Adair-based hemoglobin equilibrium with oxygen, carbon dioxide and hydrogen ion activity

Abstract

As has been known for over a century, oxygen binding onto hemoglobin is influenced by the activity of hydrogen ions (H⁺), as well as the concentration of carbon dioxide (CO₂). As is also known, the binding of both CO₂ and H⁺ on terminal valine-1 residues is competitive. One-parametric situations of these hemoglobin equilibria at specific levels of H⁺, O₂ or CO₂ are also well described. However, we think interpolating or extrapolating this knowledge into an ‘empirical’ function of three independent variables has not yet been completely satisfactory. We present a model that integrates three orthogonal views of hemoglobin oxygenation, titration, and carbamination at different temperatures. The model is based only on chemical principles, Adair's oxygenation steps and Van't Hoff equation of temperature dependences. Our model fits the measurements of the Haldane coefficient and CO₂ hemoglobin saturation. It also fits the oxygen dissociation curve influenced by simultaneous changes in H⁺, CO₂ and O₂, which makes it a strong candidate for integration into more complex models of blood acid-base with gas transport, where any combination of mentioned substances can appear.

Key Words::

• Acid-base equilibrium
• blood gas analysis
• carboxyhemoglobin
• hemoglobin A
• oxyhemoglobins

Acknowledgements

In addition, the authors want to thank doc. MUDr. Jiří Kofránek, CSc, and Prof. MUDr. Emanuel Nečas, DrSc, for critical review and Austin Schaefer for English language editing.

This work was supported by grants from the Ministry of Industry and Trade of the Czech Republic: MPO TIP TI3/869 – Virtual patient for medical education; and by The Ministry of Education, Youth and Sports via the grant SVV-2014-260033.

Declaration of interest: The authors report no conflict of interest. The authors alone are responsible for the content and writing of the paper.