Oxygen transfer of red blood cells: experimental data and model analysis

Kinetics of O2 uptake and release by human red blood cells (RBC) as measured by stopped-flow techniques were simulated using an RBC model shaped as a spheric shell. The O2 transfer mechanisms in this model include diffusion and reaction within the RBC and diffusion and convection in the medium surrounding the RBC. Unknown model parameters were determined by comparing simulations with experimental data. The following conclusions were drawn. (1) Both diffusion and convection contribute to O2 transport in the medium surrounding the RBC, and this transport importantly limits the overall O2 transfer kinetics in stopped-flow experiments. (2) Intraerythrocyte transport mechanisms become predominant in limiting O2 transfer, and can thus be investigated by stopped-flow techniques, only when the perierythrocyte O2 transport resistance is minimized, e.g. by high levels of dithionite in measurements of O2 release from RBC. (3) Intraerythrocyte O2 transfer is shown to be mainly limited by diffusion of O2 and, to a lesser extent, by diffusion of oxyhemoglobin ('facilitated O2 diffusion') and by O2/hemoglobin reaction. The results suggest that diffusion is the main process limiting O2 uptake and release by RBC, the finite reaction kinetics of O2 with hemoglobin exerting a smaller limiting effect.