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Overview :
Each contraction of the heart
results in an ejection of blood termed the stroke volume. The amount of blood
pumped per contraction compared to the maximum left ventricular volume prior to
contraction is the ejection fraction, which is a measure of the effectiveness
of the heart as a pump.
The amount of blood pumped over a
unit of time is the cardiac output. These can be divided to by the body surface
area (BSA) which approximates blood volume and body size, thus allowing an
index that can be used to compare individual patients.
stroke volume =
=
((end diastolic volume) - (end systolic volume))
stroke volume index =
= (stroke volume) / (body surface
area)
ejection fraction =
= ((stroke volume) * (100%)) /
(end diastolic volume)
= ((end diastolic volume) - (end
systolic volume)) * (100%)) / (end diastolic volume)
cardiac output =
= (stroke volume) * (heart rate)
cardiac index =
= (stroke volume) * (heart rate) /
(body surface area)
Interpretation:
• The normal stroke volume index:
40-50 mL per contraction per square meter BSA.
• The normal cardiac output: 3-7
liters per minute.
• The normal cardiac index: 2.5 - 4.5 liters per min per square meter
BSA.
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