Ventilatory Expired Gas at Constant-Rate Low-Intensity Exercise Predicts Adverse Events and is Related to Neurohormonal Markers in Patients With Heart Failure

Background: Ventilatory efficiency (VE/VCO₂ ratio) and the partial pressure of end-tidal carbon dioxide (P_ETCO₂), obtained during moderate to high levels of physical exertion demonstrate prognostic value in heart failure (HF). The present investigation assesses the clinical utility of these variables during low-intensity exercise. Methods and Results: One hundred and thirty subjects diagnosed with HF underwent a 2-minute, constant-rate treadmill session at 2 miles per hour. Both the VE/VCO₂ ratio and P_ETCO₂ were recorded during exercise (30-second average) and their change (Δ) from rest. B-type and atrial natriuretic peptide (BNP and ANP) were also determined. Only P_ETCO₂ and ΔP_ETCO₂ emerged from the multivariate Cox regression. Receiver operating characteristic curve analysis revealed the prognostic classification schemes were significant with thresholds of </≥34 mm Hg (hazard ratio: 4.2, 95% CI: 2.2-8.0, P < .001) and </≥1 mm Hg (hazard ratio: 3.5, 95% CI: 1.9-6.6, P < .001) being optimal for P_ETCO₂ and ΔP_ETCO₂, respectively. Moreover, subjects with a P_ETCO₂≥34 mm Hg had a significantly lower BNP (214.1 ± 431.9 vs. 1110.5 ± 1854.0 pg/mL, P=.005) and ANP (108.2 ± 103.6 vs. 246.2 ± 200.4 pg/mL, P < .001). Conclusions: The results of this pilot study indicate ventilatory expired gas analysis during a short bout of low-intensity exercise may provide insight into prognosis and cardiac stability.