During inspiration, which best describes the change in flow from the upper extremity to the subclavian vein?

• A. Flow reverses direction
• B. Flow remains unchanged
• C. Flow increases from the upper extremity to the SCV
• D. Flow decreases from the upper extremity to the SCV

Answer: (C)

Inspiration lowers intrathoracic pressure, creating a stronger gradient that pulls venous blood toward the heart. The diaphragm contracts and the chest expands, making the thoracic cavities more negative. This enhances venous return from peripheral veins, including the upper extremity, into central veins such as the subclavian vein. Since the subclavian vein drains toward the heart, the flow from the upper extremity to the SCV increases during inspiration. The one-way venous valves prevent backflow, so the net effect is increased forward flow toward the heart, not reversal or no change.