Stroke volume (SV)

Stroke Volume (SV) is the volume of blood in millilitres ejected from the each ventricle due to the contraction of the heart muscle which compresses these ventricles.

SV is the difference between end-diastolic volume (EDV) and end-systolic volume (ESV). Multiple factors can affect SV, eg. factors that change either EDV or ESV will change SV. The three primary factors that regulate SV are preload, afterload and contractility.

Heart rate (HR) also affects SV. Changes in HR alone inversely affects SV. However, SV can increase when there is an increase in HR (during exercise for example) when other mechanisms are activated, but when these mechanisms fail, SV cannot be maintained during an elevated HR. These mechanisms include increased venous return, venous constriction, increased atrial and ventricular inotropy and enhanced rate of ventricular relaxation.

The ODM+ calculates SV by multiplying the Stroke Distance (SD) by a constant accessed from the built-in patient nomogram.

Normal values for a resting healthy individual would be approximately 60-100mL. Patients undergoing surgery or in critical illness situations may require higher than normal SV and it may be more appropriate to aim for optimal rather than normal SV. See Stroke Volume  Optimisation and Improved Outcomes.

Regulation of Stroke Volume

Ventricular stroke volume (SV) is often thought of as the amount of blood (mL) ejected per beat by the left ventricle into the aorta (or from the right ventricle into the pulmonary artery). This assumes, however, that all the blood leaving the ventricle is ejected into the outflow tract, but this is not the case when there is atrioventricular valve regurgitation or an interventricular septal defect. Therefore, a more precise definition for SV and one that is used in echocardiography when assessing ventricular function is the difference between the ventricular end-diastolic volume (EDV) and the end-systolic volume (ESV). The EDV is the filled volume of the ventricle before contraction, and the ESV is the residual volume of blood remaining in the ventricle after ejection. In a typical heart, the EDV is about 120 mL of blood and the ESV is about 50 mL of blood. The difference in these two volumes, 70 mL, represents the SV (SV = EDV – ESV). Therefore, any factor that alters either the EDV or the ESV will change the SV. For example, an increase in EDV increases SV, whereas an increase in ESV decreases SV.

There are three primary mechanisms that regulate EDV and ESV, and therefore SV. These are preload, afterload, and inotropy.

·        Preload

·        Afterload

·        Inotropy

Stoke Volume Index

Stroke Volume Index (SVI) relates SV to body surface area (BSA), thus relating heart performance to the size of the individual. The unit of measurement is millilitres per square metre (ml/m²).

SVI = SV/BSA

​Normal values for a resting healthy individual would be approximately 35-65mL/m2. Patients undergoing surgery or in critical illness situations may require higher than normal SVI and it may be more appropriate to aim for optimal rather than normal SVI.

Cardiac Output

Cardiac Output (CO) is the amount of blood the heart pumps from each ventricle per minute. It is usually expressed in litres per minute (L/min).

CO = HR x SV

Changes in either HR or SV can alter CO. Impaired regulation of SV (including preload, afterload and contractility) can have a significant adverse affect on CO.

​Normal values for a resting healthy individual would be approximately 5-8L. Patients undergoing surgery or in critical illness situations may require higher than normal CO and it may be more appropriate to aim for optimal rather than normal CO.

Cardiac Index

Cardiac index (CI) is the cardiac output proportional to the body surface area (BSA). The unit of measurement is litres per minute per square metre (L/min/m2).

CI = CO x BSA

​Normal values for a resting healthy individual would be approximately 2.5-4.2L/m2. Patients undergoing surgery or in critical illness situations may require higher than normal CI and it may be more appropriate to aim for optimal rather than normal CI.

·        https://www.deltexmedical.com/decision_tree/stroke-volume-and-cardiac-output/#:~:text=Stroke%20Volume%20(SV)%20is%20the,factors%20can%20affect%20SV%2C%20eg.

·        https://cvphysiology.com/cardiac-function/cf002

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2.     Grossman S., and Porth C.M., Porth’s Pathophysiology: Concepts of Altered Health States. 2013 ed 9. Lippincott Williams & Wilkins. 

3.     Klabunde R.E., Cardiovascular Physiology Concepts. 2005. Lippincott Williams & Wilkins.