Persistent pulmonary hypertension of the newborn

Persistent Tachypnoea in Early Infancy: A Clinical Perspective

Tachypnoea in the newborn is common. It may arise from the many causes of the respiratory distress syndrome such as hyaline membrane disease, transient tachypnoea of the newborn, meconium aspiration etc. Congenital heart disease rarely presents with early tachypnoea on day one or two, in contrast to the early presentation of cyanosis, unless there is "pump" (ventricular) failure such as may occur in a cardiomyopathy/myocarditis, or as a result of severe obstruction to either ventricle. Space-occupying lesions within the chest, for example from a diaphragmatic hernia or a congenital cystic adenomatoid malformation, may present with early tachypnoea, as can a metabolic cause resulting in acidosis. The aim of this paper, however, is to focus on infants where the tachypnoea persists or develops beyond the newborn period, at times with minimal signs but occasionally with serious underlying pathology. They include causes that may have originated in the newborn but then persist; for example, arising from pulmonary hypoplasia or polycythemia. Many congenital cardiac abnormalities, particularly those causing left sided obstructive lesions, or those due to an increasing left to right shunt from large communications between the systemic and pulmonary circulations, need be considered. Respiratory causes, for example arising from aspiration, primary ciliary dyskinesia, cystic fibrosis, or interstitial lung disease, may lead to ongoing tachypnoea. Infective causes such as bronchiolitis or infantile wheeze generally are readily recognisable. Finally, there are a few infants who present with persistent tachypnoea over the first few weeks/months of their life who remain well and have normal investigations with the tachypnoea gradually resolving. How should one approach infants with persistent tachypnoea?

Fifteen-minute consultation: How to spot serious heart disease in the newborn

Congenital heart disease (CHD) is common and important as it remains a leading cause of neonatal morbidity and appreciable mortality. Prenatal diagnosis, the presence of a murmur, cyanosis, tachypnoea and/or poor or differential peripheral pulses raise the suspicion of CHD aided by differential pre/postductal saturations. Yet even serious CHD may not be considered when such clues are absent. Nevertheless, there are clinical cues which may alert the clinician to the possibility of a significant CHD which may lead to an early and accurate diagnosis and appropriate intervention to achieve best results. This paper addresses these issues which become especially difficult if caring for infants away from facilities provided by tertiary centres. Tachypnoea on the first postnatal day is generally non-cardiac in origin. Exceptions include large arteriovenous fistulae and/or 'pump' (ventricular) failure. In addition, attention is drawn to two important confounding factors in the newborn, namely the patency of the ductus arteriosus and the initially high pulmonary vascular resistance, both of which alter and may mask the clinical findings of a serious cardiac abnormality. An appreciation of the physiological changes that occur in early infancy will aid the clinician's understanding of CHD as it affects the newborn.

Altered cardiolipin metabolism is associated with cardiac mitochondrial dysfunction in pulmonary vascular remodeled perinatal rat pups

Pulmonary vascular remodeling (PVR) in utero results in the development of heart failure. The alterations that occur in cardiac lipid and mitochondrial bioenergetics during the development of in utero PVR was unknown. In this study, PVR was induced in pups in utero by exposure of pregnant dams to indomethacin and hypoxia and cardiac lipids, echocardiographic function and cardiomyocyte mitochondrial function were subsequently examined. Perinatal rat pups with PVR exhibited elevated left and right cardiac ventricular internal dimensions and reduced ejection fraction and fractional shortening compared to controls. Cardiac myocytes from these pups exhibited increased glycolytic capacity and glycolytic reserve compared to controls. However, respiration with glucose as substrate was unaltered. Fatty acid oxidation and ATP-insensitive respiration were increased in isolated cardiac myocytes from these pups compared to controls indicating a mitochondrial dysfunction. Although abundance of mitochondrial respiratory chain complexes was unaltered, increased trilinoleoyl-lysocardiolipin levels in these pups was observed. A compensatory increase in both cardiolipin and phosphatidylethanolamine content were observed due to increased synthesis of these phospholipids. These data indicate that alterations in cardiac cardiolipin and phospholipid metabolism in PVR rat pups is associated with the mitochondrial bioenergetic and cardiac functional defects observed in their hearts.

Effectiveness of oral sildenafil for neonates with persistent pulmonary hypertension of newborn (PPHN): a prospective study in a tertiary care hospital

INTRODUCTION

The prevalence of persistent pulmonary hypertension of newborn (PPHN) has been estimated 1.9/1000 live births. Although the efficacy of inhaled nitric oxide and extracorporeal membrane oxygenation in PPHN is well established but it is difficult to administer and monitor in resource limited countries. Owing to this, other treatment options need to be evaluated.

METHOD

This is a prospective observational study conducted in the Pediatric Cardiology Department, NICVD, Karachi, from February 2020 to October 2020 after the approval from the Institutional Ethical Review Committee. All the neonates referred to our Unit were screened by echocardiography (echo) and those who fulfilled the inclusion criteria were included. Echo were done before starting sildenafil and after 72 h to assess the pressure gradient across tricuspid valve and right to left or bidirectional shunt across patent ductus arteriosus , patent foramen ovale , or both. Sildenafil was started with a dose of 1 mg/kg/dose thrice a day and increased to 2 mg/kg/dose after 48 h if partial pressure of oxygen (PO₁] did not increase. In neonates who did not respond to increased dose of Sildenafil were added on oral Bosentan 1 mg/kg/dose twice a day.

RESULTS

Total 82 newborns were enrolled. Fifty-two patients improved after 48 h so were continued on same treatment. Sildenafil dose was increased in 30 (37.9%) patients whose PO₂ did not increase to at least 10% from baseline after 48 h of starting treatment. Three patients expired within 48-72 h. Out of 27 remaining patients, only four responded whereas 23 patients did not show any improvement. In these patients, Bosentan was supplemented along with sildenafil.

CONCLUSION

The results of our study show effectiveness of oral Sildenafil in treating PPHN. The overall improvement observed in the patients was overwhelming. Combination of Sildenafil with Bosentan is beneficial in patients who did not respond on Sildenafil alone.

The Controversy Persists: Is There a Qualification Criterion to Utilize Inhaled Nitric Oxide in Pre-term Newborns?

Inhaled nitric oxide (iNO) use in premature newborns remains controversial among clinicians. In 2014, the American Academy of Pediatrics, Committee on Fetus and Newborn released a statement that the available data do not support routine iNO use in pre-term newborns. Despite the absence of significant benefits, 2016 California data showed that clinicians continue to utilize iNO in pre-term infants. With studies as recent as January 2017, the Cochrane review confirmed no major advantages of iNO in pre-term newborns. Still, it recognized that a subset of pre-term infants with pulmonary hypertension (PHTN) had not been separately investigated. Furthermore, recent non-randomized controlled trials have suggested that iNO may benefit specific subgroups of pre-term newborns, especially those with PHTN, prolonged rupture of membranes, and antenatal steroid exposure. Those pre-term infants who showed a clinical response to iNO had increased survival without disability. These findings underscore the need for future studies in pre-term newborns with hypoxemic respiratory failure and PHTN. This review will discuss the rationale for using iNO, controversies regarding the diagnosis of PHTN, and additional novel approaches of iNO treatment in perinatal asphyxia and neonatal resuscitation in the pre-term population < 34 weeks gestation.

Endothelial dysfunction in pulmonary arterial hypertension: an evolving landscape (2017 Grover Conference Series)

Endothelial dysfunction is a major player in the development and progression of vascular pathology in pulmonary arterial hypertension (PAH), a disease associated with small vessel loss and obstructive vasculopathy that leads to increased pulmonary vascular resistance, subsequent right heart failure, and premature death. Over the past ten years, there has been tremendous progress in our understanding of pulmonary endothelial biology as it pertains to the genetic and molecular mechanisms that orchestrate the endothelial response to direct or indirect injury, and how their dysregulation can contribute to the pathogenesis of PAH. As one of the major topics included in the 2017 Grover Conference Series, discussion centered on recent developments in four areas of pulmonary endothelial biology: (1) angiogenesis; (2) endothelial-mesenchymal transition (EndMT); (3) epigenetics; and (4) biology of voltage-gated ion channels. The present review will summarize the content of these discussions and provide a perspective on the most promising aspects of endothelial dysfunction that may be amenable for therapeutic development.

Risk factors for pulmonary arterial hypertension in children and young adults

OBJECTIVES

Pulmonary hypertension (PH) has been linked to preterm birth explained by congenital heart defects and pulmonary diseases.

WORKING HYPOTHESIS

Other factors may influence the risk of PH among adolescences and children born premature.

STUDY DESIGN

This national registry-based study assess risk of PH following premature birth adjusted for known risk factors.

PATIENT-SUBJECT SELECTION AND METHODOLOGY

All cases born 1993-2010, identified by diagnostic codes applicable to PH and retrieved from the Swedish Registry of Congenital Heart Disease (N = 67). Six controls were randomly selected and matched to each case by year of birth and hospital by the Swedish Medical Birth Register (N = 402). Maternal and infant data related to preterm birth, pulmonary diseases, and congenital defects were retrieved. The association between preterm birth and pulmonary hypertension was calculated by conditional logistic regression taking into account potential confounding factors.

RESULTS

One third of the cases and seven percent of the controls were born preterm in our study. Preterm birth was associated with PH, OR = 8.46 (95%CI 2.97-24.10) (P < 0.0001) even after adjusting for confounding factors. Other factors, such as acute pulmonary diseases, congenital heart defects, congenital diaphragm herniation, and chromosomal disorders were also associated with PH in the multivariate analysis.

CONCLUSIONS

Children and young adults born preterm are known to have an increased risk of PH, previously explained by congenital heart defects and pulmonary diseases. By adjusting for such factors, our study indicates that new factors may play a role in the risk of developing PH among children born preterm. Pediatr Pulmonol. 2017;52:636-641. © 2016 Wiley Periodicals, Inc.

Some neonatal risk factors for adult pulmonary arterial hypertension remain unknown

AIM

Pulmonary hypertension has been linked to premature birth, chronic lung disease, bronchopulmonary dysplasia and congenital heart disease. This national population-based registry study assessed the risk of adult pulmonary hypertension following premature birth, adjusted for known risk factors.

METHODS

We focused on adults in the Swedish Pulmonary Arterial Hypertension Registry, who were born prematurely, and controls randomly selected from the Swedish medical birth register and matched to each case by birth year and delivery hospital. Information on perinatal factors was also retrieved from the medical birth register. Conditional multiple logistic regression was used to evaluate the association between premature birth and adult pulmonary hypertension, taking into account the potential confounding factors.

RESULTS

The study population comprised 427 adults born between 1973 and 1996, with 61 cases and 366 controls. Adult pulmonary hypertension was associated with premature birth, with an odds ratio of 3.08 and 95% confidence interval of 1.21-7.87. The association did not alter after adjusting for potential confounders.

CONCLUSION

By adjusting for factors linked to adult pulmonary hypertension, namely congenital heart defects, pulmonary diseases and premature birth, we were able to show that other unknown factors may influence the risk for pulmonary hypertension among adults who were born premature.

A role for actin polymerization in persistent pulmonary hypertension of the newborn

Persistent pulmonary hypertension of the newborn (PPHN) is defined as the failure of normal pulmonary vascular relaxation at birth. Hypoxia is known to impede postnatal disassembly of the actin cytoskeleton in pulmonary arterial myocytes, resulting in elevation of smooth muscle α-actin and γ-actin content in elastic and resistance pulmonary arteries in PPHN compared with age-matched controls. This review examines the original histological characterization of PPHN with attention to cytoskeletal structural remodeling and actin isoform abundance, reviews the existing evidence for understanding the biophysical and biochemical forces at play during neonatal circulatory transition, and specifically addresses the role of the cortical actin architecture, primarily identified as γ-actin, in the transduction of mechanical force in the hypoxic PPHN pulmonary circuit.

Outcome of oral sildenafil in neonatal persistent pulmonary hypertension of non-cardiac causes

BACKGROUND

Despite recent treatment modalities, mortality from persistent pulmonary hypertension (PPHN) remains significant. In instances where infants do not respond to inhaled nitric oxide (iNO), oral sildenafil could hold promise as a selective pulmonary vasodilator. Further studies are still needed to explore its efficacy and safety in newborns with PPHN.

OBJECTIVES

To validate the efficacy of oral sildenafil on oxygenation and its short-term safety in newborns with persistent pulmonary hypertension.

METHODS

A total of 27 newborns ≥36 weeks gestational age were admitted to NICU with oxygenation index (OI) ≥15 and confirmed diagnosis of PPHN with echocardiography. Oral sildenafil given at a dose of 1-2 mg/kg every 6 hours. We monitored improvement in oxygenation, safety and short-term outcomes.

RESULTS

Among 27 newborns, oral sildenafil was efficacious in 21 patients (78%) with reduction of OI from 34.9 ± 9.6 to 13 ± 3.2 (p <  0.001), increase of PaO2 from 42.4 ± 13.5 to 78 ± 11.5 mmHg (<0.001), and reduction of FiO2 from 1.0 ± 0 to 0.3 ± 0.06 (<0.001). OI decreased by 6.3 % from baseline after the first dose of sildenafil and continued to decrease with subsequent doses. In 6 patients (22%) sildenafil did not work; 5/6 patients (18%) transferred to another tertiary NICU and one patient (4%) died of sepsis. None of the patients had significant systemic hypotension.

CONCLUSION

Oral sildenafil is a promising pulmonary vasodilator in patients with PPHN, particularly in medical facilities with no available iNO and ECMO. It is well tolerated with no significant short term complications.

Thromboxane-induced actin polymerization in hypoxic neonatal pulmonary arterial myocytes involves Cdc42 signaling

In hypoxic pulmonary arterial (PA) myocytes, challenge with thromboxane mimetic U46619 induces marked actin polymerization and contraction, phenotypic features of persistent pulmonary hypertension of the newborn (PPHN). Rho GTPases regulate the actin cytoskeleton. We previously reported that U46619-induced actin polymerization in hypoxic PA myocytes occurs independently of the RhoA pathway and hypothesized involvement of the Cdc42 pathway. PA myocytes grown in normoxia or hypoxia for 72 h were stimulated with U46619, then analyzed for Rac/Cdc42 activation by affinity precipitation, phosphatidylinositide-3-kinase (PI3K) activity by phospho-Akt, phospho-p21-activated kinase (PAK) by immunoblot, and association of Cdc42 with neuronal Wiskott Aldrich Syndrome protein (N-WASp) by immunoprecipitation. The effect of Rac or PAK inhibition on filamentous actin was quantified by laser-scanning cytometry and by cytoskeletal fractionation; effects of actin-modifying agents were measured by isometric myography. Basal Cdc42 activity increased in hypoxia, whereas Rac activity decreased. U46619 challenge increased Cdc42 and Rac activity in hypoxic cells, independently of PI3K. Hypoxia increased phospho-PAK, unaltered by U46619. Association of Cdc42 with N-WASp decreased in hypoxia but increased after U46619 exposure. Hypoxia doubled filamentous-to-globular ratios of α- and γ-actin isoforms. Jasplakinolide stabilized γ-filaments, increasing force; cytochalasin D depolymerized all actin isoforms, decreasing force. Rac and PAK inhibition decreased filamentous actin in tissues although without decrease in force. Rho inhibition decreased myosin phosphorylation and force. Hypoxia induces actin polymerization in PA myocytes, particularly increasing filamentous α- and γ-actin, contributing to U46619-induced contraction. Hypoxic PA myocytes challenged with a thromboxane mimetic polymerize actin via the Cdc42 pathway, reflecting increased Cdc42 association with N-WASp. Mechanisms regulating thromboxane-mediated actin polymerization are potential targets for future PPHN pharmacotherapy.

Vasotrophic regulation of age-dependent hypoxic cerebrovascular remodeling

Hypoxia can induce functional and structural vascular remodeling by changing the expression of trophic factors to promote homeostasis. While most experimental approaches have been focused on functional remodeling, structural remodeling can reflect changes in the abundance and organization of vascular proteins that determine functional remodeling. Better understanding of age-dependent hypoxic macrovascular remodeling processes of the cerebral vasculature and its clinical implications require knowledge of the vasotrophic factors that influence arterial structure and function. Hypoxia can affect the expression of transcription factors, classical receptor tyrosine kinase factors, non-classical G-protein coupled factors, catecholamines, and purines. Hypoxia's remodeling effects can be mediated by Hypoxia Inducible Factor (HIF) upregulation in most vascular beds, but alterations in the expression of growth factors can also be independent of HIF. PPARγ is another transcription factor involved in hypoxic remodeling. Expression of classical receptor tyrosine kinase ligands, including vascular endothelial growth factor, platelet derived growth factor, fibroblast growth factor and angiopoietins, can be altered by hypoxia which can act simultaneously to affect remodeling. Tyrosine kinase-independent factors, such as transforming growth factor, nitric oxide, endothelin, angiotensin II, catecholamines, and purines also participate in the remodeling process. This adaptation to hypoxic stress can fundamentally change with age, resulting in different responses between fetuses and adults. Overall, these mechanisms integrate to assure that blood flow and metabolic demand are closely matched in all vascular beds and emphasize the view that the vascular wall is a highly dynamic and heterogeneous tissue with multiple cell types undergoing regular phenotypic transformation.

Recent advances in late lung development and the pathogenesis of bronchopulmonary dysplasia

In contrast to early lung development, a process exemplified by the branching of the developing airways, the later development of the immature lung remains very poorly understood. A key event in late lung development is secondary septation, in which secondary septa arise from primary septa, creating a greater number of alveoli of a smaller size, which dramatically expands the surface area over which gas exchange can take place. Secondary septation, together with architectural changes to the vascular structure of the lung that minimize the distance between the inspired air and the blood, are the objectives of late lung development. The process of late lung development is disturbed in bronchopulmonary dysplasia (BPD), a disease of prematurely born infants in which the structural development of the alveoli is blunted as a consequence of inflammation, volutrauma, and oxygen toxicity. This review aims to highlight notable recent developments in our understanding of late lung development and the pathogenesis of BPD.

Risk factors and outcomes of persistent pulmonary hypertension of the newborn in neonatal intensive care unit of Al-minya university hospital in egypt

Background:

Persistent pulmonary hypertension of the newborn (PPHN) result from the failure of the normal fetal-to-neonatal circulatory transition is associated with substantial infant mortality and morbidity.

Objective:

To estimate the possible risk factors and assess the outcome of these cases.

Materials and Methods:

Prospective study was performed enrolling all full-term and post-term newborn admitted to the NICU from January 2009 to April 2012, All neonates were subjected to complete history and physical examination, laboratory data including a complete blood count, arterial blood gases, blood glucose, serum electrolytes, and blood culture to exclude sepsis. Cases with PPHN had a continuous pulse oximeter, blood pressure and electrocardiography monitoring. Chest X-ray and echocardiogarphy were carried out to verify shunt and exclude structural congenital heart disease.

Results:

Out of the studied 640 infants, 32 infants (5%) developed PPHN, Meconium aspiration, birth asphyxia, hyaline membrane diseases, neonatal septicemia, post-term birth being large for gestational age, cesarean section, maternal overweight, and diabetes mellitus were associated with an elevated risk for PPHN. All neonates treated with O₂, 10 neonates with Mg sulphate, 16 with oral sildenafil and 12 with mechanical ventilation. After 6 months follow-up, 12 (37.54%) improved and followed-up without sequelae, 4 (12.5%) developed some neurodevelopmental impairment, 8 (25%) died, 3 (9.3%) developed chronic lungs diseases, 2 (6.2%) developed hearing defects and another 3 (9.3%) missed follow-up.

Conclusion:

PPHN was found in 5% of the studied population. Meconium aspiration, birth asphyxia, neonatal septicemia, post-term were associated with an elevated risk for PPHN. As this is a unit based study, a comprehensive countrywide survey on PPHN in Egypt is recommended to determine any regional differences in disease incidence.

Antidepressant use during pregnancy: the benefit-risk ratio

Antidepressants are used commonly in pregnancy. Physicians who provide health care for pregnant women with depression must balance maternal well-being with potential fetal risks of these medications. Over the last decade, scores of original and review articles have discussed whether selective serotonin reuptake inhibitors-selective serotonin norepinephrine reuptake inhibitors possess risks to the fetus; however, very little has been done to integrate these potential risks, if they exist, into an overall context of a benefit:risk ratio. This review aims at presenting an updated analysis of fetal and maternal exposure to selective serotonin or norepinephrine reuptake inhibitors to allow an evidence-based benefit:risk ratio. When a psychiatric condition necessitates pharmacotherapy, the benefits of such therapy far outweigh the potential minimal risks of cardiac malformations, primary pulmonary hypertension of the newborn infant, or poor neonatal adaptation syndrome.

Epigenetic mechanisms of pulmonary hypertension

Epigenetics refers to changes in phenotype and gene expression that occur without alterations in DNA sequence. Epigenetic modifications of the genome can be acquired de novo and are potentially heritable. This review focuses on the emerging recognition of a role for epigenetics in the development of pulmonary arterial hypertension (PAH). Lessons learned from the epigenetics in cancer and neurodevelopmental diseases, such as Prader-Willi syndrome, can be applied to PAH. These syndromes suggest that there is substantial genetic and epigenetic cross-talk such that a single phenotype can result from a genetic cause, an epigenetic cause, or a combined abnormality. There are three major mechanisms of epigenetic regulation, including methylation of CpG islands, mediated by DNA methyltransferases, modification of histone proteins, and microRNAs. There is substantial interaction between these epigenetic mechanisms. Recently, it was discovered that there may be an epigenetic component to PAH. In PAH there is downregulation of superoxide dismutase 2 (SOD2) and normoxic activation of hypoxia inducible factor (HIF-1α). This decrease in SOD2 results from methylation of CpG islands in SOD2 by lung DNA methyltransferases. The partial silencing of SOD2 alters redox signaling, activates HIF-1α) and leads to excessive cell proliferation. The same hyperproliferative epigenetic abnormality occurs in cancer. These epigenetic abnormalities can be therapeutically reversed. Epigenetic mechanisms may mediate gene-environment interactions in PAH and explain the great variability in susceptibility to stimuli such as anorexigens, virus, and shunts. Epigenetics may be relevant to the female predisposition to PAH and the incomplete penetrance of BMPR2 mutations in familial PAH.

ANG-1 TIE-2 and BMPR signalling defects are not seen in the nitrofen model of pulmonary hypertension and congenital diaphragmatic hernia

BACKGROUND

Pulmonary hypertension (PH) is a lethal disease that is associated with characteristic histological abnormalities of the lung vasculature and defects of angiopoetin-1 (ANG-1), TIE-2 and bone morphogenetic protein receptor (BMPR)-related signalling. We hypothesized that if these signalling defects cause PH generically, they will be readily identifiable perinatally in congenital diaphragmatic hernia (CDH), where the typical pulmonary vascular changes are present before birth and are accompanied by PH after birth.

METHODS

CDH (predominantly left-sided, LCDH) was created in Sprague-Dawley rat pups by e9.5 maternal nitrofen administration. Left lungs from normal and LCDH pups were compared at fetal and postnatal time points for ANG-1, TIE-2, phosphorylated-TIE-2, phosphorylated-SMAD1/5/8 and phosphorylated-ERK1/2 by immunoprecipitation and Western blotting of lung protein extracts and by immunohistochemistry on lung sections.

RESULTS

In normal lung, pulmonary ANG-1 protein levels fall between fetal and postnatal life, while TIE-2 levels increase. Over the corresponding time period, LCDH lung retained normal expression of ANG-1, TIE-2, phosphorylated-TIE-2 and, downstream of BMPR, phosphorylated-SMAD1/5/8 and phosphorylated-p44/42.

CONCLUSION

In PH and CDH defects of ANG-1/TIE-2/BMPR-related signalling are not essential for the lethal vasculopathy.

Inhaled nitric oxide improves systemic microcirculation in infants with hypoxemic respiratory failure

OBJECTIVES

To investigate the effect of inhaled nitric oxide on the systemic microcirculation. We hypothesized that inhaled nitric oxide improves the systemic microcirculation. Inhaled nitric oxide improves outcome in infants with persistent pulmonary hypertension of the newborn diagnosed by improving pulmonary blood flow and oxygenation. It reduces pulmonary vascular resistance without decline in systemic blood pressure. Inhaled nitric oxide is also utilized in the treatment of acute hypoxemic respiratory failure in children and adults. It is thought to improve regional ventilation perfusion by regional selective pulmonary vasodilation.

DESIGN

Pilot study.

SETTING

Intensive care unit of a level III university children's hospital.

PATIENTS

Consecutive ventilated patients who were treated with inhaled nitric oxide (20 ppm) were enrolled in this study. Eight patients (five boys, three girls) were included; five had congenital diaphragmatic hernia diagnosed, one had persistent pulmonary hypertension of the newborn diagnosed, one had acute respiratory distress syndrome diagnosed, and one had bronchiolitis diagnosed. The median age was 0 months (range, 0-38 months).

INTERVENTIONS

Inhaled nitric oxide administration.

MEASUREMENTS AND MAIN RESULTS

The microcirculation was assessed in the buccal mucosa within 1 hr before and within 1 hr after the start of inhaled nitric oxide using orthogonal polarization spectral imaging. The median functional capillary density before the inhaled nitric oxide was started was 4.0 cm/cm (range, 1.8-5.6 cm/cm) and improved to 4.9 cm/cm (range, 2.8-6.6 cm/cm; p = .017) after the start of inhaled nitric oxide.

CONCLUSIONS

Inhaled nitric oxide improves the systemic microcirculation in children with hypoxemic respiratory failure.

Persistent pulmonary hypertension results in reduced tetralinoleoyl-cardiolipin and mitochondrial complex II + III during the development of right ventricular hypertrophy in the neonatal pig heart

Persistent pulmonary hypertension of the newborn (PPHN) results in right ventricular (RV) hypertrophy followed by right heart failure and an associated mitochondrial dysfunction. The phospholipid cardiolipin plays a key role in maintaining mitochondrial respiratory and cardiac function via modulation of the activities of enzymes involved in oxidative phosphorylation. In this study, changes in cardiolipin and cardiolipin metabolism were investigated during the development of right heart failure. Newborn piglets (<24 h old) were exposed to a hypoxic (10% O(2)) environment for 3 days, resulting in the induction of PPHN. Two sets of control piglets were used: 1) newborn or 2) exposed to a normoxic (21% O(2)) environment for 3 days. Cardiolipin biosynthetic and remodeling enzymes, mitochondrial complex II + III activity, incorporation of [1-(14)C]linoleoyl-CoA into cardiolipin precursors, and the tetralinoleoyl-cardiolipin pool size were determined in both the RV and left ventricle (LV). PPHN resulted in an increased heart-to-body weight ratio, RV-to-LV plus septum weight ratio, and expression of brain naturetic peptide in RV. In addition, PPHN reduced cardiolipin biosynthesis and remodeling in the RV and LV, which resulted in decreased tetralinoleoyl-cardiolipin levels and reduced complex II + III activity and protein levels of mitochondrial complexes II, III, and IV in the RV. This is the first study to examine the pattern of cardiolipin metabolism during the early development of both the RV and LV of the newborn piglet and to demonstrate that PPHN-induced alterations in cardiolipin biosynthetic and remodeling enzymes contribute to reduced tetralinoleoyl-cardiolipin and mitochondrial respiratory chain function during the development of RV hypertrophy. These defects in cardiolipin may play an important role in the rapid development of RV dysfunction and right heart failure in PPHN.

Epigenetic regulation of pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is diagnosed as a sustained elevation of pulmonary arterial pressure to more than 25 mm Hg at rest or to more than 30 mm Hg with exercise. PAH is an intrinsic disease of the pulmonary vascular smooth muscle and endothelial cells in association with plexiform lesions, medial thickening, concentric laminar intimal fibrosis and thrombotic lesions. Pulmonary vascular remodeling is the characteristic pathological change of PAH. The pathogenesis of PAH has been studied at the level of smooth muscle and endothelial cells. Existing research does not adequately explain susceptibility to the disease, and recent evidence reveals that epigenetic alterations may be involved in PAH. Epigenetics refers to all heritable changes in phenotype or in gene expression states, including chromatin remodeling, DNA methylation, histone modification and RNA interference, which are not involved in the DNA sequence itself. This review will focus on recent advances in epigenetics related to PAH, including epigenetic changes of superoxide dismutase, endothelial nitric oxide synthase and the bone morphogenetic protein signaling pathway. This will provide new insight for improved treatment and prevention of PAH. Future work aimed at specific epigenetic treatments may prove to be an effective therapy for patients with PAH.

Regulation of the Pulmonary Circulation in the Fetus and Newborn

During the development of the pulmonary vasculature in the fetus, many structural and functional changes occur to prepare the lung for the transition to air breathing. The development of the pulmonary circulation is genetically controlled by an array of mitogenic factors in a temporo-spatial order. With advancing gestation, pulmonary vessels acquire increased vasoreactivity. The fetal pulmonary vasculature is exposed to a low oxygen tension environment that promotes high intrinsic myogenic tone and high vasocontractility. At birth, a dramatic reduction in pulmonary arterial pressure and resistance occurs with an increase in oxygen tension and blood flow. The striking hemodynamic differences in the pulmonary circulation of the fetus and newborn are regulated by various factors and vasoactive agents. Among them, nitric oxide, endothelin-1, and prostaglandin I2 are mainly derived from endothelial cells and exert their effects via cGMP, cAMP, and Rho kinase signaling pathways. Alterations in these signaling pathways may lead to vascular remodeling, high vasocontractility, and persistent pulmonary hypertension of the newborn.

Fetal pulmonary vascular remodeling in a rat model induced by hypoxia and indomethacin

OBJECTIVE

This study sought to determine the effect of combined treatment of hypoxia plus indomethacin on pulmonary vascular remodeling in fetal rats.

METHODS

Hypoxia and indomethacin were used to treat pregnant rats during 19-21 days of gestation. The adventitia, media, and intima of pulmonary arteries from fetal rats were assessed. Western blots were used for determining the abundance of smooth muscle specific alpha-actin protein (α-SMA), elastin, and endothelial nitric oxide synthase (eNOS) in lung tissues. Plasma brain-type natriuretic peptide (BNP) levels, reflecting the increased right ventricular load or pulmonary arterial pressure, were detected.

RESULTS

The ratio of left ventricular free wall plus septum to right ventricular weight significantly increased in hypoxia plus indomethacin-treated group. The medial thickness percentage of pulmonary arteries of < 100 μm and ≥100 μm in diameter from hypoxia plus indomethacin-treated group was higher than that from control or single treatment group. Vascular elastin area percentage and immunostaining density of eNOS from the combined-treated group were higher than other groups. The relative abundance of α-SMA, elastin, and eNOS and plasma BNP levels in hypoxia plus indomethacin-treated group also significantly increased compared with other groups.

CONCLUSIONS

Hypoxia and indomethacin had synergistic effect on fetal pulmonary vascular remodeling. This rat model induced by combined treatments can mimic human persistent pulmonary hypertension of the newborn.

Determination of asymmetric dimethylarginine, an endogenous nitric oxide synthase inhibitor, in umbilical blood

Endothelial cells produce nitric oxide (NO), a potent vasodilator. Asymmetric dimethylarginine (ADMA) is an endogenous inhibitor of NO synthase. Little is known about the potential physiological roles of ADMA in a perinatal setting. This study measures concentrations of ADMA in umbilical blood using enzyme-linked immunosorbent assay and those of NO as nitrite/nitrate (NOx(-)) using the Griess assay. Their relationship to the degree of prematurity and maternal clinical condition is examined. Results show that ADMA concentrations in umbilical blood from control newborns were about twice as high as those of lactating women, healthy children, and healthy adults. Umbilical blood NOx(-) concentrations from control newborns were about half of those of lactating women, healthy children, and healthy adults. Consequently, the levels of ADMA relative to NOx(-) were about 4-fold higher in umbilical blood from control newborns than in blood from lactating women, healthy children, and healthy adults. Furthermore, the umbilical blood ADMA concentrations and the ratios of ADMA to NOx(-) in newborns were higher according to their birth prematurity and lower birth weight. The umbilical ADMA concentrations were independent of the delivery mode and maternal preeclampsia. We infer that the high ADMA levels play physiological roles in maintaining vascular tone and blood redistribution to vital organs during birth, thereby favoring the circulatory transition from fetal to neonatal life.

Pulmonary vascular remodeling

The maladaptive response of the pulmonary vasculature that occurs in patients with congenital diaphragmatic hernia significantly impacts outcome. Muscularized distal pulmonary arterioles inhibit the ability of the neonate to adjust to extrauterine circulation, resulting in severe pulmonary hypertension. This review summarizes the current state of knowledge regarding normal and abnormal development of the lung vascular system and identifies current and potential therapies directed toward preserving or restoring proper pulmonary vascular function.