The stroke work output of the heart is the amount of
energy that the heart converts to work during each
heartbeat while pumping blood into the arteries. Minute
work outputis the total amount of energy converted to
work in 1 minute; this is equal to the stroke work output
imes the heart rate per minute.
Work output of the heart is in two forms. First, by far
he major proportion is used to move the blood from
he low-pressure veins to the high-pressure arteries.
This is called volume-pressure work or external work.
Second, a minor proportion of the energy is used to
accelerate the blood to its velocity of ejection through
he aortic and pulmonary valves. This is the kinetic
energy of blood flow component of the work output.
Right ventricular external work output is normally
about one sixth the work output of the left ventricle
because of the sixfold difference in systolic pressures
hat the two ventricles pump. The additional work
output of each ventricle required to create kinetic
energy of blood flow is proportional to the mass of
blood ejected times the square of velocity of ejection.
Ordinarily, the work output of the left ventricle
equired to create kinetic energy of blood flow is only
about 1 per cent of the total work output of the ventri-
cle and therefore is ignored in the calculation of the
otal stroke work output. But in certain abnormal con-
ditions, such as aortic stenosis, in which blood flows with
great velocity through the stenosed valve, more than
50 per cent of the total work output may be required to
create kinetic energy of blood flow.