5 CHAPTER Heterogeneous oxygen delivery to consumption matching during graded coronary stenosis in the porcine left ventricle

At rest, myocardial perfusion is reasonably well matched to regional metabolic demand, although both are heterogeneously distributed. Nonuniform regional metabolic vulnerability during coronary stenosis would help to explain nonuniform necrosis during myocardial infarction. We investigated two questions: (1) does the metabolism-perfusion correlation diminish during coronary stenosis? (2) is high basal blood flow and metabolism observed in small regions before stenosis associated with higher metabolic vulnerability during stenosis? Thirty anesthetized male pigs were studied: controls (n=11), Group I (n=6) with coronary perfusion pressure reduction to 70 mmHg; Group II (n=6) with coronary perfusion pressure about 35 mmHg; Group III (n=7) coronary perfusion pressure 45 mmHg combined with adenosine infusion. Regional blood flow was measured with microspheres. [2-13 C]-and [1,2-13 C]-acetate infusion was used to calculate O 2 consumption from NMR spectral multiplets measured for multiple tissue samples of about 100 mg dry mass. Mean myocardial O 2 delivery and consumption decreased during coronary stenosis, but adenosine counteracted this. Whereas regional O 2 delivery correlated to O 2 consumption in controls, this relation was progressively lost with graded coronary hypotension, but partially reestablished by adenosine infusion. Graded coronary stenosis leads to heterogeneous metabolic stress indicated by increasing regional O 2 supply to demand mismatching in myocardium even during incomplete coronary obstruction. However, compared with regions with low blood flow under basal conditions regions with high basal blood flow do not show higher oxygen uptake to supply ratios, and sometimes even tend to show lower ratios, suggesting that they are not more vulnerable and even protected during stenosis.