We quantified the magnitude of exercise-induced bronchodilation in adult asthmatics under conditions of narrowed and dilated airways. We then assessed the effect of the bronchodilation on ventilatory capacity and the extent of ventilatory limitation during exercise.
Eleven asthmatics completed three exercise bouts on a cycle ergometer. Exercise was preceded by no treatment (trialCON), inhaled β2-agonist (trialBD), or a eucapnic voluntary hyperpnea challenge (trialBC). Maximal expiratory flow-volume maneuvers (MEFV) were performed before and within 40 seconds of exercise cessation. Exercise tidal flow-volume loops were placed within the pre- and post-exercise MEFV curve and used to determine expiratory flow-limitation (EFL) and maximum ventilatory capacity (V˙ ECap).
Pre-exercise airway function was different among the trials (forced expiratory volume 1 second [FEV1] during trialCON, trialBD, and trialBC = 3.3 ± 0.8, 3.8 ± 0.8, and 2.9 ± 0.8 L, respectively; P < 0.05). Maximal expired airflow increased with exercise during all three trials, but the increase was greatest during trialBC (delta FEV1 during trialCON, trialBD, and trialBC = +12.2 ± 13.1, +5.2 ± 5.7, +28.1 ± 15.7%). Thus, the extent of EFL decreased, and V˙ ECap increased, when the post-exercise MEFV curve was used. During trialCON and trialBC, actual exercise ventilation exceeded V˙ ECap calculated with the pre-exercise MEFV curve in seven and nine subjects, respectively.
These findings demonstrate the critical importance of exercise bronchodilation in the asthmatic with narrowed airways. Of clinical relevance, the results also highlight the importance of assessing airway function during or immediately after exercise in asthmatic persons; otherwise, mechanical limitations to exercise ventilation will be overestimated.

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