New developments in bronchopulmonary dysplasia

Obstructive lung disease in children with mild to severe BPD

BACKGROUND

Bronchopulmonary dysplasia (BPD) is a common cause of respiratory insufficiency in children born very premature.

OBJECTIVES

The purpose of this study was to examine the impact of the severity of BPD on pulmonary morbidity at school age, as measured by conventional spirometry and impulse oscillometry. We also studied the association between changes in lung function and structural changes in the lungs of children with BPD via High-Resolution Computed Tomography (HRCT). Finally we studied the prevalence of atopy associated with BPD.

METHODS

We studied 60 very low birth weight (VLBW) children, 28 with respiratory distress syndrome (RDS) who did not develop BPD ("preterm non-BPD") and 32 with RDS who developed BPD. The severity of BPD was graded as mild, moderate or severe. Follow-up at age 6-8 years consisted of spirometry, oscillometry, thoracic HRCT, allergy skin-prick test, blood samples and a questionnaire.

RESULTS

All children with BPD showed some evidence of impaired lung function (more negative reactance, FEV1<80% predicted, greater reversibility), although less than half of these children were symptomatic. The majority of children with BPD (19/26) showed abnormalities on HRCT. There was no evidence that atopy was associated with BPD.

CONCLUSIONS

Children with mild BPD exhibited similar impairments in respiratory mechanics and lung structure to those diagnosed with moderate BPD. The widespread involvement of the peripheral airways suggests that all children diagnosed with BPD are potentially at risk of developing chronic obstructive pulmonary disease later in life.

Enhanced distribution of adenovirus-mediated gene transfer to lung parenchyma by perfluorochemical liquid

Although gene therapy holds great promise for the treatment of inherited and acquired diseases of the lung, a number of issues including efficient delivery and distribution of genes to pulmonary target cells must still be addressed. In this study we evaluated the use of perfluorochemical (PFC) liquid as a vehicle for delivery of recombinant adenovirus (AdCBlacZ) to lungs of juvenile rabbits. Virus was instilled into trachea of rabbits, and 4 days later the lungs were removed, cut into multiple pieces, and assayed for beta-galactosidase (beta-Gal) activity. Total lung expression of the beta-Gal reporter gene was increased two- to three-fold by instillation of the virus (10(11) particles/kg body weight) in saline (1.5 ml/kg) simultaneously with perflubron liquid (15 ml/kg) compared to virus+saline alone (control). Uniformity of beta-Gal activity between lobes was significantly improved by the PFC liquid. In perflubron-treated lungs approximately 45% of the lung pieces had beta-Gal-specific activity values within 50-150% of the mean specific activity for the total lung, compared to only approximately 15% of the pieces in control lungs. More of total lobar beta-Gal activity was recovered in the distal lung tissue (approximately two-fold greater than controls, p < 0.05). Morphological assessment of X-Gal-stained, fresh-frozen lung sections showed increased levels and more complete staining of alveolar wall cells in the PFC group. These data indicate that the PFC liquid perflubron enhances distribution of virus-mediated gene expression to the lung parenchyma in healthy rabbits. PFC liquid may be a useful treatment vehicle for accessing distal spaces of the damaged or diseased lung.

Oxygen toxicity to the developing lung of the mouse: role of reactive oxygen species

Since the description of bronchopulmonary dysplasia (BPD) in premature infants, the supplemental oxygen administered has been suspect in the etiology of BPD. This has prompted studies on the effect of hyperoxia on lung growth in neonatal animals. So far, these have not led to a treatment which either prevents or mitigates BPD. Another approach to investigate the effect of hyperoxia on the immature lung is to use lung explants from 12-d gestation mouse fetuses. Exposing explants to different concentrations of oxygen for 48 h, we found that exposures to oxygen both below (10%) and above (35% or greater) normoxia adversely affected branching morphogenesis and growth. The effect was irreversible at exposures of 50% oxygen and greater. To determine the role of reactive oxygen species (ROS) in the effect of hyperoxia, antioxidants and inhibitors of ROS formation were added to the incubating explants, and their influence on reducing the adverse effect of 50% oxygen was assessed. The combination of CuZn superoxide dismutase (SOD) and catalase, manganese SOD, manganese-3-tetrakis(1-methyl-4-pyridyl)porphorin, a low molecular weight SOD mimetic, and to a lesser extent, deferoximine, an antioxidant and inhibitor of hydroxyl radical formation, were successful in reducing the effect of 50% oxygen on morphogenesis. Not successful were N-nitro-L-arginine methyl ester (an inhibitor of nitric oxide synthase); allopurinol (an inhibitor of xanthine oxidase); N-acetylcysteine and ebselen (a glutathione peroxidase mimetic); Trolox (a synthetic tocopherol); catalase, and CuZnSOD used alone. These results provide evidence that superoxide anion and possibly hydroxyl radical are the ROS most likely responsible for the growth effects of hyperoxia on mouse fetal lung morphogenesis.

Early versus late identification of infants at high risk of developing moderate to severe bronchopulmonary dysplasia

We developed a simple method to identify neonates at high risk of bronchopulmonary dysplasia (BPD) and determined whether early (8 hours) and late (14 days) risk assessment is equally useful. A retrospective cohort design was utilized of subjects enrolled in multi-dose surfactant trials to develop each risk identification model. Prospective testing of the late 14-day model was done to determine accuracy. The primary outcome variable (moderate to severe BPD) was defined as the need for oxygen and mechanical ventilation beyond 28 days of life and significant chest X-ray changes. Variables were screened for inclusion in the models by univariate and multiple regression analysis of data available at 14 days or 8 hours of life, converted to yes-no variables by the use of receiver-operator curves; the final model was based on those variables that gave the highest sensitivity and specificity for identifying BPD risk. Thirty-eight out of 116 of the 14-day model subjects developed BPD. The 14-day model (F1O2 > or = 0.30 and ventilation index (defined as 10,000/peak pressure x rate x PCO2) < 0.510 (or < 0.800 if previously septic)] had a sensitivity of 82% and specificity of 89%. It accurately identified 83% of cases (51/61) during at 1-year prospective test. The positive predictive value was 81% and negative predictive value 88%. Forty-four of the 698 early 8-hour model subjects developed BPD. The 8-hour model [gestational age < 31 weeks, 5-minute Apgar < 9, ventilator rate > 23 breaths/min, and ventilation index < 0.895] had a sensitivity of 73%, specificity of 83%, negative predictive value of 98% but positive predictive value of only 22%. These observation indicated that clinical data can create an accurate and simple model to classify infants into high- or low-risk groups for BPD. Using such models very early in life (e.g., at 8 hours) may lead to a high number of false-positive identifications.