The top figure (A) shows the CO2 dissociation curves for blood of different O2 saturations. Note that oxygenated blood carries less CO2 for the same PCO2. The bottom figure (B) shows the "physiological" curve between arterial (a) and mixed venous (v) blood.
Data from: West JB (Ed), Respiratory Physiology, 5th ed, Williams &Wilkins, Baltimore, MD 1995.
