左室心筋局所酸素代謝の実験的検討

Left ventricular contraction progresses from the apex to the base, and because the base has a large internal diameter than the apex, the workload of the left ventricular wall is greater at the base. However, many studies have revealed that the level of regional myocardial blood flow is the same in all areas of the left ventricle. This fact strongly suggests that oxygen metabolic levels differ along the long axis of the left ventricle. To clarify the differences in local oxygen metabolism of the left ventricle, regional myocardial oxygen uptake of the left ventricle was examined in the anesthetized open chest dog. Small polyethylene catheters were inserted into the veins of the lateral, the antero-basal, the mid-anterior and the apical wall of the left ventricle. Venous blood samples were collected anaerobically, and blood gases and oxygen saturation were analyzed as aortic blood. The regional myocardial oxygen uptake of the left ventricle was not homogeneous. It was higher at the base and lower at the apex indicating that the differences in the workload and oxygen demand of the left ventricular wall were met by different levels of oxygen extraction. With left atrial pacing, a small increase in myocardial oxygen demand was compensated for by increased myocardial blood flow without changes in regional oxygen extraction. In contrast, continuous intravenous infusion of isoproterenol increased both myocardial flow and regional oxygen extraction in the middle and apical wall, while the extraction of the lateral wall did not change. Differences in the extraction between each area became smaller with isoproterenol infusion, but the gradient of myocardial oxygen uptake still existed. These findings suggest that the basal area of the left ventricle has a smaller reserved capacity of oxygen extraction.