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) cmH ₂ O.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.
Competing Interests: Dr Sabine C Zimmermann was supported by the National Health and Medical Research (NHMRC) Postgraduate Scholarship, during the conduct of the study; non-financial support from Boehringer Ingelheim, Glaxo Smith Kline, Astra Zeneca, Novartis, and Menarini, outside the submitted work. Dr Cindy Thamrin reports a patent WO 2006130922 A1 issued; and has intellectual property arrangements with THORASYS Thoracic Medical Systems Inc and Restech srl relating to scientific collaborations, but does not have any financial relationships with either company. She is also a member of a current international committee on FOT technical standards. Prof. Dr. Gregory King reports grants from NHMRC, non-financial support from Restech, during the conduct of the study; personal fees from Pharmaceutical Industry, GSK, and grants from CycloPharma, outside the submitted work. The authors report no other conflicts of interest in this work.
(© 2020 Zimmermann et al.)