Impulse-oscillometry (IOS) differences in asthma and COPD patients, and healthy-subjects

Abstract

Impulse-oscillometry (IOS) measures lung-functions during tidal-breathing with multi-frequency sound-waves. However, the differences in IOS parameters between asthma and COPD are not well understood. We aimed to compare IOS parameters of asthma and COPD patients with those from healthy-subjects. Methods: 100 stable-asthmatics, 101 stable-COPD patients and 55 healthy-subjects underwent pre-and-post-bronchodilator IOS according to ERS (2003) statement. Age-height-corrected post-bronchodilator parameters were compared between asthmatic and COPD subjects using log-transformation and ANCOVA-test. Results: Compared with healthy-subjects, both asthmatic and COPD-subjects had higher resistance (R5Hz, R20Hz), impedance at 5Hz (Z5Hz), reactance at 5Hz (X5Hz), area-of-reactance (Ax) and resonance-frequency (Rf). Compared with asthmatics, COPD-subjects had higher Z5Hz kPa/(L/s) (0.69{\textpm}0.37 vs 0.93{\textpm}0.42, p\<0.0001), X5Hz kPa/(L/s) (-0.9{\textpm}0.8 vs 1.8{\textpm}1.2, p\<0.0001), Ax kPa/L (2.6{\textpm}3.0 vs 5.4{\textpm}3.7, p\<0.0001) and Rf (23.1{\textpm}8.0 vs 30.9{\textpm}6.7, p\<0.0001). COPD-subjects demonstrated smaller differences in expiratory-inspiratory R5Hz �R5Hz: kPa/(L/s) compared to asthmatics (0.7{\textpm}0.6 vs 0.8{\textpm}0.5, p=0.03), however �R5Hz between asthma and healthy-subjects was similar. No differences were observed in R5hz, R20hz and frequency-dependence (R5hz-R20hz) between asthmatics and COPD-patients. Conclusion: Despite similarities in airway-resistances, COPD-patients exhibit lower expiratory-inspiratory resistance difference, with higher lung-impedance, lung-reactance, area of-reactance and resonant-frequency compared to asthmatics. IOS offers a comparative understanding of lung-dynamics in asthma and COPD during tidal-breathing.