Hemodynamics of congenital diaphragmatic hernia in lambs

Prenatal intervention for the management of congenital diaphragmatic hernia

Congenital diaphragmatic hernia (CDH) is the result of incomplete formation of the diaphragm that occurs during embryogenesis. The defect in the diaphragm permits the herniation of abdominal organs into the thoracic cavity contributing to the impairment of normal growth and development of the fetal lung. In addition to the hypoplastic lung, anomalies of the pulmonary arterioles worsen the pulmonary hypertension that can have detrimental effects in severe cases. Most cases of CDH can be effectively managed postnatally. Advances in neonatal and surgical care have resulted in improved outcomes over the years. When available, extracorporeal membrane oxygenation can provide temporary cardiorespiratory support for those not effectively supported by mechanical ventilation. In spite of these advances, very severe cases of CDH still carry a very high mortality and morbidity rate. Advances in imaging and evaluation now allow for early and accurate prenatal diagnosis of CDH, thereby identifying those at greatest risk who may benefit from prenatal intervention. This review article discusses some of the surgical and non-surgical prenatal interventions in the management of isolated severe congenital diaphragmatic hernia.

Acute effect of a dual ETA-ETB receptor antagonist on pulmonary arterial vasculature in preterm lamb fetuses with surgically induced diaphragmatic hernia

PURPOSE

To study the effects of tezosentan, a dual ETA and ETB receptor antagonist on the cardiopulmonary profile in a fetal lamb model of CDH in utero.

METHODS

A diaphragmatic hernia was surgically created at day 75 of gestation. During 45 min of tezosentan perfusion (1 mg/kg), hemodynamic parameters (pulmonary and aortic pressures, left pulmonary and aortic flows, left auricle pressure, heart rate) were measured at day 135 of gestation. Age-matched fetal lambs served as control animals. Secondarily, parietal tension of vessels rings of pulmonary arteries was assessed in organ baths under increasing concentration of tezosentan.

RESULTS

In CDH group, under perfusion of tezosentan, pulmonary artery pressure decreased from 45.8 ± 4.1 to 37.6 ± 5.9 mmHg (P < 0.05). Pulmonary artery flow and pulmonary vascular resistance remained constant. In control group, pulmonary artery flow increased from 153.9 ± 15.8 to 233.4 ± 26 ml/min (P < 0.05). Pulmonary artery pressure did not vary. Subsequently calculated pulmonary vascular resistance decreased. In organ bath, no significant relaxation was observed.

CONCLUSION

In this fetal lamb model of CDH, tezosentan decreased pulmonary artery pressure but did not modify pulmonary blood flow. Endothelin may play a role in the regulation of pulmonary vascular tone in utero.

Vitamin A deficiency (VAD), teratogenic, and surgical models of congenital diaphragmatic hernia (CDH)

Congenital diaphragmatic hernia (CDH) is a congenital malformation that occurs with a frequency of 0.08 to 0.45 per 1,000 births. Children with CDH are born with the abdominal contents herniated through the diaphragm and exhibit an associated pulmonary hypoplasia which is frequently accompanied by severe morbidity and mortality. Although the etiology of CDH is largely unknown, considerable progress has been made in understanding its molecular mechanisms through the usage of genetic, teratogenic, and surgical models. The following review focuses on the teratogenic and surgical models of CDH and the possible molecular mechanisms of nitrofen (a diphenyl ether, formerly used as an herbicide) in both induction of CDH and pulmonary hypoplasia. In addition, the mechanisms of other compounds including several anti-inflammatory agents that have been linked to CDH will be discussed. Furthermore, this review will also explore the importance of vitamin A in lung and diaphragm development and the possible mechanisms of teratogen interference in vitamin A homeostasis. Continued exploration of these models will bring forth a clearer understanding of CDH and its molecular underpinnings, which will ultimately facilitate development of therapeutic strategies.

Modulating effect of a selective endothelin A receptor antagonist on pulmonary endothelin system protein expression in experimental diaphragmatic hernia

BACKGROUND/PURPOSE

Previously, we reported that perinatal administration of atrasentan, a selective endothelin A receptor (ETA) antagonist, provided a beneficial effect on the cardiopulmonary profile under short-term conditions in newborn lambs with surgically induced congenital diaphragmatic hernia (CDH). We hypothesized that changes in the hemodynamic profile that we observed at birth in treated animals could be influenced by pulmonary modulation of the endothelin (ET) system.

METHODS

The effect of atrasentan on protein expression levels of ETs and ET receptors (ETA and ETB receptor) was investigated by immunohistochemistry in lung tissues of untreated control (n = 3), treated control (n = 6), untreated CDH (n = 6), and treated CDH newborn lambs (n = 8).

RESULTS

Right lung tissue of treated control lambs showed significantly higher ETA protein expression levels in both vascular adventitia and airway epithelia when compared with that of untreated control lambs (P < .05). In contrast, protein expression levels of ETA and ETB receptor were significantly lower in the vascular smooth muscle cells among other tissue subcompartments of the right lung of treated CDH newborn lambs vs CDH lambs (P < .02 and P = .005, respectively).

CONCLUSIONS

We speculate that rapid pulmonary modulation of ET system protein expression levels by atrasentan results from an indirect effect possibly dependent on ventilation and/or perfusion. In CDH groups, this could contribute to the beneficial effect of the treatment.

Effect of ABT-627 (A-147627), a potent selective ET(A) receptor antagonist, on the cardiopulmonary profile of newborn lambs with surgically-induced diaphragmatic hernia

1. Postnatal mortality in isolated congenital diaphragmatic hernia (CDH) is mainly related to the associated pulmonary hypertension (PH) and to right-to-left shunting. 2. Endothelins (ETs) are potent vasoconstrictors and pro-mitogenic peptides. Strong evidences support their participation in CDH and in the etiology of PH via the activation of ET(A) receptors (ET(A)-Rs). 3. Evaluation of the effect of ABT-627, a selective non-peptidic ET(A)-R antagonist, given from -15 to 210 min post-delivery (1 mg kg(-1) bolus +0.01 mg kg(-1) h(-1) infusion, i.v.), was conducted in the lamb model of CDH. 4. Severity of CDH was assessed in comparison to untreated controls (n=5). Untreated CDH lambs (n=7) had a higher mean pulmonary arterial pressure (MPAP; P<0.0001), lower mean blood pressure (MBP; P=0.0004), higher MPAP / MBP ratio (P<0.0001), lower arterial pH (P<0.0001), higher paCO(2) (P<0.0001), lower paO(2) (P<0.0001) and lower post-ductal pulsatile SaO(2) (P<0.0001) than untreated controls. 5. Treated controls (n=7) showed a higher MPAP, lower MBP, higher MPAP/MBP ratio, lower arterial pH, higher paCO(2), lower paO(2), lower post-ductal pulsatile SaO(2) and lower plasmatic ir-ET ratios compared to untreated controls (P<0.0001). 6. Treated CDH lambs (n=8) showed a higher MBP (P<0.0001), lower MPAP / MBP ratio (P<0.0001), higher arterial pH (P<0.0001), lower paCO(2) (P<0.0001), higher paO(2) (P=0.0228), higher post-ductal pulsatile SaO(2) (P=0.0016) and lower plasmatic ir-ET ratios (P=0.0247) when compared to untreated CDH lambs. 7. These observations revealed that, although acute perinatal treatment with a selective non-peptidic ET(A)-R antagonist had some adverse effects in controls, it attenuated the progressive cardiopulmonary deterioration that occurred after birth in CDH lambs.

Models of persistent pulmonary hypertension of the newborn (PPHN) and the role of cyclic guanosine monophosphate (GMP) in pulmonary vasorelaxation

At birth, a marked decrease in pulmonary vascular resistance allows the lung to establish gas exchange. Persistent pulmonary hypertension of the newborn (PPHN) occurs when this normal adaptation of gas exchange does not occur. We review animal models used to study the pathogenesis and treatment of PPHN. Both acute models, such as acute hypoxia and infusion of vasoconstrictors, and chronic models of PPHN created both before and immediately after birth are described. Inhaled nitric oxide is an important emerging therapy for PPHN. We review nitric oxide receptor mechanisms, including soluble guanylate cyclase, which produces cGMP when stimulated by nitric oxide, and phosphodiesterases, which control the intensity and duration of cGMP signal transduction. A better understanding of these mechanisms of regulation of vascular tone may lead to safer use of nitric oxide and improved clinical outcomes.

Pathophysiology of congenital diaphragmatic hernia. XI: Anatomic and biochemical characterization of the heart in the fetal lamb CDH model

AIM

The purpose of this study was to determine whether the presence of bowel in the chest during development in the fetal lamb model of congenital diaphragmatic hernia (CDH) results in structural and/or biochemical hypoplasia of the left venticle.

METHODS

The model was created at 80 days' gestation and delivered at term. The hearts were fixed in 4% formaldehyde solution, components weighed, and right ventricular (RV) and left ventricular (LV) wall thicknesses and both aortic (Ao) and pulmonary artery (PA) root diameters were measured. Fresh specimens were analyzed for protein, DNA, hydroxyproline, and elastin content. All CDH measurements are compared with littermate control tissues.

RESULTS

There were no differences in body weight (kg) between CDH and control littermates (4.25 +/- 0.26 versus 3.71 +/- 0.24, P = NS). CDH lambs have significantly decreased total heart (4.88 +/- .25 versus 6.75 +/- .49, P < .05), left ventricular (1.65 +/- .11 versus 2.15 +/- .19, P < .05), septal (1.29 +/- .11 versus 1.99 +/- .21, P < .05), and combined atrial (0.68 +/- .06 versus 1.14 +/- .15, P < .05) weights (g/kg lamb) without differences in RV weights (1.26 +/- .07 versus 1.57 +/- .17, P = NS). LV and RV wall thickness, and Ao root diameters (cm) were found to be identical in both CDH and control lambs. However, PA root diameters (0.47 +/- .01 versus 0.38 +/- .01, P < .005) and ductus arteriosus diameters were increased in CDH (0.35 +/- .01 versus 0.22 +/- .02, P < .005). Total protein, DNA collagen, and elastin content and DNA/total protein ratios were identical in RV and LV in both CDH and control lambs.

CONCLUSION

Newborn lambs with left-sided CDH have a significantly lower total heart, LV, septal, and atrial weights without differences of RV weight or ventricular wall thicknesses. Given these findings, the unchanged DNA/protein ratio implies that the left ventricle is hypoplastic in CDH. Ao/PA root ratios suggest that LV hypoplasia in utero may result in increased left atrial pressures, decreased right-to-left shunting through the foramen ovale, and increased PA pressures and flow, resulting in increased PA root and ductus arteriosus diameters. This model simulates the clinical data from human fetuses/neonates with CDH. Further investigations are necessary to determine the functional significance of these findings.

Pathophysiology of congenital diaphragmatic hernia. VIII: Inhaled nitric oxide requires exogenous surfactant therapy in the lamb model of congenital diaphragmatic hernia

The pathophysiology of the lamb model of congenital diaphragmatic hernia (CDH) involves pulmonary hypoplasia, pulmonary hypertension, and surfactant deficiency. Inhaled nitric oxide (NO) is a highly selective pulmonary vasodilator. The aim of this study was to determine the effects of inhaled NO on pulmonary gas exchange, acid-base balance, and pulmonary pressures in a lamb model of CDH with or without exogenous surfactant therapy. At the gestational age of 78 days (full term, 145 days) 11 lamb fetuses had a diaphragmatic hernia created via a left thoracotomy and then were allowed to continue development in utero. After cesarean section, performed at term, six lambs received exogenous surfactant therapy (50 mg/kg, Infasurf) and five served as controls. All animals were pressure-ventilated for 30 minutes and then received 80 ppm of inhaled NO at an F1O2 of .9 for a 10-minute interval. Compared with the control lambs, the lambs with exogenous surfactant therapy had higher pH (7.17 +/- .06 v 6.96 +/- .07; P < .05), lower PCO2 (73 +/- 8 v 122 +/- 20, p < .05), and higher PO2 (153 +/- 38 v 50 +/- 23; P < .05). In control CDH lambs (without surfactant), inhaled NO did not improve pH, PCO2, or PO2, or decrease pulmonary artery pressure. In CDH lambs given exogenous surfactant, NO decreased pulmonary artery pressures (42 +/- 4 v 53 +/- 5; P < .005) and further improved PCO2 and PO2. NO also made the difference between pulmonary and systemic artery pressures more negative in the surfactant-treated lambs (-15 +/- 4 v -2.3 +/- 2.4; P < .005).(ABSTRACT TRUNCATED AT 250 WORDS)

Fetal lamb pulmonary hypoplasia: pulmonary vascular and myocardial abnormalities

Neonatal pulmonary hypoplasia resulting from a congenital diaphragmatic hernia (CDH) produces hemodynamic changes and morphologic abnormalities of the pulmonary vasculature. To characterize the myocardial and pulmonary vascular status of the fetus with pulmonary hypoplasia, we studied four chronically instrumented, near-term fetal lambs with pulmonary hypoplasia, induced by producing a diaphragmatic hernia. We found an elevation in the pulmonary arterial pressure (control, 43.8 +/- 5.9 mmHg; CDH, 58.8 +/- 9.1 mmHg; p < 0.05), an elevation in the systemic arterial pressure (control, 43.8 +/- 0.48 mmHg; CDH, 58.6 +/- 6.7 mmHg; p < 0.05), and an elevation in the pulmonary vascular resistance (control, 0.47 +/- 0.11; CDH, 3.87 +/- 1.9; p < 0.05). In addition, though the total pulmonary blood flow was reduced (control, 83.5 +/- 32.9 mL/min; CDH, 22.2 +/- 17.6 mL/min; p < 0.05), the blood flow reduction was proportional to the reduction in the lung mass (control, 79.8 +/- 28.1 [in flow per 100-g lung weight]; CDH, 85.4 +/- 71.7). The increase in the pulmonary vascular resistance in relation to the unit lung mass (control, 0.55 +/- 0.33; CDH, 0.99 +/- 0.5) was not as pronounced as its increase in relation to the total pulmonary blood flow.(ABSTRACT TRUNCATED AT 250 WORDS)

Congenital diaphragmatic hernia

Congenital diaphragmatic hernia continues to be a critical problem in neonatal surgery. Despite the apparent simplicity of the anatomic defect, the physiology is complex, and survival remains uncertain. Surgical success has been achieved, but we recognize that the barrier to survival is pulmonary parenchymal and vascular hypoplasia as well as the complex syndrome of persistent fetal circulation. In many ways the problem of diaphragmatic hernia is as much of an enigma to today's physician-scientist as it was to Bochdalek in the nineteenth century. The treatment of respiratory distress after repair of congenital diaphragmatic hernia has brought out the most creative and innovative efforts of pediatric surgeons in both the laboratory and the intensive care unit.

Creation and repair of diaphragmatic hernia in the fetal lamb: lung development and morphology

Left-sided diaphragmatic hernias were created in 26 lambs at about 78 days' gestation and repaired at 106 to 124 days' gestation. Nine of these lambs were delivered at term and lived much longer than the nonrepaired lambs delivered at term. The normal development of the fetal lamb lung is compared and contrasted with the development of the lung after creation of a diaphragmatic hernia and also with the changes in morphology resulting from in-utero repair. Creation of a diaphragmatic hernia resulted in marked delay in the development of alveoli and at term the lung had small, thick-walled terminal air-spaces with few capillaries and no true alveoli when compared with the thin-walled alveoli in normal lungs. Another striking feature was an apparent increase in the frequency of type II alveolar cells in diaphragmatic hernia lungs. In-utero repair of the diaphragmatic hernia resulted in a more normal appearance with true alveoli developing by term, although capillaries appeared to be less numerous and type II cells more numerous than in normal lungs. Surprisingly, there appears to be little difference between the left and right lungs in lambs with diaphragmatic hernia.

Creation and repair of diaphragmatic hernia in the fetal lamb: techniques and survival

Diaphragmatic hernias were created in 54 fetal lambs at 72 to 82 days gestation via a left thoracotomy. The diaphragmatic hernia was repaired in 30 lambs at 106 to 123 days gestation, and 14 of these lambs subsequently aborted. The majority of those surviving to term were delivered for survival. Four lambs with an unrepaired diaphragmatic hernia were intensively resuscitated at delivery and their diaphragmatic hernias repaired; survival in these lambs ranged from 20 minutes to 89 hours. Nine lambs with repaired diaphragmatic hernia were resuscitated following delivery; survival times ranged from one hour, 45 minutes to 123 days, with three lambs surviving to be sacrificed at 43, 62, and 123 days. Three of the lambs that died before sacrifice, died of causes unrelated to their lung function. These results show that in-utero repair of the diaphragmatic hernia in the fetal lamb results in improved survival. We feel, however, that direct application of these results in humans would be premature.

Maternal ultrasonography for the antenatal diagnosis of surgically significant neonatal anomalies

The increased use of ultrasonography in the management and evaluation of pregnancy has provided a unique opportunity to observe the anatomy of the developing fetus from 12 weeks gestation until term. Twenty-eight surgically important anatomic abnormalities have been diagnosed in utero by sonographic examinations at our affiliated institutions over the past three and a half years. These include ascites (five cases), gastroschisis (four cases), omphalocele (three cases), sacrococcygeal teratoma, cystic hygroma, hydrocele, duodenal atresia, multicystic kidney (two cases each), and one each of jejunal atresia, conjoined twins, ureteropelvic junction obstruction, urethral valves, urethral agenesis, and hydronephrosis secondary to reflux. Prenatal diagnosis by ultrasonographic examination has signifcantly improved perinatal management. Elective caesarean section has benefited infants with lesions causing dystocia, such as sacrococcygeal teratoma, omphalocele, and conjoined twins. Advance notification of surgeons and neonatalogists has reduced the delays of postnatal evaluation and treatment that contribute, significantly, to complications and death. In addition, transfer of the pregnant mother carrying an infant with a significant surgical anomaly to a center with facilities for neonatal surgery and specialized postoperative care can be properly planned for in advance. In the near future, intrauterine fetal surgery or palliative intervention may provide increased salvage of patients with obstructive uropathy and diaphragmatic hernia, both of which carry high mortality rates secondary to in utero damage. Sonography has proven useful in following the dilatation of either intestinal or urinary tract structures in utero. In our hands, maternal sonography has improved the surgical care of the newborn and may open a new frontier of intrauterine fetal surgery in the future.

Tolazoline in the treatment of congenital diaphragmatic hernias

Four babies with congenital diaphragmatic hernias each developed a state of transitional circulation. Tolazoline was successfully used to lower the pulmonary vascular resistance and to treat this normally fatal postoperative complication.

Pediatric diaphragmatic hernias. An 11 year experience

A retrospective study of 36 infants and children with diaphragmatic hernia was carried out. Mortality was confined to the group of patients identified between birth and 6 hours of life. Survivors appeared to be separable early in life from those who died on the basis of clinical status at birth measured by the Apgar, by ventilatory capacity of the lung reflected by carbon dioxide pressure and by acid base balance. Oxygenation, time from birth surgery, maternal factors, and labor and delivery appeared to play no role in survival. Hypoplasia of the lung reflected in low lung weights in those who died did not correlate with initial clinical status or blood gas data. Surgical adjuncts to reduction and closure of the hernia did not appear to have an effect on survival. Definition of patients at high risk of dying will permit critical application an evaluation of modes of treatment beyond those now used regularly in the care of these desperately ill infants.

Congenital diaphragmatic hernia

A description of the pathology, clinical presentation and management of congenital diaphragmatic hernia is given together with the results obtained in Newcastle during the last seven years. Some suggestions are made for improved management.