Altered lung structure and function in mid-childhood survivors of very preterm birth

Lung abnormalities do not influence aerobic capacity in school children born preterm

PURPOSE

Children born preterm have impaired lung function and altered lung structure. However, there are conflicting reports on how preterm birth impacts aerobic exercise capacity in childhood. We aimed to investigate how neonatal history and a diagnosis of bronchopulmonary dysplasia (BPD) impact the relationship between function and structure of the lung, and aerobic capacity in school-aged children born very preterm.

METHODS

Preterm children (≤ 32 w completed gestation) aged 9-12 years with (n = 38) and without (n = 35) BPD, and term-born controls (n = 31), underwent spirometry, lung volume measurements, gas transfer capacity, a high-resolution computer tomography (CT) scan of the chest, and an incremental treadmill exercise test.

RESULTS

Children born preterm with BPD had an elevated breathing frequency to tidal volume ratio compared to term controls (76% vs 63%, p = 0.002). The majority (88%) of preterm children had structural changes on CT scan. There were no differences in peak V̇O₂ (47.1 vs 47.7 mL/kg/min, p = 0.407) or oxygen uptake efficiency slope when corrected for body weight (67.6 vs 67.3, p = 0.5) between preterm children with BPD and term controls. There were no differences in any other exercise outcomes. The severity of structural lung disease was not associated with exercise outcomes in this preterm population.

CONCLUSION

Children born preterm have impaired lung function, and a high prevalence of structural lung abnormalities. However, abnormal lung function and structure do not appear to impact on the aerobic exercise capacity of preterm children at school age.

Mortality Rate and Major Causes of Death by Gestational Age in Korean Children under 5 Years of Age

BACKGROUND

Preterm birth is associated with increased infant mortality. However, it is not clear whether prematurity is associated with mortality after 1 year of age. There is a lack of research on mortality rate and causes of death after infancy in preterm babies in Korea. We aimed to analyze the mortality rates and causes of deaths up to 5 years of age in Korea.

METHODS

Using the Microdata Integrated Service of Statistics Korea database, this retrospective cohort study screened infants born between 2010 and 2012. After applying the exclusion criteria, 1,422,913 live births were classified into the following groups by gestational age: those born at < 32 weeks' gestation (n = 10,411), those born between 32 and 36 weeks' gestation (n = 75,657), and those born at ≥ 37 weeks' gestation (n = 1,336,845). The association of gestational age with mortality in infancy (< 1 year of age) and childhood (1-5 years of age) was analyzed, with and without covariates. The major causes of death in infancy and childhood were analyzed by gestational age.

RESULTS

Overall, 4,930 (0.3%) children died between birth and 5 years of age, with 19.1% of these deaths occurring after infancy. Adjusted hazard ratios (HRs) for infant death were 78.79 (95% confidence interval [CI], 71.33-87.04) and 4.62 (95% CI, 4.07-5.24) for the < 32 and 32-36 weeks groups, respectively, compared to the full-term group; the adjusted HRs for deaths occurring at ages 1-5 years were 9.25 (95% CI, 6.85-12.50) and 2.42 (95% CI, 1.95-3.01), respectively. In infancy, conditions originating in the perinatal period were the most common cause of deaths in the < 32 and 32-36 weeks groups (88.7% and 41.9%, respectively). Contrarily, in the ≥ 37 weeks group, conditions originating in the perinatal period explained 22.7% of infant deaths, with congenital malformations primarily accounting for 29.6% of these deaths. The most common cause of death in children (after infancy) in the < 32 weeks group was perinatal causes (25.0%); in the 32-36 weeks group, congenital malformation and nervous system disease were the common causes (21.7% and 19.1%, respectively). In the ≥ 37 weeks group, injury, poisoning, and other consequences of external causes explained 26.6% of childhood deaths, followed by neoplasms and nervous system disease (15.7% and 14.7%, respectively).

CONCLUSION

Low gestational age is associated with not only infant mortality but also child mortality. The major causes of death differed by gestational age in infancy and childhood. For the care of preterm infants, especially those born at < 32 weeks' gestation, particular attention and continuous monitoring are needed in consideration of the major causes of deaths until 5 years of age.

Trajectories of Lung Function in Infants and Children: Setting a Course for Lifelong Lung Health

For healthy individuals, it is increasingly accepted that lung function follows along an individual percentile established early in life and that the level of maximal function reached as a young adult can affect the subsequent development of lung disease that occurs with the normal aging process. This emphasizes the need to maximize early lung function. The trajectories of lung function are at least partially established by perinatal factors, including prematurity and in utero exposures (tobacco exposure, nutrition, inflammation, etc), although they can also be affected by a variety of additional factors and exposures throughout the life span. Whether lung function trajectories can be impacted or reset if established under suboptimal conditions is an unanswered question, offering new avenues for research. In this review, we will summarize important articles outlining lung function trajectories and linking pediatric lung function tests to adult lung function tests decades later. We will focus on perinatal factors and outline progress and opportunities for further investigation into the potential ability to reset trajectories to impact long-term lung health.

Bronchopulmonary Dysplasia: Then, Now, and Next

Bronchopulmonary dysplasia (BPD) has evolved considerably since its first description over 50 years ago. This review aims to provide a historical framework for conceptualizing BPD and a current understanding of the changing definition, epidemiology, pathophysiology, treatment, and outcomes of BPD. The transdisciplinary approach that led to the initial phenotypic description of BPD continues to hold promise today. Investigators are refining the definition of BPD in light of changes in clinical care and increasing survival rates of very preterm infants. Despite improvements in perinatal care the incidence of BPD continues to increase. There is growing recognition that antenatal risk factors play a key role in the development of BPD. Strategies designed to prevent or limit neonatal lung injury continue to evolve. Defining the phenotype of infants with BPD can meaningfully direct treatment. Infants with BPD benefit from an interdisciplinary approach to longitudinal care with a focus on growth and neurocognitive development. While the ultimate impact of BPD on long-term pulmonary morbidity remains an active area of investigation, current data indicate that most children and adolescents with a history of BPD have a quality of life comparable to that of other preterm infants.

Respiratory and cardiopulmonary limitations to aerobic exercise capacity in adults born preterm

Adults born preterm, regardless of whether they develop bronchopulmonary dysplasia, have underdeveloped respiratory and cardiopulmonary systems. The resulting impaired respiratory and cardiopulmonary systems are inadequate for the challenges imposed by aerobic exercise, which is exacerbated by the presence of bronchopulmonary dysplasia. Thus the respiratory and cardiopulmonary systems of these preterm individuals may be the most influential contributors to the significantly lower aerobic exercise capacity compared with their term born counterparts. The precise underlying cause(s) of the lower aerobic exercise capacity in adults born preterm is not entirely known but could be a number of interrelated parameters including mechanical ventilatory constraints, impaired pulmonary gas exchange efficiency, and excessive cardiopulmonary pressures. Likewise, additional aspects, such as impaired cardiovascular function and altered muscle bioenergetics, may play additional roles in limiting aerobic exercise capacity. Whether or not all or some of these aspects are present in adults born preterm and precisely how they may contribute to the lower aerobic exercise capacity are only beginning to be systematically explored. The purpose of this mini-review is to outline what is currently known about the respiratory and cardiopulmonary limitations during exercise in this population and to identify key areas where additional knowledge will help to advance this area. Additionally, where possible, we highlight the similarities and differences between obstructive lung disease resulting from preterm birth and chronic obstructive pulmonary disease (COPD) as the physiology and pathophysiology of these two forms of obstructive lung disease may not be identical.

Predictors of urban household variability of indoor PM2.5 in low socio-economic communities

In epidemiological studies, levels of PM2.5 need to be estimated over time and space. Because of logistical constraints, very few studies have been conducted to assess the variability within and across homes and the predictors of this variability. This study evaluated within- and between-home variability of indoor PM2.5 and identified predictors for PM2.5 in homes of mothers participating in the urban Mother and Child in the Environment birth cohort study in Durban, South Africa. Thirty homes were selected from 300 homes that were previously sampled for PM2.5. Two measurements of PM2.5 levels were conducted in each home within a 1 week interval in both warm and cold seasons (four samplings per home) using Airmetrics MiniVol samplers. A linear mixed-effect model was used to evaluate within- and between-home variability and to identify fixed effects (predictors) that result in reduced variability. The PM2.5 levels in the 30 homes ranged from 2 to 303 μg m-3. The within-home variability accounted for 94% of the total variability in the log-transformed PM2.5 levels for the 30 homes. The fixed effects extracted from the repeated samplings in the present study were used to improve a previously developed multivariable linear regression model for 300 homes, and thereby increased the R2 from 0.50 to 0.54. Inclusion of fixed-effects in multivariable linear regression models resulted in a reasonably robust model that can be used to predict PM2.5 levels in unmeasured homes of the cohort.

Early inhaled budesonide in extremely preterm infants decreases long-term respiratory morbidity

BACKGROUND

There is no strict correlation between early bronchopulmonary dysplasia and long-term respiratory disease. Early inhaled corticosteroids seem to reduce the incidence of bronchopulmonary dysplasia, but the long-term outcome remains unknown.

RESEARCH QUESTION

The aim of this study was to evaluate the effect of early inhaled corticosteroids on chronic respiratory morbidity.

METHODS

Fifty-nine survivors from the Prague cohort included in Neonatal European Study of Inhaled Steroids underwent further follow-up comprising of respiratory morbidity monitoring during the first 2 years of life followed by objective lung function testing performed at the age of 5.9 years (range 5-7 years). Both outcomes were pursued and finalized before the unblinding of budesonide subgroups.

RESULTS

Fifty randomized (budesonide vs placebo group, 56% vs 44%) survivors were included in the study. Spirometry was successfully performed in 48 children. No statistically significant differences were found in the lung function test (forced expiratory flow [FEF] - FEF₇₅ , FEF_50, FEF₂₅ , and FEF_25-75; FEV₁ , forced vital capacity [FVC], FEV₁ /FVC) although mild trend to the improvement of expiratory flow pattern was observed in the budesonide group (median z-score of FEV₁ /FVC -0.376 vs -0.983, P = .13; median z-score of FEF_25-75 -1.004 vs -1.458, P = .13; median z-score of FEF₇₅ -0.527 vs -0.996, P = .17). Children assigned to budesonide had a significantly lower rate of symptoms of chronic lung disease (34.6% vs 68.2%; P = .04) than children assigned to placebo.

INTERPRETATION

Our study suggests that early inhaled budesonide was associated with the trend to the improvement of functional lung parameters and with a lower rate of symptoms of chronic lung disease within the first 2 years of life.

Asthma: A Loss of Post-natal Homeostatic Control of Airways Smooth Muscle With Regression Toward a Pre-natal State

The defining feature of asthma is loss of normal post-natal homeostatic control of airways smooth muscle (ASM). This is the key feature that distinguishes asthma from all other forms of respiratory disease. Failure to focus on impaired ASM homeostasis largely explains our failure to find a cure and contributes to the widespread excessive morbidity associated with the condition despite the presence of effective therapies. The mechanisms responsible for destabilizing the normal tight control of ASM and hence airways caliber in post-natal life are unknown but it is clear that atopic inflammation is neither necessary nor sufficient. Loss of homeostasis results in excessive ASM contraction which, in those with poor control, is manifest by variations in airflow resistance over short periods of time. During viral exacerbations, the ability to respond to bronchodilators is partially or almost completely lost, resulting in ASM being "locked down" in a contracted state. Corticosteroids appear to restore normal or near normal homeostasis in those with poor control and restore bronchodilator responsiveness during exacerbations. The mechanism of action of corticosteroids is unknown and the assumption that their action is solely due to "anti-inflammatory" effects needs to be challenged. ASM, in evolutionary terms, dates to the earliest land dwelling creatures that required muscle to empty primitive lungs. ASM appears very early in embryonic development and active peristalsis is essential for the formation of the lungs. However, in post-natal life its only role appears to be to maintain airways in a configuration that minimizes resistance to airflow and dead space. In health, significant constriction is actively prevented, presumably through classic negative feedback loops. Disruption of this robust homeostatic control can develop at any age and results in asthma. In order to develop a cure, we need to move from our current focus on immunology and inflammatory pathways to work that will lead to an understanding of the mechanisms that contribute to ASM stability in health and how this is disrupted to cause asthma. This requires a radical change in the focus of most of "asthma research."

Lung Function of Adults Born at Very Low Birth Weight

BACKGROUND

Much remains unknown about the consequences of very low birth weight (VLBW) and bronchopulmonary dysplasia (BPD) on adult lungs. We hypothesized that VLBW adults would have impaired lung function compared with controls, and those with a history of BPD would have worse lung function than those without.

METHODS

At age 26 to 30 years, 226 VLBW survivors of the New Zealand VLBW cohort and 100 term controls born in 1986 underwent lung function tests including spirometry, plethysmographic lung volumes, diffusing capacity of the lung for carbon monoxide, and single-breath nitrogen washout (SBN₂).

RESULTS

An obstructive spirometry pattern was identified in 35% VLBW subjects versus 14% controls, with the majority showing mild obstruction. Compared with controls, VLBW survivors demonstrated significantly lower forced expiratory volume in 1 second (FEV₁), FEV₁/forced vital capacity (FVC) ratio (FEV₁/FVC), forced expiratory flow at 25% to 75% of FVC and higher residual volume (RV), RV/total lung capacity (TLC) ratio (RV/TLC), decreased diffusing capacity of the lung for carbon monoxide, and increased phase III slope for SBN₂. The differences persisted after adjustment for sex and smoking status. Within the VLBW group, subjects with BPD showed significant reduction in FEV₁, FEV₁/FVC, and forced expiratory flow at 25% to 75% of FVC, and increase in RV, RV/TLC, and phase III slope for SBN₂, versus subjects without. The differences remained after adjustment for confounders.

CONCLUSIONS

Adult VLBW survivors showed a higher incidence of airflow obstruction, gas trapping, reduced gas exchange, and increased ventilatory inhomogeneity versus controls. The findings suggest pulmonary effects due to VLBW persist into adulthood, and BPD is a further insult on small airway function.

Birth weight and prematurity with lung function at ~17.5 years: "Children of 1997" birth cohort

We aimed to determine if prematurity and lower birth weight are associated with poorer lung function in a non-western developed setting with less marked confounding by socioeconomic position. Using multivariable linear regression in Hong Kong’s “Children of 1997” birth cohort, adjusted associations of prematurity and birth weight with forced expiratory volume in 1 second (FEV₁), forced vital capacity (FVC), and forced expiratory flow at 25–75% of the pulmonary volume (FEF_25–75%) at ~17.5 years were assessed. Associations for birth weight were stronger in boys for FEV₁ (boys: 0.31 L, 95% confidence interval (CI) 0.24 to 0.38, girls: 0.18 L, 95% CI 0.12 to 0.25), FVC (boys: 0.36 L, 95% CI 0.27 to 0.44, girls: 0.22 L, 95% CI 0.15 to 0.28) and FEF_25–75% (boys: 0.35 L, 95% CI 0.21 to 0.49, girls: 0.22 L, 95% CI 0.09 to 0.34) adjusted for age, socioeconomic position and infant and maternal characteristics. Similarly adjusted, preterm birth (compared to full-term birth) was associated with lower FEV₁/FVC and FEF_25–75%. Thus, associations of lower birth weight, especially in boys, and prematurity with poorer lung function at 17.5 years were found. Identifying underlying mechanism might contribute to the improvement of pulmonary health and the prevention of adult respiratory illness.

Predicting Lung Health Trajectories for Survivors of Preterm Birth

Rates of preterm birth (<37 weeks of gestation) are increasing worldwide. Improved perinatal care has markedly increased survival of very (<32 weeks gestation) and extremely (<28 weeks gestation) preterm infants, however, long term respiratory sequalae are common among survivors. Importantly, individual's lung function trajectories are determined early in life and tend to track over the life course. Preterm infants are impacted by antenatal, postnatal and early life perturbations to normal lung growth and development, potentially resulting in significant shifts from the "normal" lung function trajectory. This review summarizes what is currently known about the long-term lung function trajectories in survivors of preterm birth. Further, this review highlights how antenatal, perinatal and early life factors are likely to contribute to individual lung health trajectories across the life course.

Pulmonary Consequences of Prenatal Inflammatory Exposures: Clinical Perspective and Review of Basic Immunological Mechanisms

Chorioamnionitis, a potentially serious inflammatory complication of pregnancy, is associated with the development of an inflammatory milieu within the amniotic fluid surrounding the developing fetus. When chorioamnionitis occurs, the fetal lung finds itself in the unique position of being constantly exposed to the consequent inflammatory meditators and/or microbial products found in the amniotic fluid. This exposure results in significant changes to the fetal lung, such as increased leukocyte infiltration, altered cytokine, and surfactant production, and diminished alveolarization. These alterations can have potentially lasting impacts on lung development and function. However, studies to date have only begun to elucidate the association between such inflammatory exposures and lifelong consequences such as lung dysfunction. In this review, we discuss the pathogenesis of and fetal immune response to chorioamnionitis, detail the consequences of chorioamnionitis exposure on the developing fetal lung, highlighting the various animal models that have contributed to our current understanding and discuss the importance of fetal exposures in regard to the development of chronic respiratory disease. Finally, we focus on the clinical, basic, and therapeutic challenges in fetal inflammatory injury to the lung, and propose next steps and future directions to improve our therapeutic understanding of this important perinatal stress.

Reduced Lung Function at Preschool Age in Survivors of Very Low Birth Weight Preterm Infants

Background: Survivors of preterm birth are at risk of long-term respiratory consequences. The objective of this prospective study was to assess pulmonary function at preschool age of former very low birth weight (VLBW) preterm children. Methods: Lung function of children born preterm and term controls aged 5-6 years were assessed by spirometry. The results were converted to z-scores. A questionnaire regarding respiratory symptoms was completed. Associations to gestational age (GA), birth weight (BW), bronchopulmonary dysplasia (BPD), and perinatal factors were assessed. Results: In total, 85 VLBW preterm children and 29 term controls were studied. Of the preterm children, the mean GA was 28.6 ± 2.6 weeks and the mean BW was 1,047 ± 273 gm. Preterm children had significantly lower z-scores of forced expiratory volume in 1 s (FEV₁), FEV₁/forced vital capacity (FVC) ratio, and forced expiratory flow rate between 25-75% of FVC (FEF_25-75), compared with term controls (-0.73 vs. 0.04, p = 0.002; -0.22 vs. 0.39, p = 0.003; -0.93 vs. 0.0, p < 0.001; respectively). Further segregation of the preterm group revealed significantly impaired FEV₁, FEF_25-75 in children at earlier gestation (≤ 28 weeks, n = 45), lighter at birth (≤ 1,000 g, n = 38), or with BPD (n = 55) compared with term controls (p < 0.05). There were significant negative relationships between the severity of BPD with FEV₁, FVC, and FEF_25-75 (p < 0.05). However, no correlation between lung function measurements and respiratory symptoms was found. Conclusions: VLBW preterm infants have reduced lung function at preschool age, especially among those with younger GA, lower BW, and BPD. Additional long-term follow-up of respiratory outcomes are needed for this vulnerable population.

Bronchopulmonary dysplasia

In the absence of effective interventions to prevent preterm births, improved survival of infants who are born at the biological limits of viability has relied on advances in perinatal care over the past 50 years. Except for extremely preterm infants with suboptimal perinatal care or major antenatal events that cause severe respiratory failure at birth, most extremely preterm infants now survive, but they often develop chronic lung dysfunction termed bronchopulmonary dysplasia (BPD; also known as chronic lung disease). Despite major efforts to minimize injurious but often life-saving postnatal interventions (such as oxygen, mechanical ventilation and corticosteroids), BPD remains the most frequent complication of extreme preterm birth. BPD is now recognized as the result of an aberrant reparative response to both antenatal injury and repetitive postnatal injury to the developing lungs. Consequently, lung development is markedly impaired, which leads to persistent airway and pulmonary vascular disease that can affect adult lung function. Greater insights into the pathobiology of BPD will provide a better understanding of disease mechanisms and lung repair and regeneration, which will enable the discovery of novel therapeutic targets. In parallel, clinical and translational studies that improve the classification of disease phenotypes and enable early identification of at-risk preterm infants should improve trial design and individualized care to enhance outcomes in preterm infants.

Bronchopulmonary dysplasia: Rationale for a pathophysiological rather than treatment based approach to diagnosis

Bronchopulmonary dysplasia (BPD), also known as Chronic Lung Disease (CLD), is a chronic respiratory condition of prematurity with potential life-long consequences for respiratory well-being. BPD was first described by Northway in 1967, when the mean gestation of preterm infants with BPD was 34 weeks' postmenstrual age (PMA). Survival of preterm infants at lower gestational ages has increased steadily since 1967 associated with marked improvements in respiratory management of respiratory distress syndrome. Currently, BPD develops in approximately 45 % of all infants born extremely preterm (Stoll et al., 2015). These smaller and more immature babies are born during the late canalicular or early saccular period of lung development. Not surprisingly, the pathophysiology of BPD also evolved since classical BPD was described. As the nature and our understanding of BPD evolved, so too the definitions and classification of BPD changed over time. These differing and ever-changing definitions hamper clinical benchmarking as they are interpreted and applied inconsistently, and define BPD and its severity by non-standardised treatments rather than independent evaluations of structure or function. A standardised, unambiguous definition and classification of BPD is essential for evaluation and improvement in clinical practice, both within an individual unit, as well as across and between neonatal networks. The determination and implementation of diagnostic criteria and severity classification that is standardised, globally applicable, and that has prognostic utility for clinical outcomes and guidance of ongoing respiratory management remain of utmost importance. This review describes the evolution of BPD definitions, evaluates the benefits and limitations of each approach, and discusses alternative approaches that may improve the functional assessment of BPD severity.

Recent advances in our understanding of the mechanisms of lung alveolarization and bronchopulmonary dysplasia

Bronchopulmonary dysplasia (BPD) is the most common cause of morbidity and mortality in preterm infants. A key histopathological feature of BPD is stunted late lung development, where the process of alveolarization-the generation of alveolar gas exchange units-is impeded, through mechanisms that remain largely unclear. As such, there is interest in the clarification both of the pathomechanisms at play in affected lungs, and the mechanisms of de novo alveoli generation in healthy, developing lungs. A better understanding of normal and pathological alveolarization might reveal opportunities for improved medical management of affected infants. Furthermore, disturbances to the alveolar architecture are a key histopathological feature of several adult chronic lung diseases, including emphysema and fibrosis, and it is envisaged that knowledge about the mechanisms of alveologenesis might facilitate regeneration of healthy lung parenchyma in affected patients. To this end, recent efforts have interrogated clinical data, developed new-and refined existing-in vivo and in vitro models of BPD, have applied new microscopic and radiographic approaches, and have developed advanced cell-culture approaches, including organoid generation. Advances have also been made in the development of other methodologies, including single-cell analysis, metabolomics, lipidomics, and proteomics, as well as the generation and use of complex mouse genetics tools. The objective of this review is to present advances made in our understanding of the mechanisms of lung alveolarization and BPD over the period 1 January 2017-30 June 2019, a period that spans the 50th anniversary of the original clinical description of BPD in preterm infants.

Upper Airway Pathology Contributes to Respiratory Symptoms in Children Born Very Preterm

OBJECTIVE

To evaluate the role of upper airway dysfunction, indicated by altered vocal quality (dysphonia), on the respiratory symptoms of children surviving very preterm birth.

STUDY DESIGN

Children born <32 weeks of gestation participated in 2 separate assessments during midchildhood. The first visit assessed voice quality by a subjective evaluation using the Consensus Auditory-Perceptual Evaluation of Voice and a computerized analysis of the properties of the voice via the Acoustic Voice Quality Index. The second assessment recorded parentally reported respiratory symptoms and measures of lung function, including spirometry, lung volumes, oscillatory mechanics, and a cardiopulmonary exercise test.

RESULTS

Preterm children (n = 35; median gestation 24.3 weeks) underwent paired voice and lung assessments at approximately 11 years of age. Preterm children with dysphonia (n = 25) reported significantly more respiratory symptoms than those with normal voices (n = 10) including wheeze (92% vs 40%; P = .001) and asthma diagnosed by a physician (60% vs 10%; P = .007). Lung function outcomes were generally not different between the dysphonic group and the group with normal voice (P > .05), except for the oscillatory mechanics measures, which were all at least 0.5 z score lower in the dysphonic group (Xrs₈ mean difference = -0.91 z scores, P = .003; f_res = 1.06 z scores, P = .019; AX = -0.87 z scores, P = .010; Rrs₈ = 0.63 z scores, P = .068).

CONCLUSIONS

The upper airway may play a role in the respiratory symptoms experienced by some very preterm children and should be considered by clinicians, especially when symptoms are in the presence of normal lung function and are refractory to treatment.

Analysis of maximal expiratory flow-volume curves in adult survivors of preterm birth

Adult survivors of very preterm (≤32 wk gestational age) birth without (PRE) and with bronchopulmonary dysplasia (BPD) have variable degrees of airflow obstruction at rest. Assessment of the shape of the maximal expiratory flow-volume (MEFV) curve in PRE and BPD may provide information concerning their unique pattern of airflow obstruction. The purposes of the present study were to 1) quantitatively assess the shape of the MEFV curve in PRE, BPD, and healthy adults born at full-term (CON), 2) identify where along the MEFV curve differences in shape existed between groups, and 3) determine the association between an index of MEFV curve shape and characteristics of preterm birth (i.e., gestational age, mass at birth, duration of oxygen therapy) in PRE and BPD. To do so, we calculated the average slope ratio (SR) throughout the effort-independent portion of the MEFV curve and at increments of 5% of forced vital capacity (FVC) between 20 and 80% of FVC in PRE (n = 19), BPD (n = 25), and CON (n = 20). We found that average SR was significantly higher in PRE (1.34 ± 0.35) and BPD (1.33 ± 0.45) compared with CON (1.03 ± 0.22; both P < 0.05) but similar between PRE and BPD (P = 0.99). Differences in SR between groups occurred early in expiration (i.e., 20-30% of FVC). There was no association between SR and characteristics of preterm birth in PRE and BPD groups (all P > 0.05). The mechanism(s) of increased SR during early expiration in PRE/BPD relative to CON is unknown but may be due to differences in the structural and mechanical properties of the airways.

Preterm birth: Born too soon for the developing airway epithelium?

Birth prior to term interrupts the normal development of the respiratory system and consequently results in poor respiratory outcomes that persist throughout childhood. The mechanisms underpinning these poor respiratory outcomes are not well understood, but intrinsic abnormalities within the airway epithelium may be a contributing factor. Current evidence suggests that the airway epithelium is both structurally and functionally abnormal after preterm birth, with reports of epithelial thickening and goblet cell hyperplasia in addition to increased inflammation and apoptosis in the neonatal intensive care unit. However, studies focusing on the airway epithelium are limited and many questions remain unanswered; including whether abnormalities are a direct result of interrupted development, a consequence of exposure to inflammatory stimuli in the perinatal period or a combination of the two. In addition, the difficulty of accessing airway tissue has resulted in the majority of evidence being collected in the pre-surfactant era which may not reflect contemporary preterm birth. This review examines the consequences of preterm birth on the airway epithelium and explores the clinical relevance of currently available models whilst highlighting the need to develop a clinically relevant in vitro model to help further our understanding of the airway epithelium in preterm birth.

Neonatal respiratory status predicts longitudinal respiratory health outcomes in preterm infants

OBJECTIVES

To examine the relationship between neonatal respiratory status and longitudinal respiratory health outcomes in preterm infants with very low birth weight (VLBW, birth weight <1500 g).

METHODS

A total of 109 VLBW preterm infants were prospectively assessed for respiratory status using the Toce clinical and radiographic scoring method on a postnatal day 28, and severity of bronchopulmonary dysplasia (BPD) at 36-weeks postmenstrual age (PMA), respiratory morbidity within 1 year of corrected age (CA), pulmonary function test, and six-minute walk test at 4 years of age.

RESULTS

A high Toce clinical score on day 28 was associated with the occurrence of respiratory morbidity within 1 year of CA and poor pulmonary function and functional exercise performance at 4 years of age in VLBW preterm infants (all P < 0.05). BPD at 36-weeks PMA was associated with an increased risk of respiratory morbidity within 1 year of CA and its negative impact on pulmonary function and functional exercise performance at 4 years of age was most pronounced in the severe form (all P < 0.05).

CONCLUSIONS

Early assessments of neonatal respiratory status including Toce clinical score and the severity of BPD are valid to identify VLBW preterm infants who are at risk of adverse longitudinal respiratory health outcomes.

Docosahexaenoic acid supplementation of preterm infants and parent-reported symptoms of allergic disease at 7 years corrected age: follow-up of a randomized controlled trial

BACKGROUND

Docosahexaenoic acid (DHA, 22:6n-3) supplementation in the prenatal period is associated with a reduction in the incidence of some symptoms of allergic disease. Infants born preterm are at increased risk of allergic disease, but it is unknown if DHA supplementation reduces the risk of childhood allergies.

OBJECTIVES

The aim of this study was to determine if supplementation of infants born at <33 wk gestation with high-DHA compared with standard-DHA enteral feeds decreases the incidence and severity of parent-reported allergic disease symptoms at a corrected age (CA) of 7 y.

METHODS

This study was a follow-up of an Australian multicenter randomized controlled trial. Infants were given high-DHA (∼1% total fatty acids) or standard-DHA (∼0.3% total fatty acids) enteral feeds from 2-4 d of postnatal age until 40 wk postmenstrual age. Parent-reported incidence of respiratory allergic disease symptoms including wheeze and rhinitis at 7 y CA were the main outcomes. Other outcomes included the incidence of eczema symptoms; severity of any symptoms; and the incidence of wheeze, rhinitis, rhinoconjunctivitis, and eczema from birth to 7 y CA.

RESULTS

Data were available for 569 of 657 (87%) children originally randomized. Symptoms of wheeze or rhinitis at 7 y CA did not differ between high- and standard-DHA groups [wheeze: RR: 1.10; 95% CI: 0.73, 1.65; P = 0.66; rhinitis: RR: 1.09; 95% CI: 0.81, 1.46; P = 0.59]. There was no difference in other allergic disease symptoms at 7 y CA or in the severity of symptoms. Parent-reported symptoms of wheeze, rhinitis, rhinoconjunctivitis, or eczema from birth to 7 y CA did not differ between the groups.

CONCLUSIONS

High-dose DHA supplementation of infants born at <33 wk gestation did not alter allergic disease symptoms or severity at 7 y CA, or from birth to 7 y CA compared with standard-dose DHA. This trial was registered with the Australian New Zealand Clinical Trials Registry as ANZCTR 12606000327583 (http://www.anzctr.org.au).

Lung function in a cohort of 5-year-old children born very preterm

OBJECTIVE

We assessed lung function and respiratory health in an area-based prospective cohort of preschool children born very preterm.

DESIGN

Lung function was measured by interrupter respiratory resistance (Rint) and forced oscillation technique (FOT) (respiratory resistance (Rrs8), reactance (Xrs8), and area under the reactance curve (AX)) at a median age of 5.2 years in a cohort of 194 children born at 22-31 weeks of gestational age (GA) in Tuscany, Italy. Respiratory symptoms and hospitalizations were also assessed.

RESULTS

Mean (SD) lung function Z-scores were impaired in preterm children for Rint (0.72 (1.13)), Xrs8 (-0.28 (1.34)), and AX (0.29 (1.41)). However, only a relatively small proportion of children (14.5-17.4%) had values beyond the 95th centile or below the 5th. Children with bronchopulmonary dysplasia (BPD) (n = 24) had slightly but not significantly impaired lung function indices in comparison with those without BPD (n = 170). In a multivariable analysis, lower GA was associated with worse lung function indices. Fifty-five percent of children had a history of wheezing ever and 21% had been hospitalized in their lifetime because of lower respiratory infections; 31% had wheezing in the last 12 months and this was associated with increased Rrs8 (P = 0.04) and AX (P = 0.08), and with decreased Xrs8 (P = 0.04) Z-scores.

CONCLUSIONS

Irrespectively of BPD preschool children born very preterm had impaired lung function indices, as measured by Rint and FOT, and a slightly higher burden of respiratory problems than the general population. GA seems to be crucial for lung development.

Increased prevalence of expiratory flow limitation during exercise in children with bronchopulmonary dysplasia

Evidence regarding the prevalence of expiratory flow limitation (EFL) during exercise and the ventilatory response to exercise in children born preterm is limited. This study aimed to determine the prevalence of EFL as well as contributing factors to EFL and the ventilatory response to exercise in preterm children with and without bronchopulmonary dysplasia (BPD).

Preterm children (≤32 weeks gestational age) aged 9–12 years with (n=64) and without (n=42) BPD and term controls (n=43), performed an incremental treadmill exercise test with exercise tidal flow–volume loops.

More preterm children with BPD (53%) had EFL compared with preterm children without BPD (26%) or term controls (28%) (p<0.05). The presence of EFL was independently associated with decreased forced expiratory volume in 1 s/forced vital capacity z-score and lower gestational age (p<0.05). There was no difference in peak oxygen uptake between preterm children with BPD and term controls (48.0 versus 48.4 mL·kg⁻¹·min⁻¹; p=0.063); however, children with BPD had a lower tidal volume at peak exercise (mean difference −27 mL·kg⁻¹, 95% CI −49– −5; p<0.05). Children born preterm without BPD had ventilatory responses to exercise similar to term controls.

Expiratory flow limitation is more prevalent in children born preterm with BPD and is associated with airway obstruction and a lower gestational age.

Children born preterm have an increased prevalence of expiratory limitation during exercise associated with reduced lung function and lower gestational agehttp://ow.ly/jLsk30leOVI

Persistent and progressive long-term lung disease in survivors of preterm birth

Preterm birth accounts for approximately 11% of births globally, with rates increasing across many countries. Concurrent advances in neonatal care have led to increased survival of infants of lower gestational age (GA). However, infants born <32 weeks of GA experience adverse respiratory outcomes, manifesting with increased respiratory symptoms, hospitalisation and health care utilisation into early childhood. The development of bronchopulmonary dysplasia (BPD) - the chronic lung disease of prematurity - further increases the risk of poor respiratory outcomes throughout childhood, into adolescence and adulthood. Indeed, survivors of preterm birth have shown increased respiratory symptoms, altered lung structure, persistent and even declining lung function throughout childhood. The mechanisms behind this persistent and sometimes progressive lung disease are unclear, and the implications place those born preterm at increased risk of respiratory morbidity into adulthood. This review aims to summarise what is known about the long-term pulmonary outcomes of contemporary preterm birth, examine the possible mechanisms of long-term respiratory morbidity in those born preterm and discuss addressing the unknowns and potentials for targeted treatments.

Expiratory Flow - Vital Capacity: Airway - Lung Dysanapsis in 7 Year Olds Born Very Preterm?

An index normalizing airway dimension for lung size derived from spirometry was found inversely correlated to lung size in school children born very preterm, indicating larger alveolar volumes draining into comparatively smaller airways. In contrast in children born full term the index was independent of lung size.

Lung function trajectories throughout childhood in survivors of very preterm birth: a longitudinal cohort study

BACKGROUND

Data on longitudinal respiratory follow-up after preterm birth in the surfactant era are scarce and of increasing importance, with concerns that preterm survivors are destined for early onset chronic obstructive airway disease. We aimed to comprehensively assess lung function longitudinally from early childhood to mid-childhood in very preterm children (≤32 weeks gestation), and to explore factors negatively impacting on lung function trajectories.

METHODS

Preterm children (with and without bronchopulmonary dysplasia) and healthy term children as controls were studied. All preterm participants were born at 32 weeks' gestation or earlier at King Edward Memorial Hospital, Perth, WA, Australia, between 1997 and 2003. Bronchopulmonary dysplasia was defined as at least 28 days of supplemental oxygen requirement as assessed at 36 weeks' post-menstrual age. Spirometry, oscillatory mechanics, gas exchange, lung volumes, and respiratory symptoms were assessed at three visits, two in early childhood (4-8 years) and one in mid-childhood (9-12 years). CT of the chest was done in preterm children in mid-childhood. Respiratory symptoms were documented via questionnaire at each visit. Data were analysed longitudinally using linear mixed models.

FINDINGS

200 very preterm children (126 with bronchopulmonary dysplasia and 74 without bronchopulmonary dysplasia) and 67 healthy term control children attended 458 visits between age 4 and 12 years. Chest CT was done on 133 preterm children at a mean age of 10·9 (SD 0·6) years. Preterm children, with and without bronchopulmonary dysplasia, had declines in spirometry z-scores over time compared with controls: forced expiratory volume in 1 s (FEV₁), forced expiratory flow at 25-75% of the pulmonary volume, and FEV₁/forced vital capacity all declined by at least 0·1 z-score per year in children with bronchopulmonary dysplasia (all p<0·001). Respiratory mechanics and gas exchange also deteriorated over time in children with bronchopulmonary dysplasia (relative to term controls, respiratory system reactance at 8 Hz decreased by -0·05 z-score per year [95% CI -0·08 to -0·01; p=0·006] and diffusing capacity of the lungs for carbon monoxide decreased by -0·03 z-score per year [95% CI -0·06 to -0·01; p=0·048]). Preterm children with bronchial wall thickening on chest CT (suggestive of inflammation) had bigger decreases in spirometry outcomes through childhood. For example, children with bronchial wall thickening on chest CT had an FEV₁ z-score decline of -0·61 (95% CI -1·03 to-0·19; p=0·005) more than those without. Similarly, children exposed to tobacco smoke, those with earlier gestation, or those requiring more neonatal supplemental oxygen declined at a faster rate.

INTERPRETATION

Lung function trajectories are impaired in survivors of very preterm birth. Survivors with bronchopulmonary dysplasia, ongoing respiratory symptoms, or CT changes reflecting inflammation have the poorest trajectories and might be at increased risk of lung disease in later life. Close targeted pulmonary follow-up of these individuals is necessary.

FUNDING

National Health and Medical Research Council grants APP634519, APP1073301 (to SJS), APP1077691 (to JJP), and APP1025550 (to GLH), Princess Margret Hospital Foundation, and Raine Medical Foundation.

Longitudinal assessment of lung function in extremely prematurely born children

OBJECTIVES

To assess longitudinally small airway function in children born extremely prematurely and whether there was a correlation between airway function in infancy and at 11-14 years.

WORKING HYPOTHESES

There would be tracking of airways obstruction and small airway function would deteriorate during childhood in those born extremely prematurely.

STUDY DESIGN

A longitudinal study.

PATIENT-SUBJECT SELECTION

Thirty-five children with a mean gestational age of 26 weeks had lung function assessed at 1 year corrected and 11-14 years of age.

METHODOLOGY

Lung volumes were measured by helium gas dilution (FRC_He ) and plethysmography (FRC_pleth ) and small airway function assessed by calculating the FRC_He :FRC_pleth ratio. Airway function was assessed at 1 year corrected by measurement of airway resistance (R_aw ) and at 11-14 years by assessment of R_aw , forced expiratory flow from 75% of vital capacity (FEF₇₅ ), and forced expiratory volume at one second (FEV₁ ).

RESULTS

At the first assessment, the children had a mean (SD) FRC_He :FRC_pleth of 0.90 (0.13) and at the second, 0.83 (0.12) (P = 0.035). There was a significant 0.54% decrease (95%CI: -1.02%, -0.06%) in FRC_He :FRC_pleth for increased age per year after adjusting for birth weight, gestational age, sex, and bronchopulmonary dysplasia (P = 0.027). There were significant correlations between R_aw at the first assessment and R_aw (P = 0.012), FEF₇₅ (P = 0.034), and FEV₁ (P = 0.04) at 11-14 years.

CONCLUSIONS

These results demonstrate in those born extremely prematurely there is tracking of airway function during childhood.

Lung function after extremely preterm birth-A population-based cohort study (EXPRESS)

BACKGROUND AND OBJECTIVES

Follow-up studies of children and young adults born very-to-moderately preterm show persistent and significant lung function deficits. The aim of the study was to determine lung function and airway mechanics in school-aged children born in 2004 to 2007 and extremely preterm (after 22-26 weeks of gestation).

METHODS

In a population-based cohort of children born extremely preterm and controls born at term (n = 350), follow-up at 6½-years-of-age was performed using spirometry and impulse oscillometry. Associations to gestational age, smallness for gestational age (SGA), and bronchopulmonary dysplasia (BPD) were assessed.

RESULTS

Children born extremely preterm had lower forced vital capacity (FVC, z-score: -0.7, 95%CI: -1.0;-0.4), forced expiratory volume (FEV₁ , z-score: -1.1, 95%CI: -1.4; -0.8), higher frequency-dependence of resistance (R_5-20 , 0.09, 95%CI: 0.05; 0.12 kPa · L^-1  · s^-1 ) and larger area under the reactance curve (AX, 0.78, 95%CI: 0.49; 1.07 kPa · L^-1 ) than controls. In children born at 22-24 weeks of gestation, 24% had FVC and 44% had FEV₁ below the lower limit of normal. SGA and severe BPD only marginally contributed to pulmonary outcomes. Asthma-like disease was reported in 40% of extremely preterm children and 15% of controls.

CONCLUSION

Many children born extremely preterm have altered airway mechanics and significant obstructive reduction in lung function. This warrants consideration for treatment and continued follow-up.

Premature birth affects the degree of airway dysanapsis and mechanical ventilatory constraints

NEW FINDINGS

What is the central question of this study? Adult survivors of preterm birth without (PRE) and with bronchopulmonary dysplasia (BPD) have airflow obstruction at rest and significant mechanical ventilatory constraints during exercise compared with those born at full term (CON). Do PRE/BPD have smaller airways, indexed via the dysanapsis ratio, than CON? What is the main finding and its importance? The dysanapsis ratio was significantly smaller in BPD and PRE compared with CON, with BPD having the smallest dysanapsis ratio. These data suggest that airflow obstruction in PRE and BPD might be because of smaller airways than CON. Adult survivors of very preterm birth (≤32 weeks gestational age) without (PRE) and with bronchopulmonary dysplasia (BPD) have obstructive lung disease as evidenced by reduced expiratory airflow at rest and have significant mechanical ventilatory constraints during exercise. Airflow obstruction, in any conditions, could be attributable to several factors, including small airways. PRE and/or BPD could have smaller airways than their counterparts born at full term (CON) owing to a greater degree of dysanaptic airway development during the pre- and/or postnatal period. Thus, the purpose of the present study was to compare the dysanapsis ratio (DR), as an index of airway size, between PRE, BPD and CON. To do so, we calculated DR in PRE (n = 21), BPD (n = 14) and CON (n = 34) individuals and examined flow-volume loops at rest and during submaximal exercise. The DR, using multiple estimates of static recoil pressure, was significantly smaller in PRE and BPD (0.16 ± 0.05 and 0.10 ± 0.03 a.u.) compared with CON (0.22 ± 0.04 a.u.; both P < 0.001) and smallest in BPD (P < 0.001). The DR was significantly correlated with peak expiratory airflow at rest (r = 0.42; P < 0.001) and the extent of expiratory flow limitation during exercise (r = 0.60; P < 0.001). Our findings suggest that PRE/BPD might have anatomically smaller airways than CON, which might help to explain their lower expiratory airflow rate at rest and during exercise and further our understanding of the consequences of preterm birth and neonatal O₂ therapy.

Ventilatory Efficiency in Children and Adolescents Born Extremely Preterm

Purpose: Children and adolescents born extremely preterm (EP) have lower dynamic lung volumes and gas transfer capacity than subjects born at term. Most studies also report lower aerobic capacity. We hypothesized that ventilatory efficiency was poorer and that breathing patterns differed in EP−born compared to term−born individuals.

Methods: Two area−based cohorts of participants born with gestational age ≤28 weeks or birth weight ≤1000 g in 1982−85 (n = 46) and 1991–92 (n = 35) were compared with individually matched controls born at term. Mean ages were 18 and 10 years, respectively. The participants performed an incremental treadmill exercise test to peak oxygen uptake with data averaged over 20 s intervals. For each participant, the relationship between exhaled minute ventilation (V˙_E) and carbon dioxide output (V˙CO₂) was described by a linear model, and the relationship between tidal volume (V_T) and V˙_E by a quadratic model. Multivariate regression analyses were done with curve parameters as dependent variables, and the categories EP vs. term−born, sex, age, height, weight and forced expiratory volume in 1 s (FEV₁) as independent variables.

Results: In adjusted analyses, the slope of the V˙_E−V˙CO₂ relationship was significantly steeper in the EP than the term-born group, whereas no group difference was observed for the breathing pattern, which was related to FEV₁ only.

Conclusion: EP-born participants breathed with higher V˙_E for any given CO₂ output, indicating lower ventilatory efficiency, possibly contributing to lower aerobic capacity. The breathing patterns did not differ between the EP and term−born groups when adjusted for FEV₁.