Intrapulmonary shunting occurs when which describes blood flow?

• A. Blood coming from the right side of the heart bypasses nonfunctional alveoli and returns to the left side of the heart in an unoxygenated state.
• B. A decrease in respiratory rate and depth causes carbon dioxide accumulation in the alveoli and a decrease in blood oxygen levels.
• C. The presence of pulmonary surfactant causes a decrease in alveolar surface tension, thus impairing the exchange of gases in the lungs.
• D. Any impairment in circulatory function causes a reduced ability for oxygen and carbon dioxide to diffuse across the alveolar-capillary membrane.

Answer: (A)

Intrapulmonary shunting is about blood that moves from the right side of the heart through the lungs without coming into contact with ventilated alveoli, so it returns to the left heart in an unoxygenated state. This describes blood that bypasses the sites of gas exchange, meaning oxygen can't be picked up and carbon dioxide can't be released, and this venous blood mixes with oxygenated blood in the left heart.

That’s exactly what the description conveys when it says blood from the right side bypasses nonfunctional alveoli and returns unoxygenated. The other options point to different problems: hypoventilation reduces ventilation leading to higher CO2 and lower O2 but involves alveoli that are still participating in gas exchange; the statement about surfactant misstates its role—surfactant lowers surface tension and helps gas exchange, so its presence wouldn’t impair exchange; and diffusion impairment involves problems crossing the alveolar-capillary membrane rather than blood bypassing alveoli.