Comparison of oscillometry devices using active mechanical test loads

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.

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.

How best to choose an oscillometer and reference equations for your patients with asthma

The use of oscillometry has significantly advanced in recent years, thanks to the availability of more robust and portable measurement devices. However, a major drawback is the variability among different devices, which leads to noninterchangeable results. This lack of standardization has prevented the establishment of widely accepted reference equations, complicating the implementation of oscillometry in clinical practice. This review aims to clarify these areas, suggesting the adoption of specific guidelines based on the context.

An update on multiple breath washout in children with cystic fibrosis

INTRODUCTION

Cystic fibrosis (CF) is an autosomal recessive disorder caused by mutations in the CF transmembrane regulator (CFTR) gene, leading to progressive lung disease and systemic complications. Lung disease remains the primary cause of morbidity and mortality, making early detection of lung function decline crucial. The Lung Clearance Index (LCI), derived from the multiple breath washout (MBW) test, has emerged as a sensitive measure for identifying early airway disease.

AREAS COVERED

This review examines the technical aspects and clinical relevance of LCI, its advantages over traditional lung function tests, and its application in CF clinical trials. A focused literature review highlights LCI's utility in evaluating treatment efficacy and its potential integration into routine CF care.

EXPERT OPINION

LCI is more sensitive than spirometry for detecting early lung function decline and is predominantly used in pediatric settings. Its use is expanding in adult CF populations as advances in treatment allow adults to maintain stable lung function. In clinical trials, LCI is widely recognized as an outcome measure. While implemented into clinical care in many centers in Europe, this is not yet the case in North America. Faster testing protocols and point-of-care interpretation tools will support LCI's integration into routine CF monitoring.

Expiratory and inspiratory resistance and reactance from respiratory oscillometry defining expiratory flow limitation in obstructive lung diseases

BACKGROUND

Expiratory flow limitation (EFL) during tidal breathing and lung hyperinflation have been identified as major decisive factors for disease status, prognosis and response to therapy in obstructive lung diseases.

AIM

To investigate the delta values between expiratory and inspiratory resistance and reactance, measured using respiratory oscillometry and its correlation with air trapping and symptoms in subjects with obstructive lung diseases.

METHODS

Four hundred and seventy-one subjects (96 with chronic obstructive pulmonary disease [COPD], 311 with asthma, 30 healthy smokers and 34 healthy subjects) were included. Spirometry, body plethysmography and respiratory oscillometry measurements were performed and the differences between the expiratory and inspiratory respiratory oscillometry values (as delta values) were calculated. Questionnaires regarding symptoms and quality of life were administered.

RESULTS

Patients with COPD and healthy smokers had an increased delta resistance at 5 Hz (R5) compared with patients with asthma (p < 0.0001 and p = 0.037, respectively) and healthy subjects (p = 0.0004 and p = 0.012, respectively). Patients with COPD also had higher values of ΔR5-R19 than healthy subjects (p = 0.0001) and patients with asthma (p < 0.0001). Delta reactance at 5 Hz (X5) was significantly more impaired in COPD patients than in asthma and healthy subjects (p < 0.0001 for all). There was a correlation between the ratio of residual volume and total lung capacity and ΔR5 (p = 0.0047; r = 0.32), ΔR5-R19 (p = 0.0002; r = 0.41) and ΔX5 (p < 0.0001; r = -0.44), for all subjects. ΔX5 correlated with symptoms in COPD, healthy smokers and patients with asthma. In addition, ΔR5 correlated with asthma symptoms.

CONCLUSION

EFL was most prominent in parameters measuring peripheral resistance and reactance and correlated with air trapping and airway symptoms.

Assessment of bronchodilator response in preschoolers: A systematic review

BACKGROUND

Several techniques can be used to assess bronchodilator response (BDR) in preschool-aged children, including spirometry, respiratory oscillometry, the interrupter technique, and specific airway resistance. However, there has not been a systematic comparison of BDR thresholds across studies yet.

METHODS

A systematic review was performed on all studies up to May 2023 measuring a bronchodilator effect in children 2-6 years old using one of these techniques (PROSPERO CRD42021264659). Studies were identified using MEDLINE, Cochrane, EMBASE, CINAHL via EBSCO, Web of Science databases, and reference lists of relevant manuscripts.

RESULTS

Of 1224 screened studies, 43 were included. Over 85% were from predominantly European ancestry populations, and only 22 studies (51.2%) calculated a BDR cutoff based on a healthy control group. Five studies included triplicate testing with a placebo to account for the within-subject intrasession repeatability. A relative BDR was most consistently reported by the included studies (95%) but varied widely across all techniques. Various statistical methods were used to define a BDR, with six studies using receiver operating characteristic analyses to measure the discriminative power to distinguish healthy from wheezy and asthmatic children.

CONCLUSION

A BDR in 2- to 6-year-olds cannot be universally defined based on the reviewed literature due to inconsistent methodology and cutoff calculations. Further studies incorporating robust methods using either distribution-based or clinical anchor-based approaches to define BDR are required.

Oscillometry reference values for children and adolescents

Background

Oscillometry devices allow quantification of respiratory function at tidal breathing but device-specific reference equations are scarce: the present study aims to create sex-specific oscillometric reference values for children and adolescents using the Resmon PRO FULL device.

Methods

Healthy participants (n=981) aged 6 to 17 years of the Austrian LEAD general population cohort were included. Subjects had normal weight (body mass index ≤99th percentile) and normal lung volumes (total lung capacity (TLC) ≥ lower limit of normal). Oscillometry data were collected using a single frequency mode of 8 Hz. Sex-specific prediction equations were developed for total, inspiratory and expiratory resistance (R) and reactance (X) as well as for the modulus of impedance (Z) value using the LMS (lambda, mu, sigma) method. Height was used as a single covariate.

Results

Reference equations for all oscillometry parameters were created for Caucasian children aged 6 to 17 years with a height span from 101 to 183 cm and a lung volume span from 1.7 to 8.8 L TLC. R and Z values progressively decrease and X values increase with increasing height. Oscillometry parameters versus lung volume curves differ from those versus height curves. Stratified for lung size, no sex differences are found for oscillometry parameters.

Conclusion

Our study provides reference values for oscillometry parameters in children and adolescents using strictly defined criteria for weight and lung volumes. No sex-related differences in oscillometry parameters corrected for height or lung size are found.

[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.

Small airway dysfunction measured by impulse oscillometry is associated with exacerbations and poor symptom control in patients with asthma treated in a tertiary hospital subspecialist airways disease clinic

Introduction

Small airways dysfunction contributes to asthma pathophysiology and clinical outcomes including exacerbations and asthma control. Respiratory oscillometry is a simple, non-invasive and effort independent lung function test that provides vital information about small airway function. However, interpretation and clinical utility of respiratory oscillometry has been in part limited by lack of agreed parameters and the respective cutoffs. The aim of this study was to determine the prevalence of small airways dysfunction based on published impulse oscillometry (IOS) definition in patients with asthma referred to a tertiary asthma clinic and the extent to which it correlates with asthma clinical outcomes.

Methods

We retrospectively reviewed the medical records of all patients with asthma managed in the severe asthma clinic between January 2019 and December 2022 who underwent routine lung function tests with oscillometry and spirometry. Small airways dysfunction was determined from various published IOS parameter cutoffs, and the data were analysed to determine correlations between IOS parameters and asthma outcomes.

Results

Amongst the 148 patients, the prevalence of small airways dysfunction ranged from 53% to 78% depending on the defining oscillometry parameter. All oscillometry parameters correlated with the severity of airflow obstruction (FEV1% predicted, p < 0.001). Several oscillometry parameters correlated with asthma symptom burden, the strongest correlation was seen for frequency dependent resistance (R5-R20) with scores of Asthma Control Questionnaire (ACQ6) (Spearman's rank coefficient 0.213, p = 0.028) and Asthma Control Test (ACT) (Spearman's rank coefficient -0.248, p = 0.012). R5-R20 was predictive of poor asthma control defined by ACQ6 >1.5 (OR 2.97, p = 0.022) or ACT <20 (OR 2.44, p = 0.055). Small airways dysfunction defined by R5-R20 and area under the reactance curve (AX) also significantly increases asthma exacerbation risk (OR 2.60, p = 0.02 and OR 2.31, p = 0.03 respectively).

Conclusion

Respiratory oscillometry is a sensitive measure of small airways dysfunction that should complement spirometry in the routine assessment of asthma. Small airways dysfunction is highly prevalent in patients with asthma referred to a tertiary asthma clinic. R5-R20 was the metric most predictive in identifying patients at risk of asthma exacerbations and poor asthma control.

Longitudinal tracking of intrabreath respiratory impedance in preschool children

BACKGROUND

Longitudinal measurements of intrabreath respiratory impedance (Zrs) in preschool-aged children may be able to distinguish abnormal lung function trajectories in children with a history of wheezing compared to healthy ones.

METHODS

Children from a prospective, longitudinal community-based cohort performed annual intrabreath oscillometry (IB-OSC) measurements from age 3- to 7-years. IB-OSC was performed using a single 10 Hz sinusoid while clinically asymptomatic. Linear mixed-effects models were developed to explore the effects of wheezing phenotypes, growth, and sex on seven IB-OSC outcome variables over time: resistance at end-expiration (ReE), resistance at end-inspiration (ReI), the tidal change in resistance (∆R=ReE-ReI), reactance at end-expiration (XeE), reactance at end-inspiration (XeI), the tidal change in reactance (∆X=XeE-XeI), and ∆X normalized by tidal volume (∆X/VT).

RESULTS

Eighty-five children produced 374 acceptable IB-OSC measurements. Subjects were classified into one of three wheeze groups: never (n = 36), transient (n = 34), or persistent (n = 15). After adjusting for height, children with persistent wheezing, compared to those who never wheezed, had +0.814 hPa s L-1 ReE (95% confidence interval [CI] +0.178 to +1.451, p = 0.015), -0.792 hPa s L-1 XeE (95% CI -1.203 to -0.381, p = 0.003), -0.538 hPa s L-1 ∆X (95% CI -0.834 to -0.242, p = 0.007) and -1.672 hPa s L-2 ∆X/VT (95% CI -2.567 to -0.777, p < 0.001). Increasing height had a significant effect on all IB-OSC resistance and reactance variables when adjusted for the effect of preschool wheezing.

CONCLUSIONS

IB-OSC is feasible for tracking lung function growth in preschool-aged children and may allow abnormal lung function to be identified early in asymptomatic preschoolers with a history of persistent wheezing.

Reference Equations for Within-Breath Respiratory Oscillometry in White Adults

BACKGROUND

Within-breath analysis of oscillometry parameters is a growing research area since it increases sensitivity and specificity to respiratory pathologies and conditions. However, reference equations for these parameters in White adults are lacking and devices using multiple sinusoids or pseudorandom forcing stimuli have been underrepresented in previous studies deriving reference equations. The current study aimed to establish reference ranges for oscillometry parameters, including also the within-breath ones in White adults using multi-sinusoidal oscillations.

METHODS

White adults with normal spirometry, BMI ≤30 kg/m2, without a smoking history, respiratory symptoms, pulmonary or cardiac disease, neurological or neuromuscular disorders, and respiratory tract infections in the previous 4 weeks were eligible for the study. Study subjects underwent oscillometry (multifrequency waveform at 5-11-19 Hz, Resmon PRO FULL, RESTECH Srl, Italy) in 5 centers in Europe and the USA according to international standards. The within-breath and total resistance (R) and reactance (X), the resonance frequency, the area under the X curve, the frequency dependence of R (R5-19), and within-breath changes of X (ΔX) were submitted to lambda-mu-sigma models for deriving reference equations. For each output parameter, an AIC-based stepwise input variable selection procedure was applied.

RESULTS

A total of 144 subjects (age 20.8-86.3 years; height 146-193 cm; BMI 17.42-29.98 kg/m2; 56% females) were included. We derived reference equations for 29 oscillatory parameters. Predicted values for inspiratory and expiratory parameters were similar, while differences were observed for their limits of normality.

CONCLUSIONS

We derived reference equations with narrow confidence intervals for within-breath and whole-breath oscillatory parameters for White adults.

The role of oscillometry in asthma

PURPOSE OF REVIEW

Oscillometry is a noninvasive pulmonary function test that has gained significant interest in the evaluation of lung disease. Currently, oscillometry is primarily a research tool, but there is a growing body of evidence supporting its clinical use. This review describes the recent work evaluating the role of oscillometry in the diagnosis and treatment of asthma.

RECENT FINDINGS

A large body of observational data supports the ability of oscillometry to distinguish healthy individuals from those with respiratory symptoms or lung disease. Oscillometry may not be as useful as an isolated diagnostic test in asthma, but the combination with other pulmonary function tests may improve its diagnostic ability. Oscillometry can detect peripheral airways dysfunction in asthma, which is associated with symptoms and the risk for exacerbations. To help guide future research, minimal clinically important differences for specific oscillometry variables have been developed. Oscillometry may be useful in monitoring the response to biological therapy and has potential for personalizing treatment for individual patients. Oscillometry also has potential in uncovering unique aspects of the pathophysiology of asthma in obesity.

SUMMARY

Oscillometry is a promising tool in the diagnosis and management of asthma. More research is needed to support its routine clinical use.

Bronchodilator Efficacy of High-Flow Nasal Cannula in COPD: Vibrating Mesh Nebulizer Versus Jet Nebulizer

BACKGROUND

Jet nebulizers are commonly used for bronchodilator therapy in COPD. High-flow nasal cannula with vibrating mesh nebulizer (HFNC-VMN) is a recently developed system; however, few studies have compared the efficacy of bronchodilator administration via HFNC-VMN to jet nebulizer in stable COPD. This study aimed to compare the effect of salbutamol administered via HFNC-VMN versus jet nebulizer on airway and lung function in subjects with stable COPD.

METHODS

This randomized non-inferiority crossover physiologic study enrolled subjects with stable COPD. Salbutamol was nebulized via HFNC-VMN or jet nebulizer in random order with a 4-h washout period between crossover sequences. Spirometry, lung volume, and impulse oscillometry were performed at baseline and after each intervention. The primary outcome was change in FEV1 from baseline. Secondary outcomes included changes in other respiratory-related parameters and nebulization time compared between the 2 devices.

RESULTS

Seventeen subjects were enrolled. HFNC-VMN and jet nebulizer both significantly improved FEV1 from baseline (P = .005 and P = .002, respectively). The difference between respiratory resistance at 5 Hz and 20 Hz significantly decreased after HFNC-VMN compared to baseline (P = .02), while no significant change was observed after jet nebulizer (P = .056). Area of reactance and resonant frequency of reactance were both significantly decreased (P = .035 and P = .03, respectively), and respiratory reactance at 5 Hz significantly increased (P = .02) in the HFNC-VMN group compared to baseline indicating improved lung mechanics, with no significant changes with the jet nebulizer. HFNC-VMN had a shorter nebulization time (6 [5-9] min vs 20 [16-22] min, respectively, P < .001).

CONCLUSIONS

Bronchodilator therapy via HFNC-VMN was not inferior to jet nebulizer for subjects with stable COPD and can significantly improve airway oscillometry mechanics and decrease nebulization time compared to jet nebulizer.

Association of forced oscillation technique measurements with respiratory system compliance and resistance in a 2-compartment physical model

BACKGROUND

The forced oscillation technique (FOT) may be useful for diagnosis and follow-up of respiratory diseases. It is unclear how global or regional alterations in airway resistance (Raw) and lung compliance (CL) alter FOT measurements.

METHODS

A 2-compartment physical model of the respiratory system allowed to simulate variations in Raw, CL, and their heterogeneity during tidal breathing in an adult human. Five-Hz respiratory system resistance (Rrs5) and reactance (Xrs5), area of reactance (AX), resonance frequency (Fresp) and intrabreath variation in Rrs5 and Xrs5 were measured by FOT. Frequency dependance of resistance could not be studied in this model. Relationships between model characteristics (Raw, CL, and heterogeneity) and FOT measurements were explored by multiple regression.

RESULTS

Rrs5 and intrabreath variation in Rrs5 and Xrs5 strongly associated with model characteristics (R2=0.753, 0.5 and 0.658). Associations of Xrs5, AX, and Fresp with model characteristics were weak (R2=0.214, 0.349 and 0.076). Raw heterogeneity was the main determinant of Rrs5 (Coeff=0.594), AX (Coeff=0.566) and intrabreath variation in Rrs5 and Xrs5 (Coeff=0.586 and 0.732). Regional extremes in Raw strongly determined Rrs5 (Coeff=1.006). Xrs5 did not strongly associate with any model characteristic.

CONCLUSION

Raw heterogeneity and maximal regional Raw were the main determinants of FOT measurements, in particular Rrs5. Associations between CL and FOT measurements were weak.

Reference equations using segmented regressions for impulse oscillometry in healthy subjects aged 2.7-90 years

Background

Published reference equations for impulse oscillometry (IOS) usually encompass a specific age group but not the entire lifespan. This may lead to discordant predicted values when two or more non-coincident equations can be applied to the same person, or when a person moves from one equation to the next non-convergent equation as he or she gets older. Thus, our aim was to provide a single reference equation for each IOS variable that could be applied from infancy to old age.

Methods

This was an ambispective cross-sectional study in healthy nonsmokers, most of whom lived in Mexico City, who underwent IOS according to international standards. A multivariate piecewise linear regression, also known as segmented regression, was used to obtain reference equations for each IOS variable.

Results

In a population of 830 subjects (54.0% female) aged 2.7 to 90 years (54.8% children ≤12 years), segmented regression estimated two breakpoints for age in almost all IOS variables, except for R5-R20 in which only one breakpoint was detected. With this approach, multivariate regressions including sex, age, height and body mass index as independent variables were constructed, and coefficients for calculating predicted value, lower and upper limits of normal, percentage of predicted and z-score were obtained.

Conclusions

Our study provides IOS reference equations that include the major determinants of lung function, i.e. sex, age, height and body mass index, that can be easily implemented for subjects of almost any age.

Oscillometry in Lung Function Assessment: A Comprehensive Review of Current Insights and Challenges

Oscillometry, a non-invasive technique for assessing lung function, has gained significant recognition and importance in modern pulmonary medicine. This comprehensive review thoroughly explores its principles, applications, advantages, limitations, recent innovations, and future directions. Oscillometry's primary strength lies in its ability to offer a holistic assessment of lung mechanics. Unlike traditional spirometry, oscillometry captures the natural airflow during quiet breathing, making it suitable for patients of all ages and those with severe respiratory conditions. It provides a comprehensive evaluation of airway resistance, reactance, and compliance, offering insights into lung function that were previously challenging to obtain. In clinical practice, oscillometry finds extensive application in diagnosing and managing respiratory diseases. It plays a pivotal role in asthma, chronic obstructive pulmonary disease (COPD), and interstitial lung diseases. By detecting subtle changes in lung function before symptoms manifest, oscillometry facilitates early interventions, improving disease management and patient outcomes. Oscillometry's non-invasive and patient-friendly nature is precious in pediatric care, where traditional spirometry may be challenging for young patients. It aids in diagnosing and monitoring pediatric respiratory disorders, ensuring that children receive the care they need from an early age. Despite its many advantages, oscillometry faces challenges, such as the need for standardized protocols and the complexity of data interpretation. However, ongoing efforts to establish global standards and provide education and training for healthcare professionals aim to address these issues. Looking ahead, oscillometry holds great promise in the field of personalized medicine. With its ability to tailor treatment plans based on individualized lung function data, healthcare providers can optimize therapy selection and dosing, ultimately improving patient care and quality of life. In conclusion, oscillometry is poised to play an increasingly pivotal role in modern pulmonary medicine. As standardization efforts continue and technology evolves, it is an indispensable tool in the clinician's arsenal for diagnosing, managing, and personalizing respiratory care, ultimately leading to improved patient outcomes and better respiratory health.

Multiple breath washout and oscillometry after allogenic HSCT: a scoping review

Pulmonary chronic graft-versus-host disease (cGVHD) is a substantial cause of pulmonary morbidity and mortality post-haematopoietic stem cell transplantation (HSCT). Current spirometry-based monitoring strategies have significant limitations. Understanding the utility of novel peripheral airway function tests - multiple breath washout (MBW) and oscillometry - is critical in efforts to improve detection, facilitate earlier intervention and improve outcomes. In this scoping review, we identified 17 studies investigating MBW or oscillometry, or both, after allogenic HSCT. Despite small study numbers limiting the ability to draw firm conclusions, several themes were evident. Detectable peripheral airway abnormality in MBW occurred in a substantial proportion prior to HSCT. MBW indices post-HSCT were more frequently abnormal than spirometry when reporting group data and among those with extrapulmonary cGVHD and pulmonary cGVHD. Changes in MBW indices over time may be more indicative of pulmonary complications than absolute values at any given time point. Oscillometry indices were often normal at baseline, but more frequently abnormal in those who developed pulmonary cGVHD. Pooling currently available individual participant data across these studies may improve our ability to formally compare their respective sensitivity and specificity at specific time points and assess the trajectory of MBW and oscillometry indices over time.

Small airways in asthma: Pathophysiology, identification and management

Background

The aim of this review is to summarize the current evidence regarding small airway disease in asthma, focusing on recent advances in small airway pathophysiology, assessment and therapeutic implications.

Methods

A search in Medline was performed, using the keywords "small airways", "asthma", "oscillometry", "nitrogen washout" and "imaging". Our review was based on studies from adult asthmatic patients, although evidence from pediatric populations is also discussed.

Results

In asthma, inflammation in small airways, increased mucus production and airway wall remodelling are the main pathogenetic mechanisms of small airway disease. Small airway dysfunction is a key component of asthma pathophysiology, leading to increased small airway resistance and airway closure, with subsequent ventilation inhomogeneities, hyperresponsiveness and airflow limitation. Classic tests of lung function, such as spirometry and body plethysmography are insensitive to detect small airway disease, providing only indirect measurements. As discussed in our review, both functional and imaging techniques that are more specific for small airways, such as oscillometry and the multiple breath nitrogen washout have delineated the role of small airways in asthma. Small airways disease is prevalent across all asthma disease stages and especially in severe disease, correlating with important clinical outcomes, such as asthma control and exacerbation frequency. Moreover, markers of small airways dysfunction have been used to guide asthma treatment and monitor response to therapy.

Conclusions

Assessment of small airway disease provides unique information for asthma diagnosis and monitoring, with potential therapeutic implications.

Intra-subject variability in oscillometry correlates with acute rejection and CLAD post-lung transplant

Background

Chronic lung allograft dysfunction (CLAD) is the major cause of death post-lung transplantation, with acute cellular rejection (ACR) being the biggest contributing risk factor. Although patients are routinely monitored with spirometry, FEV₁ is stable or improving in most ACR episodes. In contrast, oscillometry is highly sensitive to respiratory mechanics and shown to track graft injury associated with ACR and its improvement following treatment. We hypothesize that intra-subject variability in oscillometry measurements correlates with ACR and risk of CLAD.

Methods

Of 289 bilateral lung recipients enrolled for oscillometry prior to laboratory-based spirometry between December 2017 and March 2020, 230 had ≥ 3 months and 175 had ≥ 6 months of follow-up. While 37 patients developed CLAD, only 29 had oscillometry at time of CLAD onset and were included for analysis. These 29 CLAD patients were time-matched with 129 CLAD-free recipients. We performed multivariable regression to investigate the associations between variance in spirometry/oscillometry and the A-score, a cumulative index of ACR, as our predictor of primary interest. Conditional logistic regression models were built to investigate associations with CLAD.

Results

Multivariable regression showed that the A-score was positively associated with the variance in oscillometry measurements. Conditional logistic regression models revealed that higher variance in the oscillometry metrics of ventilatory inhomogeneity, X5, AX, and R5-19, was independently associated with increased risk of CLAD (p < 0.05); no association was found for variance in %predicted FEV₁.

Conclusion

Oscillometry tracks graft injury and recovery post-transplant. Monitoring with oscillometry could facilitate earlier identification of graft injury, prompting investigation to identify treatable causes and decrease the risk of CLAD.

Quality control in respiratory oscillometry: reproducibility measures ignoring reactance?

This study demonstrates the inadequacy of the current technical standards of oscillometry that are based on the within-trial reproducibility of the lowest-frequency R_rs, and suggests the use of a simple variability measure encompassing both R_rs and X_rs https://bit.ly/3AYRid6.

Assessing the prognostic value of respiratory oscillometry in patients with difficult-to-treat asthma

Respiratory oscillometry is widely explored in asthma management; however, there is currently no consensus on its routine work-up in patients with difficult-to-treat asthma. We conducted a retrospective, cross-sectional study involving patients with difficult-to-treat asthma at Asia University Hospital between January 2017 and October 2020. We aimed to correlate clinical significance of respiratory oscillometry and asthma treatment outcomes including symptoms control and exacerbation in patients with difficult-to-treat asthma. Among the 69 patients enrolled in the study, a total of 26.1% of the patients experienced at least one severe or two moderate exacerbations. Patients with ACT < 20 presented a higher prevalence of higher frequency-dependent resistance (FDR; the difference in resistance at 5 Hz and 20 Hz) and frequency of resonance (Fres) than those with ACT ≥ 20. In the multivariable analysis, comorbidities, COPD or allergic rhinitis, and FDR were independent factors in increasing the odds ratio in poorly controlled asthma. (FDR ≥ 0.10 vs. < 0.10, adjusted ORR = 5.05, P = 0.037) There was a higher proportion of frequent exacerbations in patients with higher FDR (FDR ≥ 0.10 vs. < 0.10 = 30.0%:20.7%), but IOS parameters failed to predict frequent exacerbations on further analysis. FDR may be a potential clinical parameter for predicting symptom control in patients with difficult-to-treat asthma.

Lung Function Reference Equations for Indian Ethnic Groups Based on a Handheld Forced Oscillation Device for Age 9-19 Years

OBJECTIVE

To develop regression equations to predict forced oscillation technique (FOT) parameters in Indian children and adolescents.

METHODS

Lung function was assessed in a multigeographic cohort of residential school children using a portable FOT-based device (PulmoScan) and spirometry. FOT measurements were performed in 1497 study participants, aged 9-19 y, from 8 Indian districts. Bland-Altman analysis was performed for additional 32 adult subjects to compare the results of PulmoScan to a standard IOS device in an outpatient setting. Reference equations were developed for R_rs and X_rs from the data of healthy subjects with normal spirometry using multivariate regression model for Indo-European, Dravidian, and mixed ethnic groups.

RESULTS

X5 (bias = 0.02) showed a better agreement than resistance parameters (R5 bias = 0.75, R20 bias =  -0.22) in IOS/PulmoScan comparison. Anthropometric variables (age, height, and weight) were positively correlated with reactance (X5) and negatively with resistance parameters (R5, R10, R15, and R20), with most associations being stronger in boys. Final regression model considered ethnicity as a key determinant along with anthropometry.

CONCLUSION

Multiethnic reference equations were developed for Indian children aged 9-19 y based on a novel handheld FOT device.

Airwave oscillometry and spirometry in children with asthma or wheeze

OBJECTIVE

Lung function testing is used in diagnosing asthma and assessing asthma control. Spirometry is most commonly used, but younger children can find performing this test challenging. Non-volitional tests such as airwave oscillometry (AOS) may be helpful in that population. We compared the success of spirometry and AOS in assessing bronchodilator responsiveness in children.

METHODS

AOS was conducted alongside routine lung function testing. Resistance at 5 Hz (R5), the difference between the resistance at 5 and 20 Hz (R5-20) and the area under the reactance curve (AX) were assessed. Patients between 5 and 16 years old attending clinic with wheeze or asthma were assessed. Patients performed AOS, followed by spirometry and were then given 400 µg salbutamol; the tests were repeated 15 minutes later.

RESULTS

Lung function testing was performed in 47 children of whom 46 (98%) and 32 (68%) performed acceptable baseline oscillometry and spirometry, respectively (p < 0.001). Children unable to perform acceptable spirometry were younger (7.35, range: 5.4-10.3 years) than those who could (10.4, range: 5.5-16.9 years), p < 0.001. The baseline z-scores of AOS R5 correlated with FEV₁ (r = 0.499, p = 0.004), FEF₇₅ (r = 0.617, p < 0.001), and FEV₁/FVC (r = 0.618, p < 0.001). There was a positive bronchodilator response assessed by spirometry (change in FEV₁ ≥ 12%) in eight children which corresponded to a change in R5 of 36% (range: 30%-50%) and a change in X5 of 39% (range: 15%-54%).

CONCLUSIONS

Oscillometry is a useful adjunct to spirometry in assessing young asthmatic children's lung function. The degree of airway obstruction, however, might affect the comparability of the results of the two techniques.

Reference equations for oscillometry and their differences among populations: a systematic scoping review

Respiratory oscillometry is gaining global attention over traditional pulmonary function tests for its sensitivity in detecting small airway obstructions. However, its use in clinical settings as a diagnostic tool is limited because oscillometry lacks globally accepted reference values. In this scoping review, we systematically assessed the differences between selected oscillometric reference equations with the hypothesis that significant heterogeneity existed between them. We searched bibliographic databases, registries and references for studies that developed equations for healthy adult populations according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. A widely used Caucasian model was used as the standard reference and compared against other models using Bland-Altman and Lin's concordance correlational analyses. We screened 1202 titles and abstracts, and after a full-text review of 67 studies, we included 10 in our analyses. Of these, three models had a low-to-moderate agreement with the reference model, particularly those developed from non-Caucasian populations. Although the other six models had a moderate-to-high agreement with the standard model, there were still significant sex-specific variations. This is the first systematic analysis of the heterogeneity between oscillometric reference models and warrants the validation of appropriate equations in clinical applications of oscillometry to avoid diagnostic errors.

Reference values for respiratory sinusoidal oscillometry in children aged 3 to 17 years

BACKGROUND

New oscillometry devices allowing quantification of respiratory function using tidal breathing are commercially available, but reference equations are lacking for the multiethnic Canadian pediatric population.

METHODS

We conducted a prospective cross-sectional study of healthy children carefully selected for absence of asthma, atopy, tobacco smoke, obesity, prematurity, and recent respiratory infection. Triplicate measures were obtained of respiratory system resistance (Rrs) and reactance (Xrs), area under the reactance curve (AX) and resonant frequency (Fres) on four signals, whose testing order was randomized: two signals on the Resmon Pro Full (8 Hz and 5-11-19 Hz) and two signals on the tremoflo C-100 (5-37 Hz and 7-41 Hz). Feasibility was defined as the ability to obtain valid reproducible results. Prediction equations and 95% confidence intervals were derived for whole- and within-breath Rrs and Xrs and for AX and Fres, using linear regression or Generalized Additive Models for Location, Scale and Shape.

RESULTS

Of 306 children randomized, valid and reproducible results on ≥1 signal were obtained in 299 (98%) multiethnic (69% Caucasians: 8% Black: 23% Others) children aged 3-17 years, 91-189 cm tall. Standing height was the strongest predictor with no significant effect of sex, age, body mass index or ethnicity. Significant within-patient differences were observed between Resmon Pro and tremoflo C-100 measurements, justifying the derivation of device-specific reference equations.

CONCLUSION

Valid reproducible oscillometry measurements are highly feasible in children aged 3 years and older. Device-specific reference equations, valid for our multiethnic population, are derived.

An analysis of alternative forced oscillation technique reporting and validation methods for within- and between-sessions in healthy adults

Forced oscillation technique (FOT) provides unique information on respiratory system mechanical properties complementing pulmonary function testing. However, a lack of evidence guiding acquisition/reporting of parameters has slowed clinical FOT adoption. Current European Respiratory Society (ERS) standards recommend 3-5 trials per session comprising three trials with a coefficient of variation (CoV) ≤ 10% for low-frequency resistance. We present an analysis of different combinations of trial selection methods and session validity thresholding variables (low- and mid-frequency resistance and reactance [R5, R19, X5], low-frequency reactance area [AX] and tidal volume) comparing proportion of subjects achieving valid data across two test sessions (7 ± 3 days apart) and within and between session measurement variabilities. 126 (98%) subjects achieved valid data across both sessions (2666 trials). With R5 or R19 as criteria and selection of any three trials from ≥ 4 attempts, ≥ 75% of subjects achieved validity. Furthermore, with R5 or R19 criteria and selection of any trials from ≥ 5 attempts, CoVs for resistance outcomes were reduced within session while variabilities of FOT outcomes between sessions remained consistent. Within session differences in measurement variabilities were not clinically meaningful. Our analyses support current ERS reporting recommendations for healthy adults. Future work should apply this analytic approach to patient populations.

Correlation of respiratory oscillometry with CT image analysis in a prospective cohort of idiopathic pulmonary fibrosis

Background

Markers of idiopathic pulmonary fibrosis (IPF) severity are based on measurements of forced vital capacity (FVC), diffusing capacity (DLCO) and CT. The pulmonary vessel volume (PVV) is a novel quantitative and independent prognostic structural indicator derived from automated CT analysis. The current prospective cross-sectional study investigated whether respiratory oscillometry provides complementary data to pulmonary function tests (PFTs) and is correlated with PVV.

Methods

From September 2019 to March 2020, we enrolled 89 patients with IPF diagnosed according to international guidelines. We performed standard spectral (5–37 Hz) and novel intrabreath tracking (10 Hz) oscillometry followed by PFTs. Patients were characterised with the gender-age-physiology (GAP) score. CT images within 6 months of oscillometry were analysed in a subgroup (26 patients) using automated lung texture analysis. Correlations between PFTs, oscillometry and imaging variables were investigated using different regression models.

Findings

The cohort (29F/60M; age=71.7±7.8 years) had mild IPF (%FVC=70±17, %DLCO=62±17). Spectral oscillometry revealed normal respiratory resistance, low reactance, especially during inspiration at 5 Hz (X5in), elevated reactance area and resonance frequency. Intrabreath oscillometry identified markedly low reactance at end-inspiration (XeI). XeI and X5in strongly correlated with FVC (r²=0.499 and 0.435) while XeI was highly (p=0.004) and uniquely correlated with the GAP score. XeI and PVV exhibited the strongest structural-functional relationship (r²=0.690), which remained significant after adjusting for %FVC, %DLCO and GAP score.

Interpretation

XeI is an independent marker of IPF severity that offers additional information to standard PFTs. The data provide a cogent rationale for adding oscillometry in IPF assessment.

Clinical significance and applications of oscillometry

Recently, “Technical standards for respiratory oscillometry” was published, which reviewed the physiological basis of oscillometric measures and detailed the technical factors related to equipment and test performance, quality assurance and reporting of results. Here we present a review of the clinical significance and applications of oscillometry. We briefly review the physiological principles of oscillometry and the basics of oscillometry interpretation, and then describe what is currently known about oscillometry in its role as a sensitive measure of airway resistance, bronchodilator responsiveness and bronchial challenge testing, and response to medical therapy, particularly in asthma and COPD. The technique may have unique advantages in situations where spirometry and other lung function tests are not suitable, such as in infants, neuromuscular disease, sleep apnoea and critical care. Other potential applications include detection of bronchiolitis obliterans, vocal cord dysfunction and the effects of environmental exposures. However, despite great promise as a useful clinical tool, we identify a number of areas in which more evidence of clinical utility is needed before oscillometry becomes routinely used for diagnosing or monitoring respiratory disease.

This paper provides a current review of the interpretation, clinical significance and application of oscillometry in respiratory medicine, with special emphasis on limitations of evidence and suggestions for future research.https://bit.ly/3GQPViA

A portable fan-based device for evaluating lung function in horses by the forced oscillation technique

OBJECTIVE

The assessment of lung mechanics in horses is nowadays based on invasive methods that may require sedation. The forced oscillation technique (FOT) allows the non-invasive assessment of respiratory mechanics during spontaneous breathing, but current devices are complex, cumbersome, expensive, and difficult to be applied in horses.

APPROACH

We developed a portable FOT device based on a novel approach in which the pressure waveforms are generated by a servo-controlled ducted fan. This new approach allows the design of devices that are more sturdy, compact, and portable compared to already existing approaches. The prototype includes 1) a small microcontroller-based electronic board for controlling the fan and measuring flow and pressure and 2) an optimized data processing algorithm.

MAIN RESULTS

This device provides a maximum error of 0.06 cmH2O∙s/L and 0.15 cmH2O∙s/L in measuring respiratory resistance and reactance during in-vitro validation. A pilot study was also performed on three healthy horses and three horses with severe equine asthma (SEA) and it demonstrated good tolerability and feasibility of the new device. Total respiratory system resistance (Rrs) and reactance (Xrs) significantly differed (p<0.05) between groups. At 5Hz, Rrs was 0.66±0.02 cmH2O∙s/L and 0.94±0.07 cmH2O∙s/L in healthy and in SEA, respectively. Xrs 0.38±0.02 cmH2O∙s/L and -0.27±0.05 cmH2O∙s/L.

SIGNIFICANCE

This novel approach for applying FOT allowed the development of a small, affordable and portable device for the non-invasive evaluation of respiratory mechanics in spontaneously breathing horses, providing a useful new tool for improving veterinary respiratory medicine. Moreover, our results provide supporting evidence of the value of this novel approach for developing portable FOT devices also for applications in humans.

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.

Exploring the 175-year history of spirometry and the vital lessons it can teach us today

175 years have elapsed since John Hutchinson introduced the world to his version of an apparatus that had been in development for nearly two centuries, the spirometer. Though he was not the first to build a device that sought to measure breathing and quantify the impact of disease and occupation on lung function, Hutchison coined the terms spirometer and vital capacity that are still in use today, securing his place in medical history. As Hutchinson envisioned, spirometry would become crucial to our growing knowledge of respiratory pathophysiology, from Tiffeneau and Pinelli's work on forced expiratory volumes, to Fry and Hyatt's description of the flow-volume curve. In the 20th century, standardization of spirometry further broadened its reach and prognostic potential. Today, spirometry is recognized as essential to respiratory disease diagnosis, management and research. However, controversy exists in some of its applications, uptake in primary care remains sub-optimal and there are concerns related to the way in which race is factored into interpretation. Moving forward, these failings must be addressed, and innovations like Internet-enabled portable spirometers may present novel opportunities. We must also consider the physiologic and practical limitations inherent to spirometry and further investigate complementary technologies such as respiratory oscillometry and other emerging technologies that assess lung function. Through an exploration of the storied history of spirometry, we can better contextualize its current landscape and appreciate the trends that have repeatedly arisen over time. This may help to improve our current use of spirometry and may allow us to anticipate the obstacles confronting emerging pulmonary function technologies.

Small Airways Response to Bronchodilators in Adults with Asthma or COPD: A Systematic Review

BACKGROUND

Bronchodilator responsiveness (BDR) is commonly used in the diagnosis of lung disease. Although small airways dysfunction is a feature of asthma and COPD, physiological tests of small airways are not included in guidelines for BDR testing. This systematic review assessed the current evidence of BDR using small airways function in asthma and COPD.

METHODS

The systematic review used standard methodology with the protocol prospectively registered on PROSPERO (CRD42020164140). Electronic medical databases (EMBASE and Medline) were searched using related keywords. Abstracts and full texts were screened independently by two reviewers. Studies that reported the change of physiological small airways function and FEV₁ were included in the review. The revised Cochrane risk of bias tool for RCT and NIH quality assessment tool for cohort and cross-sectional studies were used to evaluate the studies.

RESULTS

A total of 934 articles were identified, with 12 meeting the inclusion criteria. Ten studies included asthma patients, 1 study included COPD patients and 1 study included both asthma and COPD. A total of 1104 participants were included, of whom 941 were asthmatic, 64 had COPD and 109 were healthy controls. Studies were heterogeneous in design including the device, dose and time intervals for BDR assessment. A small airway BDR was seen for most tests in asthma and COPD, including oscillometry (R5-20, reactance (X5), area of reactance (AX) and resonant frequency (Fres)) and Maximal Mid Expiratory Flow.

CONCLUSION

There is a measurable BDR in the small airways. However, with no consensus on how to assess BDR, studies were heterogeneous. Further research is needed to inform how BDR should be assessed, its clinical impact and place in routine clinical practice.

Normal limits for oscillometric bronchodilator responses and relationships with clinical factors

Introduction

We aimed to determine normal thresholds for positive bronchodilator responses for oscillometry in an Australian general population sample aged ≥40 years, to guide clinical interpretation. We also examined relationships between bronchodilator responses and respiratory symptoms, asthma diagnosis, smoking and baseline lung function.

Methods

Subjects recruited from Sydney, Melbourne and Busselton, Australia, underwent measurements of spirometry, resistance (R_rs6) and reactance (X_rs6) at 6 Hz, before and after inhalation of salbutamol 200 μg. Respiratory symptoms and/or medication use, asthma diagnosis, and smoking were recorded. Threshold bronchodilator responses were defined as the fifth percentile of decrease in R_rs6 and 95th percentile increase in X_rs6 in a healthy subgroup.

Results

Of 1318 participants, 1145 (570 female) were analysed. The lower threshold for ΔR_rs6 was −1.38 cmH₂O·s·L⁻¹ (−30.0% or −1.42 Z-scores) and upper threshold for ΔX_rs6 was 0.57 cmH₂O·s·L⁻¹ (1.36 Z-scores). Respiratory symptoms and/or medication use, asthma diagnosis, and smoking all predicted bronchodilator response, as did baseline oscillometry and spirometry. When categorised into clinically relevant groups according to those predictors, ΔX_rs6 was more sensitive than spirometry in smokers without current asthma or chronic obstructive pulmonary disease (COPD), ∼20% having a positive response. Using absolute or Z-score change provided similar prevalences of responsiveness, except in COPD, in which responsiveness measured by absolute change was twice that for Z-score.

Discussion

This study describes normative thresholds for bronchodilator responses in oscillometry parameters, including intra-breath parameters, as determined by absolute, relative and Z-score changes. Positive bronchodilator response by oscillometry correlated with clinical factors and baseline function, which may inform the clinical interpretation of oscillometry.

Normative values for bronchodilator responses measured by oscillometry were derived. Responsiveness related to clinical factors and baseline function. Reactance was more sensitive in detecting bronchodilator response than spirometry mild airways disease.https://bit.ly/3wtWVeV

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.

Within-session reproducibility of forced oscillometry

BACKGROUND

The forced oscillation technique (FOT) provides detailed information about the mechanics of the respiratory system, while requiring minimal co-operation by the patient. FOT may be abnormal in subjects with normal spirometry and appears to be more closely related to airway symptoms. It is, therefore, attractive in epidemiological studies, where a large number of different examinations are made in each subjects in a short period of time. Current technical standards recommend the mean of three consecutive measurements to be used, but there is limited information regarding within-session variability of FOT measurements.

OBJECTIVE

The purpose of this study was to examine the within-session variability in FOT measurements in a large, population-based sample.

METHODS

We performed three consecutive FOT measurements in 700 subjects using the impulse oscillometry system. The first measurement was compared to the mean of three measurements for resistance at 5 and 20 Hz (R5 and R20, respectively), R5-R20, reactance at 5 Hz (X5) and resonant frequency (f_res ).

RESULTS

The differences between the first and the mean of three measurements (median, interquartile range) were minimal, for example 0.002, -0.008 to 0.014 kPa L^-1  s for R5 and -0.001, -0.008 to 0.005 kPa L^-1  s for X5. Findings were numerically similar for men and women as well as for subjects with and without airflow obstruction at spirometry.

CONCLUSIONS

We conclude that, whereas in clinical situations, three FOT measurements are to be preferred, a single measurement may suffice in epidemiological studies.

Measuring the mechanical input impedance of the respiratory system with breath-driven flow oscillations

In recent years, the mechanical input impedance of the respiratory system (Z_rs) determined using the technique known as oscillometry has been gaining traction as a clinical diagnostic tool to complement conventional spirometry. Nevertheless, despite currently approved oscillometry devices being relatively compact and portable, they are still too heavy and bulky to be used in an ambulatory hands-free setting, mostly because of the mass of the motor and power supply. We therefore explored the possibility of using the subject's own respiratory musculature as the power source for creating flow oscillations at the mouth. We measured reference Z_rs in 8 normal volunteers by having them breathe tidally into a piston-driven oscillator powered by an external motor. We fit the measured Z_rs to the single-compartment model of the respiratory system characterized by the three parameters resistance (R_rs), elastance (E_rs), and inertance (I_rs). We then compared these parameter values to those obtained with two commercially available mucus-clearing devices that generate oscillations when expiratory flow drives a flapper valve. The estimates of R_rs agreed mostly within ±1 cmH₂O·s·L^-1, which is usefully accurate for most clinical needs. E_rs and I_rs agreed less well because the breath-driven oscillators provided data at essentially a single frequency close to the resonant frequency of the respiratory system. Nevertheless, we conclude that perturbing respiratory airflow and pressure with a breath-driven oscillator has the potential to provide measurements of Z_rs, possibly serving as the basis for a lightweight ambulatory oscillometry system.NEW & NOTEWORTHY The technique of oscillometry for measuring the mechanical input impedance of the respiratory system is gaining traction as a clinical diagnostic tool, but the portability of existing commercially available devices is limited by the size and weight of oscillator motors and power supplies. We show that impedance can be measured by oscillations in mouth pressure and flow generated by mucus-clearing devices that are powered by the subject's own respiratory flow.

Respiratory impedance measured using impulse oscillometry in a healthy urban population

This study derives normative prediction equations for respiratory impedance in a healthy asymptomatic urban population using an impulse oscillation system (IOS). In addition, this study uses body mass index (BMI) in the equations to describe the effect of obesity on respiratory impedance.

Data from an urban population comprising 472 healthy asymptomatic subjects that resided or worked in lower Manhattan, New York City were retrospectively analysed. This population was the control group from a previously completed case–control study of the health effects of exposure to World Trade Center dust. Since all subjects underwent spirometry and oscillometry, these previously collected data allowed a unique opportunity to derive normative prediction equations for oscillometry in an urban, lifetime non-smoking, asymptomatic population without underlying respiratory disease.

Normative prediction equations for men and women were successfully developed for a broad range of respiratory oscillometry variables with narrow confidence bands. Models that used BMI as an independent predictor of oscillometry variables (in addition to age and height) demonstrated equivalent or better fit when compared with models that used weight. With increasing BMI, resistance and reactance increased compatible with lung and airway compression from mass loading.

This study represents the largest cohort of healthy urban subjects assessed with an IOS device. Normative prediction equations were derived that should facilitate application of IOS in the clinical setting. In addition, the data suggest that modelling of lung function may be best performed using height and BMI as independent variables rather than the traditional approach of using height and weight.

Prediction equations for respiratory impedance were derived in an urban cohort incorporating the effects of mass loading from obesity. Urban exposures had minimal effect on impedance allowing application of the equations to a broad range of populations.https://bit.ly/3a3zZvd

The diagnosis of asthma. Can physiological tests of small airways function help?

Asthma is a common, chronic, and heterogeneous disease with a global impact and substantial economic costs. It is also associated with significant mortality and morbidity and the burden of undiagnosed asthma is significant. Asthma can be difficult to diagnose as there is no gold standard test and, while spirometry is central in diagnosing asthma, it may not be sufficient to confirm or exclude the diagnosis. The most commonly reported spirometric measures (forced expiratory volume in one second (FEV₁) and forced vital capacity assess function in the larger airways. However, small airway dysfunction is highly prevalent in asthma and some studies suggest small airway involvement is one of the earliest disease manifestations. Moreover, there are new inhaled therapies with ultrafine particles that are specifically designed to target the small airways. Potentially, tests of small airways may more accurately diagnose early or mild asthma and assess the response to treatment than spirometry. Furthermore, some assessment techniques do not rely on forced ventilatory manoeuvres and may, therefore, be easier for certain groups to perform. This review discusses the current evidence of small airways tests in asthma and future research that may be needed to further assess their utility.

Addressing Reduced Laboratory-Based Pulmonary Function Testing During a Pandemic

To reduce the spread of the severe acute respiratory syndrome coronavirus 2, many pulmonary function testing (PFT) laboratories have been closed or have significantly reduced their testing capacity. Because these mitigation strategies may be necessary for the next 6 to 18 months to prevent recurrent peaks in disease prevalence, fewer objective measurements of lung function will alter the diagnosis and care of patients with chronic respiratory diseases. PFT, which includes spirometry, lung volume, and diffusion capacity measurement, is essential to the diagnosis and management of patients with asthma, COPD, and other chronic lung conditions. Both traditional and innovative alternatives to conventional testing must now be explored. These may include peak expiratory flow devices, electronic portable spirometers, portable exhaled nitric oxide measurement, airwave oscillometry devices, and novel digital health tools such as smartphone microphone spirometers and mobile health technologies along with integration of machine learning approaches. The adoption of some novel approaches may not merely replace but could improve existing management strategies and alter common diagnostic paradigms. With these options comes important technical, privacy, ethical, financial, and medicolegal barriers that must be addressed. However, the coronavirus disease 19 pandemic also presents a unique opportunity to augment conventional testing by including innovative and emerging approaches to measuring lung function remotely in patients with respiratory disease. The benefits of such an approach have the potential to enhance respiratory care and empower patient self-management well beyond the current global pandemic.

Lung Function Assessment by Impulse Oscillometry in Adults

Over the past decades, impulse oscillometry (IOS) has gained ground in the battery of pulmonary function tests. Performing the test requires minimal cooperation of the patient; therefore, it is a useful tool, especially in evaluating lung mechanics in children, elderly patients, and those who cannot perform spirometry. Oscillometry has also been used in both clinical and research departments. Studies were published mainly in asthma regarding detection of bronchodilator response and the therapeutic response to different drugs. Furthermore, it has been shown to be a sensitive technique to evaluate disease control. Other studied diseases were COPD, interstitial lung diseases, small airway disease, impairment of lung function due to exposure to occupational hazards or smoking, central airways obstruction, cystic fibrosis, monitoring lung mechanics during mechanical ventilation and sleep, neuromuscular diseases, lung transplant, and graft function. The aim of this review is to present the utility of oscillometry on the previously mentioned clinical fields.

A Systematic Review of the Use of Physiological Tests Assessing the Acute Response to Treatment During Exacerbations of COPD (with a Focus on Small Airway Function)

Exacerbations are prevalent in Chronic Obstructive Pulmonary Disease (COPD) patients and associated with poor clinical outcomes. Currently, there is a lack of sensitive and specific tools that can objectively identify exacerbations and assess their progress or treatment response. FEV₁ is often reported as a study outcome, but it has significant limitations. Studies have suggested that small airways measures might provide physiological biomarkers during exacerbations. Therefore, this study was done to assess which physiological tests of small airways function have been used in the acute setting during exacerbations of COPD and the evidence to support their use. An electronic databases search was conducted in April 2019. A standard systematic review methodology was used. Eligible studies were those of ≥10 participants that compared at least one small airway test with FEV₁ to assess response to treatment with baseline and a follow-up measurement ≤2 months after. Analyses were narrative. Of 1436 screened studies, seven studies were eligible. There was heterogeneity in which tests of small airways were used and three different small airways measures were reported. Studies were small (including 20 to 87 subjects). Six articles reported improvements in small airway measurements during the recovery from exacerbation which correlated with FEV₁. Included studies varied in their timing and duration of the assessment. There is some evidence to support the use of small airway tests in acute exacerbations of COPD. However, studies have been small with different tests being utilized. Further studies to determine the usefulness of each test may be of interest.

Clinical Application of Forced Oscillation Technique (FOT) in Early Detection of Airway Changes in Smokers

The forced oscillation technique (FOT) is a non-invasive method to assess airway function by emitting oscillatory signals into the respiratory tract during tidal ventilation. This opinion piece discusses the current use, trialled modification and future directions in utilizing FOT as a novel diagnostic tool for early detection of small airway changes in smokers. The published evidence to date has shown that FOT parameters could be a sensitive diagnostic tool to detect early respiratory changes in smokers. Multiple frequencies and the frequency dependence of resistance and reactance can provide the most valuable and early information regarding smoking induced changes in airways. Considering its non-invasiveness, lower level of discomfort to patients than spirometry, feasibility, and cost effectiveness, it could be the first-choice diagnostic technique for detection of early respiratory changes in smokers. The finding of FOT could further be supported and correlated with inflammatory markers.