Normalization for peak oxygen uptake increases the prognostic power of the ventilatory response to exercise in patients with chronic heart failure

Background: Peak exercise oxygen uptake (peak VO 2) and ventilation to CO 2 production (VE/VCO 2) slope are established prognostic indicators in patients with chronic heart failure (CHF). A high VE/VCO 2 slope, however, does not take into account the level of physical performance as expressed by peak VO 2. We hypothesized that the prognostic value of a high VE/VCO 2 slope may be improved by normalization for peak VO 2 (VE/VCO 2/VO 2). Methods: One hundred patients with CHF underwent pulmonary function tests at rest (spirometry and lung diffusion capacity) and maximal cardiopulmonary exercise testing. The prognostic value of VE/VCO 2 slope, peak VO 2 and VE/VCO 2/VO 2 was probed prospectively. Results: Twenty-one patients died from cardiac reasons during a mean follow-up of 26 ± 19 months. Nonsurvivors, compared to survivors, showed a lower peak VO 2 (13.6 ± 4.0 vs 17.5 ± 4.1 mL · min -1 · kg -1, P < .01) and a steeper VE/VCO 2 slope (43 ± 11 vs 31.6 ± 5.0, P < .01). Nonetheless, in patients whose VE/VCO 2 slope exceeded 34 (upper normal limit), there was no correlation with peak VO 2 (r = -35, P = not significant). Interestingly 35% of them showed a normal exercise performance (peak VO 2 ≥18 mL · min -1 · kg -1). At multivariate analysis, the VE/VCO 2 slope showed a prognostic power stronger than that of peak VO 2; however, the VE/VCO 2/VO 2 index retained a prognostic power greater than that of both VE/VCO 2 slope and peak VO 2. A VE/VCO 2/VO 2 ≥2.4 signaled cases at higher risk. Conclusions: Discrepancies between VE/VCO 2 slope and peak VO 2 may generate uncertainty. Normalization of the former by the latter improves outcome prediction and may be considered a simple and effective way for maximizing the clinical applicability of these 2 indicators.