Mathematical formulation of CO2 dissociation curve and buffer line of human blood at rest.

The CO2 content and pH of tonometered blood were measured in nine healthy subjects. The CO2 content in the whole blood (Cb) was found to be expressed by an exponential function of PCO2 including only one parameter (B) as follows: Cb = 1.15 . B-2.548 . PBCO2. The B value was specific to the sampled blood and ranged from 0.4 to 0.45 in the deoxygenated and from 0.45 to 0.52 in the oxygenated blood. The relationship between pH and log PCO2 was also expressed by using one characteristic parameter (D) as follows: for the deoxygenated blood, log PCO2 = 2.144-D . (pH-7.045), and for the oxygenated blood, log PCO2 = 2.037-D . (pH-7.085). The D values were in a range of 1.38 to 1.58. The linear relation between log [HCO3-] and pH was also expressed by using only one parameter. Next, between Cb and [HCO3-] obtained at the same PCO2 of 40 mmHg, a high correlation was observed: the regression line was given, independently of O2 saturation, by Cb40 = 1.942 . [HCO3-]40-3.193, where [HCO3-] was expressed in mM. Using the above equations, it was possible to evaluate the approximate B and D values from a pair of pH and PCO2 measurements and subsequently to depict the CO2 dissociation curve as well as the buffer line in the true plasma.