Cardiac Output and Frank-Starling Law - Anatomy and Physiology

1. What are the three main factors that determine stroke volume?

   Preload, contractility, and afterload.

2. What does the Frank-Starling law of the heart state?

   The more the ventricle is stretched by filling (greater end-diastolic volume), the more forcefully it contracts, so stroke volume rises.

3. How is stroke volume calculated from ventricular volumes?

   Stroke volume = end-diastolic volume minus end-systolic volume ($SV = EDV - ESV$).

4. End-diastolic volume is 160 mL and end-systolic volume is 100 mL. What is the ejection fraction?

   37.5 percent. EF = SV/EDV = 60/160.

5. What is the formula for cardiac output?

   Cardiac output = heart rate times stroke volume ($CO = HR \times SV$).

6. What is preload?

   The degree of ventricular stretch at the end of diastole, mainly set by end-diastolic volume and venous return.

7. A positive inotropic drug increases contractility with end-diastolic volume unchanged. How do end-systolic volume and stroke volume change?

   End-systolic volume falls and stroke volume rises, because the ventricle ejects more of its filling volume.

8. End-diastolic volume is 120 mL and end-systolic volume is 50 mL. What is the stroke volume?

   70 mL: 120 minus 50.

9. Afterload increases from hypertension while preload and contractility stay the same. What happens to stroke volume?

   It decreases. More blood stays in the ventricle (end-systolic volume rises).

10. How does the Frank-Starling mechanism keep left and right ventricular outputs matched?

    If one ventricle receives more venous return, its greater stretch raises its stroke volume, so the two outputs stay equal over time.

11. What is afterload?

    The pressure the ventricle must overcome to eject blood. For the left ventricle this is mainly aortic pressure.

12. Heart rate is 70 beats/min and stroke volume is 70 mL. What is the cardiac output?

    4.9 L/min: 70 times 70 mL = 4,900 mL/min.

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