Mathematical Formulation of CO₂ Dissociation Curve and Buffer Line of Human Blood at Rest

抄録

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·P^B_CO2
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 [HCO^-₃] and pH was also expressed by using only one parameter. Next, between Cb and [HCO^-₃] obtained at the same P_CO2 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.