The oxygen-hemoglobin dissociation curve shifts to the right (decreased oxygen affinity) in which of the following conditions?
- A Increased pH, decreased PCO2, decreased temperature
- B Decreased pH, increased PCO2, increased temperature, increased 2,3-DPG ✓
- C Carbon monoxide poisoning
- D Fetal hemoglobin (HbF) presence
Correct answer: B. Decreased pH, increased PCO2, increased temperature, increased 2,3-DPG
Explanation
A rightward shift of the O2-Hb dissociation curve decreases O2 affinity, facilitating O2 release to tissues. This occurs with decreased pH (acidosis), increased PCO2 (Bohr effect), increased temperature, and increased 2,3-DPG. These are all conditions present in actively metabolizing tissues. HbF has a leftward shift (binds O2 more avidly, releasing it less readily). CO poisoning causes a leftward shift and also converts hemoglobin to carboxyhemoglobin with reduced O2-carrying capacity.
Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.
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