A SIMPLIFIED ALGORITHM FOR COMPUTING THE VARIATION IN OXYHEMOGLOBIN SATURATION WITH pH, PCO₂, T AND DPG

Abstract

We have modified a model for the oxyhemoglobin equilibrium curve (OHEC) and developed an algorithm for which the nonstandard OHEC can be computed. The model requires 2 parameters and a scaling factor (S_m.) The model parameters are: P*, the oxygen partial pressure where the slope of the OHEC is at its maximum, and a rate parameter K. We estimated P* = 2.76 ± 0.04 SE kPa and K = 0.544 ±0.044 (SE) kPa⁻¹ from ten previous literature reports for the human OHEC at standard conditions (T = 37°C, pH = 7.4, PCO² = 5.33kPa and the molar concentration ratio [DPG7sol;Hb] = 0.9). We also determined how P* and K vary under nonstandard conditions by comparing the modified model with two previous nonstandard OHEC algorithms in the literature. These variations can be characterized by an additional 4 parameters. The dimensionless parameter product KP* was found to be relatively insensitive to deviations from standard conditions. We propose a new algorithm for the nonstandard OHEC which requires a total of 7 parameters, is simpler to implement and is computationally more efficient than other algorithms we investigated.

KEYWORDS:

• DPG
• oxyhemoglobin equilibrium curve
• PCO₂
• pH temperature