Studies on the Changes in Myocardial Oxygen Tension

Abstract

An arterial oxygen tension (PO₂) sensor was used to measure the myocardial PO₂ at three sites in the left ventricle supplied by the paraconal interventricular branch of the left coronary artery, cranial descending coronary artery (CDCA): a subendocardial site, a subepicardial site and an intermediate point in the left ventricular wall. At first, the PO₂ sensor had been compared with the values from a blood gas analyzer. The regression equation Y=1.4×-4.9 with a correlation coefficient of 0.993 indicated a high correlation between these two measurements. The PO₂ of the arterial blood in the left ventricular cavity was assigned an index value of 100%. The PO₂ was about 70% in the subendocardial myocardium, about 15% in the mid-ventricular wall myocardium and 9% in the subepicardial myocardium, demonstrating a decreasing PO₂ gradient from the endocardial to the epicardial surface. A transient occlusion of the CDCA confirmed the pathway of myocardial oxygen supply. In the mid-ventricular and subepicardial myocardium, marked hypoxia occurred after occlusion of the CDCA. Release of the occlusion resulted in a rapid return to the normal PO₂ level. The oxygen supply to these sites is strongly influenced by coronary artery blood flow. The PO₂ in the subendocardial myocardium was not dependent on the cranial descending coronary artery. Oxygen appears to be probably supplied through arterial blood in the left ventricle via the endocardium.