Variability of within-breath reactance in COPD patients and its association with dyspnoea

Intra-breath respiratory mechanics of prematurity-associated lung disease phenotypes in school-aged children

Background

Intra-breath oscillometry potentially offers detailed information regarding airway function, with increasing magnitude of difference between resistance and reactance at end-expiration to end-inspiration potentially associated with obstructive airway disease, but less is known about specific respiratory mechanics in preterm-born children using this methodology. We investigated whether different spirometry phenotypes of prematurity-associated lung disease (PLD) have specific intra-breath oscillometry features.

Methods

167 school-aged (7-12 years) children, 14 with prematurity-associated obstructive lung disease (POLD; forced expiratory volume in 1 s (FEV1)

Results

Children with POLD showed greater resistance and more negative reactance throughout the respiratory cycle, including at zero-flow states of end-expiration and end-inspiration. The difference between end-expiration and end-inspiration did not show differences between groups until corrected for tidal volume, whereby children with POLD and pPRISm both demonstrated approximately two-fold greater difference compared to both preterm and term controls for resistance (2.24 and 2.22 versus 1.28 and 1.11 hPa·s·L-1, respectively), and in particular a greater magnitude of difference for reactance for children with POLD versus preterm and term controls only (-1.58 versus -0.26 and 0.03 hPa·s·L-1, respectively).

Conclusions

Intra-breath respiratory mechanics for preterm-born children with an obstructive lung phenotype have greater impedance throughout the respiratory cycle, features different to those observed in children with other wheeze phenotypes including preschool wheeze and asthma.

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Grants

• Medical Research Council

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Affiliation(s)

Michael Cousins Department of Child Health, Cardiff University School of Medicine, Cardiff, UK Department of Paediatrics, Cardiff and Vale University Health Board, Cardiff, UK
Kylie Hart Department of Child Health, Cardiff University School of Medicine, Cardiff, UK Department of Paediatrics, Cardiff and Vale University Health Board, Cardiff, UK
Bence Radics Department of Pathology, University of Szeged, Szeged, Hungary
A. John Henderson MRC Integrative Epidemiology Unit, Population Health Sciences, Bristol Medical School, University of Bristol, Bristol, UK
Zoltán Hantos Department of Anesthesiology and Intensive Therapy, Semmelweis University, Budapest, Hungary
Peter D. Sly Child Health Research Centre, The University of Queensland, South Brisbane, Australia
Sailesh Kotecha Department of Child Health, Cardiff University School of Medicine, Cardiff, UK

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Expiratory flow limitation development index (ELDI): a novel method of assessing respiratory mechanics in COPD

BACKGROUND

Expiratory flow limitation (EFL) can be detected using oscillometric reactance and is associated with a worse clinical presentation in chronic obstructive pulmonary disease (COPD). Reactance can show negative swings upon exhalation, which may develop at different rates between patients. We propose a new method to quantify the rate of EFL development; the EFL Development Index (ELDI).

METHODS

A retrospective analysis of data from 124 COPD patients was performed. Data included lung function tests, Impulse Oscillometry (IOS), St Georges Respiratory Questionnaire (SGRQ), modified Medical Research Council (mMRC) scale and COPD Assessment Test (CAT) score. Fifty four patients had repeat data after 6 months. Twenty two patients had data recorded after 5 days of treatment with long acting bronchodilator therapy. EDLI was calculated as the mean expiratory reactance divided by the minimum expiratory reactance.

RESULTS

The mean ELDI was used to categorise patients with rapid onset of EFL (> 0.63; n = 29) or gradual onset (≤ 0.63; n = 34). Those with rapid development had worse airflow obstruction, lower quality of life scores, and greater resting hyperinflation, compared to those with gradual development. In patients with EFL, ELDI correlated with symptoms scores, airflow obstruction, lung volumes and gas diffusion. Both EFL and ELDI were stable over 6 months. EFL and EDLI improved with bronchodilator treatment.

CONCLUSIONS

COPD patients with rapid EFL development (determined by ELDI) had worse clinical characteristics than those with gradual EFL development. The rate of EFL development appears to be associated with clinical and physiological characteristics.

Reference Equations for Within-Breath Respiratory Oscillometry in White Adults

BACKGROUND

Within-breath analysis of oscillometry parameters is a growing research area since it increases sensitivity and specificity to respiratory pathologies and conditions. However, reference equations for these parameters in White adults are lacking and devices using multiple sinusoids or pseudorandom forcing stimuli have been underrepresented in previous studies deriving reference equations. The current study aimed to establish reference ranges for oscillometry parameters, including also the within-breath ones in White adults using multi-sinusoidal oscillations.

METHODS

White adults with normal spirometry, BMI ≤30 kg/m2, without a smoking history, respiratory symptoms, pulmonary or cardiac disease, neurological or neuromuscular disorders, and respiratory tract infections in the previous 4 weeks were eligible for the study. Study subjects underwent oscillometry (multifrequency waveform at 5-11-19 Hz, Resmon PRO FULL, RESTECH Srl, Italy) in 5 centers in Europe and the USA according to international standards. The within-breath and total resistance (R) and reactance (X), the resonance frequency, the area under the X curve, the frequency dependence of R (R5-19), and within-breath changes of X (ΔX) were submitted to lambda-mu-sigma models for deriving reference equations. For each output parameter, an AIC-based stepwise input variable selection procedure was applied.

RESULTS

A total of 144 subjects (age 20.8-86.3 years; height 146-193 cm; BMI 17.42-29.98 kg/m2; 56% females) were included. We derived reference equations for 29 oscillatory parameters. Predicted values for inspiratory and expiratory parameters were similar, while differences were observed for their limits of normality.

CONCLUSIONS

We derived reference equations with narrow confidence intervals for within-breath and whole-breath oscillatory parameters for White adults.

Residual reversibility in COPD patients already on long-acting bronchodilator: The OscilloRevers Study

BACKGROUND

Dyspnea is a complex symptom of chronic obstructive pulmonary disease (COPD) which is not strongly correlated with lung function measures. Long-acting bronchodilators (LAB) may reduce this dyspnea, but some patients report persistent chronic dyspnea despite this treatment. This study aims to assess residual reversibility and clinical response after short-acting bronchodilator (SAB) in COPD patients already treated by LAB and reporting persistent dyspnea.

METHODS

COPD patients with a persistent dyspnea (modified Medical Research Council scale (mMRC) ≥1) despite current stable treatment with at least one LAB were included. Spirometry, plethysmography and impulse oscillometry (IOS) were performed at peak effect of their LAB and repeat 45 min after the intake of two SAB (400 µg of salbutamol and 80 µg of ipratropium). Dyspnea improvement was assessed at 45 min after SAB through a comparative two-sided VAS (-100 mm for maximal improvement; +100 mm for maximal degradation).

RESULTS

Twenty-two COPD patients were analyzed, mainly men (59.1 %) with a mean age of 60.6 years and a median FEV1 of 54 % of predicted values. Fifty percent of patients reported a severe basal dyspnea (mMRC ≥2). After SAB, spirometric and plethysmographic measurements were statistically improved. For IOS measurement, reactance at 5 Hz (X5) and area of reactance (AX) were also improved. Fifty percent of patients reported a clinically relevant improvement of their resting dyspnea. However, no correlation was found between dyspnea improvement and functional measures.

CONCLUSIONS

Fifty percent of COPD patients regularly treated with one or two LAB still report a relevant improvement of resting dyspnea after the adjunctive intake of double short-acting bronchodilators. Physiological mechanisms associated with this improvement remain to be determined.

CLINICAL TRIAL REGISTRATION

NCT02928744.

Oscillometry-Defined Small Airway Dysfunction in Patients with Chronic Obstructive Pulmonary Disease

BACKGROUND

The prevalence of small airway dysfunction (SAD) in patients with chronic obstructive pulmonary disease (COPD) across different ethnicities is poorly understood. This study aimed to estimate the prevalence of SAD in stable COPD patients.

METHODS

We conducted a cross-sectional study of 196 consecutive stable COPD patients. We measured pre- and post-bronchodilator (BD) lung function and respiratory impedance. The severity of COPD and lung function abnormalities was graded in accordance with the Global Initiative for Chronic Obstructive Lung Disease (GOLD) guidelines. SAD was defined as either difference in whole-breath resistance at 5 and 19 Hz > upper limit of normal or respiratory system reactance at 5 Hz < lower limit of normal.

RESULTS

The cohort consisted of 95.9% men, with an average age of 66.3 years. The mean forced expiratory volume 1 second (FEV1) % predicted was 56.4%. The median COPD assessment test (CAT) scores were 14. The prevalence of post-BD SAD across the GOLD grades 1 to 4 was 14.3%, 51.1%, 91%, and 100%, respectively. The post-BD SAD and expiratory flow limitation at tidal breath (EFLT) were present in 62.8% (95% confidence interval [CI], 56.1 to 69.9) and 28.1% (95% CI, 21.9 to 34.2), respectively. COPD patients with SAD had higher CAT scores (15.5 vs. 12.8, p<0.01); poor lung function (FEV1% predicted 46.6% vs. 72.8%, p<0.01); lower diffusion capacity for CO (4.8 mmol/min/kPa vs. 5.6 mmol/min/kPa, p<0.01); hyperinflation (ratio of residual volume to total lung capacity % predicted: 159.7% vs. 129%, p<0.01), and shorter 6-minute walk distance (367.5 m vs. 390 m, p=0.02).

CONCLUSION

SAD is present across all severities of COPD. The prevalence of SAD increases with disease severity. SAD is associated with poor lung function and higher symptom burden. Severe SAD is indicated by the presence of EFLT.

Diagnostic Potential of Oscillometry: A Population-based Approach

Rationale: Respiratory resistance (Rrs) and reactance (Xrs) as measured by oscillometry and their intrabreath changes have emerged as sensitive parameters for detecting early pathological impairments during tidal breathing. Objectives: This study evaluates the prevalence and association of abnormal oscillometry parameters with respiratory symptoms and respiratory diseases in a general adult population. Methods: A total of 7,560 subjects in the Austrian LEAD (Lung, hEart, sociAl, boDy) Study with oscillometry measurements (computed with the Resmon Pro FULL; Restech Srl) were included in this study. The presence of respiratory symptoms and doctor-diagnosed respiratory diseases was assessed using an interview-based questionnaire. Rrs and Xrs at 5 Hz, their inspiratory and expiratory components, the area above the Xrs curve, and the presence of tidal expiratory flow limitation were analyzed. Normality ranges for oscillometry parameters were defined. Measurements and Main Results: The overall prevalence of abnormal oscillometry parameters was 20%. The incidence of abnormal oscillometry increased in the presence of symptoms or diagnoses: 17% (16-18%) versus 27% (25-29%), P < 0.0001. All abnormal oscillometry parameters except Rrs at 5 Hz were significantly associated with respiratory symptoms/diseases. Significant associations were found, even in subjects with normal spirometry, with abnormal oscillometry incidence rates increasing by 6% (4-8%; P < 0.0001) in subjects with symptoms or diagnoses. Conclusions: Abnormal oscillometry parameters are present in one-fifth of this adult population and are significantly associated with respiratory symptoms and disease. Our findings underscore the potential of oscillometry as a tool for detecting and evaluating respiratory impairments, even in individuals with normal spirometry.

Intra-subject variability in oscillometry correlates with acute rejection and CLAD post-lung transplant

Background

Chronic lung allograft dysfunction (CLAD) is the major cause of death post-lung transplantation, with acute cellular rejection (ACR) being the biggest contributing risk factor. Although patients are routinely monitored with spirometry, FEV₁ is stable or improving in most ACR episodes. In contrast, oscillometry is highly sensitive to respiratory mechanics and shown to track graft injury associated with ACR and its improvement following treatment. We hypothesize that intra-subject variability in oscillometry measurements correlates with ACR and risk of CLAD.

Methods

Of 289 bilateral lung recipients enrolled for oscillometry prior to laboratory-based spirometry between December 2017 and March 2020, 230 had ≥ 3 months and 175 had ≥ 6 months of follow-up. While 37 patients developed CLAD, only 29 had oscillometry at time of CLAD onset and were included for analysis. These 29 CLAD patients were time-matched with 129 CLAD-free recipients. We performed multivariable regression to investigate the associations between variance in spirometry/oscillometry and the A-score, a cumulative index of ACR, as our predictor of primary interest. Conditional logistic regression models were built to investigate associations with CLAD.

Results

Multivariable regression showed that the A-score was positively associated with the variance in oscillometry measurements. Conditional logistic regression models revealed that higher variance in the oscillometry metrics of ventilatory inhomogeneity, X5, AX, and R5-19, was independently associated with increased risk of CLAD (p < 0.05); no association was found for variance in %predicted FEV₁.

Conclusion

Oscillometry tracks graft injury and recovery post-transplant. Monitoring with oscillometry could facilitate earlier identification of graft injury, prompting investigation to identify treatable causes and decrease the risk of CLAD.

Increased airway resistance can be related to the decrease in the functional capacity in obese women

Background and objective

Obesity can increase the airways resistance, mainly in the periphery, leading to dyspnea perception that can impair the functional capacity. This study aimed to analyze if airways resistance could be related to the walking capacity of women with morbid obesity.

Methods

Thirty-seven women with grade III obesity in preoperative bariatric surgery were evaluated using the spirometry test, impulse oscillometry system (IOS), and six-minute walk test (6MWT). Additionally, data about their daily dyspnea perception and physical activity level were collected.

Results

Variables of the spirometry test did not detect ventilator disorders. Compared to the predicted values, the IOS identified significant increase in airways resistance (kPa/L/s) (R5: 0.36 (0.34; 0.36) and 0.53 (0.47; 0.61); R20: 0.30 (0.28; 0.30) and 0.41 (0.35; 0.45); R5-20: 0.06 (0.06; 0.06) and 0.14 (0.10; 0.15); X5: -0.03 (-0.04; -0.01) and -0.20 (-0.27; -0.18), respectively). The distance walked in the 6MWT, 491.4±60.4m was significantly correlated to R5 (rho = -0.41, p = 0.01), R5-20 (rho = -0.52, p = 0.001), and X5 (rho = 0.54, p = 0.0006).

Conclusion

The IOS is able to identify changes in airway resistance even before the onset of symptoms. When evaluated by IOS women with severe obesity and normal spirometry exhibited central and peripheral airways obstruction. The correlations between the IOS and six-minute walk distance suggest that increased peripheral airways resistance could be related to worsening functional capacity.

Clinical significance and applications of oscillometry

Recently, “Technical standards for respiratory oscillometry” was published, which reviewed the physiological basis of oscillometric measures and detailed the technical factors related to equipment and test performance, quality assurance and reporting of results. Here we present a review of the clinical significance and applications of oscillometry. We briefly review the physiological principles of oscillometry and the basics of oscillometry interpretation, and then describe what is currently known about oscillometry in its role as a sensitive measure of airway resistance, bronchodilator responsiveness and bronchial challenge testing, and response to medical therapy, particularly in asthma and COPD. The technique may have unique advantages in situations where spirometry and other lung function tests are not suitable, such as in infants, neuromuscular disease, sleep apnoea and critical care. Other potential applications include detection of bronchiolitis obliterans, vocal cord dysfunction and the effects of environmental exposures. However, despite great promise as a useful clinical tool, we identify a number of areas in which more evidence of clinical utility is needed before oscillometry becomes routinely used for diagnosing or monitoring respiratory disease.

This paper provides a current review of the interpretation, clinical significance and application of oscillometry in respiratory medicine, with special emphasis on limitations of evidence and suggestions for future research.https://bit.ly/3GQPViA

Expiratory flow limitation in a cohort of highly symptomatic COPD patients

The question addressed by the study

Small airway collapse during expiration, known as expiratory flow limitation (EFL), can be detected using oscillometry and is associated with worse clinical outcomes in COPD. This study investigated the prevalence of EFL in a cohort of highly symptomatic patients, evaluated clinical and lung function characteristics of patients with EFL and studied the repeatability of EFL over 6 months.

Materials/patients and methods

70 patients were recruited. Clinical characteristics and lung function metrics were collected at baseline and 6 months. Impulse oscillometry was used to detect the presence of EFL. Patients were defined as EFL^High (change in reactance measured at 5 Hz (ΔX₅) ≥0.28 kPa·L⁻¹·s⁻¹); EFL^Intermediate (ΔX₅ 0.1–0.27 kPa·L⁻¹·s⁻¹) and EFL^None (ΔX₅ <0.1 kPa·L⁻¹·s⁻¹).

Results

EFL^High was present in 47.8% of patients at baseline. ΔX₅ showed excellent repeatability over 6 months (ρ=0.78, p<0.0001, intraclass correlation coefficient (ICC) 0.88), with the best repeatability observed in EFL^None and EFL^High patients (ICC 0.77 and 0.65, respectively). Compared to EFL^None patients, EFL^High had a higher body mass index, worse health-related quality of life and increased peripheral airway resistance. EFL^Intermediate was more variable over time with less severe physiological impairment.

Answer to the question

Overall, these data indicate that EFL^High is a common, and relatively stable, component of disease pathophysiology in highly symptomatic COPD patients. EFL^High was also associated with worse quality of life and obesity.

EFL, defined by oscillometry, is a common and relatively stable component of disease pathophysiology in highly symptomatic COPD patients. EFL is associated with worse airflow obstruction, small airway resistance, worse quality of life and obesity.https://bit.ly/3AMRjjL

Overnight variation in tidal expiratory flow limitation in COPD patients and its correction: an observational study

Background

Tidal expiratory flow limitation (EFL_T) is common among COPD patients. Whether EFL_T changes during sleep and can be abolished during home ventilation is not known.

Methods

COPD patients considered for noninvasive ventilation used a ventilator which measured within-breath reactance change at 5 Hz (∆Xrs) and adjusted EPAP settings to abolish EFL_T. Participants flow limited (∆Xrs > 2.8) when supine underwent polysomnography (PSG) and were offered home ventilation for 2 weeks. The EPAP pressure that abolished EFL_T was measured and compared to that during supine wakefulness. Ventilator adherence and subjective patient perceptions were obtained after home use.

Results

Of 26 patients with supine EFL_T, 15 completed overnight PSG and 10 the home study. In single night and 2-week home studies, EFL_T within and between participants was highly variable. This was unrelated to sleep stage or body position with only 14.6% of sleep time spent within 1 cmH₂O of the awake screening pressure. Over 2 weeks, mean EPAP was almost half the mean maximum EPAP (11.7 vs 6.4 cmH₂O respectively). Group mean ∆Xrs was ≤ 2.8 for 77.3% of their home use with a mean time to abolish new EFL_T of 5.91 min. Adherence to the ventilator varied between 71 and 100% in prior NIV users and 36–100% for naïve users with most users rating therapy as comfortable.

Conclusions

Tidal expiratory flow limitation varies significant during sleep in COPD patients. This can be controlled by auto-titrating the amount of EPAP delivered. This approach appears to be practical and well tolerated by patients.

Trial registration: The trial was retrospectively registered at CT.gov NCT04725500.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12931-021-01913-7.

The TRIFLOW study: a randomised, cross-over study evaluating the effects of extrafine beclometasone/formoterol/glycopyrronium on gas trapping in COPD

Background

The effects of triple therapy on gas trapping in COPD are not fully understood. We evaluated the effects of the long acting bronchodilator components of the extrafine single inhaler triple therapy beclometasone dipropionate/formoterol/glycopyrronium (BDP/F/G) pMDI on gas trapping.

Methods

This open-label, randomised, single centre, 2-way cross-over study recruited 23 COPD patients taking inhaled corticosteroid combination treatments and with residual volume (RV) > 120% predicted at screening. Inhaled BDP was taken during run-in and washout periods. Baseline lung function (spirometry, lung volumes, oscillometry) was measured over 12 h prior to randomisation to BDP/F/G or BDP/F for 5 days followed by washout and crossover. Lung function was measured prior to dosing on day 1 and for 12 h post-dose on day 5.

Results

Co-primary endpoint analysis: BDP/F/G had a greater effect than BDP/F on FEV₁ area under the curve over 12 h (AUC_0–12) (mean difference 104 mls, p = 0.0071) and RV AUC_0–12 (mean difference − 163 mls, p = 0.0028). Oscillometry measurements showed a greater effect of BDP/F/G on the difference between resistance at 5 and 20 Hz (R5–R20) AUC_0–12, which measures small airway resistance (mean difference − 0.045 kPa/L/s, p = 0.0002). Comparison of BDP/F with the baseline measurements (BDP alone) showed that F increased FEV₁ AUC_0–12 (mean difference 227 mls) and improved RV AUC_0–12 (mean difference − 558 mls) and R5–R20 AUC_0–12 (mean difference − 0.117 kPa/L/s), all p < 0.0001.

Conclusions

In COPD patients with hyperinflation, the G and F components of extrafine BDP/F/G improved FEV₁, RV and small airway function. These long acting bronchodilators target small airway function, thereby improving gas trapping and airflow.

Trial registration The study was retrospectively registered at ClinicalTrials.gov on 15th February 2019 (No.: NCT03842904, https://clinicaltrials.gov/ct2/show/NCT03842904).

Diagnostic Ability of Impulse Oscillometry in Diagnosis of Chronic Obstructive Pulmonary Disease

The diagnosis of chronic obstructive pulmonary disease (COPD) mainly relies on spirometry. Due to the complexity of spirometry, easier-to-do impulse oscillometry (IOS) has been introduced as a complementary approach to conventional pulmonary function testing. Therefore, this study aimed to assess the efficacy of the diagnostic ability of IOS for diagnosing chronic obstructive pulmonary disease (COPD). This cross-sectional study was conducted at the Lung Health Center, Chiang Mai University, Thailand, between June 2019 and January 2020. IOS and spirometry were performed with all subjects suspected of having COPD. A Receiver Operating Characteristic (ROC) curve was plotted, the area under the ROC (AuROC) and 95%CI were compared among COPD and chronic smokers. One hundred and seventeen subjects suspected of having COPD with a mean age of 68.6 ± 8.6 years old were enrolled. Of these 103 (88.0%) were male. Thirty healthy subjects were also enrolled. IOS parameters including resistance at 5 Hz (R5), resonant frequency (Fres), area under reactance (AX), heterogeneity of resistance (R5-R20), and reactance at 5 Hz (X5) demonstrated excellent overall accuracy relative to the diagnosis of COPD with an AuROC ranging from 0.80 - 0.84. The AX ≥ 8.66 cmH₂O/L represented an AuROC = 0.79, with a sensitivity of 79.1% and a specificity of 78.0% for the diagnosis of COPD. IOS is a valuable tool for use in the diagnosis of COPD. It may be used in subjects who cannot carry out the spirometric procedure.

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

BACKGROUND

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.

METHODS

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.

RESULTS

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 (SDX_insp)) 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). SDX_insp 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).

CONCLUSIONS

SDX_insp from FOT telemonitoring reflects COPD symptoms and may be a sensitive biomarker for early detection of AECOPD.

Airway Oscillometry Detects Spirometric-Silent Episodes of Acute Cellular Rejection

Rationale: Acute cellular rejection (ACR) is common during the initial 3 months after lung transplant. Patients are monitored with spirometry and routine surveillance transbronchial biopsies. However, many centers monitor patients with spirometry only because of the risks and insensitivity of transbronchial biopsy for detecting ACR. Airway oscillometry is a lung function test that detects peripheral airway inhomogeneity with greater sensitivity than spirometry. Little is known about the role of oscillometry in patient monitoring after a transplant.Objectives: To characterize oscillometry measurements in biopsy-proven clinically significant (grade ≥2 ACR) in the first 3 months after a transplant.Methods: We enrolled 156 of the 209 double lung transplant recipients between December 2017 and March 2019. Weekly outpatient oscillometry and spirometry and surveillance biopsies at Weeks 6 and 12 were conducted at our center.Measurements and Main Results: Of the 138 patients followed for 3 or more months, 15 patients had 16 episodes of grade 2 ACR (AR2) and 44 patients had 64 episodes of grade 0 ACR (AR0) rejection associated with stable and/or improving spirometry. In 15/16 episodes of AR2, spirometry was stable or improving in the weeks leading to transbronchial biopsy. However, oscillometry was markedly abnormal and significantly different from AR0 (P < 0.05), particularly in integrated area of reactance and the resistance between 5 and 19 Hz, the indices of peripheral airway obstruction. By 2 weeks after biopsy, after treatment for AR2, oscillometry in the AR2 group improved and was similar to the AR0 group.Conclusions: Oscillometry identified physiological changes associated with AR2 that were not discernible by spirometry and is useful for graft monitoring after a lung transplant.

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

Rationale

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

Methods

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

Results

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

Conclusion

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

Telemonitoring in Chronic Obstructive Pulmonary Disease (CHROMED). A Randomized Clinical Trial

RATIONALE

Early detection of chronic obstructive pulmonary disease (COPD) exacerbations using telemonitoring of physiological variables might reduce the frequency of hospitalization.

OBJECTIVES

To evaluate the efficacy of home monitoring of lung mechanics by the forced oscillation technique and cardiac parameters in older patients with COPD and comorbidities.

METHODS

This multicenter, randomized clinical trial recruited 312 patients with Global Initiative for Chronic Obstructive Lung Disease grades II to IV COPD (median age, 71 yr [interquartile range, 66-76 yr]; 49.6% grade II, 50.4% grades III-IV), with a history of exacerbation in the previous year and at least one nonpulmonary comorbidity. Patients were randomized to usual care (n = 158) or telemonitoring (n = 154) and followed for 9 months. All telemonitoring patients self-assessed lung mechanics daily, and in a subgroup with congestive heart failure (n = 37) cardiac parameters were also monitored. An algorithm identified deterioration, triggering a telephone contact to determine appropriate interventions.

MEASUREMENTS AND MAIN RESULTS

Primary outcomes were time to first hospitalization (TTFH) and change in the EuroQoL EQ-5D utility index score. Secondary outcomes included: rate of antibiotic/corticosteroid prescription; hospitalization; the COPD Assessment Tool, Patient Health Questionnaire-9, and Minnesota Living with Heart Failure questionnaire scores; quality-adjusted life years; and healthcare costs. Telemonitoring did not affect TTFH, EQ-5D utility index score, antibiotic prescriptions, hospitalization rate, or questionnaire scores. In an exploratory analysis, telemedicine was associated with fewer repeat hospitalizations (-54%; P = 0.017).

CONCLUSIONS

In older patients with COPD and comorbidities, remote monitoring of lung function by forced oscillation technique and cardiac parameters did not change TTFH and EQ-5D. Clinical trial registered with www.clinicaltrials.gov (NCT 01960907).

Within-breath changes in respiratory system impedance in children with cystic fibrosis

BACKGROUND

The aim of this study was to assess within-breath respiratory system impedance by the forced oscillation technique (FOT) in children with cystic fibrosis (CF) and relate it to the underlying lung disease.

METHODS

Thirty-three children with CF (median [range] age 12.0 [6-17] years) underwent FOT at 8 Hz during tidal breathing, multiple breath nitrogen washout (LCI), spirometry (FEV1), body plethysmography (RV/TLC), and magnetic resonance imaging (MRI). FOT outcomes included: mean inspiratory, expiratory, and whole breath resistance (R8_INSP , R8_EXP , R8_TOT ) and reactance (X8_INSP , X8_EXP , X8_TOT ), and the differences between X8_INSP and X8_EXP (ΔX8). Morphological changes were evaluated by MRI using CF-specific morphological scores. Spearman correlation was performed to examine the correlation between FOT indices and other parameters.

RESULTS

FEV1 was negatively correlated with R8_EXP (r = -0.52, P = 0.002) and ΔX8 (r = -0.55, P = 0.001), and positively correlated with and X8_EXP (r = 0.56, P < 0.001). RV/TLC was positively correlated with R8_EXP (r = 0.43, P = 0.013), and ΔX8 (r = 0.54, P = 0.001) and negatively correlated with X8_EXP (r = -0.54, P = 0.001). We found poor correlation between FOT parameters and LCI and no correlation between FOT parameters and MRI scores.

CONCLUSION

In children with CF, changes in within-breath FOT parameters are consistent with peripheral obstruction and dynamic airway compression, while they are not associated with ventilation heterogeneities and morphological alterations.

Assessment of within-breath impulse oscillometry parameters in children with asthma

BACKGROUND

Impulse oscillometry (IOS) measures respiratory resistance and reactance during tidal breaths and is a convenient tool for evaluation of lung function. Respiratory resistance and reactance can be measured separately during inspiration and expiration (inspiratory-expiratory analysis).

OBJECTIVE

We investigated the differences in inspiratory-expiratory measurements obtained using IOS between children with and without asthma.

METHODS

We analyzed 819 subjects aged 4-18 years, including asthmatic children (n = 600) and controls (n = 219). Asthma was diagnosed in accordance with the American Thoracic Society/European Respiratory Society guideline. Spirometry and IOS were performed in all subjects.

RESULTS

In whole-breath analysis, the asthma group had higher resistance at 5 Hz (R5) and reactance area (AX) and lower reactance at 5 Hz (X5) than the control groups. In inspiratory-expiratory analysis, the asthma group showed increased expiratory R5 and AX and decreased expiratory X5 when compared with the control group. The absolute changes in R5, X5, and AX values between inspiration and expiration were greater in children with asthma than those in controls (0.138 ± 0.195 vs 0.102 ± 0.162, P = 0.014; -0.106 ± 0.200 vs -0.086 ± 0.434, P < 0.001 and 0.460 ± 11.63 vs 0.398 ± 2.88, P = 0.002, respectively).

CONCLUSIONS

Inspiratory-expiratory IOS analysis differentiated asthmatic children from control subjects, reflecting airway narrowing on expiration in pediatric asthma. The changes in R5, X5, and AX between inspiration and expiration can be a useful index for diagnosis of asthma in children without assessment of the response to a bronchodilator.

The immediate effects of a single autogenic drainage session on ventilatory mechanics in adult subjects with cystic fibrosis

INTRODUCTION

The aim of this study was to gain insight into the physiological changes occurring in subjects with cystic fibrosis (CF) after autogenic drainage (AD). Changes in respiratory system resistance (Rrs), reactance (Xrs), and spirometry were analyzed in adult CF subjects after a single AD physiotherapy session.

METHODS

This prospective observational study was conducted during the annual check-up of adult CF subjects in stable condition. Spirometry and Rrs and Xrs measurements using the forced oscillations technique at 5, 11, and 19 hertz (Hz) were performed before and 30 min after a 20-min AD session. Control CF subjects were tested at baseline and 50 min without AD. Results are expressed as mean ± standard deviation or median [interquartile range].

RESULTS

Thirty subjects were included in the physiotherapy group (age 29 [25-34] years, forced expiratory volume in 1 s (FEV1) 40.3 [30.1-57.9]% predicted) and 11 in the control group (age 31 [28.5-36.5] years, FEV1 43.6 [31.1-51.9] % predicted). No significant changes in any parameter were observed in the control group. AD modestly but significantly increased the forced vital capacity (FVC) and FEV1 (p<0.001). Inspiratory resistance was also significantly improved by AD: Rrs5 from 5.74±2.39 to 5.24±2.17 cmH2O/L/s, p<0.05; Rrs11 from 4.83±1.98 to 4.32±1.7 cmH2O/L/s, p = 0.003; and Rrs19 from 4.18 [3.46-5.07] to 3.86 [2.76-4.98] cmH2O/L/s, p<0.001. In contrast, AD had no significant effects on frequency dependence of resistance (Rrs5-Rrs19) or expiratory resistance. Inspiratory Xrs5, but not ΔXrs5 (expiratory-inspiratory Xrs), was improved by AD (p<0.05). Moderate correlations were detected between the improvement in FEV1 and FVC and inspiratory resistance (r = 0.53, p = 0.005 and r = 0.44, p = 0.02, respectively).

CONCLUSION

A single session of AD improved inspiratory airway resistance, except in the distal airways. The forced oscillations technique provides a new tool for understanding the pathophysiological effects of airway clearance physiotherapy in CF.

Median regression spline modeling of longitudinal FEV1 measurements in cystic fibrosis (CF) and chronic obstructive pulmonary disease (COPD) patients

Rationale

Clinical phenotyping, therapeutic investigations as well as genomic, airway secretion metabolomic and metagenomic investigations can benefit from robust, nonlinear modeling of FEV₁ in individual subjects. We demonstrate the utility of measuring FEV₁ dynamics in representative cystic fibrosis (CF) and chronic obstructive pulmonary disease (COPD) populations.

Methods

Individual FEV₁ data from CF and COPD subjects were modeled by estimating median regression splines and their predicted first and second derivatives. Classes were created from variables that capture the dynamics of these curves in both cohorts.

Results

Nine FEV₁ dynamic variables were identified from the splines and their predicted derivatives in individuals with CF (n = 177) and COPD (n = 374). Three FEV₁ dynamic classes (i.e. stable, intermediate and hypervariable) were generated and described using these variables from both cohorts. In the CF cohort, the FEV₁ hypervariable class (HV) was associated with a clinically unstable, female-dominated phenotypes while stable FEV₁ class (S) individuals were highly associated with the male-dominated milder clinical phenotype. In the COPD cohort, associations were found between the FEV₁ dynamic classes, the COPD GOLD grades, with exacerbation frequency and symptoms.

Conclusion

Nonlinear modeling of FEV₁ with splines provides new insights and is useful in characterizing CF and COPD clinical phenotypes.

Small Airway Disease in Patients with Chronic Obstructive Pulmonary Disease

Small airway disease (SAD) has been recognized for many years as a central feature of chronic obstructive pulmonary disease (COPD). Histopathology studies have shown that the narrowing and destruction of small airways in COPD combined with inflammatory cell infiltration in the submucosa increases the severity of the disease. SAD is present in the early stages of COPD and becomes more widespread over time as the disease progresses to more severe COPD. The development of inhalers containing extra-fine particles allows the small airways to be pharmacologically targeted. Recent clinical trials have shown the efficacy of extra-fine triple therapy that targets the small airways in patients with COPD. This article reviews the importance and treatment of SAD in COPD.

The association of tidal EFL with exercise performance, exacerbations, and death in COPD

BACKGROUND

Tidal expiratory flow limitation (EFL_T) is frequently found in patients with COPD and can be detected by forced oscillations when within-breath reactance of a single-breath is ≥0.28 kPa·s·L^-1. The present study explored the association of within-breath reactance measured over multiple breaths and EFL_T with 6-minute walk distance (6MWD), exacerbations, and mortality.

METHODS

In 425 patients, spirometry and forced oscillation technique measurements were obtained on eight occasions over 3 years. 6MWD was assessed at baseline and at the 3-year visit. Respiratory symptoms, exacerbations, and hospitalizations were recorded. A total of 5-year mortality statistics were retrieved retrospectively. We grouped patients according to the mean within-breath reactance [Formula: see text], measured over several breaths at baseline, calculated as mean inspiratory-mean expiratory reactance over the sampling period. In addition to the established threshold of EFL_T, an upper limit of normal (ULN) was defined using the 97.5th percentile of [Formula: see text], of the healthy controls in the study; 6MWDs were compared according to [Formula: see text], as normal, ≥ ULN < EFL_T, or ≥ EFL_T. Annual exacerbation rates were analyzed using a negative binomial model in the three groups, supplemented by time to first exacerbation analysis, and dichotomizing patients at the ULN.

RESULTS

In patients with COPD and baseline [Formula: see text] below the ULN (0.09 kPa·s·L^-1), 6MWD was stable. 6MWD declined significantly in patients with [Formula: see text]. Worse lung function and more exacerbations were found in patients with COPD with [Formula: see text], and patients with [Formula: see text] had shorter time to first exacerbation and hospitalization. A significantly higher mortality was found in patients with [Formula: see text] and FEV₁ >50%.

CONCLUSION

Patients with baseline [Formula: see text] had a deterioration in exercise performance, more exacerbations, and greater hospitalizations, and, among those with moderate airway obstruction, a higher mortality. [Formula: see text] is a novel independent marker of outcome in COPD.

Systems Biology and Clinical Practice in Respiratory Medicine. The Twain Shall Meet

Respiratory diseases are highly complex, being driven by host-environment interactions and manifested by inflammatory, structural, and functional abnormalities that vary over time. Traditional reductionist approaches have contributed vastly to our knowledge of biological systems in health and disease to date; however, they are insufficient to provide an understanding of the behavior of the system as a whole. In this Pulmonary Perspective, we discuss systems biology approaches, especially but not limited to the study of the lung as a complex system. Such integrative approaches take into account the large number of dynamic subunits and their interactions found in biological systems. Borrowing methods from physics and mathematics, it is possible to study the collective behavior of these systems over time and in a multidimensional manner. We first examine the physiological basis for complexity in the respiratory system and its implications for disease. We then expand on the potential applications of systems biology methods to study complex systems, within the context of diagnosis and monitoring of respiratory diseases including asthma, chronic obstructive pulmonary disease (COPD), and critical illness. We summarize the significant advances made in recent years using systems approaches for disease phenotyping, applied to data ranging from the molecular to clinical level, obtained from large-scale asthma and COPD networks. We describe new studies using temporal complexity patterns to characterize asthma and COPD and predict exacerbations as well as predict adverse outcomes in critical care. We highlight new methods that are emerging with this approach and discuss remaining questions that merit greater attention in the field.

Clinical characteristics of COPD patients with tidal expiratory flow limitation

We have used impulse oscillometry to identify COPD patients with tidal expiratory flow limitation (EFL), which is a measurement related to small airway disease. We report that 37.4% of COPD patients had EFL; these patients had multiple clinical characteristics of more severe disease including lower forced expiratory volume in 1 second values, greater hyperinflation, reduced exercise performance, and increased small airway impairment. We highlight that EFL can be used to identify a subgroup of COPD patients with distinct characteristics associated with small airway disease.

Airway dynamics in COPD patients by within-breath impedance tracking: effects of continuous positive airway pressure

Tracking of the within-breath changes of respiratory mechanics using the forced oscillation technique may provide outcomes that characterise the dynamic behaviour of the airways during normal breathing.

We measured respiratory resistance (Rrs) and reactance (Xrs) at 8 Hz in 55 chronic obstructive pulmonary disease (COPD) patients and 20 healthy controls, and evaluated Rrs and Xrs as functions of gas flow (V′) and volume (V) during normal breathing cycles. In 12 COPD patients, additional measurements were made at continuous positive airway pressure (CPAP) levels of 4, 8, 14 and 20 hPa.

The Rrs and Xrsversus V′ and V relationships displayed a variety of loop patterns, allowing characterisation of physiological and pathological processes. The main outcomes emerging from the within-breath analysis were the Xrsversus V loop area (AXV) quantifying expiratory flow limitation, and the tidal change in Xrs during inspiration (ΔXI) reflecting alteration in lung inhomogeneity in COPD. With increasing CPAP, AXV and ΔXI approached the normal ranges, although with a large variability between individuals, whereas mean Rrs remained unchanged.

Within-breath tracking of Rrs and Xrs allows an improved assessment of expiratory flow limitation and functional inhomogeneity in COPD; thereby it may help identify the physiological phenotypes of COPD and determine the optimal level of respiratory support.

The Forced Oscillation Technique in Paediatric Respiratory Practice

The Forced Oscillation Technique (FOT) is a lung function modality based on the application of an external oscillatory signal in order to determine the mechanical response of the respiratory system. The method is in principal noninvasive and requires minimal patient cooperation, which makes it suitable for use in young paediatric patients. The FOT has been successfully applied in various paediatric respiratory disorders, such as asthma, cystic fibrosis, and chronic lung disease of prematurity, in order to assess airway obstruction, bronchodilator response, and airway responsiveness after bronchoprovocation challenge. This technique may be more sensitive than spirometry in identifying disturbances of peripheral airways and assessing the level of asthma control or the effectiveness of therapy at the long term. Further research is required to determine the exact role of the FOT in paediatric lung function testing and to incorporate the method in specific diagnostic and management algorithms.

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

Background

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

Subjects and methods

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

Results

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

Conclusion

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