- * "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.
- 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.
Oxygen-Hemoglobin Dissociation Curve
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The oxyhemoglobin dissociation curve illustrates the relationship between oxygen partial pressure and Hb saturation percentage.
- 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