Dynamic airway function during exercise in COPD assessed via impulse oscillometry before and after inhaled bronchodilators.
Introduction. Assessing airway function during exercise provides useful information regarding mechanical properties of the airways and extent of ventilatory limitation in COPD. The primary aim of this study was to use impulse oscillometry (IOS) to assess dynamic changes in airway impedance across a range of exercise intensities in GOLD 1-4 patients, before and after albuterol. A secondary aim was to assess reproducibility of IOS measures during exercise. Methods. Fifteen COPD patients (8 male; age=66±8 y; pre-bronchodilator FEV1=54.3±23.6%Pred) performed incremental cycle ergometry before and 90-min after inhaled albuterol. Pulmonary ventilation and gas exchange were measured continuously, and IOS-derived indices of airway impedance were measured every 2 min immediately preceding inspiratory capacity manoeuvres. Test-retest reproducibility of exercise IOS was assessed as mean difference between replicate tests in five healthy subjects (3 male). Results. At rest and during exercise, albuterol significantly increased airway reactance (X5), and decreased airway resistance (R5, R5-20), impedance (Z5), and end-expiratory lung volume (60±12 vs. 58±12%TLC, main effect p=0.003). At peak exercise, there were moderate-to-strong associations between IOS variables and IC, and between IOS and concavity in the expiratory limb of the flow-volume curve. Exercise IOS exhibited moderate reproducibility in healthy subjects which was strongest with R5 (mean diff. -0.01±0.05 kPa/L/s; ICC=0.68), R5-20 (mean diff. -0.004±0.028 kPa/L/s; ICC=0.65), and Z5 (mean diff. -0.006±0.021 kPa/L/s; ICC=0.69). Conclusions. Exercise evoked increases in airway resistance and decreases in reactance that were ameliorated by inhaled bronchodilators. The technique of exercise IOS may aid in the clinical assessment of dynamic airway function during exercise.