The initial increase in cardiac output in anemia is not driven by voluntary muscle ischemia, but likely by the metabolic needs of the brain and heart.
Challenges muscle ischemia as anemia output trigger; leaves open central metabolism as driver needing human validation.
Simultaneous measurements of the blood flow through the human forearm and of the arteriovenous oxygen difference of forearm blood have shown that in moderate anemia the need for oxygen was met by an increase in the arteriovenous oxygen difference without increase in blood flow. When the hemoglobin fell below 4 gm.% the blood flow rose. In subjects in whom the blood flow had increased, the venous oxygen saturation was below 15%. Cardiac output has been shown to increase when the hemoglobin falls below 8 gm.%. It is concluded that the initial increase in heart output is not due to ischemia of voluntary muscle but is required for maintaining the metabolism of the brain and the heart itself.
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Vérel et al. (1959) studied this question.
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