Haldane effect

Deoxygenated blood can carry increasing amounts of carbon dioxide, whereas oxygenated blood has a reduced carbon dioxide capacity.

The Haldane Effect describes the effect of oxygen on CO₂ transport. The Haldane Effect (along with the Bohr Effect) facilitates the release of O₂ at the tissues and the uptake of O₂at the lungs. This is represented by a right shift of the oxyhemoglobin dissociation curve and a left shift of the oxyhemoglobin dissociation curve respectively. The Haldane Effect results from the fact that deoxygenated hemoglobin has a higher affinity (~3.5 x) for CO₂ than does oxyhemoglobin. Deoxygenated hemoglobin has a higher affinity for CO₂ because it is a better proton acceptor than oxygenated hemoglobin. Therefore, when hemoglobin is deoxygenated (i.e., at tissues) there is a right shift of the carbonic acid-bicarbonate buffer equation to produce H+ which in turn increases the amount of CO₂ which can be carried by the blood back to the lungs to be exhaled. Then, with oxygenation at the lungs CO₂ dissociates more readily from hemoglobin.

CO₂ + H₂O ⇆ H₂CO3 ⇆ H+ + H+CO3-

The following is the general equation of the Haldane Effect

H+ + HbO₂ ←→ H+Hb + O₂

In the end, the Haldane effect allows for approximately 50% of the CO₂ excreted by the lungsand is physiologically much more important than its reciprocal counterpart, the Bohr effect (the effect of carbon dioxide on oxygen transport).