Effect of thoracic gas compression and bronchodilation on the assessment of expiratory flow limitation during exercise in healthy humans.

Expiratory flow limitation (EFL) during exercise may be overestimated or falsely detected when superimposing tidal breaths within a pre-exercise maximal expiratory flow volume (MEFV) curve due to thoracic gas compression (TGC) and bronchodilation. Accordingly, the purpose of this study was to determine the effects of TGC and bronchodilation on the assessment of EFL in 35 healthy subjects. A pre-exercise forced vital capacity (FVC) maneuver was performed that did not account for TGC (MEFV(pre)). Subjects then performed graded expirations from total lung capacity to residual volume at different efforts to account for TGC (MEFV(pre-TGC)). Post-exercise FVC (MEFV(post)) and post-exercise graded expirations (MEFV(post-TGC)) were performed to account for bronchodilation and TGC. EFL occurred in 29 subjects when using MEFV(pre). The magnitude of EFL in these subjects was 47+/-23% which was significantly higher than MEFV(pre-TGC) (28+/-28%), MEFV(post) (24+/-27%) and MEFV(post-TGC) (19+/-24%) (P<0.00001). Using the traditional MEFV(pre) curve overestimates and falsely detects EFL since it does not account for TGC and bronchodilation.