Myocardial blood flow

Objectives: The myocardium of the left ventricle exhibits spatial heterogen eity of blood flow under physiological conditions. This study was designed to investigate, whether oxygen supply is jeopardized in low flow areas (blo od flow <50% of mean) under physiological conditions and whether areas of h igh flow (>150% of mean) exihibit perfusion in excess of demand ("luxury pe rfusion"). Methods: The study was performed in anesthetized and ventilated beagle dogs . Local blood flow was reduced by mechanically narrowing of the r.circumfle xus of the left coronary artery; myocardial blood flow was measured by the tracer-microsphere technique, free concentrations cellular adenosin by the SAM-technique, regional metabolism of substrates by the desoxyglucose-techn ique. Results: Low flow areas exhibited normal oxygenation of the myocardium, whi le in high flow areas no luxury perfusion could be demonstrated. Conclusion: Myocardial blood flow and metabolism demonstrate significant sp atial heterogeneity. There appears to be no absolute threshold of blood flo w where regional myocardial ischemia develops. Probably biochemical evidenc e of myocardial ischemia is determined by a local ratio of oxygen supply an d demand.