Pulmonary function subsequent to expiratory muscle fatigue in healthy humans

One of the mechanisms proposed to explain the decrement in pulmonary function often seen after exercise is fatigue of the expiratory muscles. To test the hypothesis that expiratory muscle fatigue alters lung function, several indices of pulmonary function were measured before and after expiratory muscle fatigue was induced by expiratory loaded breathing. Eight subjects completed a fatigue trial (EF) in which expiratory threshold loaded breathing was performed at an initial resistance equal to 80% of their maximal expiratory pressure (MEP), at a respiratory rate of 13 bpm, and a duty cycle (T₁/T_Tot) of 0.33. MEP was taken at predefined intervals throughout the loaded breathing protocol, and loaded breathing was discontinued when MEP was less than 80% of each subject's pre EF trial MEP (T_Lim). FVC, FEV_1.0, FEF_25%, FEF_25-75%, and maximal inspiratory and expiratory pressures (MIP and MEP) were taken prior to, immediately after, and at 5, 10, and 15 min post fatigue. On a separate day a control trial (CON) was performed that was identical to each subjects EF trial with the exception that no expiratory load was utilized. At T_Lim MEP was significantly reduced (p < 0.001) by 23.5% from the pre-expiratory loaded breathing value (183.1 ± 39.56 to 140.13 ± 30.45 mmHg), whereas it remained unchanged during the CON trial (191.06±44.18 to 188.06±43.50 mmHg). FVC measured prior to and immediately after T_Lim remained unchanged following both the EF (5349.45±1130.8 to 5387.43±1139.92 mL) and CON trials (5287.75±1220.29 and 5352.78±1191.30 mL). These results suggest that any expiratory muscle fatigue developed during exercise by itself does not result in altered pulmonary function. However, any interactions between expiratory muscle fatigue and other consequences of exercise that may alter lung function cannot be ruled out.