The effect of noradrenaline on blood flow and oxygen consumption in normal and ischemic areas of myocardium

Abstract

The effects of infusions of noradrenaline (1.0 μg/Kg./min.) were studied in dogs 2 to 3 hr. after acute ligation of the anterior descending branch of the left coronary artery. The model allowed blood flow to be simultaneously measured in the ischemic (infarcting) region and in the normal myocardium. Sampling blood from a local vein (draining the ischemic region) and from the coronary sinus (draining the normal myocardium) allowed comparisons to be made of oxygen consumption by the two regions. Coronary artery ligation resulted in a marked decrease in cardiac output and external cardiac work and an increase in left ventricular end-diastolic pressure with an unchanged LV dP dt . This is indicative of reduced myocardial contractility. Blood flow in the area supplied by the ligated vessel fell to a mean of 17.6 ± 2.7 ml./100 Gm./min., which is about 20 per cent of the normal flow in this region. Infusing noradrenaline 2 to 3 hr. after ligation increased systemic arterial pressure, LV dP dt max, external cardiac work, and blood flow and oxygen consumption in normal areas of the myocardium. There was some evidence that pulmonary shunting was increased by the drug. Noradrenaline also markedly increased peripheral coronary pressure and blood flow in the ischemic region, as assessed by 133Xenon clearance and by retrograde flow from the ligated vessel. Oxygen consumption in the ischemic region was also increased by noradrenaline. It is suggested that part of the increase in flow occurs in the endocardial region since the effective subendocardial perfusion pressure is increased by noradrenaline. This increase in flow would account for the reduction in infarct size which has been observed by other workers when the systemic arterial pressure is raised.