Background Impaired right ventricular (RV) myocardial blood flow (MBF) has been associated with RV dysfunction and fatal RV failure in idiopathic pulmonary hypertension during stress. MBF and O₂ extraction from myocardial capillaries (O₂ extraction fraction (OEF)) influence myocardial O₂ supply.

Objective To determine how the baseline RV OEF affects the amount of MBF increase induced by supine exercise, the authors hypothesise that higher baseline OEF (H-OEF) results in limited O₂ extraction during exercise and that MBF must therefore be increased to obtain sufficient O₂.

Methods In 18 patients with idiopathic pulmonary hypertension, baseline OEF, resting MBF and exercise-induced MBF at 40% of maximal cardiopulmonary exercise testing load were measured using positron emission tomography and [¹⁵O]O₂, [¹⁵O]H₂O and [¹⁵O]CO.

Results For the whole population, exercise increased RV MBF from 0.68±0.16 to 1.13±0.38 ml/min/g (p<0.0001). The MBF exercise-to-rest ratio (reserve) was 1.7±0.7. The median baseline OEF was 0.73 at which the patient population was split into H-OEF and lower baseline OEF (L-OEF). Baseline MBF values (0.61±0.11 and 0.74±0.17 ml/min/g, respectively) were similar, and exercise induced a significant MBF increase in both groups (p=0.0001). However, exercise-induced increase in MBF was significantly less in the H-OEF group than in the L-OEF group (0.97±0.30 and 1.30±0.39 ml/min/g, respectively, p<0.05). Moreover, H-OEF patients had lower baseline stroke volume and cardiac output than the L-OEF group (52±19 ml and 4.0±1.1 l/min vs 78±18 ml and 5.5±0.9 l/min, respectively, both p<0.05).

Conclusions H-OEF patients were hemodynamically poorer and showed a lower exercise-induced MBF increase compared to L-OEF patients, suggesting exercise-induced O₂ supply limitation.