Bronchodilator acutely reduces expiratory flow limitation during exercise in COPD demonstrated by dynamic hyperinflation, flow-volume curve analysis and impulse oscillometry

Purpose: We sought to identify expiratory flow limitation during exercise in COPD by establishing associations among dynamic hyperinflation (DH; by inspiratory capacity, IC), concavity of spontaneous expiratory flow-volume curves (by rectangular area ratio, RAR) and airway resistance and reactance (by impulse oscillometry, IOS) pre- and post-albuterol administration. Methods: 15 patients volunteered (66.0±8.2 yrs; 8 male; GOLD PRISM/1/2/3/4: 1/4/4/4/2). IC and IOS were measured every 2 min during incremental cycling. RAR was measured breath-by-breath. Results: Albuterol increased FEV1%pred. at rest (61[31,72] vs 67[38,81]%, p=0.001) and IC at peak exercise (1.99[1.19,2.25] vs 2.16[1.27,2.37] L, p=0.012). Albuterol did not change RAR at peak exercise (0.50[0.45,0.60] vs 0.57[0.45,0.61], p=0.156), but reduced resistance (R5, 0.69[0.54,0.80] vs 0.51[0.48,0.58] cmH2O/L/s, p=0.018), reactance (AX, 2.68[1.19,5.32] vs 1.81[1.11,2.70] cmH2O/L/s, p=0.017) and resonant frequency (Fres, 27.7[22.1,34.1] vs 25.3[22.1,27.7] Hz, p=0.012). FEV1%pred., IC and RAR were significantly associated with AX at peak exercise (Figure). Conclusions: Albuterol reduces airway resistance and reactance during exercise in COPD, which are associated with reductions in dynamic hyperinflation and expiratory flow limitation. Method: Pulmonary Education and Research Foundation