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Objective To investigate whether the decrease in dyspnea in neuromuscular diseases after air stacking (AS) occurs mostly in patients with decreased inspiratory muscle force and ensuing chest wall restriction or heterogeneous ventilation across the lungs. Design Interventional, before-after study. Setting A neurorehabilitation inpatient and outpatient center. Participants Fifteen consecutive adult patients affected by neuromuscular diseases (N=15). Interventions AS treatment. Main Outcome Measures Patients had vital capacity (VC) and sniff nasal inspiratory pressure (SNIP) measured. We measured Borg score, oxygen saturation, and ventilation heterogeneity across the lung as estimated from the difference between respiratory resistance at 5 and 19 Hz (R5-19) with the forced oscillation technique before and 5, 30, 60, and 120 minutes after applying AS. Results Before AS, Borg score was significantly related to R5-19 (r2 0.46, P Conclusions These findings suggest that dyspnea in neuromuscular diseases is related to heterogeneous ventilation rather than inspiratory muscle force and/or lung volumes decrease. Restoring ventilation distribution across the lungs with AS appears to improve dyspnea.

Chronic obstructive pulmonary disease (COPD) management remains challenging due to the high heterogeneity of clinical symptoms and the complex pathophysiological basis of the disease. Airflow limitation, diagnosed by spirometry, remains the cornerstone of the diagnosis. However, the calculation of the forced expiratory volume in the first second (FEV1) alone, has limitations in uncovering the underlying complexity of the disease. Incorporating additional pulmonary function tests (PFTs) in the everyday clinical evaluation of COPD patients, like resting volume, capacity and airway resistance measurements, diffusion capacity measurements, forced oscillation technique, field and cardiopulmonary exercise testing and muscle strength evaluation, may prove essential in tailoring medical management to meet the needs of such a heterogeneous patient population. We aimed to provide a comprehensive overview of the available PFTs, which can be incorporated into the primary care physician’s practice to enhance the efficiency of COPD management.

Vocal cord dysfunction (VCD) often coexists with asthma and exacerbates respiratory symptoms. A noninvasive method could be considered beneficial for the detection and follow-up of VCD complicated by asthma. Here, we report a case of VCD complicated by asthma, highlighting the effectiveness of colored three-dimensional (3-D) imaging of respiratory impedance using a broadband frequency forced oscillation technique (MostGraph).A 74-year-old woman with difficult-to-treat asthma, in whom mepolizumab treatment was ineffective, was referred to our hospital. Stridulous sounds were loudest over the anterior neck. Pulmonary function tests' results were normal; however, a flattening of the inspiratory flow-volume curve was detected.Remarkably, prominent spikes were observed in the inspiratory phase in the colored 3-D imaging of respiratory resistance, which was superimposed on increased respiratory resistance in the expiratory phase. Flexible laryngoscopy revealed the adduction of vocal cords on inspiration. The patient was diagnosed with asthma complicated by VCD. After successful treatment of VCD by speech therapy, inspiratory spikes of respiratory resistance disappeared, and normal vocal cord movement was observed on laryngoscopy.The present case report indicates the effectiveness of forced oscillometry in evaluating dynamic changes in respiratory resistance for detecting and monitoring VCD complicated by asthma.

Background:Respiratory function declines after lung resection. However, perioperative changes in respiratory impedance and their clinical significance are unclear. The forced oscillation technique can measure respiratory impedance during quiet breathing and possibly early after surgery. We investigated respiratory impedance changes before and after lung lobectomy and examined the correlation of impedance with clinical factors., Methods:We prospectively included patients who underwent lobectomy between February 2018 and March 2020 and measured respiratory impedance by forced oscillation preoperatively and postoperative days 1 and 7. We statistically analyzed changes in perioperative forced oscillation measurements and their correlation with clinical factors, including subjective symptoms. The modified British Medical Research Council scale and the chronic obstructive pulmonary disease (COPD) assessment test were used for scoring subjective symptoms., Results:Forty-four subjects were included, in whom respiratory impedance could be measured from postoperative day 1. The respective mean values for forced oscillation measurements preoperatively and at postoperative days 1 and 7 were as follows: respiratory resistance, 5 Hz: 2.28, 2.77, and 2.75; respiratory resistance, 20 Hz: 2.00, 2.36, and 2.32; difference in respiratory resistance at 5 and 20 Hz: 0.28, 0.40, and 0.43; respiratory reactance, 5 Hz: -0.31, -0.65, and -0.56; resonant frequency: 7.45, 10.41, and 9.81; and low-frequency reactance area: 1.33, 3.27, and 2.84. These changes were statistically significant (P, Conclusions:Respiratory impedance was measurable even early after surgery and significantly changed postoperatively. As the sample size was small and appeared to be biased, assessing respiratory impedance and clinical factors in detail was difficult. Since respiratory impedance is suggested to be associated with clinical factors that affect the postoperative course, it is necessary to accumulate cases and observe them over longer periods.

Background Obstructive ventilatory disturbances occur in both chronic obstructive pulmonary disease (COPD), a typical disease representative of peripheral airway obstruction, and central airway obstruction (CAO). Pulmonary function tests (PFTs), which depend on patient effort, are traditionally used to evaluate lung function. The forced oscillation technique (FOT) is an effort-independent method for examining lung function during tidal breathing. The FOT is used universally to assess respiratory function in patients with COPD. Several studies have measured FOT to assess ventilatory disturbances in CAO. The results showed that FOT measurements in patients with CAO were similar to those reported in patients with COPD. However, no studies have compared FOT measurements directly between CAO and COPD. The aim of this study was to identify differences in ventilatory disturbances between peripheral and central airway obstructions in COPD and CAO, before patients received pharmacological therapy or bronchoscopic interventions, respectively. Patients and methods We retrospectively included 16 patients with CAO (10 cases of tracheal obstruction and 6 cases of bronchial obstruction) and 75 treatment-naive patients with COPD (60 cases in Global Initiative for Chronic Obstructive Lung Disease [GOLD] stage II and 15 cases in GOLD stage III) that were admitted from December 2013 to May 2017. Prior to treatment, patients were examined with the FOT and PFTs. Results All parameters measured with the FOT in the inspiratory phase were significantly worse in patients with CAO than in patients with COPD. The PFTs showed that the CAO group had a significantly lower peak expiratory flow rate. In the airway wall thickening phenotype of COPD, a difference between the inspiratory and expiratory phases of the resonance frequency (ΔFres) was the best indicator for distinguishing between peripheral and central airway obstructions. Conclusion This study compared differences between CAO and COPD (mainly GOLD stage II). We found that the FOT measurement, ΔFres, was the optimal indicator of the difference between the airway wall thickening COPD phenotype and CAO. Thus, the difference might be due to mechanical changes that occur in COPD with airway wall thickening.

Spirometry is considered the gold standard method for monitoring lung function of patients with cystic fibrosis (CF) but it requires patients’ cooperation and therefore it is not useful for the majority of preschool-aged children. Oscillometry is an alternative modality for lung function monitoring that requires minimal cooperation and can be applied in children as young as 3 years of age. Furthermore, it generates lesser aerosol compared to spirometry, an issue that is of considerable importance in the COVID-19 era. The aim of this review was to present the existing clinical data regarding the application of oscillometry in children and adolescents with CF. The method seems to have acceptable feasibility and repeatability. However, there is conflicting data regarding the correlation of oscillometry values with the clinical symptoms of CF patients either in clinically stable or in exacerbation periods. Furthermore, it is not clear to what extent oscillometry measurements correlate with the spirometry indices. Based on current evidence, spirometry cannot be substituted by oscillometry in the monitoring of the respiratory status of children and adolescents with CF.

The association between airflow obstruction and bronchial dilation has been researched in bronchiectasis. However, the impact of bronchial wall thickening on airflow obstruction has not been thoroughly investigated. This study assessed the underlying mechanism of airflow obstruction in bronchiectasis due to abnormal bronchial wall thickening using oscillometry. A total of 98 patients with bronchiectasis were retrospectively reviewed. At the time of diagnosis, spirometric and oscillometric parameters, high-resolution computed tomography scores, and clinical characteristics were collected. The bronchial diameter, bronchial wall thickness, and extent of emphysema were evaluated semi-quantitatively. Correlations between patient data and characteristics were analyzed. Thirty-three patients with airflow obstruction showed higher respiratory resistance, more negative respiratory reactance (Xrs) at 5 Hz (X5), and higher bronchial wall thickness score than those without airflow obstruction. The bronchial wall thickness score negatively affected forced expiration volume in 1 s /forced vital capacity and X5. Abnormal bronchial wall thickening might make Xrs more negative and progress airflow obstruction in bronchiectasis.

Pulmonary electrical impedance tomography (EIT) is a functional imaging technique that allows real-time monitoring of ventilation distribution. Ventilation heterogeneity (VH) is a characteristic feature of chronic obstructive pulmonary disease (COPD) and has previously been quantified using features derived from tidal variations in the amplitude of the EIT signal. However, VH may be better described by time-based metrics, the measurement of which is made possible by the high temporal resolution of EIT. We aimed 1) to quantify VH using novel time-based EIT metrics and 2) to determine the physiological relevance of these metrics by exploring their relationships with complex lung mechanics measured by the forced oscillation technique (FOT). We performed FOT, spirometry, and tidal-breathing EIT measurements in 11 healthy controls and 9 volunteers with COPD. Through offline signal processing, we derived 3 features from the impedance-time ( Z- t) curve for each image pixel: 1) tE, mean expiratory time; 2) PHASE, mean time difference between pixel and global Z- t curves; and 3) AMP, mean amplitude of Z- t curve tidal variation. Distribution was quantified by the coefficient of variation (CV) and the heterogeneity index (HI). Both CV and HI of the tE and PHASE features were significantly increased in COPD compared with controls, and both related to spirometry and FOT resistance and reactance measurements. In contrast, distribution of the AMP feature showed no relationships with lung mechanics. These novel time-based EIT metrics of VH reflect complex lung mechanics in COPD and have the potential to allow real-time visualization of pulmonary physiology in spontaneously breathing subjects. NEW & NOTEWORTHY Pulmonary electrical impedance tomography (EIT) is a real-time imaging technique capable of monitoring ventilation with exquisite temporal resolution. We report novel, time-based EIT measurements that not only demonstrate ventilation heterogeneity in chronic obstructive pulmonary disease (COPD), but also reflect oscillatory lung mechanics. These EIT measurements are noninvasive, radiation-free, easy to obtain, and provide real-time visualization of the complex pathophysiology of COPD.

Objective Hypersensitivity pneumonitis (HP) is an interstitial lung disease caused by the inhalation of specific organic antigens or low-molecular weight substances in genetically susceptible individuals. Although small airway involvement is prominent in patients with chronic HP, conventional pulmonary function tests (PFTs) are relatively insensitive to identify it. Thus, the authors aimed to evaluate resistance (R5) and reactance (X5) values at 5 Hz on inspiration, expiration, and whole breath, as well as small airway resistance (R5–19) values using a forced oscillation technique (FOT) in patients with chronic HP, and their responses after bronchodilator. In addition, R5 and X5 values according to the presence or absence of mosaic attenuation on computed tomography (CT) were compared. Methods PFTs with plethysmography, diffusing capacity of the lungs for carbon monoxide (DLCO) and FOT measurements were performed pre-bronchodilator and post-bronchodilator. High-resolution CT was performed at the same visit, and classified according to the presence or absence of mosaic attenuation. R5 and X5 values were then compared according to the presence or absence of mosaic attenuation on CT. Results Twenty-eight patients with chronic HP (57.1% female; mean age, 56 ± 11.5 years; mean forced vital capacity 57 ± 17% predicted) were evaluated. All patients had low X5 values, reflecting lower lung compliance, and only three (8%) demonstrated elevated R5 (whole-breath) values. No patients exhibited bronchodilator response in R5, X5 and R5–19 values. In patients who exhibited greater extension of mosaic attenuation (n = 11), R5 and X5 values could not discriminate those with a greater presence of these areas on CT. Conclusions The results suggest that FOT does not help to additionally characterise concomitant small airway involvement in patients with chronic fibrotic HP who demonstrate restrictive ventilatory pattern in conventional PFTs. Nevertheless, FOT appeared to better characterise decreased lung compliance due to fibrosis through X5. Bronchodilator therapy did not appear to induce an acute response in chronic HP patients with restrictive disease. The precise role of FOT in subacute HP and obstructive chronic HP, therefore, must be evaluated.

Airway obstruction is a common component in Chronic Obstructive Pulmonary Disease (COPD). Detection of obstruction and its grading is very essential. Obstruction in the airways, forces the accessory muscles like sternomastoid muscle (SMM) of respiration to work. Normally, only essential muscles of respiration work. In the said paper electromyographic (EMG) analysis of SMM is done for COPD and Normal subjects. We have developed improved slope based onset detection algorithm to detect the onset and offset timing of EMG. Time domain features are extracted for COPD and normal subject. The onset detection algorithm reduces the number of computations by 32.96% and increases accuracy of feature calculation by 40.19%. Dominant time domain features are selected and applied to Support Vector Machine Classifier. The SVM classification algorithm is compared with Threshold and Naïve Bayes classification algorithm. SVM gives the highest accuracy of 87.80%, sensitivity of 89.65% and specificity of 83.33%. Results are also compared with previously used FEV1/FEV6 and Forced Oscillation Technique. The activity of SMM has a significant role in the classification of Normal and COPD subject. Further analysis of SMM can be done to find different grades of COPD. Keywords: Electromyography, Onset, Obstruction, COPD

BackgroundAnimal models and, in particular, mice models, are important tools to investigate the pathogenesis of respiratory diseases and to test potential new therapeutic drugs. Lung function measurement is a key step in such investigation. In mice, it is usually performed using forced oscillation technique (FOT), negative pressure-driven forced expiratory (NPFE) and pressure-volume (PV) curve maneuvers. However, these techniques require a tracheostomy, which therefore only allows end-point measurements. Orotracheal intubation has been reported to be feasible and to give reproducible lung function measurements, but the agreement between intubation and tracheostomy generated-data remains to be tested.MethodsUsing the Flexivent system, we measured lung function parameters (in particular, forced vital capacity (FVC), forced expiratory volume in the first 0.1 s (FEV0.1), compliance (Crs) of the respiratory system, compliance (C) measured using PV loop and an estimate of inspiratory capacity (A)) in healthy intubated BALB/cJ mice and C57BL/6 J mice and compared the results with similar measurements performed in the same mice subsequently tracheostomized after intubation, by means of paired comparison method, correlation and Bland-Altman analysis. The feasibility of repetitive lung function measurements by intubation was also tested.ResultsWe identified parameters that are accurately evaluated in intubated animals (i.e., FVC, FEV0.1, Crs, C and A in BALB/cJ and FVC, FEV0.1, and A in C57BL/6 J). Repetitive lung function measurements were obtained in C57BL/6 J mice.ConclusionThis subset of lung function parameters in orotracheally intubated mice is reliable, thereby allowing relevant longitudinal studies.

Naoya Takeichi,1 Haruna Yamazaki,1 Keisaku Fujimoto21Department of Biomedical Laboratory Sciences, Graduate School of Medicine, Shinshu University, Matsumoto, Nagano, Japan; 2Department of Clinical Laboratory Sciences, Shinshu University School of Health Sciences, Matsumoto, Nagano, JapanObjective: To examine whether the parameters of impedance measured by the broadband frequency forced oscillation technique (FOT) were reflected by changes in lung compliance induced by emphysema and fibrosis, we retrospectively compared the parameters of FOT and pulmonary functions, including static lung compliance (Cst), in obstructive lung disease (OLD) and interstitial lung disease (ILD).Patients and methods: The data of 18 patients with OLD (16 with COPD, two with asthma COPD overlap), 11 with ILD, and 24 healthy volunteers, whose respiratory impedance was measured using a MostGraph-01 and other pulmonary functions including Cst and lung resistance (RL) were measured on the same day and were retrospectively collected and compared.Results: The parameters of resistance, reactance, and resonant frequency showed good correlations with ventilation unevenness (r=0.63, −0.89, 0.77, respectively) and lung elastic resistance (r=0.59, −0.80, 0.73, respectively) in all groups (N=53). These indices were significant determinants of increased respiratory resistance and more negative shift of respiratory reactance (Xrs) at lower frequency (P

Respiratory system reactance (Xrs) measured by the forced oscillation technique (FOT) is theoretically and experimentally related to lung volume. In chronic obstructive pulmonary disease (COPD), the absolute volume measured by body plethysmography includes a proportion that is inaccessible to pressure oscillations applied via the mouth, that is, a “noncommunicating” lung volume. We hypothesized that in COPD the presence of noncommunicating lung would disrupt the expected Xrs-volume relationship compared with plethysmographic functional residual capacity (FRCpleth). Instead, Xrs would relate to estimates of communicating volume, namely, expiratory reserve volume (ERV) and single-breath alveolar volume (VaSB). We examined FOT and lung function data from people with COPD ( n = 51) and from healthy volunteers ( n = 40). In healthy volunteers, we observed an expected inverse relationship between reactance at 5 Hz (X5) and FRCpleth. In contrast, there was no such relationship between X5 and FRCpleth in COPD subjects. However, there was an inverse relationship between X5 and both ERV and VaSB. Hence the theoretical Xrs-volume relationship is present in COPD but only when considering the communicating volume rather than the absolute lung volume. These findings confirm the role of reduced communicating lung volume as an important determinant of Xrs and therefore advance our understanding and interpretation of FOT measurements in COPD. NEW & NOTEWORTHY To investigate the determinants of respiratory system reactance (Xrs) measured by the forced oscillation technique (FOT) in chronic obstructive pulmonary disease (COPD), we examine the relationship between Xrs and lung volume. We show that Xrs does not relate to absolute lung volume (functional residual capacity) in COPD but instead relates only to the volume of lung in communication with the airway opening. This communicating volume may therefore be fundamental to our interpretation of FOT measurements in COPD and other pulmonary diseases.

The measurement of lung function in preschool children for the diagnosis of asthma is not routinely used. The need to perform forced expiratory manoeuvres requires active cooperation and thus limits the use of spirometry in this age group. The forced oscillation technique (FOT) is a simple and noninvasive method of assessing the mechanical properties of the respiratory system during tidal breathing. It is used in young patients and requires minimal cooperation. It provides an objective assessment of the respiratory system in a group of patients in whom we have not yet had appropriate diagnostic tools. In recent years, due to the availability of new technical solutions, FOT has been increasingly used and has a chance to become a method used routinely in diagnosing and monitoring treatment in preschool children. This article presents the possibility of the clinical application of FOT in diagnosing and monitoring of early childhood asthma.

Background Hyperoxia-induced bronchopulmonary dysplasia (BPD) models are essential for better understanding and impacting on long-term pulmonary, cardiovascular, and neurological sequelae of this chronic disease. Only few experimental studies have systematically compared structural alterations with lung function measurements. Methods In three separate and consecutive series, Sprague–Dawley infant rats were exposed from day of life (DOL) 1 to 19 to either room air (0.21; controls) or to fractions of inspired oxygen (FiO2) of 0.6, 0.8, and 1.0. Our primary outcome parameters were histopathologic analyses of heart, lungs, and respiratory system mechanics, assessed via image analysis tools and the forced oscillation technique, respectively. Results Exposure to FiO2 of 0.8 and 1.0 resulted in significantly lower body weights and elevated coefficients of lung tissue damping (G) and elastance (H) when compared with controls. Hysteresivity (η) was lower due to a more pronounced increase of H when compared with G. A positive structure–function relation was demonstrated between H and the lung parenchymal content of α-smooth muscle actin (α-SMA) under hyperoxic conditions. Moreover, histology and morphometric analyses revealed alveolar simplification, fewer pulmonary arterioles, increased α-SMA content in pulmonary vessels, and right heart hypertrophy following hyperoxia. Also, in comparison to controls, hyperoxia resulted in significantly lower plasma levels of vascular endothelial growth factor (VEGF). Lastly, rats in hyperoxia showed hyperactive and a more explorative behaviour. Conclusions Our in vivo infant rat model mimics clinical key features of BPD. To the best of our knowledge, this is the first BPD rat model demonstrating an association between lung structure and function. Moreover, we provide additional evidence that infant rats subjected to hyperoxia develop rarefaction of pulmonary vessels, augmented vascular α-SMA, and adaptive cardiac hypertrophy. Thus, our model provides a clinically relevant tool to further investigate diseases related to O2 toxicity and to evaluate novel pharmacological treatment strategies. Electronic supplementary material The online version of this article (10.1186/s12967-019-1843-1) contains supplementary material, which is available to authorized users.

Background: Lung function testing is recommended for the management of asthma. Due to certain limitations of conventional spirometry in vulnerable patients, forced oscillation technique (FOT) has been studied with promising results. As there is a paucity of data from developing world, we planned to conduct this study in children using FOT. To assess airway reversibility after inhaled salbutamol in asymptomatic children with suspected asthma. Settings: This study was conducted at pediatric asthma clinic of a tertiary care referral hospital in North India. Design: This was a prospective interventional study over 1-year period. Subjects and Methods: Asymptomatic children between 2 and 18 years of age, with history suggestive of asthma, were eligible for participation. Baseline and postbronchodilator pulmonary functions were assessed using FOT. Airway resistance and reactance were monitored at various frequencies. SPSS version 17 was used for statistical analysis. Results: Among the 345 enrolled children, baseline mean ± standard deviation total airway resistance (R5), central airway resistance (R19), peripheral airway resistance (R5–R19), reactance (X5), and resonant frequency (Fres) were 6.85 ± 2.60, 5.23 ± 1.93, 1.6 ± 1.16, and − 2.54 ± 1.36 cmH2O/L/s and 17.28 ± 3.06 Hz. The median (interquartile range) percentage change after inhaled salbutamol was 19.9 (11.40, 29.12), 22.86 (6.88, 38.76), 14.08 (3.40, 22.62), 39.20 (8.20, 62.39), and 15.79 (8.33, 27.27) in respective parameters. All changes were statistically significant. The studied respiratory variables were in maximum negative correlation with height, followed by body mass index. Conclusions: FOT is a simple technique for monitoring lung functions in children during asthma management.

The Global Initiative for Asthma report emphasises the use of spirometry in diagnosing and monitoring asthma in children from 6 years of age onwards [1]. Spirometry requires good cooperation and younger children are sometimes unable to perform repeated forced expiratory blows [2]. Alternative pulmonary function measurements, such as the forced oscillation technique (FOT), are increasingly available for children at preschool age [3]. FOT measures lung function by imposing small soundwaves over tidal breathing through a mouthpiece, where pressure and flow changes in the airways are measured to derive respiratory system properties [4, 5]. The first study on bronchodilator responses by FOT in preschool-aged children was published already two decades ago [6]. Guidelines endorse the use of respiratory oscillometry in diagnosing and following up asthma in young children [3, 7], and it has shown potential in predicting loss of asthma control in older children and adolescents [8]. However, little is known of how FOT indices correlate with flow–volume indices when this technique is used in adjunct with conventional spirometry., Evaluation of airway obstruction with forced oscillation technique can be an adjunct to spirometry or even used as a primary method in those children unable to perform spirometry https://bit.ly/34rE6x2

Introduction: Currently there is a lack of sensitive and specific tools which can objectively identify exacerbations and assess their progress or treatment response. FEV1 is often reported as a study outcome, but this forced manoeuvre has significant limitations. Studies have suggested that small airways measures might provide physiological biomarkers during exacerbations. Aims and Objectives: to assess which physiological tests of small airways function have been used in the acute setting during exacerbations of COPD and the evidence to support their use. Methods: Following PRISMA guidelines, a systematic review was conducted using several databases for relevant published studies of >10 participants which compared at least one small airway test with FEV1 at both exacerbation and a follow-up measurement up to and including two months after exacerbation onset to assess response to treatment. Results: From 1436 screened articles, seven studies were found to be eligible for inclusion. There was heterogeneity in which tests of small airways were used. Four different measures were reported (Impulse oscillometry (IOS), Maximal mid-expiratory flow (MMEF), Forced oscillation technique (FOT) and airway resistance (Raw) by body plethysmography). Studies were small (including 20 to 87 subjects). Six articles reported improvements in small airway measurements during the recovery from exacerbation which correlated with FEV1. Conclusion: There is some evidence to support the use of small airway tests in exacerbations of COPD; however, studies have been small with different tests being utilized. Further pilot studies to determine the usefulness of each test may be of interest

Chronic obstructive pulmonary disease (COPD) is a respiratory illness characterized by airflow limitation and chronic respiratory symptoms with a global prevalence estimated to be more than 10% in 2010 and still on the rise. Furthermore, hypercapnic subject COPD leads to an increased risk of mortality, morbidity, and poor QoL (quality of life) than normocapnic subjects. Series of studies showed the usefulness of the forced oscillation technique (FOT) to measure small airway closure. Traditional findings suggested that hypercapnia may not be the main treating targets, but recent findings suggested that blood stream CO2 may lead to a worse outcome. This study aimed to seek the relationship between CO2 and small airway closure by using FOT. Subjects with COPD (n = 124, hypercapnia 22 and normocapnia 102) were analyzed for all pulmonary function values, FOT values, and arterial blood gas analysis. Student&rsquo, s t-test, Spearman rank correlation, and multi linear regression analysis were used to analyze the data. COPD subjects with hypercapnia showed a significant increase in R5, R20, Fres, and ALX values, and a greater decrease in X5 value than normocapnic patients. Also, multiple linear regression analysis showed R5 was associated with hypercapnia. Hypercapnia may account for airway closure among subjects with COPD and this result suggests treating hypercapnia may lead to better outcomes for such a subject group.

OBJECTIVES Forced oscillation technique (FOT) is becoming increasingly widespread measurement method used for assessment of lung function. In the present study, we attempted to assess FOT values in patients after lobectomy in comparison with IPF and COPD patients. METHODS Twenty-two patients after lobectomy due to lung cancer stage I or II, 28 patients with idiopathic pulmonary fibrosis and 17 patients with chronic obstructive pulmonary disease were enrolled in the study. All patients performed spirometry (FEV1 , FVC, FEV1 /FVC, MEF50 , MEF25 , FEF25-75 , MIF50 ), plethysmography (Raw , TLC, RV, RV/TLC) and a test using the forced oscillation technique- resistance (R at 5Hz, 11Hz and 19Hz, inspiratory, expiratory and total), reactance (Xat 5Hz, 11Hz, inspiratory, expiratory and total), Fres and expiratory flow limitation (∆X). The ANOVA Kruskal-Wallis test followed by a multiple comparison test were used to evaluate the differences in oscillatory parameters between-groups. RESULTS Patients after lobectomy presented reduced X5, X11 and moderately increased R5, R11, R19, R5-19, ∆X and Fres. Rinsp 5 weresignificantly higher when compared with IPF patients (P = 0.001). In lobectomy patients R5, X5, X11, ∆X and Fres were significantly less affected when compared with patients with COPD (P

BACKGROUND: Persistent bronchodilator response (BDR) following diagnosis of asthma is an underrecognized treatable trait, associated with worse lung function and asthma control. The forced oscillation technique (FOT) measures respiratory system impedance, and BDR cutoffs have been proposed for healthy adults; however, the relevance in asthma is unknown. We compared BDR cutoffs, using FOT and spirometry, in asthma and the relationship with asthma control. METHODS: Data from patients with asthma who withheld bronchodilator medication for at least 8 h before a tertiary airway clinic visit were reviewed. All subjects performed FOT and spirometry before and after salbutamol administration, and completed the Asthma Control Test. FOT parameters examined included respiratory system resistance (R5) and reactance (X5) at 5 Hz, and area under the reactance curve (AX). BDR was defined by standard recommendations for spirometry and based on the 95th percentile of BDR in healthy adults for FOT. RESULTS: Fifty-two subjects (18 men; mean age, 53 ± 18 years) were included. BDR was identified more frequently by FOT than spirometry (54% vs 27% of subjects). BDR assessed by X5 and AX, but not R5, was associated with spirometric BDR (χ(2), P < .01) and correlated with asthma control (X5: r(s) = –0.36, P < .01; AX: r(s) = 0.34, P = .01). BDR measured by reactance parameters identified more subjects with poor asthma control than did spirometry (AX, 69% vs spirometry, 41%). CONCLUSIONS: BDR assessed by FOT can identify poor asthma control. Reactance parameters were more sensitive in identifying poor asthma control than spirometry, supporting the use of FOT to complement spirometry in the clinical management of asthma.

Oscillometry (forced oscillation technique, FOT) is a noninvasive method which enables to measure lung mechanics such as respiratory system impedance (Zrs), resistance (Rrs), and reactance (Xrs) during quiet breathing. Obstruction of airways can be implied from an increase in Rrs and more negative shifting in Xrs, in other words, high resonant frequency (Fres). Because oscillometry and spirometry is not identical modality, correlation between Rrs and FEV1 is generally weak. Frequency dependence of Rrs, which comes from several conditions such as shunt effects, mechanical inhomogeneity, turbulence, and peripheral airway lesion, can be a marker for smokers, COPD, asthma, infants, and some other conditions such as space occupied lesion of large central airways. Respiratory cycle dependence of Rrs or Xrs would be useful to understand the difference of ventilatory mechanics between inspiratory and expiratory phase, which can be observed as dynamic airway narrowing in patients with COPD. In conclusion, oscillometry is useful to assess the physiology of lower airways.

Background Tidal expiratory flow limitation (EFLT) promotes intrinsic PEEP (PEEPi) in patients with chronic obstructive pulmonary disease (COPD). Applying non-invasive ventilation (NIV) with an expiratory positive airway pressure (EPAP) matching PEEPi improves gas exchange, reduces work of breathing and ineffective efforts. We aimed to evaluate the effects of a novel NIV mode that continuously adjusts EPAP to the minimum level that abolishes EFLT. Methods This prospective, cross-over, open-label study randomized patients to one night of fixed-EPAP and one night of EFLT-abolishing-EPAP. The primary outcome was transcutaneous carbon dioxide pressure (PtcCO2). Secondary outcomes were: peripheral oxygen saturation (SpO2), frequency of ineffective efforts, breathing patterns and oscillatory mechanics. Results We screened 36 patients and included 12 in the analysis (age 72 ± 8 years, FEV1 38 ± 14%Pred). The median EPAP did not differ between the EFLT-abolishing-EPAP and the fixed-EPAP night (median (IQR) = 7.0 (6.0, 8.8) cmH2O during night vs 7.5 (6.5, 10.5) cmH2O, p = 0.365). We found no differences in mean PtcCO2 (44.9 (41.6, 57.2) mmHg vs 54.5 (51.1, 59.0), p = 0.365), the percentage of night time with PtcCO2 > 45 mm Hg was lower (62(8,100)% vs 98(94,100)%, p = 0.031) and ineffective efforts were fewer (126(93,205) vs 261(205,351) events/hour, p = 0.003) during the EFLT-abolishing-EPAP than during the fixed-EPAP night. We found no differences in oxygen saturation and lung mechanics between nights. Conclusion An adaptive ventilation mode targeted to abolish EFLT has the potential to reduce hypercapnia and ineffective efforts in stable COPD patients receiving nocturnal NIV. Trial registration: ClicalTrials.gov, NCT04497090. Registered 29 July 2020—Retrospectively registered, https://clinicaltrials.gov/ct2/show/NCT04497090.

The usefulness of the oscillometry, known as forced oscillation technique, for predicting exercise tolerance in subjects with COPD is unknown. To test the hypothesis, we investigated whether oscillometry could predict a 6-minute walking distance (6MWD) 1, 61.0%). Modified MRC dyspnea scale (mMRC), COPD Assessment Test (CAT), oscillometry, spirometry, and 6MWT were performed in a stable condition. The participants were classified into subjects with 6MWD ≥350 m or 6MWD 1, IC, 6MWD, lowest SpO2, maximum Borg scale, respiratory resistance (Rrs), and reactance (Xrs). In multivariate regression analysis, a 6MWD 20/L/s. In conclusion, the oscillatory parameter, inspiratory R5, predicted low exercise tolerance in COPD subjects.

Background Bronchial Thermoplasty (BT) is an endoscopic treatment for severe asthma using radiofrequency energy to target airway remodeling including smooth muscle. The correlation of pulmonary function tests and BT response are largely unknown. Forced Oscillation Technique (FOT) is an effort-independent technique to assess respiratory resistance (Rrs) by using pressure oscillations including small airways. Aim To investigate the effect of BT on pulmonary function, assessed by spirometry, bodyplethysmography and FOT and explore associations between pulmonary function parameters and BT treatment response. Methods Severe asthma patients recruited to the TASMA trial were analyzed in this observational cohort study. Spirometry, bodyplethysmography and FOT measurements were performed before and 6 months after BT. Asthma questionnaires (AQLQ/ACQ-6) were used to assess treatment response. Results Twenty-four patients were analyzed. AQLQ and ACQ improved significantly 6 months after BT (AQLQ 4.15 (±0.96) to 4.90 (±1.14) and ACQ 2.64 (±0.60) to 2.11 (±1.04), p = 0.004 and p = 0.02 respectively). Pulmonary function parameters remained stable. Improvement in FEV1 correlated with AQLQ change (r = 0.45 p = 0.03). Lower respiratory resistance (Rrs) at baseline (both 5 Hz and 19 Hz) significantly correlated to AQLQ improvement (r = − 0.52 and r = − 0.53 respectively, p = 0.01 (both)). Borderline significant correlations with ACQ improvement were found (r = 0.30 p = 0.16 for 5 Hz and r = 0.41 p = 0.05 for 19 Hz). Conclusion Pulmonary function remained stable after BT. Improvement in FEV1 correlated with asthma questionnaires improvement including AQLQ. Lower FOT-measured respiratory resistance at baseline was associated with favorable BT response, which might reflect targeting of larger airways with BT. Trial registration ClinicalTrials.gov Identifier: NCT02225392; Registered 26 August 2014.

Caroline Oliveira Ribeiro,1 Alvaro Camilo Dias Faria,1 Agnaldo José Lopes,2,3 Pedro Lopes de Melo1 1Biomedical Instrumentation Laboratory, Institute of Biology and Faculty of Engineering, State University of Rio de Janeiro, Rio de Janeiro, Brazil; 2Pulmonary Function Laboratory, State University of Rio de Janeiro, Rio de Janeiro, Brazil; 3Pulmonary Rehabilitation Laboratory, Augusto Motta University Center, Rio de Janeiro, Brazil Purpose: The aim of the present study was to evaluate the performance of the forced oscillation technique (FOT) for the early diagnosis of the effects of smoking and COPD. The contributions of the integer-order (InOr) and fractional-order (FrOr) models were also evaluated. Patients and methods: In total, 120 subjects were analyzed: 40 controls, 40 smokers (20.3±9.3 pack-years) and 40 patients with mild COPD. Results: Initially, it was observed that traditional FOT parameters and the InOr and FrOr models provided a consistent description of the COPD pathophysiology. Mild COPD introduced significant increases in the FrOr inertance, damping factor and hysteresivity (P0.8). The use of FrOr modeling significantly improved this process (P0.9). Conclusion: FrOr modeling improves our knowledge of modifications that occur in the early stages of COPD. Additionally, the findings of the present study provide evidence that these models may play an important role in the early diagnosis of COPD, which is crucial for improving the clinical management of the disease. Keywords: COPD, oscillation mechanics, smoking, respiratory modeling, integer-order modeling, respiratory impedance

Airway closure has proved to be important in a number of respiratory diseases and may be the primary functional defect in asthma. A surrogate measure of closing volume can be identified using the forced oscillation technique (FOT), by performing a deflation maneuver and examining the resultant reactance (Xrs) lung volume relationship. This study aims to determine if a slow vital capacity maneuver can be used instead of this deflation maneuver and compare it to existing more complex techniques. Three subject groups were included in the study; healthy (n = 29), asthmatic (n = 18), and COPD (n = 10) for a total of 57 subjects. Reactance lung volume curves were generated via FOT recordings during two different breathing manoeuvres (both pre and post bronchodilator). The correlation and agreement between surrogate closing volume (Volcrit) and reactance (Xrscrit) at this volume was analysed. The changes in Volcrit and Xrscrit pre and post bronchodilator were also analysed. Across all three subject groups, the two different measures of Volcrit were shown to be statistically equivalent (p > 0.05) and demonstrated a strong fit to the data (R2 = 0.49, 0.78, 0.59, for asthmatic, COPD and healthy subject groups, respectively). A bias was evident between the two measurements of Xrscrit with statistically different means (p

Importance: The forced oscillation (FOT) and multiple breath washout (MBW) techniques are passive tests of lung function, and are reliable for preschool-age children. There has not been comparison testing to determine which test could more accurately differentiate between healthy controls and poorly controlled asthmatics, or differentiate a response to bronchodilator administration. Objective: To determine whether the MBW and/or FOT could differentiate between healthy controls and poorly controlled asthmatics, and whether the two tests could detect a response to bronchodilator administration. Methods: Twenty-eight healthy controls and 23 poorly controlled asthmatics 3–6 years of age participated. All subjects were administered the MBW followed by the FOT. A bronchodilator was then administered and testing was repeated. Wilcoxon Rank Sum tests were used to compare the difference between healthy controls and poorly controlled asthmatics. Wilcoxon Signed Rank tests were used to compare the pre- and post-bronchodilator values. Results: Neither MBW nor FOT differentiated healthy controls from poorly controlled asthmatics (pre-bronchodilator data); both groups had similar baseline gas mixing and airway mechanics. There was no improvement in any MBW outcomes post-bronchodilator administration. FOT detected a significant and similar degree of improvement in the airway mechanics in both groups. Interpretation: Neither MBW nor FOT differentiated between poorly controlled asthmatics (when well) and healthy controls. MBW did not detect a significant bronchodilator response in either subject group, whereas FOT detected a similar degree of bronchodilator responsiveness in both groups. This discrepancy may reflect differential changes in airway mechanics and gas mixing properties in response to bronchodilators. Key words: Forced oscillation technique; Multiple breath washout; Pediatric lung function measurement; Pediatric asthma

Preschool children with asthma present a challenge in lung function testing, as they cannot readily cooperate with spirometry. The forced oscillation technique (FOT) measures passive pressures and flows delivered by a loudspeaker to a facemask, at frequencies much higher than those occurring physiologically. This in turn allows for rapid collection of data from a spontaneously breathing child in a timespan of seconds. However, at very rapid oscillatory flow rates, the mechanical properties opposing flows into and out of the respiratory system (collectively termed the respiratory system impedance, and comprised of elastic, resistive and inertial components) are very different from at normal breathing frequencies, with elastic properties being less important and inertial properties being more important. An understanding of how the respiratory system behaves at high frequencies is essential to understanding the physiological basis of this technique. This article presents a way to understand these oscillatory mechanics of the respiratory system. It then describes studies of the FOT in normal preschool children and in children with asthma. The technique can also measure the separate contributions of the central and peripheral airways, as well as assess for changes after bronchodilator administration. The FOT holds promise for the objective measurement of lung function in children who are too young to reliably perform spirometry.

Background and objective A single assessment of within-breath variations of respiratory system reactance (Xrs) at 5 Hz (ΔX5) measured by the forced oscillation technique (FOT) has been reported to be useful for the detection of pathophysiological changes in chronic obstructive pulmonary disease (COPD) and asthma. We examined longitudinal changes in respiratory system resistance (Rrs) and Xrs during tidal breathing between stable asthma and COPD patients in order to clarify the features of changes of respiratory system impedance and airflow limitation for these conditions. Methods Between April 2013 and September 2013, outpatients with a COPD or asthma diagnosis were recruited. We examined forced expiratory volume in 1 s (FEV1 ) and FOT every 6 months until September 2015. Annual changes were estimated from the linear regression curve slope. Results We included 57 and 93 subjects with COPD and asthma, respectively. The median follow-up period was 26 months (range: 24-29 months). Within-breath analysis showed that the difference between mean Rrs at 5 Hz and 20 Hz was significantly lower, and ΔX5 more negative, in COPD than in asthma patients. With regard to annual changes, only ΔX5 was significantly different, more negative, in COPD than in asthma patients. Comparing between COPD subjects of Global Initiative Chronic Obstructive Lung Disease (GOLD) stage I/II and those with asthma, there were no significant differences in respiratory system impedance at enrolment, while annual change in ΔX5 was significantly more negative in mild COPD than in asthma patients. Conclusion ΔX5 may be useful for long-term assessment of airflow limitation in COPD.

Anti-tumor necrosis factor alpha (TNFα) therapy is widely used to treat various inflammatory conditions. Paradoxically, there are several case reports describing the development of bronchocentric granulomatosis treated with TNFα inhibitors, and it is difficult to determine the effect of treatment using conventional spirometry because the lesions are located in small airways. However, it has been reported that the forced oscillation technique (FOT) is useful in the evaluation of small airway disease in bronchial asthma or chronic obstructive pulmonary disease. We performed the FOT to determine the effect of treatment on bronchocentric granulomatosis and found it to be useful. We report the case of a 55-year-old female with ulcerative colitis who was treated with golimumab and who developed bronchocentric granulomatosis as a sarcoid-like reaction to golimumab. She was successfully treated with prednisone, and the treatment efficacy was confirmed by the FOT. The FOT may be useful in the evaluation of small airway disease in bronchocentric granulomatosis. This case may help inform clinicians of the usefulness of the FOT to assess small airway disease in various diseases., Medicina, 57 (12), art. no. 1315; 2021

Respiratory diseases, especially asthma, are common in children. While spirometry contributes to asthma diagnosis and management in older children, it has a limited role in younger children whom are often unable to perform forced expiratory manoeuvre. The development of novel diagnostic methods which require minimal effort, such as forced oscillation technique (FOT) is, therefore, a welcome and promising addition. FOT involves applying external, small amplitude oscillations to the respiratory system during tidal breathing. Therefore, it requires minimal effort and cooperation. The FOT has the potential to facilitate asthma diagnosis and management in pre-school children by faciliting the objective measurement of baseline lung function and airway reactivity in children unable to successfully perform spirometry. Traditionally the use of FOT was limited to specialised centres. However, the availability of commercial equipment resulted in its use both in research and in clinical practice. In this article, we review the available literature on the use of FOT in childhood asthma. The technical aspects of FOT are described followed by a discussion of its practical aspects in the clinical field including the measurement of baseline lung function and associated reference ranges, bronchodilator responsiveness and bronchial hyper-responsiveness. We also highlight the difficulties and limitations that might be encountered and future research directions.

Background Classic spirometry is effort-dependent and of limited value in assessing small airways. Peripheral airway involvement, and relation to poor control, in asthma, has been highlighted recently. Forced oscillation technique (FOT) offers an effort-independent assessment of overall and peripheral lung mechanics. We studied the association between lung function variables, obtained either by spirometry or multi-frequency (5, 11 and 19 Hz) FOT, and asthma diagnosis and control. Methods Spirometry measures, resistance at 5 (R5) and 19 Hz (R19), reactance at 5 Hz (X5), resonant frequency (fres), resistance difference between 5-19 Hz (R5-R19) and Asthma Control Test scores were determined in 234 asthmatic and 60 healthy subjects (aged 13-39 years). We used standardised lung function variables in logistic regression analyses, unadjusted and adjusted for age, height, gender, weight. Results Lower FEV1/FVC (OR (95% CI) 0.47 (0.32, 0.69)) and FEF50 (0.62 (0.46, 0.85)) per standard deviation increase, and higher R5 (3.31 (1.95, 5.62)) and R19 (2.54 (1.65, 3.91)) were associated with asthma diagnosis. Independent predictive effects of FEV1/FVC and R5 or R19, respectively, were found for asthma diagnosis. Lower FEV1/FVC and altered peripheral FOT measures (X5, fres and R5-R19) were associated with uncontrolled asthma (p-values < 0.05). Conclusions Resistance FOT measures were equally informative as spirometry, related to asthma diagnosis, and furthermore, offered additive information to FEV1/FVC, supporting a complementary role for FOT. Asthma control was related to FOT measures of peripheral airways, suggesting a potential use in identifying such involvement. Further studies are needed to determine a clinical value, and relevant reference values in children, for the multi-frequency FOT measurements. This article is protected by copyright. All rights reserved.

Background and objective Selecting ‘healthy’ preschool-aged children for reference ranges may not be straightforward. Relaxing inclusion criteria for normative data does not affect spirometry z-scores. We therefore investigated the effect of similarly relaxing inclusion criteria in preschoolers on reference ranges for respiratory impedance (Zrs) using a modified forced oscillation technique (FOT). Methods The International Study of Asthma and Allergies in Childhood questionnaire classified 585 children into a healthy and five mutually exclusive groups. Zrs was measured between 4 and 26 Hz and resistance (R) and compliance (C) obtained by model fitting. Prediction models were determined using mixed effect models and z-scores compared between healthy children and the five groups. Results Zrs data were obtained for 494 participants (4.30 ± 0.7 years) on 587 occasions. Comparison of the Zrs z-scores between the healthy children and the health groups found significant differences in children with asthma, current wheeze and respiratory symptoms, but not in children born preterm or with early-life wheeze. Adding these two groups to the healthy dataset had no significant effect on the distribution of z-scores and increased the size of the dataset by 22.3%. Conclusion Our data suggest that preschool-aged children born preterm or with early-life wheeze can be included in FOT reference equations, while those with asthma, current wheeze and respiratory symptoms within 4 weeks of testing should be excluded. This more inclusive approach results in more robust FOT reference ranges.

Relapsing polychondritis (RP) is characterized by recurrent systemic inflammation of the cartilages and is accompanied by central airway collapse. We report a case wherein three-dimensional imaging of respiratory system resistance (Rrs) and respiratory system reactance (Xrs) by using MostGraph (CHEST M.I., Tokyo, Japan), a forced oscillation system, revealed that Rrs and Xrs in the inspiratory and expiratory phases correlated with proximal airway collapse. The degree of difference in Rrs and Xrs between the supine and sitting positions reflected airway collapse more closely than did the pulmonary function test. MostGraph could be a useful tool for assessing airway collapse in RP.

The forced oscillation technique (FOT) is a useful diagnostic respiratory system for children. However, the final value of the FOT in the diagnosis of bronchoconstriction is still open. The aim of the study was to evaluate the sensitivity and specificity of the FOT vs. body plethysmography tests in the measure of bronchoconstriction in asthmatic children.A total of 102 children aged 2 to 6 years diagnosed with early-onset asthma and 52 healthy controls were included in this prospective, randomized study. All asthmatic patients and healthy controls underwent a basic FOT as one measurement, according to the recommendation of the Resmon Pro FOT. Then, the reversibility test was performed 20 min after the administration of 200 mg salbutamol using the FOT and body plethysmography in all patients.The mean basic Rrs, Xrs and sRaw in asthmatic patients were, respectively, 11.13 ± 1.28 kPa sLA bronchial reversibility test with the use of the FOT is useful for the diagnosis of bronchial asthma, especially with the use of an Rrs parameter, such as the body plethysmography test.

Introduction Pigeon fanciers are recognised to suffer from acute through to chronic hypersensitivity pneumonitis (HP), and given their HP is driven by a known antigen, provide a potentially useful group to identify novel causative mechanisms for HP. The forced oscillation technique (FOT) employs sound waves to examine the relationships between pressure and flow during tidal respiration, and has been advocated as an approach to assess the small airways and lung parenchyma. It is also simple to perform, as it requires tidal breathing only. Given this we examined FOT in a group of pigeon fanciers at a recent national meeting. Methods Volunteers were recruited from among the attendees at the National Royal Pigeon Fancier’s Meeting Blackpool, 2019. Participants completed a questionnaire with experienced clinicians, which focused on; presence of a diagnosis of interstitial lung or connective tissue disease, current medication, symptoms post pigeon exposure, number of pigeons kept and occupational dust exposure. All subjects provided blood for genetic and immunological assessment, and performed spirometry. An unselected subgroup performed FOT using the Resmon Pro (Intermedical UK Ltd). Results 178 subjects participated over two days. Of these 94 performed FOT. 51 participant’s FOT results were analyzed, after exclusion of those with known interstitial lung disease, abnormal spirometry or no result due to inadequate spirometry technique. 23 subjects (45%) demonstrated abnormal FOT results, with the consistent finding being high expiratory reactance at 5Hz (exp Xrs5). Median exp Xrs5 was -3.5 cmH2O (-6.3 to -2.5), equating to 244% predicted (204 to 446) (both median (IQR)). Discussion FOT, specifically elevated expiratory Xrs at 5Hz, is abnormal in a large proportion of pigeon fanciers who have no known ILD and normal spirometry. Given this we suggest that exp Xrs5 may be able to detect sub-clinical lung inflammation in otherwise healthy subjects with known exposure to a risk factor for development of HP. Further research is required to determine how exp Xrs5 relates to interstitial changes on CT, and whether changes in FOT can predict subsequent progression to chronic fibrosis in subjects with ongoing antigen exposure.

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.

Background: Expiratory flow limitation (EFL) is an hallmark of COPD. However has not implemented in the baseline routine functional assessment yet. Aim: to evaluate if the measurement of EFL by FOT could contribute to highlight pathophysiological mechanisms of improvement after PR. Method: in 75 stable moderate to very severe COPD patients, before and after PR, EFL as the within-breath change in reactance (DXrs), pulmonary function tests and rehabilitation outcomes were evaluated. Results: In the patients as a whole, after PR, DXrs decreased significantly (p 2.81 [cmH2O/(L/s)], patients were divided into two groups: flow-limited (FL, 36 patients, DXrs 5.14±2.6) and not flow-limited (NFL, 39 patients, DXrs 1.04±0.9) patients. Before PR FL patients were more severely obstructed (FEV1% 34.6±9.6 vs 52.0±20.6, p Conclusions: FOT measures provide new supplementary information to pulmonary functional evaluation in COPD patients enrolled in PR. These preliminary data show that the change in EFL could contribute to the effect of PR in severe patients.

Introduction: Commercial Forced oscillation technique (FOT) devices use patented data acquisition protocols to measure respiratory impedance. ERS guideline recommended that short term intra-individual variability of repeated measurements of FOT indices as expressed as coefficient of variation (CV) should be Methods: FOT were carried out in triplicate and within twenty minutes intervals by using “15 accepted breaths” protocol of Resmon Pro Full device ((Restech Srl, Italy). CV of R5 in 71 healthy adults, 16 COPD, and 20 adult asthmatic patients were analyzed. Results: The median CV of R5 was 10.6% (6.5-17.7) in healthy, 7.6% (5.6-10.3) in COPD, and 14.5% (6.9-22.9) in bronchial asthma respectively. Acceptable CV ( Conclusions: Short term CV of

Background: Obstructive sleep apnea (OSA) is related to narrowing upper airway. The forced oscillation technique (FOT) is a noninvasive method to evaluate resistance and reactance in airway system. Aims and Objectives: The aim of this study was to assess the relation between the airway resistance during awakening by FOT and the severity of OSA. Methods: We examined the respiratory impedance of 35 patients with OSA during awakening in the sitting, supine, and left lateral recumbent positions using the MostGraph-01® (CHEST M.I., Tokyo, Japan) FOT instrument. Results: Significant correlations between the apnea-hypopnea index (AHI) and respiratory resistance at 5 Hz (R5), as well as respiratory resistance at 20 Hz (R20), were observed in the supine position. In addition, AHI in the supine position were significantly correlated with R5 and R20 in each the sitting, supine, and left lateral recumbent positions. Conclusions: FOT might be a useful technique to estimate the pathophysiology and severity of OSA.

Background: Biomass smoke is associated with adverse health effects on the respiratory system, including increased asthma morbidity and worsening of symptoms leading to emergency room visits. Aims and Objectives: The aim of this study was to investigate whether controlled exposure to wood smoke generated from incomplete soot-rich combustion would increase small airway resistance and reactance. Methods: Fifteen healthy subjects (20-45 ys) underwent controlled chamber exposure on two occasions to filtered air and to sooty wood smoke (PM1 ~ 450 μg/m3), generated by a common Swedish wood stove firing birch logs. The study was performed in a double-blind, randomized cross-over fashion and the subjects alternated between exercise (VE=20 L/min/m2) and rest at 15-minute intervals for 2 hours. Forced Oscillation Technique (FOT) (tremoFlo®, THORASYS) was used to determine airway resistance and reactance before and after exposure to wood smoke as well as before and after exposure to filtered air. Results: Both airway reactance (P Conclusions: Short term exposure to sooty wood smoke did not affect small airways resistance or reactance as determined using FOT in healthy subjects. Further research should study the effects in asthmatic populations, and also whether repeated exposures are needed to cause the small airways effects indicated by population-based studies.

Background: Chronic obstructive pulmonary disease (COPD) is a growing health problem, and detecting it early enough to improve prognosis remains a challenge. This study aimed to assess the ability of the forced oscillation technique (FOT) to detect COPD at an early stage. Materials and Methods: The study involved 2,297 COPD patients older than 40 yr as well as 4,416 non-COPD controls. The ability of FOT to detect COPD in different stages of the Global Initiative for Chronic Obstructive Lung Disease (GOLD) scale as well as to detect airflow limitation in small airways was evaluated. Results: The combination of five FOT parameters (Z5, Fres, R5-R20, Rp, X5) performed best at detecting COPD (selectivity, 64.90%; specificity, 79.30%; positive predictive value, 61.83%; negative predictive value, 81.20%), detecting airflow limitation in small airways (selectivity, 62.80%; specificity, 70.70%; positive predictive value, 82.47%; negative predictive value, 51.27%) and distinguishing patients with COPD in GOLD stage 1 from non-COPD controls (selectivity, 56.80%; specificity, 71.60%; positive predictive value, 19.65%; negative predictive value, 97.43%). Conclusions: These results suggest that FOT can detect early-stage COPD and small airway limitation, which may make it a useful alternative to spirometry.

Surfactant improves lung mechanics and the success of non-invasive respiratory support in preterm infants. The lack of non-invasive bedside tools for monitoring lung mechanics makes current guidelines for surfactant therapy based on O2 requirements, which may be not specific for this application. Objective: To assess feasibility and role of early, non-invasive evaluation of respiratory mechanics by FOT in non-intubated preterm infants for stratifying the severity of respiratory disease. Eligibility: 28-34wk gestation, no need of early intubation after birth. FOT at 10Hz was applied by a modified ventilator (Fabian, Acutronic) and a face-mask during CPAP=5cmH2O. Measurements were performed at 2 and 24h of life. FiO2 was titrated and surfactant given as in Sweet (2016). 4 groups (n=45) were considered: Patients not requiring respiratory support (SB); receiving CPAP for less than (CPAP-S) or more than 28d (CPAP-L) but who never received surfactant and patients who received surfactant (Surf). Xrs in Surf and CPAP-L was significantly lower at 2h compared to SB and CPAP-S (fig 1). After receiving surfactant patients improved, leaving CPAP-L only showing significantly lower Xrs at 24h. Xrs stratifies patients according to the degree of respiratory disease. CPAP-L infants presented poor Xrs at 2h, did not match clinical criteria for surfactant but had a long respiratory support dependence.

Rationale: This study used an unreleased, modified noninvasive ventilator (BiPAP A40, Philips/Respironics, Monroeville, PA) using Forced Oscillation Technique (FOT) and the method of Dellaca et al (2004) to dynamically measure ∆Xrs and display an Expiratory Flow Limitation (EFL) index and optionally, adjust PEEP (PEEPopt) to abolish EFL. This information could be used to guide a physician’s plan of care and aid in determining if a Noninvasive Ventilator (NIV) is appropriate for the patient. Methods: Twelve naive NIV participants diagnosed with COPD were fitted with an oral-nasal facemask and instructed to breathe normally in the seated position, then in the supine position. The ventilator was set to non-therapy EFL screening mode that delivered 3 cmH20 CPAP pressure. Sessions lasted 5 minutes. If the ventilator displayed the presence of EFL, the participant remained supine to complete a third session where the ventilator titrated PEEPopt starting at 4 cmH20 with a fixed PS at 6 cmH2O. Results: Demographic and physiologic variables are presented in Table 1. All participants showed an increase in their ∆Xrs value from the seated to supine position. Conclusion: A simple process of identifying patients with EFL can be incorporated into a noninvasive ventilator in order to guide clinicians towards different therapeutic strategies, as well as, the option to provide automated therapy to abolish expiratory flow limitation.