Exercise-induced arterial hypoxaemia in patients with heart failure with preserved ejection fraction.

Some patients with heart failure with preserved ejection fraction (HFpEF) have demonstrated evidence of exercise-induced arterial hypoxaemia (EIAH). However, EIAH was not quantified using $S_{a{O}_2}$ , $P_{a{O}_2}$ , and $P_{A-a{O}_2}$ measurements as previously conducted in healthy adults nor was EIAH quantified alongside simultaneous measurements of pulmonary vascular pressures, cardiorespiratory responses, or dyspnoea on exertion (DOE) in these patients. Given the effects of hypoxaemia on pulmonary vasoconstriction, cardiorespiratory responses, and DOE, we tested the hypothesis that patients with HFpEF and EIAH (EIAH⁺) would demonstrate higher pulmonary vascular pressures, worse oxygen uptake, and greater DOE compared with patients without EIAH (EIAH^-). Sixty patients with HFpEF underwent invasive (pulmonary and radial artery catheters) constant-load (20 W) and maximal incremental cycle testing. Pulmonary vascular measures (pulmonary artery catheter), arterial blood (radial artery catheter) and expired gases, and ratings of breathlessness (RPB, Borg 0-10) were assessed. EIAH was characterized by one or more of the following criteria: (1) $S_{a{O}_2}$  < 93% during exercise, (2) $P_{A-a{O}_2}$  ≥ 25 mmHg from rest to exercise or (3) $P_{a{O}_2}$  ≥ 10 mmHg from rest to exercise. About 25 patients had EIAH (EIAH⁺) and 35 did not have EIAH (EIAH^-). mPAP, PCWP, and pulmonary vascular resistance were similar between groups at rest, 20 W, and peak exercise. Although all cardiorespiratory responses were similar between groups at rest, 20 W, and peak exercise, RPB was greater in EIAH⁺ throughout rest and peak exercise. Our findings suggest that EIAH has no effect on central haemodynamics and is likely to be a consequence of pulmonary gas exchange abnormalities including ventilation-perfusion mismatch. KEY POINTS: Patients with HFpEF present with a high incidence (42%) of exercise-induced arterial hypoxaemia, which is likely to be a consequence of hypoventilation and ventilation-perfusion mismatching of the lung during exercise. Despite significant impairment in gas exchange and reductions in arterial oxygen, patients with exercise-induced arterial hypoxaemia did not have an augmented haemodynamic response to exercise but consistently reported increased feelings of breathlessness.