Abstract
BACKGROUND: The complexity of cardiopulmonary exercise testing data and their displays tends to make assessment of patients, including those with heart failure, time consuming. METHODS AND RESULTS: We postulated that a new single display that uses concurrent values of oxygen uptake / ventilation versus carbon dioxide output / ventilation ratios ([Formula: see text]-versus-[Formula: see text]), plotted on equal X-Y axes, would better quantify normality and heart failure severity and would clarify pathophysiology. Consecutive [Formula: see text]-versus-[Formula: see text] values from rest to recovery were displayed on X-Y axes for patients with Class II and IV heart failure and for healthy subjects without heart failure. The displays revealed distinctive patterns for each group, reflecting sequential changes in cardiac output, arterial and mixed venous O(2) and CO(2) content differences, and ventilation ([Formula: see text]). On the basis of exercise tests of 417 healthy subjects, reference formulas for highest [Formula: see text] and [Formula: see text], which normally occur during moderate exercise, are presented. Absolute and percent predicted values of highest [Formula: see text] and [Formula: see text] were recorded for 10 individuals from each group: Those of healthy subjects were significantly higher than those of patients with Class II heart failure, and those of patients with Class II heart failure were higher than those of patients with Class IV heart failure. These values differentiated heart failure severity better than peak [Formula: see text], anaerobic threshold, peak oxygen pulse, and [Formula: see text] slopes. Resting [Formula: see text]-versus-[Formula: see text] values were strikingly low for patients with Class IV heart failure, and with exercise, increased minimally or even decreased. With regard to the pathophysiology of heart failure, high [Formula: see text] values during milder exercise, previously attributed to ventilatory inefficiency, seem to be caused primarily by reduced cardiac output rather than increased [Formula: see text]. CONCLUSION: [Formula: see text]-versus-[Formula: see text] measurements and displays, extractable from future or existing exercise data, separate the 3 groups (healthy subjects, patients with Class II heart failure, and patients with Class IV heart failure) well and confirm the dominant role of low cardiac output rather than excessive [Formula: see text] in heart failure pathophysiology. (J Am Heart Assoc. 2012;1:e001883 doi: 10.1161/JAHA.112.001883.).