Stroke volume

In cardiovascular physiology, stroke volume (SV) is the volume of blood pumped from the left ventricle of the heart per beat. SV 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). The term stroke volume can apply to each of the two ventricles of the heart, although it usually refers to the left ventricle. The stroke volumes for each ventricle are generally equal, both being approximately 70 mL in a healthy 70-kg man.

Stroke volume is an important determinant of cardiac output, which is the product of stroke volume and heart rate, and is also used to calculate ejection 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.

Calculation

Example values in healthy 70-kg man
Measure Typical value Normal range
end-diastolic volume (EDV) 120 mL[1] 65–240 mL[1]
end-systolic volume (ESV) 50 mL[1] 16–143 mL[1]
stroke volume (SV) 70 mL 55–100 mL
ejection fraction (Ef) 58% 55–70%[2]
heart rate (HR) 75 bpm 60–100 bpm[3]
cardiac output (CO)oo 5.25 L/minute 4.0–8.0 L/min[4]

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, EDV is approximately 120 mL and ESV is approximately 50 mL, giving a difference of 70 mL for the stroke volume.

"Stroke work" refers to the work, or pressure of the blood ("P") multiplied by the stroke volume.[5]

Determinants

Major factors influencing stroke volume – Multiple factors impact preload, afterload, and contractility, and are the major considerations influencing SV.[6]

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

Prolonged aerobic exercise training may also increase stroke volume, which frequently results in a lower (resting) heart rate. Reduced heart rate prolongs ventricular diastole (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 in aortic stenosis and arterial hypertension.

Stroke Volume Index

Similar to cardiac index, is a method of relating the stroke volume to the size of the person.

SVI = {SV\over BSA} = {(CO / HR) \over BSA} = {CO \over {HR \times BSA}}

References

  1. ↑ 1.0 1.1 1.2 1.3 Schlosser, Thomas; Pagonidis, Konstantin; Herborn, Christoph U.; Hunold, Peter; Waltering, Kai-Uwe; Lauenstein, Thomas C.; Barkhausen, Jörg (2005). "Assessment of Left Ventricular Parameters Using 16-MDCT and New Software for Endocardial and Epicardial Border Delineation". Am J Roentgenol 184 (3): 765–73. doi:10.2214/ajr.184.3.01840765. PMID 15728595. Values:
    • End-diastolic volume (left ventricular) – average 118 and a range of 68 – 239mL and
    • End-systolic volume (left ventricular) – average 50.1 and range, 16 – 143 mL:
    • Also, ejection fraction was estimated in this study to be average 59.9% ± 14.4%; range, 18 – 76%, but secondary source (see above) is used in this article instead.
  2. ↑ O'Connor, Simon (2009). Examination Medicine (The Examination). Edinburgh: Churchill Livingstone. p. 41. ISBN 0-7295-3911-3.
  3. ↑ Normal ranges for heart rate are among the narrowest limits between bradycardia and tachycardia. See the Bradycardia and Tachycardia articles for more detailed limits.
  4. ↑ Edwards Lifesciences LLC > Normal Hemodynamic Parameters – Adult 2009
  5. ↑ Katz, Arnold M. (2006). Physiology of the heart. Hagerstwon, MD: Lippincott Williams & Wilkins. p. 337. ISBN 0-7817-5501-8.
  6. ↑ Betts, J. Gordon (2013). Anatomy & physiology. pp. 787–846. ISBN 1938168135. Retrieved 11 August 2014.

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