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Plasma ammonia response to incremental cycling and walking tests in COPD
L D Calvert1, M C Steiner, M D Morgan
1Department of Respiratory Medicine, Institute for Lung Health, University Hospitals of Leicester NHS Trust, Glenfield Hospital, Leicester, UK. lori.calvert@pbh-tr.nhs.uk
Respiratory Medicine
|December 17, 2009
Summary
Metabolic stress, indicated by rising plasma ammonia, occurs during walking in patients with chronic obstructive pulmonary disease (COPD). This finding suggests a new factor contributing to exercise limitation in COPD patients.
Area of Science:
- Exercise physiology
- Pulmonary medicine
Background:
- Plasma ammonia accumulation is a known indicator of metabolic stress during exercise.
- Metabolic stress, defined as a failure in skeletal muscle ATP supply to meet demand, is documented in COPD patients during cycling but not walking.
- Walking is a crucial activity for COPD patients and a common component of pulmonary rehabilitation.
Purpose of the Study:
- To investigate whether metabolic stress occurs in patients with COPD during incremental walking at the low work rates they typically achieve.
- To compare metabolic stress during walking versus cycling in COPD patients.
Main Methods:
- Twenty-nine stable COPD patients underwent maximal cardiopulmonary exercise tests on both a cycle ergometer and a treadmill.
- Plasma ammonia concentrations were measured at rest, during exercise (1 and 2 minutes, peak), and during recovery (2 minutes).
Main Results:
- Patients achieved low work rates during both cycling (57 W) and walking (284 m).
- Plasma ammonia significantly increased during both walking and cycling (p<0.001).
- Peak exercise ammonia levels were lower during walking compared to cycling (p<0.01). A subgroup (n=7) showed no ammonia rise despite similar exercise indices.
Conclusions:
- The findings indicate that metabolic stress can occur during walking in COPD patients at achievable work rates.
- This metabolic stress during walking may contribute to exercise limitation in COPD, independent of ventilatory issues.
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