Impaired oxygen uptake kinetics in heart failure with preserved ejection fraction.

OBJECTIVE

The time needed to increase oxygen utilisation to meet metabolic demand (V̇O 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 V̇O kinetics are slowed in HF with preserved ejection fraction (HFpEF). We tested the hypothesis that V̇O kinetics are slowed during submaximal exercise in HFpEF and that slower V̇O 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, Q̇), ventilatory oxygen uptake (V̇O, Douglas bags) and arterial-venous O difference (a-vO difference) derived from Q̇ and V̇O were assessed during exercise. Breath-by-breath O uptake was measured continuously throughout submaximal exercise, and V̇O kinetics was quantified as mean response time (MRT).

RESULTS

HFpEF patients had markedly slowed V̇O 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 (Q̇: 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 Q̇, and impaired peripheral oxygen extraction that was apparent during submaximal exercise compared with HFpEF with a MRT <60 s (submaximal a-vO difference: MRT <60 s: 9.7±2.1, MRT ≥60 s: 7.9±1.1 mL/100 mL; p=0.03).

CONCLUSION

HFpEF patients have slowed V̇O 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.