During inspiration, how is venous return to the right heart affected?

• A. Decreases venous return due to higher intrathoracic pressure
• B. Increases venous return due to lower intrathoracic pressure
• C. Venous return is unchanged during inspiration
• D. Increases venous return due to diaphragmatic relaxation

Answer: (B)

During inspiration, the chest expands and the diaphragm contracts, making intrathoracic pressure more negative. That drop in pressure pulls more blood into the thorax from the veins, increasing venous return to the right heart via the vena cavae. The stronger gradient for blood flow into the thoracic cavity enhances right atrial filling and preload. The idea of higher intrathoracic pressure would reduce venous return and is what happens during expiration, not inspiration. And diaphragmatic relaxation would raise intrathoracic pressure, not promote the increased return seen with inspiration.