Alkalemia is a disease associated with an abnormal increase in the pH of a patient's blood due to rapid breathing (hyperventilation). How would alkalemia affect the oxygen binding affinity of the patient's hemoglobin?

• A. P₅₀ and oxygen affinity decrease.
• B. P₅₀ and oxygen affinity increase.
• C. P₅₀ decreases and oxygen affinity increases.
• D. P₅₀ increases and oxygen affinity decreases.
• E. P₅₀ and oxygen affinity remain the same.

Answer: (C)

Verified step by step guidance

1. Understand the Bohr effect: The Bohr effect describes how pH and carbon dioxide concentration affect the oxygen binding affinity of hemoglobin. An increase in pH (alkalemia) typically increases hemoglobin's affinity for oxygen.
2. Recognize the relationship between pH and hemoglobin: In conditions of alkalemia, the blood pH is higher than normal, which stabilizes the R state (relaxed state) of hemoglobin, enhancing its ability to bind oxygen.
3. Consider the P50 value: P50 is the partial pressure of oxygen at which hemoglobin is 50% saturated. A decrease in P50 indicates an increased affinity for oxygen, as less oxygen is needed to achieve 50% saturation.
4. Apply the concept to the problem: With alkalemia, the increased pH leads to a decrease in P50, meaning hemoglobin binds oxygen more tightly, thus increasing oxygen affinity.
5. Conclude the effect: Therefore, in alkalemia, the P50 decreases and the oxygen affinity of hemoglobin increases, aligning with the correct answer provided.