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Systemic oxygen extraction during incremental exercise in patients with severe chronic obstructive pulmonary disease
D A Oelberg1, B D Medoff, D H Markowitz
1Pulmonary and Critical Care Unit and Lung Transplant Program, Massachusetts General Hospital and Harvard Medical School, Boston 02114, USA.
Summary
In severe chronic obstructive pulmonary disease (COPD), reduced oxygen extraction, not delivery, limits exercise capacity. This finding suggests abnormal O2ER contributes to exercise intolerance in COPD patients.
Area of Science:
- Cardiorespiratory Physiology
- Exercise Science
Background:
- Patients with severe chronic obstructive pulmonary disease (COPD) experience exercise limitation.
- The precise mechanisms, particularly concerning oxygen (O2) utilization, remain incompletely understood.
Purpose of the Study:
- To investigate whether diminished systemic O2 extraction contributes to exercise limitation in severe COPD.
- To compare oxygen extraction in COPD patients with those in left ventricular failure (LVF) and healthy controls.
Main Methods:
- 40 severe COPD patients, 8 LVF patients, and 10 controls underwent incremental cycle ergometer tests.
- Continuous monitoring of pulmonary gas exchange and ventilation; minute-by-minute arterial blood gases and lactate.
- Cardiac output (Qc) measured via radionuclide ventriculography; systemic O2 extraction ratio (O2ER) calculated.
Main Results:
- Peak oxygen uptake (VO2peak) was significantly reduced in COPD and LVF compared to controls.
- Lactate threshold (LT) occurred at a lower percentage of VO2peak in COPD and LVF versus controls.
- Systemic O2ER at peak exercise was markedly lower in COPD patients than in LVF patients and controls.
Conclusions:
- Reduced systemic O2ER, not impaired O2 delivery, is associated with early lactate threshold in severe COPD.
- Abnormal systemic O2 extraction appears to be a key factor contributing to exercise intolerance in severe COPD.