ANAEROBIC METABOLISM AS AN INDICATOR OF AEROBIC FUNCTION DURING EXERCISE IN CARDIAC PATIENTS

To determine whether patients with heart disease depend more than normal subjects on anaerobic metabolism to perform the same level of exercise, the anaerobic threshold, slope of the increase in carbon dioxide output with respect to oxygen uptake (DELTA-VCO2/DELTA-VO2) and the slope of the increase in oxygen uptake with respect to the increase in work rate (DELTA-VO2/DELTA-WR) both below and above the anaerobic threshold during exercise were evaluated. A total of 106 patients with chronic heart disease and 42 healthy subjects performed a symptom-limited incremental exercise test in a ramp pattern on a cycle ergometer. Peak oxygen uptake was significantly lower in the patients with heart disease than in the normal subjects. The anaerobic threshold, which was 20 +/- 4.6 ml/min per kg in normal subjects, decreased significantly with progressing severity of functional class: 16 +/- 2.4, 14.1 +/- 2.5 and 11.3 +/- 1.5 ml/min per kg, respectively, in patients in class I, class II and class III. The slope of DELTA-VO2/DELTA-WR, which represents the degree of aerobic metabolism, was also decreased both below and above the anaerobic threshold with increasing severity of heart disease. DELTA-VCO2/DELTA-VO2 below the anaerobic threshoLd was approximately 0.9 (p = NS between normal subjects and patients). However, DELTA-VCO2/DELTA-VO2 above the anaerobic threshold became steeper with increasing severity of heart disease: 1.37 +/- 0.17 in normal subjects versus 1.55 +/- 0.24, 1.67 +/- 0.3 and 1.8 +/- 0.35 respectively, in patients in functional class I, class II and class III. The steeper DELTA-VCO2/DELTA-VO2 Slope above the anaerobic threshold in patients with heart disease resulted from the greater amount of carbon dioxide production per unit of oxygen and reflected the greater extent of anaerobic metabolism needed to supplement energy output. This ratio, which was not influenced by patient age or the slope of the work rate increase, provides a useful indicator of aerobic function in patients with heart disease.