Cardiac cycle, ECG readings, and Equations

Question 1

What is SV?

Answer 1

EDV - ESV, L of blood pumped per beat per contraction.

Question 2

Typical SV values

Answer 2

60-80ml per beat.

Question 3

What is CO?

Answer 3

SV x HR, L of blood ejected from the L ventricle per minute.

Question 4

Typical CO values

Answer 4

4.8 - 6.4 l/min

Question 5

What is EF?

Answer 5

SV / EDV, the fraction of blood leaving the left ventricle per contraction relative to the total amount of blood prior to contraction.

Question 6

Typical EF values

Answer 6

50-70%, circa 60%

Question 7

Frank-Starling Law

Answer 7

It says that the more the heart muscle is stretched (due to increased blood volume), the more forcefully it will contract. This increases the stroke volume, and consequently, cardiac output.

• If venous return (the amount of blood returning to the heart) increases, End-Diastolic Volume (EDV) increases.
• As the ventricle stretches due to the increased EDV, it causes the muscle fibers to stretch more, which increases the force of contraction and therefore the stroke volume (SV).
• An increase in SV means that cardiac output (CO) also increases, helping the body cope with greater demands for blood flow (such as during exercise).