Intra-breath measures of respiratory mechanics in healthy African infants detect risk of respiratory illness in early life

Tracking of respiratory mechanics at multiple oscillation frequencies

BACKGROUND AND OBJECTIVE

Intra-breath oscillometry (IBOsc) is an emerging approach to characterize dynamic changes in respiratory mechanical impedance (Zrs). IBOsc utilizes a small-amplitude sinusoidal signal superimposed on quiet breathing to track Zrs with sufficient temporal resolution to find specific time points, such as end-expiration (eE) and end-inspiration (eI). IBOsc has demonstrated superiority to conventional multifrequency oscillometry in detecting abnormal respiratory function and predicting future impairment in several clinical settings. The aim of the present study was to construct intra-breath Zrs spectra from multifrequency recordings to demonstrate how the Zrs spectrum and its measures change during breathing.

METHODS

Conventional oscillometric recordings from groups of healthy subjects and patients with interstitial lung disease, asthma and chronic obstructive pulmonary disease (N=40 each group) were analyzed. Zrs was computed at each component of the multifrequency (5-37-Hz) signal to establish the Zrs spectra at eE and eI. This multi-frequency tracking method was validated on simulated Zrs data generated by a non-linear model of respiratory mechanics. The 2-way median test and Wilcoxon signed rank test were used to compare Zrs values and derived measures between groups and respiratory phases, respectively.

RESULTS

Large intra-breath changes in Zrs were found in all subject groups. Most pairwise comparisons of Zrs measures (such as resistance, resonance frequency, reactance area and effective compliance) revealed significant (P<0.05) or highly significant (P<0.001) differences between groups at eE, which became more uniform at eI. Similarly, the changes between eE and eI were significant in most Zrs measures and subject groups, indicating the tidal improvement of lung mechanics in the obstructive patients.

CONCLUSIONS

Our results demonstrate that re-processing of archived datasets is feasible and can provide useful additional data to further characterize respiratory mechanical phenotypes. In particular, the estimation of Zrs spectra at zero respiratory flow minimizes the contribution of upper airway nonlinearities and thus improves the assessment of intrapulmonary dynamics. However, as this study points out, most current multifrequency signals are suboptimal for exploiting the potential of IBOsc due to low signal-to-noise ratio and interaction between adjacent frequency components.

Intra-breath respiratory mechanics of prematurity-associated lung disease phenotypes in school-aged children

Background

Intra-breath oscillometry potentially offers detailed information regarding airway function, with increasing magnitude of difference between resistance and reactance at end-expiration to end-inspiration potentially associated with obstructive airway disease, but less is known about specific respiratory mechanics in preterm-born children using this methodology. We investigated whether different spirometry phenotypes of prematurity-associated lung disease (PLD) have specific intra-breath oscillometry features.

Methods

167 school-aged (7-12 years) children, 14 with prematurity-associated obstructive lung disease (POLD; forced expiratory volume in 1 s (FEV1)

Results

Children with POLD showed greater resistance and more negative reactance throughout the respiratory cycle, including at zero-flow states of end-expiration and end-inspiration. The difference between end-expiration and end-inspiration did not show differences between groups until corrected for tidal volume, whereby children with POLD and pPRISm both demonstrated approximately two-fold greater difference compared to both preterm and term controls for resistance (2.24 and 2.22 versus 1.28 and 1.11 hPa·s·L-1, respectively), and in particular a greater magnitude of difference for reactance for children with POLD versus preterm and term controls only (-1.58 versus -0.26 and 0.03 hPa·s·L-1, respectively).

Conclusions

Intra-breath respiratory mechanics for preterm-born children with an obstructive lung phenotype have greater impedance throughout the respiratory cycle, features different to those observed in children with other wheeze phenotypes including preschool wheeze and asthma.

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Grants

• Medical Research Council

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Affiliation(s)

Michael Cousins Department of Child Health, Cardiff University School of Medicine, Cardiff, UK Department of Paediatrics, Cardiff and Vale University Health Board, Cardiff, UK
Kylie Hart Department of Child Health, Cardiff University School of Medicine, Cardiff, UK Department of Paediatrics, Cardiff and Vale University Health Board, Cardiff, UK
Bence Radics Department of Pathology, University of Szeged, Szeged, Hungary
A. John Henderson MRC Integrative Epidemiology Unit, Population Health Sciences, Bristol Medical School, University of Bristol, Bristol, UK
Zoltán Hantos Department of Anesthesiology and Intensive Therapy, Semmelweis University, Budapest, Hungary
Peter D. Sly Child Health Research Centre, The University of Queensland, South Brisbane, Australia
Sailesh Kotecha Department of Child Health, Cardiff University School of Medicine, Cardiff, UK

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Oscillometry-defined small airways dysfunction as a treatable trait in asthma

The small airways, also referred to as the lung's silent zone, are closely associated with poor symptom control and more frequent asthma exacerbations. The oscillometry technique superimposes sound or airwaves onto normal tidal breathing and provides information on resistance and reactance, that is, obstacles to airflow occurring inside and outside of the bronchi. More recently, a management paradigm based on so-called "treatable traits" has been proposed to personalize and improve asthma care for individuals by proactively identifying and targeting modifiable pulmonary, extrapulmonary, and behavioral traits affecting asthma control. In this review article, we evaluate the literature on small airways dysfunction as a potential treatable trait in persistent asthma. In particular, we discuss whole- and intrabreath oscillometry and the impact of extrafine inhaled corticosteroids and systemic biologics on the peripheral airways.

[Respiratory oscillometry: Theoretical foundations and clinical applications]

Oscillometry measures the mechanical properties of the respiratory system. As they are carried out during spontaneous breathing, oscillometry measurements do not require forced breathing maneuvers or the patient's active cooperation. The technique is complementary to conventional pulmonary function testing methods for the investigation of respiratory function, diagnosis and monitoring of respiratory diseases, and assessment of response to treatment. The present review aims to describe the theoretical foundations and practical methodology of oscillometry. It describes the gaps in scientific evidence regarding its clinical utility, and provides examples of current research and clinical applications.

Determinants of lung function development from birth to age 5 years: an interrupted time series analysis of a South African birth cohort

BACKGROUND

Early life is a key period that determines long-term health. Lung development in childhood predicts lung function attained in adulthood and morbidity and mortality across the life course. We aimed to assess the effect of early-life lower respiratory tract infection (LRTI) and associated risk factors on lung development from birth to school age in a South African birth cohort.

METHODS

We prospectively followed children enrolled in a population-based cohort from birth (between March 5, 2012 and March 31, 2015) to age 5 years with annual lung function assessment. Data on multiple early-life exposures, including LRTI, were collected. The effect of early-life risk factors on lung function development from birth to age 5 years was assessed using the Generalised Additive Models for Location, Scale and Shape and Interrupted Time Series approach.

FINDINGS

966 children (475 [49·2%] female, 491 [50·8%] male) had lung function measured with oscillometry, tidal flow volume loops, and multiple breath washout. LRTI occurred in 484 (50·1%) children, with a median of 2·0 LRTI episodes (IQR 1·0-3·0) per child. LRTI was independently associated with altered lung function, as evidenced by lower compliance (0·959 [95% CI 0·941-0·978]), higher resistance (1·028 [1·016-1·041]), and higher respiratory rate (1·018 [1·063-1·029]) over 5 years. Additional impact on lung function parameters occurred with each subsequent LRTI. Respiratory syncytial virus (RSV) LRTI was associated with lower expiratory flow ratio (0·97 [0·95-0·99]) compared with non-RSV LRTI. Maternal factors including allergy, smoking, and HIV infection were also associated with altered lung development, as was preterm birth, low birthweight, female sex, and coming from a less wealthy household.

INTERPRETATION

Public health interventions targeting LRTI prevention, with RSV a priority, are vital, particularly in low-income and middle-income settings.

FUNDING

UK Medical Research Council Grant, The Wellcome Trust, The Bill & Melinda Gates Foundation, US National Institutes of Health Human Heredity and Health in Africa, South African Medical Research Council, Hungarian Scientific Research Fund, and European Respiratory Society.

Intra-breath changes in respiratory mechanics are sensitive to history of respiratory illness in preschool children: the SEPAGES cohort

BACKGROUND

Intra-breath oscillometry has been proposed as a sensitive means of detecting airway obstruction in young children. We aimed to assess the impact of early life wheezing and lower respiratory tract illness on lung function, using both standard and intra-breath oscillometry in 3 year old children.

METHODS

History of doctor-diagnosed asthma, wheezing, bronchiolitis and bronchitis and hospitalisation for respiratory problems were assessed by questionnaires in 384 population-based children. Association of respiratory history with standard and intra-breath oscillometry parameters, including resistance at 7 Hz (R7), frequency-dependence of resistance (R7 - 19), reactance at 7 Hz (X7), area of the reactance curve (AX), end-inspiratory and end-expiratory R (ReI, ReE) and X (XeI, XeE), and volume-dependence of resistance (ΔR = ReE-ReI) was estimated by linear regression adjusted on confounders.

RESULTS

Among the 320 children who accepted the oscillometry test, 281 (88%) performed 3 technically acceptable and reproducible standard oscillometry measurements and 251 children also performed one intra-breath oscillometry measurement. Asthma was associated with higher ReI, ReE, ΔR and R7 and wheezing was associated with higher ΔR. Bronchiolitis was associated with higher R7 and AX and lower XeI and bronchitis with higher ReI. No statistically significant association was observed for hospitalisation.

CONCLUSIONS

Our findings confirm the good success rate of oscillometry in 3-year-old children and indicate an association between a history of early-life wheezing and lower respiratory tract illness and lower lung function as assessed by both standard and intra-breath oscillometry. Our study supports the relevance of using intra-breath oscillometry parameters as sensitive outcome measures in preschool children in epidemiological cohorts.

The impact of antenatal and postnatal indoor air pollution or tobacco smoke exposure on lung function at 3 years in an African birth cohort

BACKGROUND AND OBJECTIVE

Indoor air pollution (IAP) and tobacco smoke exposure (ETS) are global health concerns contributing to the burden of childhood respiratory disease. Studies assessing the effects of IAP and ETS in preschool children are limited. We assessed the impact of antenatal and postnatal IAP and ETS exposure on lung function in a South African birth cohort, the Drakenstein Child Health Study.

METHODS

Antenatally enrolled mother-child pairs were followed from birth. Lung function measurements (oscillometry, multiple breath washout and tidal breathing) were performed at 6 weeks and 3 years. Quantitative antenatal and postnatal IAP (particulate matter [PM10 ], volatile organic compounds [VOC]) and ETS exposures were measured. Linear regression models explored the effects of antenatal and postnatal exposures on lung function at 3 years.

RESULTS

Five hundred eighty-four children had successful lung function testing, mean (SD) age of 37.3 (0.7) months. Exposure to antenatal PM10 was associated with a decreased lung clearance index (p < 0.01) and postnatally an increase in the difference between resistance at end expiration (ReE) and inspiration (p = 0.05) and decrease in tidal volume (p = 0.06). Exposure to antenatal VOC was associated with an increase in functional residual capacity (p = 0.04) and a decrease in time of expiration over total breath time (tE /tTOT ) (p = 0.03) and postnatally an increase in respiratory rate (p = 0.05). High ETS exposure postnatally was associated with an increase in ReE (p = 0.03).

CONCLUSION

Antenatal and postnatal IAP and ETS exposures were associated with impairment in lung function at 3 years. Strengthened efforts to reduce IAP and ETS exposure are needed.

Oscillatory mechanics trajectory in very preterm infants: a cohort study

BACKGROUND

The aim of this study was to describe the trajectory of oscillatory mechanics from the first week of life to term equivalent and evaluate whether oscillatory mechanics are associated with simultaneous lung disease in infants ≤32 weeks gestation.

METHODS

In this observational, longitudinal study, we enrolled 66 infants. Forced oscillations were applied using a neonatal mechanical ventilator (Fabian HFOi) that superimposed oscillations (10 Hz, amplitude 2.5 cmH2O) on a positive end-expiratory pressure (PEEP). Measurements were performed at 5-7-9 cmH2O of PEEP or the clinical pressure ±2 cmH2O; they were repeated at 7, 14, 28 post-natal days, and 36 and 40 weeks post-menstrual age (PMA).

RESULTS

The mean (range) gestational age of study participants was 29.2 (22.9-31.9) weeks. Nineteen infants (29%) developed bronchopulmonary dysplasia (BPD). Respiratory system reactance was significantly lower (lower compliance), and respiratory system resistance was significantly higher in infants with developing BPD from 7 post-natal days to 36 weeks PMA. All oscillatory mechanics parameters were significantly associated with the simultaneous respiratory severity score (p < 0.001 for all).

CONCLUSIONS

Serial measurements of oscillatory mechanics allow differentiating lung function trajectory in infants with and without evolving BPD. Oscillatory mechanics significantly correlate with the severity of simultaneous lung disease.

IMPACT

The results of the present study suggest that respiratory system reactance, as assessed by respiratory oscillometry, allows the longitudinal monitoring of the progression of lung disease in very premature infants. This paper describes for the first time the trajectory of oscillatory mechanics in very preterm infants with and without evolving bronchopulmonary dysplasia from the first week of life to term equivalent. Serial respiratory oscillometry measurements allow the identification of early markers of evolving bronchopulmonary dysplasia and may help personalizing the respiratory management strategy.

Oscillometry and spirometry are not interchangeable when assessing the bronchodilator response in children and young adults born preterm

INTRODUCTION

The European Respiratory Society Oscillometry Taskforce identified that clinical correlates of bronchodilator responses are needed to advance oscillometry in clinical practice. The understanding of bronchodilator-induced oscillometry changes in preterm lung disease is poor. Here we describe a comparison of bronchodilator assessments performed using oscillometry and spirometry in a population born very preterm and explore the relationship between bronchodilator-induced changes in respiratory function and clinical outcomes.

METHODS

Participants aged 6-23 born ≤32 (N = 288; 132 with bronchopulmonary dysplasia) and ≥37 weeks' gestation (N = 76, term-born controls) performed spirometry and oscillometry. A significant bronchodilator response (BDR) to 400 μg salbutamol was classified according to published criteria.

RESULTS

A BDR was identified in 30.9% (n = 85) of preterm-born individuals via spirometry and/or oscillometry, with poor agreement between spirometry and oscillometry definitions (k = 0.26; 95% confidence interval [CI] 0.18-0.40, p < .001). Those born preterm with a BDR by oscillometry but not spirometry had increased wheeze (33% vs. 11%, p = .010) and baseline resistance (Rrs5 z-score mean difference (MD) = 0.86, 95% CI 0.07-1.65, p = .025), but similar baseline spirometry to the group without a BDR (forced expiratory volume in 1 s [FEV1 ] z-score MD = -0.01, 95% CI -0.66 to 0.68, p > .999). Oscillometry was more feasible than spirometry (95% success rate vs. 85% (FEV1 ), 69% (forced vital capacity) success rate, p < .001), however being born preterm did not affect test feasibility.

CONCLUSION

In the preterm population, oscillometry is a feasible and clinically useful supportive test to assess the airway response to inhaled salbutamol. Changes measured by oscillometry reflect related but distinct physiological changes to those measured by spirometry, and thus these tests should not be used interchangeably.

Early childhood wheezing phenotypes and determinants in a South African birth cohort: longitudinal analysis of the Drakenstein Child Health Study

BACKGROUND

Developmental trajectories of childhood wheezing in low-income and middle-income countries (LMICs) have not been well described. We aimed to derive longitudinal wheeze phenotypes from birth to 5 years in a South African birth cohort and compare those with phenotypes derived from a UK cohort.

METHODS

We used data from the Drakenstein Child Health Study (DCHS), a longitudinal birth cohort study in a peri-urban area outside Cape Town, South Africa. Pregnant women (aged ≥18 years) were enrolled during their second trimester at two public health clinics. We followed up children from birth to 5 years to derive six multidimensional indicators of wheezing (including duration, temporal sequencing, persistence, and recurrence) and applied Partition Around Medoids clustering to derive wheeze phenotypes. We compared phenotypes with a UK cohort (the Avon Longitudinal Study of Parents and Children [ALSPAC]). We investigated associations of phenotypes with early-life exposures, including all-cause lower respiratory tract infection (LRTI) and virus-specific LRTI (respiratory syncytial virus, rhinovirus, adenovirus, influenza, and parainfluenza virus) up to age 5 years. We investigated the association of phenotypes with lung function at 6 weeks and 5 years.

FINDINGS

Between March 5, 2012, and March 31, 2015, we enrolled 1137 mothers and there were 1143 livebirths. Four wheeze phenotypes were identified among 950 children with complete data: never (480 children [50%]), early transient (215 children [23%]), late onset (104 children [11%]), and recurrent (151 children [16%]). Multivariate adjusted analysis indicated that LRTI and respiratory syncytial virus-LRTI, but not other respiratory viruses, were associated with increased risk of recurrent wheeze (odds ratio [OR] 2·79 [95% CI 2·05-3·81] for all LTRIs; OR 2·59 [1·30-5·15] for respiratory syncytial virus-LRTIs). Maternal smoking (1·88 [1·12-3·02]), higher socioeconomic status (2·46 [1·23-4·91]), intimate partner violence (2·01 [1·23-3·29]), and male sex (2·47 [1·50-4·04]) were also associated with recurrent wheeze. LRTI and respiratory syncytial virus-LRTI were also associated with early transient and late onset clusters. Wheezing illness architecture differed between DCHS and ALSPAC; children included in ALSPAC in the early transient cluster wheezed for a longer period before remission and late-onset wheezing started at an older age, and no persistent phenotype was identified in DCHS. At 5 years, airway resistance was higher in children with early or recurrent wheeze compared with children who had never wheezed. Airway resistance increased from 6 weeks to 5 years among children with recurrent wheeze.

INTERPRETATION

Effective strategies to reduce maternal smoking and psychosocial stressors and new preventive interventions for respiratory syncytial virus are urgently needed to optimise child health in LMICs.

FUNDING

UK Medical Research Council; The Bill & Melinda Gates Foundation; National Institutes of Health Human Heredity and Health in Africa; South African Medical Research Council; Wellcome Trust.

Characterization of chronic lung allograft dysfunction phenotypes using spectral and intrabreath oscillometry

Background: Chronic lung allograft dysfunction (CLAD) is the major cause of death beyond 2 years after lung transplantation and develops in 50% of all patients by 5 years post-transplant. CLAD is diagnosed on the basis of a sustained drop of 20% for at least 3 months in the forced expiratory volume (FEV₁), compared to the best baseline value achieved post-transplant. CLAD presents as two main phenotypes: bronchiolitis obliterans syndrome (BOS) is more common and has better prognosis than restrictive allograft syndrome (RAS). Respiratory oscillometry is a different modality of lung function testing that is highly sensitive to lung mechanics. The current study investigated whether spectral and intrabreath oscillometry can differentiate between CLAD-free, BOS- and RAS-CLAD at CLAD onset, i.e., at the time of the initial 20% drop in the FEV₁.

Methods: A retrospective, cross-sectional analysis of 263 double lung transplant recipients who underwent paired testing with oscillometry and spirometry at the Toronto General Pulmonary Function Laboratory from 2017 to 2022 was conducted. All pulmonary function testing and CLAD diagnostics were performed following international guidelines. Statistical analysis was conducted using multiple comparisons.

Findings: The RAS (n = 6) spectral oscillometry pattern differs from CLAD-free (n = 225) by right-ward shift of reactance curve similar to idiopathic pulmonary fibrosis whereas BOS (n = 32) has a pattern similar to obstructive lung disease. Significant differences were found in most spectral and intrabreath parameters between BOS, RAS, and time-matched CLAD-free patients. Post-hoc analysis revealed these differences were primarily driven by BOS instead of RAS. While no differences were found between CLAD-free and RAS patients with regards to spectral oscillometry, the intrabreath metric of reactance at end-inspiration (XeI) was significantly different (p < 0.05). BOS and RAS were differentiated by spectral oscillometry measure R5, and intrabreath resistance at end expiration, ReE (p < 0.05 for both).

Conclusion: Both spectral and intrabreath oscillometry can differentiate BOS-CLAD from CLAD-free states while intrabreath oscillometry, specifically XeI, can uniquely distinguish RAS-CLAD from CLAD-free. Spectral and intrabreath oscillometry offer complementary information regarding lung mechanics in CLAD patients to help distinguish the two phenotypes and could prove useful in prognostication.

Understanding the fundamentals of oscillometry from a strip of lung tissue

Metrics used in spirometry caught on in respiratory medicine not only because they provide information of clinical importance but also because of a keen understanding of what is being measured. The forced expiratory volume in 1 s (FEV₁), for example, is the maximal volume of air that can be expelled during the first second of a forced expiratory maneuver starting from a lung inflated to total lung capacity (TLC). Although it represents a very gross measurement of lung function, it is now used to guide the diagnosis and management of many lung disorders. Metrics used in oscillometry are not as concrete. Resistance, for example, has several connotations and its proper meaning in the context of a lung probed by an external device is not always intuitive. I think that the popularization of oscillometry and its firm implementation in respiratory guidelines starts with a keen understanding of what exactly is being measured. This review is an attempt to clearly explain the basic metrics of oscillometry. In my opinion, the fundamentals of oscillometry can be understood using a simple example of an excised strip of lung tissue subjected to a sinusoidal strain. The key notion is to divide the sinusoidal reacting force from the tissue strip into two sinusoids, one in phase with the strain and one preceding the strain by exactly a quarter of a cycle. Similar notions can then be applied to a whole lung subjected to a sinusoidal flow imposed at the mouth by an external device to understand basic metrics of oscillometry, including resistance, elastance, impedance, inertance, reactance and resonant frequency.

Intra-breath changes in respiratory mechanics assessed from multi-frequency oscillometry measurements

OBJECTIVE

Recent studies in respiratory system impedance (Zrs) with single-frequency oscillometry have demonstrated the utility of novel intra-breath measures of Zrs in the detection of pathological alterations in respiratory mechanics. In the present work, we addressed the feasibility of extracting intra-breath information from Zrs data sets obtained with conventional oscillometry.

APPROACH

Multi-frequency recordings obtained in a pulmonology practice were re-analysed to track the 11 Hz component of Zrs during normal breathing and compare the intra-breath measures to that obtained with a single 10 Hz signal in the same subjects. A non-linear model was employed to simulate changes in Zrs in the breathing cycle. The values of resistance (R) and reactance (X) at end expiration and end inspiration and their corresponding differences (R and X) were compared.

MAIN RESULTS

All intra-breath measures exhibited similar mean values at 10 and 11 Hz in each subject; however, the variabilities were higher at 11 Hz, especially for R and X. The poorer quality of the 11 Hz data was primarily caused by the overlapping of modulation side-lobes of adjacent oscillation frequencies. This cross-talk was enhanced by double breathing frequency components due to flow nonlinearities.

SIGNIFICANCE

Retrospective intra-breath assessment of large or special data bases of conventional oscillometry can be performed to better characterise respiratory mechanics in different populations and disease groups. The results also have implications in the optimum design of multiple-frequency oscillometry (avoidance of densely spaced frequencies) and the use of filtering procedures that preserve the intra-breath modulation information.

In asthma positive phase III slopes result from structural heterogeneity of the bronchial tree

We have previously identified bronchial generations 5-7 as the locus of maximum contribution to the convective portion of the phase III slope in CT-based lung models of asthma patients. In the present study, we examined how exactly phase III slope is generated locally, by specifically interrogating at individual branch points, the necessary condition for a phase III slope to occur : some degree of convective flow sequencing between any two daughter branches that have a heterogeneity in gas washout concentration between them. Flow sequencing at individual branch points showed a wide range of values, including branch points where flow sequencing was such that phase III slopes were negative locally. Yet, the net effect in the 24 bronchial trees that we studied was that flow sequencing between least and best ventilated units was of the correct sign to generate a positive phase III slope in generations 5-7. By investigating the link of local flow sequencing between any two daughter branches to the corresponding heterogeneity of mechanical lung properties, heterogeneity of compliance was seen to be a major determinant of flow sequencing. In these structures bronchial structures, compliance heterogeneity was essentially brought about by volume asymmetry resulting from terminating pathways within the 3D confines of the lung contours. We conclude that the serial and parallel combination of lung mechanical properties at individual branch points in an asymmetrical branching network generate flow sequencing in mid-range conductive airways, so as to obtain positive at-mouth phase III slopes.

Intra-breath oscillometry for the evaluation of lung function in children and adolescents with a history of preterm birth

Objective:

To assess respiratory system impedance (Z_rs) and spirometric parameters in children and adolescents with and without a history of preterm birth.

Methods:

We evaluated a sample of 51 subjects between 11 and 14 years of age: 35 who had a history of preterm birth (preterm group) and 16 who had been born at term (full-term group). Lung function was measured by spirometry, spectral oscillometry, and intra-breath oscillometry.

Results:

Neither spirometry nor spectral oscillometry revealed any statistically significant differences between the preterm and full-term groups. However, intra-breath oscillometry demonstrated significant differences between the two groups in terms of the change in resistance, reactance at end-inspiration, and the change in reactance (p < 0.05 for all).

Conclusions:

Our findings suggest that abnormalities in Z_rs persist in children and adolescents with a history of preterm birth and that intra-breath oscillometry is more sensitive than is spectral oscillometry. Larger studies are needed in order to validate these findings and to explore the impact that birth weight and gestational age at birth have on Z_rs later in life.

Lung Function in Preschool Children in Low and Middle Income Countries: An Under-Represented Potential Tool to Strengthen Child Health

BACKGROUND

The burden of respiratory disease is high in low-middle income countries (LMIC). Pulmonary function tests are useful as an objective measure of lung health and to track progression. Spirometry is the commonest test, but its use is limited in preschool children. Other lung function methods have been developed but their use in LMIC has not been well described.

AIM

To review the use of preschool lung function testing in children in LMIC, with particular reference to feasibility and clinical applications.

METHODS

Electronic databases "PubMed", "Scopus"," Web of Science", and "EBSCO host" were searched for publications in low and middle income countries on preschool lung function testing, including spirometry, fractional exhaled nitric oxide (FeNO), oscillometry, interrupter technique, tidal breathing and multiple breath washout (MBW), from 1 January 2011 to 31 January 2022. Papers in English were included and those including only children ≥6 years were excluded.

RESULT

A total of 61 papers from LMIC in Asia, South America, Africa, Eurasia or the Middle East were included. Of these, 40 included spirometry, 7 FeNO, 15 oscillometry, 2 interrupter technique, and 2 tidal breathing. The papers covered test feasibility (19/61), clinical application (46/61) or epidemiological studies (13/61). Lung function testing was successful in preschool children from LMIC. Spirometry was the most technically demanding and success gradually increased with age.

CONCLUSION

Preschool lung function testing is under-represented in LMIC for the burden of respiratory disease. These tests have the potential to strengthen respiratory care in LMIC, however access needs to be improved.

Respiratory Oscillometry in Newborn Infants: Conventional and Intra-Breath Approaches

BACKGROUND

Oscillometry has been employed widely as a non-invasive and standardized measurement of respiratory function in children and adults; however, limited information is available on infants.

AIMS

To establish the within-session variability of respiratory impedance (Zrs), to characterize the degree and profile of intra-breath changes in Zrs and to assess their impact on conventional oscillometry in newborns.

METHODS

109 healthy newborns were enrolled in the study conducted in the first 5 postpartum days during natural sleep. A custom-made wave-tube oscillometry setup was used, with an 8-48 Hz pseudorandom and a 16 Hz sinusoidal signal used for spectral and intra-breath oscillometry, respectively. A resistance-compliance-inertance (R-C-L) model was fitted to average Zrs spectra obtained from successive 30-s recordings. Intra-breath measures, such as resistance (Rrs) and reactance (Xrs) at the end-expiratory, end-inspiratory and maximum-flow points were estimated from three 90-s recordings. All natural and artifact-free breaths were included in the analysis.

RESULTS

Within-session changes in the mean R, C and L values, respectively, were large (mean coefficients of variation: 10.3, 20.3, and 26.6%); the fluctuations of the intra-breath measures were of similar degree (20-24%). Intra-breath analysis also revealed large swings in Rrs and Xrs within the breathing cycle: the peak-to-peak changes amounted to 93% (range: 32-218%) and 41% (9-212%), respectively, of the zero-flow Zrs magnitude.

DISCUSSION

Intra-breath tracking of Zrs provides new insight into the determinants of the dynamics of respiratory system, and highlights the biasing effects of mechanical non-linearities on the average Zrs data obtained from the conventional spectral oscillometry.

Intrabreath oscillometry is a sensitive test for assessing disease control in adults with severe asthma

BACKGROUND

Asthma control is not well reflected by spirometry, yet this is the most frequently used measure of lung function in asthma clinics. Oscillometry is an alternative technique suitable for those with severe asthma.

OBJECTIVE

To investigate usefulness of oscillometry in subjects with severe asthma to determine which outcome variables best reflected asthma control.

METHODS

Adults with severe asthma were recruited from a severe asthma clinic in Brazil. Oscillometry (conventional multifrequency measurements between 6 and 32 Hz; intrabreath tracking at 8 Hz) and spirometry were performed. Asthma control was determined by the asthma control test.

RESULTS

A total of 60 adults were evaluated; mean age was 56.7 years. There was predominance of women (82%), and most patients (63%) reported onset of asthma symptoms in childhood or adolescence. There were no differences between controlled and uncontrolled asthma in spirometry. Uncontrolled asthma was associated with higher resistance (at 8 and 10 Hz) and more negative reactance (for 6, 8, and 10 Hz) (P < .05) on conventional oscillometry. Intrabreath oscillometry revealed significant differences between controlled and uncontrolled patients with asthma (P < .01 for changes in resistance and reactance between end expiration and end inspiration). The accuracy of the lung function tests in discriminating between controlled and uncontrolled asthma was higher for intrabreath variables (area under the curve = 0.65-0.72).

CONCLUSION

Oscillometry, particularly the intrabreath technique, better reflected asthma control than spirometry measures. Our findings suggest that oscillometry may be a useful technique to aid management of severe asthma, with a potential to reflect loss of disease control.

Oscillometry of the respiratory system: a translational opportunity not to be missed

Airway oscillometry has become the de facto standard for quality assessment of lung physiology in laboratory animals and has demonstrated its usefulness in understanding diseases of small airways. Nowadays, it is seeing extensive use in daily clinical practice and research; however, a question that remains unanswered is how well physiological findings in animals and humans correlate? Methodological and device differences are obvious between animal and human studies. However, all devices deliver an oscillated airflow test signal and output respiratory impedance. In addition, despite analysis differences, there are ways to interpret animal and human oscillometry data to allow suitable comparisons. The potential with oscillometry is its ability to reveal universal features of the respiratory system across species, making translational extrapolation likely to be predictive. This means that oscillometry can thus help determine if an animal model displays the same physiological characteristics as the human disease. Perhaps more importantly, it can also be useful to determine whether an intervention is effective as well as to understand if it affects the desired region of the respiratory system, e.g., the periphery of the lung. Finally, findings in humans can also inform preclinical scientists and give indications as to what type of physiological changes should be observed in animal models to make them relevant as models of human disease. The present article will attempt to demonstrate the potential of oscillometry in respiratory research, an area where the development of novel therapies is plagued with a failure rate higher than in other disease areas.

Effect of nasal airway nonlinearities on oscillometric resistance measurements in infants

Oscillometric measurements of respiratory system resistance (R_rs) in infants are usually made via the nasal pathways, which not only significantly contribute to overall R_rs but also introduce marked flow (V')-dependent changes. We employed intrabreath oscillometry in casts of the upper airways constructed from head CT images of 46 infants. We examined oscillometric nasal resistance (R_n) in upper airway casts with no respiratory flow (R₀) and the effect of varying V' on R_n by simulating tidal breathing. A characteristic nonlinear relationship was found between R_n and V', exhibiting segmental linearity and a prominent breakpoint (V'_bp) after log-log transformation. V'_bp was linearly related to the preceding value of end-expiratory volume acceleration (V″_eE; on average r² = 0.96, P < 0.001). R_n depended on V', and R at end-expiration (R_eE) showed a strong dependence on V″_eE in every cast (r² = 0.994, P < 001) with considerable interindividual variability. The intercept of the linear regression of R_eE versus V″_eE was found to be a close estimate of R₀. These findings were utilized in reanalyzed R_rs data acquired in vivo in a small group of infants (n = 15). Using a graphical method to estimate R₀ from R_eE, we found a relative contribution of V'-dependent nonlinearity to total resistance of up to 33%. In conclusion, we propose a method for correcting the acceleration-dependent nonlinearity error in R_eE. This correction can be adapted to estimate R₀ from a single intrabreath oscillometric measurement, which would reduce the masking effects of the upper airways on the changes in the intrathoracic resistance.NEW & NOTEWORTHY Oscillometric measurements of respiratory system resistance (R_rs) in infants are usually made via the nasal pathways, which not only significantly contribute to overall R_rs but also introduce marked flow acceleration-dependent distortions. Here, we propose a method for correcting flow acceleration-dependent nonlinearity error based on in vitro measurements in 3D-printed upper airway casts of infants as well as in vivo measurements. This correction can be adapted to estimate R_rs from a single intrabreath oscillometric measurement.