Airway Resistance and Maximal Expiratory Flow During Exercise

Abstract

1560 Although the typical asthmatic response involves bronchodilation (BD) during exercise and bronchoconstriction (BC) after exercise stops, many asthmatics exhibit symptoms during exercise. PURPOSE: To evaluate lung function during incremental exercise using two methods. METHODS: Ten male subjects with normal lung function performed two 20-min incremental cycle ergometer rides (EX) separated by at least 48 h consisting of four 5-min stages at increasing intensities at 50, 100, 150 and 200 W. During the last min of each stage, the subject performed impulse oscillometry (IOS) and a maximal expiratory flow maneuver (MEFV). Changes in airway resistance (Raw), FEV1 and FEF25–75 were compared to pre-EX values. RESULTS: Two trials by each subject verified reliability of the measurements. No significant differences were noted in IOS covariance between intensities. Raw was significantly greater at 150 and 200W than at 50 W or pre-EX (3.25 ± 0.53 and 3.42 ± 0.65 vs 3.0 ± 0.54 and 2.94 ± 0.52, respectively; P<0.05). FEV1 did not change, although a non-significant BC was observed at 150W. FEF25–75 increased at each stage with significant differences between all but 50W and 100W (4.94 ± 1.31, 5.13 ± 1.37, 5.20 ± 1.50, 5.37 ± 1.52, 5.66 ± 1.70 Pre-EX to 200W, respectively; P<0.05). CONCLUSION: FEF25–75 increase with EX intensity suggests BD during EX, as expected. Paradoxically, the increase in Raw with EX intensity suggests small airway BC. We conclude that the differences between IOS and MEFV are due to dynamic compression and elastic recoil driving pressure for MEFV, while alveolar pressure is the driving force during the tidal breathing maneuver of IOS. Supported in part by VIASYS Health Care.