Antenatal Endotoxin Induces Dysanapsis in Experimental Bronchopulmonary Dysplasia

Bronchopulmonary dysplasia (BPD), the chronic lung disease of prematurity, is characterized by impaired lung development with sustained functional abnormalities due to alterations of airways and the distal lung. Although clinical studies have shown striking associations between antenatal stress and BPD, little is known about the underlying pathogenetic mechanisms. Whether dysanapsis, the concept of discordant growth of the airways and parenchyma, contributes to late respiratory disease as a result of antenatal stress is unknown. We hypothesized that antenatal endotoxin (ETX) impairs juvenile lung function as a result of altered central airway and distal lung structure, suggesting the presence of dysanapsis in this preclinical BPD model. Fetal rats were exposed to intraamniotic ETX (10 μg) or saline solution (control) 2 days before term. We performed extensive structural and functional evaluation of the proximal airways and distal lung in 2-week-old rats. Distal lung structure was quantified by stereology. Conducting airway diameters were measured using micro-computed tomography. Lung function was assessed during invasive ventilation to quantify baseline mechanics, response to methacholine challenge, and spirometry. ETX-exposed pups exhibited distal lung simplification, decreased alveolar surface area, and decreased parenchyma-airway attachments. ETX-exposed pups exhibited decreased tracheal and second- and third-generation airway diameters. ETX increased respiratory system resistance and decreased lung compliance at baseline. Only Newtonian resistance, specific to large airways, exhibited increased methacholine reactivity in ETX-exposed pups compared with controls. ETX-exposed pups had a decreased ratio of FEV in 0.1 second to FVC and a normal FEV in 0.1 second, paralleling the clinical definition of dysanapsis. Antenatal ETX causes abnormalities of the central airways and distal lung growth, suggesting that dysanapsis contributes to abnormal lung function in juvenile rats.

Pulmonary hypertension during respiratory syncytial virus bronchiolitis: a risk factor for severity of illness

BACKGROUND

Respiratory syncytial virus infection is the most frequent cause of acute lower respiratory tract disease in infants. A few reports have suggested that pulmonary hypertension is associated with increased severity of respiratory syncytial virus infection. We sought to determine the association between the pulmonary hypertension detected by echocardiography during respiratory syncytial virus bronchiolitis and clinical outcomes.

METHODS

We retrospectively reviewed 154 children admitted with respiratory syncytial virus bronchiolitis who had an echocardiography performed during the admission. The association between pulmonary hypertension and clinical outcomes including mortality, intensive care unit (ICU) admission, prolonged ICU stay (>10 days), tracheal intubation, and need of high frequency oscillator ventilation was evaluated.

RESULTS

Echocardiography detected pulmonary hypertension in 29 patients (18.7%). Pulmonary hypertension was observed more frequently in patients with congenital heart disease (CHD) (n = 11/33, 33%), chronic lung disease of infancy (n = 12/25, 48%), prematurity (<37 weeks gestational age, n = 17/59, 29%), and Down syndrome (n = 4/10, 40%). The presence of pulmonary hypertension was associated with morbidity (p < 0.001) and mortality (p = 0.02). However, in patients without these risk factors (n = 68), pulmonary hypertension was detected in five patients who presented with shock or poor perfusion. Chronic lung disease was associated with pulmonary hypertension (OR = 5.9, 95% CI 2.2-16.3, p = 0.0005). Multivariate logistic analysis demonstrated that pulmonary hypertension is associated with ICU admission (OR = 6.4, 95% CI 2.2-18.8, p = 0.0007), intubation (OR = 4.7, 95% CI 1.8-12.3, p = 0.002), high frequency oscillator ventilation (OR = 8.4, 95% CI 2.95-23.98, p < 0.0001), and prolonged ICU stay (OR = 4.9, 95% CI 2.0-11.7, p = 0.0004).

CONCLUSIONS

Pulmonary hypertension detected by echocardiography during respiratory syncytial virus infection was associated with increased morbidity and mortality. Chronic lung disease was associated with pulmonary hypertension detected during respiratory syncytial virus bronchiolitis. Routine echocardiography is not warranted for previously healthy, haemodynamically stable patients with respiratory syncytial virus bronchiolitis.

A Novel Method of Measuring Fractional Exhaled Nitric Oxide in Tracheostomized Ventilator-Dependent Children

BACKGROUND

The lower airway concentration of fractional exhaled nitric oxide (F_ENO) is unknown in children with chronic lung disease of infancy who have tracheostomy for long-term mechanical ventilation. We aimed to evaluate an online method of measuring F_ENO in a cohort of ventilator-dependent children with a tracheostomy and to explore the relationship between the peak F_ENO concentration (F_ENO peak) and the degree of respiratory support using the respiratory severity score.

METHODS

We conducted a prospective cross-sectional study in 31 subjects who were receiving long-term respiratory support through a tracheostomy. We measured the F_ENO peak and F_ENO plateau concentration from the tip of the tracheostomy tube using a nitric oxide analyzer in subjects during a quiet state while being mechanically ventilated. We obtained 2 consecutive 2-min duration measurements from each subject. The F_ENO peak, exhaled NO output (equal to the F_ENO peak × minute ventilation), and pulmonary NO excretion (exhaled NO output/weight) were calculated and correlated with the respiratory severity score.

RESULTS

The median F_ENO peak was 2.69 ppb, and the median F_ENO plateau was 1.57 ppb. The coefficients of repeatability between the 2 consecutive measurements for F_ENO peak and F_ENO plateau were 0.74 and 0.59, respectively. The intraclass coefficient between subjects within the cohort was 0.988 (95% CI 0.975-0.994, P < .001) for F_ENO peak and 0.991 (95% CI 0.982-0.996, P < .001) for F_ENO plateau. We found that the F_ENO peak was directly correlated with minute ventilation, but we did not find a direct relationship between the F_ENO peak concentration, exhaled NO output, or pulmonary NO excretion and respiratory severity score.

CONCLUSIONS

F_ENO peak and plateau concentration can be measured online easily with a high degree of reliability and repeatability in infants and young children with a tracheostomy. F_ENO peak concentration from the lower airway is low and influenced by minute ventilation in children receiving mechanical ventilation.

Mid-childhood lung function in a cohort of children with "new bronchopulmonary dysplasia"

OBJECTIVE

Recent advances in perinatal care and neonatal respiratory therapy have led to a new phenotype of bronchopulmonary dysplasia ("new BPD"). The long-term respiratory outcome of this new form of BPD has yet to be adequately described. Aim of this study was to provide longitudinal data on lung function of an unselected cohort of children born extremely premature (EP) with an extremely low birth weight in the post-surfactant era.

STUDY DESIGN

Respiratory function was assessed twice (at 8 and 12 years) in 48 children born at a gestational age <28 weeks with a birth weight <1,000 g. Twenty-eight of them had BPD (oxygen-dependency at 36 weeks postmenstrual age) (EP-BPD), and 20 not (EP non-BPD). Twenty-seven children born at term served as control group.

RESULTS

The EP-BPD group had significantly lower spirometric values (given as z-scores) than controls, especially in parameters indicating airflow obstruction (8 ys: zFEV1:-1.3 ± 1 vs. 0.5 ± 0.8; 12 ys:-1.6 ± 1 vs. 0.5 ± 0.8, P < 0.001). Despite their better spirometric profile, EP-non-BPD children also had significantly lower parameters than controls (8ys: zFEV1:-0.5 ± 0.8; 12 ys:-0.5 ± 0.9, P < 0.001). During the 4-year follow-up, EP-non-BPD and controls had stable mean z-scores, but EP-BPD had a significant decline in mean zFEV1 (from -1.3 ± 1 to -1.6 ± 1, P = 0.03), zFEV1/FVC (from -0.4 ± 1 to -1.1 ± 1, P = 0.008), and zFEF 25-75% (from -1.2 ± 1 to -1.8 ± 1, P = 0.03).

CONCLUSION

EP children born in the post-surfactant era showed a significant airflow limitation, particularly pronounced in BPD subjects who in addition, presented an abnormal airway growth trajectory with a decline in lung function between the ages of 8 and 12 years. Pediatr Pulmonol. 2016;51:1057-1064. © 2016 Wiley Periodicals, Inc.

Determinants of chronic lung disease severity in the first year of life; A population based study

OBJECTIVES

First, create a clinical severity score for patients with chronic lung disease of infancy (CLDi) following neonatal intensive care unit (NICU) stay. Second, using California wide population-based data, identify factors associated with clinical severity of CLDi at 4-9 months corrected gestational age (CGA).

STUDY DESIGN

Pediatric pulmonologists ranked and weighted eight factors reflecting clinical severity of CLDi. Utilizing these data we scored and assigned these to 4-9 month old CGA moderate/severe bronchopulmonary dysplasia (BPD) infants, born<30 weeks gestational age (GA), within the California High Risk Infant Follow up (HRIF) program. Infants were studied relative to factors from the California Perinatal Quality Care Collaborative (CPQCC).

RESULTS

We received survey responses from 43/88 pediatric pulmonologists from 28/53 North American training centers who are experts in CLDi. Strong agreement between ranking (72-100%) of respiratory system parameters and weighting (out of 100 points weighting was within 20 points) was observed with severity of CLDi. Data from 940 CLDi premature infants <30 weeks GA were obtained. Infants with severe CLDi scores at 4-9 months CGA (relative to a zero score) showed positive associations with being male, odds ratio[OR] = 2.45[confidence interval (CI) 1.26-4.77]), >30 ventilator days, OR = 3.82 (1.30-11.2), postnatal steroids OR = 3.94 (1.94-7.84), and a surprising inverse association with retinopathy of prematurity stage 3-4, OR = 0.24 (0.09-0.67) CONCLUSIONS: The CLDi clinical severity score allowed for standardized assessment of pulmonary morbidity, and evaluation of risk factors in the NICU for CLDi following NICU discharge. These observations point to risk factors associated with CLDi outcomes at 4-9 months CGA.

Impaired pulmonary vascular development in bronchopulmonary dysplasia

Bronchopulmonary dysplasia (BPD), the chronic lung disease associated with preterm birth, results from the disruption of normal pulmonary vascular and alveolar growth. Though BPD was once described as primarily due to postnatal injury from mechanical ventilation and oxygen therapy after preterm birth, it is increasingly appreciated that BPD results from antenatal and perinatal factors that interrupt lung development in infants born at the extremes of prematurity. The lung in BPD consists of a simplified parenchymal architecture that limits gas exchange and leads to increased cardiopulmonary morbidity and mortality. This review outlines recent advances in the understanding of pulmonary vascular development and describes how the disruption of these mechanisms results in BPD. We point to future therapies that may augment postnatal vascular growth to prevent and treat this severe chronic lung disease.

Subcutaneous treprostinil for pulmonary hypertension in chronic lung disease of infancy

Pulmonary arterial hypertension (PAH) associated with chronic lung disease of infancy can be a life-threatening disease affecting an increasing number of former premature infants. There is a need for improved delivery of targeted PAH therapies for this subgroup of patients who have severe and persistent PAH despite standard respiratory care for chronic lung disease. Currently infants who have severe PAH despite oral or inhaled therapy receive continuous intravenous prostanoid therapy (mostly epoprostenol), which is complicated because of the need for central venous access and associated catheter-related complications. We present a series of 5 infants who were successfully treated with a continuous infusion of subcutaneous treprostinil, which is a longer-acting prostanoid with similar hemodynamic effects. There were improvements in echocardiographic assessment of right ventricular function and estimated pulmonary hypertension, and in respiratory support required within weeks of therapy. Unlike commonly in adults, these 5 infants had no instances of severe site erythema, bleeding, bruising, or infection. In our experience with 5 former extremely preterm infants who had PAH associated with chronic lung disease, subcutaneous treprostinil was safe, efficacious, and well tolerated. We believe that subcutaneous treprostinil can be beneficial in a select group of former premature infants who have chronic lung disease and severe pulmonary arterial hypertension who have not responded adequately to conservative therapies.

Mesenchymal stem cell-mediated reversal of bronchopulmonary dysplasia and associated pulmonary hypertension

Clinical trials have failed to demonstrate an effective preventative or therapeutic strategy for bronchopulmonary dysplasia (BPD), a multifactorial chronic lung disease in preterm infants frequently complicated by pulmonary hypertension (PH). Mesenchymal stem cells (MSCs) and their secreted components have been shown to prevent BPD and pulmonary fibrosis in rodent models. We hypothesized that treatment with conditioned media (CM) from cultured mouse bone marrow-derived MSCs could reverse hyperoxia-induced BPD and PH. Newborn mice were exposed to hyperoxia (FiO₂=0.75) for two weeks, were then treated with one intravenous dose of CM from either MSCs or primary mouse lung fibroblasts (MLFs), and placed in room air for two to four weeks. Histological analysis of lungs harvested at four weeks of age was performed to determine the degree of alveolar injury, blood vessel number, and vascular remodeling. At age six weeks, pulmonary artery pressure (PA acceleration time) and right ventricular hypertrophy (RVH; RV wall thickness) were assessed by echocardiography, and pulmonary function tests were conducted. When compared to MLF-CM, a single dose of MSC-CM-treatment (1) reversed the hyperoxia-induced parenchymal fibrosis and peripheral PA devascularization (pruning), (2) partially reversed alveolar injury, (3) normalized lung function (airway resistance, dynamic lung compliance), (4) fully reversed the moderate PH and RVH, and (5) attenuated peripheral PA muscularization associated with hyperoxia-induced BPD. Reversal of key features of hyperoxia-induced BPD and its long-term adverse effects on lung function can be achieved by a single intravenous dose of MSC-CM, thereby pointing toward a new therapeutic intervention for chronic lung diseases.

Ventilation homogeneity improves with growth early in life

Some studies have suggested that lung clearance index (LCI) is age-independent among healthy subjects early in life, which implies that ventilation distribution does not vary with growth. However, other studies of older children and adolescents suggest that ventilation becomes more homogenous with somatic growth. We describe a new technique to obtain multiple breath washout (MBWO) in sedated infants and toddlers using slow augmented inflation breaths that yields an assessment of LCI and the slope of phase III, which is another index of ventilation inhomogeneity. We evaluated whether ventilation becomes more homogenous with increasing age early in life, and whether infants with chronic lung disease of infancy (CLDI) have increased ventilation inhomogeneity relative to full-term controls (FT). FT (N = 28) and CLDI (N = 22) subjects between 3 and 28 months corrected-age were evaluated. LCI decreased with increasing age; however, there was no significant difference between the two groups (9.3 vs. 9.5; P = 0.56). Phase III slopes adjusted for expired volume (S(ND)) increased with increasing breath number during the washout and decreased with increasing age. There was no significant difference in S(ND) between full-term and CLDI subjects (211 vs. 218; P = 0.77). Our findings indicate that ventilation becomes more homogenous with lung growth and maturation early in life; however, there is no evidence that ventilation inhomogeneity is a significant component of the pulmonary pathophysiology of CLDI.