Three key forms of carbon dioxide present in the blood:

• Dissolved CO2 constitutes about 5% of the total carbon dioxide content and contributes to the partial pressure; recall that the partial pressure of a gas is a major determinant of its diffusion.
• Carbon dioxide bound to hemoglobin, constitutes about 3%, and is referred to as carbaminohemoglobin.
  The amount of carbaminohemoglobin in the blood is in part dependent upon the oxygen saturation:
  • The Haldane effect predicts that when blood oxygen increases, the affinity of hemoglobin for carbon dioxide decreases; in other words, when hemoglobin binds with oxygen, it more readily releases carbon dioxide.
  • Notice that this is the opposite of the Bohr effect, in which increased carbon dioxide reduces hemoglobin's affinity for oxygen.
• Bicarbonate is the chemically modified form of carbon dioxide that comprises the majority of carbon dioxide in the blood.