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
Which of the following hemodynamic changes is not evident in cardiac tamponade during diastole? 
Select and explain. 
A. Right atrial and ventricular collapse, B. Absent y wave on JVP, C. Biphasic venous return, D. Elevated pericardial pressure
C: Biphasic venous return
Answer: C: Biphasic venous return 
Explanation: 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.