Explain the increase of Hb concentration on O2 Hb dissociation curve

Here's why:

1. What the Curve Represents: The O₂-Hb dissociation curve plots the percentage saturation of hemoglobin with oxygen against the partial pressure of oxygen (PO₂). It describes the affinity of hemoglobin for oxygen and how readily it binds or releases oxygen.
2. Increased Hb Concentration: If the concentration of hemoglobin in the blood increases (e.g., in polycythemia), it means there are simply more hemoglobin molecules available to bind oxygen.
3. Effect on Oxygen Carrying Capacity: This leads to an increase in the total oxygen-carrying capacity of the blood. For any given PO₂, the blood can carry a greater absolute amount of oxygen because there are more "seats" (hemoglobin molecules) available.
4. No Change in Affinity: However, the affinity of each individual hemoglobin molecule for oxygen, and thus the percentage of hemoglobin saturated at a given PO₂, remains unchanged. The curve itself, which illustrates this percentage saturation, does not shift left or right.

Therefore, while an increased Hb concentration allows the blood to transport more oxygen overall, it does not alter the fundamental relationship between PO₂ and hemoglobin saturation, meaning the O₂-Hb dissociation curve itself does not shift.