Exercise performance in chronic obstructive pulmonary diseases.

Patients with chronic obstructive pulmonary diseases demonstrate exercise limitation as a consequence of both an increased ventilatory requirement and a decreased ventilatory capacity. The increased ventilatory requirement arises from the elevated wasted ventilation fraction of each breath (VD/VT) and hypoxemia secondary to ventilation-perfusion mismatching, both of which stimulate minute ventilation of increase. The reduced ventilatory capacity is primarily the result of airflow obstruction, which causes an increased work of breathing. Respiratory muscle fatigue may also play a role in reducing ventilatory capacity. The differentiation of heart failure from chronic obstructive pulmonary diseases as a cause of dyspnea can be accomplished using a variety of noninvasive and invasive techniques during exercise, including measurements of minute ventilation, the expiratory airflow pattern, ventilatory reserve (VEmax/MVV), ventilatory efficiency (VD/VT), arterial blood gases, the anaerobic threshold, heart rate, cardiac output, pulmonary hemodynamics and ventricular ejection fraction. Exercise training of patients with chronic obstructive pulmonary diseases improves exercise intolerance but appears to have little effect on pulmonary function tests, arterial blood gases and pulmonary hemodynamics. Supplemental oxygen during exercise training may be a useful adjunct for improving exercise tolerance in patients with chronic obstructive pulmonary diseases.