Coronary reperfusion: Effects of hyperosmotic mannitol

Abstract

The purpose of this study was to determine the effects of hyperosmotic mannitol on coronary hemodynamics, regional myocardial contractility, and the distribution of myocardial blood flow during coronary reperfusion in anesthetized, thoracotomized dogs. A portion of the left ventricle was rendered ischemic by occlusion of the left anterior descending coronary artery for two hours. During reperfusion, mannitol was infused intravenously at a rate which increased serum osmolality by approximately 40 mOsm./Kg. Coronary resistance in the reperfused vasculature increased progressively during reperfusion, in spite of mannitol treatment increasing by 45 per cent above the pre-occlusion control value after four hours of reflow. Minimal resistance in the reperfused coronary vascular bed, representing the passive or structural component of resistance, also increased progressively during reperfusion. Regional myocardial blood flow was measured with radiolabelled microspheres at five minutes, two hours, and four hours of reperfusion. At five minutes of reperfusion, myocardial blood flow was elevated in all regions of the left ventricle. After two hours of reperfusion, in spite of mannitol treatment, blood flow to the reperfused region was more severely reduced, and a transmural gradient of flow favoring the subepicardium existed. Blood flow in the reperfused region was further reduced at four hours of reperfusion, and the transmural flow gradient persisted. Regional contractility in the superficial and deep myocardial fibers, measured with Walton-Brodie strain gauges, diminished during reperfusion. However, contractility in the deep fibers was more severely depressed than that in the superficial fibers. This study demonstrated that treatment with hyperosmotic mannitol did not prevent the progressive increase in coronary vascular resistance or the selective underperfusion of the subendocardium during coronary artery reperfusion.