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

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          Abstract

          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) cmH 2O.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.

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          Most cited references 41

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          Pulmonary rehabilitation for chronic obstructive pulmonary disease.

          Widespread application of pulmonary rehabilitation (also known as respiratory rehabilitation) in chronic obstructive pulmonary disease (COPD) should be preceded by demonstrable improvements in function (health-related quality of life, functional and maximal exercise capacity) attributable to the programmes. This review updates the review reported in 2006.
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            Detection of expiratory flow limitation in COPD using the forced oscillation technique.

            Expiratory flow limitation (EFL) during tidal breathing is a major determinant of dynamic hyperinflation and exercise limitation in chronic obstructive pulmonary disease (COPD). Current methods of detecting this are either invasive or unsuited to following changes breath-by-breath. It was hypothesised that tidal flow limitation would substantially reduce the total respiratory system reactance (Xrs) during expiration, and that this reduction could be used to reliably detect if EFL was present. To test this, 5-Hz forced oscillations were applied at the mouth in seven healthy subjects and 15 COPD patients (mean +/- sD forced expiratory volume in one second was 36.8 +/- 11.5% predicted) during quiet breathing. COPD breaths were analysed (n=206) and classified as flow-limited if flow decreased as alveolar pressure increased, indeterminate if flow decreased at constant alveolar pressure, or nonflow-limited. Of these, 85 breaths were flow-limited, 80 were not and 41 were indeterminate. Among other indices, mean inspiratory minus mean expiratory Xrs (deltaXrs) and minimum expiratory Xrs (Xexp,min) identified flow-limited breaths with 100% specificity and sensitivity using a threshold between 2.53-3.12 cmH2O x s x L(-1) (deltaXrs) and -7.38- -6.76 cmH2O x s x L(-1) (Xexp,min) representing 6.0% and 3.9% of the total range of values respectively. No flow-limited breaths were seen in the normal subjects by either method. Within-breath respiratory system reactance provides an accurate, reliable and noninvasive technique to detect expiratory flow limitation in patients with chronic obstructive pulmonary disease.
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              Predictors of success and failure in pulmonary rehabilitation.

              The purpose of the present study was to identify prognostic features of chronic obstructive pulmonary disease (COPD) associated with success or failure in pulmonary rehabilitation. Patients were stratified according to the Medical Research Council (MRC) dyspnoea score. A total of 74 stable COPD patients (mean+/-sd age 68+/-10 yrs), 21 MRC dyspnoea score grade 1/2, 29 grade 3/4 and 24 grade 5, with a mean forced expiratory volume in one second of 1.1+/-0.6 L, attended for rehabilitation. Assessments consisted of the following: quadriceps torque, 6-minute walking distance (6MWD), Brief Assessment Depression Cards and St George's Respiratory Questionnaire (SGRQ). Predictors of drop-out and of response (a change in SGRQ of four points or 6MWD of 54 m) were tested using binary logistic regression. In total, 51 patients completed the study. Of these, 39 (77%) showed a clinically significant benefit in either 6MWD or SGRQ. Baseline variables were poor predictors of response in each case. Significant differences were seen between MRC dyspnoea score groups for change in 6MWD and SGRQ Score. Only grade 1/2 and 3/4 patients improved. Depression was a risk factor for subject drop-out compared with nondepressed patients. Baseline state is a poor predictor of response to rehabilitation, although Medical Research Council dyspnoea score grade 5 patients showed smaller magnitudes of improvement than patients with less severe Medical Research Council dyspnoea score grades. Risk of drop-out is significantly greater in depressed compared with nondepressed patients.
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                Author and article information

                Journal
                Int J Chron Obstruct Pulmon Dis
                Int J Chron Obstruct Pulmon Dis
                COPD
                copd
                International Journal of Chronic Obstructive Pulmonary Disease
                Dove
                1176-9106
                1178-2005
                21 January 2020
                2020
                : 15
                : 157-166
                Affiliations
                [1 ]The Woolcock Emphysema Centre, Woolcock Institute of Medical Research, The University of Sydney , Glebe, NSW 2037, Australia
                [2 ]The Northern Clinical School, Faculty of Medicine and Health Sciences, The University of Sydney , Camperdown, NSW 2006, Australia
                [3 ]Department of Respiratory Medicine, Royal North Shore Hospital , St Leonards, NSW 2065, Australia
                [4 ]School of Life Sciences, Faculty of Science, University of Technology Sydney , Ultimo, NSW 2007, Australia
                Author notes
                Correspondence: Sabine C Zimmermann The Woolcock Institute of Medical Research , 431 Glebe Point Road, Glebe, NSW2037, AustraliaTel +61 2 9114 0404Fax +61 2 9114 0010 Email sabine.zimmermann@sydney.edu.au
                Article
                225543
                10.2147/COPD.S225543
                6982450
                © 2020 Zimmermann et al.

                This work is published and licensed by Dove Medical Press Limited. The full terms of this license are available at https://www.dovepress.com/terms.php and incorporate the Creative Commons Attribution – Non Commercial (unported, v3.0) License ( http://creativecommons.org/licenses/by-nc/3.0/). By accessing the work you hereby accept the Terms. Non-commercial uses of the work are permitted without any further permission from Dove Medical Press Limited, provided the work is properly attributed. For permission for commercial use of this work, please see paragraphs 4.2 and 5 of our Terms ( https://www.dovepress.com/terms.php).

                Page count
                Figures: 4, Tables: 3, References: 51, Pages: 10
                Funding
                SCZ was supported by a NHMRC Postgraduate Scholarship. This research did otherwise not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
                Categories
                Original Research

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