## Core Concept
Hyperventilation leads to a decrease in carbon dioxide (CO2) levels in the blood, which in turn affects the blood's pH level, making it more alkaline. This condition is known as respiratory alkalosis. The oxygen binding affinity of hemoglobin is influenced by the pH level of the blood, a phenomenon described by the Bohr effect.

## Why the Correct Answer is Right
The Bohr effect states that a decrease in CO2 and the consequent increase in pH (more alkaline conditions) lead to an increase in the oxygen binding affinity of hemoglobin. This means that when the blood pH increases (becomes more alkaline), hemoglobin binds oxygen more tightly, making it less likely to release oxygen to tissues. Conversely, under acidic conditions (decrease in pH), hemoglobin's affinity for oxygen decreases, facilitating the release of oxygen to tissues. Therefore, hyperventilation, by causing a decrease in CO2 levels and an increase in pH, increases the oxygen binding affinity of hemoglobin.

## Why Each Wrong Option is Incorrect
- **Option A:** This option is incorrect because hyperventilation does not decrease the oxygen binding affinity of hemoglobin; rather, it has the opposite effect.
- **Option B:** This option is incorrect because while hyperventilation does affect the blood's CO2 levels and pH, the direct effect on hemoglobin's oxygen binding affinity is an increase, not a decrease.
- **Option C:** This option might seem plausible but is incorrect because it suggests no change, whereas hyperventilation indeed changes the oxygen binding affinity of hemoglobin by altering blood pH.

## Clinical Pearl / High-Yield Fact
A key clinical pearl to remember is that during hyperventilation, despite the increased oxygen binding affinity of hemoglobin, the body's tissues may not receive adequate oxygen due to the reduced CO2 levels affecting respiratory drive and possible vasodilation. However, the primary concern with hyperventilation is usually related to the resultant respiratory alkalosis and potential for causing dizziness or syncope due to cerebral vasoconstriction.

## Correct Answer: B. Increased.