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

RATIONALE

Survivors of preterm birth are at risk of chronic and lifelong pulmonary disease. Follow-up data describing lung structure and function are scarce in children born preterm during the surfactant era.

OBJECTIVES

To obtain comprehensive data on lung structure and function in mid-childhood from survivors of preterm birth. We aimed to explore relationships between lung structure, lung function and respiratory morbidity as well as early life contributors to poorer childhood respiratory outcomes.

METHODS

Lung function was tested at 9-11 years in children born at term (controls) and at ≤32 weeks gestation. Tests included spirometry, oscillatory mechanics, multiple breath nitrogen washout and diffusing capacity of the lung for carbon monoxide. Preterm children had CT of the chest and completed a respiratory symptoms questionnaire.

MAIN RESULTS

58 controls and 163 preterm children (99 with bronchopulmonary dysplasia) participated. Preterm children exhibited pulmonary obstruction and hyperinflation as well as abnormal peripheral lung mechanics compared with term controls. FEV₁ was improved by 0.10 z-scores for every additional week of gestation (95% CI 0.028 to 0.182; p=0.008) and by 0.34 z-scores per z-score increase in birth weight (0.124 to 0.548; p=0.002). Structural lung changes were present in 92% of preterm children, with total CT score decreased by 0.64 (-0.99 to -0.29; p<0.001) for each additional week of gestation. Obstruction was associated with increased subpleural opacities, bronchial wall thickening and hypoattenuated lung areas on inspiratory chest CT scans (p<0.05).

CONCLUSIONS

Abnormal lung structure in mid-childhood resulting from preterm birth in the contemporary era has important functional consequences.

Lung Function in African Infants in the Drakenstein Child Health Study. Impact of Lower Respiratory Tract Illness

RATIONALE

Lower respiratory tract illness is a major cause of childhood morbidity and mortality. It is unknown whether infants are predisposed to illness because of impaired lung function or whether respiratory illness reduces lung function.

OBJECTIVES

To investigate the impact of early life exposures, including lower respiratory tract illness, on lung function during infancy.

METHODS

Infants enrolled in the Drakenstein child health study had lung function at 6 weeks and 1 year. Testing during quiet natural sleep included tidal breathing, exhaled nitric oxide, and multiple breath washout measures. Risk factors for impaired lung health were collected longitudinally. Lower respiratory tract illness surveillance was performed and any episode investigated.

MEASUREMENTS AND MAIN RESULTS

Lung function was tested in 648 children at 1 year. One hundred and fifty (29%) infants had a lower respiratory tract illness during the first year of life. Lower respiratory tract illness was independently associated with increased respiratory rate (4%; 95% confidence interval [CI], 1.01-1.08; P = 0.02). Repeat episodes further increased respiratory rate (3%; 95% CI, 1.01-1.05; P = 0.004), decreased tidal volume (-1.7 ml; 95% CI, -3.3 to -0.2; P = 0.03), and increased the lung clearance index (0.13 turnovers; 95% CI, 0.04-0.22; P = 0.006) compared with infants without illness. Tobacco smoke exposure, lung function at 6 weeks, infant growth, and prematurity were other independent predictors of lung function at 1 year.

CONCLUSIONS

Early life lower respiratory tract illness impairs lung function at 1 year, independent of baseline lung function. Preventing early life lower respiratory tract illness is important to optimize lung function and promote respiratory health in childhood.

End-inspiratory molar mass step correction for analysis of infant multiple breath washout tests

A refined software algorithm was recently proposed for the analysis of infant multiple breath washout (MBW) measurements. The proposed algorithm uses the change in end-inspiratory molar mass between the wash-in and wash-out curves (EIMM-step) to define the required step response correction of the MM signal and is assumed to provide an accurate evaluation of complete washout of the tracer gas, in comparison to the current software algorithm which applies the change in end-expiratory molar mass (EEMM)-step. We aimed to evaluate the use of the EIMM-step method in a broad range of infants. We performed retrospective analyses comparing the EIMM- and EEMM-step change methods in MBW data collected from infants with cystic fibrosis (CF), infants born preterm, and healthy infants using an ultrasonic flowmeter. We found that the EIMM-step correction significantly increased LCI and functional residual capacity (FRC) in infants with CF, preterm infants, and healthy infants compared with the EEMM-step method. In addition, more than half the measurements that were technically acceptable and repeatable using the EEMM-step correction in healthy infants were excluded after using the EIMM-step correction. We found a large difference between the EIMM- and EEMM-steps in healthy infants indicating incomplete washout, suggesting the need for a longer washout time with using the EIMM-step analysis method. The data indicates that the EIMM-step analysis method may have the potential to generate false abnormal LCI values in individuals without lung disease. Revised normative data may be required if this method is universally adopted. Pediatr Pulmonol. 2017;52:10-13. © 2016 Wiley Periodicals, Inc.

Mannitol challenge testing for asthma in a community cohort of young adults

BACKGROUND AND OBJECTIVE

Mannitol challenge testing is an established tool for clinical asthma diagnosis, and can be performed outside of specialized respiratory laboratories. Despite applicability in both clinical and non-clinical populations, with different pre-test asthma probabilities, differences in diagnostic properties have not been well explored. This study aimed to quantify the diagnostic utility of mannitol challenge testing for asthma in a community cohort and a symptomatic wheezing subset of this cohort.

METHODS

During the 22-year follow-up of the Western Australian Pregnancy (Raine) Cohort, 772 participants (384 males) completed mannitol challenge and skin prick testing and respiratory health questionnaires, of whom 148 reporting wheeze in the past 12 months were included in a wheezing subset.

RESULTS

Responsiveness to mannitol had low sensitivity (19%) and high specificity (97%) to identify current asthma in the complete cohort, with positive and negative predictive values (PPV and NPV) of 45% and 92%, respectively. Within the wheezing subset, sensitivity (19%) and specificity (94%) remained similar, but PPV increased to 79%, and NPV decreased to 52%.

CONCLUSION

Our findings support previously reported high specificity and good PPV for mannitol challenge testing in symptomatic wheezing populations, and highlight the need for caution when interpreting mannitol test results in non-clinical populations.

Respiratory function and symptoms in young preterm children in the contemporary era

OBJECTIVE

To determine the relationships between respiratory symptoms, lung function, and neonatal events in young preterm children.

METHODS

Preterm children (<32 w gestation), classified as bronchopulmonary dysplasia (BPD) or non-BPD, and healthy term controls were studied. Lung function was measured by forced oscillation technique (respiratory resistance [Rrs] and reactance [Xrs]) and spirometry. Respiratory symptom questionnaires were administered.

RESULTS

One hundred and fifty children (74 BPD, 44 non-BPD, 32 controls) 4-8 years were studied. Lung function (median Z-score [10,90th centile]) was significantly impaired in preterm children compared to controls for FVC (0.00 [-1.18, 1.76], 0.69 [-0.17,1.86]), FEV₁ (-0.44 [-1.94, 1.11], 0.49 [-0.83, 2.51]), Xrs (-1.26 [-3.31, 0.11], -0.11 [-0.97, 0.73]), and Rrs (0.55 [-0.48, 1.82], 0.28 [-0.99, 0.96]). Only Xrs differed between the BPD and non-BPD (-1.51 [-3.59, -0.41], -0.89 [-2.64, 0.52]). The prevalence of recent respiratory symptoms (range: 32-36%) did not differ between BPD and non-BPD children. Supplemental O₂ in hospital was positively associated with worsening Xrs and FEV₁ .

CONCLUSION

Preterm children have worse lung function than healthy controls. Only respiratory reactance differentiated between preterm children with and without BPD and was influenced by days of O₂ in hospital. Pediatr Pulmonol. 2016;51:1347-1355. © 2016 Wiley Periodicals, Inc.

A Systematic Approach to Multiple Breath Nitrogen Washout Test Quality

Background

Accurate estimates of multiple breath washout (MBW) outcomes require correct operation of the device, appropriate distraction of the subject to ensure they breathe in a manner representative of their relaxed tidal breathing pattern, and appropriate interpretation of the acquired data. Based on available recommendations for an acceptable MBW test, we aimed to develop a protocol to systematically evaluate MBW measurements based on these criteria.

Methods

50 MBW test occasions were systematically reviewed for technical elements and whether the breathing pattern was representative of relaxed tidal breathing by an experienced MBW operator. The impact of qualitative and quantitative criteria on inter-observer agreement was assessed across eight MBW operators (n = 20 test occasions, compared using a Kappa statistic).

Results

Using qualitative criteria, 46/168 trials were rejected: 16.6% were technically unacceptable and 10.7% were excluded due to inappropriate breathing pattern. Reviewer agreement was good using qualitative criteria and further improved with quantitative criteria from (κ = 0.53–0.83%) to (κ 0.73–0.97%), but at the cost of exclusion of further test occasions in this retrospective data analysis.

Conclusions

The application of the systematic review improved inter-observer agreement but did not affect reported MBW outcomes.

Lung Clearance Index and Structural Lung Disease on Computed Tomography in Early Cystic Fibrosis

RATIONALE

The lung clearance index is a measure of ventilation distribution derived from the multiple-breath washout technique. It has been suggested as a surrogate for chest computed tomography to detect structural lung abnormalities in individuals with cystic fibrosis (CF); however, the associations between lung clearance index and early structural lung disease are unclear.

OBJECTIVES

We assessed the ability of the lung clearance index to reflect structural lung disease on the basis of chest computed tomography across the entire pediatric age range.

METHODS

Lung clearance index was assessed in 42 infants (ages 0-2 yr), 39 preschool children (ages 3-6 yr), and 38 school-age children (7-16 yr) with CF before chest computed tomography and in 72 healthy control subjects. Scans were evaluated for CF-related structural lung disease using the Perth-Rotterdam Annotated Grid Morphometric Analysis for Cystic Fibrosis quantitative outcome measure.

MEASUREMENTS AND MAIN RESULTS

In infants with CF, lung clearance index is insensitive to structural disease (κ = -0.03 [95% confidence interval, -0.05 to 0.16]). In preschool children with CF, lung clearance index correlates with total disease extent. In school-age children, lung clearance index correlates with extent of total disease, bronchiectasis, and air trapping. In preschool and school-age children, lung clearance index has a good positive predictive value (83-86%) but a poor negative predictive value (50-55%) to detect the presence of bronchiectasis.

CONCLUSIONS

These data suggest that lung clearance index may be a useful surveillance tool to monitor structural lung disease in preschool and school-age children with CF. However, lung clearance index cannot replace chest computed tomography to screen for bronchiectasis in this population.

Multiple breath washout cannot be used for tidal breath parameter analysis in infants

BACKGROUND

Multiple breath washout (MBW) testing with SF6 gas mixture is routinely used to assess ventilation distribution in infants. It is currently unknown whether SF6 changes tidal breathing parameters during MBW in infants. We investigated if SF6 does change tidal breathing parameters in infants and whether a separate tidal breathing trace prior to MBW testing is necessary.

METHODS

Tidal breathing during MBW was compared to standard tidal breathing in room air in healthy infants (n = 38), preterm infants (n = 41), and infants with cystic fibrosis (n = 41). Outcomes included inspiratory and expiratory times (TI and TE ), time to peak tidal inspiratory and expiratory flow (tPTIF and tPTEF), tidal volume (VT ), respiratory rate (f), and minute ventilation (VE ).

RESULTS

Breath times were all significantly increased for both healthy (TE : -0.0790 [-0.10566, -0.05217]; mean difference [95% confidence intervals]) and CF (-0.109 [-0.15235, -0.06607]) infants during the MBW wash-in (P < 0.001). Healthy infants and those with CF showed decreased f during MBW wash-in (P < 0.001); however, no change in VT, resulting in a decreased VE (0.154 (0.086, 0.222) and 0.128 (0.069, 0.186) for healthy and CF infants, respectively, P < 0.001). Preterm infants experienced a decreased VE during both wash-in (0.134 [0.061, 0.207]; P < 0.001) and wash-out phases of MBW (P < 0.05).

CONCLUSION

There are differences in tidal breathing parameters during MBW testing with SF6 in infants. It is, therefore, important to measure a separate tidal breathing trace in room air, prior to MBW testing to ensure rigour of tidal breath indices derived from analysis.

Impact of lung disease on respiratory impedance in young children with cystic fibrosis

This study aimed to evaluate the ability of the forced oscillation technique (FOT) to detect underlying lung disease in preschool children with cystic fibrosis (CF) diagnosed following newborn screening.184 children (aged 3-6 years) with CF underwent lung function testing on 422 occasions using the FOT to assess respiratory resistance and reactance at the time of their annual bronchoalveolar lavage collection and chest computed tomography scan. We examined associations between FOT outcomes and the presence and progression of respiratory inflammation, infection and structural lung disease.Children with CF who had pronounced respiratory disease, including free neutrophil elastase activity, infection with pro-inflammatory pathogens and structural lung abnormalities had similar FOT outcomes to those children without detectable lung disease. In addition, the progression of lung disease over 1 year was not associated with worsening FOT outcomes.We conclude that the forced oscillation technique is relatively insensitive to detect underlying lung disease in preschool children with CF. However, FOT may still be of value in improving our understanding of the physiological changes associated with early CF lung disease.

Progressive ventilation inhomogeneity in infants with cystic fibrosis after pulmonary infection

Measures of ventilation distribution are promising for monitoring early lung disease in cystic fibrosis (CF). This study describes the cross-sectional and longitudinal impacts of pulmonary inflammation and infection on ventilation homogeneity in infants with CF.Infants diagnosed with CF underwent multiple breath washout (MBW) testing and bronchoalveolar lavage at three time points during the first 2 years of life.Measures were obtained for 108 infants on 156 occasions. Infants with a significant pulmonary infection at the time of MBW showed increases in lung clearance index (LCI) of 0.400 units (95% CI 0.150-0.648; p=0.002). The impact was long lasting, with previous pulmonary infection leading to increased ventilation inhomogeneity over time compared to those who remained free of infection (p<0.05). Infection with Haemophilus influenzae was particularly detrimental to the longitudinal lung function in young children with CF where LCI was increased by 1.069 units for each year of life (95% CI 0.484-1.612; p<0.001).Pulmonary infection during the first year of life is detrimental to later lung function. Therefore, strategies aimed at prevention, surveillance and eradication of pulmonary pathogens are paramount to preserve lung function in infants with CF.

Infant respiratory infections and later respiratory hospitalisation in childhood

Acute respiratory infections (ARI) cause significant morbidity in infancy. We sought to quantify the relationship between ARI and development of respiratory morbidity in early childhood. Population-based longitudinal hospitalisation data were linked to perinatal, birth and death records for 145,580 Western Australian children from 1997 to 2002. We conducted Cox regression with sensitivity analyses to quantify the risk of recurrent ARI in infancy for respiratory hospitalisation after the age of 3 years. ARI in infancy was significantly related to respiratory hospitalisation before (hazard ratio (HR) 3.5, 95% CI 3.1-3.8) and after (HR 3.0, 95% CI 2.6-3.4) adjusting for known risk factors including maternal smoking during pregnancy, season of birth, delivery mode and gestational age. We noted a dose response with the number and length of infant ARI hospitalisations and increasing risk with no effect modification by gestational age. Results were similar when later respiratory hospitalisations were restricted to asthma hospitalisations only. Recurrent hospitalisations for ARI in infancy significantly increase the risk of respiratory morbidity and asthma requiring hospitalisation after the age of 3 years in a dose-response fashion. The increase in relative risk is not modified by gestational age. Efforts to reduce the occurrence of infant ARI are likely to have significant public health benefits.

Rationale, design and methods for the 22 year follow-up of the Western Australian Pregnancy Cohort (Raine) Study

BACKGROUND

Young adulthood is a critical life period for health and health behaviours. Related measurements collected before and after birth, and during childhood and adolescence can provide a life-course analysis of important factors that contribute to health and behaviour in young adulthood. The Western Australian Pregnancy Cohort (Raine) Study has collected a large number of such measurements during the fetal, perinatal, infancy, childhood and adolescence periods and plans to relate them to common health issues and behaviours in young adults, including spinal pain, asthma, sleep disorders, physical activity and sedentary behaviour and, work absenteeism and presenteeism. The aim of this paper is to describe the rationale, design and methods of the 22 year follow-up of the Raine Study cohort.

METHODS/DESIGN

The Raine Study is a prospective cohort study. Participants still active in the cohort (n = 2,086) were contacted around the time of their 22nd birthday and invited to participate in the 22 year follow-up. Each was asked to complete a questionnaire, attend a research facility for physical assessment and an overnight sleep study, wear activity monitors for a week, and to maintain a sleep and activity diary over this week. The questionnaire was broad and included questions related to sociodemographics, medical history, quality of life, psychological factors, lifestyle factors, spinal pain, respiratory, sleep, activity and work factors. Physical assessments included anthropometry, blood pressure, back muscle endurance, tissue sensitivity, lung function, airway reactivity, allergic status, 3D facial photographs, cognitive function, and overnight polysomnography.

DISCUSSION

Describing the prevalence of these health issues and behaviours in young adulthood will enable better recognition of the issues and planning of health care resources. Providing a detailed description of the phenotype of these issues will provide valuable information to help educate health professionals of the needs of young adults. Understanding the life-course risk factors of health issues and behaviours in young adulthood will have important health planning implications, supporting the development of targeted interventions to improve current health status and reduce the onset and development of further ill-health across adulthood.

Lung function and exhaled nitric oxide in healthy unsedated African infants

Background and objective

Population-appropriate lung function reference data are essential to accurately identify respiratory disease and measure response to interventions. There are currently no reference data in African infants. The aim was to describe normal lung function in healthy African infants.

Methods

Lung function was performed on healthy South African infants enrolled in a birth cohort study, the Drakenstein child health study. Infants were excluded if they were born preterm or had a history of neonatal respiratory distress or prior respiratory tract infection. Measurements, made during natural sleep, included the forced oscillation technique, tidal breathing, exhaled nitric oxide and multiple breath washout measures.

Results

Three hundred sixty-three infants were tested. Acceptable and repeatable measurements were obtained in 356 (98%) and 352 (97%) infants for tidal breathing analysis and exhaled nitric oxide outcomes, 345 (95%) infants for multiple breath washout and 293 of the 333 (88%) infants for the forced oscillation technique. Age, sex and weight-for-age z score were significantly associated with lung function measures.

Conclusions

This study provides reference data for unsedated infant lung function in African infants and highlights the importance of using population-specific data.

The influence of sighing respirations on infant lung function measured using multiple breath washout gas mixing techniques

There is substantial interest in studying lung function in infants, to better understand the early life origins of chronic lung diseases such as asthma. Multiple breath washout (MBW) is a technique for measuring lung function that has been adapted for use in infants. Respiratory sighs occur frequently in young infants during natural sleep, and in accordance with current MBW guidelines, result in exclusion of data from a substantial proportion of testing cycles. We assessed how sighs during MBW influenced the measurements obtained using data from 767 tests conducted on 246 infants (50% male; mean age 43 days) as part of a large cohort study. Sighs occurred in 119 (15%) tests. Sighs during the main part of the wash-in phase (before the last 5 breaths) were not associated with differences in standard MBW measurements compared with tests without sighs. In contrast, sighs that occurred during the washout were associated with a small but discernible increase in magnitude and variability. For example, the mean lung clearance index increased by 0.36 (95% CI: 0.11–0.62) and variance increased by a multiplicative factor of 2 (95% CI: 1.6–2.5). The results suggest it is reasonable to include MBW data from testing cycles where a sigh occurs during the wash-in phase, but not during washout, of MBW. By recovering data that would otherwise have been excluded, we estimate a boost of about 10% to the final number of acceptable tests and 6% to the number of individuals successfully tested.

Respiratory impedance in healthy unsedated South African infants: effects of maternal smoking

Background and objective

Non-invasive techniques for measuring lung mechanics in infants are needed for a better understanding of lung growth and function, and to study the effects of prenatal factors on subsequent lung growth in healthy infants. The forced oscillation technique requires minimal cooperation from the individual but has rarely been used in infants. The study aims to assess the use of the forced oscillation technique to measure the influence of antenatal exposures on respiratory mechanics in unsedated infants enrolled in a birth cohort study in Cape Town, South Africa.

Methods

Healthy term infants were studied at 6–10 weeks of age using the forced oscillation technique. Respiratory impedance was measured in the frequency range 8–48 Hz via a face mask during natural sleep. Respiratory system resistance, compliance and inertance were calculated from the impedance spectra.

Results

Of 177 infants tested, successful measurements were obtained in 164 (93%). Median (25–75%) values for resistance, compliance and inertance were 50.2 (39.5–60.6) cmH₂O.s.L⁻¹, 0.78 (0.61–0.99) mL.cmH₂O⁻¹ and 0.062 (0.050–0.086) cmH₂O.s².L⁻¹, respectively. As a group, male infants had 16% higher resistance (P = 0.006) and 18% lower compliance (P = 0.02) than females. Infants whose mothers smoked during pregnancy had a 19% lower compliance than infants not exposed to tobacco smoke during pregnancy (P = 0.005). Neither maternal HIV infection nor ethnicity had a significant effect on respiratory mechanics.

Conclusions

The forced oscillation technique is sensitive enough to demonstrate the effects of tobacco smoke exposure and sex in respiratory mechanics in healthy infants. This technique will facilitate assessing perinatal influences of lung function in infancy.

Lung function in African infants: a pilot study

BACKGROUND

The burden of childhood respiratory illness is large in low and middle income countries (LMICs). Infant lung function (ILF) testing may provide useful information about lung growth and susceptibility to respiratory disease. However, ILF has not been widely available in LMICs settings where the greatest burden of childhood respiratory disease occurs.

AIM

To implement and evaluate a pilot study of ILF testing in a semi-rural setting in South Africa.

METHOD

Infant lung function testing was established at a community hospital in South Africa. All measures were done in unsedated infants during sleep. Measurements, made with the infant quietly breathing through a face mask and bacterial filter, included tidal breathing (TBFVL), exhaled nitric oxide (eNO), and sulphur hexafluoride multiple breath washout (MBW) measures using an ultrasonic flow meter and chemoluminescent NO analyzer.

RESULTS

Twenty infants, mean age of 7.7 (SD 2.9) weeks were tested; 8 (40%) were Black African and 12 (60%) were mixed race. Five (25%) infants were preterm. There were 19 (95%) successful TBFVL and NO tests and 18 (90%) successful MBW tests. The mean tidal volume was 30.5 ml (SD 5.9), respiratory rate 50.2 breaths per minute (SD 8.7), and eNO 10.4 ppb (SD 7.3). The mean MBW measures were: functional residual capacity 71 ml (SD 13) and the lung clearance index 7.6 (SD 0.5). The intra-subject coefficient of variations (CV) of lung function measures were similar to published normative data for Caucasian European infants.

CONCLUSION

In this study we demonstrate that unsedated infant lung function measures of tidal breathing, MBW, and eNO are feasible in a semi-rural African setting with rates comparable to those reported from high income countries.

Influence of gestational age on dead space and alveolar ventilation in preterm infants ventilated with volume guarantee

BACKGROUND

Ventilated preterm infant lungs are vulnerable to overdistension and underinflation. The optimal ventilator-delivered tidal volume (VT) in these infants is unknown and may depend on the extent of alveolarisation at birth.

OBJECTIVES

We aimed to calculate respiratory dead space (VD) from the molar mass (MM) signal of an ultrasonic flowmeter (VD,MM) in very preterm infants on volume-targeted ventilation (VT target, 4-5 ml/kg) and to study the association between gestational age (GA) and VD,MM-to-VT ratio (VD,MM/VT), alveolar tidal volume (VA) and alveolar minute volume (AMV).

METHODS

This was a single-centre, prospective, observational, cohort study in a neonatal intensive care unit. Tidal breathing analysis was performed in ventilated very preterm infants (GA range 23-32 weeks) on day 1 of life.

RESULTS

Valid measurements were obtained in 43/51 (87%) infants. Tidal breathing variables were analysed using multivariable linear regression. VD,MM/VT was negatively associated with GA after adjusting for birth weight Z score (p < 0.001, R(2) = 0.26). This association was primarily influenced by the appliance dead space. Despite similar VT/kg and VA/kg across all studied infants, respiratory rate and AMV/kg increased with GA.

CONCLUSIONS

VD,app rather than anatomical VD is the major factor influencing increased VD,MM/VT at a younger GA. A volume guarantee setting of 4-5 ml/kg in the Dräger Babylog® 8000 plus ventilator may be inappropriate as a universal target across the GA range of 23-32 weeks. Differences between measured and set VT and the dependence of this difference on GA require further investigation.