This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Circulation: Cardiac Output, Venous Return, Subject name: Physiology
End diastolic voIume increases in: 
Select and explain. 
A. Decrease in total blood volume, B. Increase in intrapericardial pressure, C. Increase in negative intrathoracic pressure, D. Decrease in ventricular compliance
C: Increase in negative intrathoracic pressure
Answer: C: Increase in negative intrathoracic pressure 
Explanation: Ans. c. Increase in negative intrathoracic pressure (Ref: Ganong 23/e p515)End diastolic volume increases in conditions associated with increase in negative intrathoracic pressure.Factors Affecting End Diastolic VolumeFactors Decreasing EDVFactors Increasing EDV* Increased intra-pericardial pressureQ (as a result of infection of pressure from a tumor):- Limits the extent to which ventricle can fill* Decrease in ventricular complianceQ:- Increase in ventricular stiffness produced by Ml, infiltrative disease.* Standing decreases venous returnQ* Increased total blood volume increases venous returnQ:* Constriction of vein reduces the size of venous reservoir, decreasing venous pooling and thus increasing venous return* Increased negative intrathoracic pressureQ:* Increases the pressure gradient along which blood flows to the heart* Muscle activityQ: Increases venous return as a result of pumping action