Relationships Between Forced Oscillatory Impedance and 6-minute Walk Distance After Pulmonary Rehabilitation in COPD
Received 31 July 2019
Accepted for publication 19 December 2019
Published 21 January 2020 Volume 2020:15 Pages 157—166
Checked for plagiarism Yes
Review by Single-blind
Peer reviewer comments 2
Editor who approved publication: Dr Richard Russell
Sabine C Zimmermann, 1–3 Cindy Thamrin, 1 Andrew SL Chan, 2, 3 Amy Bertolin, 1 David G Chapman, 1, 4 Gregory G King 1–3
1The Woolcock Emphysema Centre, Woolcock Institute of Medical Research, The University of Sydney, Glebe, NSW 2037, Australia; 2The Northern Clinical School, Faculty of Medicine and Health Sciences, The University of Sydney, Camperdown, NSW 2006, Australia; 3Department of Respiratory Medicine, Royal North Shore Hospital, St Leonards, NSW 2065, Australia; 4School of Life Sciences, Faculty of Science, University of Technology Sydney, Ultimo, NSW 2007, Australia
Correspondence: Sabine C Zimmermann
The Woolcock Institute of Medical Research, 431 Glebe Point Road, Glebe, NSW 2037, Australia
Tel +61 2 9114 0404
Fax +61 2 9114 0010
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 (Rmean, Xmean), during inspiration only (Rinsp, Xinsp), and expiratory flow limitation (DeltaXrs = Xinsp−Xexp), 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. Xinsp 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 Xmean, DeltaXrs, and FVC z-score correlated with the change in 6MWD between completion and 3 months after completion of rehabilitation (rs=0.62, p=0.03; rs=− 0.65, p=0.02; and rs=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.
Keywords: COPD, forced oscillation technique, reactance, pulmonary rehabilitation, six-minute walk test, quality of life
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