PADI Divemaster Certification Practice Exam

What happens to oxygen and CO2 levels during breath-hold diving?

1. Oxygen increases, CO2 decreases

2. Oxygen decreases, CO2 increases

3. Both increase

4. Both decrease

The correct answer is: Oxygen decreases, CO2 increases

During breath-hold diving, oxygen levels in the body decrease as the diver utilizes the stored oxygen in the lungs and bloodstream to support metabolic functions. At the same time, carbon dioxide (CO2) levels increase because it is a byproduct of metabolism. When the body uses oxygen for energy, it produces CO2, which is then released into the bloodstream. As the diver holds their breath and oxygen is consumed, the CO2 concentration rises, prompting respiratory drive signals that usually urge the diver to surface and breathe. This physiological response is crucial for maintaining a balance in gas exchange, as high levels of CO2 can trigger distressful sensations and ultimately impact the ability to ascend safely. Understanding this gas exchange is important for divers to manage their breath-hold times and ensure safety during underwater activities.