science

Stroke volume

Stroke volume is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Stroke volume rather than just read about it. In short: In cardiovascular physiology, stroke volume (SV) is the volume of blood pumped from the 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) from the volume of blood just prior to the beat (called end-diastolic volume).

Key takeaways

Stroke volume belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Stroke volume to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Stroke volume from memory before moving on to harder problems.

Reference excerpt

In cardiovascular physiology, stroke volume (SV) is the volume of blood pumped from the 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) 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 when not explicitly stated it refers to the left ventricle and should therefore be referred to as left 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 (see patent foramen ovale and atrial septal defect) between the two systems will ensue if possible to reestablish the equilibrium. 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

Its value is obtained by subtracting end-systolic volume (ESV) from end-diastolic volume (EDV) for a given ventricle.

S V = E D V − E S V {\displaystyle SV=EDV-ESV}

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 the work, or pressure of the blood ("P") multiplied by the stroke volume.

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, its force of contraction, duration of contraction, preload (end-diastolic volume), and afterload. 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 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 person's body surface area (BSA).

S V I = S V B S A = ( C O / H R ) B S A = C O H R × B S A {\displaystyle SVI={SV \over BSA}={(CO/HR) \over BSA}={CO \over {HR\times BSA}}}

Note

References

Worked examples

Example 1 — a first encounter with Stroke volume

Start with the simplest possible case. Write down what Stroke volume claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Stroke volume before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Stroke volume ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Stroke volume

In research: Stroke volume appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Stroke volume in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Stroke volume is common in secondary-school and first-year university syllabi. It links to neighbouring topics Cardiovascular physiology, so understanding it makes those chapters shorter.
In everyday life: Look for Stroke volume outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Stroke volume in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Stroke volume means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Stroke volume out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Stroke volume in simple terms?

Why does Stroke volume matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Stroke volume?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Stroke volume.