SV is the volume of blood ejected by the ventricle with a single contraction and can be defined as the difference between the end-diastolic volume and the end-systolic volume in the following equation:
Figure HE.24 Force-velocity curve for isolated muscle fibre
The normal SV is between 70 and 80 ml and may be normalized to take account of body size by dividing by body surface area (BSA). This gives a stroke index (SI) which is for a 70 kg normal person (BSA = 1.7 m2) is 30-65 ml/beat/m2. SV can also be given as a percentage of the EDV. It is then called ejection fraction (EF), a formula for is:
The normal EF is about 60-65% and is a useful index of ventricular contractility.
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