Reference values of impulse oscillometric lung function indices in adults of advanced age

Usefulness of Impulse Oscillometry in Predicting the Severity of Bronchiectasis

BACKGROUND

Bronchiectasis is a chronic respiratory disease that leads to airway inflammation, destruction, and airflow limitation, which reflects its severity. Impulse oscillometry (IOS) is a non-invasive method that uses sound waves to estimate lung function and airway resistance. The aim of this study was to assess the usefulness of IOS in predicting the severity of bronchiectasis.

METHODS

We retrospectively reviewed the IOS parameters and clinical characteristics in 145 patients diagnosed with bronchiectasis between March 2020 and May 2021. Disease severity was evaluated using the FACED score, and patients were divided into mild and moderate/severe groups.

RESULTS

Forty-four patients (30.3%) were in the moderate/severe group, and 101 (69.7%) were in the mild group. Patients with moderate/severe bronchiectasis had a higher airway resistance at 5 Hz (R5), a higher difference between the resistance at 5 and 20 Hz (R5-R20), a higher resonant frequency (Fres), and a higher area of reactance (AX) than patients with mild bronchiectasis. R5 ≥0.43, resistance at 20 Hz (R20) ≥0.234, R5-R20 ≥28.3, AX ≥1.02, reactance at 5 Hz (X5) ≤-0.238, and Fres ≥20.88 revealed significant univariable relationships with bronchiectasis severity (p<0.05). Among these, only X5 ≤-0.238 exhibited a significant multivariable relationship with bronchiectasis severity (p=0.039). The receiver operating characteristic curve for predicting moderate- to-severe bronchiectasis of FACED score based on IOS parameters exhibited an area under the curve of 0.809.

CONCLUSION

The IOS assessed by the disease severity of FACED score can effectively reflect airway resistance and elasticity in bronchiectasis patients and serve as valuable tools for predicting bronchiectasis severity.

Elevated neutrophil-to-lymphocyte ratio combined with decreased lymphocyte-to-monocyte ratio is associated with increased peripheral airway resistance in patients with hepatic steatosis

Although the link between hepatic steatosis and lung function has been confirmed, the focus has largely been on central airways. The association between hepatic steatosis and increased peripheral airway resistance has not yet been explored. Hepatic steatosis and increased peripheral resistance are connected with immunity dysregulation. High neutrophil-to-lymphocyte ratio (NLR) and low lymphocyte-to-monocyte ratio (LMR) have been recognized as indicators of immunity dysregulation. In this study, the association between hepatic steatosis and increased peripheral airway resistance was evaluated, and the effect of immunity dysregulation (high NLR/low LMR) on the increased peripheral airway resistance among patients with hepatic steatosis was explored. In this retrospective study, chest or abdomen CT scans and spirometry/impulse oscillometry (IOS) from 2018 to 2019 were used to identify hepatic steatosis and increased central/peripheral airway resistance in patients. Among 1391 enrolled patients, 169 (12.1%) had hepatic steatosis. After 1:1 age and abnormal ALT matching was conducted, clinical data were compared between patients with and without hepatic steatosis. A higher proportion of patients with hepatic steatosis had increased peripheral airway resistance than those without hepatic steatosis (52.7% vs 40.2%, P = .025). Old age, high body mass index, history of diabetes, and high NLR/low LMR were significantly correlated with increased peripheral airway resistance. The presence of hepatic steatosis is associated with increased peripheral airway. High NLR/low LMR is an independent associated factor of increased peripheral airway resistance in patients with hepatic steatosis. It is advisable for patients with hepatic steatosis to regularly monitor their complete blood count/differential count and undergo pulmonary function tests including IOS.

Beyond forced exhalation: impulse oscillometry as a promising tool for bronchial hyperresponsiveness evaluation

Introduction: The multiple forced expiratory maneuvers that must be performed during methacholine test require a high degree of collaboration and can lead to fatigue. However, impulse oscillometry (IOS) is a noninvasive test, quick and easy to perform, that does not require effort-dependent maneuvers. Objectives: The primary endpoint was to evaluate the relationship between IOS and spirometry during the methacholine test. The secondary endpoint was to study the predictive value of baseline IOS in the development of bronchial hyperreactivity. Methods: Observational, prospective, cross-sectional study, with recruitment of consecutive patients from the pulmonology department with clinical suspicion of bronchial asthma with negative bronchodilator test and normal FeNO. Results: Twenty-five patients were included, with a mean age of 49 ± 18 years. Thirteen patients (52%) had a positive methacholine test. The correlation between IOS indices and FEV1 was significant (p < 0.05) in all cases. The indices with the highest predictive power were R5-20 and AX. The optimal cutoff points were an increase of greater than 32.96% in R5, greater than 120.83% for X5, an increase of 30.30 [kPa l-1s-1] in R5-20, and an increase of 1.01 [kPa l-1] for AX. Baseline oscillometry demonstrated a strong predictive value in the development of bronchial hyperreactivity, with a sensitivity of 61.5% and a specificity of 91.7%, using the cut-off point of 160.0% for R5. Conclusions: IOS may be a valuable alternative to forced spirometry in detecting bronchial hyperreactivity during the methacholine test, showing a good correlation between both tests.

Impulse Oscillometry Versus Spirometry to Detect Bronchiolitis Obliterans Syndrome in Bilateral Lung Transplant Recipients: A Prospective Diagnostic Study

BACKGROUND

Chronic lung allograft dysfunction (CLAD), and especially bronchiolitis obliterans syndrome (BOS), remain dominant causes of morbidity and mortality after lung transplantation. Interest is growing in the forced oscillation technique, of which impulse oscillometry (IOS) is a form, as a tool to improve our understanding of these disorders. However, data remain limited and no longitudinal studies have been published, meaning there is no information regarding any capacity IOS may have for the early detection of CLAD.

METHODS

We conducted a prospective longitudinal study enrolling a consecutive sample of adult bilateral lung transplant recipients with healthy lung allografts or CLAD and performed ongoing paired IOS and spirometry tests on a clinically determined basis. We assessed for correlations between IOS and spirometry and examined any predictive value either modality may hold for the early detection of BOS.

RESULTS

We enrolled 91 patients and conducted testing for 43 mo, collecting 558 analyzable paired IOS and spirometry tests, with a median of 9 tests per subject (interquartile range, 5-12) and a median testing interval of 92 d (interquartile range, 62-161). Statistically significant moderate-to-strong correlations were demonstrated between all IOS parameters and spirometry, except resistance at 20 Hz, which is a proximal airway measure. No predictive value for the early detection of BOS was found for IOS or spirometry.

CONCLUSIONS

This study presents the first longitudinal data from IOS after lung transplantation and adds considerably to the growing literature, showing unequivocal correlations with spirometry but failing to demonstrate a predictive value for BOS.

Indices of airway resistance and reactance from impulse oscillometry correlate with aerosol particle emission in different age groups

Airborne transmission of pathogens plays a major role in the spread of infectious diseases. Aerosol particle production from the lung is thought to occur in the peripheral airways. In the present study we investigated eighty lung-healthy subjects of two age groups (20-39, 60-76 years) at rest and during exercise whether lung function parameters indicative of peripheral airway function were correlated with individual differences in aerosol particle emission. Lung function comprised spirometry and impulse oscillometry during quiet breathing and an expiratory vital capacity manoeuvre, using resistance (R5) and reactance at 5 Hz (X5) as indicators potentially related to peripheral airway function. The association between emission at different ventilation rates relative to maximum ventilation and lung function was assessed by regression analysis. In multiple regression analyses including age group, only vital capacity manoeuvre R5 at 15% to 50% of end-expiratory vital capacity as well as quiet breathing X5 were independently linked to particle emission at 20% to 50% of maximum ventilation, in addition to age group. The fact that age as predictive factor was still significant, although to a lower degree, points towards further effects of age, potentially involving surface properties not accounted for by impulse oscillometry parameters.

Inhomogeneity of ventilation in smokers and mild COPD assessed by the ratio of alveolar volume to total lung capacity

BACKGROUND

Previous studies have shown that the ratio between alveolar volume (VA) and total lung capacity (TLC) reflects ventilation heterogeneity in subjects with chronic obstructive pulmonary disease (COPD). However, the ratio and its correlation to respiratory symptoms had to our knowledge not previously been investigated in subjects with mild chronic airflow obstruction or without airflow obstruction (normal ratio FEV1/VC). The purpose of this study was to investigate potential connection between VA/TLC and respiratory symptoms, smoking habits and lung function parameters in subjects with normal spirometry and with mild chronic airflow obstruction.

METHODS

We examined 450 subjects (82 non-smokers with normal spirometry, 298 subjects who smoked or had smoked earlier but had a normal spirometry and 70 subjects with chronical airflow obstruction) with routine lung function tests and a questionnaire regarding respiratory symptoms.

RESULTS

This study showed 31 out of 54 subjects with a low VA/TLC had a normal ratio FEV1/VC. Of these subjects, 58.1 % had respiratory symptoms, compared to the group with normal ratio for both VA/TLC and FEV1/VC where 35.8 % had respiratory symptoms (p-value 0.02).

CONCLUSION

This study has shown that within the group of subjects with a normal ratio FEV1/VC, those with a decreased ratio VA/TLC had a higher prevalence of respiratory symptoms compared to subjects with a normal VA/TLC ratio. These findings indicate that including the ratio VA/TLC in the evaluation of a pulmonary function test assessment might increase the possibility to identify subjects with early or at risk of lung disease.

Impulse oscillometry and its independent role in the diagnosis of chronic obstructive pulmonary disease

Background

Pulmonary function test, particularly in patients with COVID-19, is problematic because it involves forced expiration. Impulse oscillometry (IOS) reduces the potential exposure of health-care staff to infectious droplets. In this study, we investigated the correlation between IOS and spirometry and whether IOS can precisely predict spirometry-based diagnoses of chronic obstructive pulmonary disease (COPD).

Methods

We retrospectively analyzed the data (January 1 to December 31, 2021) of patients who underwent both spirometry and IOS on the same date. One-way analysis of variance was performed to evaluate the IOS results of patients stratified into two (COPD and non-COPD) groups by spirometry results. IOS results were also analyzed using receiver operator characteristics curves to diagnose advanced COPD, which was indicated by a postbronchodilator (BD) forced expiratory volume in 1 s (FEV1)/forced vital capacity (FVC) ratio of <0.6. We further evaluated the accuracy of oscillometry as a predictor of spirometry-based COPD diagnosis.

Results

A total of 115 patients were included in the analysis. The best parameters assessed for spirometry-based COPD diagnosis were area under reactance (AX) and airway resistance (predicted R5% × resonant frequency) in relation to body mass index (BMI). However, when the post-BD FEV1/FVC ratio was <0.6, BMI-adjusted airway resistance had an area under curve (0.782; 95 % confidence interval: 0.620-0.945) value larger than the corresponding AX. A BMI-adjusted airway resistance value of >160 moderately predicted spirometry-based COPD diagnosis.

Conclusions

BMI-adjusted airway resistance is a potential predictor of spirometry-based COPD diagnosis; the cutoff values of this parameter differ between individuals with and without obesity.

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.

Relation of impulse oscillometry and spirometry with quantitative thorax computed tomography after COVID-19 pneumonia

OBJECTIVE

This study aimed to investigate if there is any correlation between the quantitative computed tomography and the impulse oscillometry or spirometry results of post-COVID-19 patients.

METHODS

The study comprised 47 post-COVID-19 patients who had spirometry, impulse oscillometry, and high-resolution computed tomography examinations at the same time. The study group consisted of 33 patients with quantitative computed tomography involvement, while the control group included 14 patients who did not have CT findings. The quantitative computed tomography technology was used to calculate percentages of density range volumes. The relationship between percentages of density range volumes for different quantitative computed tomography density ranges and impulse oscillometry-spirometry findings was statistically analyzed.

RESULTS

In quantitative computed tomography, the percentage of relatively high-density lung parenchyma, including fibrotic areas, was 1.76±0.43 and 5.65±3.73 in the control and study groups, respectively. The percentages of primarily ground-glass parenchyma areas were found to be 7.60±2.86 and 29.25±16.50 in the control and study groups, respectively. In the correlation analysis, the forced vital capacity% predicted in the study group was correlated with DRV%[(-750)-(-500)] (volume of the lung parenchyma that has density between (-750)-(-500) Hounsfield units), but no correlation with DRV%[(-500)-0] was detected. Also, reactance area and resonant frequency were correlated with DRV%[(-750)-(-500)], while X5 was correlated with both DRV%[(-500)-0] and DRV%[(-750)-(-500)] density. Modified Medical Research Council score was correlated with predicted percentages of forced vital capacity and X5.

CONCLUSION

After COVID-19, forced vital capacity, reactance area, resonant frequency, and X5 correlated with the percentages of density range volumes of ground-glass opacity areas in the quantitative computed tomography. X5 was the only parameter correlated with density ranges consistent with both ground-glass opacity and fibrosis. Furthermore, the percentages of forced vital capacity and X5 were shown to be associated with the perception of dyspnea.

Increased airway resistance among exclusive waterpipe smokers detected using impulse oscillometry

INTRODUCTION

Waterpipe smoking is increasing in popularity, yet the evidence implicating waterpipe smoking in lung disease is limited. We hypothesized that impulse oscillometry (IOS) would detect airway abnormalities in waterpipe smokers (WPS).

METHODS

We studied 210 participants, 40 years or older, from the community, of whom 92 were exclusive WPS and 118 were never-smokers. Waterpipe smoking history was assessed using a validated questionnaire. All participants underwent spirometry, and IOS and absolute and percentage predicted results (for age, sex, height, and weight) were compared between WPS and nonsmokers. The association of IOS parameters with waterpipe smoking duration and extent (waterpipe smoked/day * smoking duration) was evaluated using linear regression.

RESULTS

WPS smoked on average 1.8 ± 1.2 waterpipes/day, over an average duration of 23.3 ± 39.8 years. WPS and nonsmokers were largely asymptomatic and had similar age, body mass index, sex distribution, and spirometric values. Nevertheless, WPS had higher IOS measured resistance at 5Hz compared to nonsmokers, (0.53 ± 0.2 vs. 0.48 ± 0.2 kPa/L/s, P = 0.03) and higher percentage-predicted resistance (124.5 ± 36.3 vs. 115.7% ± 35.6%, P = 0.04). Waterpipe smoking duration was also associated with resistance (β = 0.04 kPa/L/s/year, P = 0.01) and with percentage-predicted resistance (β = 0.05/year, P = 0.02). Waterpipe smoking extent was associated with resistance (β = 0.009 kPa/L/s/waterpipe-year, P = 0.04), while the association with percentage-predicted resistance was near significance (β = 0.009/waterpipe-year, P = 0.07).

CONCLUSIONS

Waterpipe smoking is associated with increased airway resistance assessed by IOS but not by spirometry in largely asymptomatic individuals from the community.

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.

Lung disease burden assessment by oscillometry in a systematically disadvantaged urban population experiencing homelessness or at-risk for homelessness in Ottawa, Canada from a prospective observational study

Rationale

Oscillometry is an emerging technique that offers some advantages over spirometry as it does not require forced exhalation and may detect early changes in respiratory pathology. Obstructive lung disease disproportionately impacts people experiencing homelessness with a high symptoms burden, yet oscillometry is not studied in this population.

Objectives

To assess lung disease and symptom burden using oscillometry in people experiencing homelessness or at-risk of homelessness using a community-based participatory action research approach (The Bridge Model™).

Methods

Of 80 recruited, 55 completed baseline oscillometry, 64 completed spirometry, and all completed patient-reported outcomes with demographics, health, and respiratory symptom related questionnaires in the Participatory Research in Ottawa: Management and Point-of-Care for Tobacco Dependence project. Using a two-tail t-test, we compared mean oscillometry values for airway resistance (R_5–20), reactance area under the curve (A_x) and reactance at 5 Hz (X₅) amongst individuals with fixed-ratio method (FEV₁/FVC ratio < 0.70) and LLN (FEV₁/FVC ratio ≤ LLN) spirometry diagnosed chronic obstructive pulmonary disease (COPD). We compared mean oscillometry parameters based on participants’ COPD assessment test (CAT) scores using ANOVA test.

Results

There was no significant difference between the pre- and post- bronchodilator values of R_5–20 and A_x for the fixed ratio method (p = 0.63 and 0.43) and the LLN method (p = 0.45 and 0.36). There was a significant difference in all three of the oscillometry parameters, R_5–20, A_x and X₅, based on CAT score (p = 0.009, 0.007 and 0.05, respectively). There was a significant difference in R_5–20 and A_x based on the presence of phlegm (p = 0.03 and 0.02, respectively) and the presence of wheeze (p = 0.05 and 0.01, respectively). Oscillometry data did not correlate with spirometry data, but it was associated with CAT scores and correlated with the presence of self-reported symptoms of phlegm and wheeze in this population.

Conclusions

Oscillometry is associated with respiratory symptom burden and highlights the need for future studies to generate more robust data regarding the use of oscillometry in systematically disadvantaged populations where disease burden is disproportionately higher than the general population.

TrialRegistration: ClinicalTrails.gov—NCT03626064, Retrospective registered: August 2018, https://clinicaltrials.gov/ct2/show/NCT03626064

Small airway function in Finnish COVID-19 survivors

Follow-up studies of COVID-19 patients have found lung function impairment up to six months after initial infection, but small airway function has not previously been studied. Patients (n = 20) hospitalised for a severe SARS-CoV-2 infection underwent spirometry, impulse oscillometry, and multiple measurements of alveolar nitric oxide three to six months after acute infection. None of the patients had small airway obstruction, nor increased nitric oxide concentration in the alveolar level. None of the patients had a reduced FEV₁/FVC or significant bronchodilator responses in IOS or spirometry. In conclusion, we found no evidence of inflammation or dysfunction in the small airways.

Diagnostic sensitivity of impulse oscillometry in early detection of patients exposed to risk factors chronic obstructive pulmonary diseases

Background: Impulse oscillometry (IOS) is a method that does not depend on the cooperation of the patient and can detect small airway diseases with higher sensitivity than spirometry. However, the clinical application value of IOS in the screening of patients exposed to risk factors COPD and early diagnosis remains unclear. The aim of this study is to evaluate diagnostic sensitivity of IOS in the early detection of patients exposed to risk factors COPD.

Methods: A prospective cross-sectional study was conducted in Rasoul Akram Hospital, Tehran, Iran, from 2013 to 2015. 28 patients with COPD risk factors and normal spirometry participated in the study. The IOS was performed. We obtained the respiratory resistance and impedance of 5 Hz (R5) and 20 Hz (R20) and 5 Hz (Z5), respectively. The data were analyzed using SPSS version 17 using Chi-square and two independent sample t-test. Spearman correlation test was used to measure the correlation of oscillometry parameters in the diagnosis of COPD. P-value <0.05 was considered significantfor all statistical analyses.

Results: The mean patient age was 55.50±11.27 years. In this study, the sensitivity of Z5, R5, and R20 was respectively 28.5%, 25%, and 31.5%. All oscillometry parameters were significantly correlated with each other but none of the oscillometry parameters showed significant correlations with FEV1/FVC (rZ5=0.018, rR5=0.082, rR20=0.041 and PZ5=0.932, PR5=0.711, P R20=0.850). According to the results, only 9 patients (32.5%) with normal values of FEV1/FVC had abnormal values of oscillometry.

Conclusion: IOS has a low sensitivity and cannot be used in the screening of early-stage chronic obstructive pulmonary disease.

Reference values of respiratory impedance with impulse oscillometry in healthy Chinese adults

Background

Impulse oscillometry (IO) is a non-invasive pulmonary function test for measuring respiratory impedance. Available reference equations of IO indices for adults are limited. The aim of this study was to develop reference equations of IO indices for Chinese adults.

Methods

In a multicentral, cross-sessional study of IO in Chinese adults, IO data from healthy subjects were collected from 19 general hospitals across China between 2016 and 2018. Oscillometry measurements were conducted in accordance with recommendations of the European Respiratory Society (ERS). Multiple linear regression was performed to develop sex-specific reference equations of IO indices.

Results

IO measurements were performed in 1,318 subjects, of which 567 subjects were defined as healthy individuals with acceptable IO data and were included in the final analysis. Reference equations and limits of normal [lower limit of normal (LLN)/upper limit of normal (ULN)] of IO indices were developed separately for males and females. Height but not age was shown to be the most influential contributor to IO indices. The reference equations currently used in lung function laboratories predicted higher R5 and X5. Normal ranges of R5 and X5 recommended by the equipment manufacturer were clearly different from the ULN/LLN derived from the reference equations.

Conclusions

Reference equations of IO indices for Chinese adults from a wide region were provided in this study. It is necessary to update new IO reference equations and adopt ULN/LLN as normal ranges of IO indices.

Trial Registration

This study was registered at www.clinicaltrials.gov as part of a larger study NCT03467880.

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.

The associations between red cell distribution width and lung function measures in a general population

BACKGROUND

Red cell distribution width (RDW) reflects heterogeneity of the erythrocyte volumes. High RDW is a novel risk marker, which has been associated with mortality and morbidity both from cardiovascular and respiratory diseases, but the association between RDW and measures of lung function in the general population remains unclear.

METHODS

The associations of RDW with spirometry, diffusing capacity (D_LCO) and impulse oscillometry (IOS) were investigated among 5767, 5496 and 5598 subjects (aged 50-64 years), respectively, from the Swedish CArdioPulmonary bioImage Study (SCAPIS). Multiple linear regression and general linear models were performed to examine the relationships of lung function measures and RDW, with adjustment for potential confounding factors.

RESULTS

Forced expiratory volume in 1 s (FEV₁), forced vital capacity (FVC) and FEV₁/FVC were significantly and inversely associated with RDW after multivariate adjustments. For 1- standard deviation (SD) increase in RDW, FEV₁ decreased with 0.034 L (95%CI: -0.046 to -0.022 L), p < 0.001; FVC with 0.031 L (95%CI: -0.045 to -0.017 L), p < 0.001; and FEV₁/FVC with 0.003 (95%CI: -0.004 to -0.001), p = 0.002. Significant associations of RDW and D_LCO were only found among smokers. For IOS, pulmonary reactance rather than resistance was significantly associated with RDW: X₅ decreased 0.002 kPa/(L/s) (95%CI: -0.003 to -0.0002 kPa/(L/s)), p = 0.025, per 1-SD higher RDW.

CONCLUSIONS

We found significant negative associations between RDW and measures of lung function. However, the effect sizes are small and RDW is not likely to be a sensitive marker of impaired lung function in middle-aged individuals from the general population.

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 roles of impulse oscillometry in detection of poorly controlled asthma in adults with normal spirometry

BACKGROUND

Impulse oscillometry (IOS) has been introduced as a method of assessing asthma control. However, the cutoff IOS values for the detection of asthma control in adults are still unclear.

OBJECTIVE

To assess the diagnostic ability of IOS for distinguishing between poorly controlled and well controlled adult asthmatic subjects with normal spirometry.

METHODS

This cross-sectional study was conducted at the Lung Health Center, Chiang Mai, Thailand, between July 2019 and June 2020. IOS and spirometry were performed in all adult asthmatic subjects but only subjects with normal spirometry were enrolled. Poorly controlled asthma was defined in accordance with the Global Initiative for Asthma (GINA) plus an asthma control test (ACT) score ≤19. A Receiver Operating Characteristic (ROC) curve was plotted to detect poorly controlled asthma using the area under the ROC (AuROC) and 95%CI.

RESULTS

One hundred and forty-two adult asthmatic subjects registering normal spirometry with a mean age of 53.4 ± 15.8 years were enrolled. Eighty-nine (62.7%) subjects were female. IOS parameters including heterogeneity of resistance at 5 Hz and resistance at 20 Hz (R5-R20) and area under reactance (AX) demonstrated excellent detection of poorly controlled asthma with an AuROC of 0.911 and 0.904, respectively. The z-score or absolute value of R5-R20 ≥ 0 and 1 cmH₂O/L/s, respectively, represented the highest AuROC of 0.86, with a sensitivity and a specificity of ≥80.0% for the detection of poorly controlled asthma.

CONCLUSION

IOS is a valuable tool for the detection of poorly controlled asthma in adults with normal spirometry.

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.

Reference equations for parameters of impulse oscillometry in Egyptian children and adolescents

Background

Impulse oscillometry (IOS) is important in diagnosing respiratory functions in non-cooperative children. Studies are rising nowadays to establish reliable reference values of IOS for children of different ethnicities. No available data about the regression equations for parameters of IOS for Egyptian children and adolescents. So, our study aimed to develop regression equations for parameters of IOS in Egyptian children and adolescents in relation to their age, weight, height, and body mass index.

Results

Height and age affected the regression equation of impedance at 5 Hz (Z5 Hz) and resistance at 5 Hz (R5 Hz) in both males and females, resistance at 20 Hz (R20 Hz) in males and reactance at 5 Hz (X5 Hz) in females. Height affected the regression equation of R20 Hz in females, resonant frequency (Fres) in males, and the area of reactance (AX) in both males and females. While age affected the equation of X5 Hz in males and Fres in males.

Conclusions

Height and age were the most predictive values affecting the regression equation of IOS in Egyptian children and adolescents.

Small airway dysfunction as predictor and marker for clinical response to biological therapy in severe eosinophilic asthma: a longitudinal observational study

BACKGROUND

Anti-T2 biological therapies have proven to effectively reduce acute exacerbations and daily doses of oral steroids in severe eosinophilic asthma. Despite the remarkable clinical efficacy, there are usually only moderate improvements in airflow limitation, suggesting that other measures of lung function like small airway dysfunction (SAD) might better reflect the clinical response. We aimed to investigate if measures of small airway function would predict and correlate with the clinical response to anti-T2 therapy.

METHODS

We studied data of patients who were previously included in the German prospective longitudinal All Age Asthma Cohort (ALLIANCE) that recruits asthma patients of all severity grades and inflammatory phenotypes. The selection criteria for this analysis were adult patients with severe eosinophilic asthma under treatment with anti-T2 biological agents. Asthma control was assessed by asthma control test (ACT) and number of severe exacerbations. Small airway function was assessed by the frequency dependence of resistance (FDR, R5-20)) derived from impulse oscillometry (IOS) and the mean forced expiratory flow between 25 and 75% of the forced vital capacity (FEF_25-75). We also studied air trapping (RV and RV/TLC), blood eosinophils and FeNO. Patients were classified into responders and partial or non-responders. Clinical response was defined as at least 50% reduction in annualized severe exacerbations and daily oral steroid doses accompanied with a minimum increase of 3 points in the ACT score. We used a Receiver Operator Characteristic (ROC) to study the capacity of FDR in predicting clinical response compared to other clinical variable like blood eosinophils. We studied the correlation between FDR measures and clinical response, represented by the ACT score and number of exacerbations, using linear regressions.

RESULTS

20 patients were included (mean age, 59 ± 9 years; 60% female; mean body mass index (BMI), 27.6 ± 5.4 kg/m²; mean absolute blood eosinophils, 570 ± 389/µl; mean number of severe exacerbations 12 months prior to initiating the biological therapy, 5.0 ± 3; mean predicted FEV1, 76 ± 21%; mean predicted FDR, 224 ± 140%; mean daily prednisolone dose, 6.4 ± 4.9 mg; mean ACT score, 15 ± 5). Responders had significantly higher baseline FDR compared to partial or non-responders but similar FEV1, FEF_25-75, RV and RV/TLC. ROC analysis showed that the combination of FDR and blood eosinophils had the best predictive capacity of the clinical response among all tested clinical markers (FeNO, FEV1, FDR, blood eosinophils) with an AUC of 85% [67-100%], (CI = 0.95, p = 0.01). Linear regressions indicated better associations between improvements in FDR and ACT score (R² = 0.42, p = 0.001) than with FEV1 and ACT score (R² = 0.25, p = 0.013). Likewise, we observed better associations between improvements in FDR and reduction of exacerbations (R² = 0.41, p = 0.001) than with FEV1 (R² = 0.20, p = 0.025).

CONCLUSION

Our data suggest that severe SAD may represent a distinct phenotype of eosinophilic asthma that substantially improves under anti-T2 biological therapy. Measures of small airway function might be useful in selecting appropriate patients qualifying for anti-T2 biological therapy in addition to blood eosinophil count.

Application of Impulse Oscillometry in Adult Asthmatic Patients With Preserved Lung Function

PURPOSE

It is difficult to assess airway obstruction using spirometry in adult asthmatic patients with preserved lung function. Impulse oscillometry (IOS) can detect not only airway resistance but also reactance. Therefore, IOS may be useful in assessing pulmonary function in such patients. We investigated the applicability of IOS for asthma patients with preserved lung function.

METHODS

Between 2015 and 2018, 1,248 adult asthmatic patients suspected of having asthma who visited the Allergy and Asthma Center of Severance Hospital underwent both spirometry and IOS. Consequently, 784 patients had asthma, 111 had chronic obstructive lung disease (COPD) or asthma-COPD overlap, and 7 had parenchymal lung disease. The remaining 346 patients had chronic cough without underlying lung or airway disease. Among the 784 asthmatic patients, 191 with decreased lung function (predicted forced expiratory volume in 1 second [FEV1] < 80%) were excluded. Propensity score matching was performed to adjust baseline characteristics between 346 non-asthmatic and 593 asthmatic patients with preserved lung function. Subsequently, we compared the spirometry and IOS parameters between the 329 asthmatic and 329 non-asthmatic patients.

RESULTS

Multiple logistic regression analysis showed that the area of reactance (AX) was associated with asthma with preserved lung function. In receiver operating characteristic (ROC) curve analysis, the area under the curve (AUC) of AX (AUC = 0.6823) for asthma was not significantly different from that of FEV1 (AUC = 0.6758). However, the AUC of a combination of AX and FEV1 (AUC = 0.7437) for asthma was significantly higher than that of FEV1 alone. The cutoff value of AX was 0.51 kPa/L in univariate ROC analysis.

CONCLUSIONS

AX is associated with adult asthma with preserved lung function. Performing spirometry together with IOS is more beneficial than performing spirometry alone for diagnosing asthma in adult patients with preserved lung function.

Nonlinear parametric quantile models

Quantile regression is widely used to estimate conditional quantiles of an outcome variable of interest given covariates. This method can estimate one quantile at a time without imposing any constraints on the quantile process other than the linear combination of covariates and parameters specified by the regression model. While this is a flexible modeling tool, it generally yields erratic estimates of conditional quantiles and regression coefficients. Recently, parametric models for the regression coefficients have been proposed that can help balance bias and sampling variability. So far, however, only models that are linear in the parameters and covariates have been explored. This paper presents the general case of nonlinear parametric quantile models. These can be nonlinear with respect to the parameters, the covariates, or both. Some important features and asymptotic properties of the proposed estimator are described, and its finite-sample behavior is assessed in a simulation study. Nonlinear parametric quantile models are applied to estimate extreme quantiles of longitudinal measures of respiratory mechanics in asthmatic children from an epidemiological study and to evaluate a dose-response relationship in a toxicological laboratory experiment.

Measures of lung function and their relationship with advanced glycation end-products

Background

Advanced glycation end-products (AGEs) have been implicated in the pathophysiology of chronic obstructive pulmonary disease (COPD). However, the association between AGE accumulation in the skin measured by skin autofluorescence (SAF) and lung function in healthy subjects has not been explored in detail. We use a population-based study of 50–64-year-olds to assess spirometry, diffusing capacity of the lung for carbon monoxide (D_LCO) and impulse oscillometry (IOS) in relation to SAF.

Methods

Participants with information on SAF, lung function and potential confounding variables were included from the Swedish Cardiopulmonary Bioimage Study (SCAPIS) cohort (spirometry, n=4111; D_LCO, n=3889; IOS, n=3970). Linear regression was used to assess changes in lung function (as measured by spirometry (forced expiratory volume in 1 s (FEV₁), forced vital capacity (FVC) and FEV₁/FVC), D_LCO and IOS (resistance measured at 5 (R₅) and 20 Hz (R₂₀), R₅−R₂₀, area of reactance, reactance measured at 5 Hz (X­₅), and resonant frequency)) by a 1-sd increase in SAF.

Results

FEV₁, FVC and D_LCO were significantly and inversely associated with SAF after adjustment for potential confounding factors (per 1-sd increase in SAF: FEV₁ −0.03 L (95% CI −0.04– −0.02 L), p<0.001; FVC −0.03 L (95% CI −0.05– −0.02 L), p<0.001; D_LCO −0.07 mmol·min⁻¹·kPa⁻¹ (95% CI −0.11– −0.03 mmol·min⁻¹·kPa⁻¹), p<0.001). This association was also found in nonsmokers and in non-COPD subjects. Pulmonary reactance (X₅) but not pulmonary resistance (R₅, R₂₀ and R₅−R₂₀) was significantly associated with SAF (per 1-sd increase in SAF: X₅ −0.001 kPa·L⁻¹·s (95% CI −0.003–0.00 kPa·L⁻¹·s), p=0.042), which was mirrored in non-COPD patients but not in current nonsmokers.

Conclusions

AGE accumulation, as measured by SAF, is significantly associated with lung function decrements indicative of changes in the lung parenchyma

AGEs accumulation as measured by SAF is significantly associated with lung function decrements indicative of changes in the lung parenchymahttp://bit.ly/2IRgSWz

"Current place of impulse oscillometry in the assessment of pulmonary diseases."

In 1956, a diagnostic tool using the forced oscillation technique (FOT) was developed to examine respiratory functions. A modification of this method is impulse oscillometry (IOS). In the latter, a loudspeaker delivers to the respiratory system a regular, square pressure wave at a constant frequency from which all other individual frequencies are derived using spectral analysis. The usefulness of IOS has been examined in relation to COPD, asthma, interstitial lung diseases, obstructive sleep apnea, and other conditions. The greatest advantage, most notable in children, is the ability to monitor the course of a disease and to assess the response to therapy in a simple way, i.e., minimal requirements for the cooperation of the patient, rapid and reproducible measurements. The IOS shows similar or even higher sensitivity than spirometry in detecting small airways dysfunction (SAD). The most well-known result observed in peripheral airways disease (PAD) is the frequency dependence of resistance. Importantly, the abnormal resistance at a specific frequency may occur with normal spirometry in those with early PAD. Moreover, IOS is particularly useful if the patient cannot perform effort dependent exhalation. Despite its advantages, the technique is still poorly found in official worldwide recommendations. Nonetheless, considering the promising results of many studies, an increase in interest in IOS is expected, and it could soon be on par with standard pulmonary function tests. The aim of this work is to present the basics, current views, and various aspects of IOS. To carry out our analysis, we searched for relevant publications on PubMed, Web of Science. Original and review articles were selected and discussed.

Lung Computational Models and the Role of the Small Airways in Asthma

Rationale: Asthma is characterized by disease within the small airways. Several studies have suggested that forced oscillation technique-derived resistance at 5 Hz (R5) - resistance at 20 Hz (R20) is a measure of small airway disease; however, there has been limited validation of this measurement to date.Objectives: To validate the use of forced oscillation R5 - R20 as a measure of small airway narrowing in asthma, and to investigate the role that small airway narrowing plays in asthma.Methods: Patient-based complete conducting airway models were generated from computed tomography scans to simulate the impact of different degrees of airway narrowing at different levels of the airway tree on forced oscillation R5 - R20 (n = 31). The computational models were coupled with regression models in an asthmatic cohort (n = 177) to simulate the impact of small airway narrowing on asthma control and quality of life. The computational models were used to predict the impact on small airway narrowing of type-2 targeting biologics using pooled data from two similarly design randomized, placebo-controlled biologic trials (n = 137).Measurements and Main Results: Simulations demonstrated that narrowing of the small airways had a greater impact on R5 - R20 than narrowing of the larger airways and was associated (above a threshold of approximately 40% narrowing) with marked deterioration in both asthma control and asthma quality of life, above the minimal clinical important difference. The observed treatment effect on R5 - R20 in the pooled trials equated to a predicted small airway narrowing reversal of approximately 40%.Conclusions: We have demonstrated, using computational modeling, that forced oscillation R5 - R20 is a direct measure of anatomical narrowing in the small airways and that small airway narrowing has a marked impact on both asthma control and quality of life and may be modified by biologics.

Regression equations of respiratory impedance of Indian adults measured by forced oscillation technique

Background

Forced oscillation technique (FOT) is a technique to measure the mechanical properties of the lung. The present study was aimed to develop regression equations of within- and whole-breath respiratory impedance (Zrs) of healthy Indian adults.

Methods

Total 323 adults were sequentially screened. Smokers, individuals with respiratory symptoms or diseases, and unable to perform acceptable FOT were excluded. Within- and whole-breath resistance (Rrs) and reactance (Xrs) were measured at 5, 11, and 19 Hz by Resmon Pro^® Full device. The regression equations of within- and whole-breath Rrs and Xrs were generated separately for men and women by multiple linear regression models.

Results

The FOT data of 253 individuals (122 men) aged 18-81 years were included in the analysis. The magnitudes of whole-breath Rrs at 5 Hz (4.53 ± 1.05 cmH₂O/L/s in women vs. 3.26 ± 1.05 cmH₂O/L/s in men; P = 0.000) and whole-breath Xrs at 5 Hz (-1.23 ± 0.66 cmH₂O/L/s in women vs. -1.00 ± 0.54 cmH₂O/L/s in men; P = 0.003) of women were significantly of higher magnitude as compared to men. The standing height was the best determinant of Zrs, followed by body weight; the effect of age was negligible and was observed in men only. The magnitudes of both Rrs and Xrs decrease with an increase in standing height of both men and women.

Conclusions

The present study provides regression equations of within- and whole-breath respiratory impedance of Indian adults.

A Rapid, Handheld Device to Assess Respiratory Resistance: Clinical and Normative Evidence

INTRODUCTION

Following reports of respiratory symptoms among service members returning from deployment to South West Asia (SWA), an expert panel recommended pre-deployment spirometry be used to assess disease burden. Unfortunately, testing with spirometry is high cost and time-consuming. The airflow perturbation device (APD) is a handheld monitor that rapidly measures respiratory resistance (APD-Rr) and has promising but limited clinical data. Its speed and portability make it ideally suited for large volume pre-deployment screening. We conducted a pilot study to assess APD performance characteristics and develop normative values.

MATERIALS AND METHODS

We prospectively enrolled subjects and derived reference equations for the APD from those without respiratory symptoms, pulmonary disease, or tobacco exposure. APD testing was conducted by medical technicians who received a 10-min in-service on its use. A subset of subjects performed spirometry and impulse oscillometry (iOS), administered by trained respiratory therapists. APD measures were compared with spirometry and iOS.

RESULTS

The total study population included 199 subjects (55.8% males, body mass index 27.7 ± 6.0 kg/m2, age 49.9 ± 18.7 yr). Across the three APD trials, mean inspiratory (APD-Ri), expiratory (APD-Re), and average (APD-Ravg) resistances were 3.30 ± 1.0, 3.69 ± 1.2, and 3.50 ± 1.1 cm H2O/L/s. Reference equations were derived from 142 clinically normal volunteers. Height, weight, and body mass index were independently associated with APD-Ri, APD-Re, and APD-Ravg and were combined with age and gender in linear regression models. APD-Ri, APD-Re, and APD-Ravg were significantly inversely correlated with FEV1 (r = -0.39 to -0.42), FVC (r = -0.37 to -0.40), and FEF25-75 (r = -0.31 to -0.35) and positively correlated with R5 (r = 0.61-0.62), R20 (r = 0.50-0.52), X5 (r = -0.57 to -0.59), and FRES (r = 0.42-0.43). Bland-Altman plots showed that the APD-Rr closely approximates iOS when resistance is normal.

CONCLUSION

Rapid testing was achieved with minimal training required, and reference equations were constructed. APD-Rr correlated moderately with iOS and weakly with spirometry. More testing is required to determine whether the APD has value for pre- and post-deployment respiratory assessment.

Correlation between impulse oscillometry parameters and asthma control in an adult population

Purpose: Impulse oscillometry (IOS) has been proposed as an alternative test to evaluate the obstruction of small airways and to detect changes in airways earlier than spirometry. In this study, we sought to determine the utility and association of IOS parameters with spirometry and asthma control in an adult population. Patients and methods: Adults 14-82 years of age with asthma were classified into uncontrolled asthma (n=48), partially controlled asthma (n=45), and controlled asthma (n=49) groups, and characterized with fractional exhaled nitric oxide (FE_NO), IOS, and spirometry in a transversal analysis planned as a one-visit study. The basic parameters evaluated in IOS are resistance at 5 Hz (R₅), an index affected by the large and small airway; resistance at 20 Hz (R₂₀), an index of the resistance of large airways; difference between R₅ and R₂₀ (R₅-R₂₀), indicative of the function of the small peripheral airways; reactance at 5 Hz (X₅), indicative of the capacitive reactance in the small peripheral airways; resonance frequency (Fres), the intermediate frequency at which the reactance is null, and reactance area (XA), which represents the total reactance (area under the curve) at all frequencies between 5 Hz to Fres. Results: There were statistical differences between groups in standard spirometry and IOS parameters reflecting small peripheral airways (R₅, R₁₀, R₅-R₂₀, Fres, XA and X₅) (P<0.001). Accuracy of IOS and/or spirometry to discriminate between controlled asthma vs partially controlled asthma and uncontrolled asthma was low (AUC=0.61). Using linear regression models, we found a good association between spirometry and IOS. In order to evaluate IOS as an alternative or supplementary method for spirometry, we designed a predictive model for spirometry from IOS applying a penalized regression model (Lasso). Then, we compared the original spirometry values with the values obtained from the predictive model using Bland-Altman plots, and the models showed an acceptable bias in the case of FEV₁/FVC, FEV₁%, and FVC%. Conclusion: IOS did not show a discriminative capacity to correctly classify patients according to the degree of asthma control. However, values of IOS showed good association with values of spirometry. IOS could be considered as an alternative and accurate complement to spirometry in adults. In a predictive model, spirometry values estimated from IOS tended to overestimate in low values of "real" spirometry and underestimate in high values.

Usefulness of impulse oscillometry for the assessment of bronchodilator response in elderly patients with chronic obstructive airway disease

BACKGROUND

Impulse oscillometry (IOS) is a noninvasive and convenient technique to measure both airway resistance and reactance. This study aimed to evaluate whether IOS can be used to measure bronchodilator response (BDR) in elderly patients with asthma and chronic obstructive pulmonary disease (COPD) and also describe the difference between asthma and COPD.

METHODS

Seventy patients (30 and 40 with asthma and COPD, respectively) over 65 years of age were enrolled. IOS and spirometry measurements were obtained before and after bronchodilator administration. Correlation analysis was used to compare the percentage changes in spirometry and IOS parameters after bronchodilator administration between the asthma and COPD groups.

RESULTS

The changes in IOS parameters after bronchodilator administration were strongly correlated with changes in forced expiratory volume at 1 second (FEV₁) and forced expiratory flow at 25-75% (FEF_25-75). However, the percentage changes in IOS parameters failed to discriminate between the asthma and COPD groups. Receiver operating characteristic curve (ROC) analysis of resistance at 5 and 20 Hz (R5-20) at the best cutoff (-15.4% change) showed both high sensitivity and specificity for BDR.

CONCLUSIONS

IOS serves as a reliable and useful technique for identifying BDR in elderly patients with chronic obstructive airway disease. There was a difference in IOS parameters between the asthma and COPD groups; however, it was difficult to distinguish between both diseases. Further larger studies are required to investigate the real implications of using IOS in the clinical practice.

Measuring the effects of bronchial thermoplasty using oscillometry

BACKGROUND AND OBJECTIVE

Bronchial thermoplasty (BT) has been consistently shown to reduce symptoms, exacerbations and the need for reliever medication in patients with severe asthma. Paradoxically, no consistent improvement in spirometry has been demonstrated. It has been suggested that this is due to a reduction in peripheral resistance in small airways, not captured by spirometry. Therefore, in this study, we evaluate the response to BT using oscillometry.

METHODS

A total of 43 patients with severe asthma from two centres were evaluated at baseline, 6 weeks and 6 months post BT, using spirometry, plethysmography and oscillometry, in addition to medication usage, exacerbation frequency and the Asthma Control Questionnaire (5-item version) (ACQ-5).

RESULTS

The mean age was 58.4 ± 11.2 years, forced expiratory volume in 1 s (FEV₁ ) 55.5 ± 20.1% predicted, forced expiratory ratio 53.0 ± 14.5% and FEV₁ response to salbutamol was 14.0 ± 14.5%. Following BT, the group responded to treatment with an improvement in ACQ-5 from 2.9 ± 0.9 at baseline to 1.7 ± 1.1 at 6 months (P < 0.005). There was an 81% reduction in exacerbation frequency (P < 0.001) and 50% of patients were weaned completely from maintenance oral corticosteroids. No changes after treatment were observed in spirometry but the residual volume reduced from 147 ± 38% to 139 ± 39% predicted (P < 0.01). Baseline oscillometry demonstrated high levels of resistance at 5 Hz with normal resistance at 20 Hz, indicating resistance in the small airways was elevated, but no changes were observed in any oscillometry parameter after BT treatment.

CONCLUSION

Lung impedance measured with oscillometry did not change following BT despite marked clinical improvements in patients with severe asthma.

Impulse oscillometry and nitrogen washout test in the assessment of small airway dysfunction in asthma: Correlation with quantitative computed tomography

OBJECTIVE

Small airway dysfunction (SAD) and airway remodeling influence the disease control and progression in asthma. We investigated whether impulse oscillometry (IOS) and single breath nitrogen washout (SBN₂W) could be reliable tests in evaluating SAD and airway remodeling by correlating their data with radiological parameters derived from quantitative chest multidetector computed tomography (MDCT) imaging.

METHODS

Lung function tests were performed before and after bronchodilator. The MDCT lung scans were acquired at full inspiration and expiration using a portable spirometer to control the respiratory manoeuvres. Symptom control was assessed using the Asthma Control Test (ACT) questionnaire.

RESULTS

Twenty six patients were enrolled. The bronchial lumen area (LA) measured with MDCT lung scan, correlated inversely with airway resistance (Raw, p < 0.001) and with total and large airway oscillometric resistance (R5, p = 0.002 and R20, p = 0.006, respectively). However these two last correlations became non-significant after Bonferroni correction for multiple comparisons. The radiological quantification of air trapping correlated with Raw (p < 0.001), residual volume (RV, p < 0.001), and the slope of phase III of SBN₂W (DeltaN₂, p < 0.001) whereas the correlation with small airway oscillometric resistance (R5-20) was non-significant after Bonferroni adjustment. Finally, air trapping was significantly higher in patients with a fixed bronchial obstruction in comparison to patients with reversible obstruction.

CONCLUSIONS

Plethysmographic method remains the main tool to investigate SAD and airway remodeling in asthmatic patients. The integration with the SBN₂W test proved useful to better evaluate the small airway involvement whereas IOS showed a weaker correlation with both radiological and clinical data.

Impedance Oscillometry: Emerging Role in the Management of Chronic Respiratory Disease

PURPOSE OF REVIEW

Chronic respiratory diseases affecting adults and children are widely prevalent, so lung function testing is imperative for diagnosis and management. Spirometry is the traditional standard measure of lung function; however, certain groups of patients are unable to provide accurate and reproducible exhalation maneuvers. Consequently, the impedance oscillometry system (IOS) has been developed as an effort, independent technique to assess airway function in children and the elderly. To better understand this emerging modality, the following review will compare IOS with spirometry, examine the function of the device, provide interpretation strategies, and discuss the evidence supporting its use in adults and children with chronic lung disease.

RECENT FINDINGS

In a population of symptomatic adults with suspected COPD, impedance oscillometry resistance measurements correlate with FEV₁ and lung resistance increases with the severity of airflow limitation. In patients with asthma, IOS is a sensitive measure of airway hyperresponsiveness and bronchodilator response. Impedance oscillometry is evolving as an alternative measure to assess lung function pediatric and adult populations.

Small airway dysfunction in chronic hypersensitivity pneumonitis

BACKGROUND AND OBJECTIVE

Lung biopsies from patients with hypersensitivity pneumonitis (HP) have demonstrated small airway (SA) involvement, but there is no information concerning SA function in HP, and it is unknown whether pharmacological treatment could modify its function. SA function in patients with chronic HP using ultrasonic pneumography (UPG) and impulse oscillometry (IOS) was explored. We also compared initial results with those obtained after 4 weeks of standardized treatment with azathioprine and prednisone.

METHODS

The study group consisted of adults with recent diagnoses of HP. All patients completed UPG, IOS, spirometry, body plethysmography, single-breath carbon monoxide diffusing capacity (DL_CO ) and the 6-min walk test (6MWT). The fraction of exhaled nitric oxide (FE_NO ) was obtained to assess eosinophilic airway inflammation. Measurements were taken at diagnosis and after 4 weeks of treatment.

RESULTS

A total of 20 consecutive patients (16 women) with chronic HP participated in the study. Median age was 50 years (interquartile range (IQR): 42-54). At diagnosis, the UPG phase 3 slope was abnormally high, consistent with maldistribution of ventilation. For IOS, all patients had low reactance at 5 Hz (X5) and elevated reactance area (AX) reflecting low compliance, and only eight (40%) patients had elevated R5 (resistance at 5 Hz (total)) and R5-20 (resistance at 5 Hz-resistance at 20 Hz (peripheral)) attributed to SA resistance. In contrast, FE_NO parameters were within normal limits. After treatment, forced vital capacity (FVC), the 6-min walk distance and the distribution of ventilation showed significant improvement, although DL_CO did not.

CONCLUSION

Patients with chronic HP have SA abnormalities that are partially revealed by the UPG and IOS tests. Lung volumes, but not gas exchange, improved after treatment with azathioprine and prednisone.

Bronchodilator Response Assessment of the Small Airways Obstructive Pattern

Background:

A concomitant decrease in FEV₁ and FVC with normal FEV₁/FVC ratio and TLC defines small airways obstructive pattern (SAOP) and constitutes a classic pitfall of pulmonary-function-tests interpretation.

Objective:

To evaluate the prevalence of flow- (FEV₁ increase≥12% and 200 mL), volume- (FVC or inspiratory capacity [IC] increase≥12% and 200 mL), flow and volume-, and non-response to bronchodilation in patients with SAOP. An additional objective was to assess whether impulse oscillometry (IOS) parameters allow the diagnosis of SAOP and its reversibility.

Methods:

Fifty consecutive adult patients with SAOP (FEV₁ and FVC < lower limit of normal, FEV₁/FVC and TLC > lower limit of normal) diagnosed on spirometry and plethysmography underwent the assessment of reversibility (400 µg salbutamol) on FEV₁, FVC, IC and IOS parameters.

Results:

The diseases most frequently associated with SAOP were COPD and asthma (26 and 15 patients, respectively). Six patients were flow-responders, 20 were volume-responders, 9 were flow and volume-responders and 15 patients were non-responders. Overall, 26 patients had a significant improvement of IC, and 35 / 50 (70%, 95%CI: 57-83) exhibited a significant bronchodilator response. The difference between Rrs_5Hz and Rrs_20Hz was increased in 28/50 patients (56%, 95%CI: 42-70 with value higher than upper limit of normal) and its decrease after bronchodilator significantly correlated to FEV₁ increase only, suggesting proximal airway assessment.

Conclusion:

A significant reversibility, mainly assessed on IC increase, is frequent in Small Airways Obstructive Pattern. Impulse oscillometry is of limited value in this context because of its low sensitivity.

The case for impulse oscillometry in the management of asthma in children and adults

OBJECTIVE

To provide a clinical rationale for including impulse oscillometry (IOS) as a part of standard office-based asthma assessment.

DATA SOURCES

PubMed and Google search, limited to English language and human disease, with the keywords IOS and asthma.

STUDY SELECTIONS

Articles included in this review were based on the expert opinion and previous publications by the authors.

RESULTS

In children, IOS was more useful than spirometry in identifying asthma and uncontrolled asthma and predicting loss of control and exacerbations. IOS predicts young children at risk for loss of lung function with age and the potential for early intervention to prevent further sequelae. In adults, peripheral airway impairment detected by IOS or spirometry (ie, forced expiratory flow between 25% and 75%) commonly occurs across severity, and each measure may be complementary in predicting loss of control even with normal forced expiratory volume in 1 second. Extrafine inhaled corticosteroids with or without long-acting β-agonists proved superior to standard particle aerosols in improving IOS-detected peripheral airway obstruction. Our data also suggest that currently available commercial reference values for lung resistance at 5 Hz and lung reactance at 5 Hz are applicable across diverse populations, but further studies are needed.

CONCLUSION

The findings of this review suggest that IOS can add value to traditional clinical and spirometric assessment and thus improve management of asthma in children and adults, as well as have the potential to detect early dysfunction of the peripheral airways, which may result in better outcomes.

Clinical characteristics of adult asthma associated with small airway dysfunction

Suboptimal asthma control is common despite modern asthma therapy. The degree of peripheral airway involvement remains unclear and poor medication delivery to these regions might be a contributing reason for this failure in obtaining adequate symptom control. A cohort of 196 adults (median (range) age 44 (18-61) years, 109 females, 54 ex-smokers, six current smokers) with physician-diagnosed asthma were recruited from primary care. Subjects were characterized clinically by interviews, questionnaires, skin prick tests (SPT) and blood eosinophil counts. Lung function was assessed by spirometry, impulse oscillometry (IOS) and nitrogen multiple breath washout (N2 MBW). IOS assessed peripheral airway resistance (FDR, frequency dependence of resistance). N2 MBW assessed global ventilation inhomogeneity (LCI, lung clearance index), specific indices of peripheral airway function (Scond × VT and Sacin × VT; VT, tidal volume), and inter-regional inhomogeneity (specific ventilation ratio). Never-smoking healthy cohorts of 158 and 400 adult subjects provided local reference values for IOS and N2 MBW variables, respectively. Peripheral airway dysfunction was detected in 31% (FDR or specific ventilation ratio) to 47% (Scond x VT) of subjects. Risk factors for peripheral airway dysfunction were identified. Among subjects with low FEV1 and either positive smoking history and/or blood eosinophilia (>4.0%), 63% had abnormality across all peripheral airway outcomes, whilst only one subject was completely normal. Abnormal peripheral airway function was present in a large proportion of adult asthmatics at baseline. Reduced FEV1, a positive smoking history, and/or blood eosinophilia identified "a small airway asthma subtype" that might benefit from peripheral airway targeted therapy.

Pacientes com doença de Parkinson sob assistência fisioterapêutica apresentam parâmetros pulmonares melhores do que controles sedentários

RESUMO Este estudo teve como objetivo investigar os parâmetros pulmonares (espirometria e oscilometria de impulso) de pacientes com doença de Parkinson (DP) e controles eutróficos, comparando os valores dos sujeitos participantes e os não participantes de um programa de assistência fisioterapêutica. Trinta e sete sujeitos foram divididos em quatro grupos independentes: dois grupos formados por pacientes com DP (praticantes e não praticantes de um protocolo de exercícios fisioterapêuticos realizados com frequência de dois atendimentos semanais durante 6 meses) e dois grupos compostos por sujeitos controles eutróficos (praticantes e não praticantes do mesmo programa terapêutico). Os sujeitos foram submetidos à avaliação de cirtometria torácica, espirometria e oscilometria de impulso, sendo os pacientes com DP avaliados na fase off da medicação. A análise dos dados ocorreu por meio do teste não paramétrico de Kruskal-Wallis, sendo a comparação aos pares realizada pelo pós-teste de Dunett T3. A significância foi estipulada em 5%. Sobre os resultados, com similaridade entre grupos para mobilidade da caixa torácica, os pacientes com DP que realizaram atendimento fisioterapêutico apresentaram parâmetros pulmonares melhores do que os pacientes sedentários. A comparação com os sujeitos eutróficos vislumbra melhores resultados dos participantes com DP em relação a controles sedentários. Não houve diferença significativa entre os sujeitos com DP e controles submetidos ao mesmo protocolo terapêutico. Em conclusão, os achados delimitam resultados promissores do tratamento fisioterapêutico sobre parâmetros pulmonares na DP, e sentenciam a necessidade de novos estudos longitudinais do tipo ensaio clínico para comprovação da relação causa e efeito das variáveis em questão.

The effect of body weight on distal airway function and airway inflammation

BACKGROUND/OBJECTIVES

Obesity is a global health problem that adversely influences the respiratory system. We assessed the effects of body mass index (BMI) on distal airway function and airway inflammation.

SUBJECTS/METHODS

Impulse oscillometry (IOS) as a measure of distal airway function, together with spirometry, were assessed in adults with a range of different BMIs. Airway inflammation was assessed with the fraction of exhaled nitric oxide (FeNO) and participants exhaled at various exhalation flows to determine alveolar and bronchial NO.

RESULTS

In total 34 subjects were enrolled in the study; 19 subjects had a normal BMI (18.50-24.99), whilst 15 subjects were overweight (BMI 25.00-29.99), or obese (BMI ≥30). All subjects had normal spirometry. However, IOS measures of airway resistance (R) at 5Hz, 20Hz and frequency dependence (R_5-20) were elevated in overweight/obese individuals, compared to subjects with a normal BMI (median (interquartile range)); 5Hz: 0.41 (0.37, 0.45) vs. 0.32 (0.30, 0.37)kPa/l/s; 20Hz: 0.34 (0.30, 0.37) vs. 0.30 (0.26, 0.33)kPa/l/s; R_5-20: 0.06 (0.04, 0.11) vs. 0.03 (0.01, 0.05)kPa/l/s; p<0.05), whereas airway reactance at 20Hz was decreased in overweight/obese individuals (20Hz: 0.07 (0.03, 0.09) vs. 0.10 (0.07, 0.13)kPa/l/s, p=0.009; 5Hz: -0.12 (-0.15, -0.10) vs. -0.10 (-0.13, -0.09)kPa/l/s, p=0.07). In contrast, within-breath IOS measures (a sign of expiratory flow limitation) and FeNO inflammatory measures, did not differ between groups (p>0.05).

CONCLUSIONS

Being overweight has significant effects on distal and central airway function as determined by IOS, which is not detected by spirometry. Obesity does not influence airway inflammation as measured by FeNO. IOS is a reliable technique to identify airway abnormalities in the presence of normal spirometry in overweight people.

Transfer factor, lung volumes, resistance and ventilation distribution in healthy adults

Monitoring of chronic lung disease requires reference values of lung function indices, including putative markers of small airway function, spanning a wide age range.We measured spirometry, transfer factor of the lung for carbon monoxide (TLCO), static lung volume, resistance and ventilation distribution in a healthy population, studying at least 20 subjects per sex and per decade between the ages of 20 and 80 years.With respect to the Global Lung Function Initiative reference data, our subjects had average z-scores for forced expiratory volume in 1 s (FEV1), forced vital capacity (FVC) and FEV1/FVC of -0.12, 0.04 and -0.32, respectively. Reference equations were obtained which could account for a potential dependence of index variability on age and height. This was done for (but not limited to) indices that are pertinent to asthma and chronic obstructive pulmonary disease studies: forced expired volume in 6 s, forced expiratory flow, TLCO, specific airway conductance, residual volume (RV)/total lung capacity (TLC), and ventilation heterogeneity in acinar and conductive lung zones.Deterioration in acinar ventilation heterogeneity and lung clearance index with age were more marked beyond 60 years, and conductive ventilation heterogeneity showed the greatest increase in variability with age. The most clinically relevant deviation from published reference values concerned RV/TLC values, which were considerably smaller than American Thoracic Society/European Respiratory Society-endorsed reference values.

Measuring lung function using sound waves: role of the forced oscillation technique and impulse oscillometry system

Measuring lung function is an important component in the decision making process for patients with obstructive airways disease (OAD). Not only does it help in arriving at a specific diagnosis, but it also helps in evaluating severity so that appropriate pharmacotherapy can be instituted, it helps determine prognosis and it helps evaluate response to therapy. Spirometry is currently the most commonly performed lung function test in clinical practice and is considered to be the gold standard diagnostic test for asthma and COPD. However, spirometry is not an easy test to perform because the forceful expiratory and inspiratory manoeuvres require good patient co-operation. Children aged <5 years, elderly people and those with physical and cognitive limitations cannot perform spirometry easily.