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Oxygen-Hemoglobin Dissociation Curve
    * "P 50" reflects the partial pressure value at which hemoglobin reaches 50% saturation.
  • If the curve shifts left or right, the P 50 will change to reflect hemoglobin's altered affinity for oxygen.
  • These changes can be predicted, as follows:
    • Factors that shift the curve to the right decrease hemoglobin's affinity for oxygen, and increase the P50 value; in other words, hemoglobin readily releases oxygen at lower partial pressures.
    • Factors that cause a leftward shift have the opposite effects: affinity is increased, and the P50 value decreases.
Some common causes of shifts include:
  • Increases in carbon dioxide and subsequent decreases in pH are shift the curve to the right; this phenomenon, called the Bohr effect, ensures that oxygen delivery meets tissue demand.
  • Alternatively, a decrease in carbon dioxide and increase in pH will increase affinity; this conserves oxygen when demand is low.
  • Increased body temperature, such as during strenuous activity, oxygen release is made easier, and, vice versa.
  • Increased altitude induces hypoxia, which decreases hemoglobin's affinity for oxygen to ensure oxygen release to the tissues.
  • Fetal hemoglobin (Hemoglobin F) causes a leftward shift; increased affinity facilitates oxygen loading from the maternal blood supply, despite very low placental partial pressure oxygen levels.
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Oxygen-Hemoglobin Dissociation Curve

Oxyhemoglobin dissociation curve
Sigmoid curve demonstrates how hemoglobin saturation changes in response to increasing partial pressure of oxygen.
Steep portion of the curve is due to positive cooperative binding: each time hemoglobin binds an oxygen molecule, its affinity for oxygen increases. It's as if hemoglobin is offered potato chips; after it gets one, it "craves" more.
Healthy systemic arterial blood is nearly 100% saturated.
"P 50" reflects the partial pressure value at which hemoglobin reaches 50% saturation.
Left & Right Shifts:
If the curve shifts left or right, the P 50 will change to reflect hemoglobin's altered affinity for oxygen.
These changes can be predicted, as follows:
    • Factors that shift the curve to the right decrease hemoglobin's affinity for oxygen, and increase the P50 value; in other words, hemoglobin readily releases oxygen at lower partial pressures.
    • Factors that cause a leftward shift have the opposite effects: affinity is increased, and the P50 value decreases.
Some common causes of shifts include:
    • Bohr Effect: Increases in carbon dioxide and subsequent decreases in pH are shift the curve to the right; this phenomenon, called the Bohr effect, ensures that oxygen delivery meets tissue demand.
    • Alternatively, a decrease in carbon dioxide and increase in pH will increase affinity; this conserves oxygen when demand is low.
    • Increased body temperature, such as during strenuous activity, oxygen release is made easier, and, vice versa.
    • Increased altitude induces hypoxia, which decreases hemoglobin's affinity for oxygen to ensure oxygen release to the tissues, and,
Fetal hemoglobin (Hemoglobin F) causes a leftward shift; increased affinity facilitates oxygen loading from the maternal blood supply, despite very low placental partial pressure oxygen levels.

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