This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: C.V.S., Subject name: Medicine
[{'content': 'Which of the following hemodynamic changes is not evident in cardiac tamponade during diastole? \nSelect and explain. \nA. Right atrial and ventricular collapse, B. Absent y wave on JVP, C. Biphasic venous return, D. Elevated pericardial pressure', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Ans. is \'c\' i.e., Biphasic venous return Hemodynamics of cardiac Tamponade inDiastole* During the diastole the pericardial pressure remains elevated.* It is greater than the intracavitary pressure thus there is no filling during the diastole.* The absence of venous return during the diastole leads to absence of "y" waves on the /. V.P. and the "diastolic collapse" of the right atria and ventricle.Systole* During systole, the decrease in size of the heart due to ventricular contraction reduces the pericardial pressure.* Thus in cardiac tamponade heart filling occurs only in systole.* So, the venous return in cardiac tamponade is unimodal instead of the normal biphasic mode.* The ventricular contraction causes the atria to relax and produce the "x" wave of the J.V.P.', 'role': 'assistant'}]