biology

Small heart syndrome

Small heart syndrome is a biology 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 Small heart syndrome rather than just read about it. In short: Small heart syndrome is a cardiovascular condition in which the heart is small and cardiac output is low. It has been defined as a small heart shadow on chest roentgenogram and more specifically as a cardiothoracic ratio (CTR) of less than or equal to 42%.

Key takeaways

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

Reference excerpt

Small heart syndrome is a cardiovascular condition in which the heart is small and cardiac output is low. It has been defined as a small heart shadow on chest roentgenogram and more specifically as a cardiothoracic ratio (CTR) of less than or equal to 42%. It has been hypothesized that a small heart in relation to body size may be inadequate for work and that the condition may result in cerebral hypoperfusion, orthostatic intolerance, and exaggerated sympathetic activation. This in turn may result in a variety of symptoms including malaise, weakness, fatigue, tachycardia, heart palpitations, low blood pressure, chest pain, dizziness, shortness of breath, nervousness, trembling, sweating, fainting, and cold feet, among others. The symptoms of small heart syndrome show some parallels to those of chronic heart failure and resemble the symptoms of myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS). Small heart syndrome is known to be present at high rates in people with ME/CFS. General cardiovascular findings in these individuals have included small hearts, left ventricular dysfunction, poor cardiac performance, low stroke volume, low cardiac output, low total blood volume, low blood pressure, cerebral hypoperfusion, and heart rate abnormalities. Exaggerated diurnal variation in blood pressure has also been observed, and diurnal blood pressure variation has been found to correlate with fatigue severity. In addition to ME/CFS, people with postural orthostatic tachycardia syndrome (POTS) frequently show small hearts. ME/CFS and POTS additionally co-occur at high rates. Small heart syndrome has been associated with symptoms and their severity in people with ME/CFS. Dehydration, for instance due to inadequate fluid intake, diarrhea, or sweating, may worsen symptoms of small heart syndrome due to reduced venous return and cardiac output. Relatedly, adequate hydration in people with ME/CFS may be beneficial. Habitual exercise may improve cardiac and pulmonary conditioning, increase cardiac output, and thereby improve symptoms in the condition. Treatments like antihypotensive agents such as the α1-adrenergic receptor agonist phenylephrine and medications to increase fluid retention and thus blood volume like the mineralocorticoid fludrocortisone may be helpful in small heart syndrome. Compression stockings may increase venous return and improve symptoms as well. Small heart syndrome in for instance ME/CFS may in part be related to physical inactivity, prolonged bed rest, and associated cardiac deconditioning. Alternatively, cardiovascular dysfunction and other symptoms in ME/CFS may not be due to deconditioning and may instead be related to autonomic dysfunction, for example caused by viral infection. However, even if not a major cause, small heart syndrome may still contribute to symptom burden in ME/CFS. There is said to be no organic heart disease or systemic disease in small heart syndrome. Small heart syndrome due to anorexia nervosa has been reported and may also occur in other situations such as cancer-induced cachexia. The concept of small heart syndrome was first described by René Laennec in 1826. Subsequently, Commander A. M. Master described small heart as the cause of a condition he referred to as "neurocirculatory asthenia", considered to be synonymous with small heart syndrome, in 1944. Kunihisa Miwa and colleagues described small heart syndrome as a possible cause or contributor to ME/CFS in 2008 and thereafter. Small heart syndrome as a contributor to ME/CFS has also since been studied by Julia Newton and colleagues.

See also Sedentary lifestyle Deconditioning Effect of spaceflight on the human body

References

External links Small heart syndrome - MEpedia Chronic Fatigue Syndrome: the Small Heart Disease? - HealthRising

Worked examples

Example 1 — a first encounter with Small heart syndrome

Start with the simplest possible case. Write down what Small heart syndrome claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In biology, 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 Small heart syndrome 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 Small heart syndrome 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 Small heart syndrome

In research: Small heart syndrome appears in biology 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 Small heart syndrome 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: Small heart syndrome is common in secondary-school and first-year university syllabi. It links to neighbouring topics Heart diseases, Myalgic encephalomyelitis/chronic fatigue syndrome, so understanding it makes those chapters shorter.
In everyday life: Look for Small heart syndrome 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 Small heart syndrome in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Small heart syndrome 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 Small heart syndrome out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Small heart syndrome in simple terms?

Why does Small heart syndrome matter?

Because it connects several biology 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 Small heart syndrome?

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 Small heart syndrome.