72 respectively, p <0.02). Overall, the CBF decreased by 9 ± 11% and the APC flow decreased by 0.73 ± 0.67 l/min/m2. The evolution of CBF and APC flow were significantly and inversely related when adjusting for time since Fontan operation, gender, and BI on the multivariate modeling. Every unit increase in APC flow change was associated with an 8% decrease in CBF change. In conclusion, CBF and APC flow change are inversely related across serial imaging, adjusting for time from Fontan operation, gender, and BI. CBF and APC aortic flow decrease over a 6-year period. This may adversely impact neurodevelopment. Because APCs can be embolized, this may be a modifiable risk factor. Clinical trials numbers: NCT02135081 and NCT02919956.

Diagnostic and predictive value of Doppler ultrasound for evaluation of the brain circulation in preterm infants: a systematic review

INTRODUCTION

Very and extremely preterm infants frequently have brain injury-related long-term neurodevelopmental problems. Altered perfusion, for example, seen in the context of a hemodynamically significant patent ductus arteriosus (PDA), has been linked to injury of the immature brain. However, a direct relation with outcome has not been reviewed systematically.

METHODS

A systematic review was conducted to provide an overview of the value of different cerebral arterial blood flow parameters assessed by Doppler ultrasound, in relation to brain injury, to predict long-term neurodevelopmental outcome in preterm infants.

RESULTS

In total, 23 studies were included. Because of heterogeneity of studies, a meta-analysis of results was not possible. All included studies on resistance index (RI) showed significantly higher values in subjects with a hemodynamically significant PDA. However, absolute differences in RI values were small. Studies using Doppler parameters to predict brain injury and long-term neurodevelopmental outcome were inconsistent.

DISCUSSION

There is no clear evidence to support the routine determination of RI or other Doppler parameters in the cerebral arteries to predict brain injury and long-term neurodevelopmental outcome in the preterm infant. However, there is evidence that elevated RI can point to the presence of a hemodynamically significant PDA.

Neurological Injury and Cerebral Blood Flow in Single Ventricles Throughout Staged Surgical Reconstruction

BACKGROUND

Patients with a single ventricle experience a high rate of brain injury and adverse neurodevelopmental outcome; however, the incidence of brain abnormalities throughout surgical reconstruction and their relationship with cerebral blood flow, oxygen delivery, and carbon dioxide reactivity remain unknown.

METHODS

Patients with a single ventricle were studied with magnetic resonance imaging scans immediately prior to bidirectional Glenn (pre-BDG), before Fontan (BDG), and then 3 to 9 months after Fontan reconstruction.

RESULTS

One hundred sixty-eight consecutive subjects recruited into the project underwent 235 scans: 63 pre-BDG (mean age, 4.8±1.7 months), 118 BDG (2.9±1.4 years), and 54 after Fontan (2.4±1.0 years). Nonacute ischemic white matter changes on T2-weighted imaging, focal tissue loss, and ventriculomegaly were all more commonly detected in BDG and Fontan compared with pre-BDG patients (P<0.05). BDG patients had significantly higher cerebral blood flow than did Fontan patients. The odds of discovering brain injury with adjustment for surgical stage as well as ≥2 coexisting lesions within a patient decreased (63%-75% and 44%, respectively) with increasing amount of cerebral blood flow (P<0.05). In general, there was no association of oxygen delivery (except for ventriculomegaly in the BDG group) or carbon dioxide reactivity with neurological injury.

CONCLUSIONS

Significant brain abnormalities are commonly present in patients with a single ventricle, and detection of these lesions increases as children progress through staged surgical reconstruction, with multiple coexisting lesions more common earlier than later. In addition, this study demonstrated that BDG patients had greater cerebral blood flow than did Fontan patients and that an inverse association exists of various indexes of cerebral blood flow with these brain lesions. However, CO₂ reactivity and oxygen delivery (with 1 exception) were not associated with brain lesion development.

CLINICAL TRIAL REGISTRATION

URL: http://www.clinicaltrials.gov. Unique identifier: NCT02135081.

Umbilical Arterial Blood Sampling Alters Cerebral Tissue Oxygenation in Very Low Birth Weight Neonates

OBJECTIVE

To evaluate the magnitude, consistency, and natural history of reductions in cerebral regional tissue oxygenation (CrSO2) during umbilical arterial (UA) blood sampling in very low birth weight neonates.

STUDY DESIGN

Data were collected during a prospective observational near-infrared spectroscopy survey conducted on a convenience sample of 500-1250 g neonates during the first 10 postnatal days. A before-after analysis of UA blood sampling effects on CrSO2 absolute values and variability was performed. The present analysis was not designed a priori and was conducted following the bedside observation of CrSO2 decrements contiguous with UA blood draws.

RESULTS

Fifteen very low birth weight neonates had 201 UA blood draws. Baseline CrSO2 (mean ± SEM) decreased following UA blood sampling, from 70 ± 1% to a nadir of 63 ± 1% (P < .001) occurring 4 ± 3 (range 2-24) minutes following blood draws. CrSO2 subsequently increased to 70 ± 1% (P < .001 compared with nadir) at 10 ± 4 (range 4-28) minutes following UA blood sampling. Coefficients of variation (mean ± SEM) increased from 0.02 ± 0.001 at baseline to 0.05 ± 0.004 (P < .001), followed by a decrease to 0.03 ± 0.003 (P < .001 for all comparisons), thus denoting increased CrSO2 variability following UA blood sampling.

CONCLUSIONS

UA blood sampling is associated with significant CrSO2 decrements with increased variability over clinically significant intervals. Whether these changes impact complications of prematurity, including intraventricular hemorrhage and periventricular leukomalacia, remain unknown.

Submicron-bubble-enhanced focused ultrasound for blood-brain barrier disruption and improved CNS drug delivery

The use of focused ultrasound (FUS) with microbubbles has been proven to induce transient blood-brain barrier opening (BBB-opening). However, FUS-induced inertial cavitation of microbubbles can also result in erythrocyte extravasations. Here we investigated whether induction of submicron bubbles to oscillate at their resonant frequency would reduce inertial cavitation during BBB-opening and thereby eliminate erythrocyte extravasations in a rat brain model. FUS was delivered with acoustic pressures of 0.1-4.5 MPa using either in-house manufactured submicron bubbles or standard SonoVue microbubbles. Wideband and subharmonic emissions from bubbles were used to quantify inertial and stable cavitation, respectively. Erythrocyte extravasations were evaluated by in vivo post-treatment magnetic resonance susceptibility-weighted imaging, and finally by histological confirmation. We found that excitation of submicron bubbles with resonant frequency-matched FUS (10 MHz) can greatly limit inertial cavitation while enhancing stable cavitation. The BBB-opening was mainly caused by stable cavitation, whereas the erythrocyte extravasation was closely correlated with inertial cavitation. Our technique allows extensive reduction of inertial cavitation to induce safe BBB-opening. Furthermore, the safety issue of BBB-opening was not compromised by prolonging FUS exposure time, and the local drug concentrations in the brain tissues were significantly improved to 60 times (BCNU; 18.6 µg versus 0.3 µg) by using chemotherapeutic agent-loaded submicron bubbles with FUS. This study provides important information towards the goal of successfully translating FUS brain drug delivery into clinical use.

Early cerebral oxygen extraction and the risk of death or sonographic brain injury in very preterm infants

OBJECTIVE

To evaluate the relationship between cerebral fractional tissue oxygen extraction (cFTOE), a measure of oxygen delivery-consumption equilibrium, and the risk of early poor outcome in very preterm infants.

STUDY DESIGN

Cerebral blood flow, tissue oxygenation index (by near-infrared spectroscopy), and arterial oxygen content were measured, and cerebral oxygen delivery, consumption, and cFTOE were calculated at 3 intervals in the first 72 hours of life in infants ≤ 30 weeks gestational age (GA). A receiver operating characteristic curve was derived with an a priori defined dichotomized outcome of good or poor, defined as death or sonographic brain injury (grade ≥ II intraventricular hemorrhage) by day 7.

RESULTS

Seventy-one infants were enrolled, with a mean (SD) GA of 27 (2) weeks. cFTOE demonstrated better discrimination for the study outcome at <24 hours of age than at 48 or 72 hours of age (P = .01). The area under the curve for cFTOE at the initial measurement was no different from that for GA alone (0.87; 95% CI, 0.77-0.95 vs 0.81; 95% CI, 0.69-0.92), but the combined measure of cFTOE and GA had better discrimination (0.96; 95% CI, 0.91-1.0) than either cFTOE (P = .03) or GA (P = .016) alone. A cFTOE of 0.4 had a sensitivity of 82% and specificity of 75% for risk of early poor outcome.

CONCLUSION

Elevated cFTOE values are associated with increased risk of early poor outcome in very preterm infants. Its predictive value is further improved with the addition of GA.

The Estimated Cost of Early Cord Clamping at Birth Within Europe

Early cord clamping has been a common although variable practice at all births throughout Europe for the past 40 years. It is known to result in a variable degree of hypovolemia, reduced cardiac output, reduced cerebral circulation, and an immediate loss of placental oxygenated blood. Hypoxic ischemia of the brain at birth is recognized to be a major underlying cause of cerebral palsy. Using very conservative estimates of the adverse effects of early cord clamping in a proportion of births according to the survey of its use in Europe and an estimate of the cost of care for an individual with cerebral palsy, we have calculated a possible cost for the intervention which is unnecessary and continued practice is largely the result of habit and poor understanding of the physiology of transition.

Fetal growth restriction caused by MIMT1 deletion alters brain transcriptome in cattle

We examined levels of gene expression in the brains of bovine fetuses carrying a truncated MIMT1 allele, MIMT1(Del), shown to cause late abortion and stillbirth as a result of fetal growth restriction. MIMT1 is a non-protein coding gene that forms part of the imprinted PEG3 (paternally expressed gene 3) domain. Microarray analysis of brain cortex samples from mid-gestation MIMT1(Del/WT) bovine fetuses and wild-type siblings was performed to study the effect of fetal growth restriction on brain gene expression. Statistical analysis revealed 134 genes with increased mRNA levels and 22 with reduced levels in MIMT1(Del/WT) fetuses. Gene set enrichment analysis identified a relatively small number of significant functional clusters representing three major biological processes: response to oxidative stress, angiogenesis, and epithelial cell proliferation. Gene expression microarray analyses identified increased expression of VIPR2, HTRA1, S100A4 and MYH8 in fetuses carrying the deletion and decreased expression of DRD2, ADAM18, miR345, ZNF585A. ADAM18, DRD2 and S100A4 are known to be involved in prenatal brain development. ZNF585A, miR-345, VIPR2, HTRA1, and MYH8 are known to be involved in cell growth and differentiation, but any role in neural developmental has yet to be elucidated.

Subventricular zone-derived oligodendrogenesis in injured neonatal white matter in mice enhanced by a nonerythropoietic erythropoietin derivative

Perinatal hypoxia-ischemia (HI) frequently causes white-matter injury, leading to severe neurological deficits and mortality, and only limited therapeutic options exist. The white matter of animal models and human patients with HI-induced brain injury contains increased numbers of oligodendrocyte progenitor cells (OPCs). However, the origin and fates of these OPCs and their potential to repair injured white matter remain unclear. Here, using cell-type- and region-specific genetic labeling methods in a mouse HI model, we characterized the Olig2-expressing OPCs. We found that after HI, Olig2+ cells increased in the posterior part of the subventricular zone (pSVZ) and migrated into the injured white matter. However, their oligodendrocytic differentiation efficiency was severely compromised compared with the OPCs in normal tissue, indicating the need for an intervention to promote their differentiation. Erythropoietin (EPO) treatment is a promising candidate, but it has detrimental effects that preclude its clinical use for brain injury. We found that long-term postinjury treatment with a nonerythropoietic derivative of EPO, asialo-erythropoietin, promoted the maturation of pSVZ-derived OPCs and the recovery of neurological function, without affecting hematopoiesis. These results demonstrate the limitation and potential of endogenous OPCs in the pSVZ as a therapeutic target for treating neonatal white-matter injury.

The expression profile of microRNAs in wistar rats with lipopolysaccharide-induced periventricular leukomalacia

Over the recent decades, with numbers of premature infants being cured, clinical diseases on brain damage like periventricular leukomalacia (PVL) have become much more common. Meanwhile, since the discovery of first miRNA lin-4, an increasing number of important studies about this small RNA have been performed not only in the normal organ development but also in the pathogenic mechanism of diseases. However, throughout the past several years, there have been rare miRNA researches discussing the connection between the PVL and miRNA. In view of this situation, we constructed an animal model of PVL induced by lipopolysaccharide (LPS) and performed a miRNA microarray which was repeated three times to profile the expression of microRNAs (miRNAs) between two groups (PVL group versus control group). Then, miRNAs with notable fold changes (fold change >1.5) were found; some of them were further validated by real-time PCR. As a result, 104 differentially expressed miRNAs were identified using the microarray, including 64 upregulated and 40 downregulated miRNAs. Then, five miRNAs of them were selected, characterized by consistent trend in expression in all three microarrays. Among these five miRNAs (miRNA-451, miRNA-200b, miRNA-29a, miRNA-21, and miRNA-138), we subsequently selected miRNA-451 and miRNA-200b for real-time PCR because they possess the highest fold changes. Finally, the results of PCR are basically in accord with the microarray. We guess these new identified miRNAs may play an important role in the pathogenesis of PVL and may provide certain pathophysiological basis for the future research of related diseases in preterm infants.

Can anomalies of fetal brain circulation be useful in the management of growth restricted fetuses?

Assessment of the fetal cerebral circulation provides important information on the hemodynamic changes associated with chronic hypoxia and intrauterine growth restriction. Despite the incorporation of new US parameters, the landmark for the fetal brain hemodynamic evaluation is still the middle cerebral artery. However, new vascular territories, such as the anterior and posterior cerebral arteries, might provide additional information on the onset of the brain sparing effect. The fractional moving blood volume estimation and three-dimensional power Doppler ultrasound indices are new techniques that seem to be promising in identifying cases at earlier stages of vascular deterioration; still, they are not available for clinical application and more information is needed on the reproducibility and advantages of three-dimensional power Doppler ultrasound blood flow indices. In the past, the brain sparing effect was considered as a protective mechanism; however, recent information challenges this concept. There is growing evidence of an association between brain sparing effect and increased risk of abnormal neurodevelopment after birth. Even in mild late-onset intrauterine growth restriction affected fetuses with normal umbilical artery blood flow, increased cerebral blood perfusion can be associated with a substantial risk of abnormal neuroadaptation and neurodevelopment during childhood.

Oxidative stress disrupts oligodendrocyte maturation

Periventricular white matter injury (PWMI) is the leading cause of chronic neurologic injury among survivors of preterm birth. The hallmark of PWMI is hypomyelination and a lack of mature, myelinating oligodendrocytes. Oligodendrocytes undergo a well-characterized lineage progression from neural stem cell to mature oligodendrocyte. Oligodendrocyte precursors have increased susceptibility to oxidative and free radical-mediated injury compared with mature oligodendrocytes as a result of lower levels of antioxidant enzymes and free radical scavengers. In this study, we show that oxidative stress disrupts oligodendrocyte differentiation by two mechanisms. First, oxidizing agents decrease the expression of key genes that promote oligodendrocyte differentiation from neural stem cells and increase the expression of genes known to inhibit differentiation. Second, global histone acetylation persists under conditions of oxidative stress, further contributing to the prevention of oligodendrocyte differentiation. Both of these mechanisms result in the arrest of oligodendrocyte differentiation without an increase in cell death.

Cerebral oxygen saturation and extraction in preterm infants with transient periventricular echodensities

OBJECTIVE

Our aim was to determine regional cerebral tissue oxygen saturation and fractional tissue oxygen extraction in preterm infants with transient periventricular echodensities. We hypothesized that as a result of reduced cerebral perfusion, regional cerebral tissue oxygen saturation will be lower and fractional tissue oxygen extraction will be higher during the first days after birth.

PATIENTS AND METHODS

This was a prospective, observational study of 49 preterm infants (gestational age median: 30.1 weeks [26.0-31.8 weeks]; birth weight median: 1220 g [615-2250 g]). We defined transient periventricular echodensities as echodensities that persisted for >7 days. Regional cerebral tissue oxygen saturation was measured on days 1-5, 8, and 15 after birth. Fractional tissue oxygen extraction was calculated as (transcutaneous arterial oxygen saturation--regional cerebral tissue oxygen saturation)/transcutaneous arterial oxygen saturation.

RESULTS

Transient periventricular echodensities were found in 25 of 49 infants. During the first week we found no difference between the 2 groups for cerebral tissue oxygen saturation and fractional tissue oxygen extraction values. On day 15 after birth, cerebral tissue oxygen saturation was lower in preterm infants with transient periventricular echodensities (66%) compared with infants without echodensities (76%) (P = .003). Fractional tissue oxygen extraction in infants with transient periventricular echodensities (0.30) was higher than fractional tissue oxygen extraction in infants without transient periventricular echodensities (0.20) (P < .001). The differences could not be explained by confounding variables.

CONCLUSIONS

Persistent transient periventricular echodensities may be associated with increased cerebral oxygen demand after the first week after birth, which is contrary to our hypothesis. Cerebral oxygenation may be involved in the recovery of perinatal white matter damage.

The role of resuscitation drugs and placental transfusion in the delivery room management of newborn infants

Medications are used rarely in newborn resuscitations and are probably justifiable in less than 0.1% of births. Doses used are mainly extrapolated from animal and adult data. Despite this, the drugs used, their order and route of administration have all been sources of controversy for many years. There have been polarised views, often focusing upon adrenaline and sodium bicarbonate and more recently new drugs such as vasopressin have been suggested, once again extrapolating from adult experience. This article examines the sparse data behind the use of any medication at birth and the poor outcome data available. The appropriate decline in the indiscriminate use of volume expansion is considered and balanced by the increasing evidence in favour of delayed clamping of the umbilical cord. Focusing on the basic steps of resuscitation, improving the quality of their application and avoiding relative hypovolaemia, must improve the quality of outcome data. The place of medications in newborn resuscitation should be regarded as experimental and still requires evidence to justify their use especially in premature babies.

A drop in gas temperature in the external part of the endotracheal tube is problematic during neonatal respiratory support

During neonatal respiratory support, maintaining optimal humidity minimizes the risk of airway occlusion and chronic lung disease. With neonatal respiratory support using a heated humidifier,condensation following decreases in temperature within the unheated part of the inspiratory circuit represents a serious problem, due to the resulting drop in absolute humidity. Several reports describing the temperature/humidity gradient in the unheated inspiratory limb have excluded the endotracheal tube (ETT). The present study investigated the extent to which the temperature gradient in the ETT affects breathing gas conditioning in premature infants, who display tiny minute volumes. By measuring temperature/dew point at various sites along the inspiratory circuit, including inside the ETT, we evaluated the effects of temperature change in the ETT using an in vitro model of a micropremie on mechanical respirator care in an incubator. We confirmed significant moisture loss (absolute humidity loss; 7.5-10.1 mg/L) with decreasing gas temperature in the ETT external to the body, with subsequent drying of the gas (relative humidity drop, 10.7-22.3%) as temperature increased in the ETT inside the body. The present results suggest that temperature decreases in the ETT represent an important issue in the respiratory care of very premature infants.

The posterior part of the human cerebral arterial circle (CAC): arterial caliber from gestational weeks 13 to 24

Numerous studies have reported that all components of the cerebral arterial circle in the 4-month-old human fetus are more slender than adult vessels, and of equal caliber. After that period, a degree of caliber differentiation is present, especially at the level of the posterior communicating arteries. The aim of this study was to determine arterial diameters in the posterior part of the fetal cerebral arterial circle from the 4th month (IV) to the 6th (VI). One hundred and seventy-two fetal cerebral arterial circles were examined by means of a surgical microscope. It was determined that average diameters of the left (right) pre-communicating parts of the posterior cerebral artery ranged from 0.30 +/- 0.03 (0.29 +/- 0.02) mm in month IV, to 0.36 +/- 0.04 (0.36 +/- 0.03) mm during month V and up to 0.55 +/- 0.22 (0.50 +/- 0.18) mm in month VI. The average diameters of the left (right) posterior communicating artery ranged from 0.24 +/- 0.02 mm (0.25 +/- 0.02) in month IV, to 0.30 +/- 0.03 mm (0.29 +/- 0.05) during month V and up to 0.38 +/- 0.08 (0.44 +/- 0.10) in month VI. Gender differences between posterior cerebral artery and posterior communicating artery diameters were not significant. Average posterior cerebral artery diameters were significantly larger than posterior communicating artery diameters in months IV and V, but not in month VI. It was established that caliber differentiation in the posterior part of the cerebral arterial circle began from gestational month IV, and that gender differences in arterial diameters were not significant until month VI of gestation.

Activated protein C reduces endotoxin-induced white matter injury in the developing rat brain

Periventricular leukomalacia (PVL), the dominant form of brain injury in premature infants, is characterized by white matter injury (WMI) and is associated with cerebral palsy. The pathogenesis of PVL is complex and likely involves ischemia/reperfusion, free radical formation, excitotoxicity, impaired regulation of cerebral blood flow, a procoagulant state, and inflammatory mechanisms associated with maternal and/or fetal infection. Using an established animal model of human PVL, we investigated whether activated protein C (APC), an anti-coagulant factor with anti-inflammatory, anti-apoptotic, anti-oxidant, and cytoprotective activities, could reduce endotoxin-induced WMI in the developing rat brain. Intraperitoneal injections of lipopolysaccharide (LPS) (0.5 mg/kg body weight) were given at embryonic days 18 (E18) and 19 (E19) to pregnant Sprague-Dawley rats; control rats were injected with sterile saline. A single intravenous injection of recombinant human (rh) APC (0.2 mg /kg body weight) was given to pregnant rats following the second LPS dose on embryonic day 19 (E19). Reduced cell death in white matter and hypomyelination were shown on TUNEL and myelin basic protein (MBP) staining, respectively, on late postnatal days (P7) in APC-treated groups. There were significantly fewer TUNEL+nuclei in the periventricular WM in the APC+LPS group than in the untreated LPS group. Compared to the APC+LPS and control group, MBP expression was weak in the LPS group on P7, indicating endotoxin-induced hypomyelination in the developing rat brain. APC attenuated the LPS-induced protein expression of inflammatory cytokines, tumor necrosis factor-alpha, and interleukin-6, as evaluated by ELISA in neonatal rat brains. A single intraperitoneal injection of rhAPC (0.2 mg/kg body weight) to neonatal rats on P1 also had similar protective and anti-inflammatory effects against maternally administered LPS. Collectively, these data support the hypothesis that APC may provide protection against an endotoxin-evoked inflammatory response and WMI in the developing rat brain. Moreover, our results suggest that the possible use of APC in treatment of preterm infants and pregnant women with maternal or placental infection may minimize the risk of PVL and cerebral palsy.