Fetal Cerebrovascular Maturation: Effects of Hypoxia

Risk of Cerebrovascular Events Among Childhood and Adolescent Patients Receiving Cranial Radiation Therapy: A PENTEC Normal Tissue Outcomes Comprehensive Review

PURPOSE

Radiation-induced cerebrovascular toxicity is a well-documented sequelae that can be both life-altering and potentially fatal. We performed a meta-analysis of the relevant literature to create practical models for predicting the risk of cerebral vasculopathy after cranial irradiation.

METHODS AND MATERIALS

A literature search was performed for studies reporting pediatric radiation therapy (RT) associated cerebral vasculopathy. When available, we used individual patient RT doses delivered to the Circle of Willis (CW) or optic chiasm (as a surrogate), as reported or digitized from original publications, to formulate a dose-response. A logistic fit and a Normal Tissue Complication Probability (NTCP) model was developed to predict future risk of cerebrovascular toxicity and stroke, respectively. This NTCP risk was assessed as a function of prescribed dose.

RESULTS

The search identified 766 abstracts, 5 of which were used for modeling. We identified 101 of 3989 pediatric patients who experienced at least one cerebrovascular toxicity: transient ischemic attack, stroke, moyamoya, or arteriopathy. For a range of shorter follow-ups, as specified in the original publications (approximate attained ages of 17 years), our logistic fit model predicted the incidence of any cerebrovascular toxicity as a function of dose to the CW, or surrogate structure: 0.2% at 30 Gy, 1.3% at 45 Gy, and 4.4% at 54 Gy. At an attained age of 35 years, our NTCP model predicted a stroke incidence of 0.9% to 1.3%, 1.8% to 2.7%, and 2.8% to 4.1%, respectively at prescribed doses of 30 Gy, 45 Gy, and 54 Gy (compared with a baseline risk of 0.2%-0.3%). At an attained age of 45 years, the predicted incidence of stroke was 2.1% to 4.2%, 4.5% to 8.6%, and 6.7% to 13.0%, respectively at prescribed doses of 30 Gy, 45 Gy, and 54 Gy (compared with a baseline risk of 0.5%-1.0%).

CONCLUSIONS

Risk of cerebrovascular toxicity continues to increase with longer follow-up. NTCP stroke predictions are very sensitive to model variables (baseline stroke risk and proportional stroke hazard), both of which found in the literature may be systematically erring on minimization of true risk. We hope this information will assist practitioners in counseling, screening, surveilling, and facilitating risk reduction of RT-related cerebrovascular late effects in this highly sensitive population.

Breath-holding as model for the evaluation of EEG signal during respiratory distress

PURPOSE

Research describes the existence of a relationship between cortical activity and the regulation of bulbar respiratory centers through the evaluation of the electroencephalographic (EEG) signal during respiratory challenges. For example, we found evidences of a reduction in the frequency of the EEG (alpha band) in both divers and non-divers during apnea tests. For instance, this reduction was more prominent in divers due to the greater physiological disturbance resulting from longer apnea time. However, little is known about EEG adaptations during tests of maximal apnea, a test that voluntarily stops breathing and induces dyspnea.

RESULTS

Through this mini-review, we verified that a protocol of successive apneas triggers a significant increase in the maximum apnea time and we hypothesized that successive maximal apnea test could be a powerful model for the study of cortical activity during respiratory distress.

CONCLUSION

Dyspnea is a multifactorial symptom and we believe that performing a successive maximal apnea protocol is possible to understand some factors that determine the sensation of dyspnea through the EEG signal, especially in people not trained in apnea.

Fetal head-down posture may explain the rapid brain evolution in humans and other primates: An interpretative review

Evolutionary cerebrovascular consequences of upside-down postural verticality of the anthropoid fetus have been largely overlooked in the literature. This working hypothesis-based report provides a literature interpretation from an aspect that the rapid evolution of the human brain has been promoted by fetal head-down position due to maternal upright and semi-upright posture. Habitual vertical torso posture is a feature not only of humans, but also of monkeys and non-human apes that spend considerable time in a sitting position. Consequently, the head-down position of the fetus may have caused physiological craniovascular hypertension that stimulated expansion of the intracranial vessels and acted as an epigenetic physiological stress, which enhanced neurogenesis and eventually, along with other selective pressures, led to the progressive growth of the anthropoid brain and its organization. This article collaterally opens a new insight into the conundrum of high cephalopelvic proportions (i.e., the tight fit between the pelvic birth canal and fetal head) in phylogenetically distant lineages of monkeys, lesser apes, and humans. Low cephalopelvic proportions in non-human great apes could be accounted for by their energetically efficient horizontal nest-sleeping and consequently by their larger body mass compared to monkeys and lesser apes that sleep upright. One can further hypothesize that brain size varies in anthropoids according to the degree of exposure of the fetus to postural verticality. The supporting evidence for this postulation includes a finding that in fossil hominins cerebral blood flow rate increased faster than brain volume. This testable hypothesis opens a perspective for research on fetal postural cerebral hemodynamics.

Wnt5a-Flt1 activation contributes to preterm altered cerebral angiogenesis after prenatal inflammation

OBJECTIVE

Intraventricular hemorrhage (IVH) causes morbidity and mortality in preterm infants and prenatal exposure to inflammation contributes to brain injury. Moreover, prenatal exposure to severe inflammation increases the risk of IVH in preterm neonates. The current study investigated whether intrauterine exposure to inflammation affects cerebral angiogenesis and its underlying mechanisms.

METHODS

Wnt5a, flt1, and vascular endothelial growth factor (VEGF)-A levels in cord blood serum (stored in a bio-bank) of the enrolled patients were measured via enzyme-linked immunosorbent assay. A preterm prenatal inflammation exposure model was established in rats by intraperitoneal injection intraperitoneally during pregnancy. Angiogenesis of cerebral tissue was analyzed using immunohistochemistry. Wnt5a, flt1, and VEGF-A expression levels were measured via immunohistochemistry, immunofluorescence, or western blotting. The correlation between Wnt5a and flt1 expression and the cerebral vessel area was also analyzed.

RESULTS

The Wnt5a and flt1 levels in the cord blood serum were significantly higher in the amnionitis group than in the non-amnionitis group. The VEGF-A level in the cord blood serum was significantly lower in the amnionitis group. In the rat model, preterm rats in the prenatal inflammation group exhibited increased microglial cell infiltration and decreased vessel area and diameter in the cerebral tissue compared to the control group. Wnt5a was located in microglial cells, and Wnt5a and flt1 expression in brain tissue significantly increased after prenatal lipopolysaccharide (LPS) exposure. VEGF-A expression declined after prenatal LPS exposure. The cerebral vessel area was negatively correlated with Wnt5a and flt1 expression.

CONCLUSION

Disordered cerebral angiogenesis is associated with increased Wnt5a-Flt1 activation in microglial cells after exposure to intrauterine inflammation.

Does Perinatal Intermittent Hypoxia Affect Cerebrovascular Network Development?

Perinatal hypoxia is an inadequate delivery of oxygen to the fetus in the period immediately before, during, or after the birth process. The most frequent form of hypoxia occurring in human development is chronic intermittent hypoxia (CIH) due to sleep-disordered breathing (apnea) or bradycardia events. CIH incidence is particularly high with premature infants. During CIH, repetitive cycles of hypoxia and reoxygenation initiate oxidative stress and inflammatory cascades in the brain. A dense microvascular network of arterioles, capillaries, and venules is required to support the constant metabolic demands of the adult brain. The development and refinement of this microvasculature is orchestrated throughout gestation and in the initial weeks after birth, at a critical juncture when CIH can occur. There is little knowledge on how CIH affects the development of the cerebrovasculature. However, since CIH (and its treatments) can cause profound abnormalities in tissue oxygen content and neural activity, there is reason to believe that it can induce lasting abnormalities in vascular structure and function at the microvascular level contributing to neurodevelopmental disorders. This mini-review discusses the hypothesis that CIH induces a positive feedback loop to perpetuate metabolic insufficiency through derailment of normal cerebrovascular development, leading to long-term deficiencies in cerebrovascular function.

Persistent reversed end-diastolic flow of the middle cerebral artery: A rare and concerning finding

Fetal reversed end-diastolic flow of the middle cerebral artery is a rare ultrasound finding associated with pathological fetal conditions. Herein, we report the case of a fetus presenting with reversed end-diastolic flow of the middle cerebral artery caused by extensive intracranial hemorrhage from maternal warfarin therapy. From a literature review, we present the clinical findings, etiologies, and outcomes of cases with fetal reversed end-diastolic flow of the middle cerebral artery.

Neuronal GPR81 regulates developmental brain angiogenesis and promotes brain recovery after a hypoxic ischemic insult

Perinatal hypoxic/ischemic (HI) brain injury is a major clinical problem with devastating neurodevelopmental outcomes in neonates. During HI brain injury, dysregulated factor production contributes to microvascular impairment. Glycolysis-derived lactate accumulated during ischemia has been proposed to protect against ischemic injury, but its mechanism of action is poorly understood. Herein, we hypothesize that lactate via its G-protein coupled receptor (GPR81) controls postnatal brain angiogenesis and plays a protective role after HI injury. We show that GPR81 is predominantly expressed in neurons of the cerebral cortex and hippocampus. GPR81-null mice displayed a delay in cerebral microvascular development linked to reduced levels of various major angiogenic factors and augmented expression of anti-angiogenic Thrombospondin-1 (TSP-1) in comparison to their WT littermates. Coherently, lactate stimulation induced an increase in growth factors (VEGF, Ang1 and 2, PDGF) and reduced TSP-1 expression in neurons, which contributed to accelerating angiogenesis. HI injury in GPR81-null animals curtailed vascular density and consequently increased infarct size compared to changes seen in WT mice; conversely intracerebroventricular lactate injection increased vascular density and diminished infarct size in WT but not in GPR81-null mice. Collectively, we show that lactate acting via GPR81 participates in developmental brain angiogenesis, and attenuates HI injury by restoring compromised microvasculature.

In utero hypoxia attenuated acetylcholine-mediated vasodilatation via CHRM3/p-NOS3 in fetal sheep MCA: role of ROS/ERK1/2

Hypoxia can lead to adult middle cerebral artery (MCA) dysfunction and increase the risk of cerebrovascular diseases. It is largely unknown whether intrauterine hypoxia affects fetal MCA vasodilatation. This study investigated the effects and mechanisms of intrauterine hypoxia on fetal MCA vasodilatation. Near-term fetal sheep were exposed to intrauterine hypoxia. Human umbilical vein endothelial cells (HUVECs) were exposed to hypoxia in cellular experiments. Vascular tone measurement, molecular analysis, and transmission electron microscope (TEM) were utilized to determine vascular functions, tissue anatomy, and molecular pathways in fetal MCA. In fetal MCA, acetylcholine (ACh) induced reliable relaxation, which was markedly attenuated by intrauterine hypoxia. Atropine, P-F-HHSiD, L-NAME, and u0126 blocked most ACh-mediated dilation, while AF-DX 116 and tropicamide partially inhibited the dilation. Indomethacin and SB203580 did not significantly change ACh-mediated dilation. Tempol and PS-341 could restore the attenuated ACh-mediated vasodilatation following intrauterine hypoxia. The mRNA expression levels of CHRM2 and CHRM3 and the protein levels of CHRM3, p-NOS3, SOD2, ERK1/2, p-ERK1/2, MAPK14, and p-MAPK14 were significantly reduced by intrauterine hypoxia. The dihydroethidium assay showed that the production of ROS was increased under intrauterine hypoxia. TEM analysis revealed endothelial cells damaged by intrauterine hypoxia. In HUVECs, hypoxia increased ROS formation and decreased the expression of CHRM3, p-NOS3, SOD1, SOD2, SOD3, ERK1/2, p-ERK1/2, and p-MAPK14, while tempol and PS-341 potentiated p-NOS3 protein expression. In conclusion, in utero hypoxia reduced ACh-mediated vasodilatation in ovine MCA predominantly via decreased CHRM3 and p-NOS3, and the decreased NOS3 bioactivities might be attributed to ROS and ERK1/2.

Transfontanellar Contrast-enhanced US for Intraoperative Imaging of Cerebral Perfusion during Neonatal Arterial Switch Operation

Background Brain injury and subsequent neurodevelopmental disorders are major determinants for later-life outcomes in neonates with transposition of the great arteries (TGA). Purpose To quantitatively assess cerebral perfusion in neonates with TGA undergoing arterial switch operation (ASO) using transfontanellar contrast-enhanced US (T-CEUS). Materials and Methods In a prospective single-center cross-sectional diagnostic study, neonates with TGA scheduled for ASO were recruited from February 2018 to February 2020. Measurements were performed at five time points before, during, and after surgery (T₁-T₅), and 11 perfusion parameters were derived per cerebral hemisphere. Neonate clinical characteristics, heart rate, mean arterial pressure, central venous pressure, near-infrared spectroscopy, blood gas analyses, ventilation time, time spent in the pediatric intensive care unit, and time in hospital were correlated with imaging parameters. Analysis of variance or a mixed-effects model were used for groupwise comparisons. Results A total of 12 neonates (mean gestational age, 39 6/7 weeks ± 1/7 [SD]) were included and underwent ASO a mean of 6.9 days ± 3.4 after birth. When compared with baseline values, T-CEUS revealed a longer mean time-to-peak (right hemisphere, 4.3 seconds ± 2.1 vs 17 seconds ± 6.4 [P < .001]; left hemisphere, 4.0 seconds ± 2.3 vs 21 seconds ± 8.7 [P < .001]) and rise time (right hemisphere, 3.5 seconds ± 1.7 vs 11 seconds ± 5.1 [P = .002]; left hemisphere, 3.4 seconds ± 2.0 vs 22 seconds ± 7.8 [P = .004]) in both cerebral hemispheres during low-flow cardiopulmonary bypass and hypothermia (T₄) for all neonates. Neonate age at surgery negatively correlated with T-CEUS parameters during ASO, as calculated with the area under the flow curve (AUC) during wash-in (R = -0.60, P = .020), washout (R = -0.82, P = .002), and both wash-in and washout (R = -0.79, P = .004). Mean AUC values were lower in neonates older than 7 days compared with younger neonates during wash-in ([87 arbitrary units {au} ± 77] × 10² vs [270 au ± 164] × 10², P = .049]), washout ([15 au ± 11] × 10³ vs [65 au ± 38] × 10³, P = .020]) and both wash-in and washout ([24 au ± 18] × 10³ vs [92 au ± 53] × 10³, P = .023). Conclusion Low-flow hypothermic conditions resulted in reduced cerebral perfusion, as measured with transfontanellar contrast-enhanced US, which inversely correlated with age at surgery. Clinical trial registration no. NCT03215628 © RSNA, 2022 Online supplemental material is available for this article.

Differential age-dependent development of inter-area brain connectivity in term and preterm neonates

BACKGROUND

Among preterm infants, higher morbidities of neurological disturbances and developmental delays are critical issues. Resting-state networks (RSNs) in the brain are suitable measures for assessing higher-level neurocognition. Since investigating task-related brain activity is difficult in neonates, assessment of RSNs provides invaluable insight into their neurocognitive development.

METHODS

The participants, 32 term and 71 preterm neonates, were divided into three groups based on gestational age (GA) at birth. Cerebral hemodynamic activity of RSNs was measured using functional near-infrared spectroscopy in the temporal, frontal, and parietal regions.

RESULTS

High-GA preterm infants (GA ≥ 30 weeks) had a significantly stronger RSN than low-GA preterm infants and term infants. Regression analyses of RSNs as a function of postnatal age (PNA) revealed a steeper regression line in the high-GA preterm and term infants than in the low-GA infants, particularly for inter-area brain connectivity between the frontal and left temporal areas.

CONCLUSIONS

Slower PNA-dependent development of the frontal-temporal network found only in the low-GA group suggests that significant brain growth optimal in the intrauterine environment takes place before 30 weeks of gestation. The present study suggests a likely reason for the high incidence of neurodevelopmental impairment in early preterm infants.

IMPACT

Resting-state fNIRS measurements in three neonate groups differing in gestational age (GA) showed stronger networks in the high-GA preterm infants than in the term and low-GA infants, which was partly explained by postnatal age (PNA). Regression analyses revealed a similar PNA-dependence in the development of the inter-area networks in the frontal and temporal lobes in the high-GA and term infants, and significantly slower development in the low-GA infants. These results suggest that optimal intrauterine brain growth takes place before 30 weeks of gestation. This explains one of the reasons for the high incidence of neurodevelopmental impairment in early preterm infants.

Maternal Undernutrition Modulates Neonatal Rat Cerebrovascular Structure, Function, and Vulnerability to Mild Hypoxic-Ischemic Injury via Corticosteroid-Dependent and -Independent Mechanisms

The present study explored the hypothesis that an adverse intrauterine environment caused by maternal undernutrition (MUN) acted through corticosteroid-dependent and -independent mechanisms to program lasting functional changes in the neonatal cerebrovasculature and vulnerability to mild hypoxic-ischemic (HI) injury. From day 10 of gestation until term, MUN and MUN-metyrapone (MUN-MET) group rats consumed a diet restricted to 50% of calories consumed by a pair-fed control; and on gestational day 11 through term, MUN-MET groups received drinking water containing MET (0.5 mg/mL), a corticosteroid synthesis inhibitor. P9/P10 pups underwent unilateral carotid ligation followed 24 h later by 1.5 h exposure to 8% oxygen (HI treatment). An ELISA quantified MUN-, MET-, and HI-induced changes in circulating levels of corticosterone. In P11/P12 pups, MUN programming promoted contractile differentiation in cerebrovascular smooth muscle as determined by confocal microscopy, modulated calcium-dependent contractility as revealed by cerebral artery myography, enhanced vasogenic edema formation as indicated by T2 MRI, and worsened neurobehavior MUN unmasked HI-induced improvements in open-field locomotion and in edema resolution, alterations in calcium-dependent contractility and promotion of contractile differentiation. Overall, MUN imposed multiple interdependent effects on cerebrovascular smooth muscle differentiation, contractility, edema formation, flow-metabolism coupling and neurobehavior through pathways that both required, and were independent of, gestational corticosteroids. In light of growing global patterns of food insecurity, the present study emphasizes that infants born from undernourished mothers may experience greater risk for developing neonatal cerebral edema and sensorimotor impairments possibly through programmed changes in neonatal cerebrovascular function.

Fetal cardiovascular magnetic resonance imaging

Fetal cardiovascular MRI is showing promise as a clinical diagnostic tool in the setting of congenital heart disease when the cardiac anatomy is unresolved by US or when complementary quantitative data on blood flow, oxygen saturation and hematocrit are required to aid in management. Compared with postnatal cardiovascular MRI, prenatal cardiovascular MRI still has some technical limitations. However, ongoing technical advances continue to improve the robustness and usability of fetal cardiovascular MRI. In this review, we provide an overview of the state of the art of fetal cardiovascular MRI and summarize the current focus of clinical application for this versatile technique.

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.

The Neurovascular Unit: Effects of Brain Insults During the Perinatal Period

The neurovascular unit (NVU) is a relatively recent concept in neuroscience that broadly describes the relationship between brain cells and their blood vessels. The NVU incorporates cellular and extracellular components involved in regulating cerebral blood flow and blood-brain barrier function. The NVU within the adult brain has attracted strong research interest and its structure and function is well described, however, the NVU in the developing brain over the fetal and neonatal period remains much less well known. One area of particular interest in perinatal brain development is the impact of known neuropathological insults on the NVU. The aim of this review is to synthesize existing literature to describe structure and function of the NVU in the developing brain, with a particular emphasis on exploring the effects of perinatal insults. Accordingly, a brief overview of NVU components and function is provided, before discussion of NVU development and how this may be affected by perinatal pathologies. We have focused this discussion around three common perinatal insults: prematurity, acute hypoxia, and chronic hypoxia. A greater understanding of processes affecting the NVU in the perinatal period may enable application of targeted therapies, as well as providing a useful basis for research as it expands further into this area.