Developmental biology of the pulmonary circulation

Cardiovascular Sequelae of Bronchopulmonary Dysplasia in Preterm Neonates Born before 32 Weeks of Gestational Age: Impact of Associated Pulmonary and Systemic Hypertension

Bronchopulmonary dysplasia (BPD) remains the most common respiratory disorder of prematurity for infants born before 32 weeks of gestational age (GA). Early and prolonged exposure to chronic hypoxia and inflammation induces pulmonary hypertension (PH) with the characteristic features of a reduced number and increased muscularisation of the pulmonary arteries resulting in an increase in the pulmonary vascular resistance (PVR) and a fall in their compliance. BPD and BPD-associated pulmonary hypertension (BPD-PH) together with systemic hypertension (sHTN) are chronic cardiopulmonary disorders which result in an increased mortality and long-term problems for these infants. Previous studies have predominantly focused on the pulmonary circulation (right ventricle and its function) and developing management strategies accordingly for BPD-PH. However, recent work has drawn attention to the importance of the left-sided cardiac function and its impact on BPD in a subset of infants arising from a unique pathophysiology termed postcapillary PH. BPD infants may have a mechanistic link arising from chronic inflammation, cytokines, oxidative stress, catecholamines, and renin-angiotensin system activation along with systemic arterial stiffness, all of which contribute to the development of BPD-sHTN. The focus for the treatment of BPD-PH has been improvement of the right heart function through pulmonary vasodilators. BPD-sHTN and a subset of postcapillary PH may benefit from afterload reducing agents such as angiotensin converting enzyme inhibitors. Preterm infants with BPD-PH are at risk of later cardiac and respiratory morbidities as young adults. This paper reviews the current knowledge of the pathophysiology, diagnosis, and treatment of BPD-PH and BPD-sHTN. Current knowledge gaps and emerging new therapies will also be discussed.

Identifying sensitive windows of prenatal household air pollution on birth weight and infant pneumonia risk to inform future interventions

BACKGROUND

Prenatal household air pollution impairs birth weight and increases pneumonia risk however time-varying associations have not been elucidated and may have implications for the timing of public health interventions.

METHODS

The Ghana Randomized Air Pollution and Health Study (GRAPHS) enrolled 1,414 pregnant women from Kintampo, Ghana and measured personal carbon monoxide (CO) exposure four times over pregnancy. Birth weight was measured within 72-hours of birth. Fieldworkers performed weekly pneumonia surveillance and referred sick children to study physicians. The primary pneumonia outcome was one or more physician-diagnosed severe pneumonia episode in the first year of life. We employed reverse distributed lag models to examine time-varying associations between prenatal CO exposure and birth weight and infant pneumonia risk.

RESULTS

Analyses included n = 1,196 mother-infant pairs. In models adjusting for child sex; maternal age, body mass index (BMI), ethnicity and parity at enrollment; household wealth index; number of antenatal visits; and evidence of placental malaria, prenatal CO exposures from 15 to 20 weeks gestation were inversely associated with birth weight. Sex-stratified models identified a similar sensitive window in males and a window at 10-weeks gestation in females. In models adjusting for child sex, maternal age, BMI and ethnicity, household wealth index, gestational age at delivery and average postnatal child CO exposure, CO exposure during 34-39 weeks gestation were positively associated with severe pneumonia risk, especially in females.

CONCLUSIONS

Household air pollution exposures in mid- and late- gestation are associated with lower birth weight and higher pneumonia risk, respectively. These findings support the urgent need for deployment of clean fuel stove interventions beginning in early pregnancy.

Pulmonary Vasodilator Therapy in Persistent Pulmonary Hypertension of the Newborn

Inhaled nitric oxide (iNO) therapy had a transformational impact on the management of infants with persistent pulmonary hypertension of the newborn (PPHN). iNO remains the only approved pulmonary vasodilator for PPHN; yet 30% to 40% of patients do not respond or have incomplete response to iNO. Lung recruitment strategies with early surfactant administration and high-frequency ventilation can optimize the response to iNO in the presence of parenchymal lung diseases. Alternate pulmonary vasodilators are used commonly as rescue, life-saving measures, though there is a lack of high-quality evidence supporting their efficacy and safety. This article reviews the available evidence and future directions for research in PPHN.

Prematurity and postnatal alterations in intermittent hypoxaemia

Intermittent hypoxaemia (IH) events are well described in extremely preterm infants, but the occurrence of IH patterns in more mature preterm infants remains unclear. The objective of this study was to characterise the effect of gestational age on early postnatal patterns of IH in extremely (<28 weeks), very (28-<32 weeks) and moderately (32-<34 weeks) preterm infants. As expected, extremely preterm infants had a significantly higher frequency of IH events of longer durations and greater time with hypoxaemia versus very and moderately preterm infants. In addition, the postnatal decrease in IH duration was comparable in the very and moderately preterm infants. This progression of IH events should assist clinicians and families in managing expectations for resolution of IH events during early postnatal life.

Intrauterine Hypoxia and Epigenetic Programming in Lung Development and Disease

Clinically, intrauterine hypoxia is the foremost cause of perinatal morbidity and developmental plasticity in the fetus and newborn infant. Under hypoxia, deviations occur in the lung cell epigenome. Epigenetic mechanisms (e.g., DNA methylation, histone modification, and miRNA expression) control phenotypic programming and are associated with physiological responses and the risk of developmental disorders, such as bronchopulmonary dysplasia. This developmental disorder is the most frequent chronic pulmonary complication in preterm labor. The pathogenesis of this disease involves many factors, including aberrant oxygen conditions and mechanical ventilation-mediated lung injury, infection/inflammation, and epigenetic/genetic risk factors. This review is focused on various aspects related to intrauterine hypoxia and epigenetic programming in lung development and disease, summarizes our current knowledge of hypoxia-induced epigenetic programming and discusses potential therapeutic interventions for lung disease.

Delta-like 4 is required for pulmonary vascular arborization and alveolarization in the developing lung

The molecular mechanisms by which endothelial cells (ECs) regulate pulmonary vascularization and contribute to alveolar epithelial cell development during lung morphogenesis remain unknown. We tested the hypothesis that delta-like 4 (DLL4), an EC Notch ligand, is critical for alveolarization by combining lung mapping and functional studies in human tissue and DLL4-haploinsufficient mice (Dll4+/lacz). DLL4 expressed in a PECAM-restricted manner in capillaries, arteries, and the alveolar septum from the canalicular to alveolar stage in mice and humans. Dll4 haploinsufficiency resulted in exuberant, nondirectional vascular patterning at E17.5 and P6, followed by smaller capillaries and fewer intermediate blood vessels at P14. Vascular defects coincided with polarization of lung EC expression toward JAG1-NICD-HES1 signature and decreased tip cell-like (Car4) markers. Dll4+/lacZ mice had impaired terminal bronchiole development at the canalicular stage and impaired alveolarization upon lung maturity. We discovered that alveolar type I cell (Aqp5) markers progressively decreased in Dll4+/lacZ mice after birth. Moreover, in human lung EC, DLL4 deficiency programmed a hypersprouting angiogenic phenotype cell autonomously. In conclusion, DLL4 is expressed from the canalicular to alveolar stage in mice and humans, and Dll4 haploinsufficiency programs dysmorphic microvascularization, impairing alveolarization. Our study reveals an obligate role for DLL4-regulated angiogenesis in distal lung morphogenesis.

Pulmonary artery and lung parenchymal growth following early versus delayed stent interventions in a swine pulmonary artery stenosis model

OBJECTIVES

Compare lung parenchymal and pulmonary artery (PA) growth and hemodynamics following early and delayed PA stent interventions for treatment of unilateral branch PA stenosis (PAS) in swine.

BACKGROUND

How the pulmonary circulation remodels in response to different durations of hypoperfusion and how much growth and function can be recovered with catheter directed interventions at differing time periods of lung development is not understood.

METHODS

A total of 18 swine were assigned to four groups: Sham (n = 4), untreated left PAS (LPAS) (n = 4), early intervention (EI) (n = 5), and delayed intervention (DI) (n = 5). EI had left pulmonary artery (LPA) stenting at 5 weeks (6 kg) with redilation at 10 weeks. DI had stenting at 10 weeks. All underwent right heart catheterization, computed tomography, magnetic resonance imaging, and histology at 20 weeks (55 kg).

RESULTS

EI decreased the extent of histologic changes in the left lung as DI had marked alveolar septal and bronchovascular abnormalities (p = .05 and p < .05 vs. sham) that were less prevalent in EI. EI also increased left lung volumes and alveolar counts compared to DI. EI and DI equally restored LPA pulsatility, R heart pressures, and distal LPA growth. EI and DI improved, but did not normalize LPA stenosis diameter (LPA/DAo ratio: Sham 1.27 ± 0.11 mm/mm, DI 0.88 ± 0.10 mm/mm, EI 1.01 ± 0.09 mm/mm) and pulmonary blood flow distributions (LPA-flow%: Sham 52 ± 5%, LPAS 7 ± 2%, DI 44 ± 3%, EI 40 ± 2%).

CONCLUSION

In this surgically created PAS model, EI was associated with improved lung parenchymal development compared to DI. Longer durations of L lung hypoperfusion did not detrimentally affect PA growth and R heart hemodynamics. Functional and anatomical discrepancies persist despite successful stent interventions that warrant additional investigation.

Sildenafil for Antenatal Treatment of Congenital Diaphragmatic Hernia: From Bench to Bedside

BACKGROUND

Persistent pulmonary hypertension (PPH) is one of the main causes of mortality and morbidity in infants affected by congenital diaphragmatic hernia (CDH). Since the structural changes that lead to PPH take place already in utero, a treatment starting in the prenatal phase may prevent the occurrence of this complication.

OBJECTIVE

To summarize the development process of antenatal sildenafil for CDH.

METHODS

The pharmacokinetics and efficacy of sildenafil have been assessed in the rat and the rabbit model. The transfer of the drug through the human placenta has been measured with the ex-vivo placenta perfusion model. Results from this experiment are being incorporated in a pregnancy-physiologically based pharmacokinetic (p- PBPK) model. A phase I-IIb placental transfer and safety study is ongoing.

RESULTS

Sildenafil administration to pregnant rats and rabbits led to therapeutic foetal drug levels without maternal and foetal toxicity, although it was associated with impaired vascular development in foetuses with nonhypoplastic lungs. Peak concentrations and 24-hour exposure were higher in pregnant rabbits compared to nonpregnant ones. In rat and rabbit foetuses with CDH, sildenafil rescued the lung vascular anomalies and partially improved parenchymal development. Sildenafil crossed the human placenta at a high rate ex-vivo, independently from the initial maternal concentration.

CONCLUSION

There is preclinical evidence that maternally administered sildenafil prevents the vascular changes that lead to PPH in CDH newborns. The phase I/IIb clinical study together with the p-PBPK model will define the maternal dose needed for a therapeutic effect in the foetus. Foetal safety will be investigated both in the clinical study and in the sheep. The final step will be a multicentre, randomized, placebo-controlled trial.

Oxyhemoglobin desaturation as a function of age and hypercapnia from ventilatory pump failure (VPF)

Background:

Supplemental O₂ is often administered without knowledge of CO₂ levels for patients with ventilatory pump failure (VPF). This can render oximetry ineffective as a gauge of alveolar ventilation, airway secretions, and lung disease. We have noted that diurnal hypoventilation with hypercapnia tends to be symptomatic when O₂ saturation levels decrease below 95% and patients extend sleep noninvasive ventilatory support (NVS) into daytime hours. We also noted that with advancing age, less hypercapnia results in desaturation. This study was designed to explore oxyhemoglobin desaturations (O₂ desats) as a function of age and hypercapnia for patients with VPF.

Methods:

A retrospective analysis of 8933 consecutive patient visits for whom end-tidal CO₂ and O₂ sats were measured. O₂ sats < 95% at CO₂ levels of 45, 50, and 60 cmH₂O were correlated with 10 years age intervals to age 80.

Results:

Of 8933 visits, 8642 had complete data. Outcomes for CO₂ levels > 50 cmH₂O were the most significant including for visit-ages < 30 and ≥ 30 years. There was a statistically significant 4% decrease in the odds of O₂ desat for every one-year increase in age to age 30 (OR = 0.96, 95% CI = [0.93, 0.99], p = 0.02) and for visit-ages ≥ 30 a significant 30% increase in the odds of O₂ desat for every 10-year increase in age (OR 1.3, 95% CI = [1.1, 1.6], p = 0.006). Relationship for ages ≥ 30 years were also significant for CO₂ levels over 45 mmHg also. 40% of the time when CO₂ was greater than 45 mmHg O₂ sat was low.

Discussion:

This study demonstrated a significantly lower risk of O₂ desat occurring at EtCO₂ levels ≥ 50 mmHg for patients from 10 to 20 years of age than those younger than 10 and a significantly greater risk of O₂ desat for 10 years intervals after age 20. Thus, with age, less hypercapnia results in desats and dyspnea with patients tending to extend NVS into daytime hours. This may be due to increases in physiological shunting, decreased pulmonary elasticity, and worsening ventilation/perfusion ratios with age.

Current strategies and opportunities to manufacture cells for modeling human lungs

Chronic lung diseases remain major healthcare burdens, for which the only curative treatment is lung transplantation. In vitro human models are promising platforms for identifying and testing novel compounds to potentially decrease this burden. Directed differentiation of pluripotent stem cells is an important strategy to generate lung cells to create such models. Current lung directed differentiation protocols are limited as they do not 1) recapitulate the diversity of respiratory epithelium, 2) generate consistent or sufficient cell numbers for drug discovery platforms, and 3) establish the histologic tissue-level organization critical for modeling lung function. In this review, we describe how lung development has formed the basis for directed differentiation protocols, and discuss the utility of available protocols for lung epithelial cell generation and drug development. We further highlight tissue engineering strategies for manipulating biophysical signals during directed differentiation such that future protocols can recapitulate both chemical and physical cues present during lung development.

Early onset children's interstitial lung diseases: Discrete entities or manifestations of pulmonary dysmaturity?

Interstitial lung diseases in children (chILD) are rare and diverse. The current classifications include a group of early onset chILD specific to infancy, namely neuro-endocrine cell hyperplasia of infancy (NEHI), pulmonary interstitial glycogenosis (PIG) and the alveolar capillary-congenital acinar dysplasia (ACD-CAD) spectrum, as well as alveolar growth disorders. NEHI and PIG cells are seen in the normal developing foetal lung. We hypothesise that these conditions are in fact overlapping manifestations of pulmonary dysmaturity, respectively of airway, mesenchymal and vascular elements, rather than discrete clinical conditions in their own right. Clinically, these present as respiratory distress in early life. Mild cases rightly never undergo lung biopsy, and for these the clinical description 'persistent tachypnoea of infancy' has been proposed. In terms of pathology, we reviewed current literature, which showed that NEHI cells decline with age, and are not specific to NEHI, which we confirmed by unpublished re-analysis of a second dataset. Furthermore, specific genetic disorders which affect pulmonary maturation lead to a histological picture indistinguishable from NEHI. PIG and ACD-CAD are also associated with pulmonary growth disorders, and manifestations of PIG and NEHI may be present in the same child. We conclude that, contrary to current classifications, NEHI, PIG, and ACD-CAD should be considered as overlapping manifestations of pulmonary dysmaturation, frequently associated with disorders of alveolar growth, rather than as separate conditions. Identification of one of these patterns should be the start, not the end of the diagnostic journey, and underlying in particular genetic causes should be sought.

How high resolution 3-dimensional imaging changes our understanding of postnatal lung development

During the last 10 + years biologically and clinically significant questions about postnatal lung development could be answered due to the application of modern cutting-edge microscopic and quantitative histological techniques. These are in particular synchrotron radiation based X-ray tomographic microscopy (SRXTM), but also ³Helium Magnetic Resonance Imaging, as well as the stereological estimation of the number of alveoli and the length of the free septal edge. First, the most important new finding may be the following: alveolarization of the lung does not cease after the maturation of the alveolar microvasculature but continues until young adulthood and, even more important, maybe reactivated lifelong if needed to rescue structural damages of the lungs. Second, the pulmonary acinus represents the functional unit of the lung. Because the borders of the acini could not be detected in classical histological sections, any investigation of the acini requires 3-dimensional (imaging) methods. Based on SRXTM it was shown that in rat lungs the number of acini stays constant, meaning that their volume increases by a factor of ~ 11 after birth. The latter is very important for acinar ventilation and particle deposition.

Evidence of Echocardiographic Markers of Pulmonary Vascular Disease in Asymptomatic Infants Born Preterm at One Year of Age

OBJECTIVE

To test the hypothesis that echocardiographic markers of pulmonary vascular disease (PVD) exist in asymptomatic infants born preterm at 1-year corrected age.

STUDY DESIGN

We conducted a prospective cohort study of 80 infants born preterm (<29 weeks of gestation) and 100 age- and weight-matched infants born at term and compared broad-based conventional and quantitative echocardiographic measures of pulmonary hemodynamics at 1-year corrected age. Pulmonary artery acceleration time (PAAT), a validated index of pulmonary vascular resistance, arterial pressure, and compliance, was used to assess pulmonary hemodynamics. Lower PAAT is indicative of PVD. Subanalyses were performed in infants with bronchopulmonary dysplasia (BPD, n = 48, 59%) and/or late-onset pulmonary hypertension (n = 12, 15%).

RESULTS

At 1 year, there were no differences between conventional measures of pulmonary hypertension in the infants born at term and preterm. All infants born preterm had significantly lower values of PAAT than infants born at term (73 ± 8 milliseconds vs 98 ± 5 milliseconds, P < .001). Infants born preterm with BPD had even lower PAAT than those without BPD (69 ± 5 milliseconds vs 79 ± 4 milliseconds, P < .01). The degree of PVD at 1-year corrected age was inversely related to gestation in all infants born preterm. Data analysis included adjustment for ventricular function and other confounding factors.

CONCLUSIONS

In comparison with infants born at term, infants born preterm exhibit abnormal PAAT at 1-year corrected age irrespective of neonatal lung disease status, suggesting the existence of PVD beyond infancy. PAAT measurements offer a reliable, noninvasive tool for screening and longitudinal monitoring of pulmonary hemodynamics in infants.

Prenatal fine particulate exposure and early childhood asthma: Effect of maternal stress and fetal sex

BACKGROUND

The impact of prenatal ambient air pollution on child asthma may be modified by maternal stress, child sex, and exposure dose and timing.

OBJECTIVE

We prospectively examined associations between coexposure to prenatal particulate matter with an aerodynamic diameter of less than 2.5 microns (PM2.5) and maternal stress and childhood asthma (n = 736).

METHODS

Daily PM2.5 exposure during pregnancy was estimated using a validated satellite-based spatiotemporally resolved prediction model. Prenatal maternal negative life events (NLEs) were dichotomized around the median (high: NLE ≥ 3; low: NLE < 3). We used Bayesian distributed lag interaction models to identify sensitive windows for prenatal PM2.5 exposure on children's asthma by age 6 years, and determine effect modification by maternal stress and child sex.

RESULTS

Bayesian distributed lag interaction models identified a critical window of exposure (19-23 weeks' gestation, cumulative odds ratio, 1.15; 95% CI, 1.03-1.26; per interquartile range [1.7 μg/m3] increase in prenatal PM2.5 level) during which children concomitantly exposed to prenatal PM2.5 and maternal stress had increased risk of asthma. No significant association was seen in children born to women reporting low prenatal stress. When examining modifying effects of prenatal stress and fetal sex, we found that boys born to mothers with higher prenatal stress were most vulnerable (19-21 weeks' gestation; cumulative odds ratio, 1.28; 95% CI, 1.15-1.41; per interquartile range increase in PM2.5).

CONCLUSIONS

Prenatal PM2.5 exposure during sensitive windows is associated with increased risk of child asthma, especially in boys concurrently exposed to elevated maternal stress.

Reactive Oxygen Species, Biomarkers of Microvascular Maturation and Alveolarization, and Antioxidants in Oxidative Lung Injury

The lungs of extremely low gestational age neonates (ELGANs) are deficient in pulmonary surfactant and are incapable of efficient gas exchange necessary for successful transition from a hypoxic intrauterine environment to ambient air. To improve gas exchange and survival, ELGANs often receive supplemental oxygen with mechanical ventilation which disrupts normal lung developmental processes, including microvascular maturation and alveolarization. Factors that regulate these developmental processes include vascular endothelial growth factor and matrix metalloproteinases, both of which are influenced by generation of oxygen byproducts, or reactive oxygen species (ROS). ELGANs are also deficient in antioxidants necessary to scavenge excessive ROS. Thus, the accumulation of ROS in the preterm lungs exposed to prolonged hyperoxia, results in inflammation and development of bronchopulmonary dysplasia (BPD), a form of chronic lung disease (CLD). Despite advances in neonatal care, BPD/CLD remains a major cause of neonatal morbidity and mortality. The underlying mechanisms are not completely understood, and the benefits of current therapeutic interventions are limited. The association between ROS and biomarkers of microvascular maturation and alveolarization, as well as antioxidant therapies in the setting of hyperoxia-induced neonatal lung injury are reviewed in this article.

G-Protein-Coupled Receptor-2-Interacting Protein-1 Controls Stalk Cell Fate by Inhibiting Delta-like 4-Notch1 Signaling

The spatiotemporal localization and expression of Dll4 are critical for sprouting angiogenesis. However, the related mechanisms are poorly understood. Here, we show that G-protein-coupled receptor-kinase interacting protein-1 (GIT1) is a robust endogenous inhibitor of Dll4-Notch1 signaling that specifically controls stalk cell fate. GIT1 is highly expressed in stalk cells but not in tip cells. GIT1 deficiency remarkably enhances Dll4 expression and Notch1 signaling, resulting in impaired retinal sprouting angiogenesis, which can be rescued by treatment with the Notch inhibitor or Dll4 neutralizing antibody. Notch1 regulates Dll4 expression by binding to recombining binding protein suppressor of hairless (RBP-J, a transcriptional regulator of Notch) via a highly conserved ankyrin (ANK) repeat domain. We show that GIT1, which also contains an ANK domain, inhibits the Notch1-Dll4 signaling pathway by competing with Notch1 ANK domain for binding to RBP-J in stalk cells.

Deregulated angiogenesis in chronic lung diseases: a possible role for lung mesenchymal progenitor cells (2017 Grover Conference Series)

Chronic lung disease (CLD), including pulmonary fibrosis (PF) and chronic obstructive pulmonary disease (COPD), is the fourth leading cause of mortality worldwide. Both are debilitating pathologies that impede overall tissue function. A common co-morbidity in CLD is vasculopathy, characterized by deregulated angiogenesis, remodeling, and loss of microvessels. This substantially worsens prognosis and limits survival, with most current therapeutic strategies being largely palliative. The relevance of angiogenesis, both capillary and lymph, to the pathophysiology of CLD has not been resolved as conflicting evidence depicts angiogenesis as both reparative or pathologic. Therefore, we must begin to understand and model the underlying pathobiology of pulmonary vascular deregulation, alone and in response to injury induced disease, to define cell interactions necessary to maintain normal function and promote repair. Capillary and lymphangiogenesis are deregulated in both PF and COPD, although the mechanisms by which they co-regulate and underlie early pathogenesis of disease are unknown. The cell-specific mechanisms that regulate lung vascular homeostasis, repair, and remodeling represent a significant gap in knowledge, which presents an opportunity to develop targeted therapies. We have shown that that ABCG2^pos multipotent adult mesenchymal stem or progenitor cells (MPC) influence the function of the capillary microvasculature as well as lymphangiogenesis. A balance of both is required for normal tissue homeostasis and repair. Our current models suggest that when lymph and capillary angiogenesis are out of balance, the non-equivalence appears to support the progression of disease and tissue remodeling. The angiogenic regulatory mechanisms underlying CLD likely impact other interstitial lung diseases, tuberous sclerosis, and lymphangioleiomyomatosis.

Pulmonary hypertension associated with bronchopulmonary dysplasia in preterm infants

Bronchopulmonary dysplasia (BPD) and BPD-associated pulmonary hypertension (BPD-PH) are chronic inflammatory cardiopulmonary diseases with devastating short- and long-term consequences for infants born prematurely. The immature lungs of preterm infants are ill-prepared to achieve sufficient gas exchange, thus usually necessitating immediate commencement of respiratory support and oxygen supplementation. These therapies are life-saving, but they exacerbate the tissue damage that is inevitably inflicted on a preterm lung forced to perform gas exchange. Together, air-breathing and necessary therapeutic interventions disrupt normal lung development by aggravating pulmonary inflammation and vascular remodelling, thus frequently precipitating BPD and PH via an incompletely understood pathogenic cascade. BPD and BPD-PH share common risk factors, such as low gestational age at birth, fetal growth restriction and perinatal maternal inflammation; however, these risk factors are not unique to BPD or BPD-PH. Occurring in 17-24% of BPD patients, BPD-PH substantially worsens the morbidity and mortality attributable to BPD alone, thus darkening their outlook; for example, BPD-PH entails a mortality of up to 50%. The absence of a safe and effective therapy for BPD and BPD-PH renders neonatal cardiopulmonary disease an area of urgent unmet medical need. Besides the need to develop new therapeutic strategies, a major challenge for clinicians is the lack of a reliable method for identifying babies at risk of developing BPD and BPD-PH. In addition to discussing current knowledge on pathophysiology, diagnosis and treatment of BPD-PH, we highlight emerging biomarkers that could enable clinicians to predict disease-risk and also optimise treatment of BPD-PH in our tiniest patients.

Pulmonary hypoplasia

To survive the transition to extrauterine life, newborn infants must have lungs that provide an adequate surface area and volume to allow for gas exchange. The dynamic activities of fetal breathing movements and accumulation of lung luminal fluid are key to fetal lung development throughout the various phases of lung development and growth, first by branching morphogenesis, and later by septation. Because effective gas exchange is essential to survival, pulmonary hypoplasia is among the leading findings on autopsies of children dying in the newborn period. Management of infants born prematurely who had disrupted lung development, especially at the pre-glandular or canalicular periods, may be challenging, but limited success has been reported. Growing understanding of stem cell biology and mechanical development of the lung, and how to apply them clinically, may lead to new approaches that will lead to better outcomes for these patients.

The innate immune response in fetal lung mesenchymal cells targets VEGFR2 expression and activity

In preterm infants, soluble inflammatory mediators target lung mesenchymal cells, disrupting airway and alveolar morphogenesis. However, how mesenchymal cells respond directly to microbial stimuli remains poorly characterized. Our objective was to measure the genome-wide innate immune response in fetal lung mesenchymal cells exposed to the bacterial endotoxin lipopolysaccharide (LPS). With the use of Affymetrix MoGene 1.0st arrays, we showed that LPS induced expression of unique innate immune transcripts heavily weighted toward CC and CXC family chemokines. The transcriptional response was different between cells from E11, E15, and E18 mouse lungs. In all cells tested, LPS inhibited expression of a small core group of genes including the VEGF receptor Vegfr2 Although best characterized in vascular endothelial populations, we demonstrated here that fetal mouse lung mesenchymal cells express Vegfr2 and respond to VEGF-A stimulation. In mesenchymal cells, VEGF-A increased cell migration, activated the ERK/AKT pathway, and promoted FOXO3A nuclear exclusion. With the use of an experimental coculture model of epithelial-mesenchymal interactions, we also showed that VEGFR2 inhibition prevented formation of three-dimensional structures. Both LPS and tyrosine kinase inhibition reduced three-dimensional structure formation. Our data suggest a novel mechanism for inflammation-mediated defects in lung development involving reduced VEGF signaling in lung mesenchyme.

Development of the lung

To fulfill the task of gas exchange, the lung possesses a huge inner surface and a tree-like system of conducting airways ventilating the gas exchange area. During lung development, the conducting airways are formed first, followed by the formation and enlargement of the gas exchange area. The latter (alveolarization) continues until young adulthood. During organogenesis, the left and right lungs have their own anlage, an outpouching of the foregut. Each lung bud starts a repetitive process of outgrowth and branching (branching morphogenesis) that forms all of the future airways mainly during the pseudoglandular stage. During the canalicular stage, the differentiation of the epithelia becomes visible and the bronchioalveolar duct junction is formed. The location of this junction stays constant throughout life. Towards the end of the canalicular stage, the first gas exchange may take place and survival of prematurely born babies becomes possible. Ninety percent of the gas exchange surface area will be formed by alveolarization, a process where existing airspaces are subdivided by the formation of new walls (septa). This process requires a double-layered capillary network at the basis of the newly forming septum. However, in parallel to alveolarization, the double-layered capillary network of the immature septa fuses to a single-layered network resulting in an optimized setup for gas exchange. Alveolarization still continues, because, at sites where new septa are lifting off preexisting mature septa, the required second capillary layer will be formed instantly by angiogenesis. The latter confirms a lifelong ability of alveolarization, which is important for any kind of lung regeneration.

Aberrant Pulmonary Vascular Growth and Remodeling in Bronchopulmonary Dysplasia

In contrast to many other organs, a significant portion of lung development occurs after birth during alveolarization, thus rendering the lung highly susceptible to injuries that may disrupt this developmental process. Premature birth heightens this susceptibility, with many premature infants developing the chronic lung disease, bronchopulmonary dysplasia (BPD), a disease characterized by arrested alveolarization. Over the past decade, tremendous progress has been made in the elucidation of mechanisms that promote postnatal lung development, including extensive data suggesting that impaired pulmonary angiogenesis contributes to the pathogenesis of BPD. Moreover, in addition to impaired vascular growth, patients with BPD also frequently demonstrate alterations in pulmonary vascular remodeling and tone, increasing the risk for persistent hypoxemia and the development of pulmonary hypertension. In this review, an overview of normal lung development will be presented, and the pathologic features of arrested development observed in BPD will be described, with a specific emphasis on the pulmonary vascular abnormalities. Key pathways that promote normal pulmonary vascular development will be reviewed, and the experimental and clinical evidence demonstrating alterations of these essential pathways in BPD summarized.

Cardiorespiratory events in preterm infants: etiology and monitoring technologies

Every year, an estimated 15 million infants are born prematurely (<37 weeks gestation) with premature birth rates ranging from 5 to 18% across 184 countries. Although there are a multitude of reasons for this high rate of preterm birth, once birth occurs, a major challenge of infant care includes the stabilization of respiration and oxygenation. Clinical care of this vulnerable infant population continues to improve, yet there are major areas that have yet to be resolved including the identification of optimal respiratory support modalities and oxygen saturation targets, and reduction of associated short- and long-term morbidities. As intermittent hypoxemia is a consequence of immature respiratory control and resultant apnea superimposed upon an immature lung, improvements in clinical care must include a thorough knowledge of premature lung development and pathophysiology that is unique to premature birth. In Part 1 of a two-part review, we summarize early lung development and diagnostic methods for cardiorespiratory monitoring.

Antenatal BAY 41-2272 reduces pulmonary hypertension in the rabbit model of congenital diaphragmatic hernia

Infants with congenital diaphragmatic hernia (CDH) fail to adapt at birth because of persistent pulmonary hypertension (PH), a condition characterized by excessive muscularization and abnormal vasoreactivity of pulmonary vessels. Activation of soluble guanylate cyclase by BAY 41-2272 prevents pulmonary vascular remodeling in neonatal rats with hypoxia-induced PH. By analogy, we hypothesized that prenatal administration of BAY 41-2272 would improve features of PH in the rabbit CDH model. Rabbit fetuses with surgically induced CDH at day 23 of gestation were randomized at day 28 for an intratracheal injection of BAY 41-2272 or vehicle. After term delivery (day 31), lung mechanics, right ventricular pressure, and serum NH2-terminal-pro-brain natriuretic peptide (NT-proBNP) levels were measured. After euthanasia, lungs were processed for biological or histological analyses. Compared with untouched fetuses, the surgical creation of CDH reduced the lung-to-body weight ratio, increased mean terminal bronchial density, and impaired lung mechanics. Typical characteristics of PH were found in the hypoplastic lungs, including increased right ventricular pressure, higher serum NT-proBNP levels, thickened adventitial and medial layers of pulmonary arteries, reduced capillary density, and lower levels of endothelial nitric oxide synthase. A single antenatal instillation of BAY 41-2272 reduced mean right ventricular pressure and medial thickness of small resistive arteries in CDH fetuses. Capillary density, endothelial cell proliferation, and transcripts of endothelial nitric oxide synthase increased, whereas airway morphometry, lung growth, and mechanics remained unchanged. These results suggest that pharmacological activation of soluble guanylate cyclase may provide a new approach to the prenatal treatment of PH associated with CDH.

Emergency Management of Pediatric Pulmonary Hypertension

Pulmonary hypertension (PH) does not refer to a specific disease but rather a clinical manifestation emanating from a decrease in functional pulmonary vasculature resulting in progressively elevated right ventricle pressure and ultimately right heart failure. It is an uncommon disease process, but because of advancements in treatment, improved survival, and increasing prevalence, there is a greater likelihood that the emergency clinician will have to care for a child with PH. This review article, intended for emergency medical providers for children, is aimed at familiarizing clinicians with pediatric PH including the pathophysiology, clinical presentation and initial diagnostic strategies, basic chronic management, and management of a pulmonary hypertensive crisis.

Heterochrony and early left-right asymmetry in the development of the cardiorespiratory system of snakes

Snake lungs show a remarkable diversity of organ asymmetries. The right lung is always fully developed, while the left lung is either absent, vestigial, or well-developed (but smaller than the right). A 'tracheal lung' is present in some taxa. These asymmetries are reflected in the pulmonary arteries. Lung asymmetry is known to appear at early stages of development in Thamnophis radix and Natrix natrix. Unfortunately, there is no developmental data on snakes with a well-developed or absent left lung. We examine the adult and developmental morphology of the lung and pulmonary arteries in the snakes Python curtus breitensteini, Pantherophis guttata guttata, Elaphe obsoleta spiloides, Calloselasma rhodostoma and Causus rhombeatus using gross dissection, MicroCT scanning and 3D reconstruction. We find that the right and tracheal lung develop similarly in these species. By contrast, the left lung either: (1) fails to develop; (2) elongates more slowly and aborts early without (2a) or with (2b) subsequent development of faveoli; (3) or develops normally. A right pulmonary artery always develops, but the left develops only if the left lung develops. No pulmonary artery develops in relation to the tracheal lung. We conclude that heterochrony in lung bud development contributes to lung asymmetry in several snake taxa. Secondly, the development of the pulmonary arteries is asymmetric at early stages, possibly because the splanchnic plexus fails to develop when the left lung is reduced. Finally, some changes in the topography of the pulmonary arteries are consequent on ontogenetic displacement of the heart down the body. Our findings show that the left-right asymmetry in the cardiorespiratory system of snakes is expressed early in development and may become phenotypically expressed through heterochronic shifts in growth, and changes in axial relations of organs and vessels. We propose a step-wise model for reduction of the left lung during snake evolution.

Oxygen differentially affects the hox proteins Hoxb5 and Hoxa5 altering airway branching and lung vascular formation

Hoxb5 and Hoxa5 transcription factor proteins uniquely impact lung morphogenesis at the developmental time point when extremely preterm infants are born. The effect of O2 exposure (0.4 FiO2) used in preterm infant care on these Hox proteins is unknown. We used ex vivo fetal mouse lung organ cultures to explore the effects of 0.4 FiO2 on lung airway and vascular formation in the context of Hoxb5 and Hoxa5 expression and regulation. Compared to room air, 48 h (h) 0.4 FiO2 adversely attenuated airway and microvasculature formation while reducing lung growth and epithelial cell volume, and increasing mesenchymal volume. 0.4 FiO2 decreased pro-angiogenic Hoxb5 and VEGFR2 while not altering protein levels of angiostatic Hoxa5. Lungs returned to RA after 24 h 0.4FiO2 had partial structural recovery but remained smaller and less developed. Mesenchymal cell apoptosis increased and proliferation decreased with time in O2 while epithelial cell proliferation significantly increased. Hoxb5 overexpression led to prominent peri-airway VEGFR2 expression and promoted lung vascular and airway patterning. Hoxa5 overexpression had the opposite effects. We conclude that 0.4 FiO2 exposure causes a profound loss of airway and lung microvascular development that occurs partially via reduction in pro-angiogenic Hoxb5 while angiostatic Hoxa5 expression is maintained.

Role of endothelin in uteroplacental circulation and fetal vascular function

Endothelins are 21-amino acid peptides involved in vascular homeostasis. Three types of peptide have been identified, with endothelin-1 (ET-1) being the most potent vasoconstrictor currently known. Two endothelin receptor subtypes are found in various tissues, including the brain, heart, blood vessel, lung, and placenta. The ETA-receptor is associated with vasoconstriction in vascular smooth muscle. Conversely, the ETB-receptor can elicit a vasoconstrictor effect in vascular smooth muscle and a vasodilator effect via its action in endothelial cells. Both receptors play a key role in maintaining circulatory homeostasis and vascular function. Changes in ET-1 expression are found in various disease states, and overexpression of ET-1 is observed in hypertension and preeclampsia in pregnancy. Placental localization of ET-1 implies a key role in regulating the uteroplacental circulation. Additionally, ET-1 is important in the fetal circulation and is involved in the pulmonary circulation and closure of the ductus arteriosus after birth, as well as fetal growth constriction in utero. ET receptor antagonists and nitric oxide donors may provide therapeutic potential in treating conditions associated with overexpression of ET and hypertension.

c-Kit immunoexpression delineates a putative endothelial progenitor cell population in developing human lungs

Expression of c-Kit and its ligand, stem cell factor (SCF), in developing human lung tissue was investigated by immunohistochemistry. Twenty-eight human fetal lungs [age range 13 to 38 gestational wk (GW)] and 12 postnatal lungs (age range 1-79 yr) were evaluated. We identified c-Kit(+) cells in the lung mesenchyme as early as 13 GW. These mesenchymal c-Kit(+) cells in the lung did not express mast cell tryptase or α-smooth muscle actin. However, these cells did express CD34, VEGFR2, and Tie-2, indicating their endothelial lineage. Three-dimensional reconstructions of confocal laser scanning images revealed that c-Kit(+) cells displayed a closed-end tube formation that did not contain hematopoietic cells. From the pseudoglandular phase to the canalicular phase, c-Kit(+) cells appeared to continuously proliferate, to connect with central pulmonary vessels, and finally, to develop the lung capillary plexus. The spatial distribution of c-Kit- and SCF-positive cells was also demonstrated, and these cells were shown to be in close association. Our results suggest that c-Kit expression in early fetal lungs marks a progenitor population that is restricted to endothelial lineage. This study also suggests the potential involvement of c-Kit signaling in lung vascular development.

Looking beyond PPHN: the unmet challenge of chronic progressive pulmonary hypertension in the newborn

Abstract Infants with forms of pulmonary hypertension (PH) that persist or develop beyond the first week of life are an understudied group of patients with up to 40%-60% mortality. The clinical management of the progressive PH that develops in these infants is challenging because of the nonspecific signs and symptoms of clinical presentation, the limited diagnostic sensitivity of standard echocardiographic techniques, and the lack of proven therapies. The signaling mechanisms that underlie the structural and functional abnormalities in the pulmonary circulation of these infants are not yet clear. The ability to improve outcomes for these patients awaits technological advances to improve diagnostic capabilities and therapeutic discoveries made in basic science laboratories that can be tested in randomized clinical trials.

Hypoxic pulmonary hypertension of the newborn

Hypoxic pulmonary hypertension of the newborn is characterized by elevated pulmonary vascular resistance and pressure due to vascular remodeling and increased vessel tension secondary to chronic hypoxia during the fetal and newborn period. In comparison to the adult, the pulmonary vasculature of the fetus and the newborn undergoes tremendous developmental changes that increase susceptibility to a hypoxic insult. Substantial evidence indicates that chronic hypoxia alters the production and responsiveness of various vasoactive agents such as endothelium-derived nitric oxide, endothelin-1, prostanoids, platelet-activating factor, and reactive oxygen species, resulting in sustained vasoconstriction and vascular remodeling. These changes occur in most cell types within the vascular wall, particularly endothelial and smooth muscle cells. At the cellular level, suppressed nitric oxide-cGMP signaling and augmented RhoA-Rho kinase signaling appear to be critical to the development of hypoxic pulmonary hypertension of the newborn.

Spatial distribution of ventilation and perfusion: mechanisms and regulation

With increasing spatial resolution of regional ventilation and perfusion, it has become more apparent that ventilation and blood flow are quite heterogeneous in the lung. A number of mechanisms contribute to this regional variability, including hydrostatic gradients, pleural pressure gradients, lung compressibility, and the geometry of the airway and vascular trees. Despite this marked heterogeneity in both ventilation and perfusion, efficient gas exchange is possible through the close regional matching of the two. Passive mechanisms, such as the shared effect of gravity and the matched branching of vascular and airway trees, create efficient gas exchange through the strong correlation between ventilation and perfusion. Active mechanisms that match local ventilation and perfusion play little if no role in the normal healthy lung but are important under pathologic conditions.

Apnea of prematurity--perfect storm

With increased survival of preterm infants as young as 23 weeks gestation, maintaining adequate respiration and corresponding oxygenation represents a clinical challenge in this unique patient cohort. Respiratory instability characterized by apnea and periodic breathing occurs in premature infants because of immature development of the respiratory network. While short respiratory pauses and apnea may be of minimal consequence if oxygenation is maintained, they can be problematic if accompanied by chronic intermittent hypoxemia. Underdevelopment of the lung and the resultant lung injury that occurs in this population concurrent with respiratory instability creates the perfect storm leading to frequent episodes of profound and recurrent hypoxemia. Chronic intermittent hypoxemia contributes to the immediate and long term co-morbidities that occur in this population. In this review we discuss the pathophysiology leading to the perfect storm, diagnostic assessment of breathing instability in this unique population and therapeutic interventions that aim to stabilize breathing without contributing to tissue injury.

Regenerative pulmonary medicine: potential and promise, pitfalls and challenges

BACKGROUND

Chronic lung diseases contribute significantly to the morbidity and mortality of the population. There are few effective treatments for many chronic lung diseases, and even fewer therapies that can arrest or reverse the progress of the disease.

DESIGN

In this review, we present the current state of regenerative therapies for the treatment of chronic lung diseases. We focus on endothelial progenitor cells, mesenchymal stem cells, and endogenous lung stem/progenitor cells; summarize the work to date in models of lung diseases for each of these therapies; and consider their potential benefits and risks as viable therapies for patients with lung diseases.

CONCLUSIONS

Cell-based regenerative therapies for lung diseases offer great promise, with preclinical studies suggesting that the next decade should provide the evidence necessary for their ultimate application to our therapeutic armamentarium.

LRP5 regulates development of lung microvessels and alveoli through the angiopoietin-Tie2 pathway

Angiogenesis is crucial for lung development. Although there has been considerable exploration, the mechanism by which lung vascular and alveolar formation is controlled is still not completely understood. Here we show that low-density lipoprotein receptor-related protein 5 (LRP5), a component of the Wnt ligand-receptor complex, regulates angiogenesis and alveolar formation in the lung by modulating expression of the angiopoietin (Ang) receptor, Tie2, in vascular endothelial cells (ECs). Vascular development in whole mouse lungs and in cultured ECs is controlled by LRP5 signaling, which is, in turn, governed by a balance between the activities of the antagonistic Tie2 ligands, Ang1 and Ang2. Under physiological conditions when Ang1 is dominant, LRP5 knockdown decreases Tie2 expression and thereby, inhibits vascular and alveolar development in the lung. Conversely, when Ang2 dominates under hyperoxia treatment in neonatal mice, high LRP5 and Tie2 expression suppress angiogenesis and lung development. These findings suggest that the LRP5-Tie2-Ang signaling axis plays a central role in control of both angiogenesis and alveolarization during postnatal lung development, and that deregulation of this signaling mechanism might lead to developmental abnormalities of the lung, such as are observed in bronchopulmonary dysplasia (BPD).

The molecular genetics and cellular mechanisms underlying pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is an incurable disorder clinically characterised by a sustained elevation of mean arterial pressure in the absence of systemic involvement. As the adult circulation is a low pressure, low resistance system, PAH represents a reversal to a foetal state. The small pulmonary arteries of patients exhibit luminal occlusion resultant from the uncontrolled growth of endothelial and smooth muscle cells. This vascular remodelling is comprised of hallmark defects, most notably the plexiform lesion. PAH may be familial in nature but the majority of patients present with spontaneous disease or PAH associated with other complications. In this paper, the molecular genetic basis of the disorder is discussed in detail ranging from the original identification of the major genetic contributant to PAH and moving on to current next-generation technologies that have led to the rapid identification of additional genetic risk factors. The impact of identified mutations on the cell is examined, particularly, the determination of pathways disrupted in disease and critical to pulmonary vascular maintenance. Finally, the application of research in this area to the design and development of novel treatment options for patients is addressed along with the future directions PAH research is progressing towards.

Expression of hypoxia-inducible factors, regulators, and target genes in congenital diaphragmatic hernia patients

Congenital diaphragmatic hernia (CDH) is associated with lung hypoplasia and pulmonary hypertension and has high morbidity and mortality rates. The cause and pathophysiology of CDH are not fully understood. However, impaired angiogenesis appears to play an important role in the pathophysiology of CDH. Therefore, we examined different components of an important pathway in angiogenesis: hypoxia-inducible factors (HIFs); HIF regulators von Hippel-Lindau (VHL) and prolyl 3-hydroxylase (PHD3); and HIF target genes vascular endothelial growth factor A ( VEGF-A ) and vascular endothelial growth factor receptor 2 ( VEGFR-2 ). Quantitative polymerase chain reaction of lung tissue showed a significantly decreased expression of VEGF-A mRNA in the alveolar stage of lung development in CDH patients compared with matched control patients. In the canalicular stage, no differences for VEGF-A were seen between the lungs of CDH patients and those of control patients. Other components of angiogenesis (VHL, HIF-1α, HIF-2α, HIF-3α, VEGFR-2 mRNA, PHD3 protein) that were analyzed showed no differences in expression between CDH and control patients, independent of the developmental stage. A lower expression of VEGF mRNA in CDH patients in the alveolar stage, possibly as a result of downregulation of HIF-2α might indicate a role for these factors in the pathophysiology of CDH.

Pro-angiogenic hematopoietic progenitor cells and endothelial colony-forming cells in pathological angiogenesis of bronchial and pulmonary circulation

Dysregulation of angiogenesis is a common feature of many disease processes. Vascular remodeling is believed to depend on the participation of endothelial progenitor cells, but the identification of endothelial progenitors in postnatal neovascularization remains elusive. Current understanding posits a role for circulating pro-angiogenic hematopoietic cells that interact with local endothelial cells to establish an environment that favors angiogenesis in physiologic and pathophysiologic responses. In the lung, increased and dysregulated angiogenesis is a hallmark of diseases of the bronchial and pulmonary circulations, manifested by asthma and pulmonary arterial hypertension (PAH), respectively. In asthma, T(Helper)-2 immune cells produce angiogenic factors that mobilize and recruit pro-inflammatory and pro-angiogenic precursors from the bone marrow into the airway wall where they induce angiogenesis and fuel inflammation. In contrast, in PAH, upregulation of hypoxia-inducible factor (HIF) in vascular cells leads to the production of bone marrow-mobilizing factors that recruit pro-angiogenic progenitor cells to the pulmonary circulation where they contribute to angiogenic remodeling of the vessel wall. This review focuses on current knowledge of pro-angiogenic progenitor cells in the pathogenesis of asthma and PAH.

G protein coupled receptor kinase 2 interacting protein 1 (GIT1) is a novel regulator of mitochondrial biogenesis in heart

G-protein-coupled receptor (GPCR)-kinase interacting protein-1 (GIT1) is a multi-function scaffold protein. However, little is known about its physiological role in the heart. Here we sought to identify the cardiac function of GIT1. Global GIT1 knockout (KO) mice were generated and exhibited significant cardiac hypertrophy that progressed to heart failure. Electron microscopy revealed that the hearts of GIT1 KO mice demonstrated significant morphological abnormities in mitochondria, including decreased mitochondrial volume density, cristae density and increased vacuoles. Moreover, mitochondrial biogenesis-related gene peroxisome proliferator-activated receptor γ (PPARγ) co-activator-1α (PGC-1α), PGC-1β, mitochondrial transcription factor A (Tfam) expression, and total mitochondrial DNA were remarkably decreased in hearts of GIT1 KO mice. These animals also had impaired mitochondrial function, as evidenced by reduced ATP production and dissipated mitochondrial membrane potential (Ψ(m)) in adult cardiomyocytes. Concordant with these mitochondrial observations, GIT1 KO mice showed enhanced cardiomyocyte apoptosis and cardiac dysfunction. In conclusion, our findings identify GIT1 as a new regulator of mitochondrial biogenesis and function, which is necessary for postnatal cardiac maturation.

Maternal hyperoxygenation test in fetuses undergoing FETO for severe isolated congenital diaphragmatic hernia

OBJECTIVES

To predict neonatal survival and pulmonary hypertension by measurement of fetal pulmonary artery reactivity to maternal hyperoxygenation in fetuses with severe congenital diaphragmatic hernia treated by fetoscopic endoluminal tracheal occlusion (FETO).

METHODS

Thirty-eight fetuses underwent FETO at around 28 weeks' gestation and the balloon was removed at 34 weeks in most cases. We performed a hyperoxygenation test and measured the lung-to-head ratio of each fetus before and after each procedure. Outcome measures were neonatal survival, occurrence of pulmonary hypertension and its response to inhaled nitric oxide (iNO).

RESULTS

Fetuses that survived had a larger increase in lung size and decrease of resistance in the first branch of the main pulmonary artery than did those that died. Both measures were also predictive of pulmonary hypertension unresponsive to iNO. The hyperoxygenation test and lung-to-head ratio were both best predictive for neonatal survival when measured following removal of the balloon (P < 0.002). Discriminant analysis confirmed that these two parameters are independent predictors of outcome.

CONCLUSIONS

In fetuses undergoing FETO, pulmonary vascular reactivity in relation to oxygen and lung size are independent predictors of neonatal survival and pulmonary hypertension. The hyperoxygenation test merits further study in expectantly managed cases.

3D Imaging in Unilateral Primary Pulmonary Hypoplasia in an Adult: A Case Report

Unilateral primary pulmonary hypoplasia is rare in adulthood (UPHA); it is characterized by a decreased number of bronchial segmentation and decreased/absent alveolar air space. Classical chest X-ray may be confusing, and the biological tests are unspecific. We present a case of UPHA in a 60-year-old female, smoker, with 3 term normal deliveries, who presented with late recurrent pneumonias and bronchiectasis-type symptomathology, arterial hypertension, and obesity. Chest X-rays revealed opacity in the left lower pulmonary zone, an apparent hypoaerated upper left lobe and left deviation of the mediastinum. Preoperatory multidetector computer tomography (MDCT) presented a small retrocardiac left lung with 5-6 bronchial segmentation range and cystic appearance. After pneumonectomy the gross specimen showed a small lung with multiple bronchiectasis and small cysts, lined by hyperplasic epithelium, surrounded by stromal fibrosclerosis. We concluded that this UPHA occurred in the 4–7 embryonic weeks, and the 3D MDCT reconstructions offered the best noninvasive diagnosis.

Emergence of matched airway and vascular trees from fractal rules

The bronchial, arterial, and venous trees of the lung are complex interwoven structures. Their geometries are created during fetal development through common processes of branching morphogenesis. Insights from fractal geometry suggest that these extensively arborizing trees may be created through simple recursive rules. Mathematical models of Turing have demonstrated how only a few proteins could interact to direct this branching morphogenesis. Development of the airway and vascular trees could, therefore, be considered an example of emergent behavior as complex structures are created from the interaction of only a few processes. However, unlike inanimate emergent structures, the geometries of the airway and vascular trees are highly stereotyped. This review will integrate the concepts of emergence, fractals, and evolution to demonstrate how the complex branching geometries of the airway and vascular trees are ideally suited for gas exchange in the lung. The review will also speculate on how the heterogeneity of blood flow and ventilation created by the vascular and airway trees is overcome through their coordinated construction during fetal development.