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
Preload measures? 
Select and explain. 
A. End systolic volume, B. End diastolic volume, C. Peripheral resistance, D. Stroke volume
B: End diastolic volume
Answer: B: End diastolic volume 
Explanation: ANSWER: (B) End diastolic volumeREF: Guytons physiology 22nd edition page 111, http://en.wikipedia.org/wiki/Preload_% 28cardiology%29"For cardiac contraction, the preload is usually considered to be the end-diastolic pressure when the ventricle has become filled"Quantitatively, preload can be calculated asLV EDT . LV EDR2hWhere LVEDP = Left ventricular end diastolic pressure, LVEDR = Left ventricular end diastolic radius (at the ventricle s midpoint), and h = thickness of the ventricle. This calculation is based on the Law of Laplace.