Tracheal ligation does not correct the surfactant deficiency associated with congenital diaphragmatic hernia

The Cellular and Molecular Effects of Fetoscopic Endoluminal Tracheal Occlusion in Congenital Diaphragmatic Hernia

Congenital diaphragmatic hernia (CDH) is a complex disease associated with pulmonary hypoplasia and pulmonary hypertension. Great strides have been made in our ability to care for CDH patients, specifically in the prenatal improvement of lung volume and morphology with fetoscopic endoluminal tracheal occlusion (FETO). While the anatomic effects of FETO have been described in-depth, the changes it induces at the cellular and molecular level remain a budding area of CDH research. This review will delve into the cellular and molecular effects of FETO in the developing lung, emphasize areas in which further research may improve our understanding of CDH, and highlight opportunities to optimize the FETO procedure for improved postnatal outcomes.

Modern fetal surgery-a historical review of the happenings that shaped modern fetal surgery and its practices

The history of fetal surgery is one of constant evolution. Over the last 50 years, fetal surgery has progressed from a mere idea to an internationally respected innovative field of surgery. This article aims to provide a historical review of how the enterprise of maternal-fetal surgery came to be its modern version. This review is less focused on the history of specific therapies for a relatively small number of conditions, and more on how the whole field of maternal-fetal surgery evolved. The various internal and external influences that steered the field's evolution are discussed in chronologic order. Since the start of modern fetal surgery in the 1980s, large paradigm shifts have characterized the growth of the field as a whole. Innovative interventions are now based on physiologic manipulation as opposed to simple anatomic repair, fetoscopy has become the more frequently preferred surgical approach, and rigorous scientific evaluation with randomized controlled trials is now the standard expected by the community. In a very similar fashion to when the field first began in the early 1980s, recently community's leaders have risen to protect the integrity of maternal-fetal surgery by publishing ethical guidelines for innovation and clinical practice. This incredible history of innovation, rigorous science and ethical contemplation is the foundation on which modern maternal-fetal surgery rests.

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.

Perfluorocarbons Prevent Lung Injury and Promote Development during Artificial Placenta Support in Extremely Premature Lambs

BACKGROUND

Extremely premature neonates suffer high morbidity and mortality. An artificial placenta (AP) using extracorporeal life support (ECLS) is a promising therapy.

OBJECTIVES

We hypothesized that intratracheal perfluorocarbon (PFC) instillation during AP support would reduce lung injury and promote lung development relative to intratracheal amniotic fluid or crystalloid.

METHODS

Lambs at an estimated gestational age (EGA) 116-121 days (term 145 days) were placed on venovenous ECLS with jugular drainage and umbilical vein reinfusion and intubated. Airways were managed by the instillation of amniotic fluid and tracheal occlusion (TO; n = 4), or lactated Ringer's (LR; n = 4) or perfluorodecalin (a PFC) without occlusion (n = 4). After 7 days, the animals were sacrificed. Early (EGA 116-121 days) and late (EGA 125-131 days) tissue control lambs were delivered and sacrificed. Lungs were formalin-inflated to 30 cm H2O and sectioned for histology. Injury was scored by an unbiased pathologist. Slides were immunostained for PDGFR-α and α-actin; development was quantified by the area fraction of double-positive tips. Surfactant protein-C (SP-C) concentration in bronchoalveolar lavage fluid was quantified using ELISA.

RESULTS

Total injury scores were lower in PFC lungs (1.8 ± 1.7) than in TO (6.5 ± 2.1; p = 0.01) and LR lungs (5.5 ± 2.4; p = 0.01). The area fraction of double-positive alveolar tips appeared higher in PFC lungs than in TO lungs (0.18 ± 0.007 vs. 0.008 ± 0.004; p = 0.07). SP-C concentration was higher in PFC lungs than in TO lungs (37.9 ± 7.6 vs. 20.0 ± 5.4 pg/mL; p = 0.005), and both early (12.4 ± 1.7 g/mL; p = 0.007) and late tissue control lungs (15.1 ± 5.0 pg/mL; p = 0.0008).

CONCLUSION

During AP support, intratracheal PFC prevents lung injury and promotes normal lung development better than crystalloid or amniotic fluid with TO.

Fetal imaging and therapy for CDH-Current status

In congenital diaphragmatic hernia (CDH), herniation of the abdominal organs into the fetal chest causes pulmonary hypoplasia and pulmonary hypertension, the main causes of neonatal mortality. As antenatal ultrasound screening improves, the risk of postnatal death can now be better predicted, allowing for the identification of fetuses that might most benefit from a prenatal intervention. Fetoscopic tracheal occlusion is being evaluated in a large international randomized controlled trial. We present the antenatal imaging approaches that can help identify fetuses that might benefit from antenatal therapy, and review the evolution of fetal surgery for CDH to date.

Fetal surgery: a critical review

Therapeutic fetal surgical procedures are predicated upon the ability to make an accurate fetal diagnosis. The earliest open fetal surgical procedures were introduced in the 1960s to treat Rh isoimmunisation. They were introduced when it became possible to predict impending fetal demise. Open procedures were abandoned when percutaneous approaches proved superior. The introduction of fetal ultrasound allowed the diagnosis of other congenital anomalies, some being amenable to fetal interventions. Open fetal surgical procedures were initially utilised, with significant maternal morbidity. For some anomalies, percutaneous approaches became favoured. In general, all of these procedures involved significant risks to the mother, to save a baby that was likely to die before or shortly after birth without fetal intervention. Fetal repair for myelomeningocele was a "sea change" in approach. The same maternal risks were taken to improve the quality of life of the affected fetus, not save its life. The completion of the "MOMs Trial" has occasioned a "tsunami" of centres in North America applying this approach. Others are attempting percutaneous repairs, with mixed results. This paper reviews the history of fetal surgery, focusing on the themes of the tension between accurate diagnosis and prognosis and open versus "minimally invasive" approaches.

Amniotic fluid derived mesenchymal stromal cells augment fetal lung growth in a nitrofen explant model

PURPOSE

Recent experimental work suggests the therapeutic role of mesenchymal stromal cells (MSCs) during lung morphogenesis. The purpose of this study was to investigate the potential paracrine effects of amniotic fluid-derived MSCs (AF-MSCs) on fetal lung growth in a nitrofen explant model.

METHODS

Pregnant Sprague-Dawley dams were gavage fed nitrofen on gestational day 9.5 (E9.5). E14.5 lung explants were subsequently harvested and cultured ex vivo for three days on filter membranes in conditioned media from rat AF-MSCs isolated from control (AF-Ctr) or nitrofen-exposed (AF-Nitro) dams. The lungs were analyzed morphometrically and by quantitative gene expression.

RESULTS

Although there were no significant differences in total lung surface area among hypoplastic lungs, there were significant increases in terminal budding among E14.5+3 nitrofen explants exposed to AF-Ctr compared to explants exposed to medium alone (58.8±8.4 vs. 39.0±10.0 terminal buds, respectively; p<0.05). In contrast, lungs cultured in AF-Nitro medium failed to augment terminal budding. Nitrofen explants exposed to AF-Ctr showed significant upregulation of surfactant protein C to levels observed in normal fetal lungs.

CONCLUSIONS

AF-MSCs can augment branching morphogenesis and lung epithelial maturation in a fetal explant model of pulmonary hypoplasia. Cell therapy using donor-derived AF-MSCs may represent a novel strategy for the treatment of fetal congenital diaphragmatic hernia.

Congenital diaphragmatic hernia: treatment and outcomes

Congenital diaphragmatic hernia (CDH) is a congenital defect in the diaphragm that allows herniation of abdominal contents into the fetal chest and leads to varying degrees of pulmonary hypoplasia and pulmonary hypertension. Advances in prenatal diagnosis and the institution of standardized delivery and postnatal care protocols have led to improved survival. Fetal endoscopic tracheal occlusion shows early promise for patients with the most severe CDH, but prospective randomized data is still required. CDH survivors have a variety of associated morbidities that require long-term follow-up and early intervention strategies for optimal care.

Tracheal occlusion alters pulmonary circulation in the fetal lamb with normally developing lungs

BACKGROUND

Tracheal occlusion (TO) promotes fetal lung growth through an increase in intraluminal pressure. Although evidence suggests that fetal TO (FETO) decreases the occurrence of pulmonary hypertension in severe congenital diaphragmatic hernia, controversies on its effect on the pulmonary circulation remain. Therefore, we investigated the effects of FETO on the lung hemodynamics in a chronically catheterized fetal lamb model.

METHODS

Fifteen pregnant ewes were operated on between 125 and 128 days of gestation (term: 145 days). Catheters and ultrasonic flow transducer were placed through a left thoracotomy in the lamb fetus to determine aortic, pulmonary and left atrial pressures, and left pulmonary artery blood flow. A balloon was positioned between the carina and vocal cords under fetoscopic control. The animals were assigned to either control (n=6) or FETO (n=9) groups. TO was performed by inflating the balloon. We studied the acute effects of temporary (2-h) and prolonged (4-day) TO on basal pulmonary vascular tone and on the pulmonary vascular reactivity to acetylcholine and to increased fetal oxygen tension.

RESULTS

We found that left pulmonary blood flow (LPA) increased and pulmonary vascular resistance (PVR) decreased by 20% during brief TO (p<0.05). After balloon deflation, LPA blood flow further increased by 40%, and PVR decreased by 50% compared to baseline values (p<0.05). In contrast, no change in LPA blood flow or PVR was observed during prolonged TO. Moreover, the vasodilator responses to acetylcholine and to increased fetal PaO2 were blunted during TO.

CONCLUSIONS

These data indicate that antenatal tracheal occlusion promotes active pulmonary vasodilation, which is partly blunted by the mechanical effects of elevation of the intraluminal pressure.

Management of prenatally diagnosed congenital diaphragmatic hernia

Congenital diaphragmatic hernia (CDH) is a congenital anomaly that presents with a broad spectrum of severity that is dependent upon components of pulmonary hypoplasia and pulmonary hypertension. While advances in neonatal care have improved the overall survival of CDH in experienced centers, mortality and morbidity remain high in a subset of CDH infants with severe CDH. Prenatal predictors have been refined for the past two decades and are the subject of another review in this issue. So far, all randomized trials comparing prenatal intervention to standard postnatal therapy have shown no benefit to prenatal intervention. Although recent non-randomized reports of success with fetoscopic endoluminal tracheal occlusion (FETO) and release are promising, prenatal therapy should not be widely adopted until a well-designed prospective randomized trial demonstrating efficacy is performed. The increased survival and subsequent morbidity of CDH survivors has resulted in the need to provide resources for the long-term follow up and support of the CDH population.

Advances in prenatal diagnosis and treatment of congenital diaphragmatic hernia

Congenital diaphragmatic hernia (CDH) is a common birth anomaly. Absence or presence of liver herniation and determination of lung-to-head ratio are the most accurate predictors of prognosis for fetuses with CDH. Though open fetal CDH repair has been abandoned, fetal endoscopic balloon tracheal occlusion promotes lung growth in fetuses with severe CDH. Although significant improvements in lung function have not yet been shown in humans, reversible or dynamic tracheal occlusion is promising for select fetuses with severe CDH. This article reviews advances in prenatal diagnosis of CDH, the experimental basis for tracheal occlusion, and its translation into human clinical trials.

The making of fetal surgery

Fetal diagnosis prompts the question for fetal therapy in highly selected cases. Some conditions are suitable for in utero surgical intervention. This paper reviews historically important steps in the development of fetal surgery. The first invasive fetal intervention in 1963 was an intra-uterine blood transfusion. It took another 20 years to understand the pathophysiology of other candidate fetal conditions and to develop safe anaesthetic and surgical techniques before the team at the University of California at San Francisco performed its first urinary diversion through hysterotomy. This procedure would be abandoned as renal and pulmonary function could be just as effectively salvaged by ultrasound-guided insertion of a bladder shunt. Fetoscopy is another method for direct access to the feto-placental unit. It was historically used for fetal visualisation to guide biopsies or for vascular access but was also abandoned following the introduction of high-resolution ultrasound. Miniaturisation revived fetoscopy in the 1990 s, since when it has been successfully used to operate on the placenta and umbilical cord. Today, it is also used in fetuses with congenital diaphragmatic hernia (CDH), in whom lung growth is triggered by percutaneous tracheal occlusion. It can also be used to diagnose and treat urinary obstruction. Many fetal interventions remain investigational but for a number of conditions randomised trials have established the role of in utero surgery, making fetal surgery a clinical reality in a number of fetal therapy programmes. The safety of fetal surgery is such that even non-lethal conditions, such as myelomeningocoele repair, are at this moment considered a potential indication. This, as well as fetal intervention for CDH, is currently being investigated in randomised trials.

Management of prenatally diagnosed congenital diaphragmatic hernia

Congenital diaphragmatic hernia (CDH) is a congenital anomaly that presents with a broad spectrum of severity dependent upon components of pulmonary hypoplasia and pulmonary hypertension. While advances in neonatal care have improved the overall survival of CDH in experienced centers, mortality and morbidity remain high in a subset of CDH infants with severe CDH. The most important prenatal predictor of outcome in left-sided CDH is liver position. More precise and reproducible prenatal predictive parameters need to be developed to allow standardization of results between centers and appropriate design of clinical trials in CDH. Thus far, all randomized trials comparing prenatal intervention to standard postnatal therapy have shown no benefit to prenatal intervention. Although recent non-randomized reports of success with balloon tracheal occlusion (and release) are promising, prenatal therapy should not be widely adopted until a well-designed prospective randomized trial demonstrating efficacy is performed. The increased survival and subsequent morbidity of CDH survivors has resulted in the need to provide resources for the long-term follow-up and support of the CDH population.

Tracheal occlusion for fetal congenital diaphragmatic hernia: the US experience

Congenital diaphragmatic hernia (CDH) is characterized by a defect in the diaphragm that permits abdominal viscera to herniate into the chest. These herniated viscera are thought to compress the growing lung and cause lung parenchymal and vascular hypoplasia. The genetic defects that cause the diaphragmatic defect may also contribute primarily to lung hypoplasia. Postnatal reduction of the herniated abdominal viscera and correction of the diaphragmatic defect are easily achievable, but the lung hypoplasia persists, often leading to persistent fetal circulation and respiratory failure. This article reviews the experimental basis of fetal therapy for CDH and the US clinical experience with tracheal occlusion.

Antenatal prediction of lung volume and in-utero treatment by fetal endoscopic tracheal occlusion in severe isolated congenital diaphragmatic hernia

Congenital diaphragmatic hernia (CDH) is a severe malformation with an overall survival between 30% and 90%. Survival in the presence of associated malformations is very low. The condition should be detected in ultrasound screening programmes, but whether and how prenatal imaging can accurately predict outcome remains a matter of debate. Predictions based on the lung area:head circumference ratio and liver position are best studied. This information is highly relevant in counselling patients, leaving to severe cases the option of termination of pregnancy as experimental prenatal intervention aiming to reverse pulmonary hypoplasia. The purpose of this review is to update current knowledge regarding predictive value of prenatal assessment in terms of neonatal survival. We will also discuss experimental evidence and clinical data regarding fetal tracheal occlusion.

Pulmonary arteriole muscularization in lambs with diaphragmatic hernia after combined tracheal occlusion/glucocorticoid therapy

OBJECTIVE

A morphometric study was performed to examine the effects of prenatal glucocorticoids, which were administered 48 hours before birth, on muscularization of small pulmonary arterioles (<60 microm diameter) in lambs with diaphragmatic hernia (DH) after fetal tracheal occlusion (TO).

STUDY DESIGN

DH was created in 23 fetal sheep at 65 days gestation. TO was performed in 16 of 24 fetuses between 110 and 140 days of gestation; 9 of the fetuses were exposed prenatally to betamethasone (0.5 mg/kg body weight) 48 hours before delivery. Six sham-operated animals served as controls. Sections of paraffin that were embedded in lung tissues were stained with Elastin-Van Gieson, and the percentage of medial wall thickness (MWT) was determined.

RESULTS

The percentage of MWT in DH lambs (29.6% +/- 1.9%) was increased compared with sham animals (18.1% +/- 1.3%) and was not different from that of DH/TO animals (30.3% +/- 1.7%). In DH/TO + glucocorticoid lambs, the percentage of MWT (24.6% +/- 1.2%) was significantly lower than in the DH/TO group but was higher than the sham group.

CONCLUSION

In fetuses who underwent prolonged TO therapy for severe DH, prenatal glucocorticoid treatment decreased medial hypertrophy of pulmonary arterioles by approximately 19%. We speculate that such structural changes may have contributed to improve gas exchange that was observed in this model.

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.

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 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.

Congenital diaphragmatic hernia: searching for answers

BACKGROUND

Pulmonary hypoplasia and hypertension are the primary causes of morbidity and mortality in infants with congenital diaphragmatic hernia (CDH). At present, the origin of CDH and the causes of pulmonary hypoplasia and hypertension are unknown.

DATA SOURCES

This article reviews the available published data regarding the origin of CDH and the pathogenesis of the associated pulmonary hypertension and hypoplasia. These investigations have employed human tissues as well as two types of CDH animal models.

CONCLUSIONS

Investigations performed to date have not yet provided definitive answers regarding the pathogenesis of CDH. However, they have yielded many new and exciting discoveries and several opportunities for intervention. Ongoing research should open new possibilities to improve the outcome for these unfortunate babies with CDH.

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.

Fetal lung and diaphragm development in congenital diaphragmatic hernia

Congenital Diaphragmatic Hernia (CDH) is a congenital disorder with an incidence of 1 in 2500 live births. Respiratory distress of newborns with CDH is the result of pulmonary hypoplasia and pulmonary hypertension. Hypoplastic lungs are characterized by a decreased number of airways with smaller airspaces, whereas the combination of a decreased number of vascular branches and an increased adventitia and medial thickness of the pulmonary arterial walls result in pulmonary hypertension. The appearance of the CDH lungs suggests that its complete formation is stalled during development. Understanding the basic mechanisms of lung development is mandatory to unravel the origin of CDH. Although the histological abnormalities in CDH lungs have been well described, less is known about the underlying molecular mechanisms. In this review we will discuss the current molecular and genetic background of lung formation, as well as a reflection of this knowledge towards CDH.

Can maternal vitamin e supplementation prevent lung hypoplasia in the nitrofen-induced rat model of congenital diaphragmatic hernia?

Recent studies suggest a role for antioxidants in the prevention of pulmonary hypoplasia associated with congenital diaphragmatic hernia (CDH). We studied the effects of vitamin E in the nitrofen-rat model of CDH. After an initial fast, timed-pregnant Sprague-Dawley rats were gavage-fed nitrofen at gestational day 11 (term is 22 d). On the same day, one group was given a s.c. injection of vitamin E in alcohol; a second group was given an injection of alcohol alone. A third group received no treatment (control). Fetuses were delivered on day 21, and static pressure-volume curves were measured by immersion. Lungs were analyzed for total DNA and protein content by standard methods. A total of 203 fetuses were studied. Of 151 nitrofen-exposed fetuses, 77% had CDH; 92% of these were right-sided. CDH was present in 82% of vehicle-treated fetuses and 71% of vitamin E-treated fetuses (p=0.17). Nitrofen-exposed fetuses not only were smaller than control fetuses but also had disproportionately smaller lungs and poorer lung function, even when CDH was absent; however, lung function was worse when CDH was present. Vitamin E treatment did not improve either lung growth or function, although there was a trend toward less CDH. We have shown, for the first time, that the lung hypoplasia seen in nitrofen-exposed rat fetuses is associated with a dramatic reduction in static lung function, even when CDH is not present. Finally, our findings support the notion that lung hypoplasia in the nitrofen-rat model is independent of CDH formation.

Extralobar sequestration with congenital diaphragmatic hernia: a complicated case study

This article presents a case study of an infant (JG) with an antenatal diagnosis of a left diaphragmatic hernia and an extralobar sequestration of his right lung, which was noted postnatally. JG's course was complicated by persistent pulmonary hypertension of the newborn (PPHN) and suspected pulmonary hypoplasia, and he required support with extracorporeal life support (ECLS). JG's case was unusual in his presentation of extreme PPHN that was unresponsive to inhaled nitric oxide and ECLS. His PPHN was nearly intractable, requiring treatment with vasodilators combined with intravenous sildenafil, which had never been tried in our institution before this case. The article concludes with a discussion of the etiology, diagnosis, and management of congenital diaphragmatic hernia and extralobar sequestration, singly and in combination.

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.

Hyperoncotic enhancement of pulmonary growth after fetal tracheal occlusion: a comparison between dextran and albumin

BACKGROUND/PURPOSE

This study was aimed at comparing albumin and dextran as intrapulmonary hyperoncotic enhancers of fetal lung growth after tracheal occlusion.

METHODS

Fetal lambs (n = 27) were divided proportionally into 5 groups: group I consisted of sham-operated controls; group II underwent tracheal occlusion (TO); groups III, IV, and V underwent TO and intratracheal infusion of 60 mL of either saline, 6% dextran-70, or 25% albumin, respectively. Multiple fetal lung analyses were performed near term. Statistical analysis was by 1-way analysis of variance (ANOVA) and post-hoc analyses by the Bonferroni correction for multiple comparisons (P <.05).

RESULTS

The lung volume-to-body weight ratio was significantly higher in groups IV and V than in all other groups with no differences between groups II and III, nor between groups IV and V. Airspace fraction was not significantly different among the groups, nor was there any evidence of alveolar cellular damage. Type-II pneumocyte density was higher in group I than in groups II, IV, and V, with no differences among the latter 3 groups. Lung liquid biochemical profile was normal in all groups.

CONCLUSIONS

Albumin is as effective as dextran as an intrapulmonary hyperoncotic booster of lung growth acceleration after fetal tracheal occlusion, with no lasting effects on its fetal lung liquid levels. As a naturally occurring oncotic agent, albumin may be a safer option in the clinical application of this therapeutic concept.

Lung pathology in patients with congenital diaphragmatic hernia treated with fetal surgical intervention, including tracheal occlusion

Fetal intervention for congenital diaphragmatic hernia was developed to lessen the high morbidity and mortality of pulmonary hypoplasia. Lung pathology and morphometry in patients treated with fetal intervention have not been described. We report clinical and autopsy findings, as well as basic lung morphometry in 16 cases of congenital diaphragmatic hernia with fetal intervention (12 cases tracheal occlusion; 4 cases hernia repair), and 19 cases of congenital diaphragmatic hernia without fetal intervention. All patients who underwent fetal intervention were born premature. Lung enlargement with increased lung-to-body weight ratio was observed with fetal tracheal occlusion, accompanied by lower than normal radial alveolar counts and increased alveolar size. Patients treated with tracheal occlusion also had early alveolar development (at 29.8, 30.6, and 30.9 wk postconceptual age) as well as mucous fluid pooling in airways and alveoli. All cases showed severe alveolar septal widening, more extensive in patients without fetal intervention. When grouped by postconceptual age, no statistically significant difference was found between patients with and without fetal intervention with respect to lung-to-body weight ratio, radial alveolar count, mean alveolar length, and relative arteriolar media thickness. Lung enlargement has been observed with fetal tracheal occlusion sonographically; our studies suggest that this is due in part to emphysema and mucous fluid pooling. The lung remains abnormal with low radial alveolar counts and increased alveolar size. Tracheal occlusion did not prevent development of lung pathology associated with pulmonary hypoplasia.

Down-regulation of sonic hedgehog expression in pulmonary hypoplasia is associated with congenital diaphragmatic hernia

The pathogenesis of pulmonary hypoplasia associated with congenital diaphragmatic hernia (CDH) is unknown. The sonic hedgehog (Shh) cascade is crucial for the patterning of the early respiratory system in mice. To establish whether Shh plays a role in the pathogenesis of lung hypoplasia in CDH, we investigated the gestation-specific expression of Shh in normal rat and human lungs using in situ hybridization and immunohistochemistry. The expression pattern was compared with that of age-matched samples of hypoplastic lungs associated with CDH in humans and in the 2,4-dichlorophenyl-p-nitrophenylether (nitrofen) rat model. Our results showed that in normal controls the expression of Shh increased with advancing gestation, peaked in the late pseudoglandular stage, and declined thereafter. The expression of Shh is initially down-regulated in pulmonary hypoplasia associated with CDH and peaks instead during the late canalicular stage. These data indicate that maximal expression of Shh occurs when respiratory bronchioles develop and thinning of the interstitium takes place, suggesting that Shh may play a role in these processes. Furthermore, we observed that Shh inhibited fetal lung fibroblast proliferation in vitro. Therefore, it is tempting to speculate that alterations in Shh expression may affect these developmental processes, thereby contributing to the pulmonary abnormality in CDH.

Congenital diaphragmatic hernia

Congenital diaphragmatic hernia occurs in approximately 1 in every 2500 live births and is associated with a reported mortality of almost 35% in live-born patients and a higher mortality when in utero deaths are counted. Ventilator-induced lung injury, pulmonary hypoplasia, and other associated anomalies account for the high death rate. Numerous adjunctive measures have been used to treat these patients. Inhaled vasodilators (nitric oxide), intravenous vasodilators, and fetal therapy have no proven benefit. While animal models of congenital diaphragmatic hernia are surfactant deficient, controversy remains over the use of surfactant in infants. There has been no clinical trial showing any clear benefit with the use of exogenous surfactant in these patients. Similarly, prenatal corticosteroids show some improvements in animal models, but again, there is a complete absence of supportive data to show benefit in humans. Mechanical ventilator strategies that limit ventilator-induced lung injury by avoiding hyperventilation and lung over inflation are the strategies currently in use that have been associated with improved survival. Long-term follow-up of these patients is quite important since gastroesophageal reflux, developmental delay, chronic lung disease, and chest wall deformity are all seen with increased frequency in these children.

Pulmonary effects of in utero tracheal occlusion are dependent on gestational age in a rabbit model of diaphragmatic hernia

PURPOSE

The authors investigated the effect of gestational age on lung development and maturation after in utero tracheal occlusion (TO) in a rabbit model of congenital diaphragmatic hernia (CDH).

METHODS

In 46 fetal rabbits, CDH was created at 23 days' gestational age (GA; term, 31 days), corresponding to the pseudoglandular phase of lung development. A second intervention was performed at either 26, 27, or 28 days on 6 fetuses in each GA group. At that time, either TO (CDH + TO), or a sham operation (CDH + sham) was performed. Nonoperated littermates served as internal normal controls (CTR). All fetuses were delivered by cesarean section at 30 days GA to assess lung response by lung-to-body-weight ratio, pulmonary morphometry, and the density of type II pneumocytes.

RESULTS

After TO, the lungs were significantly larger than in CDH animals; their weight was proportional to the duration of TO. Pulmonary morphometry in TO fetuses was comparable with that of controls. The density of type II cells was inversely related to the gestational age at which TO was performed, with normal values with TO at GA at 28 days.

CONCLUSION

Timing of TO is critical to subsequent pulmonary development: early in gestation TO leads to pulmonary overgrowth and type II pneumocyte depletion, whereas normal values are obtained when TO is delayed till 28 of 32 days.

Use of antenatal steroids to counteract the negative effects of tracheal occlusion in the fetal lamb model

Tracheal occlusion (TO) in fetal lambs induces pulmonary hyperplasia but has negative effects on type II cells. The purpose of this study was to determine whether antenatal steroids could reverse the adverse effects of TO on lung maturation in fetal lambs. Sixteen time-dated pregnant ewes (term, 145 d) and 24 of their fetuses were divided into six groups: 1) TO at 117 d gestation; 2) TO at 117 d with a single maternal intramuscular injection of 0.5 mg/kg betamethasone 24 h before delivery; 3) TO at 117 d and release of the occlusion 2 d before delivery; 4) TO and release of the occlusion with maternal steroids; 5) unoperated controls without antenatal steroid treatment; and 6) unoperated controls, littermates of groups 1-4, treated with antenatal steroids. All fetuses were killed at 137 d gestation. Outcome measurements consisted of lung weight-to-body weight ratio; lung morphometry determined by mean terminal bronchial density; and assessment of type II pneumocytes by in situ hybridization to the mRNA of surfactant proteins B and C. Lung weight-to-body weight ratio and mean terminal bronchial density were significantly different among groups with TO and controls, indicating increased lung growth and structural maturation. The density of type II pneumocytes was markedly decreased by TO. Release 2 d before sacrifice significantly increased the density and surfactant activity of type II pneumocytes, but to levels still far from controls. Steroids alone had an effect similar to release. An additive effect was noted with steroids and 2-d release resulting in type II cell density comparable to controls. After fetal TO, a single maternal intramuscular dose of 0.5 mg/kg of betamethasone 24 h before delivery allows partial recuperation of the type II pneumocytes, an effect that is potentiated by 2-d release.

Surfactant levels after reversible tracheal occlusion and prenatal steroids in experimental diaphragmatic hernia

BACKGROUND/PURPOSE

In normal lungs, fetal tracheal occlusion (TO) induces lung growth but decreases the number of type II cells; this is remedied if TO is released (TR) before delivery. In the current study, the effects of TO with or without TR on pulmonary structure and surfactant were assessed in the ovine model in which lung hypoplasia was induced by creation of a diaphragmatic hernia (CDH).

METHODS

A left-sided CDH was created in fetal lambs at 80 days gestation; TO was done at 108 days; and TR at 129 days. All ewes were given 1 dose of glucocorticoids at 135 days. At 136 days, the fetus was delivered. Lung weight to body weight ratio, mean terminal bronchiole density, type II cell density, bronchoalveolar lavage fluid (BAL) phosphatidylcholine (PC), BAL surfactant protein A (SP-A) and B (SP-B), and lung tissue SP-A and SP-B were assessed in CDH, CDH with TO, CDH with TO and TR, and controls.

RESULTS

CDH lungs were hypoplastic and structurally immature, but had increased type II cell density. TO with or without TR caused lung growth with normalization of lung parenchymal architecture and type II cell density. Although the BAL SP-A and BAL SP-B were similar in all 4 groups, the BAL PC was low in CDH with or without TO or TR. Also, lung tissue SP-B levels were low in CDH with or without TO or TR. However, lung tissue SP-A levels were normal in CDH, but low in CDH with TO with or without TR.

CONCLUSIONS

Despite the finding that lung morphology was improved in CDH with TO with or without TR animals, surfactant content and composition remained abnormal. Although surfactant secreted early by the fetus into alveolar spaces contained normal levels of BAL SP-A and BAL SP-B, the low levels of BAL PC and low lung tissue stores of SP-B indicate that these experimental lambs may experience respiratory insufficiency soon after birth. This implies that prophylactic surfactant at birth might be beneficial for CDH.

Upregulation of keratinocyte growth factor in the tracheal ligation lamb model of congenital diaphragmatic hernia

PURPOSE

Congenital diaphragmatic hernia (CDH) carries a high mortality rate of 60% because of associated anomalies, pulmonary hypoplasia, pulmonary hypertension, and type II cell dysfunction. Prenatal tracheal ligation has been shown to improve lung growth in experimental models. This could be caused by a direct effect of increased endothoracic pressure in utero, secondary to the induction of specific growth factors, or both. Keratinocyte growth factor (KGF) is involved in normal lung organogenesis and is a potent mitogen of alveolar type II cells. The authors have therefore investigated the protein and mRNA levels of keratinocyte growth factor in the lung tissue of control, CDH, and CDH tracheal ligation lambs.

METHODS

Eight lambs had left-sided diaphragmatic hernias surgically created at 80 days' gestation. Tracheal ligation was performed at 110 days in 4 lambs, and they were delivered by cesarean section at 140 to 145 days. Twin littermates served as controls. The lungs were dissected en bloc and snap frozen. KGF protein levels were determined by ELISA. Total RNA was isolated, and a RNase protection assay was performed using an ovine cDNA probe for KGF, and a human cDNA probe for GAPDH (house keeping control). Densitometric analysis was used to quantify the relative amounts of mRNA in each sample.

RESULTS

There was a significant decrease in the KGF protein levels of the CDH samples (110 v 73.2 pg/mg protein, P =.02). This decrease was mirrored by a significant fall in the level of mRNA expression for KGF (0.694 v 0.235, P = .02). Tracheal ligation normalized the KGF protein levels (96.1 pg/mg protein). This elevation of KGF protein was accompanied by an upregulation of KGF gene expression to control levels (0.56).

CONCLUSIONS

Tracheal ligation clearly is accompanied by an upregulation of keratinocyte growth factor protein and gene expression. It is not yet clear whether keratinocyte growth factor is solely responsible for the growth observed in these tracheal ligation preparations. Further growth factor blocking experiments are required.

Effect of immediate versus slow intrauterine reduction of congenital diaphragmatic hernia on lung development in the sheep: a morphometric analysis of term pulmonary structure and maturity

The incidence of congenital diaphragmatic hernia (CDH) is 1:1,200-5, 000, and the condition is associated with high mortality and morbidity attributed principally to associated pulmonary hypoplasia. One treatment approach has been for intrauterine intervention to induce lung growth to a sufficient level to allow survival at birth. Repair of the hernia in utero has been attempted, using a method of immediate reduction and repair of the hernia (patch) compared to a slow reduction method using a silastic "silo" sewn over the diaphragm defect to contain the hernial contents. In animal studies, this second method has been associated with lower fetal morbidity and mortality. This study, utilizing the sheep model of CDH, focuses on analysis of lung structural development and maturation, comparing the efficacy of the immediate vs. slow methods of hernial repair in preventing/reversing pulmonary hypoplasia. We hypothesized that: a) Both the immediate (patch) and slow (silo) methods of hernia repair performed in the lamb model of CDH will stimulate lung growth and structural development and restore lung structure and maturity towards normal levels by term gestation; b) Effects will be detectable by morphometric measurement of the following parameters: lung volume; parenchyma to nonparenchyma tissue ratio; volume density of connective tissue in nonparenchyma; gas exchange tissue to airspace ratio; gas exchange surface area; capillary loading; alveolar/airspace density; and alveolar perimeter; c) Effects will be seen in all lobes of the lung; and d) There will be no significant difference in lung size or structural parameters between the two groups. Forty-four pregnant ewes were allocated randomly to one of four groups. Fetal lambs in three groups (n = 36) underwent CDH creation at days 72-74 of gestation. Of surviving lambs showing an adequate hernia, 9 were not operated on further, 11 underwent "repair" using a silastic chimney around the hernial contents (slow reduction), and 11 underwent "repair" by a silastic patch over the diaphragmatic defect (immediate reduction). The fourth group were normal controls. All surviving lambs (n = 8 in each group) were delivered by Cesarian section at 141-143 days (term = 145-149 days). Lungs were obtained at autopsy, inflation-fixed, divided into lobes, and sampled, and morphometric analysis was performed. Comparisons were made between these groups and with matched normal controls and CDH untreated animals prepared in conjunction and previously reported. The lungs from the CDH animals treated by both methods of fetal hernia repair showed significant lung growth and structural development and maturation, although they remained significantly hypoplastic compared to normal. There were minor differences in the lung parameters between these two groups, with a tendency for the slow method to provide more normal parameter values. An exception was the increase in lung volume that was greater for the immediate (patch) method, particularly in the left lower lobe. In conclusion, intrauterine hernia repair by both methods is capable of partially reversing total lung and lobar structural hypoplasia and immaturity. The slow reduction method, with reduced potential for mortality and morbidity, is at least as good at reversing pulmonary hypoplasia as the immediate method. Alternative intrauterine interventions to prevent or reverse pulmonary hypoplasia are discussed and compared with the hernia repair methods used in this study.

Short-term tracheal occlusion corrects pulmonary vascular anomalies in the fetal lamb with diaphragmatic hernia

BACKGROUND

Sustained fetal tracheal occlusion (TO) results in accelerated lung growth but causes severe type II cell depletion. Temporary TO fails to cause lung growth in a congenital diaphragmatic hernia (CDH) model but preserves type II cells and corrects pulmonary hypertension. Herein, we study the pulmonary vascular changes caused by temporary TO.

METHODS

CDH was created in 12 fetal lambs (65-70 d; term, 145 days). In 6 lambs, the trachea was occluded for 2 weeks (CDH + TO; 108-122 d). Animals were killed at 136 days. The lungs were processed with elastin stains and anti-alpha-smooth muscle actin antibody. Partial or circumferential presence of inner and outer elastic lamina was used to determine muscularization of pulmonary arterioles. The percent of medial wall thickness was plotted against vessel diameter for each group.

RESULTS

Lung weight/body weight was smaller in lambs with CDH (1. 35% +/- 0.56%) and CDH + TO (1.70% +/- 0.34%) than in control lambs (3.55% +/- 0.56%; P <.05, single-factor analysis of variance). The smallest muscularized vessel was 113 +/- 50 microm, and the largest nonmuscularized vessel was 138 +/- 49 microm in lambs with CDH, significantly different from control lambs (185 +/- 69 microm and 350 +/- 116 microm, respectively) and lambs with CDH + TO (185 +/- 97 microm and 245 +/- 100 microm, respectively; P <.05). In lambs with CDH, only 25% of vessels of less than 60 microm were nonmuscularized, compared with 81% in control lambs (P <.05) and 74% in lambs with CDH + TO.Conclusions. Temporary tracheal occlusion, from 108 to 122 days, corrects the abnormal muscularization of pulmonary arterioles seen in CDH. These morphometric findings parallel physiologic results at birth and further suggest that short-term occlusion, which preserves surfactant-producing type II pneumocytes without lung growth, may be sufficient to improve neonatal outcome of diaphragmatic hernia.

Late-gestation tracheal occlusion in the fetal lamb causes rapid lung growth with type II cell preservation

BACKGROUND

Fetal tracheal occlusion (TO) results in varying degrees of lung growth. This study examines whether gestational age influences lung growth response following TO.

MATERIALS AND METHODS

Fetal lambs (term = 145 days) underwent TO early (108 days, n = 6) or late (122 days, n = 6) in gestation. Aspirated lung fluid volume (LFV) and intratracheal pressure (ITP) were recorded daily. Two weeks after TO, the fetuses were sacrificed. Lung growth was assessed by lung weight and stereologic volumetry. Type II cellular density was assessed by computer-assisted morphometry using antisurfactant protein B antibody.

RESULTS

After early TO, ITP remained below 2 mm Hg for all but one of the first 5 days. In late TO, ITP rose to 4.8 +/- 1.7 mm Hg by Day 1 and remained elevated. LFV remained lower after early than after late TO (P < 0.05) for 8 days. Thereafter, pressure and volume reached similar levels in both TO groups; both were significantly higher than their respective controls (P < 0.05). Parenchymal fraction (1 - air-space fraction) was significantly smaller after late TO (22.8 +/- 1.2%) than after early TO (31.3 +/- 0.5%). Type II density was 38.0 +/- 12.4 x 10(6)/mL after early TO and 84.0 +/- 24.3 x 10(6)/mL in control (P < 0.05); the difference between late TO and control was not significant.

CONCLUSIONS

Late tracheal occlusion in fetal lambs caused more rapid lung growth than earlier TO, although ultimate lung size was similar in both groups. Late TO also resulted in greater air-space fraction and better preservation of the type II cell population than early TO. Late-gestation tracheal occlusion may therefore be preferable to prolonged occlusion initiated earlier.

Short-term tracheal occlusion in fetal lambs with diaphragmatic hernia improves lung function, even in the absence of lung growth

BACKGROUND/PURPOSE

Prolonged tracheal occlusion (TO) accelerates lung growth but impairs surfactant production. Short-term TO results in less lung growth but preserves type II cell function. The authors studied the effects of short-term TO on lung physiology in diaphragmatic hernia.

METHODS

Diaphragmatic hernia was created in 9 fetal lambs at 90 to 95 days. Five were left uncorrected (CDH), 4 underwent 2-week TO (108 to 122 days; CDH + TO). Five unoperated lambs served as controls. Near-term (136 days) fetuses were ventilated for 90 to 150 minutes. Pulmonary arterial pressure, postductal blood gases, quasistatic compliance, total lung capacity (TLC), and lung weight to body weight (LW/BW) were measured.

RESULTS

There was an overall survival rate of 89% at full term. Short-term occlusion did not induce lung growth (TLC and LW/BW, 6.07 +/- 2.92 mL/kg and 0.022 +/- 0.008 in CDH, 4.86 mL/kg and 0.019 +/- 0.005 in CDH + TO, 10.81 +/- 3.55 mL/kg and 0.036 +/- 0.006 in controls, respectively). However, pulmonary hypertension in CDH (47.4 +/- 12.32/35.8 +/- 12.19 torr) was corrected by short-term occlusion (20.2 +/- 4.0/16.0 +/- 4.8 torr in CDH + TO, P< .05, single-factor analysis of variance [ANOVA]; similar to control). Best pO2 and pCO2 improved after occlusion (CDH, 48.6 +/- 6.7 torr and 107.1 +/- 34.3 torr, respectively; CDH + TO, 101.5 +/- 16.3 torr and 81.9 +/- 2.4 torr; control, 291.4 +/- 4.7 torr and 37.7 +/- 17.3), as did oxygenation index (P < .05, CDH vCDH + TO; CDH, 97.2 +/- 23.0; CDH + TO, 28.7 +/- 3.1; control, 5.6 +/- 0.6).

CONCLUSIONS

Short-term TO corrects pulmonary hypertension and improves gas exchange in fetal lambs with diaphragmatic hernia despite failure to produce accelerated lung growth. Inducing lung maturation and correcting the physiological derangement in diaphragmatic hernia may be more important than achieving lung growth alone.

The effects of mechanical forces on lung functions

The lung is a dynamic organ that is subjected to mechanical forces throughout development and adult life. This review article addresses the types of mechanical forces in the lung and their effects on development and normal lung functions. The effects of mechanical forces on the various different cell types of the lung are discussed, as are the mechanisms underlying mechanotransduction.

Respiratory function in lambs after in utero treatment of lung hypoplasia by tracheal obstruction

Tracheal obstruction (TO) stimulates growth of hypoplastic lungs in the fetus, but there is little knowledge of subsequent postnatal respiratory function. We have determined the effectiveness of TO in fetal sheep with existing lung hypoplasia in restoring postnatal respiratory function. Lung hypoplasia was induced by lung liquid drainage from 112 days of gestation to term ( approximately 148 days). We used an untreated group (ULH), a treated group (TLH) in which the trachea was obstructed for 10 days, and a control group. ULH lambs died within 4 h of birth. TLH lambs were hypoxic for the first week and were hypercapic at 2 days. Pulmonary diffusing capacity, gas volumes, and respiratory compliances were not different between control and TLH lambs. Minute ventilation was not different between the two groups; however, tidal volumes were lower and respiratory frequencies were higher in TLH lambs than in controls for 2 wk after birth. We conclude that 10 days of TO in the presence of initial lung hypoplasia prevents death at birth and returns most aspects of pulmonary function to normal by 1-2 wk after birth.

Fetal tracheal occlusion in the rat model of nitrofen-induced congenital diaphragmatic hernia

Prenatal tracheal occlusion (TO) consistently accelerates lung growth in the sheep model of congenital diaphragmatic hernia (CDH). However, significant variability in lung growth has been observed in early clinical trials of TO. We hypothesized that lung hypoplasia created at relatively late stages of lung development may not be equivalent to human CDH-induced lung hypoplasia, which begins early in gestation. To test this hypothesis, we performed TO in the rat model of nitrofen-induced CDH. Left-sided CDH was induced by administering 100 mg of nitrofen to timed pregnant rats on day 9 of gestation. On day 19 of gestation, four to five fetuses per dam underwent surgical ligation of the trachea. At death (day 21.5), lungs from non-CDH (non-CDH group), left-CDH (CDH group), and trachea-occluded left-CDH fetuses (CDH-TO group) were harvested and compared by weight, DNA and protein content, and stereological morphometry. Wet and dry lung weight-to-body weight ratio, total lung DNA and protein contents, the volume of lung parenchyma, and the total saccular surface area of the CDH-TO group were significantly increased relative to the CDH group and were either greater than or comparable to the non-CDH controls. We conclude that TO accelerates lung growth and increases lung parenchyma in an early-onset model of CDH-induced lung hypoplasia.

Lung growth response after tracheal occlusion in fetal rabbits is gestational age-dependent

In utero tracheal occlusion (TO) is a potent stimulus of fetal lung growth, and is currently being applied in clinical trials to treat severe forms of pulmonary hypoplasia. The aim of this study was to examine the effect of timing of TO on pulmonary growth and maturation rates. Fetal rabbits (term = 31 d) were subjected to in utero tracheal clipping at 24 (late pseudoglandular stage) or 27 d of gestation (late canalicular/early terminal sac stage). Sham-operated littermates served as controls (C). Animals were killed at time intervals ranging from 1 to 6 d (early group) or 1 to 3 d (late group) after occlusion. Lung growth was measured by computerized stereologic volumetry and 5'-bromo-2'-deoxyuridine (BrdU) pulse labeling. Pneumocyte II population kinetics were analyzed using a combination of anti-surfactant protein-A and BrdU immunohistochemistry and computer-assisted morphometry. Statistical analysis was performed using unpaired Student's t test. Early TO was followed by an initial 3-d stagnation of growth and subsequently a dramatic acceleration of growth (BrdU-labeling index [LI] 10.1 +/- 0. 6% in TO versus 2.7 +/- 0.5% in C at 29 d, P < 0.001). In contrast, late TO induced an immediate and sustained moderate increase of lung growth (BrdU-LI 2.8 +/- 0.9% in TO versus 1.1 +/- 0.2% in C at 30 d, P < 0.05), associated with relatively more pronounced air-space distension. Whereas late TO caused no significant alterations in type II cell density or proliferation, early TO was followed by a marked increase in type II cell proliferation, paradoxically associated with dramatic reduction of type II cell density after 29 d. The effects of intrauterine TO on fetal lung growth and type II cell kinetics critically depend on the gestational age, and thus on the maturity of the lungs at the time of surgery. These findings have important clinical implications with respect to the timing of fetal interventions aimed at promoting lung growth. The fetal rabbit provides an invaluable model to study the mechanics and age dependency of TO-induced lung growth.

Tracheal ligation increases mitogen-activated protein kinase activity and attenuates surfactant protein B mRNA in fetal sheep lungs

BACKGROUND

Tracheal ligation has been shown to accelerate fetal pulmonary growth in normal and hypoplastic lungs. Our aim was to study the effects of tracheal ligation on established molecular markers of growth and differentiation [mitogen-activated protein (MAP) kinase] and maturity [surfactant protein B (SPB) and fatty acid synthase (FAS)].

MATERIALS AND METHODS

Tracheal ligation was performed on four 100-day-gestation fetal sheep, with four age-matched fetuses undergoing maternal laparotomy and hysterotomy as control. Lungs from surviving fetuses (n = 2 in each group) were harvested after 4 days and frozen in liquid nitrogen. Protein lysates were prepared, and MAP kinase enzymatic assays [extracellular signal regulated protein kinase (ERK)-1 and -2] and Western blots were performed. Total RNA was isolated, and a fetal sheep lung cDNA library was created. The sheep SPB and FAS genes were cloned and sequenced. Northern blots were performed with the new clones, normalizing to beta-actin.

RESULTS

Tracheal ligation lungs contained a larger volume of fluid (40 ml) compared with age-matched controls (8 ml). MAP kinase enzymatic ERK-1 activity was increased and SPB mRNA expression was reduced in fetal lungs after tracheal ligation. Neither ERK-2 enzymatic activities and FAS mRNA nor ERK protein levels were affected by tracheal ligation, by Western blot analysis.

CONCLUSION

Tracheal ligation-induced fetal lung growth may be mediated in part via the MAP kinase pathway. Expression of SPB mRNA is attenuated by tracheal ligation, whereas FAS, one of the key enzymes that synthesizes the lipid portion of surfactant, is not affected.

The role of apoptosis in normal and accelerated lung development in fetal rabbits

BACKGROUND/PURPOSE

During fetal development, the mammalian lung undergoes progressive parenchymal involution. Intrauterine tracheal occlusion induces accelerated architectural maturation of the fetal lungs associated with depletion of the surfactant-producing type II cells. This study investigates the spatiotemporal pattern of apoptosis during normal fetal lung development and its modulation in tracheal occlusion-induced accelerated fetal lung growth.

METHODS

Fetal rabbit lungs were studied at 25 to 31 days' gestational age (DGA; term, 31 DGA), corresponding to late pseudoglandular through terminal air sac stages of fetal lung development. Intrauterine tracheal ligation (TL) was performed at 24 DGA. TL fetuses were monitored until 29 DGA, a time-point previously shown to coincide with significant type II cell depletion. Apoptotic cells were identified by light and electron microscopy, as well as terminal deoxynucleotidyl transferase-mediated dUTP-FITC nick-end labeling (TUNEL). Epithelial (type I and II) cell apoptosis was studied by TUNEL labeling in conjunction with antisurfactant protein and anticytokeratin immunohistochemistry. DNA fragmentation was analyzed by gel electrophoresis. Sham-operated littermates served as controls.

RESULTS

The number of apoptotic cells progressively increased with advancing lung growth and architectural maturation (apoptotic index [Al] 1.2 +/- 0.7 x 10(-3) at 25 DGA v 4.2 +/- 1.4 x 10(-3) at 31 DGA; P< .05, analysis of variance). In TL fetuses, the apoptotic rate was significantly higher than in non-TL fetuses from the third postligation day on, coinciding with the onset of significantly increased airspace distension (Al 4.9 +/- 1.3 x 10(-3) in TL v2.6 +/- 0.4 x 10(-3) in controls at 29 DGA; P< .05, Student's ttest). Apoptosis occurred in parenchymal cells and in isolated cells within the airspaces. The apoptotic activity of type II cells was significantly higher in TL fetuses than C fetuses at 29 DGA (type II Al 25.5 +/- 6.3 x 10(-3) in TL v2.3 +/- 0.8 x 10(-3) in C; P< .001). Electron microscopic studies confirmed the presence of apoptotic nuclei in interstitial macrophages and in degenerating intraluminal type II cells. DNA analysis showed nucleosomal bands.

CONCLUSIONS

Normal fetal lung development is associated with a progressive increase of epithelial and interstitial apoptotic activity, a process enhanced by TL. Tracheal occlusion induces a significant increase of type II cell apoptosis, which likely contributes to the observed type II cell depletion after TL. We speculate that fetal type II cell apoptosis after TL may be induced by mechanical distension (stretch) of the airspaces.

Ultrastructural evaluation of lung maturation in a sheep model of diaphragmatic hernia and tracheal occlusion

In fetuses with diaphragmatic hernia (DH) lung development is impaired, and pulmonary hypoplasia is one of the main factors responsible for the poor outcome of the disease. A possible treatment consists of occluding trachea during lung development to retain pulmonary fluid and to force the lung to expand. Although it appeared promising at first, this technique has recently been reported to decrease type II cell number and to induce surfactant deficiency. The aim of this study was to investigate lung maturation further through ultrastructural examination in a fetal lamb model of DH created at 85 d, followed or not by endoscopic balloon tracheal occlusion (TO) at 120 d of gestation. The proportion of alveolar epithelial type I and type II cells was altered by both treatments: the type I/type II cell ratio, which was about 2 in control lungs, was decreased 4.5-fold in DH lungs but was increased 4.5-fold in DH+TO lungs. The proportion of undifferentiated cells was increased in DH lungs. Indeterminate cells sharing features of type II and type I cells that were not observed in controls were seldom seen in DH lungs and were numerous in DH+TO lungs. The number of lamellar bodies per type II cell was decreased in both DH and DH+TO groups. In DH lungs, wall structure presented an immature appearance, with cellular connective tissue and poor secondary septation of saccules. In DH+TO lungs, primary septa appeared more mature, with reduced connective tissue, but secondary septa were still buds, although elastin was present at their tips. A single capillary layer was found in all three groups (control, DH, and DH+TO) with no sign of septal capillary pairing. This first investigation in DH and DH+TO lungs through transmission electron microscopy thus enabled us to show that compression and forced expansion of the lung are both responsible for alterations in type II cell differentiation and septal development.

Tracheal ligation and mechanical ventilation do not improve the antioxidant enzyme status in the lamb model of congenital diaphragmatic hernia

BACKGROUND/PURPOSE

The antioxidant enzyme (AOE) system is the primary intracellular defense system of the lung against oxygen toxicity. The authors recently demonstrated depressed levels of catalase, glutathione peroxidase, and superoxide dismutase in congenital diaphragmatic hernia (CDH) lambs compared with controls. The aim of this study was to determine whether tracheal ligation (TL) or mechanical ventilation (recently shown to stimulate growth and surfactant metabolism, respectively) could induce an elevation in AOE activity.

METHODS

Four nonventilated lambs with surgically created CDH and TL and five CDH lambs ventilated for 4 hours were studied. Lung tissue was analyzed for AOE and the results compared with untreated CDH lambs.

RESULTS

Both ventilation and TL failed to elevate AOE activity above that of untreated CDH lambs.

CONCLUSIONS

The data provide further evidence that TL does not improve lung metabolism or maturation. Mechanical ventilation, which often involves high oxygen delivery, is a necessary and often beneficial therapeutic modality. In the CDH neonate compromised not only by low baseline levels of the AOE, but also by an inability to induce enzyme synthesis in response to hyperoxia, mechanical ventilation may, by causing lung injury, be contributing to the high morbidity and mortality rate associated with CDH.

[Congenital diaphragmatic hernia. II. Is pulmonary hypoplasia an indefinable obstacle?]

Despite major insights into the pathogenesis and pathophysiology of congenital diaphragmatic hernia, and despite the availability of an antenatal diagnosis and continuous progress in neonatal intensive care, little improvement has been obtained in the prognosis of this malformation. Thus obstetricians, neonatologists and pediatric surgeons are still facing a several dilemma: dilemma before birth to predict the prognosis, i.e., to evaluate the severity of the associated pulmonary hypoplasia in order to decide whether or not to interrupt pregnancy; dilemma after birth in case of severe respiratory failure to decide how far to go in life support. Based on a review of the literature and their own experience, the authors attempt to recapitulate the perinatal management and outcome of this severe malformation.