Venous Return and Muscle Pump in Prolonged Sitting

Steps:

• Blood returns to the heart via veins, aided by skeletal muscle contractions that compress veins and push blood upward.
• In veins, one-way valves prevent backflow, but without muscle activity, blood pools in lower extremities.
• Prolonged sitting in aircraft reduces leg muscle contractions, leading to venous stasis and fluid leakage into tissues.
• This causes edema (swelling) in the legs due to increased hydrostatic pressure.

Why A is correct:

• Leg muscle contractions act as a "peripheral pump" to propel venous blood against gravity, per circulatory physiology; fewer contractions impair this mechanism, causing blood pooling and swelling.

Why the others are wrong:

• B: Heart rate remains normal or elevates slightly in flight due to stress, not reduced from lack of exercise.
• C: Arterial pressure is unchanged and sufficient to deliver blood; the issue is venous return, not arterial force.
• D: Vein valves function normally but cannot compensate without muscle action to fill and propel blood forward.

Final answer: A