Procedures to improve the repeatability of forced oscillation measurements in school-aged children

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.

Ultrafine particle exposure and biomarkers of effect on small airways in children

The small size and large surface area of ultrafine particles (UFP) enhance their ability to deposit in the lung periphery and their reactivity. The Ultrafine Particles from Traffic Emissions and Children's Health (UPTECH) cross-sectional study was conducted in 8-11-year-old schoolchildren attending 25 primary (elementary) schools, randomly selected from the Brisbane Metropolitan Area, Queensland, Australia. Main study findings outlined indirect evidence of distal airway deposition (raised C reactive protein) but as yet, there is no direct evidence in the literature of effects of UFP exposure on peripheral airway function. We present further UPTECH study data from two sensitive peripheral airway function tests, Oscillometry and Multiple Breath Nitrogen Washout (MBNW), performed in 577 and 627 children (88% and 96% of UPTECH study cohort) respectively: mean(SD) age 10.1(0.9) years, 46% male, with 50% atopy and 14% current asthma. Bayesian generalised linear mixed effects regression models were used to estimate the effect of UFP particle number count (PNC) exposure on key oscillometry (airway resistance, (Rrs), and reactance, (Xrs)) and MBNW (lung clearance index, (LCI) and functional residual capacity, (FRC)) indices. We adjusted for age, sex, and height, and potential confounders including socio-economic disadvantage, PM_2.5 and NO₂ exposure. All models contained an interaction term between UFP PNC exposure and atopy, allowing estimation of the effect of exposure on non-atopic and atopic students. Increasing UFP PNC was associated with greater lung stiffness as evidenced by a decrease in Xrs [mean (95% credible interval) -1.63 (-3.36 to -0.05)%] per 1000#.cm^-3]. It was also associated with greater lung stiffness (decrease in Xrs) in atopic subjects across all models [mean change ranging from -2.06 to -2.40% per 1000#.cm^-3]. A paradoxical positive effect was observed for Rrs across all models [mean change ranging from -1.55 to -1.70% per 1000#.cm^-3] (decreases in Rrs indicating an increase in airway calibre), which was present for both atopic and non-atopic subjects. No effects on MBNW indices were observed. In conclusion, a modest detrimental effect of UFP on peripheral airway function among atopic subjects, as assessed by respiratory system reactance, was observed extending the main UPTECH study findings which reported a positive association with a biomarker for systemic inflammation, C-reactive protein (CRP). Further studies are warranted to explore the pathophysiological mechanisms underlying increased respiratory stiffness, and whether it persists through to adolescence and adulthood.

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

Within-session variability as quality control for oscillometry in health and disease

Oscillometry is increasingly adopted in respiratory clinics, but many recommendations regarding measurement settings and quality control remain subjective. The aim of this study was to investigate the optimal number of measurements and acceptable within-session coefficient of variation (CoV) in health, asthma and COPD. 15 healthy, 15 asthma and 15 COPD adult participants were recruited. Eight consecutive 30-s measurements were made using an oscillometry device, from which resistance at 5 Hz (R rs5 ) was examined. The effect of progressively including a greater number of measurements on R rs5 and its within-session CoV was investigated. Data were analysed using one-way repeated-measures ANOVA with Bonferroni post hoc test. The CoV(R rs5 ) of the first three measurements was 6.7±4.7%, 9.7±5.7% and 12.6±11.2% in healthy, asthma and COPD participants, respectively. Both mean R rs5 and CoV(R rs5 ) were not statistically different when progressively including four to eight measurements. Selecting the three closest R rs5 values over an increasing number of measurements progressively decreased the CoV(R rs5 ). In order for ≥95% of participants to fall within a target CoV(R rs5 ) of 10%, four or more, five and six measurements were needed in health, asthma and COPD, respectively. Within-session variability of oscillometry is increased in disease. Furthermore, the higher number of measurements required to achieve a set target for asthma and COPD patients may not be practical in a clinical setting. Provided technical acceptability of measurements is established, i.e. by removing artefacts and outliers, then a CoV of 10% is a marker of quality in most patients, but we suggest higher CoVs up to 15-20% should still be reportable.

Artificial intelligence for quality control of oscillometry measures

BACKGROUND

The forced oscillation technique (FOT) allows non-invasive lung function testing during quiet breathing even without expert guidance. However, it still relies on an operator for excluding breaths with artefacts such as swallowing, glottis closure and coughing. This manual selection is operator-dependent and time-consuming. We evaluated supervised machine learning methods to exclude breaths with artefacts from data analysis automatically.

METHODS

We collected 932 FOT measurements (Resmon Pro Full, Restech) from 155 patients (6-87 years) following the European Respiratory Society (ERS) technical standards. Patients were randomly assigned to either a training (70%) or test set. For each breath, we computed 71 features (including anthropometric, pressure stimulus, breathing pattern, and oscillometry data). Univariate filter, multivariate filter and wrapper methods for feature selection combined with several classification models were considered.

RESULTS

Trained operators identified 4333 breaths with- and 10244 without artefacts. Features selection performed by a wrapper method combined with an AdaBoost tree model provided the best performance metrics on the test set: Balanced Accuracy = 85%; Sensitivity = 79%; Specificity = 91%; AUC-ROC = 0.93. Differences in FOT parameters computed after manual or automatic breath selection was less than ∼0.25 cmH₂O*s/L for 95% of cases.

CONCLUSION

Supervised machine-learning techniques allow reliable artefact detection in FOT diagnostic tests. Automating this process is fundamental for enabling FOT for home monitoring, telemedicine, and point-of-care diagnostic applications and opens new scenarios for respiratory and community medicine.

Technical standards for respiratory oscillometry

Oscillometry (also known as the forced oscillation technique) measures the mechanical properties of the respiratory system (upper and intrathoracic airways, lung tissue and chest wall) during quiet tidal breathing, by the application of an oscillating pressure signal (input or forcing signal), most commonly at the mouth. With increased clinical and research use, it is critical that all technical details of the hardware design, signal processing and analyses, and testing protocols are transparent and clearly reported to allow standardisation, comparison and replication of clinical and research studies. Because of this need, an update of the 2003 European Respiratory Society (ERS) technical standards document was produced by an ERS task force of experts who are active in clinical oscillometry research.The aim of the task force was to provide technical recommendations regarding oscillometry measurement including hardware, software, testing protocols and quality control.The main changes in this update, compared with the 2003 ERS task force document are 1) new quality control procedures which reflect use of "within-breath" analysis, and methods of handling artefacts; 2) recommendation to disclose signal processing, quality control, artefact handling and breathing protocols (e.g. number and duration of acquisitions) in reports and publications to allow comparability and replication between devices and laboratories; 3) a summary review of new data to support threshold values for bronchodilator and bronchial challenge tests; and 4) updated list of predicted impedance values in adults and children.

Relationships Between Forced Oscillatory Impedance and 6-minute Walk Distance After Pulmonary Rehabilitation in COPD

Rationale

Pulmonary rehabilitation for chronic obstructive pulmonary disease (COPD) reduces dyspnoea and improves exercise capacity and quality of life. The improvement in exercise capacity is variable and unpredictable, however. Respiratory system impedance obtained by forced oscillation technique (FOT) as a measure of ventilatory impairment in COPD may relate to improvement in exercise capacity with pulmonary rehabilitation. We aimed to determine if baseline FOT parameters relate to changes in exercise capacity following pulmonary rehabilitation.

Methods

At the start of rehabilitation, 15 COPD subjects (mean(SD) 75.2(6.1) years, FEV1 z-score −2.61(0.84)) had measurements by FOT, spirometry, plethysmographic lung volumes and 6-minute walk distance (6MWD). Respiratory system resistance (Rrs) and reactance (Xrs) parameters as the mean over all breaths (R_mean, X_mean), during inspiration only (R_insp, X_insp), and expiratory flow limitation (DeltaXrs = X_insp−X_exp), were calculated. FOT and 6MWD measurements were repeated at completion of rehabilitation and 3 months after completion.

Results

At baseline, Xrs measures were unrelated to 6MWD. X_insp improved significantly with rehabilitation (from mean(SD) −2.35(1.02) to −2.04(0.85) cmH₂O.s.L⁻¹, p=0.008), while other FOT parameters did not. No FOT parameters related to the change in 6MWD at program completion. Baseline X_mean, DeltaXrs, and FVC z-score correlated with the change in 6MWD between completion and 3 months after completion of rehabilitation (r_s=0.62, p=0.03; r_s=−0.65, p=0.02; and r_s=0.62, p=0.03, respectively); with worse ventilatory impairment predicting loss of 6MWD. There were no relationships between Rrs parameters, FEV1 or FEV1/FVC z-scores and changes in 6MWD.

Conclusion

Baseline reactance parameters may be helpful in predicting those patients with COPD at most risk of loss of exercise capacity following completion of pulmonary rehabilitation.

Long-term morbidity of respiratory viral infections during chemotherapy in children with leukaemia

BACKGROUND

Respiratory viruses are a common cause of infection in immunosuppressed children undergoing cancer therapy. Pulmonary sequelae have been documented following respiratory viral infections (RVIs) in hematopoietic stem cell transplant (HSCT) recipients; however potential late effects in children undergoing nonmyeloablative chemotherapy have not been investigated.

AIM

To evaluate the long-term pulmonary morbidity of respiratory viral infections during chemotherapy in children with acute lymphoblastic leukemia (ALL).

METHODS

Childhood ALL survivors, aged 7 to 18 years, greater than 6 months posttreatment were recruited. Exclusion criteria included HSCT or proven bacterial/fungal respiratory infection during treatment. Subjects were classified into "viral" or "control" groups according to retrospective medical records that documented the presence of laboratory-proven RVIs during chemotherapy. Symptom questionnaires (Liverpool, ISAAC) and lung function testing (spirometry, plethysmography, diffusing capacity, forced oscillation technique to ATS/ERS standards) were then performed cross-sectionally at the time of recruitment.

RESULTS

Fifty-four patients (31 viral, 23 control) were recruited: median (range) age 11.2 (7.2-18.1) years, and at 4.9 (0.5-13) years posttherapy. Abnormalities were detected in 17 (31%) individuals (8 viral, 9 control), with the most common being DLCO impairment (3 viral, 4 control) and reduced respiratory reactance at 5 Hz (5 viral, 6 control). Children with RVIs during chemotherapy reported more current respiratory symptoms, particularly wheeze (odds ratio [OR], 3.0; 95% confidence interval [CI]: 0.9-10.0; P = .09) and cough (OR, 2.7; 95% CI: 0.8-9.5; P = .11). No differences in lung function tests were observed between the two groups.

CONCLUSIONS

Our study found children with RVIs during chemotherapy developed more long-term respiratory symptoms than controls; however, differences did not reach statistical significance. No differences in static lung function were found between the two groups. Overall, pulmonary abnormalities and/or significant ongoing respiratory symptoms were detected in nearly a third of ALL survivors treated without HSCT. Larger, prospective studies are warranted to evaluate the etiology and clinical significance of these findings.

How the acoustic resonances of the subglottal tract affect the impedance spectrum measured through the lips

Experimental determinations of the acoustic properties of the subglottal airway, from the trachea below the larynx to the lungs, may provide useful information for detecting airway pathologies and aid in the understanding of vocal fold auto-oscillation. Here, minimally invasive, high precision impedance measurements are made through the lips (7 men, 3 women) over the range 14-4200 Hz during inspiration, expiration, and with a closed glottis. Closed glottis measurements show the expected resonances and anti-resonances of the supraglottal vocal tract. As the glottis is gradually opened, and the glottal inertance decreases, maxima in the subglottal impedance increasingly affect the measured impedance spectrum, producing additional pairs of maxima and minima. The pairs with the lowest frequency appear first. Measurements during a cycle of respiration show the disappearance and reappearance of these extrema. For a wide glottal opening during inspiration, and for the frequency range 14-4200 Hz, the impedance spectrum semi-quantitatively resembles that of a single, longer duct, open at the remote end, and whose total effective length is 37 ± 4 cm for men and 34 ± 3 cm for women. Fitting to simple models of the subglottal tract yields mean effective acoustic lengths of 19.5 cm for the men and 16.0 cm for the women in this study.

Automated quality control of forced oscillation measurements: respiratory artifact detection with advanced feature extraction

The forced oscillation technique (FOT) can provide unique and clinically relevant lung function information with little cooperation with subjects. However, FOT has higher variability than spirometry, possibly because strategies for quality control and reducing artifacts in FOT measurements have yet to be standardized or validated. Many quality control procedures rely on either simple statistical filters or subjective evaluation by a human operator. In this study, we propose an automated artifact removal approach based on the resistance against flow profile, applied to complete breaths. We report results obtained from data recorded from children and adults, with and without asthma. Our proposed method has 76% agreement with a human operator for the adult data set and 79% for the pediatric data set. Furthermore, we assessed the variability of respiratory resistance measured by FOT using within-session variation (wCV) and between-session variation (bCV). In the asthmatic adults test data set, our method was again similar to that of the manual operator for wCV (6.5 vs. 6.9%) and significantly improved bCV (8.2 vs. 8.9%). Our combined automated breath removal approach based on advanced feature extraction offers better or equivalent quality control of FOT measurements compared with an expert operator and computationally more intensive methods in terms of accuracy and reducing intrasubject variability.NEW & NOTEWORTHY The forced oscillation technique (FOT) is gaining wider acceptance for clinical testing; however, strategies for quality control are still highly variable and require a high level of subjectivity. We propose an automated, complete breath approach for removal of respiratory artifacts from FOT measurements, using feature extraction and an interquartile range filter. Our approach offers better or equivalent performance compared with an expert operator, in terms of accuracy and reducing intrasubject variability.

Measurement duration impacts variability but not impedance measured by the forced oscillation technique in healthy, asthma and COPD subjects

The forced oscillation technique (FOT) is gaining clinical acceptance, facilitated by more commercial devices and clinical data. However, the effects of variations in testing protocols used in FOT data acquisition are unknown. We describe the effect of duration of data acquisition on FOT results in subjects with asthma, chronic obstructive pulmonary disease (COPD) and healthy controls.

FOT data were acquired from 20 healthy, 22 asthmatic and 18 COPD subjects for 60 s in triplicate. The first 16, 30 and 60 s of each measurement were analysed to obtain total, inspiratory and expiratory resistance of respiratory system (R_rs) and respiratory system reactance (X_rs) at 5 and 19 Hz.

With increasing duration, there was a decrease in total and expiratory R_rs for healthy controls, total and inspiratory R_rs for asthmatic subjects and magnitude of total and inspiratory X_rs for COPD subjects at 5 Hz. These decreases were small compared to the differences between clinical groups. Measuring for 16, 30 and 60 s provided ≥3 acceptable breaths in at least 90, 95 and 100% of subjects, respectively. The coefficient of variation for total R_rs and X_rs also decreased with duration. Similar results were found for R_rs and X_rs at 19 Hz.

FOT results are statistically, but likely minimally, impacted by acquisition duration in healthy, asthmatic or COPD subjects.

Effect of duration on forced oscillation measurements in health, asthma and COPDhttp://ow.ly/Z9Wlk

Expiratory flow limitation relates to symptoms during COPD exacerbations requiring hospital admission

Background

Expiratory flow limitation (EFL) is seen in some patients presenting with a COPD exacerbation; however, it is unclear how EFL relates to the clinical features of the exacerbation. We hypothesized that EFL when present contributes to symptoms and duration of recovery during a COPD exacerbation. Our aim was to compare changes in EFL with symptoms in subjects with and without flow-limited breathing admitted for a COPD exacerbation.

Subjects and methods

A total of 29 subjects with COPD were recruited within 48 hours of admission to West China Hospital for an acute exacerbation. Daily measurements of post-bronchodilator spirometry, resistance, and reactance using the forced oscillation technique and symptom (Borg) scores until discharge were made. Flow-limited breathing was defined as the difference between inspiratory and expiratory respiratory system reactance (EFL index) greater than 2.8 cmH₂O·s·L⁻¹. The physiological predictors of symptoms during recovery were determined by mixed-effect analysis.

Results

Nine subjects (31%) had flow-limited breathing on admission despite similar spirometry compared to subjects without flow-limited breathing. Spirometry and resistance measures did not change between enrolment and discharge. EFL index values improved in subjects with flow-limited breathing on admission, with resolution in four patients. In subjects with flow-limited breathing on admission, symptoms were related to inspiratory resistance and EFL index values. In subjects without flow-limited breathing, symptoms related to forced expiratory volume in 1 second/forced vital capacity. In the whole cohort, EFL index values at admission was related to duration of stay (Rs=0.4, P=0.03).

Conclusion

The presence of flow-limited breathing as well as abnormal respiratory system mechanics contribute independently to symptoms during COPD exacerbations.

Ultrafine Particles from Traffic Emissions and Children's Health (UPTECH) in Brisbane, Queensland (Australia): study design and implementation

Ultrafine particles are particles that are less than 0.1 micrometres (µm) in diameter. Due to their very small size they can penetrate deep into the lungs, and potentially cause more damage than larger particles. The Ultrafine Particles from Traffic Emissions and Children's Health (UPTECH) study is the first Australian epidemiological study to assess the health effects of ultrafine particles on children's health in general and peripheral airways in particular. The study is being conducted in Brisbane, Australia. Continuous indoor and outdoor air pollution monitoring was conducted within each of the twenty five participating school campuses to measure particulate matter, including in the ultrafine size range, and gases. Respiratory health effects were evaluated by conducting the following tests on participating children at each school: spirometry, forced oscillation technique (FOT) and multiple breath nitrogen washout test (MBNW) (to assess airway function), fraction of exhaled nitric oxide (FeNO, to assess airway inflammation), blood cotinine levels (to assess exposure to second-hand tobacco smoke), and serum C-reactive protein (CRP) levels (to measure systemic inflammation). A pilot study was conducted prior to commencing the main study to assess the feasibility and reliably of measurement of some of the clinical tests that have been proposed for the main study. Air pollutant exposure measurements were not included in the pilot study.

Changes in oscillatory impedance and nitrogen washout with combination fluticasone/salmeterol therapy in COPD

INTRODUCTION

Combination inhaled corticosteroid/long-acting bronchodilator (ICS/LABA) therapy reduces the exacerbation rate and improves spirometry and quality of life in COPD. We hypothesized that ICS/LABA therapy also improves small airway function measured by FOT.

METHODS

14 subjects with COPD were commenced on combination fluticasone propionate/salmeterol therapy for 3 months. At baseline, subjects completed the St George Respiratory Questionnaire (SGRQ) and underwent standard pulmonary function tests as well as forced oscillation technique (FOT) and single and multiple breath nitrogen washouts. All tests were repeated at the completion of 3 months of therapy.

RESULTS

Subjects were of mean (SD) age 65.9 years (8.4), BMI 30.0 (5.6), pack years 51.4 (21.1), post-bronchodilator FEV1% predicted 62.7 (20). At baseline, mean SGRQ total was 39.0 (17.7) and FRC% predicted 125.4 (31.3). From FOT, Rrs-total was 5.69 (1.29) cmH2O/L/s, Xrs-total -3.48 (2.16) cmH2O/L/s, EFL Index 3.51 (2.45) cmH2O/L/s. After 3 months of therapy, there were significant improvements in SGRQ score (-13.81, p < 0.0001) despite no change in FEV1 (+40 mL, p = 0.14). From FOT, total resistance (-0.63 cmH2O/L/s, p = 0.0004), reactance (+1.2 cmH2O/L/s, p = 0.013), and expiratory flow limitation (-1.21 cmH2O/L/s, p = 0.02) also improved. There were no significant changes in ventilation heterogeneity indices.

CONCLUSION

Combination therapy is associated with improvements in small airways function in COPD, despite an absence of change in FEV1. FOT may be a clinically useful marker of small airway function in COPD that is responsive to treatment.

The effect of low lung volume on airway function in obesity

INTRODUCTION

Obesity is associated with reduced operating lung volume. We hypothesized that obesity induces airway dysfunction independent of reduced FRC.

METHODS

18 obese (BMI: 41.3 ± 6.8) and 17 non-obese subjects (BMI: 24.8 ± 2.3 kg/m(2)) had measurements of conductance (Grs) and reactance (Xrs) by forced oscillation technique, ventilation heterogeneity (lung clearance index (LCI), Scond, Sacin) by multiple breath nitrogen washout and closing capacity (CC) by single breath nitrogen washout.

RESULTS

Obese had higher LCI and Sacin and lower Grs and Xrs. After adjustment for FRC, Grs (r=-0.52, p=0.001), and Sacin (r=0.47, p=0.004) still correlated with BMI. Closing capacity (as % predicted TLC) was not increased but was closer to FRC in the obese (CC/FRC: 95.0 ± 21.7% vs 71.7 ± 19.2%, p<0.001). Xrs and LCI correlated with CC/FRC.

CONCLUSIONS

In obesity, there are abnormalities in airway function that are independent of reduced FRC. Airway closure is not increased but CC occurs close to FRC, affecting Xrs and LCI.

A study of artifacts and their removal during forced oscillation of the respiratory system

Respiratory impedance measured by the forced oscillation technique (FOT) can be contaminated by artifacts such as coughing, vocalization, swallowing or leaks at the mouthpiece. We present a novel technique to detect these artifacts using multilevel discrete wavelet transforms. FOT was performed with artifacts introduced during separate 60 s recordings at known times in 10 healthy subjects. Brief glottal closures were generated phonetically and confirmed by nasopharyngoscopic imaging of the glottis. Artifacts were detected using Daubechies wavelets by applying a threshold to squared detail coefficients from the wavelet transforms of both pressure and flow signals. Sensitivity and specificity were compared over a range of thresholds for different level squared detail coefficients. Coughs could be identified using 1st level detail (cd1) coefficients of pressure achieving 96% sensitivity and 100% specificity while swallowing could be identified using cd2 thresholds of pressure with 95% sensitivity and 97% specificity. Male vocalizations could be identified using cd1 coefficients with 88% sensitivity and 100% specificity. For leaks at the mouthpiece, cd3 thresholds of flow could identify these events with 98% sensitivity and 99% specificity. Thus, this method provided an accurate, easy, and automated technique for detecting and removing artifacts from measurements of respiratory impedance using FOT.

The relationship between airflow obstruction, emphysema extent, and small airways function in COPD

BACKGROUND

The severities of COPD (FEV(1) % predicted) and airflow obstruction (FEV(1)/FVC) are considered to be due to both emphysema and small airways disease. To our knowledge, this has not been previously confirmed by combined measurements of emphysema and of small airway function. We hypothesized that small airways disease and emphysema extent contribute independently to the severity of both COPD and airflow obstruction.

METHODS

Twenty-six subjects with COPD underwent measurements with forced oscillation technique (FOT) at 6 Hz and single-breath nitrogen washout. Respiratory system resistance, respiratory system reactance (Xrs), and expiratory flow limitation (EFL) index (measured as mean inspiratory Xrs − expiratory Xrs) were derived from FOT. Closing volume/vital capacity (CV/VC) was derived from the washout. Emphysema extent was measured as low attenuation areas < -910 Hounsfield units, expressed as a percentage of CT scan lung volume from multislice CT scans taken at total lung capacity.

RESULTS

Subjects were aged (mean ± SD) 69.6 ± 8.0 years. Postbronchodilator FEV(1) was 64.8 ± 19.8% predicted, and diffusing capacity of lung for carbon monoxide was 50.7 ± 15.8% predicted. Emphysema extent was 22.6% ± 15.0% CT scan volume. CV/VC was 16.9% ± 7.9%; Xrs, -3.72 ± 3.03 cm H(2)O/L/s; and EFL index, 3.88 ± 3.93 cm H(2)O/L/s. In multiple regression analyses, FEV(1)/FVC was predicted by both emphysema and CV/VC (model r(2) = 0.54, P < .0001) whereas FEV(1) % predicted was predicted by emphysema and EFL index (model r(2) = 0.38, P = .0014).

CONCLUSIONS

The severities of COPD and airflow obstruction are independently predicted by both small airways disease and emphysema extent.

Day-to-day variability of oscillatory impedance and spirometry in asthma and COPD

Variability in airway function may be a marker of disease activity in COPD and asthma. The aim was to determine the effects of repeatability and airway obstruction on day-to-day variability in respiratory system resistance (Rrs) and reactance (Xrs) measured by forced oscillation technique (FOT). Three groups of 10 subjects; normals, stable asthmatic and stable COPD subjects underwent daily FOT recordings for 7 days. Mean total and inspiratory Rrs and Xrs, and expiratory flow limitation (EFL) Index (inspiratory - expiratory Xrs), were calculated. The ICC's were high for all parameters in all groups. Repeatability, in terms of absolute units, correlated with airway obstruction and was therefore lowest in COPD. Day-to-day variability was due mostly to repeatability, with a small contribution from the mean value for some parameters. FOT measures are highly repeatable in health, stable asthma and COPD in relation to the wide range of measures between subjects. For home monitoring in asthma and COPD, either the coefficient of variation or individualized SDs could be used to define day-to-day variability.

Obesity, expiratory flow limitation and asthma symptoms

Obesity is associated with poor asthma control, but the reason for this is unclear. Reduction in operating lung volume, as occurs in obesity, and bronchoconstriction, as occurs in asthma, can increase expiratory flow limitation during tidal breathing (EFLt), which may in turn increase respiratory symptoms. The aim of this study was to determine the effect of obesity on EFLt at baseline and after bronchoconstriction in non-asthmatic and asthmatic subjects, and to determine the association between EFLt, and respiratory symptoms. Data from previously published studies in non-asthmatic and asthmatic subjects were reanalyzed using an index of EFLt derived from respiratory system reactance measured by the forced oscillation technique. The analysis showed that during bronchoconstriction both non-asthmatic and asthmatic obese individuals were more likely to develop EFLt than non-obese subjects, despite similar changes in FEV1. Furthermore the index of EFLt was a significant determinant of the severity of breathlessness during challenge in non-asthmatic subjects, and of asthma symptom control in asthmatic subjects following anti-inflammatory treatment. These studies suggest that the combination of bronchoconstriction and low resting lung volume increase the risk of EFLt, and that this altered response to bronchoconstriction may increase the severity of symptoms and lead to worse asthma control.

Cutting edge technologies in respiratory research: lung function testing

Pulmonary function testing is part of routine clinical practice in respiratory medicine. It is based around spirometry, which will remain the central measurement of lung function given its prognostic significance and its integral role in defining severity of airways disease. However, there is an increasing body of evidence from studies using new methods of lung function measurement which are providing new insights into pathophysiology of disease. This body of data is forming a basis for their future clinical role, once the economics of producing the relevant devices becomes attractive. The forced oscillation technique and multiple breath nitrogen washout are currently the most commonly used of the newer lung function techniques, which are refinements of long-established techniques. Optical coherence tomography, optical reflection, electrical impedance and vibration response imaging have arisen by development of novel devices. The recent use of these techniques is reviewed.