*Eur J Appl Physiol.*115(8), 2015. PMID: 26298270 PMCID: PMC4699875

### Abstract

**PURPOSE:**

Equations for blood oxyhemoglobin (HbO2) and carbaminohemoglobin (HbCO2) dissociation curves that incorporate nonlinear biochemical interactions of oxygen and carbon dioxide with hemoglobin (Hb), covering a wide range of physiological conditions, are crucial for a number of practical applications. These include the development of physiologically-based computational models of alveolar-blood and blood-tissue O2-CO2 transport, exchange, and metabolism, and the analysis of clinical and in vitro data.**METHODS AND RESULTS:**

To this end, we have revisited, simplified, and extended our previous models of blood HbO2 and HbCO2 dissociation curves (Dash and Bassingthwaighte, Ann Biomed Eng 38:1683-1701, 2010), validated wherever possible by available experimental data, so that the models now accurately fit the low HbO2 saturation ([Formula: see text]) range over a wide range of values of [Formula: see text], pH, 2,3-DPG, and temperature. Our new equations incorporate a novel [Formula: see text]-dependent variable cooperativity hypothesis for the binding of O2 to Hb, and a new equation for P 50 of O2 that provides accurate shifts in the HbO2 and HbCO2 dissociation curves over a wide range of physiological conditions. The accuracy and efficiency of these equations in computing [Formula: see text] and [Formula: see text] from the [Formula: see text] and [Formula: see text] levels using simple iterative numerical schemes that give rapid convergence is a significant advantage over alternative [Formula: see text] and [Formula: see text] models.**CONCLUSION:**

The new [Formula: see text] and [Formula: see text] models have significant computational modeling implications as they provide high accuracy under non-physiological conditions, such as ischemia and reperfusion, extremes in gas concentrations, high altitudes, and extreme temperatures.