Objective The time needed to increase oxygen utilisation to meet metabolic demand (VO2 kinetics) is impaired in heart failure (HF) with reduced ejection fraction and is an independent risk factor for HF mortality. It is not known if VO2 kinetics are slowed in HF with preserved ejection fraction (HFpEF). We tested the hypothesis that VO2 kinetics are slowed during submaximal exercise in HFpEF and that slower VO2 kinetics are related to impaired peripheral oxygen extraction. Methods Eighteen HFpEF patients (68±7 years, 10 women) and 18 healthy controls (69±6 years, 10 women) completed submaximal and peak exercise testing. Cardiac output (acetylene rebreathing, Qc), ventilatory oxygen uptake (VO2, Douglas bags) and arterial-venous O2 difference (a-vO2 difference) derived from Qc and VO2 were assessed during exercise. Breath-by-breath O2 uptake was measured continuously throughout submaximal exercise, and VO2 kinetics was quantified as mean response time (MRT). Results HFpEF patients had markedly slowed VO2 kinetics during submaximal exercise (MRT: control: 40.1±14.2, HFpEF: 65.4±27.7 s; p<0.002), despite no relative impairment in submaximal cardiac output (Qc: control: 8.6±1.7, HFpEF: 9.7±2.2 L/min; p=0.79). When stratified by MRT, HFpEF with an MRT ≥60 s demonstrated elevated Qc, and impaired peripheral oxygen extraction that was apparent during submaximal exercise compared with HFpEF with a MRT <60s (submaximal a-vO2 difference: MRT <60s: 9.7±2.1, MRT ≥60 s: 7.9±1.1 mL/100 mL; p=0.03). Conclusion HFpEF patients have slowed VO2 kinetics that are related to impaired peripheral oxygen utilisation. MRT can identify HFpEF patients with peripheral limitations to submaximal exercise capacity and may be a target for therapeutic intervention.
All Science Journal Classification (ASJC) codes
- Cardiology and Cardiovascular Medicine