The hemoglobin-oxygen association -dissociation curve (ODC) is "S" shaped, or sigmoidal (Figure 1.09). The saturation of hemoglobin with oxygen increases with an increasing partial pressure of oxygen, reaching approximately 98% at 100 mmHg. A shift to the right of the ODC means that a higher partial pressure of oxygen will have to be present in order to achieve the same saturation; i.e. the affinity of the hemoglobin for oxygen is less.
Since the P50 value is that partial pressure of oxygen that yields 50% saturation of the hemoglobin, an increasing P50 value will also indicate a decreased hemoglobin affinity for oxygen.
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