Page 20, Turbulence & Rheology, Dr. D. Penney

Circulatory Design (continued..)

Finally, let us consider the best concentration for the packets in the blood, i.e. the optimal hematocrit (Figure 6.07). As hematocrit rises, oxygen content increases directly because hemoglobin is being added per unit of blood. On the other hand, rising hematocrit depresses cardiac output because of the increased work required by the heart to move the more viscous fluid through peripheral resistance. At the opposite extreme, high cardiac output is possible at low hematocrit due to the low viscosity of the blood. The oxygen content of such blood however is low.

Thus the effects of hematocrit on blood oxygen content and on cardiac output are directly opposite. The optimal hematocrit in terms of maximal oxygen transport lies somewhere in between, a compromise between low and high hematocrit. Oxygen transport is the product of cardiac output and blood oxygen content. Optimal hematocrit lies between 35% and 60%.

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