Measurement of physiological recovery from exacerbation of chronic obstructive pulmonary disease using within-breath forced oscillometry

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Abstract
Background: Within-breath reactance from forced oscillometry estimates resistance via its inspiratory component (Xrs,insp) and flow limitation via its expiratory component (Xrs,exp). Aim: To assess whether reactance can detect recovery from an exacerbation of chronic obstructive pulmonary disease (COPD). Method: 39 subjects with a COPD exacerbation were assessed on three occasions over 6 weeks using post-bronchodilator forced oscillometry, arterial blood gases, spirometry including inspiratory capacity, symptoms and health-related quality of life (HRQOL). Results: Significant improvements were seen in all spirometric variables except the ratio of forced expiratory volume in 1 s (FEV1) to vital capacity, ranging in mean (SEM) size from 11.0 (2.2)% predicted for peak expiratory flow to 12.1 (2.3)% predicted for vital capacity at 6 weeks. There was an associated increase in arterial partial pressure of oxygen (PaO2). There were significant mean (SEM) increases in both Xrs,insp and Xrs,exp (27.4 (6.7)% and 37.1 (10.0)%, respectively) but no change in oscillometry resistance (Rrs) values. Symptom scales and HRQOL scores improved. For most variables, the largest improvement occurred within the first week with spirometry having the best signal-to-noise ratio. Changes in symptoms and HRQOL correlated best with changes in FEV1, PaO2 and Xrs,insp. Conclusions: The physiological changes seen following an exacerbation of COPD comprised both an improvement in operating lung volumes and a reduction in airway resistance. Given the ease with which forced oscillometry can be performed in these subjects, measurements of Xrs,insp and Xrs,exp could be useful for tracking recovery.