Lung growth and maturation after tracheal occlusion in diaphragmatic hernia

Fetoscopic endoluminal tracheal occlusion vs expectant management for fetuses with severe left-sided congenital diaphragmatic hernia

BACKGROUND

The treatment of fetuses with a congenital diaphragmatic hernia is challenging, but there is evidence that fetoscopic endoluminal tracheal occlusion has a benefit over expectant care. In addition, standardization and expertism have a great impact on survival and are probably crucial in centers that rely on expectant management with extracorporeal membrane oxygenation after birth.

OBJECTIVE

This study aimed to examine the survival and morbidity rates of fetuses with a severe isolated left-sided congenital diaphragmatic hernia who underwent fetoscopic endoluminal tracheal occlusion vs expectant management in high-volume centers.

STUDY DESIGN

This was a multicenter, retrospective study that included all consecutive fetuses with severe isolated left-sided congenital diaphragmatic hernia who were expectantly managed in a German center or who underwent fetoscopic endoluminal tracheal occlusion in 3 other European centers (Belgium, France, and Italy). Severe congenital diaphragmatic hernia was defined as having an observed to expected total fetal lung volume ≤35% with intrathoracic position of the liver diagnosed with magnetic resonance imaging. All magnetic resonance images were centralized, and lung volumes were measured by 2 experienced operators who were blinded to the pre- and postnatal data. Multiple logistic regression analyses were performed to examine the effect of the management strategy in the 2 groups on the short- and long-term outcomes.

RESULTS

A total of 147 patients who were managed expectantly and 47 patients who underwent fetoscopic endoluminal tracheal occlusion were analyzed. Fetuses who were managed expectantly had lower observed to expected total fetal lung volumes (20.6%±7.5% vs 23.7%±6.8%; P=.013), higher gestational age at delivery (median weeks of gestation, 37.4; interquartile range, 36.6-38.00 vs 35.1; interquartile range, 33.1-37.2; P<.001), and more frequent use of extracorporeal membrane oxygenation (55.8% vs 4.3%; P<.001) than the fetuses who underwent fetoscopic endoluminal tracheal occlusion. The survival rates at discharge and at 2 years of age in the expectant management group were higher than the survival rates of the fetoscopic endoluminal tracheal occlusion group (74.3% vs 44.7%; P=.001 and 72.8% vs 42.5%; P=.001, respectively). After adjustment for maternal age, gestational age at birth, observed to expected total fetal lung volume, and birth weight Z-score, the odds ratios were 4.65 (95% confidence interval, 1.9-11.9; P=.001) and 4.37 (95% confidence interval, 1.8-11.0; P=.001), respectively.

CONCLUSION

Fetuses with a severe isolated left-sided congenital diaphragmatic hernia had a higher survival rate when treated in an experienced center in Germany with antenatal expectant management and frequent use of extracorporeal membrane oxygenation during the postnatal period than fetuses who were treated with fetoscopic endoluminal tracheal occlusion in 3 centers in Belgium, France, and Italy.

Impact of fetal treatments for congenital diaphragmatic hernia on lung development

The extent of lung hypoplasia impacts the survival and severity of morbidities associated with congenital diaphragmatic hernia (CDH). The alveoli of CDH infants and in experimental models of CDH have thickened septa with fewer type II pneumocytes and capillaries. Fetal treatments of CDH-risk preterm birth. Therefore, treatments must aim to balance the need for increased gas exchange surface area with the restoration of pulmonary epithelial type II cells and the long-term respiratory and neurodevelopmental consequences of prematurity. Achievement of sufficient lung development in utero for successful postnatal transition requires adequate intra-thoracic space for lung growth, maintenance of sufficient volume and appropriate composition of fetal lung fluid, regular fetal breathing movements, appropriate gas exchange area, and ample surfactant production. The review aims to examine the rationale for current and future therapeutic strategies to improve postnatal outcomes of infants with CDH.

How should fetal surgery for congenital diaphragmatic hernia be implemented in the post-TOTAL trial era: a discussion. Prenat Diagn 2022;42:301-309. [PMID: 35032132 DOI: 10.1002/pd.6091]

Following prenatal diagnosis of congenital diaphragmatic hernia, severity can be predicted based on the presence of associated abnormalities, and in isolated cases, on lung size and position of the liver. Severe hypoplasia is defined by a contralateral lung size < 25% on ultrasound; moderate hypoplasia is when that lung measures between 25 and 45% of the normal. In fetuses with predicted poor postnatal outcome a procedure that reverses pulmonary hypoplasia may be considered. In uncontrolled studies, fetoscopic endoluminal tracheal occlusion (FETO) improved neonatal outcome. Recently, two randomized controlled trials compared the neonatal and infant outcomes in fetuses with isolated CDH (www.totaltrial.eu). In severe cases, FETO was carried out at 27⁺⁰ -29⁺⁶ weeks' gestation (referred to as "early") and in moderate at 30⁺⁰ -31⁺⁶ weeks ("late"). Survival to discharge from the neonatal intensive care unit increased by 25% (95%-CI:+6 - +46; P=.0091) and 13% (-1 - +28; P=.059), in fetuses with severe and moderate cases, respectively. Following FETO gestational age at delivery was on average 3.2 (2.3-4.1) weeks earlier following early and 1.7 (1.1 - 2.3) following late FETO. Here the strengths and weaknesses of the TOTAL trials and their translation to the clinic are debated. Discussants are the lead for the trial (JD) and a colleague (AF) not involved. The discussant notes that the observed survival, both in treated and expectantly managed fetuses, was overall less than what is reported by some high volume centers, particularly in North America. Additional criticisms are the potential effects of prematurity on the long term, the inclusion of low-volume centers, and the potential of FETO for severe iatrogenic complications. Therefore results may not be generalizable. The discussants concluded that although FETO may have its value it remains a procedure with a high risk for prematurity and it can be lethal when the balloon cannot be removed prior to delivery. This article is protected by copyright. All rights reserved.

Stretch increases alveolar type 1 cell number in fetal lungs through ROCK-Yap/Taz pathway

Accurate fluid pressure in the fetal lung is critical for its development, especially at the beginning of the saccular stage when alveolar epithelial type 1 (AT1) and type 2 (AT2) cells differentiate from the epithelial progenitors. Despite our growing understanding of the role of physical forces in lung development, the molecular mechanisms that regulate the transduction of mechanical stretch to alveolar differentiation remain elusive. To simulate lung distension, we optimized both an ex vivo model with precision cut lung slices and an in vivo model of fetal tracheal occlusion. Increased mechanical tension showed to improve alveolar maturation and differentiation toward AT1. By manipulating ROCK pathway, we demonstrate that stretch-induced Yap/Taz activation promotes alveolar differentiation toward AT1 phenotype via ROCK activity. Our findings show that balanced ROCK-Yap/Taz signaling is essential to regulate AT1 differentiation in response to mechanical stretching of the fetal lung, which might be helpful in improving lung development and regeneration.

Unsuccessful Intubation and Stabilization by Laryngeal Mask Airway in the Delivery Room: A Case of Tracheal Atresia

A term male newborn infant was apneic at birth, and endotracheal intubation was unsuccessful. He was stabilized for transport with a laryngeal mask airway. Laryngoscopy revealed tracheal atresia with intrathoracic distal tracheoesophageal fistula. A laryngeal mask airway may provide ventilation in tracheal atresia patients with a fistula.

Reversible Fetal Tracheal Occlusion in Mice: A Novel Minimal Invasive Technique

BACKGROUND

There is a certain need for reversible, cheap, and reproducible animal models for understanding the impact of tracheal occlusion (TO) in the congenital diaphragmatic hernia and pathophysiology. We aimed to present an easy, reversible, and minimally invasive murine TO model with optimized time points for introduction and removal of TO.

METHODS

Time-mated C57BL/6 mice underwent laparotomy at embryonic day 16.5 (E16.5) with transuterine TO performed on two fetuses in each uterine horn. In the TO group, the fetuses were harvested at E18.5 without suture removal; the suture was released at E17.5 in the TO-R group, and all fetuses were harvested at E18.5. The lungs of the fetuses were compared by morphometric and histologic analysis.

RESULTS

Successful TO was confirmed in 34 of 37 fetuses. Twenty-nine of them survived to E18.5 (90.6%), six of the fetuses had a spontaneous vaginal delivery. Fetal weights were comparable, but there was significant difference in lung weights and lung-to-body weight ratios (0.020 ± 0.006 [control] versus 0.026 ± 0.002 [TO] versus 0.023 ± 0.005 [TO-R]; P = 0.013). DNA/protein and DNA/lung weight ratios were elevated, whereas protein/lung weight ratio was lower in TO compared with the control group.

CONCLUSIONS

Reversal of fetal transuterine TO at E17.5, which was put at E16.5 in mice, is feasible with comparable outcomes to other current animal models with certain advantages and potential to translate the studies to the human.

Update on Congenital Diaphragmatic Hernia

Congenital diaphragmatic hernia (CDH) is a rare developmental defect of the diaphragm, characterized by herniation of abdominal contents into the chest that results in varying degrees of pulmonary hypoplasia and pulmonary hypertension (PH). Significant advances in the prenatal diagnosis and identification of prognostic factors have resulted in the continued refinement of the approach to fetal therapies for CDH. Postnatally, protocolized approaches to lung-protective ventilation, nutrition, prevention of infection, and early aggressive management of PH have led to improved outcomes in infants with CDH. Advances in our understanding of the associated left ventricular (LV) hypoplasia and myocardial dysfunction in infants with severe CDH have allowed for the optimization of hemodynamics and management of PH. This article provides a comprehensive review of CDH for the anesthesiologist, focusing on the complex pathophysiology, advances in prenatal diagnosis, fetal interventions, and optimal postnatal management of CDH.

Artificial placenta and womb technology: Past, current, and future challenges towards clinical translation

Extreme prematurity remains a major cause of neonatal mortality and severe long-term morbidity. Current neonatal care is associated with significant morbidity due to iatrogenic injury and developmental immaturity of extreme premature infants. A more physiologic approach, replacing placental function and providing a womb-like environment, is the foundational principle of artificial placenta (AP) and womb (AW) technology. The concept has been studied during the past 60 years with limited success. However, recent technological advancements and a greater emphasis on mimicking utero-placental physiology have improved the success of experimental models, bringing the technology closer to clinical translation. Here, we review the rationale for and history of AP and AW technology, discuss the challenges that needed to be overcome, and compare recent successful models. We conclude by outlining some remaining challenges to be addressed on the path towards clinical translation and opportunities for future research.

Complementary Effect of Maternal Sildenafil and Fetal Tracheal Occlusion Improves Lung Development in the Rabbit Model of Congenital Diaphragmatic Hernia

OBJECTIVE

To evaluate the effect of combining antenatal sildenafil with fetal tracheal occlusion (TO) in fetal rabbits with surgically induced congenital diaphragmatic hernia (CDH).

BACKGROUND

Although antenatal sildenafil administration rescues vascular abnormalities in lungs of fetal rabbits with CDH, it only partially improves airway morphometry. We hypothesized that we could additionally stimulate lung growth by combining this medical treatment with fetal TO.

METHODS

CDH was created on gestational day (GD)23 (n=54). Does were randomized to receive either sildenafil 10 mg/kg/d or placebo by subcutaneous injection from GD24 to GD30. On GD28, fetuses were randomly assigned to TO or sham neck dissection. At term (GD30) fetuses were delivered, ventilated, and finally harvested for histological and molecular analyses. Unoperated littermates served as controls.

RESULTS

The lung-to-body-weight ratio was significantly reduced in sham-CDH fetuses either (1.2 ± 0.3% vs 2.3 ± 0.3% in controls, P=0.0003). Sildenafil had no effect on this parameter, while CDH fetuses undergoing TO had a lung-to-body-weight ratio comparable to that of controls (2.5 ± 0.8%, P<0.0001). Sildenafil alone induced an improvement in the mean terminal bronchiolar density (2.5 ± 0.8 br/mm vs 3.5 ± 0.9 br/mm, P=0.043) and lung mechanics (static elastance 61 ± 36 cmH2O /mL vs 113 ± 40 cmH2O/mL, P=0.008), but both effects were more pronounced in fetuses undergoing additional TO (2.1 ± 0.8 br/mm, P=0.001 and 31 ± 9 cmH2O/mL, P<0.0001 respectively). Both CDH-sham and CDH-TO fetuses treated with placebo had an increased medial wall thickness of peripheral pulmonary vessels (41.9 ± 2.9% and 41.8 ± 3.2%, vs 24.0 ± 2.9% in controls, P<0.0001). CDH fetuses treated with sildenafil, either with or without TO, had a medial thickness in the normal range (29.4% ± 2.6%). Finally, TO reduced gene expression of vascular endothelial growth factor and surfactant protein A and B, but this effect was counteracted by sildenafil.

CONCLUSION

In the rabbit model for CDH, the combination of maternal sildenafil and TO has a complementary effect on vascular and parenchymal lung development.

Heterogeneous Response in Rabbit Fetal Diaphragmatic Hernia Lungs After Tracheal Occlusion

BACKGROUND

Fetal tracheal occlusion (TO) is an experimental therapeutic approach to stimulate lung growth in the most severe congenital diaphragmatic hernia (CDH) cases. We have previously demonstrated a heterogeneous response of normal fetal rabbit lungs after TO with the appearance of at least two distinct zones. The aim of this study was to examine the fetal lung response after TO in a left CDH fetal rabbit model.

METHODS

Fetal rabbits at 25 d gestation underwent surgical creation of CDH followed by TO at 27 d and harvest on day 30. Morphometric analysis, global metabolomics, and fluorescence lifetime imaging microscopy (FLIM) were performed to evaluate structural and metabolic changes in control, CDH, and CDH + TO lungs.

RESULTS

Right and left lungs were different at the baseline and had a heterogeneous pulmonary growth response in CDH and after TO. The relative percent growth of the right lungs in CDH + TO was higher than the left lungs. Morphometric analyses revealed heterogeneous tissue-to-airspace ratios, in addition to size and number of airspaces within and between the lungs in the different groups. Global metabolomics demonstrated a slower rate of metabolism in the CDH group with the left lungs being less metabolically active. TO stimulated metabolic activity in both lungs to different degrees. FLIM analysis demonstrated local heterogeneity in glycolysis, oxidative phosphorylation (OXPHOS), and FLIM "lipid-surfactant" signal within and between the right and left lungs in all groups.

CONCLUSIONS

We demonstrate that TO leads to a heterogeneous morphologic and metabolic response within and between the right and left lungs in a left CDH rabbit model.

Characterization of a reversible thermally-actuated polymer-valve: A potential dynamic treatment for congenital diaphragmatic hernia

BACKGROUND

Congenital diaphragmatic hernia (CDH) is a fetal defect comprising an incomplete diaphragm and the herniation of abdominal organs into the chest cavity that interfere with fetal pulmonary development. Though the most promising treatment for CDH is via interventional fetoscopic tracheal occlusion (TO) surgery in-utero, it has produced mixed results due to the static nature of the inserted occlusion. We hypothesize that a suitable noninvasively-actuatable, cyclic-release tracheal occlusion device can be developed to enable dynamic tracheal occlusion (dTO) implementation.

OBJECTIVE

To conduct an in-vitro proof-of-concept investigation of the construction of thermo-responsive polymer valves designed for targeted activation within a physiologically realizable temperature range as a first step towards potential development of a noninvasively-actuatable implantable device to facilitate dynamic tracheal occlusion (dTO) therapy.

METHODS

Six thermo-responsive polymer valves, with a critical solution temperature slightly higher than normal physiological body temperature of 37°C, were fabricated using a copolymer of n-isopropylacrylamide (NIPAM) and dimethylacrylamide (DMAA). Three of the valves underwent ethylene oxide (EtO) sterilization while the other three served as controls for EtO-processing compatibility testing. Thermal response actuation of the valves and their steady-state flow performances were evaluated using water and caprine amniotic fluid.

RESULTS

All six valves consisting of 0.3-mole fraction of DMAA were tested for thermal actuation of caprine amniotic fluid flow at temperatures ranging from 30-44°C. They all exhibited initiation of valve actuation opening at ~40°C with full completion at ~44°C. The overall average coefficient of variation (CV) for the day-to-day flow performance of the valves tested was less than 12%. Based on a Student t-test, there was no significant difference in the operational characteristics for the EtO processed versus the non-EtO processed valves tested.

CONCLUSIONS

We successfully fabricated and demonstrated physiological realizable temperature range operation of thermo-responsive polymer valves in-vitro and their suitability for standard EtO sterilization processing, a prerequisite for future in-vivo surgical implantation testing.

Comparative analysis of the mechanical signals in lung development and compensatory growth

This review compares the manner in which physical stress imposed on the parenchyma, vasculature and thorax and the thoraco-pulmonary interactions, drive both developmental and compensatory lung growth. Re-initiation of anatomical lung growth in the mature lung is possible when the loss of functioning lung units renders the existing physiologic-structural reserves insufficient for maintaining adequate function and physical stress on the remaining units exceeds a critical threshold. The appropriate spatial and temporal mechanical interrelationships and the availability of intra-thoracic space, are crucial to growth initiation, follow-on remodeling and physiological outcome. While the endogenous potential for compensatory lung growth is retained and may be pharmacologically augmented, supra-optimal mechanical stimulation, unbalanced structural growth, or inadequate remodeling may limit functional gain. Finding ways to optimize the signal-response relationships and resolve structure-function discrepancies are major challenges that must be overcome before the innate compensatory ability could be fully realized. Partial pneumonectomy reproducibly removes a known fraction of functioning lung units and remains the most robust model for examining the adaptive mechanisms, structure-function consequences and plasticity of the remaining functioning lung units capable of regeneration. Fundamental mechanical stimulus-response relationships established in the pneumonectomy model directly inform the exploration of effective approaches to maximize compensatory growth and function in chronic destructive lung diseases, transplantation and bioengineered lungs.

Lung Structure and the Intrinsic Challenges of Gas Exchange

Structural and functional complexities of the mammalian lung evolved to meet a unique set of challenges, namely, the provision of efficient delivery of inspired air to all lung units within a confined thoracic space, to build a large gas exchange surface associated with minimal barrier thickness and a microvascular network to accommodate the entire right ventricular cardiac output while withstanding cyclic mechanical stresses that increase several folds from rest to exercise. Intricate regulatory mechanisms at every level ensure that the dynamic capacities of ventilation, perfusion, diffusion, and chemical binding to hemoglobin are commensurate with usual metabolic demands and periodic extreme needs for activity and survival. This article reviews the structural design of mammalian and human lung, its functional challenges, limitations, and potential for adaptation. We discuss (i) the evolutionary origin of alveolar lungs and its advantages and compromises, (ii) structural determinants of alveolar gas exchange, including architecture of conducting bronchovascular trees that converge in gas exchange units, (iii) the challenges of matching ventilation, perfusion, and diffusion and tissue-erythrocyte and thoracopulmonary interactions. The notion of erythrocytes as an integral component of the gas exchanger is emphasized. We further discuss the signals, sources, and limits of structural plasticity of the lung in alveolar hypoxia and following a loss of lung units, and the promise and caveats of interventions aimed at augmenting endogenous adaptive responses. Our objective is to understand how individual components are matched at multiple levels to optimize organ function in the face of physiological demands or pathological constraints.

Intrapulmonary instillation of perflurooctylbromide improves lung growth, alveolarization, and lung mechanics in a fetal rabbit model of diaphragmatic hernia

OBJECTIVES

Fetal tracheal occlusion of hypoplastic rabbit lungs results in lung growth and alveolarization although the surfactant protein messenger RNA expression is decreased and the transforming growth factor-β pathway induced. The prenatal filling of healthy rabbit lungs with perfluorooctylbromide augments lung growth without suppression of surfactant protein synthesis. We hypothesizes that Intratracheal perfluorooctylbromide instillation improves lung growth, mechanics, and extracellular matrix synthesis in a fetal rabbit model of lung hypoplasia induced by diaphragmatic hernia.

SETTING AND INTERVENTIONS

On day 23 of gestation, DH was induced by fetal surgery in healthy rabbit fetuses. Five days later, 0.8ml of perfluorooctylbromide (diaphragmatic hernia-perfluorooctylbromide) or saline (diaphragmatic hernia-saline) was randomly administered into the lungs of previously operated fetuses. After term delivery (day 31), lung mechanics, lung to body weight ratio, messenger RNA levels of target genes, assessment of lung histology, and morphological distribution of elastin and collagen were determined. Nonoperated fetuses served as controls.

MEASUREMENTS AND MAIN RESULTS

Fetal instillation of perfluorooctylbromide in hypoplastic lungs resulted in an improvement of lung-to-body weight ratio (0.016 vs 0.013 g/g; p = 0.05), total lung capacity (23.4 vs 15.4 μL/g; p = 0.03), and compliance (2.4 vs 1.2 mL/cm H2O; p = 0.007) as compared to diaphragmatic hernia-saline. In accordance with the results from lung function analysis, elastin staining of pulmonary tissue revealed a physiological distribution of elastic fiber to the tips of the secondary crests in the diaphragmatic hernia-perfluorooctylbromide group. Likewise, messenger RNA expression was induced in genes associated with extracellular matrix remodeling (matrix metalloproteinase-2, tissue inhibitor of metalloproteinase-1, and tissue inhibitor of metalloproteinase-2). Surfactant protein expression was similar in the diaphragmatic hernia-perfluorooctylbromide and diaphragmatic hernia-saline groups. Distal airway size, mean linear intercept, as well as airspace and tissue fractions were similar in diaphragmatic hernia-perfluorooctylbromide, diaphragmatic hernia-saline, and control groups.

CONCLUSIONS

Fetal perfluorooctylbromide treatment improves lung growth, lung mechanics, and extracellular matrix remodeling in hypoplastic lungs, most probably due to transient pulmonary stretch, preserved fetal breathing movements, and its physical characteristics. Perfluorooctylbromide instillation is a promising approach for prenatal therapy of lung hypoplasia.

Airway and vascular maturation stimulated by tracheal occlusion do not correlate in the rabbit model of diaphragmatic hernia

BACKGROUND

In animal models of congenital diaphragmatic hernia (CDH), tracheal occlusion (TO) has induced maturation of both airway spaces and vascular structures. Airway and vascular response to TO are assumed to occur in parallel. This study aims to describe and measure the relationship between airway and vascular maturation induced by TO.

METHODS

A rabbit model of CDH on gestational day (GD) 23 and TO on GD 28 (term = GD 31) has been used. Two study groups have been defined: DH (diaphragmatic hernia) and TO (DH treated with TO). Animals were collected on GD 30 and blood flow data of the pulmonary artery (pulsatility index (PI) and fractional moving blood volume) were ultrasonographically measured. Lung morphometry consisted of measurements of radial alveolar count (RAC) and arterial muscular thickness.

RESULTS

Animals in the DH group (n = 9) had the worst hemodynamic parameters; their lungs were hypoplastic and had the thickest arterial muscular layer. Animals in the TO group (n = 10) had all these effects reversed. There were no correlations among hemodynamic, airway, and vascular parameters, except for RAC and PI (r = -0.528, P = 0.043).

CONCLUSION

Airway and vascular maturation after TO appear to be uncorrelated effects. TO could trigger several pathways that separately regulate airway and vascular responses.

Alveolarization genes modulated by fetal tracheal occlusion in the rabbit model for congenital diaphragmatic hernia: a randomized study

Background

The mechanisms by which tracheal occlusion (TO) improves alveolarization in congenital diaphragmatic hernia (CDH) are incompletely understood. Therefore transcriptional and histological effects of TO on alveolarization were studied in the rabbit model for CDH. The question of the best normalization strategy for gene expression analysis was also addressed.

Methods

Fetal rabbits were randomized for CDH or sham operation on gestational day 23/31 and for TO or sham operation on day 28/31 resulting in four study groups. Untouched littermates were added. At term and before lung harvest, fetuses were subjected to mechanical ventilation or not. Quantitative real-time PCR was performed on lungs from 4–5 fetuses of each group with and without previous ventilation. Stability of ten housekeeping genes (HKGs) and optimal number of HKGs for normalization were determined, followed by assessment of HKG expression levels. Expression levels of eleven target genes were studied in ventilated lungs, including genes regulating elastogenesis, cell-environment interactions, and thinning of alveolar walls. Elastic staining, immunohistochemistry and Western blotting completed gene analysis.

Results

Regarding HKG expression, TO increased β-actin and β-subunit of ATP synthase. Mechanical ventilation increased β-actin and β2-microglobulin. Flavoprotein subunit of succinate dehydrogenase and DNA topoisomerase were the most stable HKGs. CDH lungs showed disorganized elastin deposition with lower levels for tropoelastin, fibulin-5, tenascin-C, and α6-integrin. After TO, CDH lungs displayed a normal pattern of elastin distribution with increased levels for tropoelastin, fibulin-5, tenascin-C, α6-integrin, ß1-integrin, lysyl oxidase, and drebrin. TO increased transcription and immunoreactivity of tissue inhibitor of metalloproteinase-1.

Conclusions

Experimental TO might improve alveolarization through the mechanoregulation of crucial genes for late lung development. However part of the transcriptional changes involved genes that were not affected in CDH, raising the question of TO-induced disturbances of alveolar remodeling. Attention should also be paid to selection of HKGs for studies on mechanotransduction-mediated gene expressions.

The use of ruminant models in biomedical perinatal research

Animal models are of critical importance in biomedical research. Although rodents and lagomorphs are the most commonly used species, larger species are required, especially when surgical approaches or new medical devices have to be evaluated. In particular, in the field of perinatal medicine, they are critical for the evaluation of new pharmacologic treatments and the development of new invasive procedures in fetuses. In some areas, such as developmental genetics, reproductive biotechnologies and metabolic programming, the contribution of ruminants is essential. The current report focuses on some of the most outstanding examples of great biomedical advances carried out with ruminant models in the field of perinatal research. Experiments recently carried in our research unit using ruminants are also briefly described.

Intraluminal tracheal occlusion using a modified 8-mm Z-stent in a sheep model of left-sided congenital diaphragmatic hernia

OBJECTIVE

To evaluate pulmonary growth and development after fetoscopic intraluminal tracheal occlusion (FITO) using a modified 8-mm Z-stent in an ovine model of congenital left-sided diaphragmatic hernia (CDH).

METHODS

Thirty-three time-dated ewes were studied: Group I: healthy controls; Group II: CDH controls (untreated); Group III: CDH treated with FITO. CDH was created in Groups II and III at 70-80 days' gestation. FITO was performed at 100-110 days. Left lung histological, morphometric, immunohistochemical and biochemical studies were conducted after delivery and euthanasia at 138 days.

RESULTS

Fifteen (45%) animals (Group I: 3; Group II: 5; Group III: 7) were available for analysis. The left lung parenchymal volume to fetal weight ratios were similar between Groups I and III (p = 0.24), and higher than Group II (p < 0.05III (79 versus 75%, p = 0.26), compared to 41% in Group II (p < 0.05). Pulmonary hypoplasia occurred in 1/7 (16%) in the FITO group, compared to 100% in Group II and 0% in Group I (p = .003). DNA and protein were significantly increased in Group III (p < 0.001). The concentration of type II pneumocytes was similar between healthy controls and the FITO group, and was paradoxically increased in untreated hernia fetuses. There was no histological evidence of tracheal injury.

CONCLUSION

FITO with a modified 8-mm Z-stent is associated with lung growth and maturation similar to controls without obvious deleterious effects. A phase I clinical trial of FITO with the modified 8-mm Z-stent in severe CDH patients seems warranted.

The long-term follow-up of patients with a congenital diaphragmatic hernia: a broad spectrum of morbidity

Congenital diaphragmatic hernia (CDH) is a life-threatening anomaly with a mortality rate of approximately 40-50%, depending on case selection. It has been suggested that new therapeutic modalities such as nitric oxide (NO), high frequency oxygenation (HFO) and extracorporal membrane oxygenation (ECMO) might decrease mortality associated with pulmonary hypertension and the sequelae of artificial ventilation. When these new therapies indeed prove to be beneficial, a larger number of children with severe forms of CDH might survive, resulting in an increase of CDH-associated complications and/or consequences. In follow-up studies of infants born with CDH, many complications including pulmonary damage, cardiovascular disease, gastro-intestinal disease, failure to thrive, neurocognitive defects and musculoskeletal abnormalities have been described. Long-term pulmonary morbidity in CDH consists of obstructive and restrictive lung function impairments due to altered lung structure and prolonged ventilatory support. CDH has also been associated with persistent pulmonary vascular abnormalities, resulting in pulmonary hypertension in the neonatal period. Long-term consequences of pulmonary hypertension are unknown. Gastro-esophageal reflux disease (GERD) is also an important contributor to overall morbidity, although the underlying mechanism has not been fully understood yet. In adult CDH survivors incidence of esophagitis is high and even Barrett's esophagus may ensue. Yet, in many CDH patients a clinical history compatible with GERD seems to be lacking, which may result in missing patients with pathologic reflux disease. Prolonged unrecognized GERD may eventually result in failure to thrive. This has been found in many young CDH patients, which may also be caused by insufficient intake due to oral aversion and increased caloric requirements due to pulmonary morbidity. Neurological outcome is determined by an increased risk of perinatal and neonatal hypoxemia in the first days of life of CDH patients. In patients treated with ECMO, the incidence of neurological deficits is even higher, probably reflecting more severe hypoxemia and the risk of ECMO associated complications. Many studies have addressed the substantial impact of the health problems described above, on the overall well-being of CDH patients, but most of them concentrate on the first years after repair and only a few studies focus on the health-related quality of life in CDH patients. Considering the scattered data indicating substantial morbidity in long-term survivors of CDH, follow-up studies that systematically assess long-term sequelae are mandatory. Based on such studies a more focused approach for routine follow-up programs may be established.

Fetal tracheal occlusion for severe congenital diaphragmatic hernia in humans: a morphometric study of lung parenchyma and muscularization of pulmonary arterioles

OBJECTIVE

The aim of this study is to examine structure of lung parenchyma (Pp) and muscularization of pulmonary arterioles (PAs) in human fetuses that underwent tracheal occlusion (TO) therapy for severe congenital diaphragmatic hernia (CDH).

MATERIAL

Fifteen fetuses underwent TO, with 5 survivors (Am J Obstet Gynecol. 2000:183;1059-1066). Paraffin-embedded lung specimens from 7 of 10 nonsurvivors (CDH-TO) and 6 age-matched fetuses (CDH) were available for morphometric analysis, which included measurements of point fraction of lung Pp and surface density. The PAs were categorized according to external diameter (<70 microm and 70 <or= 140 microm). Percent medial wall thickness (%MWT) was calculated by dividing raw measurements of MWT by external diameter.

RESULTS

Gestational age at TO was 27.6 +/- 0.9 weeks with a mean duration of TO of 32.6 +/- 6.8 days. Gestational age at delivery (CDH-TO 31.9 +/- 0.9 vs CDH 35.4 +/- 1.8 weeks; P = .18) and postnatal survival time (CDH-TO 20.5 +/- 6.0 vs CDH 18.6 +/- 7.8 days; P = .85) were not significantly different between groups. Tracheal occlusion significantly increased the lung-to-body weight ratio (CDH-TO 13.0 +/- 2.2 vs CDH 6.6 +/- 0.9; P = .02). Tracheal occlusion tended to decrease right-lung Pp (CDH-TO 54.6% +/- 2.6% vs CDH 65.7% +/- 5.9%; P = .05), whereas left-lung Pp was not different between groups (CDH-TO 63.0% +/- 3.5% vs CDH 66.7% +/- 4.1%; P = .51). Surface density of airspaces was not different between groups in either left (CDH-TO 171.3 +/- 16.1 cm(-1) vs CDH 151.1 +/- 8.1 cm(-1); P = .34) or right (CDH-TO 172.0 +/- 10.6 cm(-1) vs CDH 160.8 +/- 3.6 cm(-1); P = .33) lungs. The %MWT in small and large PA was similar between groups.

CONCLUSIONS

Open prenatal TO in human fetuses increased lung growth, as evidenced by an increase in lung weight, but did not improve parenchymal structure or muscularization of PAs.

Main bronchus occlusion for treatment of congenital diaphragmatic hernia in fetal lambs

PURPOSE

The present study investigates a new surgical approach in the treatment of left diaphragmatic hernia in fetal sheep. We postulated that unlike tracheal occlusion where both lungs are occluded, selective left main bronchus occlusion (LMBO) would accelerate growth of only the left lung, reduce left visceral herniation, and recover space in the both thoraces necessary for lung development.

METHODS

Left-sided congenital diaphragmatic hernia (CDH) was surgically created in 8 fetal lambs at approximately 65 days of gestation; in 4 of these animals, LMBO was performed at approximately 118 days. Four sham-operated animals served as controls. Lambs were delivered by hysterotomy at 137 days. We measured lung-to-body weight ratios, alveolar surface area, septal wall thickness, and AE2 cell density in the left and right lungs.

RESULTS

Left main bronchus occlusion increased (P < .05) left lung growth causing severe right mediastinal shift but failed to reduce herniated abdominal viscera in 3 of 4 lambs. Wet lung-to-body weight ratio in LMBO group was similar to that of the control group; however, this was achieved by overgrowth of left lung, whereas the right wet lung-to-body weight ratio remained low. In the LMBO group, right lung AE2 cell density was higher than that of control group and not different to that of the CDH group.

CONCLUSIONS

Left main bronchus occlusion failed to restore normal pulmonary development in CDH.

Surfactant maturation is not delayed in human fetuses with diaphragmatic hernia

BACKGROUND

Pulmonary hypoplasia and persistent pulmonary hypertension account for significant mortality and morbidity in neonates with congenital diaphragmatic hernia (CDH). Global lung immaturity and studies in animal models suggest the presence of surfactant deficiency that may further complicate the pathophysiology of CDH. However, data about surfactant status in human fetuses with CDH at birth are contradictory. The lack of a chronological study of surfactant content in late pregnancy has been a significant limitation. The appropriateness of administering surfactant supplements to neonates with CDH is therefore a debated question.

METHODS AND FINDINGS

We investigated surfactant content in human fetuses with CDH compared to age-matched fetuses with nonpulmonary diseases used as controls. Concentrations of disaturated phosphatidylcholine and surfactant proteins were found to be similar at a given stage of pregnancy, with both components showing a similar pattern of increase with progressing pregnancy in fetuses with CDH and in control fetuses. Thyroid transcription factor 1, a critical regulator of surfactant protein transcription, similarly displayed no difference in abundance. Finally, we examined the expression of three glucocorticoid-regulated diffusible mediators involved in lung epithelial maturation, namely: keratinocyte growth factor (KGF), leptin, and neuregulin 1 beta 1 (NRG1-beta1). KGF expression decreased slightly with time in control fetuses, but remained unchanged in fetuses with CDH. Leptin and NRG1-beta1 similarly increased in late pregnancy in control and CDH lungs. These maturation factors were also determined in the sheep fetus with surgical diaphragmatic hernia, in which surfactant deficiency has been reported previously. In contrast to the findings in humans, surgical diaphragmatic hernia in the sheep fetus was associated with decreased KGF and neuregulin expression. Fetoscopic endoluminal tracheal occlusion performed in the sheep model to correct lung hypoplasia increased leptin expression, partially restored KGF expression, and fully restored neuregulin expression.

CONCLUSIONS

Our results indicate that CDH does not impair surfactant storage in human fetuses. CDH lungs exhibited no trend toward a decrease in contents, or a delay in developmental changes for any of the studied surfactant components and surfactant maturation factors. Surfactant amounts are likely to be appropriate to lung size. These findings therefore do not support the use of surfactant therapy for infants with CDH. Moreover, they raise the question of the relevance of CDH animal models to explore lung biochemical maturity.

Prenatal intervention for congenital diaphragmatic hernia

Advances in prenatal ultrasound have revealed the poor natural history of fetal congenital diaphragmatic hernia (CDH) and its hidden mortality during gestation and immediately after birth. Attempts to improve this poor outcome led to the development of prenatal surgical intervention for severe CDH by Harrison and his colleagues at the University of California San Francisco. Prenatal surgical intervention for CDH has seen four phases: open fetal surgical repair, open surgical tracheal occlusion, endoscopic external tracheal occlusion, and endoscopic endoluminal tracheal occlusion. After extensive work in the laboratory, prenatal intervention has been applied in humans since 1984. With the most recent techniques, maternal risk is significantly reduced as is the incidence of preterm labor. In the meantime, the survival rate of fetuses with CDH without fetal intervention has improved mainly due to the minimization of iatrogenic lung injury by gentle ventilation, first described in 1985. However, the morbidity of the survivors with severe CDH remains high. Prenatal intervention for CDH will be justified if improvement in survival or morbidity can be demonstrated when compared to planned delivery and postnatal management with gentle ventilation strategy.

Decreased lung fibroblast growth factor 18 and elastin in human congenital diaphragmatic hernia and animal models

RATIONALE

Lung hypoplasia in congenital diaphragmatic hernia (CDH) seems to involve impaired alveolar septation. We hypothesized that disturbed deposition of elastin and expression of fibroblast growth factor 18 (FGF18), an elastogenesis stimulus, occurs in CDH.

OBJECTIVES

To document FGF18 and elastin in human CDH and ovine surgical and rat nitrofen models and to use models to evaluate the benefit of treatments.

METHODS

Human CDH and control lungs were collected post mortem. Diaphragmatic hernia was created in sheep at 85 days; fetal lungs were collected at 139 days (term = 145 days). Pregnant rats received nitrofen at 12 days; fetal lungs were collected at 21 days (term = 22 days). Some of the sheep fetuses with hernia underwent tracheal occlusion (TO); some of the nitrofen-treated pregnant rats received vitamin A. Both treatments are known to promote lung growth.

MEASUREMENTS AND MAIN RESULTS

Coincidental with the onset of secondary septation, FGF18 protein increased threefold in control human lungs, which failed to occur in CDH. FGF18 labeling was found in interstitial cells of septa. Elastin staining demonstrated poor septation and markedly decreased elastin density in CDH lungs. Consistently, lung FGF18 transcripts were diminished 60 and 83% by CDH in sheep and rats, respectively, and elastin density and expression were diminished. TO and vitamin A restored FGF18 and elastin expression in sheep and rats, respectively. TO restored elastin density.

CONCLUSIONS

Impaired septation in CDH is associated with decreased FGF18 expression and elastic fiber deposition. Simultaneous correction of FGF18 and elastin defects by TO and vitamin A suggests that defective elastogenesis may result, at least partly, from FGF18 deficiency.

Tracheal occlusion: A review of obstructing fetal lungs to make them grow and mature

Fetal lung growth and functional differentiation are affected strongly by the extent that pulmonary tissue is distended (expanded) by liquid that naturally fills developing future airspaces. Methods that prevent normal egress of this lung fluid through the trachea magnify mechanical stretching of lung parenchymal cells, thereby promoting lung development. Indeed, experimental observations demonstrate that in utero tracheal occlusion (TO) performed on fetuses during the late canalicular-early saccular stage potently stimulates pulmonary growth and maturation. In this review, we present the four principle non-human animal models of TO/obstruction and discuss them in relation to their utility in elucidating lung development, in remedying congenital diaphragmatic hernia (CDH) as well as in investigating the stretching effects on growth and remodeling of the fine vasculature.

Prenatal glucocorticoids improve lung morphology and partially restores surfactant mRNA expression in lambs with diaphragmatic hernia undergoing fetal tracheal occlusion

In fetal sheep with surgically created diaphragmatic hernia (DH), tracheal occlusion (TO) can restore lung growth but does not ameliorate the increase in inter-alveolar wall thickness (T(W)). We determined whether prenatal exposure to glucocorticoids (GC) could reduce T(w) in fetuses with DH undergoing TO. At 65 days of gestation, DH was created in 12 fetal sheep, and TO subsequently performed at 110 days (DH/TO). Six of these fetuses were exposed to betamethasone (DH/TO + GC; 0.5 mg/kg; maternal, IM) 48 hr before delivery; Sham operated fetuses (n = 7) served as controls. At 139 days, we measured alveolar surface density (S(V)), parenchymal tissue fraction, T(W), alveolar type 2 (AE2) cell density and lung surfactant protein (SP) mRNA expression. Prenatal GC decreased T(W) and S(V) by 33% and 27% respectively, and increased fixed lung volume (by 55%), AE2 cell density and partially restored SPmRNA expression. Our data indicate that prenatal exposure to GC can reverse some of the negative effects of prolonged fetal TO. We hypothesize that a GC-induced reduction in lung liquid volume during TO contributes, in part, to the observed increase in AE2 cell density and SPmRNA expression.

Prenatal glucocorticoids and exogenous surfactant therapy improve respiratory function in lambs with severe diaphragmatic hernia following fetal tracheal occlusion

Fetal tracheal occlusion (TO) accelerates lung growth and can reverse severe lung hypoplasia associated with diaphragmatic hernia (DH), however, lung compliance (Cl) and respiratory gas exchange remain abnormal. We determined the individual and combined effects of prenatal glucocorticoids (GC) and exogenous surfactant therapy (S) on postnatal pulmonary function in lambs with DH that underwent prolonged TO. DH was created in 22 fetal sheep at 65 d of gestation and TO performed at 110 d. Eleven DH/TO animals received prenatal GC (betamethasone, 0.5 mg/kg) 48 h before delivery; six GC-treated and five non-GC lambs were administered surfactant (Infasurf, 3 mg/kg) at birth. Six sham-operated lambs served as controls. Lambs were delivered at 139 d gestation and ventilated for 2 h. GC or surfactant therapy alone significantly improved respiratory gas exchange, Cl, and ventilatory efficiency index. Total lung capacity was normalized only in DH/TO lambs that received both GC and S.

Physiological consequences of intrauterine insults

Fetal lung development occurs as a complicated series of interactions between the different cell types in the lung in response to different growth factors and hormones. At birth, the human lung is in the stage of alveolar development in which the gas exchange units (alveoli) are being actively formed. The alveolar growth continues into postnatal life. Different intrauterine insults perturb this sequence of lung development in different ways. The ultimate result of aberrant lung development depends on the type of intrauterine insult, the severity, the duration of the insult and the developmental stage at which the insult occurs. This review article focuses on the common intrauterine insults encountered in clinical practice, such as infections, disorders of amniotic fluid volume, nutrition and maternal smoking. The information derived from clinical studies is juxtaposed with data from animal experiments to discuss the physiological consequences of intrauterine insults on fetal lung growth.

Role of the physicochemical environment in lung development

Mechanical forces, exerted on lung tissue via alterations in lung expansion are a major determinant of fetal lung development, having a potent effect on the rate of cellular proliferation, the differentiated state of alveolar epithelial cells and the three-dimensional tissue structure. As a result, much research is currently focused on understanding the molecular mechanisms involved. 2. Although it is likely that mechanical forces exert similar influences on lung development after birth, the types of forces applied to the air-filled lung are very different and more complex. For example, lung aeration causes surface tension to form, which greatly increases lung recoil, leading to a reduction in interstitial tissue and pleural pressures, as well as lung expansion. 3. Because of the loss of the distending influence of lung liquid, the chest wall assumes the role of maintaining resting lung volumes after birth by acting as an external brace that opposes lung recoil. As a result, the distribution of force throughout lung tissue changes markedly. 4. Little is known of how changing the mechanical environment of the lung influences its development after birth, but this has important implications for understanding the impact of assisted ventilation on patients, particularly very preterm infants, who are often ventilated using high positive pressures. 5. Although the application of positive internal distending pressures may, in part, duplicate the fetal environment, the effect of gas versus liquid is unknown and high positive airway pressures are known to adversely affect cardiopulmonary physiology. Understanding the role of mechanical forces in regulating lung development as well as pulmonary physiology in the fetus and newborn is central to improving the care and management of infants suffering respiratory failure.

Tracheal occlusion in fetal rats alters expression of mesenchymal nuclear transcription factors without affecting surfactant protein expression

BACKGROUND/PURPOSE

Mesenchymal nuclear transcription factors (MNTF) are involved in lung development and maturation and regulate surfactant protein (SP) expression. Prolonged (>2 weeks) fetal tracheal occlusion (TO) has been shown to accelerate lung growth and inhibit pulmonary surfactant synthesis. The effects of TO on SP expression and MNTF, however, have not been formally assessed. The objectives of this study were to evaluate the effects of short-term (3 days) TO on normal lung growth and protein expression of pulmonary MNTF involved in SP synthesis.

METHODS

At E19 (term, 22 days), 2 fetuses per time-dated Sprague-Dawley rats underwent either TO (n = 23) or a sham (n = 22) operation. Lungs were harvested 72 hours post surgery. Pulmonary SP-A; SP-B; SP-C messenger RNA (mRNA) expression; and SP-A and SP-B, Hoxb5, thyroid transcription factor 1, and retinoic X receptor-alpha protein expression were analyzed.

RESULTS

Lung weight was significantly increased by TO (TO 0.32 +/- 0.02g vs SHAM 0.14 +/- 0.01 g; P < .001), resulting in 123% increase of the lung-to-body-weight ratio. No difference of SP-A-mRNA (177 +/- 4.3 TO vs 169 +/- 4.4 SHAM; P = .25), SP-B-mRNA (87.7 +/- 0.2 TO vs 87.4 +/- 0.02 SHAM; P = .33), and SP-C-mRNA (186.5 +/- 3.2 TO vs 183.2 +/- 2.7 SHAM; P = .45) expression was found. Surfactant protein A (175.6 +/- 25.3 TO vs 192.5 +/- 19.8 SHAM; P = .59) and SP-B (163.4 +/- 5.2 TO vs 166.8 +/- 9.3 SHAM; P = .75) protein expression were similar in both groups; however, Hoxb5 (70.3 +/- 18.9 TO vs 130.6 +/- 5.1 SHAM; P = .02) and thyroid transcription factor 1 (102.6 +/- 19 TO vs 181.1 +/- 6.3 SHAM; P = .007) expression were significantly decreased. Retinoic X receptor-alpha expression tended to be increased by TO (171.9 +/- 6.0 TO vs 155.4 +/- 6.7 SHAM; P = .06).

CONCLUSIONS

Short-term TO late in gestation induces rapid lung growth. Surfactant protein-mRNA and protein expression are not significantly altered. Thyroid transcription factor 1 and Hoxb5 are down-regulated by TO, suggesting that duration and timing of occlusion are important in balancing the effects of TO on lung growth vs lung maturation.

Fetal surgery for congenital diaphragmatic hernia

Congenital diaphragmatic hernia (CDH) continues to account for significant mortality in neonates. Advances in postnatal therapies have reduced mortality rates in the less severely affected infants, though surviving infants continue to display significant comorbid conditions. The history of fetal treatment for CDH is a microcosm for the development of fetal therapy in general. This paper traces this history from early clinical observations and imaging advances to experimental animal studies and finally to safe human application and development of clinical trails. Encouraging recent results and improved outcomes lend credence to the idea than prenatal interventions may give clinicians and families more hope.

Effect of temporary tracheal occlusion on the endothelin system in experimental cases of diaphragmatic hernia

Previously, the authors have shown that tracheal occlusion (TO) partially reverses the onset of congenital diaphragmatic hernia (CDH)-induced pulmonary hypertension (PH) and abnormal pulmonary vascular development whereas release of the occlusion (TR) abolishes these clinical benefits. As a consequence of their mitogenic and vasoactive properties, the authors hypothesize that the expression of endothelin (ET)-1 and ET receptor (ETA) genes is increased in lungs of CDH lambs, and that this increase is abolished partially in CDH + TO but not in CDH + TO + TR. A surgical left-sided CDH was created in fetal lambs at 80 days of gestation (gd), followed by TO at 108 gd, and by TR at 129 gd. Four groups were compared: CDH, CDH + TO, CDH + TO + TR, and nonoperated controls (C). Assessment of mRNA expression by Northern blot showed significantly lower ET-1 and ETA levels in the CDH group than in the CDH + TO +/- TR groups (P < .05). Endothelin protein expression levels were lower in CDH +/- TO +/- TR groups when compared with controls for airways and vessels (P < .05) with the exception of endothelial cells. In contrast, ETA protein expression levels were higher in CDH +/- TO +/- TR groups compared with controls for airways and blood vessels smooth muscles (P < .05). These results suggest that involvement of the endothelin system in the pulmonary hypertension associated with CDH is limited. However, the endothelin system appears to be modulated during development.

Congenital diaphragmatic hernia, tracheal occlusion, thyroid transcription factor-1, and fetal pulmonary epithelial maturation

Congenital diaphragmatic hernia (CDH) occurs in ∼1:2,500 human births and has high morbidity and mortality rates, primarily due to pulmonary hypoplasia and pulmonary hypertension. Tracheal occlusion (TO), in experimental animals, distends lungs and increases lung growth and alveolar type I cell maturation but decreases surfactant components and reduces alveolar type II cell density. We examined effects of CDH and CDH+TO on lung growth and maturation in fetal rats. To induce CDH, we administered nitrofen (100 mg) to dams at 9.5 days of gestation. We compared lungs from fetuses with CDH, CDH+TO, and those exposed to nitrofen without CDH. CDH decreased lung wet weight bilaterally ( P < 0.0001) and DNA content in lung ipsilateral to CDH ( P < 0.05). CDH+TO significantly increased lung wet weights bilaterally; DNA content was intermediate between CDH and NC. To evaluate effects on the distal pulmonary epithelium, we examined surfactant mRNA and protein levels, type I and II cell-specific markers (RTI40 and RTII70, respectively), and transcriptional regulator thyroid transcription factor-1 (TTF-1). Decreased lung distension (due to CDH) increased SP-C mRNA and TTF-1 protein expression and reduced RTI40 ( P < 0.05 for all). Increased lung distension (due to CDH+TO) reduced expression of SP mRNAs and pro-SP-C and TTF-1 proteins and enhanced expression of RTI40 (mRNA and protein; P < 0.05 for all). We conclude that CDH+TO partially reverses effects of CDH; it corrects the pulmonary hypoplasia and restores type I cell differentiation but adversely affects SP expression in type II cells. These effects may be mediated through changes in TTF-1 expression.

Rescue of the Hypoplastic Lung by Prenatal Cyclical Strain

We determined the effects of sustained and cyclical prenatal mechanical strain on the hypoplastic lung of the ovine model of congenital diaphragmatic hernia. Over a period of 4 weeks in late gestation, repeated cyclical tracheal occlusion for 23 hours with 1-hour release stimulated minimal growth, but promoted maturation with the development of a saccular lung. In contrast, a cycle consisting of 47 hours with 1-hour release induced optimal lung growth and morphologic maturation of the hypoplastic lung parenchyma. Sustained occlusion resulted in exaggerated lung growth, exceeding that of unaffected controls, and abnormal alveolar development. The extent of induction of lung growth by mechanical strain was inversely proportional to the number of alveolar type II cells remaining in the lung epithelium. These studies show that, although mechanical strain is capable of inducing lung growth and differentiation, cyclical strain is a prerequisite for normal development and that mechanically induced growth occurs at the expense of the alveolar type II cell. We conclude that cyclical strain may allow optimal alveolar development while maintaining a population of alveolar type II cells and may thus facilitate an improvement in postnatal lung function in infants with congenital diaphragmatic hernia.

Surfactant phospholipids and proteins are increased in fetal sheep with pulmonary hypertension secondary to fetal systemic arteriovenous fistula

To determine whether prenatal surfactant storage was altered in a model of systemic arteriovenous fistula (SAVF) with pulmonary hypertension, a fistula was created between the internal jugular vein and the carotid artery in 120-day fetal lambs, and surfactant material was explored at 134 days. Total phospholipids (TPL) and disaturated phosphatidylcholine (DSPC) were increased in whole lung tissue. Phospholipid analysis of isolated lamellar body fraction evidenced a specific increase of surfactant pool size: TPL and DSPC in this fraction were enhanced 1.9 and 2.9 times, respectively, when referred to DNA. Although the steady-state level of transcripts of surfactant protein (SP)-A and SP-B was not found to be changed at the time of death, semiquantitative Western blot analysis revealed elevated SP-A and SP-B protein contents three- and twofold, respectively. These findings indicate markedly enhanced accumulation of surfactant material in the presence of surgically induced prenatal pulmonary hypertension. Although total lung cell number was increased by 26%, SP-B immunolabeling indicated that increased surfactant amount did not result from an increased alveolar type II cell proportion, but rather from an increased rate of storage. Whether similar changes in surfactant are encountered in human neonates with persistent pulmonary hypertension is worthy of investigation.

Infant pulmonary function in a randomized trial of fetal tracheal occlusion for severe congenital diaphragmatic hernia

Congenital diaphragmatic hernia (CDH) carries a high mortality risk secondary to pulmonary hypoplasia and respiratory failure. In experimental animals, fetal tracheal occlusion (TO) induces lung growth and morphologic maturation. We measured indicators of pulmonary function in 20 infants who were enrolled in a randomized trial of fetal TO as treatment for severe CDH [nine with conventional treatment (controls); 11 with TO]. We hypothesized that TO would improve lung function. At birth, the TO group had a lower mean gestational age (30.8 +/- 2.0 versus 37.4 +/- 1.0 wk; p=0.0002). All infants required assisted ventilation. Mortality did not differ between groups (64 versus 78%, TO and control, respectively; p=0.64). We measured respiratory mechanics at four study points: 1) first 24 h, 2) before CDH operative repair (5.9 +/- 2.2 d), 3) immediately after repair (7.0 +/- 2.2 d), and 4) before elective extubation (32.5 +/- 16.1 d). We calculated perioperative oxygenation index and alveolar-arterial oxygen difference to assess efficiency of pulmonary gas exchange. Data were analyzed by univariate and repeated measures techniques. Respiratory system compliance (Crs) was low. The rate of increase in Crs over the four study points was greater in the TO group than in control subjects. Crs in the TO group was significantly greater at study 2 (0.28 +/- 0.12 versus 0.17 +/- 0.04 mL.cm H2O(-1).kg(-1); p=0.02) and study 4 (0.93 +/- 0.45 versus 0.51 +/- 0.16 mL.cmH2O(-1).kg(-1); p=0.02). oxygenation index did not differ between groups, but alveolar-arterial oxygen difference was lower in the TO infants. We conclude that fetal TO for severe CDH results in modest improvements in neonatal pulmonary function that are of questionable clinical significance.

Lung function in lambs with diaphragmatic hernia after reversible fetal tracheal occlusion

BACKGROUND/PURPOSE

Short-duration resuscitation (< or =4 hours) of lambs with diaphragmatic hernia treated in utero with tracheal occlusion have shown improved lung function compared with untreated diaphragmatic hernia. This may be a transient phenomenon in the treated diaphragmatic hernia lambs because of surfactant deficiency. Our objective was to analyze the effect of fetal tracheal occlusion with or without release of the occlusion 1 week before delivery on pulmonary function during a longer period of resuscitation (8 hours) in the diaphragmatic hernia lamb model.

METHODS

Four groups were compared: diaphragmatic hernia (n = 5), diaphragmatic hernia and tracheal occlusion until delivery (n = 5), diaphragmatic hernia and tracheal occlusion with release of the occlusion 1 week before delivery (n = 5), and normal controls (n = 4).

RESULTS

Despite persistently decreased surfactant levels, diaphragmatic hernia lambs treated with tracheal occlusion had normal-sized lungs with marked improvement in lung function and gas exchange over 8 hours when compared with untreated lambs with diaphragmatic hernia. Release of the tracheal occlusion 1 week before delivery added no benefit.

CONCLUSIONS

It appears that surfactant-independent mechanisms such as pulmonary growth and structural changes are of foremost importance in relating to improved compliance, oxygenation, and ventilation of diaphragmatic hernia lambs treated with tracheal occlusion.

Effect of tracheal occlusion on peripheric pulmonary vessel muscularization in a fetal rabbit model for congenital diaphragmatic hernia

OBJECTIVE

This study was undertaken to evaluate the effects on peripheric pulmonary vessel muscularization by tracheal occlusion (TO) performed at different gestational ages in fetal rabbits with surgically induced diaphragmatic hernia.

STUDY DESIGN

In 23 New Zealand white does, both ovarian end fetuses underwent surgical creation of diaphragmatic hernia at 23 days of gestation (pseudoglandular phase). At 26, 27, or 28 days 1 fetus underwent TO, the contralateral one underwent a sham operation for a total of 46 fetuses. At 30 days (alveolar phase), fetuses were harvested together with 1 nonoperated internal control. Lungs were processed for vascular morphometry. Proportionate medial thickness and muscularization of intra-acinar vessels were evaluated.

RESULTS

Late TO (day 28; saccular phase) normalizes the lung-to-body weight ratio and causes significant medial thinning in vessels up to 35 microm diameter.

CONCLUSION

Tracheal occlusion decreases muscularization of intra-acinar pulmonary vessels in a gestational age-dependent fashion, with maximal effect when TO is performed at 28 days.

Congenital diaphragmatic hernia: advances in prenatal therapy

Despite intensive clinical and experimental efforts, mortality from CDH remains high. More than two decades of research in multiple centers has led to a better understanding of the pathophysiology, prognosis, and treatment options for fetuses that have CDH. It now appears that fetuses that have prenatally diagnosed CDH can be stratified into high- and low-risk groups based upon sonographic parameters. Fetuses that do not have liver herniation into the chest that have a favorable LHR have an excellent chance of survival with postnatal therapy. Prenatal diagnosis allows the time and place of delivery to be planned in advance so these infants can be treated in a tertiary care nursery that has maximal medical and surgical therapy. Fetuses that have liver herniation into the chest and an unfavorable LHR have a grim prognosis. These fetuses might benefit from in utero intervention. There is no role for open fetal repair of the diaphragmatic detect; however, fetoscopic temporary tracheal occlusion might improve lung growth and development and might decrease morbidity and mortality in these infants. The FETENDO strategy appears to work, and for the first time it offers hope to the fetus that has high-risk CDH, but its efficacy must be proven in a proper randomized, controlled trial.

Tracheal occlusion stimulates cell cycle progression and type I cell differentiation in lungs of fetal rats

Fetal tracheal occlusion (TO) has been reported to stimulate lung growth but decreases number and maturation of type II cells, effects that vary with gestational age and duration of TO. We examined effects of a novel method of TO (unipolar microcautery to seal the trachea) produced at 19.5-20 days (d) of gestation in fetal rats; fetuses were delivered at term, 22 d. Controls were sham operated and unoperated littermates. TO increased wet lung weight but not dry lung weight or lung DNA and protein. To evaluate further the effects of TO, we examined the cell cycle regulators, cyclins D1 and A, in fetal lungs. Cyclin D1 increased with TO (P < 0.005). TO also increased expression of the type I epithelial cell marker RTI40 (mRNA and protein). TO decreased mRNA for surfactant proteins (SP)-A and -C but did not affect protein levels of SP-A and -B and of RTII70, a type II epithelial cell marker. We conclude that TO by microcautery, even of short duration, has diverse pulmonary effects including stimulating increased levels of cyclin D1 with probable cell cycle progression, type I cell differentiation, and possibly inhibiting type II cell function.

Continuous mechanical contraction modulates expression of alveolar epithelial cell phenotype

We have previously reported that mechanical distention of alveolar epithelial type II cells in culture favored the expression of the type I cell phenotype and inhibited the expression of the type II cell phenotype. The objective of the present study was to investigate the effects of continuous mechanical contraction on the expression of specific markers for the type I and type II cell phenotypes in cultured alveolar type II cells. Type II cells were mechanically contracted in culture at varying amplitudes and times. Cells were analyzed for mRNA and protein content of markers of the type I (RTI40) and type II (surfactant proteins [SPs] A, B, and C) phenotypes. Continuous contraction of culture membrane surface area by 25% for a duration of 4 h resulted in an 83% increase in SP-A, a 42% increase in SP-B, and a 230% increase in SP-C, in comparison with controls. After 12 h of contraction, RTI40 mRNA content decreased to 59% of control levels. A minimal contraction of 20% of culture membrane surface area was required to modulate expression of the type II cell markers. In summary, mechanical contraction favors expression of the type II cell phenotype and inhibits expression of the type I cell phenotype in a time- and amplitude-dependent manner.

Fetoscopic temporary tracheal occlusion for congenital diaphragmatic hernia: prelude to a randomized, controlled trial

OBJECTIVE

As previously reported, high postnatal mortality seen in fetuses with congenital diaphragmatic hernia (CDH) with liver herniation and low lung-to-head ratio (LHR) appears to be improved in fetuses who undergo fetoscopic temporary tracheal occlusion (TO). To test whether further evolution of this technique produces results that justify a randomized controlled trial comparing prenatal intervention to postnatal care, the authors analyzed 11 additional cases and the cumulative experience with 19 cases.

METHODS

The authors analyzed retrospectively the outcome of 11 new and 8 previously reported cases of fetoscopic temporary tracheal occlusion. Various factors were studied including maternal morbidity, antenatal outcome, physiologic lung response, and neonatal course.

RESULTS

Temporary TO can be accomplished using 3 5-mm radially expanding uterine ports without hysterotomy. Obstetric morbidity included mild pulmonary edema in 6 cases, chorioamniotic separation and premature rupture of membranes in 12 patients, and preterm labor and delivery in all patients. Thirteen of 19 (68%) neonates survived for 90 days after delivery; one died in utero, and 5 died after birth. Late mortality included one death caused by sepsis and 2 by complications associated with tracheostomies. Morbidity from gastroesophageal reflux requiring Nissen fundoplication, tracheal injury requiring repair or tracheostomy, and recurrent hernias after diaphragmatic repair were characteristic in longterm survivors.

CONCLUSIONS

Fetoscopic temporary TO may improve outcome in poor-prognosis fetuses with CDH. However, complications related to tracheal dissection, premature delivery and late morbidity are significant. This experience has led to simpler techniques for fetoscopic tracheal occlusion and to an National Institutes of Health-sponsored randomized controlled trial comparing fetoscopic tracheal occlusion with optimal postnatal care.

Temporary tracheal occlusion in fetal sheep with lung hypoplasia does not improve postnatal lung function

Prolonged fetal tracheal occlusion (TO) accelerates lung growth but leads to loss of alveolar epithelial type II (AE2) cells. In contrast, temporary TO leads to recovery of AE2 cells and their ability to produce surfactant. The aim of this study was to determine the effects of temporary TO in fetal sheep with lung hypoplasia on postnatal lung function, structure, and surfactant protein mRNA expression. Diaphragmatic hernia (DH) was created in 22 fetal sheep at 65 days of gestation. TO was performed between 110 days of gestation and full term (DH/TO, n = 7) and between 110 and 130 days of gestation (DH/TO+R, n = 6). Sham-operated fetuses (n = 11) served as controls. Lambs were delivered at approximately 139 days of gestation, and blood gas tensions were monitored over a 2-h resuscitation period. Temporary TO increased growth of the hypoplastic lung and restored surfactant protein mRNA expression and AE2 cell density but did not improve respiratory function above that of animals that underwent prolonged TO; DH/TO and DH/TO+R lambs were hypoxic and hypercapnic compared with Sham animals. Lung compliance remained low in DH/TO+R lambs, most likely as a consequence of the persistent increase in alveolar wall thickness in these animals.

A prospective, randomized pilot trial of perfluorocarbon-induced lung growth in newborns with congenital diaphragmatic hernia

BACKGROUND/PURPOSE

Initial laboratory and clinical data suggest that partial liquid ventilation (PLV) can enhance pulmonary function and that lung growth can be induced via distension of the newborn lung using perfluorocarbon in patients with congenital diaphragmatic hernia (CDH). The authors, therefore, performed a prospective, randomized pilot study evaluating PLV and perfluorocarbon-induced lung growth (PILG) in newborns with CDH on extracorporeal life support (ECLS) at 6 medical centers.

METHODS

Patients were selected randomly using a permuted block design to PLV/PILG (n = 8) or conventional mechanical ventilation (CMV/control, n = 5). Patients in the PILG group received daily doses which filled the lungs with perflubron for up to 7 days and were placed on continuous positive airway pressure of 5 to 8 cm H2O. CMV patients were treated with standard mechanical ventilation while on extracorporeal membrane oxygenation (ECMO).

RESULTS

A total of 13 patients were evaluated in this study. All 3 patients enrolled without being on ECLS rapidly transitioned to ECLS. The study, therefore, effectively evaluated PILG (n = 8) versus standard ventilation (control, n = 5) on ECLS. Mean (+/- SE) gestational age was 37 +/- 1 weeks and weight was 3.1 +/- 0.1 kg. Time on ECMO was 9.8 +/- 2.3 days in the PILG and 14.5 +/- 3.5 days (P =.58) in the control group. Survival rate in the PILG group was 6 of 8 (75%), whereas survival rate was 2 of 5 (40%) in the control group (P =.50). The number of days free from the ventilator in the first 28 days (VFD) was 6.3 +/- 3.3 days with PILG and 4.6 +/- 4.6 days with control (P =.9). Causes of death in the PILG group included sepsis and renal failure in one patient and pulmonary hypertension in the other. There were no safety issues, and the deaths in the PILG group did not appear to be related to the administration of perflubron.

CONCLUSIONS

These data show that PILG can be performed safely. The survival rate, VFD, and time on ECMO data, although not conclusive, are encouraging and indicate the need for a definitive trial of this novel intervention in these neonates with high mortality.

Evolution of a percutaneous fetoscopic access system for single-port tracheal occlusion

BACKGROUND/PURPOSE

Prenatal tracheal occlusion currently is being assessed as a treatment modality for congenital diaphragmatic hernia (CDH). The development of a totally percutaneous fetoscopic access system would help avoid the need for maternal laparotomy and reduce the morbidity rate of fetal surgical procedures for the mother. Laparoscopic radial expansion sheaths and Seldinger technique-based vascular catheters both have been advocated as means of achieving amniotic cavity access. The authors have investigated these 2 systems in an attempt to develop a reliable method for achieving safe percutaneous fetoscopic access and present the first successful attempt to deploy an intratracheal balloon using an entirely percutaneous approach through a single port in an ovine model.

METHODS

A number of prototype systems were evaluated sequentially over a 3-year period in an ovine model: (1) the radially expanding InnerDyne step port system, (2) a new rigid cannula with a bulbous/sharp end preloaded onto the radially expanding InnerDyne port, (3) a conical removable addition to the rigid cannula in 2, (4) a modified bulbous/sharp ended cannula incorporating a circumferential protective insert, (5) a rigid split sheath with the radially expanding port placed through the lumen of the split sheath, (6) a flexible introducer and dilator with the split sheath (used in the Seldinger placement of central lines), and (7) a 2-needle approach using a superelastic shape-memory alloy Nickel-Titanium wire with the flexible dilator and sheath, incorporating a side perfusion port. For balloon tracheal occlusion, live anaesthetized time-mated pregnant ewes were used at 110 days' gestation. Tracheobronchoscopy was achieved using a 3-mm 0 degrees telescope, and the cutaneotracheal tract was secured by a 3.3-mm sheath incorporating a side-perfusion port. The rigid telescope was replaced by a flexible choledochoscope preloaded with a silicone balloon. The balloon was deployed 2 cm above the carina proximal to the right upper lobe bronchus.

RESULTS

The many problems encountered in the evolution of the preferred system related mainly to separation and tenting of the chorioamniotic membranes in the ovine uterus and inconsistent access to the fetal parts of interest. Each resulted in significant modifications to our approach. Furthermore, the use of rigid access devices commonly caused fetal injury. Successful access to the intrauterine cavity and cannulation of the trachea was achieved consistently with minimal trauma, irrespective of fetal position by method 7. Multiple port placement allowed visualization of the entry of all components of the system confirming minimal chorioamniotic membrane separation and tenting. Single port tracheal occlusion was undertaken first on 6 cadavers before being performed successfully on 3 live anaesthetized ewes. Fetoscopic access and cannulation of the trachea was achieved consistently in all live animals irrespective of fetal position.

CONCLUSIONS

This modified Seldinger technique using the unique properties of the memory-shaped alloy wire for initial uterine access offers a safe method for the percutaneous placement of fetoscopic ports in the ovine model for prenatal intervention. Successful placement of a tracheal balloon entirely through a single percutaneously placed port represents a further advance in prenatal therapy for CDH.

Expression of surfactant proteins and thyroid transcription factor 1 in an ovine model of congenital diaphragmatic hernia

BACKGROUND/PURPOSE

The question of delayed lung maturation in congenital diaphragmatic hernia (CDH) is pending. Data about surfactant proteins (SPs) are sparse in human fetuses and discrepant in the ovine CDH model. The purpose of this study was to investigate, in the ovine surgically created CDH model, the expression of SPs and of thyroid transcription factor 1 (TTF-1), a key regulator of lung development that also controls the expression of surfactant proteins.

METHODS

Diaphragmatic hernia (DH) was created surgically in lamb fetuses on day 85 of gestation. On day 139, 5 DH and 6 control fetuses were retrieved by cesarean section. The mRNA levels for SPs and TTF-1 were determined by Northern blot analysis; SP-A and SP-B protein levels were assessed by Western blot analysis.

RESULTS

In DH lungs, SP-A, SP-B, and SP-C messenger RNAs were diminished by 82%, 67%, and 32%, respectively, compared with control level. SP-A and SP-B protein amounts were decreased consistently. TTF-1 expression was not altered in the surgical model.

CONCLUSIONS

SP's deficiency appears to be a common feature of the various CDH models. By contrast with the nitrofen model, TTF-1 expression was not altered in the surgical model indicating different underlying molecular mechanisms in both models.