A simple new visualization of exercise data discloses pathophysiology and severity of heart failure

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.).

Keywords: cardiac output; exercise; heart failure; oxygen; ventilation.

Figure 1.

Displays of concurrent 90-s averages of O₂ uptake and CO₂ output, both divided by exhaled ventilation (–versus–) during cardiopulmonary exercise testing from rest through early recovery, with “+” and “×” showing transitions between rest and exercise and exercise and recovery. Vertical and horizontal dashed lines are reference highest and highest . A, Healthy 38-year-old man with peak 106% of predicted. B, Healthy 52-year-old woman with peak 101% of predicted. Note that with exercise, both numerators increase more than denominators until reaching highest and then highest before rapid declines, especially in values, during high-intensity exercise and recovery. C, Fifty-seven-year-old woman (NYHA Class II) with moderate left heart failure, oscillatory breathing, and peak 63% of predicted. The shape of the early exercise pattern is reasonable, but the highest and are well below normal. The rise in during the transition to recovery is abnormal. D, Seventy-three-year-old man (NYHA class IV) with peak 21% of predicted who died several weeks later. All values are very low. The resting, exercise, and recovery values overlay each other and on magnification can be seen to oscillate. Immediate movement to the lower left at the onset of exercise is an ominous pattern. E and F, Left heart failure in 64-year-old man before and after treatment. Raw data were obtained every 30 s rather than 10 s. In E, values move to the left ( is decreasing) and upward with exercise. After treatment, peak values increased from 45% to 66% of predicted. In F, resting values start higher and move upward and to the right (indicating is also increasing) before moving leftward. In both studies, the highest occurred when ≈21 L/min, at which time was 25×21=≈520 mL/min (E) and was 370×21=≈780 mL/min (F). Thus, this 50% increase in from E to F was primarily due to increased perfusion, not increased ventilation.