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Myocardial Oxygen Consumption and Segmental Shortening during Selective Coronary Hemodilution in Dogs

Department of Anesthesiology, Illinois Masonic Medical Center and the Departments of Anesthesiology and of Physiology and Biophysics, University of Illinois College of Medicine, Chicago, Illinois. Accepted for publication December 28, 1987

Abstract

Experiments were conducted in 33 open chest, anesthetized dogs to evaluate direct effects ofhemodilution on myocardial oxygenation and contractile function. The left anterior descending coronary artery (LAD) was perfused selectively from a controlled pressure reservoir with either normal arterial blood or arterial blood diluted with lactated Ringer's solution. Systemic hemodynamic parameters were held stable. In the LAD bed, values were obtained for coronary blood flow (CBF) with an electromagnetic flowmeter, myocardial oxygen consumption (MVo₂) using the Fick principle, and percentage segmental shortening (%SS), an index of local myocardial contractility, by sonomicrometry. Studies were conducted with LAD perfusion pressure (PP) set at control(100 mm Hg) and at 50% of that level to simulate coronary insufficiency (CI). CI abolished coronary reactive hyperemia after release of a 90-second occlusion, indicating exhausted vasodilator reserve capacity. With PP at control, reductions in LAD hematocrit to as low as 10% had no effecton MVo₂ or %SS, because increases in blood flow were sufficient to offset induced fallsin arteriovenous oxygen content difference. However, during CI, a more modest reduction in hematocrit to 17% caused reductions in both MVo₂ and %SS, because of inadequate flow responses during hemodilution. The following conclusions can be made: 1) Extreme hemodilution is well tolerated by the normal heart with a stable work requirement and; 2) Relatively modest hemodilution may compromise myocardial oxygenation and contractile function when in the presence of exhausted or severely depleted vasodilator reserve capacity.

Key Words: HEART, BLOOD FLOW—oxygen consumption • BLOOD—hemodilution

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Anesthesia & Analgesia® is published for the International Anesthesia Research Society® by Lippincott Williams & Wilkins with the assistance of Stanford University Libraries' HighWire Press®. Copyright 2006 by the International Anesthesia Research Society. Online ISSN: 1526-7598   Print ISSN: 0003-2999