Mechanical Increase of Vascular Resistance in Experimental Myocardial Infarction with Shock

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Abstract
The hemodynamic and cardiac metabolic effects of increasing central aortic pressure by obstructing the abdominal aorta with a balloon catheter introduced via a femoral artery were determined in 28 anesthetized dogs with acute myocardial infarction and shock produced by coronary embolization with plastic spheres. Following coronary embolization, aortic pressure, cardiac output, and left ventricular mechanical efficiency declined in all animals; left ventricular "excess lactate" appeared in about one-half. With abdominal aortic obstruction for 1 hour, there were significant elevations of postembolic aortic pressure, coronary flow, cardiac output, left ventricular oxygen consumption and mechanical efficiency. Left atrial pressure rose slightly but not beyond normal limits. Arterial-coronary sinus oxygen difference diminished, and left ventricular excess lactate diminished or disappeared in 60% of the animals in which it was noted in the postembolic state. After 1 hour of abdominal aortic obstruction, cardiac output, central aortic pressure, and coronary flow diminished moderately. It is concluded that mechanical increase of vascular resistance for periods up to 1 hour may improve myocardial performance in acute myocardial infarction with shock. The increased left ventricular oxygen needs are met adequately by the increase of coronary flow associated with the increase of perfusion pressure.