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
[{'content': 'Orthopnea is heart failure develops due to \nSelect and explain. \nA. Reservoir function of pulmonary veins, B. Reservoir function of leg veins, C. Reservoir function of pulmonary arteries, D. Reservoir function of leg arteries', 'role': 'user'}, {'content': 'Answer: C \nExplanation: When a normal individual lies down, the\xa0pulmonary blood volume increases by up to 400 mL\nWhen the person stands up this blood is discharged into the general circulation.\nThis shift is the cause of the decrease in vital capacity in the supine position and is responsible for the occurrence of\xa0orthopnea in heart failure.', 'role': 'assistant'}]