Effect of estrogen receptor α on cardiopulmonary adaptation to chronic developmental hypoxia in a rat model.

Humans living at high-altitude (HA) have adapted to this environment by increasing pulmonary vascular and alveolar growth. RNA sequencing data from a novel murine model that mimics this phenotypical response to HA suggested estrogen signaling via estrogen receptor alpha (ERα) may be involved in this adaptation. We hypothesized ERα was a key mediator in the cardiopulmonary adaptation to chronic hypoxia and sought to delineate the mechanistic role ERα contributes to this process by exposing novel loss-of-function ERα mutant (ERαMut) rats to simulated HA. ERα mutant or wild-type (wt) rats were exposed to normoxia or hypoxia starting at conception and continued postnatally until 6 wk of age. Both wt and ERαMut animals born and raised in hypoxia exhibited lower body mass and higher hematocrits, total alveolar volumes (Va), diffusion capacities of carbon monoxide (DLCO), pulmonary arteriole (PA) wall thickness, and Fulton indices than normoxia animals. Right ventricle adaptation was maintained in the setting of hypoxia. Although no major physiologic differences were seen between wt and ERαMut animals at either exposure, ERαMut animals exhibited smaller mean linear intercepts (MLI) and increased PA total and lumen areas. Hypoxia exposure or ERα loss-of-function did not affect lung mRNA abundance of vascular endothelial growth factor, angiopoietin 2, or apelin. Sexual dimorphisms were noted in PA wall thickness and PA lumen area in ERαMut rats. In summary, in room air-exposed rats and rats with peri- and postnatal hypoxia exposure, ERα loss-of-function was associated with decreased alveolar size (primarily driven by hypoxic animals) and increased PA remodeling.NEW & NOTEWORTHY By exposing novel loss-of-function estrogen receptor alpha (Erα) mutant rats to a novel model of human high-altitude exposure, we demonstrate that ERα has subtle but inconsistent effects on endpoints relevant to cardiopulmonary adaptation to chronic hypoxia. Given that we observed some histologic, sex, and genotype differences, further research into cell-specific effects of ERα during hypoxia-induced cardiopulmonary adaptation is warranted.

Decreased vascular reactivity associated with increased IL-8 in 6-month-old infants of mothers with pre-eclampsia.

BACKGROUND: Offspring born to mothers with pre-eclampsia (Pre-E) suffer higher risks of adult cardiovascular diseases, suggesting that exposure to an antiangiogenic environment in-utero has a lasting impact on the development of endothelial function. The goal of this study is to test the hypothesis that in-utero exposure to Pre-E results in alterations of angiogenic factors/cytokines that negatively impact vascular development during infancy. METHODS: Infants born from mothers with and without Pre-E were recruited and followed up at 6 months. Plasma cytokines, blood pressure, microvessel density, and vascular reactivity were assessed. RESULTS: 6-month-old infants born to mothers with Pre-E had unchanged blood pressure (p = 0.86) and microvessel density (p = 0.57). Vascular reactivity was decreased in infants born to mothers with Pre-E compared to infants born to healthy mothers (p = 0.0345). Interleukin 8 (IL-8) (p = 0.03) and Angiopoeitin-2 (Ang-2) (p = 0.04) were increased in infants born to mothers with Pre-E. We observed that higher IL-8 was associated with lower vascular reactivity (rho = -0.14, p < 0.0001). CONCLUSION: At 6 months of age, infants born to mothers with Pre-E had impaired vascular reactivity and higher IL-8 and Ang-2, but similar blood pressure and microvessel density compared to infants born to non-Pre-E mothers. IMPACT STATEMENT: Changes in cord blood antiangiogenic factors are documented in infants of mothers with pre-eclampsia and may contribute to offspring risks of adult cardiovascular disease. How these factors evolve during early infancy and their correlation with offspring vascular development have not been studied. This study found that 6-month-old infants born to mothers with pre-eclampsia had decreased vascular reactivity, which was correlated with higher IL-8. These findings underscore the lasting impact of maternal pre-eclampsia on offspring vascular development and highlight the need for long-term follow-up in children born to mothers with pre-eclampsia.

Long-term childhood outcomes for babies born at term who were exposed to antenatal corticosteroids.

BACKGROUND: Antenatal corticosteroids improve neonatal outcomes when administered to infants who are at risk of preterm delivery. Many women who receive antenatal corticosteroids for threatened preterm labor proceed to deliver at term. Thus, long-term outcomes should be evaluated for term-born infants who were exposed to antenatal corticosteroids in utero. OBJECTIVE: This study aimed to compare long-term outcomes between term-born children aged ≥5 years who were born to women who received antenatal corticosteroids for threatened preterm labor and children whose mothers were also evaluated for threatened preterm labor but did not receive antenatal corticosteroids. STUDY DESIGN: We performed a retrospective cohort study of children born at ≥37 weeks' gestation, aged ≥5 years, and born to mothers diagnosed with threatened preterm labor during pregnancy. The primary exposure of interest was receiving antenatal corticosteroids. Among the collected childhood medical conditions, the primary outcome of interest was a diagnosis of asthma. RESULTS: Of the 3556 term-born children aged ≥5 years, 629 (17.6%) were exposed to antenatal corticosteroids (all betamethasone), and 2927 (82.3%) were controls whose mothers were evaluated for threatened preterm birth but did not get antenatal corticosteroid injections. Women receiving antenatal corticosteroids had higher rates of maternal comorbidities (diabetes mellitus, hypertension; P≤.01). Antenatal corticosteroid-exposed children had no difference in diagnosis of asthma (12.6% vs 11.6%), attention deficit disorder, or developmental delay (P=.47, .54, and .10, respectively). Controlling for maternal and neonatal characteristics, asthma was not different between those exposed to antenatal corticosteroids and controls (odds ratio, 1.05; 95% confidence interval, 0.79-1.39). The odds of the child's weight percentile being <10% were increased for antenatal corticosteroid-exposed children born at term (odds ratio, 2.00; 95% confidence interval, 1.22-3.25). CONCLUSION: Children born at term who were exposed to antenatal corticosteroids may have increased odds of being in a lower growth percentile than those not exposed. However, rates of diagnoses such as asthma, developmental delay, and attention deficit disorders were not different.

The transcription factor PU.1 is required for the development of IL-9-producing T cells and allergic inflammation.

CD4(+) helper T cells acquire effector phenotypes that promote specialized inflammatory responses. We show that the ETS-family transcription factor PU.1 was required for the development of an interleukin 9 (IL-9)-secreting subset of helper T cells. Decreasing PU.1 expression either by conditional deletion in mouse T cells or the use of small interfering RNA in human T cells impaired IL-9 production, whereas ectopic PU.1 expression promoted IL-9 production. Mice with PU.1-deficient T cells developed normal T helper type 2 (T(H)2) responses in vivo but showed attenuated allergic pulmonary inflammation that corresponded to lower expression of Il9 and chemokines in peripheral T cells and in lungs than that of wild-type mice. Together our data suggest a critical role for PU.1 in generating the IL-9-producing (T(H)9) phenotype and in the development of allergic inflammation.

Interleukin-9 is required for allergic airway inflammation mediated by the cytokine TSLP.

Thymic stromal lymphopoietin (TSLP) is an epithelial cell-derived cytokine important for the initiation and development of T helper (Th2) cell-mediated allergic inflammation. In this study, we identified a positive association between interleukin-9 (IL-9) and TSLP concentration in the serum of infants with atopic dermatitis. In primary cell cultures, the addition of TSLP led to an increase in IL-9 production from human and mouse Th9 cells, and induced an increase in signal transducer and activator of transcription 5 (STAT5) activation and binding to the Il9 promoter. In vivo, use of an adoptive transfer model demonstrated that TSLP promoted IL-9-dependent, Th9 cell-induced allergic inflammation by acting directly on T cells. Moreover, transgenic expression of TSLP in the lung stimulated IL-9 production in vivo, and anti-IL-9 treatment attenuated TSLP-induced airway inflammation. Together, our results demonstrate that TSLP promotes Th9 cell differentiation and function and define a requirement for IL-9 in TSLP-induced allergic inflammation.

Predictive biomarker modeling of pediatric atopic dermatitis severity based on longitudinal serum collection.

The pathogenesis of atopic dermatitis (AD) results from complex interactions between environmental factors, barrier defects, and immune dysregulation resulting in systemic inflammation. Therefore, we sought to characterize circulating inflammatory profiles in pediatric AD patients and identify potential signaling nodes which drive disease heterogeneity and progression. We analyzed a sample set of 87 infants that were at high risk for atopic disease based on atopic dermatitis diagnoses. Clinical parameters, serum, and peripheral blood mononuclear cells (PBMCs) were collected upon entry, and at one and four years later. Within patient serum, 126 unique analytes were measured using a combination of multiplex platforms and ultrasensitive immunoassays. We assessed the correlation of inflammatory analytes with AD severity (SCORAD). Key biomarkers, such as IL-13 (rmcorr=0.47) and TARC/CCL17 (rmcorr=0.37), among other inflammatory signals, significantly correlated with SCORAD across all timepoints in the study. Flow cytometry and pathway analysis of these analytes implies that CD4 T cell involvement in type 2 immune responses were enhanced at the earliest time point (year 1) relative to the end of study collection (year 5). Importantly, forward selection modeling identified 18 analytes in infant serum at study entry which could be used to predict change in SCORAD four years later. We have identified a pediatric AD biomarker signature linked to disease severity which will have predictive value in determining AD persistence in youth and provide utility in defining core systemic inflammatory signals linked to pathogenesis of atopic disease.

Are newborn outcomes different for term babies who were exposed to antenatal corticosteroids?

BACKGROUND: Antenatal corticosteroids improve newborn outcomes for preterm infants. However, predicting which women presenting for threatened preterm labor will have preterm infants is inaccurate, and many women receive antenatal corticosteroids but then go on to deliver at term. OBJECTIVE: This study aimed to compare the short-term outcomes of infants born at term to women who received betamethasone for threatened preterm labor with infants who were not exposed to betamethasone in utero. STUDY DESIGN: We performed a retrospective cohort study of infants born at or after 37 weeks' gestational age to mothers diagnosed as having threatened preterm labor during pregnancy. The primary neonatal outcomes of interest included transient tachypnea of the newborn, neonatal intensive care unit admission, and small for gestational age and were evaluated for their association with betamethasone exposure while adjusting for covariates using multiple logistic regression. RESULTS: Of 5330 women, 1459 women (27.5%) received betamethasone at a mean gestational age of 32.2±3.3 weeks. The mean age of women was 27±5.9 years and the mean gestational age at delivery was 38.9±1.1 weeks. Women receiving betamethasone had higher rates of maternal comorbidities (P<.001 for diabetes mellitus, asthma, and hypertensive disorder) and were more likely to self-identify as White (P=.022). Betamethasone-exposed neonates had increased rates of transient tachypnea of the newborn, neonatal intensive care unit admission, small for gestational age, hyperbilirubinemia, and hypoglycemia (all, P<.05). Controlling for maternal characteristics and gestational age at delivery, betamethasone exposure was not associated with a diagnosis of transient tachypnea of the newborn (adjusted odds ratio, 1.10; 95% confidence interval, 0.80-1.51), although it was associated with more neonatal intensive care unit admissions (adjusted odds ratio, 1.49; 95% confidence interval, 1.19-1.86) and higher odds of the baby being small for gestational age (adjusted odds ratio, 1.78; 95% confidence interval, 1.48-2.14). CONCLUSION: Compared with women evaluated for preterm labor who did not receive betamethasone, women receiving betamethasone had infants with higher rates of neonatal intensive care unit admission and small for gestational age. Although the benefits of betamethasone to infants born preterm are clear, there may be negative impacts for infants delivered at term.

Decision tree-based rules outperform risk scores for childhood asthma prognosis.

BACKGROUND: There are no widely accepted prognostic tools for childhood asthma; this is in part due to the multifactorial and time-dependent nature of mechanisms and risk factors that contribute to asthma development. Our study objective was to develop and evaluate the prognostic performance of conditional inference decision tree-based rules using the Pediatric Asthma Risk Score (PARS) predictors as an alternative to the existing logistic regression-based risk score for childhood asthma prediction at 7 years in a high-risk population. METHODS: The Canadian Asthma Primary Prevention Study data were used to develop, compare, and contrast the prognostic performance (area under the curve [AUC], sensitivity, and specificity) of conditional inference tree-based decision rules to the pediatric asthma risk score for the prediction of childhood asthma at 7 years. RESULTS: Conditional inference decision tree-based rules have higher prognostic performance (AUC: 0.85; 95% CI: 0.81, 0.88; sensitivity = 47%; specificity = 93%) than the pediatric asthma risk score at an optimal cutoff of ≥6 (AUC: 0.71; 95% CI: 0.67, 0.76; sensitivity = 60%; specificity = 74%). Moreover, the pediatric asthma risk score is not linearly related to asthma risk, and at any given pediatric asthma risk score value, different combinations of its pediatric asthma risk score clinical variables differentially predict asthma risk. CONCLUSION: Conditional inference tree-based decision rules could be a useful childhood asthma prognostic tool, providing an alternative way to identify unique subgroups of at-risk children, and insights into associations and effect mechanisms that are suggestive of appropriate tailored preventive interventions. However, the feasibility and effectiveness of such decision rules in clinical practice is warranted.

Transcriptomic modifications in developmental cardiopulmonary adaptations to chronic hypoxia using a murine model of simulated high-altitude exposure.

Mechanisms driving adaptive developmental responses to chronic high-altitude (HA) exposure are incompletely known. We developed a novel rat model mimicking the human condition of cardiopulmonary adaptation to HA starting at conception and spanning the in utero and postnatal timeframe. We assessed lung growth and cardiopulmonary structure and function and performed transcriptome analyses to identify mechanisms facilitating developmental adaptations to chronic hypoxia. To generate the model, breeding pairs of Sprague-Dawley rats were exposed to hypobaric hypoxia (equivalent to 9,000 ft elevation). Mating, pregnancy, and delivery occurred in hypoxic conditions. Six weeks postpartum, structural and functional data were collected in the offspring. RNA-Seq was performed on right ventricle (RV) and lung tissue. Age-matched breeding pairs and offspring under room air (RA) conditions served as controls. Hypoxic rats exhibited significantly lower body weights and higher hematocrit levels, alveolar volumes, pulmonary diffusion capacities, RV mass, and RV systolic pressure, as well as increased pulmonary artery remodeling. RNA-Seq analyses revealed multiple differentially expressed genes in lungs and RVs from hypoxic rats. Although there was considerable similarity between hypoxic lungs and RVs compared with RA controls, several upstream regulators unique to lung or RV were identified. We noted a pattern of immune downregulation and regulation patterns of immune and hormonal mediators similar to the genome from patients with pulmonary arterial hypertension. In summary, we developed a novel murine model of chronic hypoxia exposure that demonstrates functional and structural phenotypes similar to human adaptation. We identified transcriptomic alterations that suggest potential mechanisms for adaptation to chronic HA.

Vitamin C to Pregnant Smokers Persistently Improves Infant Airway Function to 12†Months of Age: A Randomised Trial.

BACKGROUND: Vitamin C (500 mg·day-1) supplementation for pregnant smokers has been reported to increase newborn pulmonary function and infant forced expiratory flows (FEFs) at 3 months of age. Its effect on airway function through 12 months of age has not been reported. OBJECTIVE: To assess whether vitamin C supplementation to pregnant smokers is associated with a sustained increased airway function in their infants through 12 months of age. METHODS: This is a prespecified secondary outcome of a randomised, double-blind, placebo-controlled trial that randomised 251 pregnant smokers between 13 and 23 weeks of gestation: 125 to 500 mg·day-1 vitamin C and 126 to placebo. Smoking cessation counselling was provided. FEFs performed at 3 and 12 months of age were analysed by repeated measures analysis of covariance. RESULTS: FEFs were performed in 222 infants at 3 months and 202 infants at 12 months of age. The infants allocated to vitamin C had significantly increased FEFs over the first year of life compared to those allocated to placebo. The overall increased flows were: 40.2 mL·sec-1 for FEF75 (adjusted 95% CI for difference 6.6 to 73.8; p=0.025); 58.3 mL·sec-1 for FEF50 (95% CI 10.9 to 105.8; p=0.0081); and 55.1 mL·sec-1 for FEF25-75 (95% CI, 9.7 to 100.5; p=0.013). CONCLUSIONS: In offspring of pregnant smokers randomised to vitamin C versus placebo, vitamin C during pregnancy was associated with a small but significantly increased airway function at 3 and 12 months of age, suggesting a potential shift to a higher airway function trajectory curve. Continued follow-up is underway.

Oral Vitamin C (500 mg/d) to Pregnant Smokers Improves Infant Airway Function at 3 Months (VCSIP). A Randomized Trial.

Rationale: We reported a randomized trial demonstrating daily supplemental vitamin C to pregnant smokers significantly improved newborn pulmonary function tests. The current study tests these results in a new cohort using infant pulmonary function tests. Objectives: To determine if infants of pregnant smokers randomized to daily supplemental vitamin C would have improved forced expiratory flows (FEFs) at 3 months of age compared with those randomized to placebo, and to investigate the association of the α5 nicotinic acetylcholine receptor. Methods: A randomized, double-blind, placebo-controlled trial was conducted at three centers. Two hundred fifty-one pregnant smokers were randomized at 13-23 weeks of gestation: 125 randomized to vitamin C (500 mg/d) and 126 to placebo. Measurements and Main Results: The primary outcome was FEF75 at 3 months of age performed with the raised volume rapid thoracic compression technique (Jaeger/Viasys). FEF50 and FEF25-75 obtained from the same expiratory curves were prespecified secondary outcomes. The infants of pregnant smokers randomized to vitamin C (n = 113) had the following FEFs at 3 months of age compared with those randomized to placebo (n = 109) as measured by FEF75 (200.7 vs. 188.7 ml/s; adjusted 95% confidence interval [CI] for difference, -3.33 to 35.64; P = 0.10), FEF50 (436.7 vs. 408.5 ml/s; adjusted 95% CI for difference, 6.10-61.30; P = 0.02), and FEF25-75 (387.4 vs. 365.8 ml/s; adjusted 95% CI for difference, 0.92-55.34; P = 0.04). Infant FEFs seemed to be negatively associated with the maternal risk alleles for the α5 nicotinic acetylcholine receptor (rs16969968). Conclusions: Although the primary outcome of FEF75 was not improved after vitamin C supplementation to pregnant smokers, the predetermined secondary outcomes FEF50 and FEF25-75 were significantly improved. These results extend our previous findings and demonstrate improved airway function (FEF50 and FEF25-75) at 3 months of age in infants after vitamin C supplementation to pregnant smokers. Clinical trial registered with www.clinicaltrials.gov (NCT01723696).

Expired Tidal Volume Variation in Extremely Low Birth Weight and Very Low Birth Weight Infants on Volume-Targeted Ventilation.

In a prospective study we describe the delivery of small tidal volumes to extremely low birth weight (ELBW) and very low birth weight (VLBW) infants using a volume-targeted ventilation mode (VTV). Tidal volume delivery was consistent for both ELBW and VLBW infants independent of gestational age, birth weight, and the target volume.

Effect of CPAP on airway reactivity and airway inflammation in children with moderate-severe asthma.

BACKGROUND AND OBJECTIVE: Asthma is characterized by airway hyperreactivity and airway inflammation. We previously demonstrated that adults with mild well-controlled asthma exhibited a marked decrease in airway reactivity (PC20 increased >2-fold) after using nocturnal continuous positive airway pressure (CPAP) for 1 week. If CPAP produces a similar suppression of airway reactivity in children with moderate-severe asthma, who require chronic use of corticosteroids, then this non-pharmacological therapy might provide a beneficial alternative or supplemental therapy in these subjects. METHODS: Children aged 8-17 years with moderate-severe asthma were treated with 4 weeks of nocturnal CPAP (8-10 cm H2 O) or sham CPAP (<2 cm H2 O). Adherence was monitored with a modem installed in the equipment or by memory cards. Airway reactivity, assessed by methacholine bronchial challenge, was measured prior to and following treatment. RESULTS: The percentage of subjects adherent to treatment was similar in both groups (19/27 CPAP vs 19/28 sham, ~70%). There was a tendency for PC20 to increase with treatment in both groups (3.0-5.3 mg/mL CPAP vs 3.2 to 4.3 mg/mL sham, P = 0.083); however, the change did not differ significantly between groups (P = 0.569). CONCLUSION: We found that the 4-week treatment with nocturnal CPAP did not produce a twofold suppression of airway reactivity in children with moderate-severe asthma.

Neonatal hyperoxia promotes asthma-like features through IL-33-dependent ILC2 responses.

BACKGROUND: Premature infants often require oxygen supplementation and, therefore, are exposed to oxidative stress. Following oxygen exposure, preterm infants frequently develop chronic lung disease and have a significantly increased risk of asthma. OBJECTIVE: We sought to identify the underlying mechanisms by which neonatal hyperoxia promotes asthma development. METHODS: Mice were exposed to neonatal hyperoxia followed by a period of room air recovery. A group of mice was also intranasally exposed to house dust mite antigen. Assessments were performed at various time points for evaluation of airway hyperresponsiveness, eosinophilia, mucus production, inflammatory gene expression, and TH and group 2 innate lymphoid cell (ILC2) responses. Sera from term- and preterm-born infants were also collected and levels of IL-33 and type 2 cytokines were measured. RESULTS: Neonatal hyperoxia induced asthma-like features including airway hyperresponsiveness, mucus hyperplasia, airway eosinophilia, and type 2 pulmonary inflammation. In addition, neonatal hyperoxia promoted allergic TH responses to house dust mite exposure. Elevated IL-33 levels and ILC2 responses were observed in the lungs most likely due to oxidative stress caused by neonatal hyperoxia. IL-33 receptor signaling and ILC2s were vital for the induction of asthma-like features following neonatal hyperoxia. Serum IL-33 levels correlated significantly with serum levels of IL-5 and IL-13 but not IL-4 in preterm infants. CONCLUSIONS: These data demonstrate that an axis involving IL-33 and ILC2s is important for the development of asthma-like features following neonatal hyperoxia and suggest therapeutic potential for targeting IL-33, ILC2s, and oxidative stress to prevent and/or treat asthma development related to prematurity.

Membrane and Capillary Components of Lung Diffusion in Infants with Bronchopulmonary Dysplasia.

RATIONALE: Autopsied lungs of infants with bronchopulmonary dysplasia (BPD) demonstrate impaired alveolar development with larger and fewer alveoli, which is consistent with our previous physiologic findings of lower pulmonary diffusing capacity of the lung for carbon monoxide (DL(CO)) in infants and toddlers with BPD compared with healthy controls born at full term (FT). However, it is not known whether the decreased DL(CO) in infants with BPD results from a reduction in both components of DL(CO): pulmonary membrane diffusing capacity (D(M)) and Vc. OBJECTIVES: We hypothesized that impairment of alveolar development in BPD results in a decrease in both D(M) and Vc components of DlCO but that the D(M)/Vc ratio would not differ between the BPD and FT groups. METHODS: DL(CO) was measured under conditions of room air and high inspired oxygen (90%), which enabled D(M) and Vc to be calculated. MEASUREMENTS AND MAIN RESULTS: D(M) and Vc increased with increasing body length; however, infants with BPD had significantly lower D(M) and Vc than FT subjects after adjustment for race, sex, body length, and corrected age. In contrast to D(M) and Vc, the D(M)/Vc ratio remained constant with increasing body length and did not differ for infants with BPD and FT subjects. CONCLUSIONS: Our findings are consistent with infants with BPD having impaired alveolar development with fewer but larger alveoli, as well as a reduced Vc.

Chronic Hypoxia Accentuates Dysanaptic Lung Growth.

RATIONALE: Adults born and raised at high altitudes have larger lung volumes and greater pulmonary diffusion capacity compared with adults at low altitude; however, it remains unclear whether the air and tissue volumes have comparable increases and whether there is a difference in airway size. OBJECTIVES: To assess the effect of chronic hypoxia on lung growth using in vivo high-resolution computed tomography measurements. METHODS: Healthy adults born and raised at moderate altitude (2,000 m above sea level; n = 19) and at low altitude (400 m above sea level; n = 23) underwent high-resolution computed tomography. Differences in total lung, air, and tissue volume, mean lung density, as well as airway lumen and wall areas in anatomically matched airways were compared between groups. MEASUREMENTS AND MAIN RESULTS: No significant differences for age, sex, weight, or height were found between the two groups (P > 0.05). In a multivariate regression model, altitude was a significant contributor for total lung volume (P = 0.02), air volume (P = 0.03), and tissue volume (P = 0.03), whereby the volumes were greater for the moderate- versus the low-altitude group. However, altitude was not a significant contributor for mean lung density (P = 0.35) or lumen and wall areas in anatomically matched segmental, subsegmental, and subsubsegmental airways. CONCLUSIONS: Our findings suggest that the adult lung did not increase lung volume later in life by expansion of an existing number of alveoli, but rather from increased alveolarization early in life. In addition, chronic hypoxia accentuates dysanaptic lung growth by increasing the lung parenchyma but not the airways.

Relationship of structural to functional impairment during alveolar-capillary membrane development.

Bronchopulmonary dysplasia is a chronic lung disease of extreme preterm infants and results in impaired gas exchange. Although bronchopulmonary dysplasia is characterized histologically by alveolar-capillary simplification in animal models, it is clinically defined by impaired gas diffusion. With the use of a developmentally relevant model, we correlated alveolar-capillary structural simplification with reduced functional gas exchange as measured by the diffusing factor for carbon monoxide (DFCO). Neonatal mouse pups were exposed to >90% hyperoxia or room air during postnatal days 0 to 7, and then all pups were returned to room air from days 7 to 56. At day 56, DFCO was measured as the ratio of carbon monoxide uptake to neon dilution, and lungs were fixed for histologic assessment of alveolar-capillary development. Neonatal hyperoxia exposure inhibited alveolar-capillary septal development as evidenced by significantly increased mean linear intercept, increased airspace-to-septal ratio, decreased nodal density, and decreased pulmonary microvasculature. Importantly, alveolar-capillary structural deficits in hyperoxia-exposed pups were accompanied by a significant 28% decrease in DFCO (0.555 versus 0.400; P < 0.0001). In addition, DFCO was highly and significantly correlated with structural measures of reduced alveolar-capillary growth. Simplification of alveolar-capillary structure is highly correlated with impaired gas exchange function. Current mechanistic and therapeutic animal models of inhibited alveolar development may benefit from application of DFCO as an alternative physiologic indicator of alveolar-capillary development.