Pulmonary vascular damage and the development of cor pulmonale following hyaline membrane disease

Right ventricular function indices and platelet parameters for early prediction value of bronchopulmonary dysplasia: a retrospective study

BACKGROUND

To examine the value of early echocardiographic indices for the right ventricular function combined with platelet(PLT) parameters for predicting bronchopulmonary dysplasia (BPD) in preterm infants.

METHODS

This retrospective study included infants with gestational age (GA) below 32 weeks, who were admitted to the neonatal intensive care unit(NICU). The detection rate of tricuspid regurgitation jet velocity (TRVJ), ventricular septal flattening, pulmonary artery widening, right ventricular dilation, and right atrial enlargement on the 7th day of life (DOL 7) were compared between BPD and non-BPD infants. Echocardiographic indices of the right ventricular function including tricuspid annular plane systolic excursion (TAPSE) and right ventricular index of myocardial performance (RIMP) were measured on 1 day of life (DOL 1)、on DOL 7 and on 14 day of life (DOL 14) respectively. The PLT parameters including the PLT count, mean platelet volume (MPV), platelet hematocrit (PCT) level, and platelet distribution width (PDW) were measured on the DOL 1,DOL 7, and DOL 14. Multivariate logistic regression was used to analyze the relationship between these parameters and BPD. Receiver operating characteristic curve analysis was performed to assess the predictive value of the right ventricular function indices and PLT parameters for BPD.

RESULTS

A total of 220 preterm infants were included in this study, and of these, 85 infants developed BPD among them. The RIMP of the BPD group on DOL 14 was higher than that of the non-BPD group (P < 0.05). The TAPSE of the BPD group on DOL 14 was lower than that of the non-BPD group (P < 0.05). The PLT count of the BPD group on DOL 1 was lower than that of the non-BPD group (P < 0.05), and the MPV of the BPD group on DOL 1 was higher than that of the non-BPD group (P < 0.05). Using multivariate logistic regression, GA、invasive mechanical ventilation duration ≥ 7 days、 PLT、 MPV、 TAPSE and RIMP were found to be independent risk factors for BPD. The area under the receiver operating characteristic curve was 0.846 (95CI: 0.794∼0.899), which improved when using right ventricular function indices combined with platelet parameters.

CONCLUSION

TAPSE and RIMP combined with PLT count and MPV can help identify preterm infants at an increased risk of developing BPD.

High Stretch Associated with Mechanical Ventilation Promotes Piezo1-Mediated Migration of Airway Smooth Muscle Cells

Ventilator-induced lung injury (VILI) during mechanical ventilation (MV) has been attributed to airway remodeling involving increased airway smooth muscle cells (ASMCs), but the underlying mechanism is not fully understood. Thus, we aimed to investigate whether MV-associated high stretch (>10% strain) could modulate mechanosensitive Piezo1 expression and thereby alter cell migration of ASMCs as a potential pathway to increased ASMCs in VILI. C57BL/6 mice and ASMCs were subjected to MV at high tidal volume (VT, 18 mL/kg, 3 h) and high stretch (13% strain, 0.5 Hz, 72 h), respectively. Subsequently, the mice or cells were evaluated for Piezo1 and integrin mRNA expression by immunohistochemical staining and quantitative PCR (qPCR), and cell migration and adhesion by transwell and cell adhesion assays. Cells were either treated or not with Piezo1 siRNA, Piezo1-eGFP, Piezo1 knockin, Y27632, or blebbistatin to regulate Piezo1 mRNA expression or inhibit Rho-associated kinase (ROCK) signaling prior to migration or adhesion assessment. We found that expression of Piezo1 in in situ lung tissue, mRNA expression of Piezo1 and integrin αVβ1 and cell adhesion of ASMCs isolated from mice with MV were all reduced but the cell migration of primary ASMCs (pASMCs) isolated from mice with MV was greatly enhanced. Similarly, cell line mouse ASMCs (mASMCs) cultured in vitro with high stretch showed that mRNA expression of Piezo1 and integrin αVβ1 and cell adhesion were all reduced but cell migration was greatly enhanced. Interestingly, such effects of MV or high stretch on ASMCs could be either induced or abolished/reversed by down/up-regulation of Piezo1 mRNA expression and inhibition of ROCK signaling. High stretch associated with MV appears to be a mechanical modulator of Piezo1 mRNA expression and can, thus, promote cell migration of ASMCs during therapeutic MV. This may be a novel mechanism of detrimental airway remodeling associated with MV, and, therefore, a potential intervention target to treat VILI.

Characterising airway obstructive, dysanaptic and PRISm phenotypes of prematurity-associated lung disease

INTRODUCTION

Although obstructive airway disease has been shown to be associated with prematurity, other spirometry phenotypes are less well described.

OBJECTIVES

We characterised abnormal spirometry phenotypes in preterm-born children, including prematurity-associated obstructive lung disease (POLD, forced expiratory volume in 1 s (FEV1)

METHODS

768 children, aged 7-12 years, underwent FENO measurements and spirometry before and after salbutamol. Groups were compared using parametric tests; multinomial regression was used.

RESULTS

22.6% of 544 preterm-born (mean gestation: 31 weeks) and 9.2% of 195 term-born children, with satisfactory data available, were classified into one of four abnormal spirometry groups. Each phenotype was generally more prevalent in preterm-born children than in the term-born children. For the preterm group, POLD-reversible (4.4%) was associated with increased FENO, bronchopulmonary dysplasia (BPD) and intrauterine growth restriction. POLD-fixed group (3.3%) did not have increased FENO but was associated with BPD. 41% of the pDysanapsis group (5.9%) had bronchodilator response, 31% had increased FENO and was associated with postnatal weight gain. In the pPRISm group (9%), 13% responded to bronchodilators, FENO was not increased and was non-significantly associated with body mass index (p=0.064).

CONCLUSIONS

Further to airway obstruction, we describe airway dysanapsis and pPRISm spirometry phenotypes in survivors of prematurity, both of which have poor outlook in other disease groups. By identifying specific phenotypes, targeted therapy can be developed to improve long-term outcomes.

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Key Words

• paediatric lung disaese

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MESH Headings

• Humans
• Infant, Newborn
• Bronchodilator Agents/therapeutic use
• Bronchopulmonary Dysplasia/complications
• Forced Expiratory Volume/physiology
• Lung
• Lung Diseases, Obstructive
• Pulmonary Disease, Chronic Obstructive
• Spirometry
• Vital Capacity/physiology
• Premature Birth
• Infant, Premature

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Grants

• MR/M022552/1 Medical Research Council

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Affiliation(s)

Michael Cousins Department of Child Health, Cardiff University School of Medicine, Cardiff, UK
Kylie Hart Department of Child Health, Cardiff University School of Medicine, Cardiff, UK
Sarah J Kotecha Department of Child Health, Cardiff University School of Medicine, Cardiff, UK
A John Henderson MRC Integrative Epidemiology Unit, Population Health Sciences, Bristol Medical School, University of Bristol, Bristol, UK
W John Watkins Department of Child Health, Cardiff University School of Medicine, Cardiff, UK
Andrew Bush Centre for Paediatrics and Child Health, Imperial College of Medicine, London, UK
Sailesh Kotecha Department of Child Health, Cardiff University School of Medicine, Cardiff, UK

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Right ventricular function and vasoactive peptides for early prediction of bronchopulmonary dysplasia

BACKGROUND

To assess the prognostic value of early echocardiographic indices of right ventricular function and vasoactive peptides for prediction of bronchopulmonary dysplasia (BPD) or death in very preterm infants.

METHODS

Prospective study involving 294 very preterm infants (median [IQR] gestational age 28.4 [26.4-30.4] weeks, birth weight 1065 [800-1380] g), of whom 57 developed BPD (oxygen supplementation at 36 weeks postmenstrual age) and 10 died. Tricuspid annular plane systolic excursion (TAPSE), right ventricular index of myocardial performance (RIMP), plasma concentrations of mid-regional pro-atrial natriuretic peptide (MR-proANP) and C-terminal pro-endothelin-1 (CT-proET1) were measured on day 7 of life.

RESULTS

RIMP was significantly increased (median [IQR] 0.3 [0.23-0.38] vs 0.22 [0.15-0.29]), TAPSE decreased (median [IQR] 5.0 [5.0-6.0] vs 6.0 [5.4-7.0] mm), MR-proANP increased (median [IQR] 784 [540-936] vs 353 [247-625] pmol/L), and CT-proET1 increased (median [IQR] 249 [190-345] vs 199 [158-284] pmol/L) in infants who developed BPD or died, as compared to controls. All variables showed significant but weak correlations with each other (rS -0.182 to 0.359) and predicted BPD/death with similar accuracy (areas under receiver operator characteristic curves 0.62 to 0.77). Multiple regression revealed only RIMP and birth weight as independent predictors of BPD or death.

CONCLUSIONS

Vasoactive peptide concentrations and echocardiographic assessment employing standardized measures, notably RIMP, on day 7 of life are useful to identify preterm infants at increased risk for BPD or death.

Pulmonary vascular disease is evident in gene regulation of experimental bronchopulmonary dysplasia

Objective: To examine the gene expression regarding pulmonary vascular disease in experimental bronchopulmonary dysplasia in young mice. Premature delivery puts babies at risk of severe complications. Bronchopulmonary dysplasia (BPD) is a common complication of premature birth leading to lifelong affection of pulmonary function. BPD is recognized as a disease of arrested alveolar development. The disease process is not fully described and no complete cure or prevention is known. The focus of interest in the search for treatment and prevention of BPD has traditionally been at airspace level; however, the pulmonary vasculature is increasingly acknowledged in the pathology of BPD. The aim of the investigation was to study the gene expression in lungs with BPD with regards to pulmonary vascular disease (PVD).Methods: We employed a murine model of hyperoxia-induced BPD and gene expression microarray technique to determine the mRNA expression in lung tissue from young mice. We combined gene expression pathway analysis and analyzed the biological function of multiple single gene transcripts from lung homogenate to study the PVD relevant gene expression.Results: There were n = 117 significantly differentially regulated genes related to PVD through down-regulation of contractile elements, up- and down-regulation of factors involved in vascular tone and tissue-specific genes. Several genes also allowed for pinpointing gene expression differences to the pulmonary vasculature. The gene Nppa coding for a natriuretic peptide, a potent vasodilator, was significantly down-regulated and there was a significant up-regulation of Pde1a (phosphodiesterase 1A), Ptger3 (prostaglandin e receptor 3), and Ptgs1 (prostaglandin-endoperoxide synthase one).Conclusion: The pulmonary vasculature is affected by the arrest of secondary alveolarization as seen by differentially regulated genes involved in vascular tone and pulmonary vasculature suggesting BPD is not purely an airspace disease. Clues to prevention and treatment may lie in the pulmonary vascular system.

Gestational Age Influences the Early Microarchitectural Changes in Response to Mechanical Ventilation in the Preterm Lamb Lung

Background: Preterm birth is associated with abnormal lung architecture, and a reduction in pulmonary function related to the degree of prematurity. A thorough understanding of the impact of gestational age on lung microarchitecture requires reproducible quantitative analysis of lung structure abnormalities. The objectives of this study were (1) to use quantitative histological software (ImageJ) to map morphological patterns of injury resulting from delivery of an identical ventilation strategy to the lung at varying gestational ages and (2) to identify associations between gestational age-specific morphological alterations and key functional outcomes. Method: Lung morphology was compared after 60 min of a standardized ventilation protocol (40 cm H₂O sustained inflation and then volume-targeted positive pressure ventilation with positive end-expiratory pressure 8 cm H₂O) in lambs at different gestations (119, 124, 128, 133, 140d) representing the spectrum of premature developmental lung states and the term lung. Age-matched controls were compared at 124 and 128d gestation. Automated and manual functions of Image J were used to measure key histological features. Correlation analysis compared morphological and functional outcomes in lambs aged ≤128 and >128d. Results: In initial studies, unventilated lung was indistinguishable at 124 and 128d. Ventilated lung from lambs aged 124d gestation exhibited increased numbers of detached epithelial cells and lung tissue compared with 128d lambs. Comparing results from saccular to alveolar development (120-140d), lambs aged ≤124d exhibited increased lung tissue, average alveolar area, and increased numbers of detached epithelial cells. Alveolar septal width was increased in lambs aged ≤128d. These findings were mirrored in the measures of gas exchange, lung mechanics, and molecular markers of lung injury. Correlation analysis confirmed the gestation-specific relationships between the histological assessments and functional measures in ventilated lambs at gestation ≤128 vs. >128d. Conclusion: Image J allowed rapid, quantitative assessment of alveolar morphology, and lung injury in the preterm lamb model. Gestational age-specific patterns of injury in response to delivery of an identical ventilation strategy were identified, with 128d being a transition point for associations between morphological alterations and functional outcomes. These results further support the need to develop individualized respiratory support approaches tailored to both the gestational age of the infant and their underlying injury response.

Accuracy of Brain Natriuretic Peptide for Diagnosing Pulmonary Hypertension in Severe Bronchopulmonary Dysplasia

BACKGROUND

Premature infants with severe bronchopulmonary dysplasia (sBPD) are at risk of pulmonary hypertension (PH). Serum brain natriuretic peptide (BNP) is used to predict disease severity in adult PH. Its diagnostic utility in sBPD-associated PH is unknown.

OBJECTIVE

The aim of this paper was to determine the accuracy of BNP, against echocardiogram (echo), to diagnose PH in infants born <32 weeks' gestation with sBPD.

METHODS

We conducted a retrospective cohort study of all infants with sBPD with an echo and BNP within a 24-h period, at ≥36 weeks postmenstrual age. PH was defined as: right ventricular pressure >½ systemic blood pressure estimated from tricuspid regurgitant jet or patent ductus arteriosus (PDA) velocity, bidirectional or right-to left-PDA, and/or flat/bowing ventricular septum at end-systole. Receiver-operating characteristic (ROC) curves were constructed to test the diagnostic accuracy of BNP.

RESULTS

Of 128 infants, 68 (53%) had echo evidence of PH. BNP was higher among the infants with PH (median [interquartile range]: 127 pg/mL [39-290] vs. 35 [20-76], p < 0.001). The area under the ROC curve for diagnosing PH using BNP was 0.74 (95% CI 0.66-0.83). At an optimal cutpoint of 130 pg/mL, BNP correctly classified the presence or absence of PH in 70% of the infants (specificity: 92, sensitivity: 50%).

CONCLUSIONS

BNP, relative to concurrent echo, demonstrated moderate accuracy for diagnosing PH in this cohort of preterm infants with sBPD. BNP may help rule in PH in this population but has low utility to rule out the disease.

Maternal omega-3 PUFA supplementation prevents hyperoxia-induced pulmonary hypertension in the offspring

Pulmonary hypertension (PH) and right ventricular hypertrophy (RVH) affect 16-25% of premature infants with bronchopulmonary dysplasia (BPD), contributing significantly to perinatal morbidity and mortality. Omega-3 polyunsaturated fatty acids (PUFA ω-3) can improve vascular remodeling, angiogenesis, and inflammation under pathophysiological conditions. However, the effects of PUFA ω-3 supplementation in BPD-associated PH are unknown. The present study aimed to evaluate the effects of PUFA ω-3 on pulmonary vascular remodeling, angiogenesis, and inflammatory response in a hyperoxia-induced rat model of PH. From embryonic day 15, pregnant Sprague-Dawley rats were supplemented daily with PUFA ω-3, PUFA ω-6, or normal saline (0.2 ml/day). After birth, pups were pooled, assigned as 12 per litter, randomly assigned to either air or continuous oxygen exposure (fraction of inspired oxygen = 85%) for 20 days, and then euthanized for pulmonary hemodynamic and morphometric analysis. We found that PUFA ω-3 supplementation improved survival, decreased right ventricular systolic pressure and RVH caused by hyperoxia, and significantly improved alveolarization, vascular remodeling, and vascular density. PUFA ω-3 supplementation produced a higher level of total ω-3 in lung tissue and breast milk and was found to reverse the reduced levels of VEGFA, VEGF receptor 2, angiopoietin-1 (ANGPT1), endothelial TEK tyrosine kinase, endothelial nitric oxide synthase, and nitric oxide concentrations in lung tissue and the increased ANGPT2 levels in hyperoxia-exposed rats. The beneficial effects of PUFA ω-3 in improving lung injuries were also associated with an inhibition of leukocyte infiltration and reduced expression of the proinflammatory cytokines IL-1β, IL-6, and TNF-α. These data indicate that maternal PUFA ω-3 supplementation strategies could effectively protect against infant PH induced by hyperoxia.

Premature birth affects the degree of airway dysanapsis and mechanical ventilatory constraints

NEW FINDINGS

What is the central question of this study? Adult survivors of preterm birth without (PRE) and with bronchopulmonary dysplasia (BPD) have airflow obstruction at rest and significant mechanical ventilatory constraints during exercise compared with those born at full term (CON). Do PRE/BPD have smaller airways, indexed via the dysanapsis ratio, than CON? What is the main finding and its importance? The dysanapsis ratio was significantly smaller in BPD and PRE compared with CON, with BPD having the smallest dysanapsis ratio. These data suggest that airflow obstruction in PRE and BPD might be because of smaller airways than CON. Adult survivors of very preterm birth (≤32 weeks gestational age) without (PRE) and with bronchopulmonary dysplasia (BPD) have obstructive lung disease as evidenced by reduced expiratory airflow at rest and have significant mechanical ventilatory constraints during exercise. Airflow obstruction, in any conditions, could be attributable to several factors, including small airways. PRE and/or BPD could have smaller airways than their counterparts born at full term (CON) owing to a greater degree of dysanaptic airway development during the pre- and/or postnatal period. Thus, the purpose of the present study was to compare the dysanapsis ratio (DR), as an index of airway size, between PRE, BPD and CON. To do so, we calculated DR in PRE (n = 21), BPD (n = 14) and CON (n = 34) individuals and examined flow-volume loops at rest and during submaximal exercise. The DR, using multiple estimates of static recoil pressure, was significantly smaller in PRE and BPD (0.16 ± 0.05 and 0.10 ± 0.03 a.u.) compared with CON (0.22 ± 0.04 a.u.; both P < 0.001) and smallest in BPD (P < 0.001). The DR was significantly correlated with peak expiratory airflow at rest (r = 0.42; P < 0.001) and the extent of expiratory flow limitation during exercise (r = 0.60; P < 0.001). Our findings suggest that PRE/BPD might have anatomically smaller airways than CON, which might help to explain their lower expiratory airflow rate at rest and during exercise and further our understanding of the consequences of preterm birth and neonatal O₂ therapy.

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.

Imaging Bronchopulmonary Dysplasia-A Multimodality Update

Bronchopulmonary dysplasia is the most common form of infantile chronic lung disease and results in significant health-care expenditure. The roles of chest radiography and computed tomography (CT) are well documented but numerous recent advances in imaging technology have paved the way for newer imaging techniques including structural pulmonary assessment via lung magnetic resonance imaging (MRI), functional assessment via ventilation, and perfusion MRI and quantitative imaging techniques using both CT and MRI. New applications for ultrasound have also been suggested. With the increasing array of complex technologies available, it is becoming increasingly important to have a deeper knowledge of the technological advances of the past 5–10 years and particularly the limitations of some newer techniques currently undergoing intense research. This review article aims to cover the most salient advances relevant to BPD imaging, particularly advances within CT technology, postprocessing and quantitative CT; structural MRI assessment, ventilation and perfusion imaging using gas contrast agents and Fourier decomposition techniques and lung ultrasound.

Pulmonary hypertension's variegated landscape: a snapshot

The many types of pulmonary hypertension (PH) are so protean in their biological origin, histological expression, and natural history that it is difficult to create a summary picture of the disease, or to easily compare and contrast characteristics of one type of PH with another. For newcomers to the field, however, such a picture would facilitate a broad understanding of PH. In this paper, we suggest that four characteristics are fundamental to describing the nature of various types of PH, and that taken together they define a number of patterns of PH expression. These characteristics are histopathology, developmental origin, associated clinical conditions, and potential for resolution. The “snapshot” is a way to concisely display the ways that these signal characteristics intersect in select specific types of PH, and is an effort to summarize these patterns in a way that facilitates a “big picture” comprehension of this disease.

Right ventricular performance using myocardial deformation imaging in infants with bronchopulmonary dysplasia

OBJECTIVE

Right ventricular (RV) performance among infants with bronchopulmonary dysplasia (BPD) remains poorly understood. We tested the hypothesis that myocardial deformation imaging (MDI) strain and strain rate would allow for differentiation between infants with severe and milder forms of BPD, independent of tissue Doppler imaging (TDI) and superior to conventional echocardiographic measurements.

STUDY DESIGN

Infants with various severities of BPD (11 with none or mild, 13 with moderate and 10 with severe) underwent conventional echocardiography, TDI and MDI assessments at >36 weeks of corrected gestational age. BPD severity grading was determined according to the National Institutes of Child Health and Disease workshop rating scale by physicians blinded to the echocardiogram results. Group data were compared with one-way analysis of variance or Kruskal-Wallis tests, with post hoc multiple comparisons.

RESULTS

No differences in traditional echocardiographic parameters or TDI among the three BPD severity groups were observed; none of the infants had evidence of pulmonary hypertension. Using MDI, infants with severe BPD had lower peak global systolic strain than did infants with moderate BPD (P<0.01) or mild/none BPD (P<0.01). Early and late diastolic strain rate measurements were similar across the three groups.

CONCLUSIONS

Among infants with severe forms of BPD, evidence of abnormal RV systolic function was detected with MDI, but not traditional echocardiographic or TDI measurements. Infants with severe forms of BPD may represent a particularly high-risk subgroup for decreased RV performance warranting cardiac surveillance. MDI should be considered as a method to quantitate RV function in this population.

Pulmonary arterial response to hypoxia in survivors of chronic lung disease of prematurity

BACKGROUND

It is unclear whether increased pulmonary arterial (PA) reactivity to hypoxia observed in preterm infants who develop chronic lung disease of prematurity (CLD) persists into childhood.

AIM

We assessed and compared PA pulse wave velocity (PWV) in air and after 12% hypoxia using velocity-encoded MRI between children who had CLD in infancy and preterm-born and term-born controls.

METHODS

From 67 recruited children, 59 (13 CLD, 21 preterm, 25 term), 9-12-year-old children successfully completed the study. Velocity-encoded phase-contrast MR PA images were acquired breathing air and during breathing 12% hypoxia. PA PWV was derived as the ratio of flow to area changes during early systole.

RESULTS

There were no differences in mean (SD) PA PWV between the groups breathing air (CLD=1.3 (0.4) m/s, preterm control=1.3 (0.4) m/s, term control=1.3 (0.3) m/s)) but increased following hypoxia to 1.9 (0.7) m/s, 1.6 (0.6) m/s and 1.5 (0.5) m/s in CLD, preterm and term groups, respectively. The mean differences (95% CI) for PA PWV between CLD and the preterm and control groups were 0.37 (0.08 to 0.70) and 0.34 (0.05 to 0.70), respectively. There was no difference for change in PA PWV with hypoxia between the two control groups, mean difference 0.23 (-0.2 to 0.3).

CONCLUSIONS

Children who had CLD in infancy had increased pulmonary arterial reactivity during hypoxia, thus long-term follow-up is warranted in this population.

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.

Dose-dependent effects of glucocorticoids on pulmonary vascular development in a murine model of hyperoxic lung injury

BACKGROUND

Exposure of neonatal mice to hyperoxia results in pulmonary vascular remodeling and aberrant phosphodiesterase type 5 (PDE5) signaling. Although glucocorticoids are frequently utilized in the NICU, little is known about their effects on the developing pulmonary vasculature and on PDE5. We sought to determine the effects of hydrocortisone (HC) on pulmonary vascular development and on PDE5 in a neonatal mouse model of hyperoxic lung injury.

METHODS

C57BL/6 mice were placed in 21% O2 or 75% O2 within 24 h of birth and received HC (1, 5, or 10 mg/kg subcutaneously every other day) or vehicle. At 14 d, right ventricular hypertrophy (RVH), medial wall thickness (MWT), lung morphometry, and pulmonary artery (PA) PDE5 activity were assessed. PDE5 activity was measured in isolated pulmonary artery smooth muscle cells exposed to 21 or 95% O2 ± 100 nmol/l HC for 24 h.

RESULTS

Hyperoxia resulted in alveolar simplification, RVH, increased MWT, and increased PA PDE5 activity. HC decreased hyperoxia-induced RVH and attenuated MWT. HC had dose-dependent effects on alveolar simplification. HC decreased hyperoxia-induced PDE5 activity both in vivo and in vitro.

CONCLUSIONS

HC decreases hyperoxia-induced pulmonary vascular remodeling and attenuates PDE5 activity. These findings suggest that HC may protect against hyperoxic injury in the developing pulmonary vasculature.

Pulmonary Vascular Disease in Bronchopulmonary Dysplasia

Pulmonary vascular disease and pulmonary hypertension (PH) contributes significantly to the pathogenesis, pathophysiology, and clinical course of infants with bronchopulmonary dysplasia (BPD). This article briefly reviews the impact of premature birth on the developing lung circulation, mechanisms that contribute to the development of PH in premature newborns, and the diagnostic evaluation and management of severe PH in infants with BPD.

Pulmonary Hypertension and Vascular Abnormalities in Bronchopulmonary Dysplasia

Despite advances in the care of preterm infants, these infants remain at risk bronchopulmonary dysplasia (BPD), which results in prolonged need for supplemental oxygen, recurrent respiratory exacerbations, and exercise intolerance. Recent investigations have highlighted the important contribution of the developing pulmonary circulation to lung development, showing that these infants are also at risk for pulmonary vascular disease (PVD), including pulmonary hypertension (PH) and pulmonary vascular abnormalities. Several epidemiologic studies have delineated the incidence of PH in preterm infants and the impact on outcomes. These studies have also highlighted gaps in the understanding of PVD in BPD.

Pediatric Pulmonary Hypertension: Guidelines From the American Heart Association and American Thoracic Society

Pulmonary hypertension is associated with diverse cardiac, pulmonary, and systemic diseases in neonates, infants, and older children and contributes to significant morbidity and mortality. However, current approaches to caring for pediatric patients with pulmonary hypertension have been limited by the lack of consensus guidelines from experts in the field. In a joint effort from the American Heart Association and American Thoracic Society, a panel of experienced clinicians and clinician-scientists was assembled to review the current literature and to make recommendations on the diagnosis, evaluation, and treatment of pediatric pulmonary hypertension. This publication presents the results of extensive literature reviews, discussions, and formal scoring of recommendations for the care of children with pulmonary hypertension.

Point Prevalence, Clinical Characteristics, and Treatment Variation for Infants with Severe Bronchopulmonary Dysplasia

OBJECTIVES

Despite improvements in survival of preterm infants, bronchopulmonary dysplasia (BPD) remains a persistent morbidity. The incidence, clinical course, and current management of severe BPD (sBPD) remain to be defined. To address these knowledge gaps, a multicenter collaborative was formed to improve outcomes in this population.

STUDY DESIGN

We performed a "snapshot" in eight neonatal intensive care units (NICUs) on December 17, 2013. A standardized clinical data form for each inpatient born at < 32 weeks was completed and collated centrally for analysis. sBPD was defined as receiving ≥ 30% supplemental oxygen and/or receiving positive pressure ventilation at 36 weeks postmenstrual age (PMA).

RESULTS

Of a total census of 710 inpatients, 351 infants were born at < 32 weeks and 128 of those (36.5%) met criteria for sBPD. The point prevalence of sBPD varied between centers (11-58%; p < 0.001). Among infants with sBPD there was a variation among centers in the use of mechanical ventilation at 28 days of life (p < 0.001) and at 36 weeks PMA (p = 0.001). We observed differences in the use of diuretics (p = 0.018), inhaled corticosteroids (p < 0.001), and inhaled β-agonists (p < 0.001).

CONCLUSION

The high point prevalence of sBPD and variable management among NICUs emphasizes the lack of evidence in guiding optimal care to improve long-term outcomes of this high-risk, understudied population.

Impaired pulmonary vascular development in bronchopulmonary dysplasia

Bronchopulmonary dysplasia (BPD), the chronic lung disease associated with preterm birth, results from the disruption of normal pulmonary vascular and alveolar growth. Though BPD was once described as primarily due to postnatal injury from mechanical ventilation and oxygen therapy after preterm birth, it is increasingly appreciated that BPD results from antenatal and perinatal factors that interrupt lung development in infants born at the extremes of prematurity. The lung in BPD consists of a simplified parenchymal architecture that limits gas exchange and leads to increased cardiopulmonary morbidity and mortality. This review outlines recent advances in the understanding of pulmonary vascular development and describes how the disruption of these mechanisms results in BPD. We point to future therapies that may augment postnatal vascular growth to prevent and treat this severe chronic lung disease.

Utility of large-animal models of BPD: chronically ventilated preterm lambs

This paper is focused on unique insights provided by the preterm lamb physiological model of bronchopulmonary dysplasia (BPD). Connections are also made to insights provided by the former preterm baboon model of BPD, as well as to rodent models of lung injury to the immature, postnatal lung. The preterm lamb and baboon models recapitulate the clinical setting of preterm birth and respiratory failure that require prolonged ventilation support for days or weeks with oxygen-rich gas. An advantage of the preterm lamb model is the large size of preterm lambs, which facilitates physiological studies for days or weeks during the evolution of neonatal chronic lung disease (CLD). To this advantage is linked an integrated array of morphological, biochemical, and molecular analyses that are identifying the role of individual genes in the pathogenesis of neonatal CLD. Results indicate that the mode of ventilation, invasive mechanical ventilation vs. less invasive high-frequency nasal ventilation, is related to outcomes. Our approach also includes pharmacological interventions that test causality of specific molecular players, such as vitamin A supplementation in the pathogenesis of neonatal CLD. The new insights that are being gained from our preterm lamb model may have important translational implications about the pathogenesis and treatment of BPD in preterm human infants.

Early pulmonary vascular disease in preterm infants at risk for bronchopulmonary dysplasia

RATIONALE

Pulmonary hypertension (PH) is associated with poor outcomes among preterm infants with bronchopulmonary dysplasia (BPD), but whether early signs of pulmonary vascular disease are associated with the subsequent development of BPD or PH at 36 weeks post-menstrual age (PMA) is unknown.

OBJECTIVES

To prospectively evaluate the relationship of early echocardiogram signs of pulmonary vascular disease in preterm infants to the subsequent development of BPD and late PH (at 36 wk PMA).

METHODS

Prospectively enrolled preterm infants with birthweights 500-1,250 g underwent echocardiogram evaluations at 7 days of age (early) and 36 weeks PMA (late). Clinical and echocardiographic data were analyzed to identify early risk factors for BPD and late PH.

MEASUREMENTS AND MAIN RESULTS

A total of 277 preterm infants completed echocardiogram and BPD assessments at 36 weeks PMA. The median gestational age at birth and birthweight of the infants were 27 weeks and 909 g, respectively. Early PH was identified in 42% of infants, and 14% were diagnosed with late PH. Early PH was a risk factor for increased BPD severity (relative risk, 1.12; 95% confidence interval, 1.03-1.23) and late PH (relative risk, 2.85; 95% confidence interval, 1.28-6.33). Infants with late PH had greater duration of oxygen therapy and increased mortality in the first year of life (P < 0.05).

CONCLUSIONS

Early pulmonary vascular disease is associated with the development of BPD and with late PH in preterm infants. Echocardiograms at 7 days of age may be a useful tool to identify infants at high risk for BPD and PH.

Advances in paediatric pulmonary vascular disease associated with bronchopulmonary dysplasia

Pulmonary hypertension (PH) is a common finding in infants with bronchopulmonary dysplasia (BPD). The aim of this review is to describe recent advances in the diagnosis and treatment of PH and discuss whether they will benefit infants and children with BPD related PH. Echocardiography remains the mainstay of diagnosis but has limitations, further developments in diagnostic techniques and identification of biomarkers are required. There are many potential therapies for PH associated with BPD. Inhaled nitric oxide has been shown to improve short term outcomes only. Sidenafil in resource limited settings was shown in three randomized trials to significantly reduce mortality. The efficacy of other therapies including prostacyclin, PDE3 inhibitors and endothelin receptor blockers has only been reported in case reports or case series. Randomized controlled trials with long term follow up are required to appropriately assess the efficacy of therapies aimed at improving the outcome of children with PH.

Role of reactive oxygen species in neonatal pulmonary vascular disease

SIGNIFICANCE

Abnormal lung development in the perinatal period can result in severe neonatal complications, including persistent pulmonary hypertension (PH) of the newborn and bronchopulmonary dysplasia. Reactive oxygen species (ROS) play a substantive role in the development of PH associated with these diseases. ROS impair the normal pulmonary artery (PA) relaxation in response to vasodilators, and ROS are also implicated in pulmonary arterial remodeling, both of which can increase the severity of PH.

RECENT ADVANCES

PA ROS levels are elevated when endogenous ROS-generating enzymes are activated and/or when endogenous ROS scavengers are inactivated. Animal models have provided valuable insights into ROS generators and scavengers that are dysregulated in different forms of neonatal PH, thus identifying potential therapeutic targets.

CRITICAL ISSUES

General antioxidant therapy has proved ineffective in reversing PH, suggesting that it is necessary to target specific signaling pathways for successful therapy.

FUTURE DIRECTIONS

Development of novel selective pharmacologic inhibitors along with nonantioxidant therapies may improve the treatment outcomes of patients with PH, while further investigation of the underlying mechanisms may enable earlier detection of the disease.

Cardiovascular function in children who had chronic lung disease of prematurity

OBJECTIVES

Although increased pulmonary arterial pressure is common in infancy in preterm infants who develop chronic lung disease of prematurity (CLD), it is unknown if the increase persists into childhood. We, therefore, assessed if 8-12-year-old children with documented CLD in infancy had evidence of right ventricular dysfunction or pulmonary arterial hypertension at rest or in response to acute hypoxia when compared to preterm and term-born controls.

METHODS

We studied 90 children: 60 born at ≤32 weeks of gestation (28 with CLD and 32 preterm controls), and 30 term-born controls. All had echocardiography including myocardial velocity imaging, at rest and while breathing 15% oxygen and 12% oxygen for 20 min each.

RESULTS

Baseline oxygen saturation, heart rate, blood pressure and echocardiographic markers of left and right ventricular function were similar in all three groups. While breathing 12% oxygen, the oxygen saturation decreased to 81.9% in the CLD group compared to 85.1% (p<0.05) and 84.7% (p<0.01) in the preterm and term controls, respectively. In response to hypoxia, all three groups showed increases in velocity of tricuspid regurgitation, end-diastolic velocity of pulmonary regurgitation, and right ventricular relaxation time; and decreases in pulmonary arterial acceleration time and the ratio of right ventricular acceleration time to ejection time. However, there were no differences between groups.

CONCLUSIONS

Childhood survivors of CLD have comparable left and right ventricular function at 8-12 years of age to preterm and term-born children, and no evidence of increased pulmonary arterial pressure even after hypoxic exposure.

Pulmonary gas exchange efficiency during exercise breathing normoxic and hypoxic gas in adults born very preterm with low diffusion capacity

Adults with a history of very preterm birth (<32 wk gestational age; PRET) have reduced lung function and significantly lower lung diffusion capacity for carbon monoxide (DLCO) relative to individuals born at term (CONT). Low DLCO may predispose PRET to diffusion limitation during exercise, particularly while breathing hypoxic gas because of a reduced O2 driving gradient and pulmonary capillary transit time. We hypothesized that PRET would have significantly worse pulmonary gas exchange efficiency [i.e., increased alveolar-to-arterial Po2 difference (AaDO2)] during exercise breathing room air or hypoxic gas (FiO2 = 0.12) compared with CONT. To test this hypothesis, we compared the AaDO2 in PRET ( n = 13) with a clinically mild reduction in DLCO (72 ± 7% of predicted) and CONT ( n = 14) with normal DLCO (105 ± 10% of predicted) pre- and during exercise breathing room air and hypoxic gas. Measurements of temperature-corrected arterial blood gases, and direct measure of O2 saturation (SaO2), were made prior to and during exercise at 25, 50, and 75% of peak oxygen consumption (V̇o2peak) while breathing room air and hypoxic gas. In addition to DLCO, pulmonary function and exercise capacity were significantly less in PRET. Despite PRET having low DLCO, no differences were observed in the AaDO2 or SaO2 pre- or during exercise breathing room air or hypoxic gas compared with CONT. Although our findings were unexpected, we conclude that reduced pulmonary function and low DLCO resulting from very preterm birth does not cause a measureable reduction in pulmonary gas exchange efficiency.

Disrupted lung development and bronchopulmonary dysplasia: opportunities for lung repair and regeneration

PURPOSE OF REVIEW

Advances in medical therapy have increased survival of extremely premature infants and changed the pathology of bronchopulmonary dysplasia (BPD) from one of acute lung injury to a disease of disrupted lung development. With this evolution, new questions emerge regarding the molecular mechanisms that control postnatal lung development, the effect of early disruptions of postnatal lung development on long-term lung function, and the existence of endogenous mechanisms that permit lung regeneration after injury.

RECENT FINDINGS

Recent data demonstrate that a significant component of alveolarization, the final stage of lung development, occurs postnatally. Further, clinical and experimental studies demonstrate that premature birth disrupts alveolarization, decreasing the gas exchange surface area of the lung and causing BPD. BPD is associated with significant short-term morbidity, and new longitudinal, clinical data demonstrate that survivors of BPD have long-standing deficits in lung function and may be at risk for the development of additional lung disease as adults. Unfortunately, current care is mainly supportive with few effective therapies that prevent or treat established BPD. These studies underscore the need to further elucidate the mechanisms that direct postnatal lung growth and develop innovative strategies to stimulate lung regeneration.

SUMMARY

Despite significant improvements in the care and survival of extremely premature infants, BPD remains a major clinical problem. Although efforts should remain focused on the prevention of preterm labor and BPD, novel research aimed at promoting postnatal alveolarization offers a unique opportunity to develop effective strategies to treat established BPD.

Chronic lung disease in the preterm infant. Lessons learned from animal models

Neonatal chronic lung disease, also known as bronchopulmonary dysplasia (BPD), is the most common complication of premature birth, affecting up to 30% of very low birth weight infants. Improved medical care has allowed for the survival of the most premature infants and has significantly changed the pathology of BPD from a disease marked by severe lung injury to the "new" form characterized by alveolar hypoplasia and impaired vascular development. However, increased patient survival has led to a paucity of pathologic specimens available from infants with BPD. This, combined with the lack of a system to model alveolarization in vitro, has resulted in a great need for animal models that mimic key features of the disease. To this end, a number of animal models have been created by exposing the immature lung to injuries induced by hyperoxia, mechanical stretch, and inflammation and most recently by the genetic modification of mice. These animal studies have 1) allowed insight into the mechanisms that determine alveolar growth, 2) delineated factors central to the pathogenesis of neonatal chronic lung disease, and 3) informed the development of new therapies. In this review, we summarize the key findings and limitations of the most common animal models of BPD and discuss how knowledge obtained from these studies has informed clinical care. Future studies should aim to provide a more complete understanding of the pathways that preserve and repair alveolar growth during injury, which might be translated into novel strategies to treat lung diseases in infants and adults.

B-type natriuretic peptide and mortality in extremely low birth weight infants with pulmonary hypertension: a retrospective cohort analysis

Background

B-type natriuretic peptide (BNP) is a strong predictor of mortality in adult patients with various forms of pulmonary hypertension (PH) and may be a strong prognostic marker in extremely low birth weight (ELBW) infants with bronchopulmonary dysplasia (BPD) associated PH as well. We sought to assess the relationship between BNP levels and all-cause mortality in a cohort of ELBW infants with BPD and PH.

Methods

We retrospectively identified ELBW infants with BPD and PH who had serum BNP levels measured as part of routine clinical care in the neonatal intensive care unit. Peak serum BNP levels were correlated with survival to discharge or death.

Results

Thirty-six ELBW infants (mean gestational age 26.0 ± 1.9 weeks and mean birth weight 740 ± 290 grams) with BPD and PH had available survival data and had serum BNP levels measured. Peak BNP level was significantly lower among infants who survived than among those who died (128 pg/ml, [IQR 23 to 463] vs. 997 pg/ml, [IQR 278 to 1770], P < 0.004). On multivariate Cox proportional hazard analysis, BNP predicted survival independent of age, gender, and BPD severity. Area under receiver operator characteristic analysis identified a BNP value of 220 pg/ml to have 90% sensitivity and 65% specificity in predicting mortality.

Conclusion

BNP estimation may be useful as a prognostic marker of all-cause mortality in ELBW infants with BPD associated PH.

Pulmonary Hypertension in Preterm Infants with Bronchopulmonary Dysplasia

Bronchopulmonary dysplasia (BPD), the chronic lung disease of prematurity, is a significant contributor to perinatal morbidity and mortality. Premature birth disrupts pulmonary vascular growth and initiates a cascade of events that result in impaired gas exchange, abnormal vasoreactivity, and pulmonary vascular remodeling that may ultimately lead to pulmonary hypertension (PH). Even infants who appear to have mild BPD suffer from varying degrees of pulmonary vascular disease (PVD). Although recent studies have enhanced our understanding of the pathobiology of PVD and PH in BPD, much remains unknown with respect to how PH should be properly defined, as well as the most accurate methods for the diagnosis and treatment of PH in infants with BPD. This article will provide neonatologists and primary care providers, as well as pediatric cardiologists and pulmonologists, with a review of the pathophysiology of PH in preterm infants with BPD and a summary of current clinical recommendations for managing PH in this population.

Long term cardiovascular consequences of chronic lung disease of prematurity

Pulmonary arterial (PA) hypertension in preterm infant is an important consequence of chronic lung disease of prematurity (CLD) arising mainly due to impaired alveolar development and dysregulated angiogenesis of the pulmonary circulation. Although PA pressure and resistance in these children normalise by school age, their pulmonary vasculature remains hyper-reactive to hypoxia until early childhood. Furthermore, there is evidence that systemic blood pressure in preterm born children with or without CLD is mildly increased at school age and in young adulthood when compared to term-born children. Arterial stiffness may be increased in CLD survivors due to increased smooth muscle tone of the pre-resistance and resistance vessels rather than the loss of elasticity in the large arteries. This review explores the long term effects of CLD on the pulmonary and systemic circulations along with their clinical correlates and therapeutic approaches.

Pulmonary vascular disease in bronchopulmonary dysplasia: pulmonary hypertension and beyond

PURPOSE OF REVIEW

Pulmonary hypertension contributes significantly to morbidity and mortality of chronic lung disease of infancy, or bronchopulmonary dysplasia (BPD). Advances in pulmonary vascular biology over the past few decades have led to new insights into the pathogenesis of BPD; however, many unique issues persist regarding our understanding of pulmonary vascular development and disease in preterm infants at risk for chronic lung disease.

RECENT FINDINGS

Recent studies have highlighted the important contribution of the developing pulmonary circulation to lung growth in the setting of preterm birth. These studies suggest that there is a spectrum of pulmonary vascular disease (PVD) in BPD rather than a simple question of whether or not pulmonary hypertension is present. Epidemiological studies underscore gaps in our understanding of PVD in the context of BPD, including universally accepted definitions, approaches to diagnosis and treatment, and patient outcomes. Unfortunately, therapeutic strategies for pulmonary hypertension in BPD are based on small observational studies with poorly defined endpoints and rely on results from older children and adult studies. Yet, unique characteristics of this population create other potential risks for the adoption of these strategies.

SUMMARY

Despite many recent advances, PVD remains an important contributor to poor outcomes in preterm infants with BPD. Substantial challenges persist, especially with regard to understanding mechanisms and the clinical approach to PVD. Future studies are needed to develop evidence-based definitions and clinical endpoints through which the pathophysiology can be investigated and potential therapeutic interventions evaluated.

Progress in understanding the pathogenesis of BPD using the baboon and sheep models

Bronchopulmonary dysplasia (BPD) is among the most common chronic lung diseases in infants in the US. Improved survival of preterm infants who developed BPD is becoming increasingly important because of the high risk for persistent pulmonary morbidities such as poor respiratory gas exchange, pulmonary hypertension, and excess airway expiratory resistance later in life. This review focuses on unique insights provided by the two large-animal, physiological models of neonatal chronic lung disease: preterm baboons and preterm lambs. The models' are valuable because they contribute to better understanding of the underlying molecular pathogenic mechanisms. An epigenetic hypothesis is proposed as a pathogenic mechanism for BPD and its persistent pulmonary morbidities.

Pulmonary hypertension in bronchopulmonary dysplasia

Pulmonary hypertension (PH) is a common complication of neonatal respiratory diseases, including bronchopulmonary dysplasia (BPD), and recent studies have increased awareness that PH worsens the clinical course, morbidity and mortality of BPD. Recent evidence indicates that up to 18% of all extremely low-birth-weight infants will develop some degree of PH during their hospitalization, and the incidence rises to 25-40% of the infants with established BPD. Risk factors are not yet well understood, but new evidence shows that fetal growth restriction is a significant predictor of PH. Echocardiography remains the primary method for evaluation of BPD-associated PH, and the development of standardized screening timelines and techniques for identification of infants with BPD-associated PH remains an important ongoing topic of investigation. The use of pulmonary vasodilator medications, such as nitric oxide, sildenafil, and others, in the BPD population is steadily growing, but additional studies are needed regarding their long-term safety and efficacy.

Hydralazine in infants with persistent hypoxemic respiratory failure

BACKGROUND

Most deaths of infants with chronic lung disease (CLD) are caused by respiratory failure, unremitting pulmonary artery hypertension (PAH) with cor pulmonale, or infection. Although the exact prevalence of PAH in infants with CLD is unknown, infants with CLD and severe PAH have a high mortality rate. Except for oxygen supplementation, no specific interventions have been established as effective in the treatment for PAH in premature infants with CLD. Little has been proven regarding the clinical efficacy of vasodilators and concerns remain regarding adverse effects.

OBJECTIVES

To review current evidence for the benefits and harms of hydralazine therapy to infants with persistent hypoxemic respiratory failure.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL, The Cochrane Library), MEDLINE via PubMed and EMBASE, and other clinical trials registries through November 2011 using the standard search strategy of the Cochrane Neonatal Review Group. We searched these databases using a strategy combining a variation of the Cochrane highly sensitive search strategy for identifying randomised trials in MEDLINE; sensitivity-maximising version with selected MeSH and free-text terms: hydralazine, vasodilator agent, antihypertensive agent, heart diseases, lung diseases, respiratory tract diseases, infant, and randomised controlled trial.

SELECTION CRITERIA

We considered only randomised controlled trials and quasi-randomised trials for inclusion. We included low birth weight (LBW) infants with persistent hypoxemic respiratory failure who were treated with any type of hydralazine therapy.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed trial quality according to pre-specified criteria.

MAIN RESULTS

We found no studies meeting the criteria for inclusion in this review.

AUTHORS' CONCLUSIONS

There was insufficient evidence to determine the safety and efficacy of hydralazine in LBW infants with persistent hypoxemic respiratory failure. Since hydralazine is inexpensive and potentially beneficial, randomised controlled trials are recommended. Such trials are particularly needed in settings where other medications such as sildenafil, inhaled nitric oxide (iNO), or extracorporeal membrane oxygenation (ECMO) are not available.

Persistently elevated right ventricular index of myocardial performance in preterm infants with incipient bronchopulmonary dysplasia

OBJECTIVES

Elevated pulmonary vascular resistance occurs during the first days after birth in all newborn infants and persists in infants at risk for bronchopulmonary dysplasia (BPD). It is difficult to measure in a non-invasive fashion. We assessed the usefulness of the right ventricular index of myocardial performance (RIMP) to estimate pulmonary vascular resistance in very low birth weight infants.

STUDY DESIGN

Prospective echocardiography on day of life (DOL) 2, 7, 14, and 28 in 121 preterm infants (median [quartiles] gestational age 28 [26]-[29] weeks, birth weight 998 [743-1225] g) of whom 36 developed BPD (oxygen supplementation at 36 postmenstrual weeks).

RESULTS

RIMP derived by conventional pulsed Doppler technique was unrelated to heart rate or mean blood pressure. RIMP on DOL 2 was similar in infants who subsequently did (0.39 [0.33-0.55]) and did not develop BPD (0.39 [0.28-0.51], p = 0.467). RIMP declined steadily in non-BPD infants but not in BPD infants (DOL 7: 0.31[0.22-0.39] vs. 0.35[0.29-0.48], p = 0.014; DOL 14: 0.23[0.17-0.30] vs. 0.35[0.25-0.43], p<0.001; DOL 28: 0.21[0.15-0.28] vs. 0.31 [0.21-0.35], p = 0.015).

CONCLUSIONS

In preterm infants, a decline in RIMP after birth was not observed in those with incipient BPD. The pattern of RIMP measured in preterm infants is commensurate with that of pulmonary vascular resistance.

Reproducibility of myocardial velocity and deformation imaging in term and preterm infants

AIMS

Myocardial velocity imaging has been validated in adults for assessment of ventricular function and indirect indices of pulmonary arterial pressure. To establish whether it could also be used in infants, we investigated the reproducibility of myocardial velocities and deformation indices in term and preterm neonates.

METHODS AND RESULTS

Myocardial velocity loops acquired from 16 infants were analysed by four observers for inter-observer variability, and re-analysed after 6 months by one observer for intra-observer variability. For myocardial velocities, the coefficients of variation (CVs) for the left ventricle (LV) were 10-11 (intra-observer) and 14-20% (inter-observer) and for the right ventricle (RV) 15-19 and 18-24%, respectively. Reproducibility for annular displacements was <13% (intra-observer) and <18% (inter-observer). CVs for LV strain were 14-17 (intra-observer) and 36-43% (inter-observer) and for RV 19-24 and 25-37%. CVs for isovolumic acceleration were in general >40%. In comparison, the CVs for blood pool indices were 3-15%.

CONCLUSION

Intra-observer reproducibility for myocardial velocity and deformation indices in neonates is adequate for these parameters to be used in clinical research. Inter-observer reproducibility is sub-optimal suggesting that these measurements should be used in clinical practice with caution. Myocardial acceleration, a marker of contractile function, was poorly reproducible.

Persistent bronchiolar remodeling following brief ventilation of the very immature ovine lung

Children and adults who were mechanically ventilated following preterm birth are at increased risk of reduced lung function, suggesting small airway dysfunction. We hypothesized that short periods of mechanical ventilation of very immature lungs can induce persistent bronchiolar remodeling that may adversely affect later lung function. Our objectives were to characterize the effects of brief, positive-pressure ventilation per se on the small airways in very immature, surfactant-deficient lungs and to determine whether the effects persist after the cessation of ventilation. Fetal sheep (0.75 of term) were mechanically ventilated in utero with room air (peak inspiratory pressure 40 cmH2O, positive end-expiratory pressure 4 cmH2O, 65 breaths/min) for 6 or 12 h, after which tissues were collected; another group was studied 7 days after 12-h ventilation. Age-matched unventilated fetuses were controls. The mean basement membrane perimeter of airways analyzed was 548.6+/-8.5 microm and was not different between groups. Immediately after ventilation, 21% of airways had epithelial injury; in airways with intact epithelium, there was more airway smooth muscle (ASM) and less collagen, and the epithelium contained more mucin-containing and apoptotic cells and fewer proliferating cells. Seven days after ventilation, epithelial injury was absent but the epithelium was thicker, with greater cell turnover; there were increased amounts of bronchiolar collagen and ASM and fewer alveolar attachments. The increase in ASM was likely due to cellular hypertrophy rather than hyperplasia. We conclude that brief mechanical ventilation of the very immature lung induces remodeling of the bronchiolar epithelium and walls that lasts for at least 7 days; such changes could contribute to later airway dysfunction.

Effects of long-term sildenafil treatment for pulmonary hypertension in infants with chronic lung disease

OBJECTIVE

To determine the clinical course and outcomes of infants with chronic lung disease (CLD) and pulmonary hypertension (PH) who received prolonged sildenafil therapy.

STUDY DESIGN

We conducted a retrospective review of 25 patients <2 years of age with CLD in whom sildenafil was initiated for the treatment of PH while they were hospitalized from January 2004 to October 2007. Hemodynamic improvement was defined by a 20% decrease in the ratio of pulmonary to systemic systolic arterial pressure or improvement in the degree of ventricular septal flattening with serial echocardiograms.

RESULTS

Chronic sildenafil therapy (dose range, 1.5-8.0 mg/kg/d) was initiated at a median of 171 days of age (range, 14-673 days of age) for a median duration of 241 days (range, 28-950 days). Twenty-two patients (88%) achieved hemodynamic improvement after a median treatment duration of 40 days (range, 6-600 days). Eleven of the 13 patients with interval estimates of systolic pulmonary artery pressure with echocardiogram showed clinically significant reductions in PH. Five patients (20%) died during the follow-up period. Adverse events leading to cessation or interruption of therapy occurred in 2 patients, 1 for recurrent erections, and the other had the medication held briefly because of intestinal pneumatosis.

CONCLUSION

These data suggest that chronic sildenafil therapy is well-tolerated, safe, and effective for infants with PH and CLD.

Airway dimensions in bronchopulmonary dysplasia: implications for airflow obstruction

The cause of lung function abnormalities in bronchopulmonary dysplasia (BPD) is incompletely understood, even in the "new era" of this disease. Altered airway wall dimensions are important in the pathogenesis of airflow obstruction in diseases such as asthma and chronic obstructive pulmonary disease. Whether airway wall dimensions contribute to lung function abnormalities in BPD is unknown. The purpose of this study was to investigate airway wall dimensions in relation to airway size in BPD. Lung tissue of patients with BPD was obtained at autopsy, and lung tissue from children who died from sudden infant death syndrome (SIDS) served as control. Airway wall dimensions and epithelial loss were measured in 75 airways from 5 BPD patients and 176 airways from 11 SIDS patients. Repeated measures analysis of variance was used to assess the relationships between airway wall dimensions and airway size for BPD and SIDS patients. Little epithelial loss was present in the BPD patients while extensive loss was observed in some of the SIDS patients. The inner wall area, outer wall area, epithelium area and smooth muscle area were all substantially larger (all P < 0.001) in BPD than in SIDS patients. It is likely that the increased thickness of the airway wall components contributes to airflow obstruction in BPD patients.

Pulmonary vein stenosis: prematurity and associated conditions

OBJECTIVE

Pulmonary vein stenosis is a rare, although often lethal, anomaly. Risk factors for the diagnosis of pulmonary vein stenosis are poorly characterized. In this study we sought to identify factors associated with pulmonary vein stenosis, paying particular attention to preterm birth.

METHODS

By review of the cardiac database we identified all of the subjects with pulmonary vein stenosis over a 10-year period at our institution. Those children with anomalous pulmonary venous connection were not included. Patient-related variables were analyzed for their association with pulmonary vein stenosis. Pulmonary vein stenosis was diagnosed by spectral Doppler interrogation of the pulmonary veins (continuous, turbulent flow with calculated mean gradient > 5 mm Hg) and confirmed by cardiac catheterization in nearly all of the cases.

RESULTS

Twenty-six patients with pulmonary vein stenosis were identified. The median age at diagnosis was 7.4 months; range: 1 day to 35 months. Congenital heart defects were present in the majority of subjects. Associated genetic syndromes were present in 8 subjects (31%). The 2-year survival rate from diagnosis was 43%. The majority of subjects (16 [61%]) were preterm. Gestational ages ranged from 24.2 to 41.0 weeks, and birth weights ranged from 460 to 4445 g. Preterm birth was strongly associated with the diagnosis of pulmonary vein stenosis, odds ratio 10.2 (95% CI 4.7-22.6), p < .001. Eleven (42%) of the 26 subjects were treated for bronchopulmonary dysplasia before being diagnosed with pulmonary vein stenosis.

CONCLUSIONS

Prematurity is associated with the diagnosis of pulmonary vein stenosis. It is interesting to note that many of these patients also have intracardiac shunt lesions, which may act in concert with preterm endothelium to produce pulmonary vein stenosis.

Blunted hypoxic pulmonary vasoconstriction in experimental neonatal chronic lung disease

RATIONALE

Neonatal chronic lung disease (CLD), caused by prolonged mechanical ventilation (MV) with O(2)-rich gas, is the most common cause of long-term hospitalization and recurrent respiratory illness in extremely premature infants. Recurrent episodes of hypoxemia and associated ventilator adjustments often lead to worsening CLD. The mechanism that causes these hypoxemic episodes is unknown. Hypoxic pulmonary vasoconstriction (HPV), which is partially controlled by O(2)-sensitive voltage-gated potassium (K(v)) channels, is an important adaptive response to local hypoxia that helps to match perfusion and ventilation in the lung.

OBJECTIVES

To test the hypothesis that chronic lung injury (CLI) impairs HPV.

METHODS

We studied preterm lambs that had MV with O(2)-rich gas for 3 weeks and newborn rats that breathed 95%-O(2) for 2 weeks, both of which resulted in airspace enlargement and pulmonary vascular changes consistent with CLD.

MEASUREMENTS AND MAIN RESULTS

HPV was attenuated in preterm lambs with CLI after 2 weeks of MV and in newborn rats with CLI after 2 weeks of hyperoxia. HPV and constriction to the K(v)1.x-specific inhibitor, correolide, were preferentially blunted in excised distal pulmonary arteries (dPAs) from hyperoxic rats, whose dPAs exhibited decreased K(v)1.5 and K(v)2.1 mRNA and K(+) current. Intrapulmonary gene transfer of K(v)1.5, encoding the ion channel that is thought to trigger HPV, increased O(2)-sensitive K(+) current in cultured smooth muscle cells from rat dPAs, and restored HPV in hyperoxic rats.

CONCLUSIONS

Reduced expression/activity of O(2)-sensitive K(v) channels in dPAs contributes to blunted HPV observed in neonatal CLD.

Clinical utility of echocardiography for the diagnosis and management of pulmonary vascular disease in young children with chronic lung disease

OBJECTIVE

The goal was to determine the clinical utility of Doppler echocardiography in predicting the presence and severity of pulmonary hypertension in patients with chronic lung disease who subsequently underwent cardiac catheterization.

METHODS

A retrospective review of data for all patients < 2 years of age with a diagnosis of bronchopulmonary dysplasia, congenital diaphragmatic hernia, or lung hypoplasia who underwent echocardiography and subsequently underwent cardiac catheterization for evaluation of pulmonary hypertension was performed. The accuracy of echocardiography in diagnosing pulmonary hypertension, on the basis of estimated systolic pulmonary artery pressure, was compared with the detection of pulmonary hypertension with the standard method of cardiac catheterization.

RESULTS

Thirty-one linked measurements for 25 children were analyzed. Systolic pulmonary artery pressure could be estimated in 61% of studies, but there was poor correlation between echocardiography and cardiac catheterization measures of systolic pulmonary artery pressure in these infants. Compared with cardiac catheterization measurements, echocardiographic estimates of systolic pulmonary artery pressure diagnosed correctly the presence or absence of pulmonary hypertension in 79% of the studies in which systolic pulmonary artery pressure was estimated but determined the severity of pulmonary hypertension (severe pulmonary hypertension was defined as pulmonary/systemic pressure ratio of > or = 0.67) correctly in only 47% of those studies. Seven (58%) of 12 children without estimated systolic pulmonary artery pressure demonstrated pulmonary hypertension during subsequent cardiac catheterization. In the absence of estimated systolic pulmonary artery pressure, qualitative echocardiographic findings, either alone or in combination, had worse predictive value for the diagnosis of pulmonary hypertension.

CONCLUSION

As used in clinical practice, echocardiography often identifies pulmonary hypertension in young children with chronic lung disease; however, estimates of systolic pulmonary artery pressure were not obtained consistently and were not reliable for determining the severity of pulmonary hypertension.

Pulmonary artery hypertension in formerly premature infants with bronchopulmonary dysplasia: clinical features and outcomes in the surfactant era

BACKGROUND

Although abnormal pulmonary vascular structure and function in preterm infants with bronchopulmonary dysplasia may predispose infants to pulmonary artery hypertension, little is known about the characteristics and outcomes of bronchopulmonary dysplasia-associated pulmonary artery hypertension in the surfactant era.

METHODS

We studied 42 premature infants (< 32 weeks of gestation) with bronchopulmonary dysplasia who were diagnosed as having pulmonary artery hypertension > or = 2 months after birth, between 1998 and 2006, at a median age of 4.8 months. Pulmonary artery hypertension was graded through echocardiography for all patients; 13 patients also underwent cardiac catheterization.

RESULTS

Eighteen (43%) of 42 patients had severe pulmonary artery hypertension (systemic or suprasystemic right ventricular pressure). Among 13 patients who underwent catheterization, the mean pulmonary artery pressure was 43 +/- 8 mmHg and the pulmonary vascular resistance index was 9.9 +/- 2.8 Wood units. In 12 patients, pulmonary artery pressure and pulmonary vascular resistance improved with 100% oxygen and 80 ppm inhaled nitric oxide but remained elevated. The pulmonary vascular resistance index decreased to 7.9 +/- 3.8 Wood units in 100% oxygen and to 6.4 +/- 3.1 Wood units with the addition of nitric oxide. Sixteen patients (38%) died during the follow-up period. Estimated survival rates were 64% +/- 8% at 6 months and 53% +/- 11% at 2 years after diagnosis of pulmonary artery hypertension. In multivariate analyses, severe pulmonary artery hypertension and small birth weight for gestational age were associated with worse survival rates. Among 26 survivors (median follow-up period: 9.8 months), pulmonary artery hypertension was improved, relative to its most severe level, in 24 patients (89%).

CONCLUSION

Premature infants with bronchopulmonary dysplasia and severe pulmonary artery hypertension are at high risk of death, particularly during the first 6 months after diagnosis of pulmonary artery hypertension.