- Stroke volume
Stroke volume (SV) is the volume of
blood pumped by the right/left ventricle of the heart in one contraction. Specifically, it is the volume of blood ejected from ventricles during systole.The stroke volume is not all of the blood contained in the left 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
Its value is obtained by subtracting
end-systolic volume (ESV) fromend-diastolic volume (EDV) for a given ventricle::
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
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 ), andafterload .Exercise
Prolonged
aerobic exercise training may also increase stroke volume, which frequently results in a lower (resting) heart rate. Reduced heart rate prolongs ventriculardiastole (filling), increasing end-diastolic volume, and ultimately allowing more blood to be ejected.Preload
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
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 inaortic stenosis andarterial hypertension .ee also
*
End-diastolic volume
*End-systolic volume
*Heart rate References
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*External links
* [http://www.cardiovascular.cx The Gross Physiology of the Cardiovascular System]
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