Regional coronary blood flow in awake resting and pharmacologically stressed dogs

To determine the transmural distribution of blood flow in the major regions of the heart we used the radioactive microsphere method to measure flow in multiple layers of the septum and right and left ventricle in four dogs. Studies were done in awake dogs in the resting, and isoproterenol infusion states, and in the sedated state during methoxamine- and propranolol-induced left ventricular failure. The transmural distribution of right ventricular flow was uniform at rest redistributed to higher midwall flow during isoproterenol infusion, and redistributed to a near linear decrease in flow from the endocardium to epicardium during ventricular failure. Left ventricular transmural flow decreased slightly from the endocardium to epicardium at rest, was near uniform during isoproterenol, but in failure there was a redistribution such that subendocardial flow was approximately twice subepicardial with a near linear decrease across the myocardium. Septal flow distribution tended to follow the absolute right and left ventricular flows. These results demonstrate that the transmural distribution of myocardial blood flow in septum right and left ventricles varies within and between hearts at rest and during isoproterenol and pharmacologically induced left ventricular failure.