The `P_(50)` value decreases in all of the following conditions,except

Options

A. Fall in ` pCO_2`
B. Increase in BPG level
C. Fall in temperature
D. Fall in `[H^+]` ions

Answer

To solve the question regarding the conditions under which the P50 value decreases, we need to understand what P50 represents and how various factors affect hemoglobin's affinity for oxygen.

### Step-by-Step Solution:

1. **Understanding P50**:
- P50 is defined as the partial pressure of oxygen at which 50% of hemoglobin is saturated with oxygen. A lower P50 value indicates a higher affinity of hemoglobin for oxygen, while a higher P50 value indicates a lower affinity.

2. **Factors Affecting P50**:
- Several factors can influence the P50 value:
- **Increased Temperature**: Raises metabolic activity, leading to a rightward shift in the dissociation curve (decreases affinity, increases P50).
- **Increased CO2 Levels (pCO2)**: Also causes a rightward shift, decreasing affinity and increasing P50.
- **Increased H+ Ion Concentration (Lower pH)**: This is known as the Bohr effect, which decreases affinity and increases P50.
- **Increased 2,3-Diphosphoglycerate (2,3-DPG)**: This compound binds to hemoglobin and promotes oxygen release, decreasing affinity and increasing P50.

3. **Conditions That Decrease P50**:
- Conversely, conditions that would decrease the P50 value (increase affinity) include:
- **Decreased Temperature**: Lower temperatures favor oxygen binding, shifting the curve to the left (decreases P50).
- **Decreased CO2 Levels (pCO2)**: Lower levels increase affinity, shifting the curve to the left (decreases P50).
- **Decreased H+ Ion Concentration (Higher pH)**: This also increases affinity, shifting the curve to the left (decreases P50).
- **Increased Oxygen Partial Pressure**: Higher oxygen levels can shift the curve to the left, increasing affinity (decreases P50).

4. **Identifying the Exception**:
- The question asks for the condition that does not decrease the P50 value. Based on the factors discussed, any option that indicates increased temperature, increased CO2, increased H+ concentration, or increased 2,3-DPG would be the conditions that do not decrease P50.

5. **Conclusion**:
- After analyzing the options provided in the question, the correct answer is the one condition that does not lead to a decrease in P50, thus maintaining or increasing the affinity of hemoglobin for oxygen.