Effect of increasing respiratory rate on airway resistance and reactance in COPD patients

Background and objective Airway resistance and reactance measured by forced oscillometry have been used to measure the severity of airway obstruction in chronic obstructive pulmonary disease (COPD) patients. The aims of this study were to assess the effects of tachypnoea on airway resistance and reactance and to correlate these with the severity of dyspnoea. We also evaluated the effects of short-acting β2-agonist (SABA) on these measurements. Methods Airway resistance and reactance were measured with an impulse oscillation system (IOS) in 20 COPD and 10 control participants during resting respiration and metronome-paced breathing at 20, 30 and 40 tidal breaths/min. The same measurements were made for COPD patients after SABA inhalation. Dyspnoea was evaluated using the modified Medical Research Council (MRC) scale. Results In patients with COPD, higher respiratory rates increased expiratory and inspiratory resistance at 5 Hz (R5), the difference in respiratory resistance at 5 Hz and 20 Hz (R5–R20), resonant frequency and decreased expiratory reactance. The decreases in expiratory reactance from 20 to 40 tidal breaths/min were significantly correlated with MRC scores. SABA inhalation significantly reduced the effect of increased respiratory rate on the reactance measurements. Conclusions Characteristic changes in IOS measurements, particularly expiratory reactance, induced by increased respiratory rates, were correlated with severity of dyspnoea in COPD patients during their daily lives. IOS and paced breathing may be useful for assessing breathlessness in COPD.