Regarding the oxygen dissociation curve (ODC) and factors that influence it, all of the following statements are correct EXCEPT:

Explanation

## Oxygen Dissociation Curve: Factors and Shifts ### Understanding the Bohr Effect and ODC Shifts **Key Point:** The oxygen dissociation curve describes the relationship between partial pressure of oxygen (PaO₂) and hemoglobin oxygen saturation (SaO₂). Shifts in this curve are critical for oxygen delivery to tissues. ### Analysis of Each Statement | Factor | Effect on ODC | Mechanism | Clinical Significance | |--------|---------------|-----------|----------------------| | Increased P50 | Rightward shift | Decreased Hb-O₂ affinity | Enhanced O₂ unloading to tissues | | Decreased P50 | Leftward shift | Increased Hb-O₂ affinity | Impaired O₂ unloading to tissues | | 2,3-DPG ↑ | Rightward shift | Stabilizes T state of Hb | Better tissue oxygenation | | 2,3-DPG ↓ | Leftward shift | Favors R state of Hb | Reduced tissue oxygenation | | pH ↑ (alkalosis) | Leftward shift | Bohr effect | Reduced O₂ delivery | | pH ↓ (acidosis) | Rightward shift | Bohr effect | Enhanced O₂ delivery | | Temperature ↑ | Rightward shift | Weakens Hb-O₂ bonds | Facilitates unloading | | Temperature ↓ | Leftward shift | Strengthens Hb-O₂ bonds | Impairs unloading | **High-Yield:** The **Bohr effect** encompasses the influence of pH, CO₂, and temperature on oxygen affinity. All three shift the curve rightward in metabolically active tissues (acidosis, hypercapnia, hyperthermia), promoting oxygen release exactly where it is needed. ### Why Statement 2 Is Incorrect **Warning:** This is the trap. Statement 2 claims that **increased 2,3-DPG shifts the ODC LEFT**. This is **FALSE**. - **Increased 2,3-DPG shifts the ODC to the RIGHT** (rightward shift) - 2,3-DPG binds to the central cavity of deoxygenated hemoglobin, stabilizing the T (tense) state - This **decreases** oxygen affinity, making it **easier** for hemoglobin to release oxygen to tissues - A rightward shift means at any given PaO₂, the SaO₂ is lower → oxygen is unloaded more readily **Clinical Pearl:** Chronic hypoxia (high altitude, chronic lung disease) increases 2,3-DPG to shift the curve rightward, improving oxygen delivery despite lower PaO₂. Conversely, stored blood (transfusion) has low 2,3-DPG, causing a leftward shift and reduced oxygen delivery to tissues. ### Verification of Other Statements **Statement 1 (CORRECT):** Rightward shift = increased P50 = decreased affinity = oxygen unloading favored. ✓ **Statement 3 (CORRECT):** Alkalosis (pH ↑) causes leftward shift via Bohr effect, increasing affinity. ✓ **Statement 4 (CORRECT):** Hyperthermia causes rightward shift, promoting oxygen release in warm (metabolically active) tissues. ✓ **Mnemonic:** **"CADET, face Right!"** — CO₂ ↑, Acid ↑, DPG ↑, Exercise (heat) → Rightward shift. Opposite = Leftward.