Relationship between ventilatory constraint and muscle fatigue during exercise in COPD

¹ Dept of Medicine, University of Alberta, Edmonton, Alberta, Canada, T6G 2B7; and Faculty of Physical Education and Recreation, University of Alberta, Edmonton, Alberta, Canada, T6G 2H9
² Faculty of Physical Education and Recreation, University of Alberta, Edmonton, Alberta, Canada, T6G 2H9; and Centre for Neuroscience, University of Alberta, Edmonton, Alberta, Canada, T6G 2H9
³ Dept of Medicine, University of Alberta, Edmonton, Alberta, Canada, T6G 2B7; and Division of Respiratory Medicine, University of Saskatchewan, Saskatoon, Saskatchewan, Canada, S7N 0W8
⁴ Faculty of Physical Education and Recreation, University of Alberta, Edmonton, Alberta, Canada, T6G 2H9
⁵ Dept of Medicine, University of Alberta, Edmonton, Alberta, Canada, T6G 2B7

^* To whom correspondence should be addressed. E-mail: scott.butcher{at}usask.ca.

	Abstract

Dynamic hyperinflation and leg muscle fatigue are independently associated with exercise limitation in patients with chronic obstructive pulmonary disease (COPD). The aims of the present study were to examine (1) the relationship between these limitations and (2) the effect of delaying ventilatory limitation on exercise tolerance and leg muscle fatigue.

Eleven patients with COPD (FEV₁ 52%) completed two cycling bouts breathing either room air or heliox, and one bout breathing heliox but stopping at room air isotime. End-expiratory lung volume (EELV), leg muscle fatigue, and exercise time were measured.

On room air, end-exercise EELV was negatively correlated with leg fatigue (r= -0.77). Heliox increased exercise time (346s to 530s) and leg fatigue (15%). At isotime, there was no change in leg fatigue despite a reduction in EELV compared to end-exercise in both room air and heliox. The change in exercise time with heliox was best correlated with room air leg fatigue (r= -0.79) and end-inspiratory lung volume (r=0.68).

Patients with COPD who had greater levels of dynamic hyperinflation on room air had less muscle fatigue. These patients were more likely to increase exercise tolerance with heliox, which resulted in greater leg muscle fatigue.