The role of facilitated diffusion in oxygen transport by cell-free hemoglobins: implications for the design of hemoglobin-based oxygen carriers Original Research Article

We compared rates of oxygen transport in an in vitro capillary system using red blood cells (RBCs) and cell-free hemoglobins. The axial Po2 drop down the capillary was calculated using finite-element analysis. RBCs, unmodified hemoglobin (HbA0), cross-linked hemoglobin (αα-Hb) and hemoglobin conjugated to polyethylene-glycol (PEG-Hb) were evaluated. According to their fractional saturation curves, PEG-Hb showed the least desaturation down the capillary, which most closely matched the RBCs; HbA0 and αα-Hb showed much greater desaturation. A lumped diffusion parameter, K*, was calculated based on the Fick diffusion equation with a term for facilitated diffusion. The overall rates of oxygen transfer are consistent with hemoglobin diffusion rates according to the Stokes–Einstein Law and with previously measured blood pressure responses in rats. This study provides a conceptual framework for the design of a ‘blood substitute’ based on mimicking O2 transport by RBCs to prevent autoregulatory changes in blood flow and pressure.