This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Cardiac Output, Subject name: Physiology
Cardiac output increases due to: 
Select and explain. 
A. Decrease in intrathoracic pressure, B. Decrease in blood volume, C. Decreased ventricular compliance, D. Decreased mean systemic filling pressure
A: Decrease in intrathoracic pressure
Answer: A: Decrease in intrathoracic pressure 
Explanation: Option A: Thoracic pump: Option B: Decreased blood volume - decreased mean systemic filling pressure (Psf)-decreased venous return Option C: Decreased ventricular compliance will decrease the ability of ventricle to accumulate blood during diastole - decreased EDV Option D: Decreased filling, decreases EDV Factors maintaining CO: Hea rate (chronotropic effect) Stroke volume Venous return or EDV or preload Force of contraction (inotropic effect) determines ESV Afterload, determined by total peripheral resistance (TPR)