Combined Echocardiographic and Cardiopulmonary Exercise to Assess Determinants of Exercise Limitation in Chronic Obstructive Pulmonary Disease

Abstract

Background: Current methods do not allow a thorough assessment of causes associated with limited exercise capacity in patients with chronic obstructive pulmonary disease (COPD).

Methods: Twenty patients with COPD and 20 matched control subjects were assessed using combined cardiopulmonary and stress echocardiographic testing. Various echocardiographic parameters (left ventricular [LV] volumes, right ventricular [RV] area, ejection fraction, stroke volume, S', and E/e' ratio) and ventilatory parameters (peak oxygen consumption [Vo₂] and A-Vo₂ difference) were measured to evaluate LV and RV function, hemodynamics, and peripheral oxygen extraction (A-VO₂ difference).

Results: Significant differences (both between groups and for group-by-time interaction) were seen in exercise responses (LV volume, RV area, LV volume/RV area ratio, S', E/e' ratio, tricuspid regurgitation grade, heart rate, stroke volume, and Vo₂). The major mechanisms of reduced exercise tolerance in patients with COPD were bowing of the septum to the left in 12 (60%), abnormal increases in E/e' ratio in 12 (60%), abnormal stroke volume reserve in 16 (80%), low peak A-Vo₂ difference in 10 (50%), chronotropic incompetence in 13 (65%), or a combination of several mechanisms. Patients with COPD and poor exercise tolerance showed attenuated increases in stroke volume, heart rate, and A-Vo₂ difference and exaggerated changes in LV/RV ratio and LV compliance (ratio of LV volume to E/e' ratio) compared with patients with COPD with good exercise tolerance.

Conclusions: Combined cardiopulmonary and stress echocardiographic testing can be helpful in determining individual mechanisms of exercise intolerance in patients with COPD. In patients with COPD, exercise intolerance is predominantly the result of chronotropic incompetence, limited stroke volume reserve, exercise-induced elevation in left filling pressure, and peripheral factors and not simply obstructive lung function. Limited stroke volume is related to abnormal RV contractile reserve and reduced LV compliance introduced through septal flattening and direct ventricular interaction.

Keywords: COPD; Cardiopulmonary exercise; Echocardiography; Exercise physiology.