Relationships between impulse oscillometry, spirometry and dyspnoea in COPD

Background: Severity of chronic obstructive pulmonary disease (COPD) is based either on symptoms/disability or lung function, which have no discernible correlation. We hypothesised that impulse oscillometry (IOS), a non-effort-dependent measure of central and peripheral airway mechanics, could correlate to dyspnoea in COPD. Methods: We analysed screening data from 57 COPD patients who had spirometry, IOS and Medical Research Council dyspnoea score (MRC) measurements. We searched for predictors or correlations of MRC from IOS, spirometry and demographics. Results: MRC had no significant predictors or correlations from IOS, spirometry or demographics (possibly excepting smoking history, p=0.05). IOS correlated significantly with spirometry: FEV1 and FEF25-75 vs. R5-R20 (peripheral airway resistance), r=-0.499, p<0.001 and r=-0.397, p=0.002 respectively. Conclusion: MRC is not related to IOS or spirometry in COPD. IOS correlates well with spirometry, particularly peripheral airway resistance (R5-R20). IOS is useful, but does not provide a link between symptoms and pulmonary function measurements.