Pulmonary gas exchange in relation to exercise pulmonary hypertension in patients with heart failure with preserved ejection fraction.

BACKGROUND

Exercise pulmonary hypertension, defined as a mean pulmonary arterial pressure (mPAP)/cardiac output (Q̇c) slope >3 WU during exercise, is common in patients with heart failure with preserved ejection fraction (HFpEF). However, the pulmonary gas exchange-related effects of an exaggerated exercise pulmonary hypertension (EePH) response are not well defined, especially in relation to dyspnoea on exertion and exercise intolerance.

METHODS

48 HFpEF patients underwent invasive (pulmonary and radial artery catheters) constant-load (20 W) and maximal incremental cycle testing. Haemodynamic measurements (mPAP and Q̇c), arterial blood and expired gases, and ratings of perceived breathlessness (Borg 0-10 scale) were obtained. The mPAP/Q̇c slope was calculated from rest to 20 W. Those with a mPAP/Q̇c slope ≥4.2 (median) were classified as HFpEF+EePH (n=24) and those with a mPAP/Q̇c slope <4.2 were classified as HFpEF (without EePH) (n=24). The alveolar-arterial oxygen tension difference, dead space to tidal volume ratio (Bohr equation) and the minute ventilation to carbon dioxide production slope (from rest to 20 W) were calculated.

RESULTS

Arterial oxygen tension was lower (p=0.03) and dead space to tidal volume ratio was higher (p=0.03) at peak exercise in HFpEF+EePH than in HFpEF. The alveolar-arterial oxygen tension difference was similar at peak exercise between groups (p=0.14); however, patients with HFpEF+EePH achieved the peak alveolar-arterial oxygen tension difference at a lower peak work rate (p<0.01). The minute ventilation to carbon dioxide production slope was higher in HFpEF+EePH than in HFpEF (p=0.01). Perceived breathlessness was ≥1 unit higher at 20 W and peak oxygen uptake was lower (p<0.01) in HFpEF+EePH than in HFpEF.

CONCLUSIONS

These data suggest that EePH contributes to pulmonary gas exchange impairments during exercise by causing a ventilation/perfusion mismatch that provokes both ventilatory inefficiency and hypoxaemia, both of which seem to contribute to dyspnoea on exertion and exercise intolerance in patients with HFpEF.