Which shift on the oxygen affinity curve increases the affinity for O2?

Which shift on the oxygen affinity curve increases the affinity for O2?

• A. Right
• B. Left
• C. No shift
• D. Inverse shift

Answer: (B)

A leftward shift increases oxygen affinity because it moves the oxyhemoglobin dissociation curve to the left, meaning hemoglobin becomes more saturated at any given partial pressure of oxygen. In practical terms, hemoglobin holds onto O2 more tightly, loading it more readily in the lungs (where PO2 is high) but releasing it less readily to tissues (where PO2 is lower). Conditions that promote a left shift include higher pH (alkalosis), lower CO2, lower temperature, and lower 2,3-BPG, as well as fetal hemoglobin. Conversely, a rightward shift decreases affinity and promotes O2 delivery to tissues. So the left shift is the one that increases affinity for O2.

A leftward shift increases oxygen affinity because it moves the oxyhemoglobin dissociation curve to the left, meaning hemoglobin becomes more saturated at any given partial pressure of oxygen. In practical terms, hemoglobin holds onto O2 more tightly, loading it more readily in the lungs (where PO2 is high) but releasing it less readily to tissues (where PO2 is lower). Conditions that promote a left shift include higher pH (alkalosis), lower CO2, lower temperature, and lower 2,3-BPG, as well as fetal hemoglobin. Conversely, a rightward shift decreases affinity and promotes O2 delivery to tissues. So the left shift is the one that increases affinity for O2.