If hyperventilation does not adequately increase the O2 supply in the blood during aerobic exercise, what must occur to meet the gas exchange demands?

If hyperventilation does not adequately increase the O2 supply in the blood during aerobic exercise, what must occur to meet the gas exchange demands?

• A. Increased cardiac output
• B. Increased respiratory rate
• C. Increased hemoglobin affinity
• D. Decreased venous return

Answer: (A)

When the muscles demand more oxygen during aerobic work, simply breathing harder (hyperventilating) may not raise the amount of oxygen carried in the blood to a sufficient level. The body compensates by increasing oxygen delivery through the cardiovascular system. Oxygen delivery to tissues depends on two things: how much blood is being pumped (cardiac output) and how much oxygen each unit of blood can carry (arterial O2 content). If arterial O2 content can’t be raised enough by ventilation, increasing cardiac output—by raising heart rate and stroke volume—helps deliver more oxygenated blood to active muscles, meeting the higher gas exchange demands. So, the best response is to boost cardiac output. Increasing respiratory rate alone may improve ventilation but won’t necessarily raise overall oxygen delivery if the arterial oxygen content is limiting. Increasing hemoglobin affinity would help loading in the lungs but hinder unloading to tissues during exercise. Decreasing venous return would lower preload and reduce cardiac output, making the problem worse.

When the muscles demand more oxygen during aerobic work, simply breathing harder (hyperventilating) may not raise the amount of oxygen carried in the blood to a sufficient level. The body compensates by increasing oxygen delivery through the cardiovascular system. Oxygen delivery to tissues depends on two things: how much blood is being pumped (cardiac output) and how much oxygen each unit of blood can carry (arterial O2 content). If arterial O2 content can’t be raised enough by ventilation, increasing cardiac output—by raising heart rate and stroke volume—helps deliver more oxygenated blood to active muscles, meeting the higher gas exchange demands.

So, the best response is to boost cardiac output. Increasing respiratory rate alone may improve ventilation but won’t necessarily raise overall oxygen delivery if the arterial oxygen content is limiting. Increasing hemoglobin affinity would help loading in the lungs but hinder unloading to tissues during exercise. Decreasing venous return would lower preload and reduce cardiac output, making the problem worse.