Relationship between Exercise Capacity and Ventilatory Equivalent for Carbon Dioxide in Patients with Stable Old Myocardial Infarction

Abstract

The aim of the present study was to evaluate the relationship between exercise capacity and ventilatory response in patients with stable old myocardial infarction. We performed cardiopulmonary exercise test in 61 patients with stable old myocardial infarction and in 30 healthy men. Each subject exercised on a bicycle ergometer until exhaustion. Patients who had anginal pain or electrocardiographic ischemic changes during exercise were excluded. The patients were classified into three groups according to peakVO₂ achieved during exercise, using Weber's method: group A, peakVO₂≥21 ml/min/kg (n=4); group B, 14≤peakVO₂<21 ml/min/kg (n=45); and group C, peakVO₂<14 ml/min/kg (n=12). With progressive increases in VCO₂, VE increased linearly below the anaerobic threshold (AT) level. The slope of the linear regression line between VCO₂ and VE (SLOPE) was calculated in each subject. The mean SLOPE of the healthy men (group N) and groups A, B and C were 25.8±0.5, 25.1±0.5, 28.9±0.8 and 37.1±1.7 (×10^-3), respectively. Thus, the SLOPE was steeper in patients with lower peakVO₂. It is difficult to perform a maximal exercise tolerance test on patients with chronic heart failure to evaluate their exercise capacity. We can assess exercise capacity by the slope of the linear regression line between VCO₂ and VE (SLOPE) at the lower exercise level.