[Effect of 10% carbon dioxide on regional myocardial tissue oxygen tension and myocardial metabolism]

Abstract

We investigated the effects of arterial carbon dioxide tension on myocardial blood flow, tissue oxygen tension and metabolism in the anesthetized dogs. Eighteen adult mongrel dogs weighing 13.4 +/- 3.6 kg were anesthetized with 0.5% isoflurane, intubated and ventilated mechanically with 50% oxygen to maintain normocapnia. Endtidal CO2 fraction (FECO2) was monitored continuously by capnograph. Regional myocardial tissue PO2 was measured using a monopolar polarographic needle electrode inserted to the myocardium. Electromagnetic blood flow probes were applied on the left anterior descending artery and circumflex artery. For cardiac venous blood sampling, a 23G intravenous catheter was inserted into the cardiac veins (great coronary veins) carefully. After normocapnic ventilation, hypocapnia was induced by increasing the respiratory rate, and hypercapnia was induced by adding 10% carbon dioxide to the inspired gas. The coronary blood flow and myocardial tissue oxygen tension increased during hypercapnia and the myocardial lactate extraction decreased, while excess lactate and cardiac venous L/P ratio increased during hypercapnia. These results indicate that hypercapnia increase coronary flow and myocardial tissue oxygen tension but myocardial aerobic metabolism is impaired during hypercapnia.