Impulse oscillation respiratory reactance and airway reversibility in chronic obstructive pulmonary disease

Introduction: Airway reversibility is often seen in patients with chronic obstructive pulmonary disease (COPD). Impulse oscillation technique can assess respiratory resistance (Rrs) and reactance (Xrs). Within-breath (expiratory-inspiratory) alterations in Rrs and Xrs may reflect dynamic airway compression in COPD. Aims and Objectives: To find out whether the within-breath analysis of Rrs and Xrs is valid for the assessment of airway reversibility in COPD. Methods: Before and after inhalation of sarbutamol, 48 patients with stable COPD and 16 control smokers underwent spirometry and impulse oscillation measurements of Rrs and Xrs. The COPD patients were classified as responders (R; n = 18) or non-responders (NR; n = 30) based upon whether or not post-bronchodilator forced expiration volume in 1 second (FEV 1 ) was increased by ≥12% or ≥200 mL. Within-breath differences in Rrs at 5Hz (ΔR5) and 20Hz (ΔR20), Xrs at 5Hz (ΔX5), resonant frequency (ΔFres), and low-frequency reactance area (ΔAX) were analysed. Results: Pre-bronchodilator spirometry parameters, ΔR5, ΔR20, ΔX5,and ΔFres were similar between R and NR. Only ΔAX was higher in R compared with NR. Following inhalation, ΔX5 and ΔAX were significantly improved in R when compared with NR and controls (p 1 (p Conclusions: Airway reversibility in COPD may result from the change in respiratory reactance. The within-breath analysis of Xrs may be useful for the assessment of drug responsiveness in COPD.