Need for Healthy Control Subjects when Assessing Lung Function in Infants with Respiratory Disease

Development of Lung Function in Preterm Infants During the First Two Years of Life

INTRODUCTION

It remains unclear if prematurity itself can influence post delivery lung development and particularly, the bronchial size.

AIM

To assess lung function during the first two years of life in healthy preterm infants and compare the measurements to those obtained in healthy term infants during the same time period.

METHODS

This observational longitudinal study assessed lung function in 74 preterm (30+0 to 35+6 weeks' gestational age) and 76 healthy term control infants who were recruited between 2011 and 2013. Measurements of tidal breathing, passive respiratory mechanics, tidal and raised volume forced expirations (V'maxFRC and FEF_25-75, respectively) were undertaken following administration of oral chloral hydrate sedation according to ATS/ERS recommendations at 6- and 18-months corrected age.

RESULTS

Lung function measurements were obtained from the preterm infants and full term controls initially at 6 months of age. Preterm infants had lower absolute and adjusted values (for gestational age, postnatal age, sex, body size, and confounding factors) for respiratory compliance and V'maxFRC. At 18 months corrected postnatal age, similar measurements were repeated in 57 preterm infants and 61 term controls. A catch-up in tidal volume, respiratory mechanics parameters, FEV_0.5 and forced expiratory flows was seen in preterm infants.

CONCLUSION

When compared with term controls, the lower forced expiratory flows observed in the healthy preterm group at 6 months was no longer evident at 18 months corrected age, suggesting a catch-up growth of airway function.

Forced expiratory flows and volumes in a Swedish cohort of healthy term infants

BACKGROUND

The use of pulmonary function tests (PFTs) in infants has increased during the last decades, making the need for equipment- and ethnic-specific reference data mandatory for appropriate interpretation of the results.

AIM

Our aim was to investigate how well the already published reference equations for infant spirometry fit a healthy population of Swedish infants.

METHOD

We performed forced tidal and raised volume expiratory maneuvers in healthy infants using Jaeger BabyBody equipment.

RESULTS

PFT data were collected from 91 healthy infants aged between 3 months to 2 years at 143 occasions. Mean (standard deviation) z-scores were 0.68(1.33) for maximal flow at functional residual capacity (V'_max FRC), -0.15(0.96) for forced vital capacity (FVC), 0.40(1.33) for the forced expired volume in the initial 0.5 seconds (FEV_0.5 ) and 0.52(0.93) for the ratio FEV_0.5 /FVC, respectively. Z-scores for all indices but FEV_0.5 /FVC were highly dependent on length.

CONCLUSIONS

We have shown that the use of previously published reference equations may result in an age-related misinterpretation of lung function measure in a Swedish infant population.

Elevated lung clearance index in infants with cystic fibrosis shortly after birth

It is not known at what age lung function impairment may arise in children with cystic fibrosis (CF). We assessed lung function shortly after birth in infants with CF diagnosed by newborn screening.We performed infant lung function measurements in a prospective cohort of infants with CF and healthy controls. We assessed lung clearance index (LCI), functional residual capacity (FRC) and tidal breathing parameters. The primary outcome was prevalence and severity of abnormal lung function (±1.64 z-scores) in CF.We enrolled 53 infants with CF (mean age 7.8 weeks) and 57 controls (mean age 5.2 weeks). Compared to controls, LCI and FRC were elevated (mean difference 0.30, 95% CI 0.02-0.60; p=0.034 and 14.5 mL, 95% CI 7.7-21.3 mL; p<0.001, respectively), while ratio of time to peak tidal expiratory flow to expiratory time was decreased in infants with CF. In 22 (41.5%) infants with CF, either LCI or FRC exceeded 1.64 z-scores; three infants had both elevated LCI and FRC.Shortly after birth, abnormal lung function is prevalent in CF infants. Ventilation inhomogeneity or hyperinflation may serve as noninvasive markers to monitor CF lung disease and specific treatment effects, and could thus be used as outcome parameters for future intervention studies in this age group.

Pediatric Pulmonology year in review 2015: Part 1

Our journal covers a broad range of research and scholarly topics related to children's respiratory disorders. For updated perspectives on the rapidly expanding knowledge in our field, we will summarize the past year's publications in our major topic areas, as well as selected publications in these areas from the core clinical journal literature outside our own pages. The current review covers articles on neonatal lung disease, pulmonary physiology, and respiratory infection. Pediatr Pulmonol. 2016;51:733-739. © 2016 Wiley Periodicals, Inc.

How to avoid misinterpreting lung function tests in children: a few practical tips

Assessments of pulmonary function play an integral part in the clinical management of school age children as well as providing objective outcome measures in clinical and epidemiological research studies. Pulmonary function tests (PFTs) can also be undertaken in sleeping infants and in awake young children from 3 years of age. However, the clinical utility of such assessments, which are generally confined to specialist centres, has yet to be established. Whether requesting or undertaking paediatric PFTs, or simply reading about how these tests have been applied in research studies, it is essential to question whether results have been interpreted in a meaningful way. This review summarises some of the issues that need to be considered, including: why the tests are being performed; which tests are most likely to detect the suspected pathophysiology; how often such tests should be repeated; whether results are likely to be reliable (in terms of data quality, repeatability and the availability of suitable reference equations with which to distinguish the effects of disease from those of growth and development), and whether the selected tests are likely to be feasible in the individual child or study group under investigation.

Survey of clinical infant lung function testing practices

BACKGROUND

Data supporting the clinical use of infant lung function (ILF) tests are limited making the interpretation of clinical ILF measures difficult.

OBJECTIVES

To evaluate current ILF testing practices and to survey users regarding the indications, limitations and perceived clinical benefits of ILF testing.

METHODS

We created a 26-item survey hosted on the European Respiratory Society (ERS) website between January and May 2010. Notifications were sent to members of the ERS, American Thoracic Society and the Asian Pacific Society of Respirology. Responses were sought from ILF laboratory directors and pediatric respirologists. The survey assessed the clinical indications, patient populations, equipment and reference data used, and perceived limitations of ILF testing.

RESULTS

We received 148 responses with 98 respondents having ILF equipment and performing testing in a clinical capacity. Centers in North America were less likely to perform ≥50 studies/year than centers in Europe or other continents (13% vs. 41%). Most respondents used ILF data to either "start a new therapy" (78%) or "help decide about initiation of further diagnostic workup such as bronchoscopy, chest CT or serological testing" (69%). Factors reported as limiting clinical ILF testing were need for sedation, uncertainty regarding clinical impact of study results and time intensive nature of the study.

CONCLUSIONS

Clinical practices associated with ILF testing vary significantly; centers that perform more studies are more likely to use the results for clinical purposes and decision making. The future of ILF testing is uncertain in the face of the limitations perceived by the survey respondents.

An official American Thoracic Society workshop report: optimal lung function tests for monitoring cystic fibrosis, bronchopulmonary dysplasia, and recurrent wheezing in children less than 6 years of age

Although pulmonary function testing plays a key role in the diagnosis and management of chronic pulmonary conditions in children under 6 years of age, objective physiologic assessment is limited in the clinical care of infants and children less than 6 years old, due to the challenges of measuring lung function in this age range. Ongoing research in lung function testing in infants, toddlers, and preschoolers has resulted in techniques that show promise as safe, feasible, and potentially clinically useful tests. Official American Thoracic Society workshops were convened in 2009 and 2010 to review six lung function tests based on a comprehensive review of the literature (infant raised-volume rapid thoracic compression and plethysmography, preschool spirometry, specific airway resistance, forced oscillation, the interrupter technique, and multiple-breath washout). In these proceedings, the current state of the art for each of these tests is reviewed as it applies to the clinical management of infants and children under 6 years of age with cystic fibrosis, bronchopulmonary dysplasia, and recurrent wheeze, using a standardized format that allows easy comparison between the measures. Although insufficient evidence exists to recommend incorporation of these tests into the routine diagnostic evaluation and clinical monitoring of infants and young children with cystic fibrosis, bronchopulmonary dysplasia, or recurrent wheeze, they may be valuable tools with which to address specific concerns, such as ongoing symptoms or monitoring response to treatment, and as outcome measures in clinical research studies.

Evolution of lung function during the first year of life in newborn screened cystic fibrosis infants

Rationale

Newborn screening (NBS) for cystic fibrosis (CF) allows early intervention. Design of randomised controlled trials (RCT) is currently impeded by uncertainty regarding evolution of lung function, an important trial end point in such infants.

Objective

To assess changes in pulmonary function during the first year of life in CF NBS infants.

Methods

Observational longitudinal study. CF NBS infants and healthy controls were recruited between 2009 and 2011. Lung Clearance Index (LCI), plethysmographic lung volume (plethysmographic functional residual capacity (FRC_pleth)) and forced expired volume (FEV_0.5) were measured at 3 months and 1 year of age.

Main results

Paired measurements were obtained from 72 CF infants and 44 controls. At 3 months, CF infants had significantly worse lung function for all tests. FEV_0.5 improved significantly (0.59 (95% CI 0.18 to 0.99) z-scores; p<0.01) in CF infants between 3 months and 1 year, and by 1 year, FEV_0.5 was only 0.52 (0.89 to 0.15) z-scores less than in controls. LCI and FRC_pleth remained stable throughout the first year of life, being on average 0.8 z-scores higher in infants with CF. Pulmonary function at 1 year was predicted by that at 3 months. Among the 45 CF infants with entirely normal LCI and FEV_0.5 at 3 months, 80% remained so at 1 year, while 74% of those with early abnormalities remained abnormal at 1 year.

Conclusions

This is the first study reporting improvements in FEV_0.5 over time in stable NBS CF infants treated with standard therapy. Milder changes in lung function occurred by 1 year than previously reported. Lung function at 3 months predicts a high-risk group, who should be considered for intensification of treatment and enrolment into RCTs.

New reference equations to improve interpretation of infant lung function

RATIONALE

With increasing use of infant pulmonary function tests (IPFTs) in both clinical and research studies, appropriate interpretation of results is essential.

OBJECTIVES

To investigate the potential bias associated with "normalising" IPF by expressing results as a ratio of body size and to develop reference ranges for tidal breathing parameters, passive respiratory mechanics (compliance [Crs] and resistance [Rrs]) and plethysmographic functional residual capacity (FRCp ) for white infants during the first 2 years of life.

METHODS

IPFTs were measured using the Jaeger BabyBody system and standardized protocols. Reference equations, adjusted for body size, age, and sex where appropriate, were created using multilevel modeling.

RESULTS

The ratio of lung function to body length changes markedly with growth, thereby precluding its use for any outcome. While the ratio of tidal volume and Crs to body weight remained relatively constant with growth, this was not the case for FRCp . Even in healthy infants, a strong inverse relationship was observed between lung function/body weight and weight z-score which could distort interpretation of results in growth-restricted infants with lung disease, such as cystic fibrosis. Reference equations were derived from 153 healthy white infants on 232 test occasions (median age 35.5 weeks [range: 2.6-104.7]). Crown-heel length was the strongest predictor of IPF.

CONCLUSIONS

When reporting IPF, use of size-corrected ratios should be discouraged, with interpretation instead based on appropriate reference equations. The current equations are applicable to white infants and young children up to 2 years of age, studied using the same commercially available equipment. The extent to which these equations are applicable to infants and young children of other ethnic backgrounds or who are tested with different equipment needs to be established.

Discrepancies between pediatric laboratories in pulmonary function results from healthy children

BACKGROUND

Multi-center research studies that include pulmonary function as an objective outcome are increasingly important in pediatric respiratory medicine. The need for local controls rather than depending on published normative data for lung function remains debatable.

AIM

To compare pulmonary function in childhood controls with no respiratory symptoms from three centers in the United Kingdom and ascertain the extent to which current reference equations are appropriate for this population.

METHODS

Spirometry, plethysmographic lung volumes, and specific airways resistance (sRaw) were measured within specialized pediatric laboratories in children from three geographical locations throughout the UK (London, Leicester, and Glasgow), using identical equipment, software and standard operating procedures. Results were compared between centers and in relation to recent or commonly used UK pediatric reference values.

RESULTS

Pulmonary function was assessed in 94 healthy children (mean (SD) age: 7.7 (0.6) years; 88% white Caucasians; ∼30 from each center). There were no significant differences in background demographics or spirometric outcomes when compared between centers. By contrast, statistically significant differences in plethysmographic lung volumes and sRaw were observed between-centers. Significant differences in relation to published reference data for white subjects were noted for FEV(1) in all three centers and occasionally for other lung function measures but the differences from predicted values were small (within ± 0.5 z-score) and not clinically significant.

CONCLUSION

After appropriate inter-laboratory standardization, spirometric measurements in children can be measured in different centers without evidence of systematic differences. However, even after extensive standardization procedures, plethysmographic measures appear more prone to inter-center differences and cannot, at present, be reliably compared across centers without incorporating controls at each location.