Predictors of wheezing in prematurely born children

Oxygen and mechanical stretch in the developing lung: risk factors for neonatal and pediatric lung disease

Chronic airway diseases, such as wheezing and asthma, remain significant sources of morbidity and mortality in the pediatric population. This is especially true for preterm infants who are impacted both by immature pulmonary development as well as disproportionate exposure to perinatal insults that may increase the risk of developing airway disease. Chronic pediatric airway disease is characterized by alterations in airway structure (remodeling) and function (increased airway hyperresponsiveness), similar to adult asthma. One of the most common perinatal risk factors for development of airway disease is respiratory support in the form of supplemental oxygen, mechanical ventilation, and/or CPAP. While clinical practice currently seeks to minimize oxygen exposure to decrease the risk of bronchopulmonary dysplasia (BPD), there is mounting evidence that lower levels of oxygen may carry risk for development of chronic airway, rather than alveolar disease. In addition, stretch exposure due to mechanical ventilation or CPAP may also play a role in development of chronic airway disease. Here, we summarize the current knowledge of the impact of perinatal oxygen and mechanical respiratory support on the development of chronic pediatric lung disease, with particular focus on pediatric airway disease. We further highlight mechanisms that could be explored as potential targets for novel therapies in the pediatric population.

Intermittent Hypoxia-Hyperoxia and Oxidative Stress in Developing Human Airway Smooth Muscle

Premature infants are frequently and intermittently administered supplemental oxygen during hypoxic episodes, resulting in cycles of intermittent hypoxia and hyperoxia. The relatively hypoxic in utero environment is important for lung development while hyperoxia during the neonatal period is recognized as detrimental towards the development of diseases such as bronchopulmonary dysplasia and bronchial asthma. Understanding early mechanisms that link hypoxic, hyperoxic, and intermittent hypoxic-hyperoxic exposures to altered airway structure and function are key to developing advanced therapeutic approaches in the clinic. Changes in oxygen availability can be detrimental to cellular function and contribute to oxidative damage. Here, we sought to determine the effect of oxygen on mitochondria in human fetal airway smooth muscle cells exposed to either 5% O₂, 21% O₂, 40% O₂, or cycles of 5% and 40% O₂ (intermittent hypoxia-hyperoxia). Reactive oxygen species production, altered mitochondrial morphology, and changes in mitochondrial respiration were assessed in the context of the antioxidant N-acetylcysteine. Our findings show developing airway smooth muscle is differentially responsive to hypoxic, hyperoxic, or intermittent hypoxic-hyperoxic exposure in terms of mitochondrial structure and function. Cycling O₂ decreased mitochondrial branching and branch length similar to hypoxia and hyperoxia in the presence of antioxidants. Additionally, hypoxia decreased overall mitochondrial respiration while the addition of antioxidants increased respiration in normoxic and O₂-cycling conditions. These studies show the necessity of balancing oxidative damage and antioxidant defense systems in the developing airway.

Cellular clocks in hyperoxia effects on [Ca2+]i regulation in developing human airway smooth muscle

Supplemental O2 (hyperoxia) is necessary for preterm infant survival but is associated with development of bronchial airway hyperreactivity and childhood asthma. Understanding early mechanisms that link hyperoxia to altered airway structure and function are key to developing advanced therapies. We previously showed that even moderate hyperoxia (50% O2) enhances intracellular calcium ([Ca2+]i) and proliferation of human fetal airway smooth muscle (fASM), thereby facilitating bronchoconstriction and remodeling. Here, we introduce cellular clock biology as a novel mechanism linking early oxygen exposure to airway biology. Peripheral, intracellular clocks are a network of transcription-translation feedback loops that produce circadian oscillations with downstream targets highly relevant to airway function and asthma. Premature infants suffer circadian disruption whereas entrainment strategies improve outcomes, highlighting the need to understand relationships between clocks and developing airways. We hypothesized that hyperoxia impacts clock function in fASM and that the clock can be leveraged to attenuate deleterious effects of O2 on the developing airway. We report that human fASM express core clock machinery (PER1, PER2, CRY1, ARNTL/BMAL1, CLOCK) that is responsive to dexamethasone (Dex) and altered by O2. Disruption of the clock via siRNA-mediated PER1 or ARNTL knockdown alters store-operated calcium entry (SOCE) and [Ca2+]i response to histamine in hyperoxia. Effects of O2 on [Ca2+]i are rescued by driving expression of clock proteins, via effects on the Ca2+ channels IP3R and Orai1. These data reveal a functional fASM clock that modulates [Ca2+]i regulation, particularly in hyperoxia. Harnessing clock biology may be a novel therapeutic consideration for neonatal airway diseases following prematurity.

Effects of Hyperoxia on the Developing Airway and Pulmonary Vasculature

Although it is necessary and part of standard practice, supplemental oxygen (40-90% O₂) or hyperoxia is a significant contributing factor to development of bronchopulmonary dysplasia, persistent pulmonary hypertension, recurrent wheezing, and asthma in preterm infants. This chapter discusses hyperoxia and the role of redox signaling in the context of neonatal lung growth and disease. Here, we discuss how hyperoxia promotes dysfunction in the airway and the known redox-mediated mechanisms that are important for postnatal vascular and alveolar development. Whether in the airway or alveoli, redox pathways are important and greatly influence the neonatal lung.

Risk factors for bronchiolitis, recurrent wheezing, and related hospitalization in preterm infants during the first year of life

BACKGROUND

Airway diseases are highly prevalent in infants and cause significant morbidity. We aimed to determine the incidence and risk factors for respiratory morbidity in a Spanish cohort of moderate-to-late preterm (MLP) infants prospectively followed during their first year of life.

METHODS

SAREPREM is a multicenter, prospective, longitudinal study. Preterm infants born at 32-35 weeks of gestation with no comorbidities were enrolled within 2 weeks of life and followed at 2-4 weeks, 6, and 12 months of age. Multivariate mixed-models were performed to identify independent risk factors associated with (i) development of bronchiolitis, (ii) recurrent wheezing, or (iii) related hospital admissions.

RESULTS

Overall, 977 preterm infants were included, and 766 (78.4%) completed follow-up. Of those, 365 (47.7%) developed bronchiolitis during the first year, 144 (18.8%) recurrent wheezing, and 48 (6.3%) were hospitalized. While low birthweight, day care attendance (DCA) and school-age siblings were significantly and independently associated with both the development of bronchiolitis and recurrent wheezing, lower maternal age increased the risk for bronchiolitis and respiratory-related hospitalizations. Lastly, mechanical ventilation was associated with a higher risk of bronchiolitis and history of asthma in any parent increased the likelihood of developing recurrent wheezing.

CONCLUSIONS

In this study, several non-modifiable parameters (family history of asthma, low birthweight, need for mechanical ventilation) and modifiable parameters (young maternal age, DCA, or exposure to school-age siblings) were identified as significant risk factors for the development of bronchiolitis and recurrent wheezing during the first year of life in MLP infants.

cAMP-mediated secretion of brain-derived neurotrophic factor in developing airway smooth muscle

Moderate hyperoxic exposure in preterm infants contributes to subsequent airway dysfunction and to risk of developing recurrent wheeze and asthma. The regulatory mechanisms that can contribute to hyperoxia-induced airway dysfunction are still under investigation. Recent studies in mice show that hyperoxia increases brain-derived neurotrophic factor (BDNF), a growth factor that increases airway smooth muscle (ASM) proliferation and contractility. We assessed the mechanisms underlying effects of moderate hyperoxia (50% O2) on BDNF expression and secretion in developing human ASM. Hyperoxia increased BDNF secretion, but did not alter endogenous BDNF mRNA or intracellular protein levels. Exposure to hyperoxia significantly increased [Ca2+]i responses to histamine, an effect blunted by the BDNF chelator TrkB-Fc. Hyperoxia also increased ASM cAMP levels, associated with reduced PDE4 activity, but did not alter protein kinase A (PKA) activity or adenylyl cyclase mRNA levels. However, 50% O2 increased expression of Epac2, which is activated by cAMP and can regulate protein secretion. Silencing RNA studies indicated that Epac2, but not Epac1, is important for hyperoxia-induced BDNF secretion, while PKA inhibition did not influence BDNF secretion. In turn, BDNF had autocrine effects of enhancing ASM cAMP levels, an effect inhibited by TrkB and BDNF siRNAs. Together, these novel studies suggest that hyperoxia can modulate BDNF secretion, via cAMP-mediated Epac2 activation in ASM, resulting in a positive feedback effect of BDNF-mediated elevation in cAMP levels. The potential functional role of this pathway is to sustain BDNF secretion following hyperoxic stimulus, leading to enhanced ASM contractility and proliferation.

Soluble guanylate cyclase modulators blunt hyperoxia effects on calcium responses of developing human airway smooth muscle

Exposure to moderate hyperoxia in prematurity contributes to subsequent airway dysfunction and increases the risk of developing recurrent wheeze and asthma. The nitric oxide (NO)-soluble guanylate cyclase (sGC)-cyclic GMP (cGMP) axis modulates airway tone by regulating airway smooth muscle (ASM) intracellular Ca(2+) ([Ca(2+)]i) and contractility. However, the effects of hyperoxia on this axis in the context of Ca(2+)/contractility are not known. In developing human ASM, we explored the effects of novel drugs that activate sGC independent of NO on alleviating hyperoxia (50% oxygen)-induced enhancement of Ca(2+) responses to bronchoconstrictor agonists. Treatment with BAY 41-2272 (sGC stimulator) and BAY 60-2770 (sGC activator) increased cGMP levels during exposure to 50% O2. Although 50% O2 did not alter sGCα1 or sGCβ1 expression, BAY 60-2770 did increase sGCβ1 expression. BAY 41-2272 and BAY 60-2770 blunted Ca(2+) responses to histamine in cells exposed to 50% O2. The effects of BAY 41-2272 and BAY 60-2770 were reversed by protein kinase G inhibition. These novel data demonstrate that BAY 41-2272 and BAY 60-2770 stimulate production of cGMP and blunt hyperoxia-induced increases in Ca(2+) responses in developing ASM. Accordingly, sGC stimulators/activators may be a useful therapeutic strategy in improving bronchodilation in preterm infants.

Perinatal oxygen in the developing lung

Lung diseases, such as bronchopulmonary dysplasia (BPD), wheezing, and asthma, remain significant causes of morbidity and mortality in the pediatric population, particularly in the setting of premature birth. Pulmonary outcomes in these infants are highly influenced by perinatal exposures including prenatal inflammation, postnatal intensive care unit interventions, and environmental agents. Here, there is strong evidence that perinatal supplemental oxygen administration has significant effects on pulmonary development and health. This is of particular importance in the preterm lung, where premature exposure to room air represents a hyperoxic insult that may cause harm to a lung primed to develop in a hypoxic environment. Preterm infants are also subject to increased episodes of hypoxia, which may also result in pulmonary damage and disease. Here, we summarize the current understanding of the effects of oxygen on the developing lung and how low vs. high oxygen may predispose to pulmonary disease that may extend even into adulthood. Better understanding of the underlying mechanisms will help lead to improved care and outcomes in this vulnerable population.

Chronic lung disease of prematurity and early childhood wheezing: is foetal inflammatory response syndrome to blame?

BACKGROUND

Long-lasting respiratory symptoms have a huge impact on the quality of life in prematurely born children.

AIMS

We aimed to investigate the perinatal and maternal risk factors involved in the development of chronic respiratory morbidity in preterm infants, with an emphasis on the importance of Foetal Inflammatory Response Syndrome (FIRS).

STUDY DESIGN

Prospective cohort study.

SUBJECTS

Demographic, antenatal, delivery and outcomes data were collected from 262 infants with less than 32 completed weeks of gestational age, over a 10-year period.

OUTCOME MEASURES

Presence of chronic lung disease of prematurity and early childhood wheezing.

RESULTS

In multivariate logistic regression analysis the presence of FIRS appears to be the most important risk factor for both, chronic lung disease of prematurity (OR 31.05, 95% CI 10.7-87.75, p<0.001) and early childhood wheezing (OR 5.63, 95% CI 2.42-13.05, p=0.01). In the alternative regression model for early childhood wheezing, with chronic lung disease included as a variable, the statistical significance of FIRS completely vanished (OR 1.15, 95% CI 0.39-3.34, p=0.79), whilst chronic lung disease became the most important risk factor (OR 23.45, 95% CI 8.5-63.25, p<0.001).

CONCLUSIONS

Prenatal and early neonatal events are of utmost importance in the development of chronic respiratory symptoms in children. The influence of FIRS on the development of chronic respiratory symptoms goes far beyond its impact on gestational age and may be related to direct inflammation-mediated lung tissue damage. CLD appears to be an intermittent step on the way from FIRS to ECW.

Moderately preterm children have more respiratory problems during their first 5 years of life than children born full term

RATIONALE

Pulmonary outcomes of moderate-preterm children (MP) are unknown.

OBJECTIVES

To investigate the prevalence of respiratory symptoms during infancy and at preschool age of MP compared with full-term (FT) and early preterm children (EP) and to determine factors associated with respiratory symptoms of MP at school age.

METHODS

Prospective cohort study.

OUTCOME VARIABLES

number of rehospitalizations caused by respiratory problems, prevalence of respiratory symptoms determined by ISAAC Questionnaires, and factors associated with respiratory symptoms determined by univariate and multivariate analyzes.

MEASUREMENTS AND MAIN RESULTS

A total of 988 MP, 551 EP, and 573 FT children were included. The number of hospitalizations caused by respiratory problems during the first year of life was doubled in MP compared with FT (6% vs. 3%; P < 0.001). At preschool age, compared with FT, MP reported more cough or wheeze during a cold (63% vs. 50%; P < 0.001); cough or wheeze without a cold (23% vs. 15%; P = 0.001); nocturnal cough (33% vs. 26%; P = 0.005); dyspnea (8% vs. 4%; P = 0.011); and use of medication (inhaled steroids, 9% vs. 6%; P = 0.042) (antibiotics, 12% vs. 7%; P = 0.002). Factors associated with respiratory symptoms at 5 years among MP were respiratory problems, eczema, rehospitalization in infancy, passive smoking in infancy, family history of asthma, and higher social class. Multivariate analyzes showed the same results except for rehospitalization in infancy.

CONCLUSIONS

MP have more respiratory symptoms than FT during early childhood. Factors associated with respiratory symptoms at school age are early respiratory problems, family history of asthma, higher social class, and passive smoking.

Impact of the environment on asthma control

Asthma is a complex condition that requires individualized interventions. The purpose of this article is to describe the relationship between the physical and social environments with asthma symptoms, present evidence that supports environmental interventions in asthma control and the implications for asthma management. There is evidence that indoor and outdoor allergens relate to asthma morbidity. Knowledge about which environmental exposures present risk is essential because many of these exposures can be modified, reduced, or eliminated. The community health nurse should provide care relative to the client's indoor and outdoor environment and existing allergens.

Emotional responses of mothers of late-preterm and term infants

OBJECTIVE

To compare the emotional responses of mothers of late-preterm infants (34 0/7 to 36 6/7 weeks gestation) with those of mothers of full-term infants.

DESIGN

A mixed method comparative study.

SETTING

A southeastern tertiary academic medical center postpartum unit.

PARTICIPANTS

Sixty mothers: 29 mothers of late-preterm infants and 31 mothers of full-term infants.

METHODS

Measures of maternal emotional distress (four standardized measures of anxiety, postpartum depression, posttraumatic stress symptoms, and worry about infant health) and open-ended semistructured maternal interviews were conducted in the hospital following birth and by phone at one month postpartum.

RESULTS

Mothers of late-preterm infants experienced significantly greater emotional distress immediately following delivery, and their distress levels continued to be higher at one month postpartum on each of the standardized measures. Mothers of late-preterm infants also discussed the altered trajectories in their birth and postpartum experiences and feeling unprepared for these unexpected events as a source of ongoing emotional distress.

CONCLUSION

Mothers of late-preterm infants have greater emotional distress than mothers of term infants for at least one month after delivery. Our findings suggest that it may not be a single event that leads to different distress levels in mothers of late-preterm and full-term infants but rather the interaction of multiple alterations in the labor and delivery process and the poorer-than-expected infant health outcomes. In the future, researchers need to examine how and when mothers' emotional responses change over time and how their responses relate to parenting and infant health and development.

Effects of secondhand smoke exposure on the health and development of african american premature infants

Objective. To explore the effects of secondhand smoke exposure on growth, health-related illness, and child development in rural African American premature infants through 24 months corrected age. Method. 171 premature infants (72 boys, 99 girls) of African American mothers with a mean birthweight of 1114 grams. Mothers reported on household smoking and infant health at 2, 6, 12, 18, and 24 months corrected age. Infant growth was measured at 6, 12, 18, and 24 months, and developmental assessments were conducted at 12 and 24 months. Results. Thirty percent of infants were exposed to secondhand smoke within their first 2 years of life. Secondhand smoke exposure was associated with poorer growth of head circumference and the development of otitis media at 2 months corrected age. Height, weight, wheezing, and child development were not related to secondhand smoke exposure. Conclusion. Exposure to secondhand smoke may negatively impact health of rural African American premature infants. Interventions targeted at reducing exposure could potentially improve infant outcomes.

Exploring modifiable risk factors for wheezing in African American premature infants

OBJECTIVE

To examine the degree to which obesity during infancy, consistent exposure to secondhand smoke, and parenting (positive attention, maternal involvement, and negative control) were related to early development of wheezing in a cohort of African American premature infants at 2, 6, 12, 18, and 24 months corrected age.

DESIGN

Secondary analysis of a subset of variables from a larger nursing support intervention study.

SETTING

Two regional perinatal centers in the southeastern United States.

PARTICIPANTS

One hundred and sixty-eight African American premature infants (70 boys, 98 girls) who weighed less than 1,750 g or required mechanical ventilation and their mothers.

METHODS

The presence of wheezing was obtained from maternal report at 2, 6, 12, 18, and 24 months. Infants were considered to have medically significant wheezing if they were using bronchodilators or pulmonary anti-inflammatory medications.

RESULTS

The percentage of infants who had medically significant wheezing increased from 12% at 2 months to 24% at 24 months corrected age. Infants who received more positive attention from their mothers had a slightly higher increase in the probability of developing wheezing over time. Infants of mothers who received public assistance had an increased probability of wheezing. Consistent exposure to secondhand smoke, obesity during infancy, maternal negative control, and maternal involvement were not related to the development of wheezing.

CONCLUSION

These findings suggest that the likelihood of developing wheezing in African American premature infants is associated with receiving more positive attention from their mothers and having mothers who receive public assistance. Because modifiable risk factors were not highly related to wheezing, intervention efforts need to focus on early identification and treatment of wheezing and asthma-related symptoms.

Potential Pitfalls in Collecting and Analyzing Longitudinal Data from Chronically Ill Populations

Research on the prevention and management of chronic illnesses involves understanding changes in complex and interrelated aspects of each individual. To capture these changes or to control for them, nursing and health research needs to be longitudinal. However, there are a number of potential pitfalls in analyzing longitudinal data from a chronically ill population. This paper will examine four major pitfalls: selection of time points, measurement, choosing appropriate statistical procedures, and missing values. Although the frequency of data collection is often driven primarily by practical concerns, it will affect the results. In addition, outcome measures may capture different constructs at different points in times. Traditional analysis techniques often have assumptions about data characteristics that are violated in clinical populations. Missing values are common in research with chronically ill individuals because of problems of subject retention and because individuals have frequent medical complications. Solutions to these pitfalls are also discussed.

Is there a link between wheezing in early childhood and adverse birth outcomes? A systematic review

We aimed to provide a summary of the existing published knowledge on the association between adverse birth outcomes and the development of wheezing during the first two years of life. We carried out a systematic review of epidemiological studies within the MEDLINE database. Epidemiological studies on human subjects, published in English, were included in the review. A comprehensive literature search yielded 72 studies for further consideration. Following the application of the eligibility criteria we identified nine studies. A positive association and an excess risk of wheezing during the first two years of life were revealed for adverse birth outcomes.