Search

Aim: This study aimed to analyze the Constant Phase Model (CPM) Coefficient of Determination (COD) and an index of harmonic distortion (kd) behavior in intravenous methacholine dose response curve....

Introduction Few studies have examined the influence of different water depths on the airway impedance measured by forced oscillation technique in healthy adults. Methods Eleven healthy men (23.2 ± 1.5 years old) participated in this study. We measured the respiratory impedance assessed with the resistance at frequency of 5 Hz and 20 Hz, the reactance at frequency of 5 Hz, and frequency of resonance. To compare the influence of water depths, we carried out one dryland (DL) and two water level conditions: clavicle level (CL) and xiphoid appendix level (XA). Results The respiratory resistance at frequency of 5 Hz was higher in CL and XA than DL, and at 20 Hz was significantly higher in CL than DL. The respiratory reactance at 5 Hz was lower in CL and XA than DL, and frequency of resonance was higher in CL and XA than DL. Conclusion These results suggested that water immersion above xiphoid appendix level increase airway resistance.

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

Objective: To compare impulse oscillometry system parameters of normal‐weight children with overweight and obese children. Method: All participants were submited to the evaluation of lung function (spirometry and impulse oscillometry) following the American Thoracic Society standards. The evaluation of respiratory mechanics was performed using the JaegerTM MasterScreenTM Impulse Oscillometry System (Erich Jaeger, Germany), three tests were recorded, with acquisition for at least 20 seconds. Results: The study included 81 children (30 in the control group, 21 in the overweight group, and 30 the in obesity group), matched for age and sex. Regarding spirometry data, obesity group showed higher numerical values in relation to the control group; however, there were no significant differences among the three groups. For impulse oscillometry parameters, there was a difference between control group and obesity group for respiratory impedance (p = 0.036), resistance at 5 hertz (p = 0.026), resonant frequency (p = 0.029), and reactance area (p = 0.014). For the parameters expressed in percentage of predicted, there were differences in resistance at 5 hertz, resonant frequency and reactance area between control group and obesity group. Conclusions: Obese children showed increased oscillometry parameters values representative of airway obstruction, compared to normal‐weight children. Changes in some oscillometry parameters can already be observed in overweight school‐aged children. Resumo: Objetivo: Comparar parâmetros do Sistema de Oscilometria de Impulso de crianças com peso normal com crianças com sobrepeso e obesas. Método: Todos os participantes foram submetidos à avaliação de mecanismos respiratórios utilizando o Sistema de Oscilometria de Impulso Jaeger™ (MasterScreen™ IOS, Erich Jaeger, Alemanha) seguindo as normas da Sociedade Torácica Americana. Todos os participantes foram submetidos a testes de espirometria e oscilometria (três testes foram registrados, com coleta de dados por pelo menos 20 segundos). Resultados: O estudo incluiu 81 crianças (30 no grupo de controle, 21 no grupo sobrepeso e 30 no grupo obesidade), pareadas por idade e sexo. No que diz respeito a dados de espirometria, o grupo obesidade mostrou valores numéricos mais elevados; contudo, não houve diferenças significativas entre os três grupos. No que diz respeito a parâmetros do Sistema de Oscilometria de Impulso, houve diferença entre o grupo de controle e o grupo obesidade em Z5 (p = 0,036), resistência 5 hertz (p = 0,026), frequência de ressonância (p = 0,029) e área de reatância (p = 0,014). Nos parâmetros expressos em percentual previsto, houve diferenças em resistência 5 hertz, frequência de ressonância e área de reatância entre o grupo de controle e grupo obesidade. Conclusões: Crianças obesas mostraram parâmetros de oscilometria aumentados representativos de obstrução das vias aéreas em comparação a crianças com peso normal. As alterações em alguns parâmetros oscilométricos já podem ser observadas em crianças com sobrepeso em idade escolar. Keywords: Children, Obesity, Oscillometry, Palavras‐chave: Crianças, Obesidade, Oscilometria

INTRODUCTION The forced oscillation technique (FOT) is a particularly useful test of the mechanical properties of the respiratory system that has an increasingly important role in lung function laboratories. There is general agreement in the literature that the determination of reference values is of utmost importance in the clinical use of the FOT. OBJECTIVE Our aim was to present reference values for whole-breath FOT measurements, establish which anthropometric variables were more predictive of impedance parameters, and provide all the details to adequately adopt these reference equations in individual laboratories. METHODS We prospectively evaluated a randomly selected non-smoking sample of the adult Brazilian population (288 subjects, 144 males and 144 females aged 20-86 years). The volunteers were separated by sex and divided into six groups based on decade of age. Sex-specific linear prediction equations were developed by multiple regression analysis using age, body mass and height as explanatory variables. RESULTS Age introduced a slight, but significant, reduction of resistance in men (P

Background: Sarcoidosis is a systemic inflammatory granulomatous disease which commonly affects intrathoracic lymph nodes, lung parenchyma and airways. Objectives: To measure respiratory impedance using Impulse Oscillometry (IOS) in patients with pulmonary sarcoidosis and compare the parameters with healthy controls. Methods: Patients diagnosed with sarcoidosis (n=28); and age and gender matched healthy controls (n=17) were recruited. Lung volumes and capacities were measured by spirometry and respiratory system impedance was assessed using Impulse Oscillometry System (IOS). Measurements were performed before and 15 minutes after inhalation of a short acting bronchodilator. The IOS and spirometric parameters were compared between two groups and correlated. ROC curve analysis was also performed to identify the IOS parameters which can discriminate between sarcoidosis and healthy controls. Results: Resistance at 5 and 20 Hz (R5 and R20), small airway resistance (R5-R20), resonant frequency (FRes) and area of reactance (AX) were significantly higher in Sarcoidosis subjects compared with controls. Reactance at 5 and 20 Hz (X5 and X20) were significantly lower in sarcoidosis. FEV1 (% predicted) and FVC (% predicted) were significantly lower in patients with sarcoidosis while FEV1/FVC ratio and peak expiratory flow rate (PEF) values were comparable. Post bronchodilator inhalation, there was improvement in airway resistance and reactance, but no significant changes observed in spirometric parameters. R5, X5 and R5-R20 are promising parameters to discriminate sarcoidosis from healthy controls. Conclusion: Increased airway resistance is a better indicator of airway involvement than airflow limitation by spirometry in pulmonary sarcoidosis.

Objectives The present study was aimed to compare the respiratory impedance of children residing in areas with different ambient air pollution (AAP). Methods A comparative cross-sectional pilot study was carried out in healthy school children of two cities in India i.e. Agra and Bhopal. Agra is one of the most polluted cities of India and AAP of Agra is much higher as compared to Bhopal, the reference city in the present study. The respiratory impedance was measured at 5, 11, and 19 Hz by forced oscillation technique (FOT). The anthropometric parameters, respiratory resistance at 5 Hz (R5), small airway resistance (R5-19), and reparatory reactance at 5 Hz (X5) of children from above two cities were compared by Student's t-test. Results A total 114 children (57 boys) from Agra and 151 children (76 boys) from Bhopal aged 9–16 years were recruited. The children from Agra were younger (11.9 ± 1.9 yr vs. 13.1 ± 2.2 yr, p Conclusions The present study demonstrates a higher magnitude of small airway dysfunction in children exposed to high AAP. A future study involving larger samples and longitudinal measurements of respiratory impedance will provide better insights.

Background The forced oscillation technique (FOT) measures respiratory impedance during normal tidal breathing and requires minimal patient cooperation. Objective To compare IOS and AOS devices in patients with asthma and COPD. Methods We compared two different FOT devices, namely impulse oscillometry using a loudspeaker (IOS: Jaeger Masterscreen) and airwave oscillometry using a vibrating mesh (AOS: Thorasys Tremoflo) for pre- and post-bronchodilator measurements in 84 patients with asthma and COPD. Results The overall pattern of measurement bias was for higher resistance with IOS and higher reactance with AOS, this being the case in asthma and COPD separately. There were small but significantly higher values using IOS for resistance at 5 Hz (R5) and 20(19) Hz (R20(19)). In converse, values for reactance at 5 Hz (X5), reactance area (AX) and resonant frequency (Fres) were significantly higher using AOS but to a much larger extent. The difference in AX between devices was more pronounced in COPD than in asthma. Salbutamol reversibility as % change was greater in asthma than COPD patients with AX but not FEV1. Conclusion Our study showed evidence of better agreement for resistance than reactance when comparing IOS and AOS, perhaps inferring that AOS may be more sensitive at measuring reactance in patients with airflow obstruction. Electronic supplementary material The online version of this article (10.1007/s00408-019-00247-y) contains supplementary material, which is available to authorised users.

Lung function impairment is common in Congenital Diaphragmatic Hernia (CDH) survivors. The aim of this study was to evaluate, in children who underwent CDH surgical repair, mid and long-term consequences on respiratory impedance, investigating the impact of CDH on both resistance and reactance parameters, as well as bronchodilator response. Forced Oscillation Technique (FOT) parameters were collected from 12 patients (2–11 years). Resistance and reactance values at 8 Hz (Rrs8, Xrs8) and the area under the reactance curve (AX) were measured pre and post-salbutamol. Quantitative variables were compared using Mann-Whitney U test. Differences of categorical variables were evaluated using Fisher exact test. Statistically significant differences between measured and predicted values for Rrs8 (p = 0.04), Xrs8 (p = 0.02) and AX (p = 0.01) were found. When stratifying for age, significant difference between measured and predicted values was observed only in children

Yosuke Wada,1 Yoshiaki Kitaguchi,1 Masanori Yasuo,1 Fumika Ueno,1 Satoshi Kawakami,2 Kiyoyasu Fukushima,3 Keisaku Fujimoto,4 Masayuki Hanaoka1 1First Department of Internal Medicine, Shinshu University School of Medicine, Matsumoto, Nagano, Japan; 2Department of Radiology, Shinshu University School of Medicine, Matsumoto, Nagano, Japan; 3Department of Respiratory Medicine, Japanese Red Cross Nagasaki Genbaku Isahaya Hospital, Isahaya, Nagasaki, Japan; 4Departments of Clinical Laboratory Sciences, Shinshu University School of Health Sciences, Matsumoto, Nagano, Japan Introduction: This study was conducted in order to investigate the diversity of respiratory physiology, including the respiratory impedance and reversibility of airway obstruction, based on quantitative computed tomography (CT) in patients with COPD. Patients and methods: Medical records of 174 stable COPD patients were retrospectively reviewed to obtain the patients’ clinical data, including the pulmonary function and imaging data. According to the software-based quantification of the degree of emphysema and airway wall thickness, the patients were classified into the “normal by CT” phenotype, the airway-dominant phenotype, the emphysema-dominant phenotype, and the mixed phenotype. The pulmonary function, including the respiratory impedance evaluated by using the forced oscillation technique (FOT) and the reversibility of airway obstruction in response to inhaled short-acting β2-agonists, was then compared among the four phenotypes. Results: The respiratory system resistance at 5 and 20 Hz (R5 and R20) was significantly higher, and the respiratory system reactance at 5 Hz (X5) was significantly more negative in the airway-dominant and mixed phenotypes than in the other phenotypes. The within-breath changes of X5 (ΔX5) were significantly greater in the mixed phenotype than in the “normal by CT” and emphysema-dominant phenotypes. The FOT parameters (R5, R20, and X5) were significantly correlated with indices of the degree of airway wall thickness and significantly but weakly correlated with the reversibility of airway obstruction. There was no significant correlation between the FOT parameters (R5, R20, and X5) and the degree of emphysema. Conclusion: There is a diversity of respiratory physiology, including the respiratory impedance and reversibility of airway obstruction, based on quantitative CT in patients with COPD. The FOT measurements may reflect the degree of airway disease and aid in detecting airway remodeling in patients with COPD. Keywords: FOT, respiratory impedance, MostGraph, AWT-Pi10

Inspiratory resistance (RINSP) and reactance (XINSP) were measured for 7 min at 5 Hz in 10 subjects with mild asymptomatic asthma and 9 healthy subjects to assess the effects of airway smooth muscle (ASM) activation by methacholine (MCh) and unloading by chest wall strapping (CWS) on the variability of lung function and the effects of deep inspiration (DI). Subjects were studied at control conditions, after MCh, with CWS, and after MCh with CWS. In all experimental conditions XINSP was significantly more negative in subjects with asthma than in healthy subjects, suggesting greater inhomogeneity in the former. However, the variability in both RINSP and XINSP was increased by either ASM activation or CWS, without significant difference between groups. DI significantly reversed MCh-induced changes in RINSP both in subjects with asthma and healthy subjects, but XINSP in the former only. This effect was impaired by CWS more in subjects with asthma than in healthy subjects. The velocity of RINSP and XINSP recovery after DI was faster in subjects with asthma than healthy subjects. In conclusion, these results support the opinion that the short-term variability in respiratory impedance is related to ASM tone or operating length, rather than to the disease. Nevertheless, ASM in individuals with asthma differs from that in healthy individuals in an increased velocity of shortening and a reduced sensitivity to mechanical stress when strain is reduced.

Background Although the use of e-cigarettes is increasing worldwide, their short and long-term effects remain undefined. We aimed to study the acute effect of short-term use of e-cigarettes containing nicotine on lung function and respiratory symptoms in smokers with airways obstructive disease (COPD, asthma), "healthy" smokers, and healthy never smokers. Methods Respiratory symptoms, vital signs, exhaled NO, airway temperature, airway resistance (Raw), specific airway conductance (sGaw) and single nitrogen breath test were assessed before and immediately after short term use of an e-cigarette containing 11mg of nicotine among adults with COPD, asthma, "healthy" smokers, and never-smokers. The effect of the use of nicotine-free e-cigarettes among "healthy" never smokers was also studied. Results The majority of participants reported acute cough. Short term use of nicotine e-cigarettes was associated: a) with increased heart rate in all subjects except in the COPD group, b) decreased oxygen saturation in "healthy" and COPD smokers, c) increased Raw in asthmatic smokers, "healthy" smokers, and healthy never smokers, d) decreased sGaw in healthy subjects, and e) changed slope of phase III curve in asthmatic smokers. Short-term use of nicotine-free e-cigarettes increased Raw and decreased sGaw among healthy never smokers. Conclusions Short-term use of an e-cigarette has acute effects on airways physiology and respiratory symptoms in COPD smokers, asthmatic smokers, "healthy" smokers and healthy never smokers. E-cigarette use was associated with effects in "healthy" never smokers irrespectively of nicotine concentration. More studies are needed to investigate both short and long-term effects of e-cigarette use.

Intravascular fluid shifts, mechanical ventilation and inhalational anesthetic drugs may contribute to intraoperative lung injury. This prospective observational study measured the changes in respiratory impedance resulting from inhalational anesthesia and mechanical ventilation in adults undergoing transurethral resection of bladder tumors. The components of respiratory impedance (resistance and reactance) were measured using the forced oscillation technique (FOT). Respiratory resistance at 5 Hz (R5) and 20 Hz (R20), respiratory reactance at 5 Hz (X5), resonant frequency (Fres) and area of low reactance (ALX) were measured before and immediately after surgery in 30 adults. In addition, preoperative vital capacity (VC), forced vital capacity (FVC) and forced expiratory volume in the first second (FEV1.0) were evaluated using spirometry. All patients were intubated with an endotracheal tube and were mechanically ventilated, with anesthesia maintained with sevoflurane. Pre- and postoperative FOT measurements were compared using Wilcoxon paired rank tests, and the relationships between FOT measurements and preoperative spirometry findings were determined by Spearman’s rank correlation analysis. Twenty-six patients were included in the final analysis: postoperative FOT could not be performed in four because of postoperative restlessness or nausea. The mean duration of surgery was 47 min. All components of respiratory resistance deteriorated significantly over the course of surgery, with median increases in R5, R20, and R5–R20 of 1.67 cmH2O/L/s (p

The noseclip is conventionally used in lung function testing to prevent leakage via the nasal compartments. However, some subjects exhibit a velum-opening reflex which may affect results. We performed forced oscillation measurements at frequencies (8-256 Hz) that include the first antiresonance, comparing the noseclip with a cotton wool nose plug to eliminate upper airway contribution. Three sets of measurements were made in 18 adults: with and without noseclip, and with cotton wool. Velum opening during noseclip measurements was monitored using a nasal pressure transducer. A significantly greater proportion of subjects produced a characteristic distortion to the first antiresonance with the noseclip than with either no noseclip or with cotton wool. Distortion of the spectrum coincided with the transmission of oscillations into the nasal cavity. Thus, the noseclip cannot be used in high-frequency forced oscillation measurements because of the velum reflex. The cotton wool plug offers a simple alternative. This effect has unknown impact in other lung function tests.

This review discusses the history and current state of the art of the forced oscillation technique (FOT) to measure respiratory impedance. We focus on how the FOT and its interaction with models have emerged as a powerful method to extract out not only clinically relevant information, but also to advance insight on the mechanisms and structures responsible for human lung diseases, especially asthma. We will first provide a short history of FOT for basic clinical assessment either directly from the data or in concert with lumped element models to extract out specific effective properties. We then spend several sections on the more exciting recent advances of FOT to probe the relative importance of tissue versus airway changes in disease, the impact of the disease on heterogeneous lung function, and the relative importance of small airways via synthesis of FOT with imaging. Most recently, the FOT approach has been able to directly probe airway caliber in humans and the distinct airway properties of asthmatics that seem to be required for airway hyperresponsiveness. We introduce and discuss the mechanism and clinical implications of this approach, which may be substantial for treatment assessment. Finally, we highlight important future directions for the FOT, particularly its use to probe specific lung components (e.g., isolated airways, isolated airway smooth muscle, etc.) and relate such data to the whole lung. The intent is to substantially advance an integrated understanding of structure-function relationships in the lung.

OBJECTIVE: Recent work has suggested that within-breath respiratory impedance measurements performed using the forced oscillation technique may help to noninvasively evaluate respiratory mechanics. We investigated the influence of airway obstruction on the within-breath forced oscillation technique in smokers and chronic obstructive pulmonary disease patients and evaluated the contribution of this analysis to the diagnosis of chronic obstructive pulmonary disease. METHODS: Twenty healthy individuals and 20 smokers were assessed. The study also included 74 patients with stable chronic obstructive pulmonary disease. We evaluated the mean respiratory impedance (Zm) as well as values for the inspiration (Zi) and expiration cycles (Ze) at the beginning of inspiration (Zbi) and expiration (Zbe), respectively. The peak-to-peak impedance (Zpp=Zbe-Zbi) and the respiratory cycle dependence (ΔZrs=Ze-Zi) were also analyzed. The diagnostic utility was evaluated by investigating the sensitivity, the specificity and the area under the receiver operating characteristic curve. ClinicalTrials.gov: NCT01888705. RESULTS: Airway obstruction increased the within-breath respiratory impedance parameters that were significantly correlated with the spirometric indices of airway obstruction (R=−0.65, p90%). CONCLUSIONS: We conclude the following: (1) chronic obstructive pulmonary disease introduces higher respiratory cycle dependence, (2) this increase is proportional to airway obstruction, and (3) the within-breath forced oscillation technique may provide novel parameters that facilitate the diagnosis of respiratory abnormalities in chronic obstructive pulmonary disease.

Background: The impulse oscillation system (IOS) measures respiratory impedance (Zrs) in terms of resistance (Rrs) and reactance (Xrs) at multiples of 5 Hz. These measurements can be used clinically to help diagnose and monitor respiratory disorders, independent of effort. Methodology: The predictive equation for resistance at 5 and 20 Hz and impedance at 5 Hz (R5, R20, X5), for the first time, in 299 Japanese adult subjects was determined. In addition, the within single day variation and between day variation were determined. Results: The predictive equation for R5, R20 and X5 revealed a clear difference with respect to the subject's smoking history (lifelong non-smoker, n = 166, adjusted r = 0.55, 0.46 and 0.57, respectively, vs. smoker, n = 133, adjusted r = 0.47, 0.42 and 0.47, respectively). This difference was less obvious with respect to gender (female, n = 120, adjusted r = 0.42, 0.20 and 0.47, respectively, vs. male, n = 179, adjusted r = 0.46, 0.37 and 0.47, respectively). The predictive equations were dependent on the log of height (H) for both R5 and R20, and on age and log of height for X5. The equations were: R5 (KPa/L/s) = −3.841167 × logH + 8.671580; R20 (KPa/L/s) = −2.546561 × logH + 5.841867; and X5 (KPa/L/s) = −0.000097 × Age + 1.018597 × logH − 2.343672. For these parameters there were no statistically significant differences for within day repeatability or between day variations (P > 0.05), suggesting a high degree of reproducibility for IOS measurements. Conclusion: It was possible to determine a predictive equation and confirm a high degree of reliability of IOS parameters in Japanese adult subjects.

A tracking impedance estimation technique was developed to follow the changes in total respiratory impedance (Zrs) during slow total lung capacity maneuvers in six anesthetized and mechanically ventilated BALB/c mice. Zrs was measured with the wave-tube technique and pseudorandom forced oscillations at nine frequencies between 4 and 38 Hz during inflation from a transrespiratory pressure of 0-20 cmH2O and subsequent deflation, each lasting for ∼20 s. Zrs was averaged for 0.125 s and fitted by a model featuring airway resistance (Raw) and inertance, and tissue damping and elastance ( H). Lower airway conductance (Glaw) was linearly related to volume above functional residual capacity (V) between 0 and 75-95% maximum V, with a mean slope of dGlaw/dV = 13.6 ± 4.6 cmH2O-1 · s-1. The interdependence of Raw and H was characterized by two distinct and closely linear relationships for the low- and high-volume regions, separated at ∼40% maximum V. Comparison of Raw with the highest-frequency resistance of the total respiratory system revealed a marked volume-dependent contribution of tissue resistance to total respiratory system resistance, resulting in the overestimation of Raw by 19 ± 8 and 163 ± 40% at functional residual capacity and total lung capacity, respectively, whereas the lowest frequency reactance was proportional to H; these findings indicate that single-frequency resistance values may become inappropriate as surrogates of Raw when tissue impedance is changing.

Since commercial forced oscillation technique (FOT) devices became available, they have been widely used for physiological assessments, mainly of obstructive lung diseases. However, it is not known whether the impedance values measured with different devices are identical. In this study, two FOT devices—the impulse oscillometry system (IOS) and the MostGraph (MG)—were compared using phantom models. The resistance values varied up to 10 % from estimated values in both devices. Additionally, there was a difference in frequency dependence for the resistance between the devices. The reactance values measured with MG were higher than those measured with IOS. The effects of ventilation on the measured impedance values were higher for IOS than for MG, especially at lower frequencies. We concluded that the devices do not always generate identical impedance values. Thus, differences between the devices should be taken into consideration when evaluating clinical data.

In this work, a re-visited model of the respiratory system is proposed. Identification of a recurrent electrical ladder network model of the lungs, which incorporates their specific morphology and anatomical structure, is performed on 31 healthy subjects. The data for identification has been gathered using the forced oscillation lung function test, which delivers a non-parametric model of the impedance. On the measured frequency response, the ladder network parameters have been identified and a fractional order has been calculated from the recurrent ratios of the respiratory mechanics (resistance and compliance). The paper includes also a comparison of our recurrent parameter model with another parametric model for high frequency range. The results suggest that the two models can equally well characterize the respiratory impedance over a long range of frequencies. Additionally, we have shown that the fractional order resulting from the recurrent properties of resistance and compliance in the ladder network model is independent of frequency and is not biased by the nose clip wore by the patients during measurements. An illustrative example shows that our re-visited model is sensitive to changes in respiratory mechanics and the fractional order value is a reliable parameter to capture these changes.

We used the Impulse Oscillometric System (IOS) to gain information concerning the distribution of hyper-reactivity along the bronchial tree during methacholine challenge test (MCT).37 subjects underwent MCT until reaching the provocative dose (PD20). At each dose, we estimated respiratory resistance at 5 and 20Hz (R5, R20), and reactance at 5Hz (X5). In non-responsive subjects (N=14) no changes in R5, R20, and X5 were observed during MCT. In responsive subjects, a wide spectrum of responses was found concerning frequency dependence and PD20. We describe two phenotypes representing the extremes of response. For PD20>400μg (N=13), MCT caused equal changes of resistance/reactance on varying oscillation frequencies, suggesting a homogeneous bronchoconstriction along the bronchial tree. For PD20

We hypothesized that short-term variation in airway caliber could be quantified by frequency distributions of respiratory impedance (Zrs) measured at high frequency. We measured Zrs at 6 Hz by forced oscillations during quiet breathing for 15 min in 10 seated asthmatic patients and 6 normal subjects in upright and supine positions before and after methacholine (MCh). We plotted frequency distributions of Zrs and calculated means, skewness, kurtosis, and significance of differences between normal and log-normal frequency distributions. The data were close to, but usually significantly different from, a log-normal frequency distribution. Mean lnZrs in upright and supine positions was significantly less in normal subjects than in asthmatic patients, but not after MCh and MCh in the supine position. The lnZrs SD (a measure of variation), in the upright position and after MCh was significantly less in normal subjects than in asthmatic patients, but not in normal subjects in the supine position and after MCh in the supine position. We conclude that 1) the configuration of the normal tracheobronchial tree is continuously changing and that this change is exaggerated in asthma, 2) in normal lungs, control of airway caliber is homeokinetic, maintaining variation within acceptable limits, 3) normal airway smooth muscle (ASM) when activated and unloaded closely mimics asthmatic ASM, 4) in asthma, generalized airway narrowing results primarily from ASM activation, whereas ASM unloading by increasing shortening velocity allows faster caliber fluctuations, 5) activation moves ASM farther from thermodynamic equilibrium, and 6) asthma may be a low-entropy disease exhibiting not only generalized airway narrowing but also an increased appearance of statistically unlikely airway configurations.

The forced oscillation technique is useful in detecting changes in upper airway obstruction in patients with sleep apnoea undergoing continuous positive airway pressure (CPAP) ventilation. The aim of this study was to implement and evaluate a method for estimating respiratory impedance (Zrs) from the pressure and flow recorded at the inlet of the CPAP tubing. The method is based on correcting impedance measured at the inlet of the CPAP tubing (Zi) for the effect of the tubing and the exhalation port. The method was evaluated in mechanical analogues and in a healthy subject. Sinusoidal oscillation of 5, 10 and 20 Hz were superimposed on CPAP (5-15 cmH2O). At 5 Hz, the changes in airflow obstruction were substantially underestimated by Zi. Furthermore, Zi exhibited a negative dependence on Zrs at 20 Hz. The assessment of Zrs was greatly improved after correcting Zi for the effects of the CPAP tubing and the exhalation port. Zrs was well estimated at low frequencies, reaching very high values during total occlusion (>60 cmH2O x s x L(-1) at 5-10 Hz). These results indicate that changes in airflow obstruction can be detected using the forced oscillation technique from pressure and flow recorded on the continuous positive airway pressure device. This facilitates the clinical application of the forced oscillation technique for monitoring upper airway patency during sleep.

The airflow perturbation device (APD) is an instrument for the measurement of respiratory resistance. The APD is small, lightweight, fast and requires no special breathing manoeuvres. Airflow perturbation determines resistance by superimposing a periodic signal onto spontaneous breathing with a variable resistance device. Respiratory impedance is the ratio of magnitude of pressure perturbation to magnitude of flow perturbation, and respiratory resistance is the in-phase portion of respiratory impedance. The APD was tested to determine its responses to repeated resistance measurements and to changes in resistance. A mechanical model test showed that the APD could detect increased resistance levels, but overestimated resistance when resistance increased with flow. Tests with human subjects showed that the APD gave results consistent from day to day, was able to detect added resistances, and gave resistance values correlated with airway resistance values obtained by body plethysmography. Accelerometers placed on the chests of the subjects showed that perturbations extend to the chest surface. Thus, the APD must measure total respiratory resistance. Keywords: respiration, resistance

The purpose of this study was to test a plethysmographic method of measuring thoracic gas volume (TGV) that, contrary to the usual panting method, would not require any active cooperation from the subject. It is based on the assumption that the out-of-phase component of airway impedance varies linearly with frequency. By using that assumption, TGV may be computed by combining measurements of total respiratory impedance (Zrs) and of the relationship between the plethysmographic signal (Vpl) and airway flow (V˙) during forced oscillations at several frequencies. Zrs and Vpl/V˙were measured at 10 noninteger multiple frequencies ranging from 4 to 29 Hz in 15 subjects breathing gas in nearlybtps conditions. Forced oscillation measurements were immediately followed by determination of TGV by the standard method. The data were analyzed on different frequency ranges, and the best agreement was seen in the 6- to 29-Hz range. Within that range, forced oscillation TGV and standard TGV differed little (3.92 ± 0.66 vs. 3.83 ± 0.73 liters, n = 77, P < 0.05) and were strongly correlated ( r = 0.875); the differences were not correlated to the mean of the two estimates, and their SD was 0.35 liter. In seven subjects the differences were significantly different from zero, which may, in part, be due to imperfect gas conditioning. We conclude that the method is not highly accurate but could prove useful when, for lack of sufficient cooperation, the panting method cannot be used. The results of computer simulation, however, suggest that the method would be unreliable in the presence of severe airway inhomogeneity or peripheral airway obstruction.

International audience; Bronchospasm may be part of the response to systemic anaphylaxis in humans. The anaphylactic shock has been characterized in allergic rats, but little data are available on the concurrent changes in airway–lung mechanics. The aim was to describe the respiratory resistance (Rrs) and reactance (Xrs) response to ovalbumin (OVA) induced systemic anaphylaxis in allergic rats. Thirty five anesthetized and mechanically ventilated Brown Norway rats were randomly allocated to OVA (n = 20) or vehicle (n = 15) sensitization and provocation. Rrs and Xrs were obtained by the forced oscillation technique at 20 Hz. Allergic rats showed dramatic and reproducible concurrent Rrs peak and Xrs through within 4 min of OVA injection (p < 0.0001). Thereafter, Rrs returned to baseline while Xrs remained significantly more negative (p < 0.0001). It is concluded that systemic anaphylaxis in allergic rats is associated with severe early acute inhomogeneous bronchoconstriction followed by pulmonary interstitial/small airspace edema. The model may be of interest to assess treatments targeting the associated bronchoconstriction and/or airway vascular leakage.

Low-frequency respiratory impedance (Zrs) data permit the separate estimation of the mechanical properties of the airways and the tissues, but they are difficult to collect in humans because of the need for apneic conditions. We exploited the apneic phase produced by invoking the Hering-Breuer reflex with end-inspiratory airway occlusion in five sedated infants aged 9 to 16 mo. A computer-controlled pump and solenoid valves were used to inflate the supine infants through a face mask to a transrespiratory pressure of 20 cm H2O and to affect the airway occlusion. A loudspeaker-in-box system was connected to the mask through a side-arm, and small-amplitude pseudorandom oscillations containing 23 frequency components between 0.5 and 20.75 Hz were applied for 6 s. Four consecutive measurements were made in each infant, and the averaged Zrs spectra were evaluated on the basis of a model containing the frequency-independent resistance (Raw) and inertance (law) of the airways, and the viscous damping (G) and elastance (H) parameters of the constant-phase compartment of the chest wall and parenchymal tissues. The measured Zrs values were consistent with the model up to 15 Hz, and the average fitting error was 0.89 +/- 0.11 (SD) cm H2O.s/L. The following parameter values were obtained: Raw = 10.0 +/- 2.1 cm H2O.s/L, law = 0.061 +/- 0.014 cm H2O.s2/L, G = 28.6 +/- 4.9 cm H2O/L, H = 141 +/- 55 cm H2O/L. The tissue hysteresivity (G/H) values were 0.218 +/- 0.061. Our results indicate that, in short apneic periods evoked by the Hering-Breuer reflex, reliable low-frequency Zrs data can be collected to partition the tissue and airway impedances in sedated infants.

Measurement of respiratory impedance (Zrs) in intubated patients requires corrections for flow-dependent resistance and air compression inside the endotracheal tube (ET). The purpose of this study was to test a new correction technique for these effects. We therefore studied 110 patients in two conditions: breathing normally (C1), or breathing through an ET placed at the mouth (C2). In C1, we measured pressure and flow signals at the mouth, and in C2, at the ET inlet, during application of a pseudorandom forced excitation (4-32 Hz). In C1, respiratory impedance was calculated directly as Z1. In C2, pressure data were first corrected for the flow-dependent resistance of the ET, and respiratory impedance was then corrected both for gas compression inside the set-up and ET inertance (impedance Z2). Strong linear relationships were found between the reference and corrected estimates of the resistance at 6 Hz, the frequency dependence of resistance and the resonant frequency. The mean normalized distance between Z1 and Z2 observed in the patients over the 4-32 Hz frequency range was about 14% for resistance and 12% for reactance (-9% and -4%, respectively, when considering the algebraic value of the distance). This slight underestimation of both components of impedance might be due to an overcorrection of pressure for the flow-dependent resistance of the ET. We conclude that, in intubated patients, newly tested corrections for the mechanical contribution of the endotracheal tube may yield a fair estimate of respiratory impedance when pressure is measured at the inlet of the endotracheal tube.

The respiratory impedance was measured by means of the forced oscillation technique (Landser et al.) and the lung tissue compliance was measured with an oesophageal balloon in 30 patients with a wide range of values of lung tissue compliance. According to the model of respiratory impedance of Nagels et al. it is unlikely that the impedance data are markedly affected by the lung tissue compliance. This hypothesis has not been clinically tested yet.The semistatic compliance (Css) or specific compliance (Cspec) were not statistically correlated with any of the impedance data. Consequently the oscillatory respiratory measurements are not systematically influenced by the compliance of the lung tissue during quiet breathing. However, the dynamic compliance and the frequency dependence of the compliance showed a low but significant correlation with the reactance and resonant frequency (varying from r=0·41, P

We present a broad-band optimal ventilator waveform (OVW), the concept of which was to create a computer-driven ventilator waveform containing increased energy at specific frequencies (f). Values of f were chosen such that nonlinear harmonic distortion and intermodulation were minimized. The phases at each f were then optimized such that the resulting flow waveform delivered sufficient volume to maintain gas exchange while minimizing peak-to-peak airway opening pressure. Simulations with a linear anatomically consistent branching airway model and a nonlinear viscoelastic model showed that respiratory resistance (Rrs) and elastance (Ers) estimates at 0.1–2 Hz from the OVW are far superior to those from a standard step ventilator waveform (SVW) during healthy and obstructed conditions and that the OVW reduces the influences of harmonic interactions. Using a servo-controlled oscillator, we applied individual sine waves, an OVW containing energy at 0.15625–2.4 Hz, and an SVW to healthy humans and one symptomatic asthmatic subject before and after bronchodilation. The OVW was markedly superior to the SVW and always provided smooth estimates of Rrs and Ers. Before bronchodilation in the asthmatic subject Rrs was highly elevated and Ers was markedly increased with f; after bronchodilation the level of Rrs and the f dependence of Ers decreased. Although based on results from only one asthmatic subject, these data suggest a dominant influence of airway constriction and lung inhomogeneities during asthmatic bronchoconstriction that is alleviated by bronchodilators. These and other results indicate that the OVW approach has high potential for simultaneously probing f and amplitude dependence in the mechanical properties of clinical subjects during physiological breathing conditions and perhaps during dynamic bronchoconstriction.

The resistance (Rrs) and reactance (Xrs) of the total respiratory system were determined at various frequencies in 14 healthy conscious beagle dogs. A pseudorandom noise pressure wave was produced at the nostrils of the animals by means of a loudspeaker adapted to the nose by a tightly fitting mask. A Fourier analysis of the pressure and flow signals yielded mean Rrs and Xrs, over 16 s, at frequencies from 2 to 26 Hz. The influence of the posture of the dog, the position of its head, the linearity of the respiratory system, the reproducibility of the method and the effects of upper and lower airway obstructions were studied. In sitting and standing healthy dogs with the head in the extended position, Rrs values increased progressively with frequency from 5.4 +/- 0.4 (SEM) cmH2O L-1s at 6 Hz up to 8.8 +/- 0.7 cmH2O L-1s at 26 Hz, the mean resonant frequency being 6.1 +/- 0.5 Hz. No significant differences were observed between measurements performed with the head in the normal or the extended position. In a recumbent posture, all Rrs values were increased but Rrs was still dependent on the frequency in the same way (7.1 +/- 0.7 cmH2O L-1s at 6Hz up to 10.0 +/- 0.5 cmH2O L-1s at 26 Hz). Tracheal compression also induced higher Rrs values without changes in the frequency dependence or in the resonant frequency. In anaesthetized dogs, airway obstruction was induced by inhalation of histamine (4 mg/ml for 5 min; the Rrs values tended to decrease with increasing frequency, and the resonant frequency was markedly increased.

This study aimed to implement low-frequency forced oscillation technique (LFFOT) in neonatal total liquid ventilation (TLV) and to provide the first insight into respiratory impedance under this new modality of ventilation. Thirteen newborn lambs, weighing 2.5 ± 0.4 kg (mean ± SD), were premedicated, intubated, anesthetized, and then placed under TLV using a specially design liquid ventilator and a perfluorocarbon. The respiratory mechanics measurements protocol was started immediately after TLV initiation. Three blocks of measurements were first performed: one during initial respiratory system adaptation to TLV, followed by two other series during steady-state conditions. Lambs were then divided into two groups before undergoing another three blocks of measurements: the first group received a 10-min intravenous infusion of salbutamol (1.5 μg·kg−1·min−1) after continuous infusion of methacholine (9 μg·kg−1·min−1), while the second group of lambs was chest strapped. Respiratory impedance was measured using serial single-frequency tests at frequencies ranging between 0.05 and 2 Hz and then fitted with a constant-phase model. Harmonic test signals of 0.2 Hz were also launched every 10 min throughout the measurement protocol. Airway resistance and inertance were starkly increased in TLV compared with gas ventilation, with a resonant frequency ≤1.2 Hz. Resistance of 0.2 Hz and reactance were sensitive to bronchoconstriction and dilation, as well as during compliance reduction. We report successful implementation of LFFOT to neonatal TLV and present the first insight into respiratory impedance under this new modality of ventilation. We show that LFFOT is an effective tool to track respiratory mechanics under TLV.

Respiratory impedance measurements by means of the technique of forced oscillations together with spirometry and measurements of maximal mouth pressures were performed in 27 patients with a variety of neuromuscular disorders to assess the value of adding respiratory impedance measurements in the evaluation of lung function in neuromuscular disease. Using the technique of forced oscillations, impedance measurements are easily performed in physically disabled persons, since they require little active cooperation and no forced respiratory maneuvers. Normal respiratory impedance characteristics were found, although resistance values were somewhat higher than those found in normal subjects, signifying the absence of airflow limitation. Spirometrie values were markedly reduced, as were maximal mouth pressures. No significant correlations were found between the forced expiratory volumes in 1 s (FEV 1 ) and the impedance data. A strong curvilinear relationship was observed between PEmax and the RV/TLC ratio and a strong correlation existed between FEV 1 and PEmax. It is concluded from our study that forced oscillometry is a useful tool for the assessment or exclusion of airflow obstruction in patients with neuromuscular disorders when plethysmography is difficult to perform and forced expiratory flow-volume data reflect muscle weakness rather than airflow limitation.

INTRODUCTION: The within-breath analysis of respiratory mechanics by the monofrequency Forced Oscillation Technique (mFOT) is of great interest in both physiopathology studies and the diagnosis of respiratory diseases. However, there are limited data on the use of this technique in the analysis of asthma. This study evaluates within-breath mechanics of asthmatic individuals and the contribution of the mFOT in the asthma diagnosis. METHODS: Twenty-two healthy and twenty-two asthmatic subjects, including patients with mild (n=8), moderate (n=8), and severe (n=6) obstruction, were studied. Forced Oscillation Technique data were interpreted using the mean respiratory impedance (Zt), the impedance during inspiration (Zi), expiration (Ze), at the beginning of inspiration (Zii), and at expiration (Zie). The peak-to-peak impedance (Zpp) was also calculated by the subtraction of Zii from Zie. Receiver operating characteristic curves were used to determine the sensitivity (Se) and specificity (Sp) of m Forced Oscillation Technique parameters in identifying asthma. RESULTS: Respiratory impedance values were significantly higher in asthmatics: Zt (p

Past studies in humans and other species have revealed the presence of resonances and antiresonances, i.e., minima and maxima in respiratory system impedance (Zrs), at frequencies much higher than those commonly employed in clinical applications of the forced oscillation technique (FOT). To help understand the mechanisms behind the first occurrence of antiresonance in the Zrs spectrum, the frequency response of the rat was studied by using FOT at both low and high frequencies. We measured Zrs in both Wistar and PVG/c rats using the wave tube technique, with a FOT signal ranging from 2 to 900 Hz. We then compared the high-frequency parameters, i.e., the first antiresonant frequency (far,1) and the resistive part of Zrs at that frequency [Rrs(far,1)], with parameters obtained by fitting a modified constant-phase model to low-frequency Zrs spectra. The far,1 was 570 ± 43 (SD) Hz and 456 ± 16 Hz in Wistar and PVG/c rats, respectively, and it did not shift with respiratory gases of different densities (air, heliox, and a mixture of SF6). The far,1 and Rrs(far,1) were relatively independent of methacholine-induced bronchoconstriction but changed significantly with increasing transrespiratory pressures up to 20 cmH2O, in the same way as airway resistance but independently of changes to tissue parameters. These results suggest that, unlike the human situation, the first antiresonance in the rat is not primarily dependent on the acoustic dimensions of the respiratory system and can be explained by interactions between compliances and inertances localized to the airways, but this most likely does not include airway wall compliance.

Forced oscillation impedance (Zrs) measurements are frequently corrupted by noisy data in children. Our aim was to improve the reliability of respiratory resistance (Rrs) and routine identification of its flow (V') and volume (V) dependence during tidal breathing, according to Rrs = K1 + K2 x /V'/ + K3 x V. Zrs was measured at 12 Hz, using a head generator in 23 children aged 4-13 years undergoing methacholine (Mch) challenge. Rrs, K1, K2, K3, and residual mean square error (RMSD), as well as reproducibility of the parameters, were obtained. Calculations were performed separately in inspiration and expiration on the raw data, and after eliminating values lying outside confidence intervals ranging from 99% (F3SD) to 95% (F2SD) of the mean Zrs. Filtering decreased RMSD and Rrs, F3SD improved reproducibility of Rrs in expiration compared to raw data. F2SD increased K1 and decreased the amplitude of K2 and K3 before and after Mch compared to F3SD. Rrs and K2 were significantly larger and K3 significantly more negative in expiration than in inspiration at all levels of filtering, probably because of the upper airways. F3SD appeared efficient in eliminating aberrant data, while allowing the identification of physiological variations of Rrs.