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: Medicine
[{'content': 'Pulsus paradoxus is characteristically seen in cardiac tamponade. Absence of pulsus paradoxus is seen when cardiac tamponade is associated with all except one \nSelect and explain. \nA. ASD, B. VSD, C. MR, D. AR', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Mechanism of pulsus paradoxus:\nInspiration → increased RV filling and decreased LV filling\xa0→ left shift of IVS → LV compression and decreased systolic arterial pressure.\nPulsus paradoxus\xa0 is absent\xa0 when cardiac tamponade occurs in a condition which permits equal filling of both ventricles or more filling of LV.\n\nASD= equal filling of both ventricles in both phases of respiration.\nVSD=free communication between ventricles preventing differential filling.\nAR= filling of LV is maintained irrespective of respiration', 'role': 'assistant'}]