The plasma ammonia response to cycle exercise in chronic obstructive pulmonary disease

¹ Dept of Respiratory Medicine, Institute for Lung Health, Glenfield Hospital, Groby Road, Leicester, UK
² Dept of Biomedical Sciences, University of Nottingham, Derby Road, Nottingham, UK

^* To whom correspondence should be addressed. E-mail: lori.calvert{at}uhl-tr.nhs.uk.

	Abstract

We examined plasma ammonia response to exercise in COPD and explored the relationship between plasma ammonia concentration and muscle adenine nucleotide metabolism.

Twenty-five stable COPD patients and 13 similar-aged controls underwent incremental and constant workrate cycle exercise tests. Arterialised-venous blood was sampled at rest, 1-minute intervals during, and up to 5minutes after exercise for ammonia and lactate concentration.

Peak incremental workrate was significantly less in COPD subjects (67[21]W) than similar-aged controls (156[46]W),p<0.001. In COPD and control subjects, plasma ammonia concentration increased during incremental exercise (p<0.001) until 2minutes post-exercise, then declined by 5minutes post-exercise. However, two distinct patterns were seen in COPD subjects. In one group (n=16), ammonia increased [42.8(3.3)umol·l^-1] by a similar magnitude as controls [55.5(7.0)umol·l^-1], p=0.12. In a second COPD group (n=9) no ammonia increase was observed despite a similar lactate increase. Ammonia change with incremental and constant workrate exercise strongly correlated in COPD subjects (r=0.88, p<0.001). Plasma ammonia increase correlated with muscle IMP formation after constant workrate exercise (r=0.61, p=0.029).

Plasma ammonia concentration increases during incremental and constant workrate cycle exercise in COPD subjects at lower absolute workrates compared with similar-aged controls. The plasma ammonia response may provide useful information about adenine nucleotide metabolism and therefore muscle fatigue during exercise in patients with COPD.

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