ORIGINAL RESEARCH A Simple New Visualization of Exercise Data Discloses Pathophysiology and Severity of Heart Failure

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 (V̇O2/V̇E–versus–V̇CO2/V̇E), plotted on equal X–Y axes, would better quantify normality and heart failure severity and would clarify pathophysiology. Consecutive V̇O2/V̇E–versus–V̇CO2/V̇E 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 O2 and CO2 content differences, and ventilation (V̇E). On the basis of exercise tests of 417 healthy subjects, reference formulas for highest V̇O2/V̇E and V̇CO2/V̇E, which normally occur during moderate exercise, are presented. Absolute and percent predicted values of highest V̇O2/V̇E and V̇CO2/V̇E 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 V̇O2, anaerobic threshold, peak oxygen pulse, and V̇E/V̇CO2 slopes. Resting V̇O2/V̇E–versus–V̇CO2/V̇E 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 V̇E/V̇CO2 values during milder exercise, previously attributed to ventilatory inefficiency, seem to be caused primarily by reduced cardiac outpu