This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Physiology
Orthopnea is heart failure develops due to 
Select and explain. 
A. Reservoir function of pulmonary veins, B. Reservoir function of leg veins, C. Reservoir function of pulmonary arteries, D. Reservoir function of leg arteries
C: Reservoir function of pulmonary arteries
Answer: C: Reservoir function of pulmonary arteries 
Explanation: When a normal individual lies down, the pulmonary blood volume increases by up to 400 mL
When the person stands up this blood is discharged into the general circulation.
This shift is the cause of the decrease in vital capacity in the supine position and is responsible for the occurrence of orthopnea in heart failure.