If alkalosis occurs with lower temperature and CO2, what shift on the O2 affinity curve occurs?

• A. Right shift
• B. No shift
• C. Left shift
• D. Inverted shift

Answer: (C)

Oxygen binding to hemoglobin rises and falls with pH, CO2, and temperature. Alkalosis raises the pH, and when CO2 is low and the temperature is cooler, each of these factors increases hemoglobin’s affinity for oxygen. This tightens binding and shifts the dissociation curve to the left, meaning a lower p50 and more O2 bound at the same PO2. In practical terms, loading of O2 in the lungs is favored under these conditions. The opposite shifts occur with higher CO2, lower pH (acidosis), or higher temperature, which move the curve to the right and promote easier O2 release to tissues.