Effect of a reduction in blood viscosity on maximal myocardial oxygen delivery distal to a moderate coronary stenosis ALBERT

This study tested the hypothesis that a reduction in blood viscosity by means of isovolumetric hemodilution will permit an increase in maximal oxygen delivery to myocardium distal to a moderate coronary arterial stenosis. It is known that blood viscosity is a determinent of resistance to blood flow at both the stenotic and the arteriolar levels. Accordingly, a reduction in blood viscosity could exert a favorable influence on maximal myocardial oxygen delivery in the setting of stenosis, provided that the oxygen-carrying capacity of the blood is not compromised excessively. Closed-chest, sedated domestic swine (n = 8) were instrumented with an artificial coronary arterial stenosis that reduced vessel diameter by 64%. Measurements of hemodynamics, regional myocardial blood flow (microspheres), lactate and oxygen metabolism, and whole blood viscosity were made at control and after two successive 10 min intracoronary infusions of adenosine (400 and 800 ,ug/min) distal to the stenosis. Next, albumin/saline solution was given intravenously to reduce the animal's hematocrit by approximately 50%. Repeat measurements of all experimental variables were then made at a second control and again after two successive 10 min intracoronary infusions of adenosine (400 and 800 gg/min) distal to the stenosis. Myocardial blood flow (ml/min/g) distal to the stenosis increased from 1.52 + 0.21 (mean 1 SD) to 4.10 0.86 in response to adenosine (peak dose) before hemodilution (p < .01) and from 2.07 + 0.59 to 4.08 + 0.93 (p < .01) after hemodilution. Minimum resistance (mm Hg/ml/min/g) distal to the stenosis, however, was approximately 33% lower (p < .05) during infusion of adenosine after hemodilution than it was before hemodilution (endocardium 15.8 6.3 vs 24.5 14.1 and epicardium 9.0 ± 2.3 vs 14.0 ± 8.0). Maximal oxygen delivery (ml/min/lOOg) to myocardium distal to the stenosis failed to improve and in fact was reduced (p < .01 vs before hemodilution) after hemodilution (34.6 ± 9.5 vs 19.9 ± 6.8 to endocardium and 65.5 ± 16.4 vs 38.0 + 10.5 to epicardium). Regional myocardial lactate metabolism, however, did not change vs initial control during the study. Finally, hematocrit was reduced from 32 3% to 17 + 3% (p < .01) and blood viscosity was reduced from 3.4 ± 0.2 to 2.4 ± 0.3 centipoise (p < .01) by hemodilution. The results of the study indicate that reducing blood viscosity by isovolumetric hemodilution may not enhance maximal myocardial oxygen delivery in the setting of a moderate coronary arterial stenosis. However, because minimal endocardial resistance is lowered by a reduction in blood viscosity, it is likely that maximal oxygen delivery could be improved by this intervention if hemodilution were accomplished with a fluid capable of transporting oxygen (e.g., perfluorocarbon emulsion). Circulation 74, No. 5, 1085-1092, 1986. DELIVERY OF OXYGENATED blood to the myocardium in the setting of a coronary arterial stenosis is influenced by a number of factors. Many of these (e.g., stenosis dimensions, heart rate, and perfusion pressure) have been investigated in considerable detail From the Division of Cardiology, Rhode Island Hospital, and Brown University Program in Medicine, Providence, RI. Supported in part by a grant from the NIH-NHLBI (HL 31664). Address for correspondence: Henry Gewirtz, M.D., Division of Cardiology, Rhode Island Hospital, Providence, RI 02902. Received March 4, 1986; revision accepted July 24, 1986. Vol. 74, No. 5, November 1986 in earlier studies. Rheologic factors, however, have received relatively little attention. It is known that for any given level of flow across a coronary stenosis the pressure gradient required to maintain flow increases as the viscosity of blood increases," 2 and that effective resistance to flow also increases at the arteriolar level as blood viscosity increases.3 4 At shear rates equal to or greater than 100/sec (representative of values observed in the coronary circulation5' 6), blood viscosity is independent of shear rate and is primarily a function of hematocrit and fibrinogen concentration.3 4' 7 These 1085 by gest on N ovem er 2, 2017 http://ciajournals.org/ D ow nladed from