Prognostic Comparison of the Minute Ventilation/Carbon Dioxide Production Ratio and Slope in Patients with Heart Failure

Abstract

Background: The relationship between minute ventilation (VE) and carbon dioxide production (VCO2) consistently demonstrates prognostic value in patients with heart failure (HF). This relationship has been expressed both as a VE/VCO2 slope during progressive exercise and a ratio at a given time point in previous investigations. Objectives: The purpose of this study was to compare the prognostic value of the VE/VCO2 slope and ratio in a group of patients with HF. Methods: 235 subjects (204 male/31 female) diagnosed with HF underwent exercise testing. Mean age and ejection fraction were 57.5 years (±13.5) and 32.1% (±12.1). The VE/VCO2 slope was calculated using data from the onset of exercise to peak. The VE/VCO2 ratio was calculated using 10-second averaged data at peak exercise. The ability of the VE/VCO2 slope and ratio to predict 1-year cardiac-related mortality and hospitalization were compared. Results: There were 65 hospitalizations and 16 deaths during the 1-year tracking period. Both VE/VCO2 expressions were significant predictors of 1-year cardiac-related hospitalization (χ2: slope = 56.4; ratio = 47.6, p < 0.001) and mortality (χ2: slope = 36.6; ratio = 31.6, p < 0.001). Receiver-operating characteristic curve analysis revealed the predictive power of VE/VCO2 slope and ratio classification schemes were not significantly different (hospitalization = 0.78 vs. 0.75; mortality = 0.87 vs. 0.85). Conclusion: These results indicate that, although not identical, VE/VCO2 slope and ratio provide similar prognostic information. Standardizing expression of the VE/VCO2 relationship may, however, enhance clinical application and should be considered.