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

Abstract

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, intrauteri...

Diaphragm defects occur in a CDH hernia model independently of myogenesis and lung formation

“…Thus the diaphragmatic defects associated with CDH are a primary defect and not a secondary result of lung malformation. The concept that the lung hypoplasia is in fact secondary to the diaphragmatic defect is supported by data from the surgically induced sheep model of CDH that clearly demonstrates that a hole in the posterolateral diaphragm results in marked lung underdevelopment because of the invasion of abdominal contents and abnormal fetal breathing movements (16,17,23,25). However, there is convincing evidence demonstrating that the teratogens used in the rodent CDH model can directly interfere with lung development (1,6,13,20).…”

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

“…The synergistic effects of tracheal occlusion and intrapulmonary hyperoncotic agents were studied [Kunisaki et al, 2006]. Developmental airway morphometrics in the sheep CDH model were studied, with the observation that relative hypoplasia worsened with gestational age [Lipsett et al, 2000]. Studies on nitric oxide (NO) signaling demonstrated that the NO signaling pathway is intact in the sheep CDH model [Thebaud et al, 1999a].…”

“…There have been numerous studies on the effects of repair of CDH in fetal lambs [Montgomery et al, 1995; Parsons et al, 1994]. Morphometric studies revealed differences between immediate versus slow reduction of CDH on lung development [Lipsett et al, 2000]. Liquid and partial liquid ventilation as treatment strategies were investigated [Major et al, 1995; Wilcox et al, 1995].…”

Safety and efficacy of smart tracheal occlusion device in diaphragmatic hernia lamb model

“…The lambs underwent standardized obduction, during which we first evaluated the presence of herniated viscera inside the thorax. Animals without a defect and stomach and bowel into the chest were excluded from the analysis 17 , because hypoplasia may not have been severe. The trachea and lungs were harvested, separated, and the lung‐to‐body‐weight ratio (LBWR) was calculated 18 .…”

“…We also excluded five fetuses that did not have a diaphragmatic defect at term. We did so because those animals may not have developed pulmonary hypoplasia 17 , making interpretation of the primary outcome measure (LBWR) difficult.…”