AEMCA Practice Exam

Which of the following factors leads to a left shift in the oxygen dissociation curve?

1. Increase in 2,3 DPG, increase in CO2, acidosis

2. Decrease in temperature, decrease in 2,3 DPG, alkalosis

3. High levels of carbon dioxide, low pH, increased DPG

4. Increase in pH, increase in temperature, decrease in hemoglobin

The correct answer is: Decrease in temperature, decrease in 2,3 DPG, alkalosis

A left shift in the oxygen dissociation curve signifies an increased affinity of hemoglobin for oxygen, meaning that hemoglobin holds onto oxygen more tightly and releases it less readily to the tissues. The factors that contribute to this leftward shift include a decrease in temperature, a decrease in 2,3 DPG, and alkalosis (an increase in pH). When the temperature is lower, hemoglobin's affinity for oxygen increases, preventing its release. Similarly, lower levels of 2,3 DPG—an important metabolite that promotes the release of oxygen from hemoglobin—lead to an increased bond strength between hemoglobin and oxygen, further enhancing the likelihood of hemoglobin being saturated with oxygen. Lastly, alkalosis, or a rise in pH, also promotes this leftward shift; a higher pH reduces the release of hydrogen ions, which can compete with oxygen for binding on hemoglobin, thus enhancing hemoglobin's affinity for oxygen. In contrast, the other choices involve factors that would typically cause a right shift or have no significant effect on the curve's position. Increased levels of carbon dioxide (hypercapnia), acidosis (lower pH), and higher temperatures generally result in a right shift, as they promote the release of