Contribution of central and peripheral factors at peak exercise in heart failure patients with progressive severity of exercise limitation

Background A reduced cardiac output (CO) response during exercise is a major limiting factor in heart failure (HF). Oxygen consumption (VO₂) is directly proportional to CO. Peripheral mechanisms via arteriovenous oxygen difference (Δ(a-v)O₂) play a pivotal role in chronic HF. We hypothesized a weak correlation between peak VO₂ and peak CO with a greater Δ(a-v)O₂ variability in most severe HF. Methods We analyzed 278 HF patients (NYHA II–III) who performed maximal cardiopulmonary exercise test with non-invasive CO measurement by inert gas rebreathing. Results Median peakVO₂, CO and Δ(a-v)O₂ were 0.96 (0.78–1.28) L/min, 6.3 (5.1–8.0) L/min and 16.0 (14.2–18.0) mL/100 mL respectively, with a linear relationship between VO₂ and CO: CO = 5.3 × VO₂ + 1.13 (r² = 0.705, p < 0.001). Patients were grouped according to exercise limitation. Group 1 (101 patients) peakVO₂ < 50% pred: peakVO₂ 0.80 (0.67–0.94) L/min, peakCO 5.6 (4.7–6.5) L/min, peakΔ(a-v)O₂ 14.8 (12.9–17.1) mL/100 mL. Group 2 (89 patients) peakVO₂ ≥ 50–<65% pred: peakVO₂ 1.02 (0.84–1.29) L/min, peakCO 6.4 (5.1–8.0) L/min, peakΔ(a-v)O₂ 16.7 (15.0–18.5) mL/100 mL. Group 3 (88 patients) peakVO₂ ≥ 65% pred: peakVO₂ 1.28 (0.93–1.66) L/min, peakCO 8.0 (6.2–9.7) L/min, peakΔ(a-v)O₂ 16.8 (14.6–18.3) mL/100 mL. A peakVO₂ and peakCO linear relationship was observed in Group 1 (r² = 0.381, p < 0.001), Group 2 (r² = 0.756, p < 0.001) and Group 3 (r² = 0.744, p < 0.001). Conclusions With worsening HF we observed a progressive reduction of peak CO and peak VO₂. However in most compromised patients also peripheral mechanisms play a role as indicated by reduced Δ(a-v)O₂.