Stroke volume calculation: which expression is correct?

Stroke volume calculation: which expression is correct?

• A. SV = EDV + ESV
• B. SV = ESV − EDV
• C. SV = EDV − ESV
• D. SV = CO ÷ HR

Answer: (C)

Stroke volume is the amount of blood ejected with each heartbeat, determined by the difference between the volume in the ventricle at the end of filling (end-diastolic volume) and the volume remaining after contraction (end-systolic volume). Because the ventricle fills to EDV and contracts down to ESV, the amount ejected equals EDV minus ESV. That is why the correct expression is EDV − ESV. For example, with EDV around 120 mL and ESV around 50 mL, stroke volume is about 70 mL. The other forms don’t represent the ejected volume. Adding EDV and ESV isn’t meaningful for stroke volume. Reversing the subtraction yields a negative value, which can’t represent a volume. The relation involving cardiac output and heart rate (CO = SV × HR) is true, but it’s a different way to relate SV to overall output and rate, not the direct ventricular-volume subtraction that defines stroke volume.

Stroke volume is the amount of blood ejected with each heartbeat, determined by the difference between the volume in the ventricle at the end of filling (end-diastolic volume) and the volume remaining after contraction (end-systolic volume). Because the ventricle fills to EDV and contracts down to ESV, the amount ejected equals EDV minus ESV. That is why the correct expression is EDV − ESV. For example, with EDV around 120 mL and ESV around 50 mL, stroke volume is about 70 mL.

The other forms don’t represent the ejected volume. Adding EDV and ESV isn’t meaningful for stroke volume. Reversing the subtraction yields a negative value, which can’t represent a volume. The relation involving cardiac output and heart rate (CO = SV × HR) is true, but it’s a different way to relate SV to overall output and rate, not the direct ventricular-volume subtraction that defines stroke volume.