In cardiovascular physiology, stroke volume (SV) is the volume of

blood Blood is a body fluid in the circulatory system of humans and other vertebrates that delivers necessary substances such as nutrients and oxygen to the cells, and transports metabolic waste products away from those same cells. Blood in th ...

pumped from the left ventricle per beat. 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 End-systolic volume (ESV) is the volume of blood in a ventricle at the end of contraction, or systole, and the beginning of filling, or diastole. ESV is the lowest volume of blood in the ventricle at any point in the cardiac cycle. The main fact ...

) 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 In cardiac physiology, cardiac output (CO), also known as heart output and often denoted by the symbols Q, \dot Q, or \dot Q_ , edited by Catherine E. Williamson, Phillip Bennett is the volumetric flow rate of the heart's pumping output: th ...

, which is the product of stroke volume and

heart rate Heart rate (or pulse rate) is the frequency of the heartbeat measured by the number of contractions (beats) of the heart per minute (bpm). The heart rate can vary according to the body's physical needs, including the need to absorb oxygen and e ...

, and is also used to calculate

ejection fraction An ejection fraction (EF) is the volumetric fraction (mathematics), fraction (or portion of the total) of fluid (usually blood) ejected from a chamber (usually the heart) with each contraction (or cardiac cycle, heartbeat). It can refer to the card ...

, 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

Its value is obtained by subtracting

(ESV) from end-diastolic volume (EDV) for a given ventricle. :

SV = EDV - ESV

In a healthy 70-kg man, ESV is approximately 50 mL and EDV is approximately 120mL, 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. ESV and EDV are fixed variables. Heart rate and Stroke volume are unfixed.

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), and

afterload Afterload is the pressure that the heart must work against to eject blood during systole (ventricular contraction). Afterload is proportional to the average arterial pressure. As aortic and pulmonary pressures increase, the afterload increases on ...

. 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.

Exercise

Prolonged

aerobic exercise Aerobic exercise (also known as endurance activities, cardio or cardio-respiratory exercise) is physical exercise of low to high intensity that depends primarily on the aerobic energy-generating process. "Aerobic" is defined as "relating to, inv ...

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 and afterload

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. 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 in aortic stenosis and arterial hypertension.

Stroke volume index

Similar to cardiac index, stroke volume index is a method of relating the stroke volume (SV) to the size of the person body surface area (BSA).

SVI =  =  =

Note

References

External links

The Gross Physiology of the Cardiovascular System

The Determinants of Cardiac Output (online video)
{{Cardiovascular physiology Cardiovascular physiology