Optimal hematocrit in an artificial microvascular network

Area of Science:

• Physiology
• Biomedical Engineering
• Hematology

Background:

• Elevated hematocrit increases oxygen transport but also blood viscosity, potentially impairing microvascular flow and tissue oxygenation.
• An optimal hematocrit likely exists to maximize oxygen delivery to tissues.

Purpose of the Study:

• To determine the optimal hematocrit for oxygen delivery in vitro using viscometry and an artificial microvascular network.
• To evaluate the influence of red blood cell (RBC) status (fresh vs. stored) and plasma composition on optimal hematocrit.

Main Methods:

• Viscometry and an artificial microvascular network were used to assess blood viscosity and flow.
• Suspensions of fresh and stored RBCs in plasma, saline, or buffer were tested across a range of hematocrits (10-80%).

Main Results:

• Optimal hematocrit varied significantly with shear rate in viscometry, ranging from 10% to 37.5% for fresh RBCs.
• In the microvascular network, optimal hematocrits for fresh RBCs ranged from 51.1% to 64.6% and for stored RBCs from 46.4% to 66.5%, depending on perfusion pressure.

Conclusions:

• The optimal hematocrit for microvascular oxygen delivery is dependent on perfusion pressure.
• Anemia in chronic conditions with reduced perfusion may be a beneficial adaptation.
• These findings may explain adverse outcomes from RBC transfusions aimed at increasing hematocrit in such patients.