Technical considerations related to the minute ventilation/carbon dioxide output slope in patients with heart failure

Background: The minute ventilation (VE)-carbon dioxide output (Vco(2)) relationship has recently been demonstrated to have prognostic significance in the heart failure (HF) population. However, the, method by which the VE/VCO2 Slope is expressed has been inconsistent. Methods: One hundred eighty-eight subjects, who had received diagnoses of HF, underwent exercise testing. Two VE/VCO2 slope calculations were made, one using exercise data prior to the ventilatory threshold (VT), and one using all data points from rest to peak exercise. Four separate peak exercise VE/VCO2 slope calculations also were derived with unaveraged, 10-s, 30-s, and 60-s ventilatory expired gas sampling intervals. Results: Although univariate Cox regression analysis demonstrated pre-VT and peak VE/VCO2 slope calculations to both be significant predictors of cardiac-related mortality and hospitalization (p < 0.001), the peak classification scheme was significantly better (p < 0.01). The ventilatory expired gas-sampling interval that was used did not impact the predictive ability of the peak VE/VCO2 slope. Conclusion: Although both the pre-VT and peak VE/VCO2 slope calculations were prognostically significant, the peak expression was superior. The sampling interval did not appear to have a significant impact on prognostic utility. We hope that the results of the present study will contribute to the standardization of the VE/VCO2 slope and will enhance its clinical application.