Contrasting cardiovascular and respiratory responses to exercise in mitral valve and chronic obstructive pulmonary diseases.

The role of cardiovascular and pulmonary limitation in performing maximal exercise is contrasted in patients with mitral valve disease (MVD) and chronic obstructive pulmonary disease (COPD). The ventilatory (VE) gas exchange (VO2 and VCO2) and heart rate (HR) responses to an incremental cycle ergometer exercise were measured in six patients with MVD, seven patients with COPD, and six normal subjects. The VE requirement for the work (VE-VO2 relationship) was increased in both COPD and MVD groups compared with control subjects, but the breathing reserve was significantly lower in COPD (13 percent) compared with MVD (49 percent) and control groups (44 percent). In contrast, the VO2 at the anaerobic threshold was significantly lower in MVD (12.2 +/- .5 ml/kg) compared with COPD (15.7 +/- 1.2 ml/kg) and control subjects (16.6 +/- .9 ml/kg). Also, the heart rate reserve and the VO2-HR slope were significantly reduced in MVD (9 +/- 6 percent and 6.9 +/- 1.0 ml/min/beat, respectively) compared with COPD patients (44 +/- 7 percent and 2.0 ml/min/beat, respectively). Both patient groups experienced an acidosis in their terminal work rate, but the acidosis was primarily respiratory in the COPD and totally metabolic in the MVD group. These studies indicate that at maximal work rate, MVD but not COPD patients, manifest compromised O2 delivery to the muscles, while COPD but not MVD patients were unable to increase VE sufficiently to match the exercise-induced CO2 production.