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

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Abstract
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 determinant 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 micrograms/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 micrograms/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 less than .01) and from 2.07 +/- 0.59 to 4.08 +/- 0.93 (p less than .01) after hemodilution.(ABSTRACT TRUNCATED AT 250 WORDS)