The P50 of normal hemoglobin is approximately

The P50 of normal hemoglobin is approximately

• A. 19 mm Hg
• B. 26-27 mm Hg
• C. 31 mm Hg
• D. 35 mm Hg

Answer: (B)

P50 is the partial pressure of oxygen at which hemoglobin is 50% saturated with O2. For normal adult hemoglobin, that PO2 is about 26–27 mm Hg. This value reflects the oxygen affinity of hemoglobin under typical physiological conditions: when PO2 falls to around the mid-20s, half of the binding sites are occupied. A lower P50 indicates higher affinity (left shift), meaning oxygen is loaded more readily in the lungs, while a higher P50 indicates lower affinity (right shift), meaning unloading in tissues is favored. The numbers 19 mm Hg would imply a stronger than normal affinity, whereas 31–35 mm Hg would imply a weaker than normal affinity. Therefore, the normal P50 is approximately 26–27 mm Hg.

P50 is the partial pressure of oxygen at which hemoglobin is 50% saturated with O2. For normal adult hemoglobin, that PO2 is about 26–27 mm Hg. This value reflects the oxygen affinity of hemoglobin under typical physiological conditions: when PO2 falls to around the mid-20s, half of the binding sites are occupied. A lower P50 indicates higher affinity (left shift), meaning oxygen is loaded more readily in the lungs, while a higher P50 indicates lower affinity (right shift), meaning unloading in tissues is favored. The numbers 19 mm Hg would imply a stronger than normal affinity, whereas 31–35 mm Hg would imply a weaker than normal affinity. Therefore, the normal P50 is approximately 26–27 mm Hg.