Exercise-induced flow limitation, dynamic hyperinflation and exercise capacity in patients with bronchial asthma.

It is known that, in stable asthmatics at rest, tidal expiratory flow limitation (EFL) and dynamic hyperinflation (DH) are seldom present. This study investigated whether stable asthmatics develop tidal EFL and DH during exercise with concurrent limitation of maximal exercise work rate (WRmax). A total of 20 asthmatics in a stable condition and aged 32+/-13 yrs (mean+/-SD) with a forced expiratory volume in one second (FEV1) of 101+/-21% of the predicted value were studied. Only three patients exhibited an FEV1 below the normal limits. On a first visit, patients performed a symptom-limited incremental (20 W.min(-1)) bicycle exercise test. On the second visit, the occurrence of EFL (using the negative expiratory pressure technique) and DH (via reduction in inspiratory capacity) were assessed at rest and when cycling at 33, 66 and 90% of their predetermined WRmax. FEV1 was measured to detect exercise-induced asthma, 5 and 15 min after stopping exercise at 90% WRmax. Only one patient showed EFL at rest, whereas 13 showed EFL and DH during exercise. In these 13 asthmatics, exercise capacity was significantly reduced (WRmax 75+/-9% pred) compared to the seven non-EFL patients (WRmax 95+/-13% pred). Moreover, a significant correlation of WRmax (% pred) to the change in inspiratory capacity (percentage of resting value) from rest to 90% WRmax was found. Tidal EFL during exercise was not associated with exercise-induced asthma, which was detected in only three patients. In conclusion, tidal expiratory flow limitation and dynamic hyperinflation during exercise are common in stable asthmatics with normal spirometric results and without exercise-induced asthma, and may contribute to reduction in exercise capacity.