Abstract
Introduction: The survival prognosis of COPD patients with severely reduced exercise capacity is extremely poor. However, the dynamic pathophysiology of these patients, including sympathetic activation and lactic acidosis, remains to be accurately established. Thus, we performed this study to clarify the differences in the dynamic pathophysiology of four COPD patient groups classified according to their exercise capacity.
Methods: Ninety-one COPD patients (82 males, 9 females; average age, 69.7±6.8 years) underwent incremental CPET using a cycle ergometer. During CPET, we measured the patient levels of arterial blood gases, lactate, and catecholamines.
Results: We found that the pathophysiology of the COPD patients was different among the groups. Patients with severely reduced exercise capacity (peak oxygen uptake < 654 ml/min) were characterized by the following: (i) exercise-induced rapid decrease of arterial oxygen pressure (PaO2-slope: -7.8±7.0 mmHg/100 ml); (ii) sympathetic activation at low-grade workload (plasma norepinephrine level, 1.4±0.94 ng/ml at 20 W); (iii) little change in lactic acidosis; (iv) a limitation in the increase of ventilation; and (v) impaired gas exchange. The norepinephrine increase exhibited during exercise was significantly correlated (r = 0.94±0.08) with the dyspnoea ratings.
Conclusions: The COPD pathophysiology significantly varied among patients with different exercise capacities. Patients with lower exercise capacity suffered from severe gas exchange disorder, sympathetic overactivation, and ventilatory disturbance during exercise. CPET should consistently be performed to assess the factors that contribute to exercise limitation in COPD patients.
- © 2011 ERS