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Abstract
Subendocardial ischemia with patent coronary arteries is recognized increasingly as
a cause of previously unexplained cardiac failure. Subendocardial muscle flow is diastolic,
and subendocardial oxygen delivery is determined by oxygen content as well as coronary
blood flow. Hemodilution (open-heart surgery, refusal of transfusion) reduces oxygen
content by acutely lowering the hemoglobin levels; this study assesses its effects
on the adequacy of myocardial oxygen delivery. In ten anesthetized dogs, we produced
anemia by exchanging blood with a dextran solution while measuring aortic and left
atrial blood pressure, cardiac output, coronary blood flow, and endocardial and epicardial
EKG's. Myocardial blood flow distribution, aortic blood pressure, and cardiac output
remained normal with hemoglobins ranging from 14 to 5 Gm. percent. Myocardial oxygen
delivery was maintained by increasing coronary blood flow from 75 to 127 c.c. per
100 Gm. per minute. Coronary flow became redistributed away from subendocardial muscle
(P < 0.025) and myocardial failure occurred with hemoglobins below 5 Gm. percent.
Failure was associated with ischemic endocardial EKG's despite total left ventricular
coronary blood flow increasing to 310 percent above control levels. We conclude that
(1) oxygen delivery to the entire left ventricle remains adequate over a wide range
of hemoglobin levels in normal hearts, and (2) subendocardial ischemia and cardiac
failure occur when coronary blood flow becomes maldistributed and cannot compensate
for decreased oxygen-carrying capacity of the blood. We would expect these adverse
changes to occur at higher hemoglobin levels with valvular or ischemic heart disease,
abnormal circulatory dynamics, or increased myocardial oxygen requirement.
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Article info
Publication history
Accepted:
January 7,
1974
Footnotes
☆This study was supported by Grants-in-Aid from the Wilbur May Foundation, Frank W. Clark Charities, and the United States Public Health Service.
Identification
Copyright
© 1974 Published by Elsevier Inc.
