Purpose: Patients with chronic obstructive pulmonary disease (COPD) report more dyspnea during arm than during leg exercise. One of the major causes of dyspnea is dynamic hyperinflation (DH), which is caused by airflow limitation as well as increase in ventilation. The aims of our study were to compare DH at equal ventilation (isoventilation) during arm and legwork and to investigate the effects of breathing pattern on DH.
Methods: Thirteen clinically stable patients with mild to very severe COPD (forced expiratory volume in 1 s = 59% ± 21%) participated in this study. Arm and leg constant work rate (CWR) ergometry were performed in random order with ventilation equal to that at 50% of peak armload. The corresponding leg load of that level of ventilation was determined from the incremental leg test. Respiratory physiology was measured breath-by-breath. Change in inspiratory capacity, measured at rest and at 2-min intervals, was used to reflect DH.
Results: At steady-state isoventilation (37 ± 2 and 36 ± 2 L·min−1 for arm and leg CWR tests, respectively, P > 0.05), armload was 29 ± 5 W and leg load was 52 ± 6 W (P < 0.001). The level of DH, 0.32 ± 0.09 and 0.27 ± 0.08 L during arm and leg exercises, respectively, was not significantly different. However, breathing frequency was greater during arm than during leg exercise (24 ± 1 vs 21 ± 1 breaths per minute, P < 0.01), and the opposite was true for tidal volume (1.56 ± 0.15 vs 1.69 ± 0.14 L, P < 0.01).
Conclusions: At similar ventilation, we found a similar degree of DH during arm and leg CWR tests in patients with mild to very severe COPD. Although differences in breathing pattern were observed between arm and leg exercises, these did not affect the level of DH.