Incardiovascular physiology,stroke volume (SV) is the volume ofblood pumped from theventricle per beat. Stroke volume is calculated using measurements of ventricle volumes from anechocardiogram and subtracting the volume of the blood in the ventricle at the end of a beat (calledend-systolic volume[note 1]) from the volume of blood just prior to the beat (calledend-diastolic volume). The termstroke volume can apply to each of the two ventricles of the heart, although when not explicitly stated it refers to the left ventricle and should therefore be referred to asleft stroke volume (LSV). The stroke volumes for each ventricle are generally equal, both being approximately 90 mL in a healthy 70-kg man. Any persistent difference between the two stroke volumes, no matter how small, would inevitably lead to venous congestion of either the systemic or the pulmonary circulation, with a corresponding state of hypotension in the other circulatory system. A shunt (seepatent foramen ovale andatrial septal defect) between the two systems will ensue if possible to reestablish the equilibrium.
Stroke volume is an important determinant ofcardiac output, which is the product of stroke volume andheart rate, and is also used to calculateejection fraction, which is stroke volume divided by end-diastolic volume. Because stroke volume decreases in certain conditions and disease states, stroke volume itself correlates with cardiac function.[citation needed]
| Ventricular volumes | ||
|---|---|---|
| Measure | Right ventricle | Left ventricle |
| End-diastolic volume | 144 mL (± 23 mL)[1] | 142 mL (± 21 mL)[2] |
| End-diastolic volume / body surface area (mL/m2) | 78 mL/m2 (± 11 mL/m2)[1] | 78 mL/m2 (± 8.8 mL/m2)[2] |
| End-systolic volume | 50 mL (± 14 mL)[1] | 47 mL (± 10 mL)[2] |
| End-systolic volume / body surface area (mL/m2) | 27 mL/m2 (± 7 mL/m2)[1] | 26 mL/m2 (± 5.1 mL/m2)[2] |
| Stroke volume | 94 mL (± 15 mL)[1] | 95 mL (± 14 mL)[2] |
| Stroke volume / body surface area (mL/m2) | 51 mL/m2 (± 7 mL/m2)[1] | 52 mL/m2 (± 6.2 mL/m2)[2] |
| Ejection fraction | 66% (± 6%)[1] | 67% (± 4.6%)[2] |
| Heart rate | 60–100bpm[3] | 60–100bpm[3] |
| Cardiac output | 4.0–8.0L/minute[4] | 4.0–8.0L/minute[4] |
Its value is obtained by subtractingend-systolic volume (ESV) fromend-diastolic volume (EDV) for a given ventricle.
In a healthy 70-kg man, ESV is approximately 50 mL and EDV is approximately 140 mL, giving a difference of 90 mL for the stroke volume.
Stroke work refers to thework, or pressure of the blood ("P") multiplied by the stroke volume.[5]
Men, on average, have higher stroke volumes than women due to the larger size of their hearts.[7] However, stroke volume depends on several factors such as heart size, its force ofcontraction, duration of contraction,preload (end-diastolic volume), andafterload. Corresponding to the oxygen uptake, women's need for blood flow does not decrease and a higher cardiac frequency makes up for their smaller stroke volume.[7]
Prolongedaerobic 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.[8]
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 theFrank–Starling law of the heart, will increase stroke volume. Decreased venous return has the opposite effect, causing a reduction in stroke volume.[9]
Elevated afterload (commonly measured as the aortic pressure during systole) reduces stroke volume. It usually does not affect stroke volume in healthy individuals, but increased afterload will hinder the ventricles in ejecting blood, causing reduced stroke volume. Increased afterload may be found inaortic stenosis andarterial hypertension.[10]
Similar tocardiac index, stroke volume index is a method of relating the stroke volume (SV) to the person'sbody surface area (BSA).
