What happens to venous blood flow to the heart during expiration?

• A. increased
• B. decreased
• C. unchanged
• D. variable

Answer: (B)

During expiration, intrathoracic pressure rises. That higher pressure compresses the thoracic veins, especially the venae cavae, and reduces the pressure gradient that normally drives blood back to the right atrium. The net result is a decrease in venous return to the heart during expiration. (Inspiration lowers intrathoracic pressure and increases venous return, giving the opposite effect.) The decrease during expiration is a normal, transient part of the respiratory cycle and can vary with effort and posture.