During expiration, how does the flow in the subclavian veins typically change?

• A. Flow increases markedly
• B. Flow stops
• C. Flow remains non-pulsatile
• D. Flow slows and decreases but remains pulsatile

Answer: (D)

The flow pattern in central chest veins like the subclavian is phasic with breathing because intrathoracic pressure changes alter the driving gradient for venous return. During expiration, the intrathoracic pressure rises, which reduces the pressure gradient toward the heart and slows the venous flow. However, the flow does not stop and continues to reflect the cardiac cycle, so it remains pulsatile. This combination—slower flow with a pulsatile waveform—is the typical pattern seen during expiration. In contrast, inspiration lowers intrathoracic pressure and tends to increase venous return, making the flow faster, though still pulsatile.