DOT Certification Practice Exam

What happens to PaO2 levels as altitude increases?

1. It remains constant

2. It decreases

3. It increases

4. It fluctuates

The correct answer is: It decreases

As altitude increases, the partial pressure of oxygen (PaO2) decreases due to the reduction in atmospheric pressure. At sea level, atmospheric pressure is higher, resulting in a greater partial pressure of oxygen available for absorption in the lungs. However, as one ascends to higher altitudes, the total atmospheric pressure drops, which directly reduces the amount of oxygen available in each breath and impairs the diffusion of oxygen into the bloodstream. This phenomenon is a key principle of respiratory physiology, illustrating how environmental factors such as altitude affect gas exchange. While the concentration of oxygen in the air remains constant (around 21% at different altitudes), the significant drop in atmospheric pressure means that PaO2 levels will decrease, leading to potential issues such as hypoxia if the ascent is rapid or if an individual is not acclimatized.