MYOCARDIAL OXYGENATION IN DOGS DURING PARTIAL AND COMPLETE CORONARY-ARTERY OCCLUSION

Regional myocardial oxygenation was assessed during partial and.comple te coronary artery occlusion using near infrared spectroscopy. In eigh t open-chest dogs, partial occlusions resulting in an almost-equal-to 42% decrease in left anterior descending coronary artery (LAD) blood f low produced an almost-equal-to 21% decrease in tissue O2 stores (tiss ue oxyhemoglobin plus oxymyoglobin) and no change in the oxidation lev el of mitochondrial cytochrome aa3. An almost-equal-to 81% reduction i n LAD blood flow produced nadir levels of tissue oxyhemoglobin plus ox ymyoglobin, maximal levels of deoxyhemoglobin plus deoxymyoglobin, a d ecline in tissue blood volume, and an almost-equal-to 39% decrease in cytochrome aa3 oxidation level. These changes were associated with an almost-equal-to 52% decrease from the preischemic baseline in mean tra nsmural myocardial blood flow, measured by radiolabeled microspheres, and an almost-equal-to 41% decrease in myocardial O2 consumption. Comp lete occlusion resulted in further decreases in myocardial blood flow, O2 consumption, tissue blood volume, and cytochrome aa3 oxidation sta te but also produced increases in tissue O2 stores to above the nadir levels noted during partial occlusion. These results indicate that dec reases in O2 delivery during partial coronary occlusion increase O2 ex traction to sustain mitochondrial O2 availability, but as little as a 52% reduction in myocardial blood flow produces maximal O2 extraction and depletion of tissue O2 stores. Mitochondrial O2 availability is re stricted further during complete occlusion because of limited O2 deliv ery and, possibly, decreases in tissue blood volume and O2 extraction.