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

Area of Science:

• Physiology
• Biophysics
• Biochemistry

Background:

• Human red blood cells (RBCs) are crucial for oxygen (O2) transport.
• Understanding the kinetics of O2 uptake and release by RBCs is vital for physiological studies.
• Previous models have simplified the complex mechanisms of O2 transfer across RBC membranes and within the cell.

Purpose of the Study:

• To simulate and elucidate the O2 transfer kinetics in human RBCs using a detailed biophysical model.
• To identify the rate-limiting steps in O2 transport, including diffusion, convection, and reaction within RBCs.
• To determine unknown model parameters by fitting simulation results to experimental data.

Main Methods:

• Utilized a computational model of a human RBC, represented as a spheric shell.
• Incorporated O2 transport mechanisms: diffusion and reaction within the RBC, and diffusion and convection in the surrounding medium.
• Employed stopped-flow techniques and compared simulation outputs with experimental measurements to calibrate the model.

Main Results:

• Simulations indicated that both diffusion and convection in the medium surrounding the RBC significantly limit overall O2 transfer kinetics during stopped-flow experiments.
• Intraerythrocyte transport mechanisms, primarily O2 diffusion and facilitated O2 diffusion by oxyhemoglobin, become rate-limiting only when external transport resistance is minimized.
• The O2/hemoglobin reaction rate was found to have a lesser limiting effect compared to diffusion within the RBC.

Conclusions:

• Diffusion is the predominant factor limiting O2 uptake and release by human RBCs.
• External O2 transport significantly influences observed kinetics in stopped-flow experiments.
• Stopped-flow techniques can effectively probe intraerythrocyte O2 transport limitations under conditions of minimized external resistance.