Abstract

Dyspnea and decreased exercise capacity are the main factors that limit the daily living activities in patients with chronic respiratory diseases. The cardinal symptoms limiting exercise capacity in most patients with chronic obstructive pulmonary disease (COPD) are dyspnea and fatigue, which could be caused by alveolar ventilation and gas exchange disturbances, skeletal muscle dysfunction and/or cardiovascular failure. Anxiety, lack of motivation and depression were also associated with reduced exercise capacity, probably affecting the perception of symptoms. The relationship between psychological status and mood disorders in patients with COPD and exercise tolerance is complex and not yet fully understood. The origin of the exercise capacity limitation in COPD patients is multifactorial, so the separation of the variables involved for academic purposes is not always feasible. The pathogenic mechanisms may interact in complex ways, as an example, muscle deconditioning and hypoxemia can increase alveolar ventilation causing exercise limitation. Therefore, physical training and supplemental oxygen can reduce ventilatory limitation during exercise without changing lung function and maximum ventilatory capacity. The analysis of these factors could potentially identify reversible conditions that can improve the exercise performance and quality of life ofpatients with COPD, such as hypoxemia, bronchospasm, heart failure, arrhythmias, musculoskeletal dysfunction and myocardial ischemia. This review examines the principal mechanisms contributing to physical activity limitation in patients with COPD: alveolar ventilation and gas exchange abnormalities, cardiovascular and musculoskeletal system dysfunction, and respiratory muscles dysfunction.