Oxygen tension (PaO2) has what effect on the position of the oxyhemoglobin dissociation curve?

Oxygen tension (PaO2) has what effect on the position of the oxyhemoglobin dissociation curve?

• A. It strongly shifts the curve to the right
• B. It has minimal effect on the curve position
• C. It shifts the curve to the left at high PaO2
• D. It reverses the Bohr effect

Answer: (B)

The position of the oxyhemoglobin dissociation curve reflects how tightly hemoglobin holds onto oxygen, i.e., its affinity. PaO2 mainly determines how much oxygen is bound at a given affinity, so changing PaO2 moves you along the same curve rather than shifting the curve itself. What actually shifts the curve left or right are factors that alter hemoglobin’s affinity: the Bohr effect describes how pH and CO2 can move the curve (increased CO2 or decreased pH shifts it to the right, decreasing affinity; the opposite shifts it to the left, increasing affinity). Temperature and 2,3-BPG levels also modulate affinity similarly. So oxygen tension has minimal effect on the curve’s position; it changes saturation along the curve depending on the ambient affinity.

The position of the oxyhemoglobin dissociation curve reflects how tightly hemoglobin holds onto oxygen, i.e., its affinity. PaO2 mainly determines how much oxygen is bound at a given affinity, so changing PaO2 moves you along the same curve rather than shifting the curve itself.

What actually shifts the curve left or right are factors that alter hemoglobin’s affinity: the Bohr effect describes how pH and CO2 can move the curve (increased CO2 or decreased pH shifts it to the right, decreasing affinity; the opposite shifts it to the left, increasing affinity). Temperature and 2,3-BPG levels also modulate affinity similarly.

So oxygen tension has minimal effect on the curve’s position; it changes saturation along the curve depending on the ambient affinity.