CO2 dissociation curve

Describes the relationship between PCO₂ and total CO₂ concentration in blood.

Three Forms of Carbon Dioxide in the Blood

1. Physically dissolved CO₂ (~5%)

Henry’s law : dissolved CO₂ increases linearly with increases in PCO₂

CO₂ solubility = 0.06 mL CO₂/dL blood/mm Hg (20 times higher than O₂ solubility)

2. Carbamino compounds (small)

CO₂ joins reversibly with non-ionized terminal amino groups (-NH₂) of blood borne proteins

3. Lost CO₂ in the blood is transported in the bicarbonate ion form via carbonic anhydrase:

CO₂ + H₂O ⇔ H₂CO3⇔ H+ + HCO₃–

RBCs are source of carbonic anhydrase, and histidine residue of Hb carries the H+

The CO₂ dissassociation curve is linear in shape and steep compared to O₂ dissociation curve. Thus, when increasing ventilation, the CO₂ excretion is increased in lung regions of high and low V/Q ratios. In contrast, increasing ventilation preferentially increases O₂ content of blood in low V/Q ratio areas of lung.

Haldane effect: Deoxygenation of the blood increases its ability to carry carbon dioxide, and vice versa.