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.