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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Overview[edit]
Stroke volume is the amount of blood pumped by the left ventricle of the heart in one
contraction.
The stroke volume is not all of the blood contained in the left ventricle. The heart does not pump all the blood out of the ventricle. Normally, only about two-thirds of the blood in the ventricle is put out with each beat. What blood is actually pumped from the left ventricle is the stroke volume and it, together with the heart rate, determines the
cardiac output.
Calculation[edit]
Its value is obtained by subtracting
end-systolic volume [ESV] from end-diastolic volume [EDV] for a given ventricle:
SV = EDV - ESV
In a healthy 70-kg man, the left ventricular EDV is 120 ml and the corresponding ESV is 50 ml, giving a stroke volume of 70 ml.
Determinants[edit]
Men, on average, have higher stroke volumes than women due to the larger size of their hearts. However, stroke volume depends on several factors such as heart size,
contractility, duration of contraction, preload [end-diastolic volume], and
afterload.
Exercise[edit]
Prolonged aerobic exercise may also increase stroke
volume, which frequently results in a slower heart rate. Reduced heart rate prolongs ventricular diastole [filling], increasing end-diastolic volume, and ultimately allowing more blood to be ejected.
Preload[edit]
Stroke volume is intrinsically controlled by preload [the degree to which the ventricles are stretched prior to contracting]. An increase in the volume or speed of venous return will increase preload and, through the
Frank-Starling law of the heart, will increase stroke volume. Decreased venous return has the opposite effect, causing a reduction in stroke volume.
Afterload[edit]
Elevated afterload [commonly measured as the aortic pressure during systole] reduces stroke volume. Though not usually affecting stroke volume in healthy individuals, increased afterload
will hinder the ventricles in ejecting blood, causing reduced stroke volume. Increased afterload may be found in aortic stenosis and arterial hypertension.
See
also[edit]
- Cardiac output
- End-diastolic volume
- End-systolic volume
- Heart rate
References[edit]
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External links[edit]
- The Gross Physiology of the Cardiovascular System
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Template:WikiDoc Sources
How is SV measured?
Stroke volume is calculated using measurements of ventricle volumes from an echocardiogram and subtracting the volume of the blood in the ventricle at the end of a beat [called end-systolic volume] from the volume of blood just prior to the beat [called end-diastolic volume].
What are the 3 factors that determine stroke volume?
There are three variables affecting stroke volume, which include contractility, preload, and afterload. [8] The definition of contractility is the force of myocyte contraction, referred to as the heart's inotropy.
What is the accurate formula of stroke volume?
This is called the stroke volume or SV, and the formula is: [stroke volume [SV]=end diastolic volume [EDV]–end systolic volume [ESV]].
How do you calculate stroke volume and heart rate?
Therefore, we can use the equation CO = HR x SV. This equation tells us that the cardiac output equals the heart rate [HR], which is the number of heartbeats per minute, times the stroke volume [SV], which is the volume of blood pumped by the ventricles with each heartbeat.