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/VCO(2) slope is expressed has been inconsistent.
METHODS: One hundred eighty-eight subjects, who had received diagnoses of HF, underwent exercise testing. Two VE/VCO(2) 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/VCO(2) 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/VCO(2) 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/VCO(2) slope.
CONCLUSION: Although both the pre-VT and peak VE/VCO(2) 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/VCO(2) slope and will enhance its clinical application.