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Description
Expiratory flow limitation is a primary characteristic in chronic obstructive pulmonary disease (COPD). Bronchoconstriction, parenchymal destruction, and mucus hypersecretion lead to obstruction, causing dynamic hyperinflation, dyspnea, and exercise intolerance. However, high airway resistance is just one of many abnormalities in COPD and isolating the effects of expiratory airflow limitation is challenging. In order to study abnormal lung mechanics in isolation, we aimed to measure pulmonary function in young healthy volunteers with and without imposed external expiratory resistance. METHODS Forty-three participants (25.4 ± 4.5 years) completed pulmonary function testing according to the ATS/ERS standards with and without imposed expiratory loading of 7 cmH2O, 11 cmH2O, and 20 cmH2O. Resistance was imposed with a threshold inspiratory muscle trainer installed in reverse on the spirometer. RESULTS Expiratory loading of 7 and 11 cmH2O vs. control reduced all variables (n=43): FEV1 (3.23 ± 0.81 and 3.23 ± 0.80 vs. 4.04 ± 1.05 L), FVC (4.10 ± 1.02 and 4.14 ± 1.03 vs. 5.03 ± 1.34 L), FEV1/FVC (77.6 ± 8.48 and 78.7 ± 6.18 vs. 80.7 ± 5.30 %), and PEF (6.12 ± 1.73 and 6.07 ± 1.91 vs. 8.70 ± 2.87 L/s). Additional supra-physiologic loading of 20 cmH2O in a subsample (n=15) only modestly reduced FEV1 vs. control (3.07 ± 0.52 vs. 4.09 ± 0.91 L); FVC vs. control (3.89 ± 0.81 vs. 4.81 ± 1.10L); FEV1/FVC vs. control (78.5 ± 5.99 % vs. 81.9 ± 5.48 %); and PEF vs. control (5.50 ± 1.78 vs. 8.05 ± 2.47 L/s). CONCLUSIONS Imposed expiratory resistance reduced key spirometric variables. A concave expiratory flow-volume relationship or meaningfully reduced FEV1/FVC was consistently absent – a key limitation for model comparison with pulmonary function in COPD. It appears that imposed resistance leads to higher airway pressures that resist dynamic airway compression.
