Walking versus cycling : Sensitivity to bronchodilation in chronic obstructive pulmonary disease

Rationale: There is no consensus regarding which exercise test to use to evaluate the functional impact of bronchodilators in patients with chronic obstructive pulmonary disease. Objective and Methods: Bronchodilator-induced changes in endurance time were evaluated during cycling and walking in 17 patients with chronic obstructive pulmonary disease who completed two cycle endurance tests and two endurance shuttle walks at 80% of peak capacity. Each endurance test was preceded by the nebulization of a placebo or 500 μg of ipratropium bromide using a randomized, double-blind, crossover design. Quadriceps twitch force was measured with magnetic stimulation of the femoral nerve before and after each endurance test. Results: Cycling endurance time did not improve significantly after bronchodilation despite a significant increase in FEV1 (Aendurance time ipratropium bromide - placebo: 51 ±255s, p= 0.42). A similar change in FEV1 was associated with a significant improvement in walking endurance time (Aendurance time ipratropium bromide -placebo: 164 ± 177 s, p < 0.01). A 22 ± 17% fall in quadriceps twitch force was observed after cycling, whereas no significant change was seen after walking. Conclusion: The endurance shuttle walk is a sensitive test to detect changes in exercise tolerance after bronchodilation. Differences in the occurrence of quadriceps muscle fatigue may explain, in part, the different responsiveness to change between cycling and walking.