Forced Oscillation Technique Measurements Research Articles

Bronchial obstruction in osteogenesis imperfecta can be detected by forced oscillation technique.

Respiratory insufficiency is a leading cause of death in individuals with osteogenesis imperfecta (OI). However, evaluating pulmonary function in OI presents challenges. Commonly used pulmonary function tests such as spirometry and body plethysmography are sometimes difficult to perform for OI patients, and reference intervals are not always applicable. The forced oscillation technique (FOT) is a patient-friendly method for detecting respiratory abnormalities that requires no effort from the patient. This study investigates the feasibility of FOT in the evaluation of respiratory function in the clinical management of OI patients. Twelve OI patients, comprising eight with Sillence OI I, two with OI IV, and two with OI III, underwent spirometry, body plethysmography, and FOT, both pre-and post-administration of salbutamol. FOT measurements exhibited consistent trends that aligned with spirometry and body plethysmography findings. The resistance at 8 Hz decreased after the administration of salbutamol, indicating that FOT is able to detect bronchial obstruction and its alleviation by medication (p < 0.05). The resonant frequency during expiration was higher than during inspiration in nearly all patients, suggesting obstructive disease. The technique gives insight into both inspiratory and expiratory impairment of pulmonary ventilation. The main FOT parameters showed a relatively high repeatability in duplicate measurements. Bronchial obstruction can be detected by FOT in patients with OI during quiet breathing, making it an easily executable alternative to other lung function measurements. The technique can detect the bronchodilator effect of sympathomimetic medication. It has the potential to provide information on expiratory flow limitation, pulmonary restriction, and reduced lung compliance.

Pattern recognition of forced oscillation technique measurement results using deep learning can identify asthmatic patients more accurately than setting reference ranges

No official clinical reference values have been established for MostGraph, which measures total respiratory resistance and reactance using the forced oscillation technique, complicating result interpretation. This study aimed to establish a reference range for MostGraph measurements and examine its usefulness in discriminating participants with asthma from controls (participants without any respiratory diseases). The study also aimed to investigate the effectiveness of deep learning in discriminating between the two aforementioned groups. To establish reference ranges, the MostGraph measurements of healthy controls (n = 215) were power-transformed to distribute the data more normally. After inverse transformation, the mean ± standard deviation × 2 of the transformed values were used to establish the reference ranges. The number of measured items outside the reference ranges was evaluated to discriminate patients with asthma (n = 941) from controls. Additionally, MostGraph measurements were evaluated using deep learning. Although reference ranges were established, patients with asthma could not be discriminated from controls. However, with deep learning, we could discriminate between the two groups with 78% accuracy. Therefore, deep learning, which considers multiple measurements as a whole, was more effective in interpreting MostGraph measurement results than use of reference ranges, which considers each result individually.

Optimization based on performance of lungs in body: Lungs performance-based optimization (LPO)

The development of efficient optimization algorithms is crucial across various scientific disciplines. As the complexity and diversity of optimization problems continue to grow, researchers seek faster and stronger algorithms capable of optimizing a wide range of functions. This paper introduces Lung performance-based optimization (LPO), a novel and efficient algorithm inspired by the regular and intelligent performance of lungs in the human body. LPO draws inspiration from the intricate mechanisms and adaptability of the respiratory system. The lungs exhibit remarkable efficiency in oxygen exchange, demonstrating a high level of optimization in their function. The forced oscillation technique measures air pressure and airflow rate to evaluate the respiratory system as an electrical impedance. The impedance curves have two distinct components, respiratory resistance (ZR) and respiratory reactance (ZX), which can be analyzed clinically and from an engineering perspective to gain insights into the respiratory system's workings. LPO aims to provide an innovative approach to solving complex optimization problems by emulating and harnessing this natural efficiency. To evaluate the effectiveness of LPO, experiments were conducted using the unconstrained optimization functions CEC2005 and CEC2014, as well as engineering design optimization problems. These problems were compared against numerous contemporary algorithms proposed in the literature. The results demonstrate that LPO excels in handling these optimization problems and exhibits the potential to tackle a wide range of modern optimization challenges. The findings highlight the power and effectiveness of LPO as a new optimization algorithm. With its inspiration rooted in the sophisticated performance of the lungs, LPO offers a unique perspective in the optimization landscape. Its ability to handle diverse optimization problems and its potential for application in various domains make LPO a promising algorithm for future research and practical implementation. Note that the source code of the LPO is publicly available at https://www.optim-app.com/projects/lpo.

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

BackgroundThe forced oscillation technique (FOT) may be useful for diagnosis and follow-up of respiratory diseases. It is unclear how global or regional alterations in airway resistance (Raw) and lung compliance (CL) alter FOT measurements. MethodsA 2-compartment physical model of the respiratory system allowed to simulate variations in Raw, CL, and their heterogeneity during tidal breathing in an adult human. Five-Hz respiratory system resistance (Rrs5) and reactance (Xrs5), area of reactance (AX), resonance frequency (Fresp) and intrabreath variation in Rrs5 and Xrs5 were measured by FOT. Frequency dependance of resistance could not be studied in this model. Relationships between model characteristics (Raw, CL, and heterogeneity) and FOT measurements were explored by multiple regression. ResultsRrs5 and intrabreath variation in Rrs5 and Xrs5 strongly associated with model characteristics (R2=0.753, 0.5 and 0.658). Associations of Xrs5, AX, and Fresp with model characteristics were weak (R2=0.214, 0.349 and 0.076). Raw heterogeneity was the main determinant of Rrs5 (Coeff=0.594), AX (Coeff=0.566) and intrabreath variation in Rrs5 and Xrs5 (Coeff=0.586 and 0.732). Regional extremes in Raw strongly determined Rrs5 (Coeff=1.006). Xrs5 did not strongly associate with any model characteristic. ConclusionRaw heterogeneity and maximal regional Raw were the main determinants of FOT measurements, in particular Rrs5. Associations between CL and FOT measurements were weak.

Forced Oscillation Measurements in Patients with Idiopathic Interstitial Pneumonia Subjected to Pulmonary Rehabilitation.

(1) Background: Pulmonary rehabilitation (PR) plays a significant therapeutic role for patients with idiopathic interstitial pneumonia (IIP). The study assessed the impact of physical activity on lung function measured by forced oscillation technique (FOT). (2) Methods: The study involved 48 patients with IIP subjected to a 3-week inpatient PR. The control group included IIP patients (n = 44) on a 3-week interval without PR. All patients were assessed at baseline and after 3 weeks of PR by FOT, spirometry, plethysmography, grip strength measurement and the 6-minute walk test. (3) Results: There were no significant changes in FOT measurements in the PR group, except for reduced reactance at 11 Hz, observed in both groups (p < 0.05). Patients who completed PR significantly improved their 6-min walk distance (6MWD) and forced vital capacity (FVC). The change in 6MWD was better in patients with higher baseline reactance (p = 0.045). (4) Conclusions: Patients with IIP benefit from PR by an increased FVC and 6MWD; however, no improvement in FOT values was noticed. Slow disease progression was observed in the study and control groups, as measured by reduced reactance at 11 Hz. Patients with lower baseline reactance limitations achieve better 6MWD improvement.

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

To develop regression equations to predict forced oscillation technique (FOT) parameters in Indian children and adolescents. Lung function was assessed in a multigeographic cohort of residential school children using a portable FOT-based device (PulmoScan) and spirometry. FOT measurements were performed in 1497 study participants, aged 9-19 y, from 8 Indian districts. Bland-Altman analysis was performed for additional 32 adult subjects to compare the results of PulmoScan to a standard IOS device in an outpatient setting. Reference equations were developed for Rrs and Xrs from the data of healthy subjects with normal spirometry using multivariate regression model for Indo-European, Dravidian, and mixed ethnic groups. X5 (bias = 0.02) showed a better agreement than resistance parameters (R5 bias = 0.75, R20 bias = -0.22) in IOS/PulmoScan comparison. Anthropometric variables (age, height, and weight) were positively correlated with reactance (X5) and negatively with resistance parameters (R5, R10, R15, and R20), with most associations being stronger in boys. Final regression model considered ethnicity as a key determinant along with anthropometry. Multiethnic reference equations were developed for Indian children aged 9-19 y based on a novel handheld FOT device.

Forced Oscillation Technique Measurement Apparatus Using Fan-Speaker Hybrid

The number of patients suffering from asthma and chronic obstructive pulmonary disease (COPD) increases due to deteriorating air quality and smoking. A measurement technique known as the forced oscillation technique (FOT) helps physicians to assess the current state of their patient’s lungs. Measurement devices based on either fans or speakers have been developed in the past that can carry out this measurement, but their performance and/or robustness often fall short. This article proposes a combination of a fan- and speaker-based measurement apparatus that employs the FOT to help physicians diagnose patients with these diseases. First, we discuss the currently available measurement devices and their specific problems. Next, a fan-speaker hybrid measurement apparatus is proposed. This fan-speaker hybrid FOT measurement apparatus is then characterized and its performance is improved with a feed forward compensation. Finally, measurements on two test subjects with the proposed measurement apparatus are shown and discussed.

Self-reported exercise-induced dyspnea and airways obstruction assessed by oscillometry and spirometry in adolescents.

BackgroundSelf‐reported exercise‐induced dyspnea (EID) is common among adolescents. Possible underlying pathologies are exercise‐induced bronchoconstriction (EIB) and laryngeal obstruction (EILO). The forced oscillation technique (FOT) may evaluate exercise‐induced changes in airway caliber.AimTo investigate in adolescents the relationship between EID, EIB (post‐exercise fall in forced expiratory volume in 1s (FEV1)≥10%), EILO, and post‐exercise challenge changes in FOT parameters.MethodsOne hundred and forty‐three subjects (97 with EID) of 13–15 years old underwent a standardized exercise challenge with FOT measurement and spirometry repeatedly performed between 2 and 30 min post‐exercise. EILO was studied in a subset of 123 adolescents. Subjects showing greater changes than the healthy subgroup in the modulus of the inspiratory impedance were considered FOT responders.ResultsEID‐nonEIB subjects presented similar post‐exercise changes in all FOT parameters to nonEID‐nonEIB adolescents. Changes in all FOT parameters correlated with FEV1 fall. 45 of 97 EID subjects responded neither by FEV1 nor FOT to exercise. 19 and 18 subjects responded only by FEV1 (onlyFEV1responders) or FOT (onlyFOTresponders), respectively. Only a lower baseline forced vital capacity (FVC)%predicted and a higher FEV1/FVC distinguished the onlyFEV1responders from onlyFOTresponders. FOT parameters did not present specific post‐exercise patterns in EILO subjects.ConclusionFOT can be used to identify post‐exercise changes in lower airway function. However, EID has a modest relation with both FEV1 and FOT responses, highlighting the need for objective testing. More research is needed to understand whether onlyFEV1responders and onlyFOTresponders represent different endotypes.

Artificial intelligence for quality control of oscillometry measures

BackgroundThe forced oscillation technique (FOT) allows non-invasive lung function testing during quiet breathing even without expert guidance. However, it still relies on an operator for excluding breaths with artefacts such as swallowing, glottis closure and coughing. This manual selection is operator-dependent and time-consuming. We evaluated supervised machine learning methods to exclude breaths with artefacts from data analysis automatically. MethodsWe collected 932 FOT measurements (Resmon Pro Full, Restech) from 155 patients (6–87 years) following the European Respiratory Society (ERS) technical standards. Patients were randomly assigned to either a training (70%) or test set. For each breath, we computed 71 features (including anthropometric, pressure stimulus, breathing pattern, and oscillometry data). Univariate filter, multivariate filter and wrapper methods for feature selection combined with several classification models were considered. ResultsTrained operators identified 4333 breaths with- and 10244 without artefacts. Features selection performed by a wrapper method combined with an AdaBoost tree model provided the best performance metrics on the test set: Balanced Accuracy = 85%; Sensitivity = 79%; Specificity = 91%; AUC-ROC = 0.93. Differences in FOT parameters computed after manual or automatic breath selection was less than ∼0.25 cmH2O*s/L for 95% of cases. ConclusionSupervised machine-learning techniques allow reliable artefact detection in FOT diagnostic tests. Automating this process is fundamental for enabling FOT for home monitoring, telemedicine, and point-of-care diagnostic applications and opens new scenarios for respiratory and community medicine.

Within-session reproducibility of forced oscillometry.

The forced oscillation technique (FOT) provides detailed information about the mechanics of the respiratory system, while requiring minimal co-operation by the patient. FOT may be abnormal in subjects with normal spirometry and appears to be more closely related to airway symptoms. It is, therefore, attractive in epidemiological studies, where a large number of different examinations are made in each subjects in a short period of time. Current technical standards recommend the mean of three consecutive measurements to be used, but there is limited information regarding within-session variability of FOT measurements. The purpose of this study was to examine the within-session variability in FOT measurements in a large, population-based sample. We performed three consecutive FOT measurements in 700 subjects using the impulse oscillometry system. The first measurement was compared to the mean of three measurements for resistance at 5 and 20Hz (R5 and R20, respectively), R5-R20, reactance at 5Hz (X5) and resonant frequency (fres ). The differences between the first and the mean of three measurements (median, interquartile range) were minimal, for example 0.002, -0.008 to 0.014kPa L-1 s for R5 and -0.001, -0.008 to 0.005kPa L-1 s for X5. Findings were numerically similar for men and women as well as for subjects with and without airflow obstruction at spirometry. We conclude that, whereas in clinical situations, three FOT measurements are to be preferred, a single measurement may suffice in epidemiological studies.

Reference value of Forced Oscillation Technique for healthy preschool children.

The reference values of Forced Oscillation Technique (FOT) parameters of the inspiratory and expiratory phase for preschool children have not yet been established. To evaluate FOT measures in Thai healthy preschool children. Preschool children, aged 3-6 years, were screened. Children who were positive for the International Study of Asthma and Allergies in Childhood (ISAAC) questionnaire for asthma, positive family history of allergic diseases, recent lower respiratory tract infections, and environmental tobacco smoke were excluded. FOT parameters, including resistance (Rrs), reactance (Xrs), frequency of resonance (Fres) and area of reactance (ALX), were measured. A total of 390 healthy children with the mean age of 5.1 ± 0.9 years were enrolled. FOT was successfully performed in 378 children (96.9%). The mean (SD) for the whole breath (WB) resistance at 5Hz (R5), 20 Hz (R20) and R5-20 were 11.49 (2.69) cmH2O/L/s, 9.46 (2.19) cmH2O/L/s and 2.02 (0.82) cmH2O/L/s, respectively. The median (IQR) for WB reactance at 5Hx (X5), Fres and ALX were -1.51 (-2.37 to -0.96) cmH2O/L/s, 11.17 (8.50-15.65) Hz, and 7.53 (3.72-14.32) cmH2O/L/s, respectively. Significantly difference in WB R5, R20, X5, Fres and ALX between male and female children were demonstrated. The expiratory phase R5, R20, R5-20 were significantly higher than those of the inspiratory phase (p < 0.001). There are significant correlations between the height and FOT parameters. Reference curve for the FOT parameters was generated based on height using the lambda-mu-sigma (LMS) method. Reference curve of FOT parameters measured in healthy preschool children were demonstrated. Majority of preschool children could perform FOT method.

Adaptive Excitation Signals for Low-Frequency Forced Oscillation Technique Measurements in Patients

The low-frequency forced oscillation technique (FOT) has a high diagnostic potential for the detection of respiratory diseases. However, it is not yet widely accepted in clinical practice, partly because the natural breathing frequency usually interferes with the measurement, thus requiring patient-unfriendly breathing maneuvers. The presence of a subject’s breathing generally results in patient-unfriendly measurement protocols. These are needed to extract the important low-frequency information about the subject’s respiratory system. This work presents a technique enabling the application of low-frequency FOT during spontaneous breathing. This is accomplished by adding an external visual stimulus to encourage the subject to synchronize his/her breathing to the measurement apparatus, in combination with an excitation signal that is adapted to the subject’s natural breathing frequency. In this way, the contributions of the breathing and the excitation signal can be separated. This article discusses the implementation, testing, and actual measurement results in a clinical setting using this method.

Differences Between Central Airway Obstruction and Chronic Obstructive Pulmonary Disease Detected with the Forced Oscillation Technique.

BackgroundObstructive 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 MethodsWe retrospectively included 16 patients with CAO (10 cases of tracheal obstruction and 6 cases of bronchial obstruction) and 75 treatment-naïve 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.ResultsAll 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.ConclusionThis 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.

Day-to-day variability of forced oscillatory mechanics for early detection of acute exacerbations in COPD.

Telemonitoring trials for early detection of acute exacerbations of chronic obstructive pulmonary disease (AECOPD) have provided mixed results. Day-to-day variations in lung function measured by the forced oscillation technique (FOT) may yield greater insight. We evaluated the clinical utility of home telemonitoring of variability in FOT measures in terms of 1) the relationship with symptoms and quality of life (QoL); and 2) the timing of variability of FOT measures and symptom changes prior to AECOPD. Daily FOT parameters at 5 Hz (resistance (R) and reactance (X); Resmon Pro Diary, Restech Srl, Milan, Italy), daily symptoms (COPD Assessment Test (CAT)) and 4-weekly QoL data (St George's Respiratory Questionnaire (SGRQ)) were recorded over 8-9 months from chronic obstructive pulmonary disease (COPD) patients. Variability of R and X was calculated as the standard deviation (sd) over 7-day running windows and we also examined the effect of varying window size. The relationship of FOT versus CAT and SGRQ was assessed using linear mixed modelling, daily changes in FOT variability and CAT prior to AECOPD using one-way repeated measures ANOVA. Fifteen participants with a mean±sd age of 69±10 years and a % predicted forced expiratory volume in 1 s (FEV1) of 39±10% had a median (interquartile range (IQR)) adherence of 95.4% (79.0-98.8%). Variability of the inspiratory component of X (indicated by the standard deviation of inspiratory reactance (SDXinsp)) related to CAT and weakly to SGRQ (fixed effect estimates 1.57, 95% CI 0.65-2.49 (p=0.001) and 4.41, 95% CI -0.06 to 8.89 (p=0.05), respectively). SDXinsp changed significantly on the same day as CAT (1 day before AECOPD, both p=0.02) and earlier when using shorter running windows (3 days before AECOPD, p=0.01; accuracy=0.72 for 5-day windows). SDXinsp from FOT telemonitoring reflects COPD symptoms and may be a sensitive biomarker for early detection of AECOPD.

Resistance of the respiratory system measured with forced oscillation technique (FOT) correlates with bronchial thermoplasty response

BackgroundBronchial 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.AimTo 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.MethodsSevere 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.ResultsTwenty-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).ConclusionPulmonary 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 registrationClinicalTrials.gov Identifier: NCT02225392; Registered 26 August 2014.

Cut-off values for positive bronchodilator response in healthy Thai preschool children using forced oscillation technique.

Forced oscillation technique (FOT) requires minimal patient cooperation and is particularly useful in young children. Bronchodilator test is a valuable tool for wheezy and asthmatic patients. The cut-off value for bronchodilator response by FOT in healthy Thai children has not been reported. To determine the cut-off values for positive bronchodilator response in healthy Thai preschool children using pseudorandom FOT. FOT was used to measure respiratory function at baseline and after 400 mcg MDI salbutamol in healthy Thai children aged 3-6 years. Respiratory resistance (Rrs) and reactance (Xrs) at 6, 8, and 10 Hz were collected. Pre- and post-bronchodilator tests were compared using paired t-test. Absolute and percent changes after bronchodilator were calculated and their cut-off values were defined as mean ± 1.96 SD. Correlation between each of those and baseline data was analyzed using Pearson's correlation coefficient. Of the 150 enrolled children, FOT measurement at baseline and after bronchodilator was successfully completed in 111 children (51 boys). The mean ± standard deviation age, height, and arm span was 5.2 ± 1.1 years, 109.3 ± 8.7 cm, and 107.2 ± 9.1 cm, respectively. No correlation was observed between any absolute or percent changes in bronchodilator response and gender, age, height, or arm span. The cut-off values established for bronchodilator response by percent change were, as follows: Rrs6: -23%, Rrs8: -20%, Rrs10: -20%, Xrs6: 36%, Xrs8: 60%, and Xrs10: 43%. The cut-off values identified in this study will be useful for evaluating bronchodilator response by FOT in wheezy and asthmatic young children.

Forced oscillation technique as a predictor for loss of control in asthmatic children.

BackgroundA reliable objective tool using as a predictor of asthma control status could assist asthma management.ObjectiveTo find the parameters of forced oscillation technique (FOT) as predictors for the future loss of asthma symptom control.MethodsChildren with well-controlled asthma symptom, aged 6–12 years, were recruited for a 12-week prospective study. FOT and spirometer measures and their bronchodilator response were evaluated at baseline. The level of asthma symptom control was evaluated according to Global Initiative for Asthma.ResultsAmong 68 recruited children, 41 children (60.3%) maintain their asthma control between 2 visits (group C-C), and 27 children (39.7%) lost their asthma control on the follow-up visit (group C-LC). Baseline FOT parameters, including the values of respiratory resistance at 5 Hz (R5), respiratory resistance at 20 Hz (R20), respiratory reactance at 5 Hz, area of reactance, %predicted of R5 and percentage of bronchodilator response (%∆) of R5 and R20 were significantly different between C-C and C-LC groups. In contrast, only %∆ of forced vital capacity, forced expiratory volume in 1 second (FEV1), and FEF25%–75% (forced expiratory flow 25%–75%) were significantly different between groups. Multiple logistic regression analysis revealed that %predicted of R5, %∆R5, %predicted of FEV1 and %∆FEV1 were the predictive factors for predicting the future loss of asthma control. The following cutoff values demonstrated the best sensitivity and specificity for predicting loss of asthma control: %predicted of R5=91.28, %∆R5=21.2, %predicted of FEV1=89.5, and %∆FEV1=7.8. The combination of these parameters predicted the risk of loss of asthma control with area under the curve of 0.924, accuracy of 83.8%.ConclusionResistance FOT measures have an additive role to spirometric parameter in predicting future loss of asthma control.

Forced Oscillation Technique and Small Airway Involvement in Chronic Hypersensitivity Pneumonitis

ObjectiveHypersensitivity 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 5Hz 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. MethodsPFTs 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. ResultsTwenty-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. ConclusionsThe 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.

Time-based pulmonary features from electrical impedance tomography demonstrate ventilation heterogeneity in chronic obstructive pulmonary disease.

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.

Respiratory Resistance And Reactance (FOT) Classifications In Chronic Obstructive Pulmonary Disease And Healthy Control Patients.

Forced oscillation technique (FOT) is a method of measuring lung obstruction of central airways (resistance, Rrs) and elastic properties/distal airway ventilation (reactance, Xrs), which is different from spirometry since it is performed during tidal breathing, utilizing various sound frequencies (5, 11, and 19 Hz) to separate out regions of the lungs and isolates breathing cycles (inspiration and expiration). PURPOSE: To evaluate FOT metrics of lung mechanics and obstruction within a chronic obstructive pulmonary disease (COPD) population based upon severity (mild [MLD], moderate [MOD], and severe [SEV]). METHODS: Seventeen COPD, and fourteen healthy (H) patients (age: 69.5±5.8 vs. 49.3±17.6 yr.*; height: 169.9±11.3 vs.163.7±18.1cm; weight: 77.8±18.8 vs. 83.3±32.4 kg, COPD vs. H respectively, *p<0.05) completed spirometry and FOT measurements. COPD participants completed the St. George Respiratory Questionnaire (SGRQ) and severity was classified based on GOLD spirometry (MLD, MOD, and SEV) RESULTS: In those with MOD&SEV COPD, total Rrs and Xrs at all frequencies, except expiratory R11, were significantly different (p<0.05) from H, but only R19 was different for MLD participants. R5: 3.9±1.1 v 3.1±1.3, 5.9±2.5*cmH2O/L/s; X5: -1.1±0.9, -1.4±0.6, -4.8±3.2*cmH2O/L/s; R19: 0.3±0.07, 2.4±0.9*, 3.3±1.0*cmH2O/L/s; X19: 0.4±0.03, -0.2±0.7, -1.1±1.0*cmH2O/L/s, for H, MLD, and MOD&SEV groups respectively, *p<0.05 vs. H. No significant difference (p>0.05) between COPD severities were shown for Rrs or Xrs at 5, 11, or 19Hz. SGRQ scores were not different based on spirometric severity (M: 44.6±18.6; MOD: 42.9±15.2; S: 43.8±11.8). CONCLUSION: FOT metrics made distinctions between COPD MOD&SEV and H, as well as MLD and H for mixed respiratory tract obstruction. However, no distinctions between COPD severities could be made. Obstruction increased with severity highlighting that more heterogeneous total airway obstruction (frequency dependent) is observed with mild severity patients, followed by more homogeneous obstruction as severity increased. Elastic properties and efficiency of ventilation decreased (became more negative) with increased COPD severity as airflow to and from distal airways become more limited due to hyperinflation from loss of alveolar support and elastic recoil.