What happens to oxygen transport during extreme physical activity?

• A. It becomes diffusion limited
• B. It is enhanced
• C. It remains perfusion limited
• D. It decreases significantly

Answer: (A)

During extreme physical activity, oxygen transport can indeed become diffusion limited in certain situations, particularly due to the high demand for oxygen by the muscles. This scenario occurs when the rate of oxygen consumption exceeds the rate at which oxygen can diffuse from the alveoli in the lungs into the bloodstream.

In a well-functioning respiratory system at rest or during moderate exercise, oxygen transport is typically perfusion limited, meaning that sufficient blood flow allows for complete equilibration of oxygen between the alveoli and the blood. However, during intense physical exertion, the increased metabolic demand can lead to situations where the diffusion capacity of the lungs and the rate of blood flow may not satisfy the high oxygen requirements of the muscles. As a result, the process can shift to being diffusion limited, as the ability of oxygen to enter the blood from the alveoli becomes the factor that limits oxygen transport rather than simply the amount of blood or perfusion present.

This distinction highlights the body’s physiological response to varying exercise intensities and illustrates the complexities involved in gas exchange under different conditions of physical stress.