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STROKE VOLUME

Stroke volume: The amount of blood pumped by the left ventricle of the heart in one contraction. The stroke volume is not all the blood contained in the left ventricle; normally, only about two-thirds of the blood in the ventricle is expelled with each beat. Together with the heart rate, the stroke volume determines the output of blood by the heart per minute (cardiac output).

or simply put,

Stoke volume is the amount of blood that is pumped out of the heart at every beat. There are two ways to find Stroke volume. If the cardiac output and the heart is known, the stroke volume can be found using this equation:

stroke volume = cardiac output / heart rate.

Another way to determine the Stroke volume is to subtrack the end systolic volume from the end diastolic volume. Thus you take the volume at the end of relaxation, and subtract the amount of blood that is left in the heart after contraction.

Both end diastolic volume and end systolic volume effect the stroke volume. The can be effected by the amount of venous flow into the heart, the heart rate, total peripheral resistance, starlings law, and ventrical contractility.

Sample Problems:

Question #1:

If a heart fills up to 200ml of blood before contraction, and leaves 50ml in the heart after contraction, what is the stroke volume? If heart rate was 80 beats per minute, what would the cardiac output be? Question #2:

if the total peripheral resistance goes up, what is likely to happen to the stroke volume?

Answers:

Answer #1:

a) 150ml/beat

b) 12 L/minute

Answer #2:

The stroke volume will go down.


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