Pulmonary function and respiratory morbidity in school-age children born prematurely and ventilated for neonatal respiratory insufficiency

Lung developmental arrest caused by PDGF-A deletion: consequences for the adult mouse lung

PDGF-A is a key contributor to lung development in mice. Its expression is needed for secondary septation of the alveoli and deletion of the gene leads to abnormally enlarged alveolar air spaces in mice. In humans, the same phenotype is the hallmark of bronchopulmonary dysplasia (BPD), a disease that affects premature babies and may have long lasting consequences in adulthood. So far, the knowledge regarding adult effects of developmental arrest in the lung is limited. This is attributable to few follow-up studies of BPD survivors and lack of good experimental models that could help predict the outcomes of this early age disease for the adult individual. In this study, we used the constitutive lung-specific Pdgfa deletion mouse model to analyze the consequences of developmental lung defects in adult mice. We assessed lung morphology, physiology, cellular content, ECM composition and proteomics data in mature mice, that perinatally exhibited lungs with a BPD-like morphology. Histological and physiological analyses both revealed that enlarged alveolar air spaces remained until adulthood, resulting in higher lung compliance and higher respiratory volume in knockout mice. Still, no or only small differences were seen in cellular, ECM and protein content when comparing knockout and control mice. Taken together, our results indicate that Pdgfa deletion-induced lung developmental arrest has consequences for the adult lung at the morphological and functional level. In addition, these mice can reach adulthood with a BPD-like phenotype, which makes them a robust model to further investigate the pathophysiological progression of the disease and test putative regenerative therapies.

Impact of influenza on hospitalization rates in children with a range of chronic lung diseases

BACKGROUND

Data on burden of severe influenza in children with a range of chronic lung diseases (CLDs) remain limited.

METHOD

We performed a cohort study to estimate burden of influenza-associated hospitalization in children with CLDs using population-based linked data. The cohort comprised all children in New South Wales, Australia, born between 2001 and 2010 and was divided into five groups, children with: (a) severe asthma; (b) bronchopulmonary dysplasia (BPD); (c) cystic fibrosis (CF); (d) other congenital/chronic lung conditions; and (e) children without CLDs. Incidence rates and rate ratios for influenza-associated hospitalization were calculated for 2001-2011. Average cost/episode of hospitalization was estimated using public hospital cost weights.

RESULTS

Our cohort comprised 888 157 children; 11 058 (1.2%) had one of the CLDs. The adjusted incidence/1000 child-years of influenza-associated hospitalization in children with CLDs was 3.9 (95% CI: 2.6-5.2) and 0.7 (95% CI: 0.5-0.9) for children without. The rate ratio was 5.4 in children with CLDs compared to children without. The adjusted incidence/1000 child-years (95% CI) in children with severe asthma was 1.1 (0.6-1.6), with BPD was 6.0 (3.7-8.3), with CF was 7.4 (2.6-12.1), and with other congenital/chronic lung conditions was 6.9 (4.9-8.9). The cost/episode (95% CI) of influenza-associated hospitalization was AUD 19 704 (95% CI: 11 715-27 693) for children with CLDs compared to 4557 (95% CI: 4129-4984) for children without.

DISCUSSION

This large population-based study suggests a significant healthcare burden associated with influenza in children with a range of CLDs.

Bronchopulmonary dysplasia: clinical aspects and preventive and therapeutic strategies

BACKGROUND

Bronchopulmonary dysplasia (BPD) is the result of a complex process in which several prenatal and/or postnatal factors interfere with lower respiratory tract development, leading to a severe, lifelong disease. In this review, what is presently known regarding BPD pathogenesis, its impact on long-term pulmonary morbidity and mortality and the available preventive and therapeutic strategies are discussed.

MAIN BODY

Bronchopulmonary dysplasia is associated with persistent lung impairment later in life, significantly impacting health services because subjects with BPD have, in most cases, frequent respiratory diseases and reductions in quality of life and life expectancy. Prematurity per se is associated with an increased risk of long-term lung problems. However, in children with BPD, impairment of pulmonary structures and function is even greater, although the characterization of long-term outcomes of BPD is difficult because the adults presently available to study have received outdated treatment. Prenatal and postnatal preventive measures are extremely important to reduce the risk of BPD.

CONCLUSION

Bronchopulmonary dysplasia is a respiratory condition that presently occurs in preterm neonates and can lead to chronic respiratory problems. Although knowledge about BPD pathogenesis has significantly increased in recent years, not all of the mechanisms that lead to lung damage are completely understood, which explains why therapeutic approaches that are theoretically effective have been only partly satisfactory or useless and, in some cases, potentially negative. However, prevention of prematurity, systematic use of nonaggressive ventilator measures, avoiding supraphysiologic oxygen exposure and administration of surfactant, caffeine and vitamin A can significantly reduce the risk of BPD development. Cell therapy is the most fascinating new measure to address the lung damage due to BPD. It is desirable that ongoing studies yield positive results to definitively solve a major clinical, social and economic problem.

Understanding the Short- and Long-Term Respiratory Outcomes of Prematurity and Bronchopulmonary Dysplasia

Bronchopulmonary dysplasia (BPD) is a chronic respiratory disease associated with premature birth that primarily affects infants born at less than 28 weeks' gestational age. BPD is the most common serious complication experienced by premature infants, with more than 8,000 newly diagnosed infants annually in the United States alone. In light of the increasing numbers of preterm survivors with BPD, improving the current state of knowledge of long-term respiratory morbidity for infants with BPD is a priority. We undertook a comprehensive review of the published literature to analyze and consolidate current knowledge of the effects of BPD that are recognized at specific stages of life, including infancy, childhood, and adulthood. In this review, we discuss both the short-term and long-term respiratory outcomes of individuals diagnosed as infants with the disease and highlight the gaps in knowledge needed to improve early and lifelong management of these patients.

[Adult respiratory sequelae of premature birth]

INTRODUCTION

Between 5 and 7% of babies are born prematurely. In the paediatric age group, the respiratory morbidity of these patients is well known, particularly in cases of bronchopulmonary dysplasia (BPD). On the other hand, very few data are available concerning their adult respiratory status.

BACKGROUND

There are currently three different groups of ex-premature babies: (1) those with no BPD who are usually not considered as respiratory high-risk adults but have not been well studied; (2) ex-premature babies with BPD who have an increased risk of asthma, respiratory infections, bronchial obstruction aggravated by smoking, and non-atopic bronchial hyperreactivity; this group has been well studied but not beyond 30 years of age; (3) the babies born very prematurely and affected with a new form of BPD due to neonatal intensive care at a very immature stage of pulmonary development, and for whom the future in adult life is unknown but worrying because of reduced lung volumes since birth.

VIEWPOINTS AND CONCLUSIONS

The respiratory physician must be aware of these groups of adults who he may encounter and who may develop, sooner or later, a certain type of chronic obstructive pulmonary disease.

Preterm birth and respiratory disease in later life

Chronic respiratory diseases are a common complication of preterm birth, particularly among very immature infants or those suffering from bronchopulmonary dysplasia. Major progress in the treatment of preterm newborns has changed the pattern of late respiratory complications. The major respiratory problem in infancy and early childhood is respiratory exacerbations caused by infections (particularly viral ones), which need hospitalization. The symptoms become mild in school-age children; however, a group of children still present with chronic airway obstruction defined by recurrent episodes of wheezing and decreased lung function tests (decreased forced expiratory volume). For some preterm infants, particularly those with bronchopulmonary dysplasia, obstructive lung disease persists into adulthood. They are very likely to develop chronic obstructive pulmonary disease or similar disease later in life. In these patients, a program of lung function monitoring and pulmonary prophylaxis by means of elimination of specific risk factors in adulthood is advisable.

[Bronchopulmonary dysplasia and prematurity. Short-and long-term respiratory changes]

Bronchopulmonary dysplasia (BPD) is the most frequent chronic lung disease in premature children. With the inclusion of antenatal steroid therapy, surfactant use and novel mechanical ventilation strategies, survival of premature newborns has increased, whereupon the incidence of BPD has not only decreased but has also risen in extremely premature newborns. This has led to a high respiratory morbidity in the first 2-3 years of life, with numerous admissions to hospital and respiratory exacerbations mostly due to viral infections. Although there is a trend towards improvement, during school age and adolescence, respiratory symptoms may persist, due to changes in pulmonary function often showing a lower exercise capacity. Although BPD symptoms are similar to those of asthma, as there is limitation in airflow and bronchial hyperresponsiveness (BHR), pathophysiological mechanisms could be different in both diseases. On the other hand, isolated prematurity plays an important role in the child's respiratory pathology, proving that pulmonary function alterations in preterm children are present since the first months of life. A higher respiratory morbidity has also been observed in these children when compared to full-term newborns, not only during the first years of life but also subsequently. In this study, different aspects of chronic respiratory disease associated with prematurity will be analysed, drawing special attention to clinical symptoms, respiratory function changes, BHR and exercise capacity. All these aspects will be reviewed from early childhood until adolescence and young adult age. Similarities and differences between BPD and asthma will also be discussed.

Obstructive lung disease in children with mild to severe BPD

BACKGROUND

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

OBJECTIVES

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Birth weight and adult lung function: a within-pair analysis of twins followed up from birth

BACKGROUND

The aim of the study was to evaluate whether there is any association between intrauterine growth and later lung function or bronchial reactivity in early adulthood in line with Barker's hypothesis.

METHODS

Nineteen twin pairs with disproportionate intrauterine growth pattern were followed up from birth: either one of the pairs had intrauterine growth retardation (birth weight <2 SD) or the within-pair birth weight difference was >1.3 SD. Flow-volume spirometry, followed by isocapnic hyperventilation of cold air, was performed at the ages of 8-16 and 14-22 years in 1993 and 1999. Wilcoxon's matched-pairs analysis was used to compare smaller and larger twin pairs.

RESULTS

In 1993, there were no significant differences between the groups in either spirometry or cold air challenge. In 1999, such a difference was found in forced expiratory volume % (FEV%) and forced expiratory flow (FEF) at 25%-75%, the smaller twin pairs having lower values. In 1993, nine subjects reacted to cold air (>9% decrease in FEV in 1 second). In 1999, only four subjects reacted to cold air, and they all belonged to the group of smaller twins (P=0.04).

CONCLUSION

Lung function evaluated by FEV% and FEF25-75 was lower and responses to cold air were more common at the median age of 16 years in twins with impaired intrauterine growth.

Chronic lung disease of prematurity and respiratory outcome at eight years of age

AIM

The study aimed to determine the respiratory outcome of children who had chronic lung disease of prematurity (CLD) compared with a preterm control group of children at school age.

METHODS

Fifty-two preterm infants with CLD born between 26 and 33 weeks gestation were assessed regarding respiratory illness with 47 having lung function testing. Information regarding respiratory illness was obtained from 52 children in the birthweight-matched control group of whom 45 had lung function testing. The results were compared between the CLD and control groups.

RESULTS

There was no difference in respiratory symptomatology between CLD groups and control preterm infants. On lung function testing, a significantly lower mean forced expiratory flow at 25-75% of vital capacity was identified compared with the preterm controls (P=0.024). This significant difference did not persist after bronchodilator therapy. There was no evidence of increased air trapping or bronchial hyper-reactivity in the CLD children compared with the controls.

CONCLUSION

Lung function in CLD children is largely normal in comparison with preterm controls, apart from some evidence of reversible small airway obstruction. Respiratory symptomatology is not increased in chronic disease children in comparison with control preterm children.

Pulmonary outcomes in bronchopulmonary dysplasia

The incidence of bronchopulmonary dysplasia (BPD), defined as oxygen need at 36 weeks of postmenstrual age, is about 30% for infants with birth weights <1000 g. BPD is associated with persistent structural changes in the lung that result in significant effects on lung mechanics, gas exchange, and pulmonary vasculature. Up to 50% of infants with BPD require readmission to the hospital for lower respiratory tract illness in the first year of life. Long-term measurements of lung function in BPD include normalization of pulmonary mechanics and some lung volumes over time as somatic and lung growth occur, whereas abnormality of small airway function persists. The majority of data reveals no long-term decrease in exercise capacity. Mild to moderate radiological abnormalities persist. BPD is a result of dynamic processes involving inflammation, injury, repair, and maturation. Infants with BPD have significant pulmonary sequelae during childhood and adolescence, and continued surveillance of young adults with BPD is critical.

Respiratory Function in Adolescence in Relation to Low Birth Weight, Preterm Delivery, and Intrauterine Growth Restriction

OBJECTIVES

To study the associations between respiratory function in 18-year-old male subjects and birth weight, preterm delivery, and intrauterine growth restriction (IUGR).

METHODS

Population-based birth cohort. Subsamples of 118 male subjects with low birth weight (LBW) [< 2,500 g] and 236 male subjects with normal birth weight were examined at the age of 18 years.

RESULTS

In the crude analysis, subjects with LBW showed reductions in FEV1 and FVC of 0.166 L and 0.141 L, respectively, compared to those born weighing > or = 2,500 g. These differences were not significant after adjustment for confounding. When subjects with LBW were stratified into those with preterm delivery and those with IUGR, the latter presented a significant reduction in both FEV1 and FVC, when compared to the reference group. These differences also disappeared after adjustment for confounders. Preterm delivery per se was also not associated with poor lung function.

CONCLUSIONS

In this population, LBW was not associated with respiratory function in 18-year-old male subjects.

[Respiratory morbidity after hospital discharge in premature infants born at < or = 32 weeks gestation with bronchopulmonary dysplasia]

BACKGROUND

Bronchopulmonary dysplasia (BPD) is the most frequent cause of respiratory morbidity in the first 2 years of life among preterm infants who survive the first 28 days.

OBJECTIVES

To evaluate respiratory morbidity in the first 2 years of life in a group of preterm infants born at (32 weeks' gestation with BPD (oxygen requirement at 36 weeks' postconceptional age) by comparing it with that in preterm infants born at (32 weeks without BPD and with a control group of full term infants without neonatal morbidity. To determine whether respiratory morbidity in children with BPD decreases after the age of 2 years.

PATIENTS AND METHOD

Group I: preterm children with BPD (n = 29). Group II: preterm children without BPD (n = 29). Group III: children with appropriate gestational age and weight (n = 32). A cross-sectional, descriptive study of the three groups was performed over a 2-year period. In 17 children in group 1, the study was prolonged to the age of 4 years. We analyzed wheezing on at least two occasions, use of inhaled bronchodilators, use of inhaled glucocorticosteroids for more than 6 months, and hospitalization for respiratory illness. The chi-square test and Fischer's exact test were performed.

RESULTS

At least one episode of wheezing occurred in 25 children (86.2%) in group I compared with 12 children (41.4%) in group II and 6 (18.8%) in group III. Nineteen children (65.5%) in group I and none in the remaining two groups received treatment with inhaled glucocorticosteroids for more than 6 months (p < 0.001). Inhaled bronchodilators were used by 25 children (86.2%) in group I compared with 12 (41.4%) in group II and 6 (18.8%) in the control group (p < 0.001). Twelve children (41.3%) in group I were hospitalized for respiratory illness compared with 8 (27.6%) in group II. There were no admissions among the control group. None of the children with BPD who received prophylaxis with palivizumab contracted respiratory syncytial virus infection. Seventeen children with BPD were evaluated until the age of 4 years. Episodes of wheezing decreased from 88.2% in the first year to 41 % between the third and fourth years (p < 0.001). Treatment with inhaled glucocorticosteroids for more than 6 months was given to 88.2% in the first year, 41.2 % between the first and second year and to 0 % after the second year (p < 0.001). Hospital admissions for respiratory illness decreased from 52.9% in the first year to 17.6% in the second year. None of the children were hospitalized after the age of 2 years (p < 0.001).

CONCLUSIONS

During the first 2 years of life, children with BPD showed a greater number of admissions and episodes of wheezing and a greater need for medical treatment. Respiratory morbidity improved with age, 40% showed recurrent wheezing episodes at the age of 4 years.

Lung mechanics and high-resolution computed tomography of the chest in very low birth weight premature infants

CONTEXT

Premature infant lung development may be affected by lung injuries during the first few weeks of life. Lung injuries have been associated with changes in lung mechanics.

OBJECTIVE

To evaluate an association between lung mechanics and lung structural alterations in very low birth weight infants (birth weight less than 1500 g).

DESIGN

A cross-sectional evaluation of pulmonary mechanics (lung compliance and lung resistance) and high resolution computed tomography of the chest at the time of discharge, in 86 very low birth weight infants born at Instituto Fernandes Figueira, a tertiary public healthcare institution in Rio de Janeiro, Brazil. Lung compliance and resistance were measured during quiet sleep. High resolution computed tomography was performed using Pro Speed-S equipment.

MAIN MEASUREMENTS

Statistical analysis was performed by means of variance analysis (ANOVA/Kruskal Wallis). The significance level was set at 0.05.

RESULTS

Abnormal values for both lung compliance and lung resistance were found in 34 babies (43%), whereas 20 (23.3%) had normal values for both lung compliance and lung resistance. The mean lung compliance and lung resistance for the group were respectively 1.30 ml/cm H2O/kg and 63.7 cm H2O/l/s. Lung alterations were found via high-resolution computed tomography in 62 (72%) infants. Most infants showed more than one abnormality, and these were described as ground glass opacity, parenchymal bands, atelectasis and bubble/cyst. The mean compliance values for infants with normal (1.49 ml/cm H2O/kg) high resolution computed tomography, 1 or 2 abnormalities (1.31 ml/cm H2O/kg) and 3 or more abnormalities (1.16 ml/cm H2O/kg) were significantly different (p=0.015). Our data were insufficient to find any association between lung resistance and the number of alterations via high-resolution computed tomography.

CONCLUSION

The results show high prevalence of lung functional and tomographic abnormalities in asymptomatic very low birth weight infants at the time of discharge. They also show an association between lung morphological and functional abnormalities.

Discharge and aftercare in chronic lung disease of the newborn

This article deals with the discharge planning and continuing care of babies with chronic lung disease of the newborn (CLD), especially those with a continuing oxygen requirement, with some reference to longer term outcome. The pattern of CLD has changed since early descriptions, and the most useful definition for persisting morbidity in a baby with lung disease is a continuing oxygen requirement beyond 36 weeks post-menstrual age. Long-term oxygen therapy to maintain oxygen saturation at a mean of 95% or more and prevent levels below 90% is the cornerstone of management, and with adequate oxygen therapy the excess mortality previously reported in CLD can largely be avoided. Care must be given to the method of assessing oxygen saturation: overnight monitoring using appropriate recording devices is recommended. Exposure to respiratory viruses should be minimized where possible. Metabolic requirements are increased, but if efforts are made to maintain adequate energy input the long-term outlook for catch-up growth in height is good. Respiratory morbidity is increased in early life, but this improves in later childhood, along with lung function and exercise tolerance. Although respiratory symptoms should be treated as they arise, there is no evidence for long-term benefit from any pharmacological intervention in CLD.

Exhaled nitric oxide at school age in prematurely born infants with neonatal chronic lung disease

Prematurely born infants with neonatal chronic lung disease (CLD) have increased respiratory morbidity and bronchial obstruction at school age. To evaluate the possible inflammatory basis of lung function abnormalities, we studied 40 children, 7.5-9.6 years of age, born very prematurely (birth weights, 600-1,575 g) and 14 nonatopic term-born controls, using flow-volume spirometry and exhaled nitric oxide (eNO) measurements. In children born prematurely, eNO was significantly higher in atopics than in nonatopics (respective means, 14.8 vs. 6.3 ppb, P = 0.02). Nonatopic prematurely born infants did not differ significantly from controls (means, 6.3 vs. 6.4 ppb, P = ns). Of the 27 nonatopic children not on regular glucocorticoid inhalations, 9 had a history of CLD. Spirometry indicated bronchial obstruction and values that were significantly lower in prematurely born infants with or without CLD than in controls, and they were lower in the CLD than the non-CLD group. However, no significant differences were observed in eNO levels between CLD, non-CLD, and control groups (means, 6.8, 5.9, and 6.4 ppb, P = ns). In nonatopic schoolchildren born very prematurely and with a history of CLD, we found no evidence of airway inflammation associated with increased eNO concentrations. Neither were eNO levels associated with severity of chronic lung disease, as determined by conventional lung function tests. eNO levels were higher in atopic children born prematurely than in controls.

Pulmonary morbidity in 100 survivors of congenital diaphragmatic hernia monitored in a multidisciplinary clinic

BACKGROUND/PURPOSE

In 1990, the authors began a multidisciplinary follow-up clinic for congenital diaphragmatic hernia (CDH) patients. Although the nonpulmonary complications associated with CDH have been reported previously from this clinic, the purpose of this report is to detail the pulmonary outcome in survivors of CDH with severe pulmonary hypoplasia.

METHODS

Between 1990 and 1999, one hundred patients were seen in the clinic. Before hospital discharge, all patients had baseline tests performed, which were repeated per protocol at clinic during follow-up. The data were analyzed by regression analysis to identify and determine the impact of factors on outcomes associated with the long-term pulmonary morbidity.

RESULTS

The average birth weight was 3.16 kg (+/-0.7) with a mean Apgar score of 7 (+/- 2) at 5 minutes. Forty-one patients had an antenatal diagnosis performed. Extracorporeal membrane oxygenation (ECMO) was utilized in 29 patients, and a patch repair was required in 32, whereas 16 patients received both. Average time to extubation was 20.7 (+/- 20) days and mean time to discharge was 59.7 (+/- 61) days. Regression analysis showed that both the need for ECMO and a patch repair were independent predictors of delay in extubation (P <. 001, R(2) = 36%), and delay in discharge from the hospital (P =.001, R(2) = 29%). ECMO also was significantly correlated with the need for diuretics at discharge (P <.001, R(2) = 18%), and with the presence of left-right mismatch (P =.009, R(2) = 9%) and V/Q mismatch (P =.005, R(2) = 11%) on subsequent pulmonary ventilation-perfusion examinations. Sixteen patients required O(2) at discharge, and diuretics were necessary in 43 patients. Seventeen patients at discharge required bronchodilators, and during the first year an additional 36 required at least transient therapy. Similarly, 6 patients at discharge required steroids, and an additional 35 patients required at least transient therapy during the first year. Chest x-rays, although frequently abnormal, had little correlation with clinical outcome, but did influence medical therapy. V/Q scans had limited utility in patient management, and the presence of V/Q mismatch was not highly specific for future obstructive airway disease. Nevertheless, V/Q mismatch was sensitive for obstructive airway disease assessed by spirometry. Twenty-five patients over 5 years of age performed pulmonary function tests (PFTs), which showed 72% normal PFT results and 28% with evidence of obstructive airway disease. Before January 1997, 2 of 8 patients who required urgent treatment in the emergency department (ED) were admitted to the intensive care unit (ICU) secondary to acute respiratory distress. After the implementation of respiratory syncytial viral prophylaxis in January 1997, 8 patients were treated in the ED for acute respiratory distress, but none required admission to the ICU.

CONCLUSIONS

Pulmonary problems continue to be a source of morbidity for survivors of CDH long after discharge. The need for ECMO and the presence of a patch repair are both predictive of more significant morbidity, but the data clearly show that non-ECMO CDH survivors also require frequent attention to pulmonary issues beyond the neonatal period. These data show the need for long-term follow-up of CDH patients preferably with a multidisciplinary team approach.

Pediatric origins of adult lung disease. 1. The contribution of airway development to paediatric and adult lung disease

In summary, factors that affect airway growth early in development appear to cause physiological effects that can be persistent. Reduced airway function early in life does not necessarily result in persistent symptoms, but the long term effects and impact on the development of chronic airflow limitation in adults are yet to be determined. Generally, long term sequelae seem to be related to the severity of the initial insult, but the development of persistent increased bronchial responsiveness is an independent risk factor for symptoms and abnormal lung function in later life. In addition, there appear to be separate genetic factors that influence atopy, airway development, and bronchial responsiveness.

Lung function outcome in children of premature birth

Since the 1960s there has been a continual improvement in the survival of premature infants of birthweight less than 1500 g. This has resulted in an increase in the prevalence of bronchopulmonary dysplasia (BPD), or its milder form, chronic lung disease (CLD) of prematurity. In children with BPD; the initial air trapping improves in the first 3-4 years of life, but small airway obstruction is often slow to improve, suggesting dysanaptic lung growth. Despite this, the majority of older children and adolescents with BPD/CLD do not have significant respiratory symptoms. Children born prematurely with or without hyaline membrane disease may also have a reduction in expiratory flows during childhood, albeit less severe. The clinical significance of this in the longer term is unclear. Although significant associations between decrements in expiratory flows, neonatal oxygen therapy and assisted ventilation have been demonstrated. Airway function has also been reported to be largely unrelated with perinatal events but strongly associated with birthweight. The latter suggests that intra-uterine factors such as under-nutrition may be more important than hitherto recognized. Because of a lack of longitudinal studies, it is unclear how lung function will track during adolescence and adult life. Bronchial hyper-responsiveness is significantly increased in children with BPD and to a lesser extent in those born prematurely with or without hyaline membrane disease. It is unclear whether this is due to a genetic predisposition, neonatal lung injury or anatomically smaller airways. Given the morbidity and fiscal cost of a premature birth, effective strategies to reduce the premature birth rate are needed.

Pulmonary function at school-age in surfactant-treated preterm infants

A follow-up study was conducted in 40 children who had been enrolled in a prospective randomized study of exogenous surfactant therapy for respiratory distress syndrome (RDS) (n = 22; S) or placebo (n = 18; P) to determine long-term pulmonary sequelae of surfactant treatment in premature infants with RDS. At follow-up, mean (SD) age was 6.63 (0.18) and 6.55 (0.23) years for S and P, respectively. Complete lung function tests (LFT) were attempted in all patients. Satisfactory data were obtained in 17/22 surfactant-treated and in 12/18 control children. There was no significant difference between groups for any of the parameters measured. Mean (SD) functional residual capacity (FRC) was 92% (16%) and 90% (21%) predicted, mean (SD) airway resistance (R(aw,exp)) was 122% (25%) and 127% (61%), and mean (SD) forced expiratory volume in 1 s (FEV1) was 104% (12%) and 99% (17%) predicted for S and P. Only maximal expiratory flow at 25% vital capacity (L/s) was significantly below the predicted range in S and P groups, with 74% (23%) and 77% (28%), respectively. To test bronchial hyperreactivity, a simple standardized running test was performed: 4 children in S and 5 in P showed a significant response as defined by clinical airway obstruction or changes in FEV1 and/or R(aw), with no significant difference between groups. Although we found no major abnormalities in lung function and no difference between S and P at early school-age, lack of cooperation during lung function tests makes further follow-up necessary.

Effect of preterm birth on pulmonary function at school age: a prospective controlled study

OBJECTIVE

To assess long-term pulmonary outcome of a regional cohort of children born at < 32 weeks' gestation compared with a matched term control group.

STUDY DESIGN

All 125 surviving children born at 24 to 31 weeks' gestation during a 1-year period and a sociodemographically matched term control group were evaluated at age 7 years.

RESULTS

Preterm children with previous bronchopulmonary dysplasia (BPD) were twice as likely to require rehospitalization during the first 2 years of life than were preterm children without BPD (53% vs 26%, P < .01). At 7 years of age the BPD group had more airway obstruction than did both preterm children without BPD and the term control group (significantly reduced mean forced vital capacity, forced expiratory volume in 1 second, and forced expiratory flow, 25% to 75% vital capacity, all, P < .001). Lung function among preterm children without previous BPD was similar to that of the term control group. Bronchodilator responsiveness was observed twice as often in preterm children with previous BPD (20 of 43, 47%) compared with preterm children without BPD (13 of 53, 25%) or the term control group (23 of 108, 21%, P < .001). These differences remained significant after adjustment was done for birth weight and gestational age.

CONCLUSION

Preterm children without BPD demonstrate pulmonary function at school age similar to that of children in a healthy term control group, whereas preterm children with previous BPD demonstrate abnormal pulmonary function.

Effects of intrauterine growth retardation and prematurity on spirometric flow values and lung volumes at school age in twin pairs

Lung volumes and pulmonary expiratory flow values were investigated in 67 children from multiple pregnancies (30 twins, one set of triplets, one set of quadruplets) at the age of 7-15 years. At birth, 30 of 67 children (44%) had intrauterine growth retardation (IUGR, birth weight <-2 SD or birth weight difference between twin-pairs >1.3 SD). The median gestational age was 35 weeks (range, 28-38 weeks), and the median birth weight was 2,050 g (800-3,150 g). Lung functions were measured with a heated pneumotachograph. Data were standardized using height-based reference equations. No differences were found in lung volumes between children with IUGR and those children who had normal birth weight. Gestational age did not correlate with either airway flow rates or lung volumes. Maximum mid-expiratory flow (FEF50) did not correlate with standardized birth weight or with gestational age. In discordant twin pairs, the IUGR twins had significantly lower FEF50 than their normal birth weight counterparts (p=0.03, Z=-2.13). In the whole study group (67 children), children with IUGR had significantly lower FEF50 than children with normal birth weight (p=0.04; CI, 0.3-19.9). We propose that IUGR has the most pronounced effect on the growth of airways, and no detectable influence on lung volumes. This study confirms the crucial effect of appropriate intrauterine growth on subsequent growth on pulmonary airways.

Pulmonary function in children with initial low birth weight

The objective of this analysis was to examine the effect of low birth weight and prematurity on bronchial air-flow, bronchial reactivity, airway symptoms and asthma diagnosis at school age. A cross-sectional epidemiological study was performed in three small towns in the eastern part of Germany on 2470 school children aged 5-14 (89.1% of eligible children). A 78 item questionnaire to determine risk factors at birth and in early childhood was employed. 7.8% of the children were born before completing 38 gestational weeks; 6.6% had a birth weight less than 2500 g. Pulmonary function analysis were done by a mobile plethysmography at the school. There were only weak restrictions in lung volume in term low birth weight (LBW) children (100 ml lower TLC, p = 0.107), and flow (257 ml lower PEFR, p = 0.108), were low. However, bronchial hyper-responsiveness indicated by 292 ml lower FEV1.0 after cold air bronchial provocation, was significantly increased compared to term normal birth weight children (p < 0.001). The effect of LBW was less in older children, only slightly stronger in girls and increased in children mechanically ventilated during the postnatal period. Correspondingly, there was a higher prevalence of diagnosed asthma in term LBW children (OR 1.6, 95%-confidence interval 1.0-2.6), however these were without an increased risk for any allergic sensitization. LBW, therefore, seems to be a risk factor for smaller lungs and hyperreactive airways primarily in term born children, whereas in preterm children the immature bronchial system seems to be recover by school age.

Pediatric reference values for respiratory resistance measured by forced oscillation

OBJECTIVES

To determine, in North American children, reference values for respiratory resistance measurements by the forced oscillation (Rfo) technique and to examine whether sitting height, as index of truncal length, is a better determinant of resistance, less influenced by race and gender, than standing height.

DESIGN/SETTING

A prospective cross-sectional study of healthy nonobese children, carefully selected for absence of atopy, exposure to tobacco smoke, and recent upper respiratory tract infection.

MEASUREMENTS

Three measurements of respiratory resistance by forced oscillation were obtained at the fixed frequencies of 8 Hz (Rfo8), 12 Hz (Rfo12), and at 16 Hz (Rfo16) using the Custo Vit R (Custo Med GMBH; Munich, Germany). In cooperative children, routine spirometry (FEV1, FVC, and peak expiratory flow rate [PEFR]) was also performed.

RESULTS

We recruited 217 healthy children aged 3 to 17 years. Reproducible measurements of Rfo8 were obtained for 206 children, Rfo12 for 197 children, and Rfo16 for 209 children. Normal FEV1, FVC, and PEFR values were documented in all 69 subjects who were able to reproducibly cooperate with spirometry. Multiple linear regression identified measurements of either sitting or standing height as the best, and equally strong, determinants of respiratory resistance at all three frequencies. Gender and race were not important factors once either sitting or standing height measurement was considered. Our regression equations at 8 Hz are comparable to published reference values obtained at fixed frequencies of 6, 8, and 10 Hz using other instruments. However, in comparison to our results, prior values tended to underestimate resistance in the shortest children or to overestimate it in the tallest ones. Our regression equation for Rfo12 is similar to the only previously published one, while no reference values at 16 Hz were available for comparison.

CONCLUSIONS

Height is the best predictor for total respiratory resistance at 8, 12, and 16 Hz in children aged > or = 3 years. Use of sitting height does not appear to be a stronger determinant of resistance than standing height.

Bronchial lability and responsiveness in school children born very preterm

We evaluated bronchial lability and responsiveness in 29 prematurely born children (birth weight < 1,250 g) 8 to 14 yr of age, 12 with histories of bronchopulmonary dysplasia (BPD). Flow-volume spirometry, a bronchodilator test, and histamine challenge at the office and home monitoring of peak expiratory flow (PEF) values twice daily for 4 wk with and without a beta2-agonist were performed with a novel device, the Vitalograph Data Storage Spirometer. The spirometric values at the office and the results of home monitoring were compared with those for a control group of children born at term. All spirometric values except FEV1/FVC were significantly lower in the BPD group than in the non-BPD group (p < 0.0001). Ten children (83%) in the BPD group and four (24%) in the non-BPD group had subnormal spirometric values at the office, indicating bronchial obstruction. Of the children with obstruction, 79% reported respiratory symptoms during the preceding year, and 57% had increased diurnal PEF variation and/or responded to administration of a beta2-agonist during home monitoring or at the office. The BPD children were significantly more responsive to histamine than the non-BPD children (p = 0.002). All spirometric values were significantly lower in both preterm groups than in the control group born at full term (p < 0.01). In conclusion, regardless of BPD, bronchial obstruction, bronchial lability, and increased bronchial responsiveness are common in prematurely born children of school age.

Medical outcomes in preterm infants

Many survivors of the newborn intensive care units who were premature do very well; some, however, go on to have a variety of medical complications related, in part, to their prematurity. An overview of the medical outcomes of prematurity are discussed in the areas of respiratory disease (bronchopulmonary dysplasia), gastrointestinal disorders (short gut syndrome and gastroesophageal reflux), growth and nutrition problems, vision, and hearing outcomes. These complications can be managed on a regular or vigilant outpatient basis and, if exacerbated, may require hospital management. Concepts to assist in family counseling on expected long-term medical outcomes of prematurity are discussed.

Respiratory morbidity in preschool children born prematurely. Relationship to adverse neonatal events

Respiratory morbidity, recurrent cough and/or wheeze and lung function abnormalities are common even outside infancy in preschool children born prematurely. Throughout the first 5 years of life, adverse neonatal events such as immaturity at birth and a requirement for prolonged respiratory support are significantly associated with positive symptom status. In the older preschool child, however, there is some evidence to suggest that other factors, such as a family history of atopy, may be equally important. The development of recurrent symptoms even at 4 years of age can be predicted accurately from the results of lung function measurements made in infancy, and hopefully such data will facilitate the introduction of effective intervention strategies. Lung function abnormalities are more marked in symptomatic patients and, in older children, seem to reflect increased airway responsiveness rather than having a significant relationship to adverse neonatal events. The hospital readmission rate for respiratory disorders, however, is certainly adversely affected by extremely low birthweight and neonatal chronic lung disease, as well as current symptom status. These data highlight that strategies to reduce extremely premature delivery and its consequences should favourably influence respiratory morbidity in preschool children.

Diffusing capacity of the lung in school-aged children born very preterm, with and without bronchopulmonary dysplasia

The aim of this study was to determine the extent to which bronchopulmonary dysplasia (BPD) affects the diffusing properties of lung tissue in childhood. Pulmonary function in 31 prematurely born children (BW. < 1250 g) was examined at ages 7-11 years. Twenty out of 31 prematurely born children met the criteria for BPD. The remaining 11 children had milder forms of neonatal lung disease. Twenty healthy children of the same age and born at term served as a control group. The diffusing capacity of the lung for carbon monoxide (DLCO) was measured by the single breath method. Lung volumes were determined in a body plethysmograph and expiratory flow rates with a flow/volume spirometer. DLCO values of children with histories of BPD did not differ significantly from those of the prematurely born children without BPD. However, DLCO values in both prematurely born study groups were significantly lower than those in controls born at term. Thoracic gas volumes measured with a body plethysmograph were similar in all groups. Spirometry demonstrated reduced flow rates in both BPD and non-BPD prematurely born children. The results suggest that some structural changes in lung tissues and airways persist for years in children who are born very preterm regardless of whether they develop BPD or not.

Longitudinal follow-up of lung function from childhood to adolescence in prematurely born patients with neonatal chronic lung disease

We investigated whether early lung function abnormalities in prematurely born children with a history of chronic lung disease improve in late childhood and adolescence. We performed a prospective, longitudinal evaluations of pulmonary function over an 8 year period. In seventeen patients from the age (mean +/- SD) of 8.2 +/- 1.2 years to the age of 15.1 +/- 1.6 years. They had been born at 29.1 +/- 1.9 weeks of gestation, with a birthweight of 1120 +/- 190 g, and they had received supplemental oxygen, with or without mechanical ventilation, for 40.4 +/- 23.8 days during the neonatal period. They all had radiographic evidence of chronic lung disease at 4 weeks of age. Annual measurements of lung volumes using the helium dilution technique, and of airway function with spirometry and maximal expiratory flow-volume curves over a 5 to 8 year period, were obtained. The results indicated that total lung capacity (TLC) and vital capacity (VC) were within the predicted normal range in all patients and increased over time. In contrast, the initially abnormal residual volume (RV) and RV/TLC ratio decreased over time, suggesting gradual resolution of air-trapping. The peak expiratory flow rate (PEFR), forced expiratory volume in 1 second (FEV1), and the ratio FEV1/FVC remained at or above the predicted normal range in all patients. FEF25-75, FEF50, and FEF75 were within normal limits in eight patients and abnormally low (more than 2 SD below the predicted normal value) in the remaining nine patients, indicating small airway obstruction. Eight of the nine patients with lower airway obstruction showed significant response to inhaled bronchodilator, and four responded to a histamine challenge. None of the eight patients with normal airway function responded to histamine, but four responded to bronchodilators. The perinatal history, family history of asthma, and exposure to smoking were similar in patients with and without airway obstruction. The height and weight were and remained within the normal range. We conclude that gradual normalization of air-trapping continues well into adolescence in virtually all patients with a history of prematurity and chronic lung disease. in contrast, airflow obstruction may persist but does not get worse later in life. Although chronic airflow obstruction probably is the consequence of injury to the small airways during the neonatal period, it is present in only some of the children, and it does not appear to be directly related to the perinatal history. Finally, there is evidence that airway hyperresponsiveness may be a contributing factor to the development and/or persistence of airflow obstruction in chronic lung disease of prematurity.

Long-term pulmonary functional outcome of bronchopulmonary dysplasia and premature birth

Pulmonary function and exercise tolerance were evaluated in late childhood in two groups of prematurely born children: one group with bronchopulmonary dysplasia (BPD) [n = 15; gestational age at birth (GA): 29.6 +/- 2.8 weeks; birth weight (BW): 1,367 +/- 548 g; age at test: 7.9 +/- 0.6 years], and a second group without significant neonatal lung disease [pre-term (PT)] (n = 9; GA: 30.3 +/- 1.7 weeks; BW: 1,440 +/- 376 g; age at test: 7.8 +/- 0.22 years). The results were compared with a control group of children of similar ages and heights, born at term [term born (TB)]. We observed that total lung resistance (RL) was significantly higher in BPD (11 +/- 3 cmH2O/L/s), and in PT (9 +/- 2) than in TB [5 +/- 1; (P < 0.001 and P < 0.05, respectively)]. In BPD RL was higher than in PT (P < 0.05). Dynamic lung compliance (CLdyn) was decreased in BPD (43 +/- 11 mL/cmH2O) and in PT (56 +/- 17) compared with TB (76 +/- 20) (P < 0.001 and P < 0.05), and also in BPD compared with PT (P < 0.05). Forced expiratory volume in 1 second (FEV1) and FEV1/forced vital capacity (FVC) were lower in BPD (1.07 +/- 0.15 L and 72 +/- 7%) than in PT (1.29 +/- 0.23 L, and 80 +/- 7%) (P < 0.05). Exercise tests were performed in six boys with BPD. The ratio between minute ventilation at maximal workload (VEmax) and the predicted value of maximal voluntary ventilation (MVV) was elevated in the six BPD boys tested, compared with five boys of Group 2 and five TB boys (87 +/- 15% vs. 62 +/- 14% and 65 +/- 13%) (P < 0.05). We conclude that: 1) prematurity and BPD is followed by long-term airway obstruction and a mild degree of exercise intolerance and; 2) premature birth without BPD may be followed by a milder degree of airway obstruction in childhood than in infants who developed BPD during the neonatal period.

Cardiopulmonary function in premature infants with bronchopulmonary dysplasia--a 2-year follow up

Twenty-three premature infants (GA 28.8 +/- 0.5 weeks) with bronchopulmonary dysplasia (BPD) and 14 premature infants (controls, GA 33.0 +/- 1.2 weeks) with moderate respiratory distress syndrome or with mild respiratory disturbances, were evaluated for impairment of cardiopulmonary function at 50 and 120 weeks corrected age. Respiratory system compliance was reduced in both groups, but improved with advancing age. Respiratory system resistance was initially increased, especially in the BPD group, but improved gradually. Maximum flow at functional residual capacity (VmaxFRC ml/s) indicated, nevertheless, severe peripheral obstruction (flow < 84 ml/s) in 16/20 of infants with BPD and in 7/12 of control infants at 50 weeks corrected age. At 120 weeks corrected age none of the control patients had severe peripheral pulmonary obstruction (flow < 120 ml/s), while this was still found in 5/13 infants with BPD. Doppler echocardiography indicated cardiac involvement (shortened pulmonary acceleration time) in patients with the most severe peripheral pulmonary obstruction. Pulmonary morbidity was also higher in the BPD group, and these infants were shorter and weighed less than the control infants. CONCLUSION. Measurements of maximum flow at functional residual capacity as well as cardiac evaluation are essential elements in follow up of infants with severe BPD.

Subclinical persisting pulmonary hypertension in chronic neonatal lung disease

The development of pulmonary hypertension is one of the adverse factors in the outcome of infants with chronic neonatal lung disese (CNLD). The purpose of this cross sectional study was to evaluate the prevalence and degree of pulmonary hypertension in a cohort of survivors of CNLD stable in air. Pulmonary artery pressure was assessed using its inverse correlation with the ratio of time to peak velocity and right ventricular ejection time (TPV:RVET) as measured from Doppler velocity time signals in the main pulmonary artery. A normal ratio is > or = 0.35, a possibly low ratio lies between 0.31 and 0.35, and a definitely low ratio is < 0.31. The subjects were divided into three groups. Group A comprised 58 infants with oxygen dependence and an abnormal chest radiograph at 28 days of age; group B comprised 18 infants with oxygen dependence and a normal chest radiograph at 28 days of age; and group C (controls) comprised 21 siblings without oxygen dependence by 10 days and a normal chest radiograph. There were significant differences in mean (SD) TPV:RVET ratio between group A 0.346 (0.045), group B 0.335 (0.057), and groups A + B 0.344 (0.048) when compared with group C controls 0.385 (0.034). The prevalence of a definitely low TPV:RVET ratio suggesting a raised pulmonary artery pressure was 19% in group A, 39% in group B, 24% in groups A + B, and none in group C. There were no clinical signs of pulmonary hypertension in any patient studied. Stepwise multiple linear regression failed to find significant associations with antenatal or neonatal putative risk factors. Additionally, there were no associations with childhood respiratory morbidity. These data suggest a high prevalence of subclinical pulmonary hypertension in CNLD patients. It is speculated that occult hypoxaemia may be occurring in this group of infants.

Does the duration of oxygen dependence after birth influence subsequent respiratory morbidity?

The relationship of respiratory morbidity at follow up to the development and type of "neonatal" chronic lung disease has been assessed. Three groups, each of ten infants matched for gestational age and gender, were compared. Group A had Type I chronic lung disease and group B bronchopulmonary (BPD), the most severe form of neonatal chronic lung disease (Type II CLD); group C had developed neither Type I or Type II CLD. Group B compared to group A compared to group C required a significantly longer duration of oxygen therapy on the neonatal unit. All three groups were prospectively followed; the occurrence of symptoms was documented in each of the first 3 years of life and lung function was measured using a plethysmographic technique at the end of year 1. In all 3 years a significantly greater proportion of groups A and B were symptomatic compared to group C, but there was no significant difference in the proportion so affected between groups A and B. Airway resistance was higher in both groups A and B compared to C but only reached statistical significance on comparing groups A and C. We conclude oxygen dependency beyond 1 month of age, irrespective of the development of BPD, significantly increases respiratory morbidity at follow up.

Persistence of respiratory symptoms into the second year of life: predictive factors in infants born preterm

Preterm infants frequently suffer from recurrent respiratory symptoms in the first year of life. Our aims were to assess if such respiratory morbidity persisted beyond the first year and to define the predictive factors. One hundred and seventeen infants (median gestational age 29 weeks) were followed prospectively for two years. Thirty-eight infants had symptoms only in the first year (group A) and in a further 20 infants, symptoms were present in both years (group B). Comparison of these two groups revealed no significant difference in birth weight or gestational age, but the duration of ventilation and increased inspired oxygen concentration were significantly longer in group B. Significantly more infants in group B had had an air leak in the neonatal period, and airways resistance at six months of age was also significantly higher in group B. We conclude that infants with severe neonatal respiratory distress are likely to have persisting respiratory morbidity and that respiratory function measurements at six months of age provide the most accurate predictor of chronic respiratory symptoms.