Heart sounds

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Image:Gray1216.png The heart sounds are the noises (sound) generated by the beating heart and the resultant flow of blood through it. In cardiac auscultation, an examiner uses a stethoscope to listen for these sounds, which include heart tones, or sounds, produced by sudden blood deceleration after the heart valves close, heart murmurs, and adventitious sounds, or clicks.

Heart sounds are usually divided into the normal heart sounds and the pathological sounds which indicate disease. The two distinct normal heart tones are often described as a lub and a dub (or dup), and occur in sequence with each heart beat. Murmurs are generated by turbulent flow of blood within the heart. Stenosis, or impaired opening of a heart valve, causes turbulence as blood flows through it. Valve insufficiency, or regurgitation, allows backflow of blood when the valve is supposed to be closed. In these situations, murmurs will be heard in the corresponding part of each cardiac cycle.

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Types of sounds

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The normal heart sounds


The first heart tone, or S1, is caused by the closure of the atrioventricular valves, mitral and tricuspid, at the beginning of ventricular contraction, or systole. When the pressure in the ventricles rises above the pressure in the atria, these valves close to prevent regurgitation of blood from the ventricles into the atria.

The second heart tone, or S2, is caused by the closure of the aortic and pulmonic valves at the end of ventricular systole. As the left ventricle empties, its pressure falls below the pressure in the aorta, and the aortic valve closes. Similarly, as the pressure in the right ventricle falls below the pressure in the pulmonary artery, the pulmonic valve closes.

Due to the higher pressure in the aorta compared to the pulmonary artery, the aortic valve normally closes before the pulmonic valve, so the second heart tone may have an audible split. A split S2 is made up of an A2 and a P2 components, caused by the closure of the aortic and pulmonic valves, respectively.

The splitting of the second heart tone varies with the phases of respiration. During inspiration, negative intrathoracic pressure causes increased blood return into the right side of the heart. The increased blood volume in the right ventricle causes the pulmonic valve to stay open longer during ventricular systole. This causes an increased delay in the P2 component of S2. During expiration, the positive intrathoracic pressure causes decreased blood return to the right side of the heart. The reduced volume in the right ventricle allows the pulmonic valve to close earlier at the end of ventricular systole, causing P2 to occur earlier, and "closer" to A2. It is physiological to hear the splitting of the second heart tone by younger people and during inspiration. During expiration normally the interval between the two components shortens and the tone becomes merged.

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Abnormal sounds

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Heart murmurs

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Murmurs are produced as a result of turbulent flow of blood, turbulence sufficient to produce audible noise. This most commonly results from narrowing or leaking of valves or the presence of abnormal passages through which blood flows in or near the heart. Without their cause being known, murmurs can still be designated as systolic or diastolic according to the part of the cardiac cycle in which they are heard. More accurately, the phases of the cardiac cycle can be divided into three parts: early-, mid- and late-systole or diastole.

The overwhelmingly most common murmur heard in adults, over about 30 years old, is due to leaking of the mitral valve after the leaflets have closed, called insufficiency or regurgitation. Much less commonly, a heart murmur is due to a reduced opening size of the aortic valve, called sclerosis or stenosis depending on severity. Both of these are systolic murmurs. Yet, even though these two conditions are responsible for most adult heart murmurs, it is common for either or both to be present and yet no murmur can be heard, even using a sensitive electronically amplified stethoscope.

So-called accidental or innocent murmurs are commonly heard in children as their hearts gradually attain adult form, or in athletes or pregnant women due to increased cardiac output passing through normal-sized valves. These murmurs are never diastolic. Their loudness depends on the body position and breathing.

At other times flow murmurs occur when cardiac output increases, as in febrile illnesses or hyperthyroidism, without cardiac disease.

Heart murmurs affect around 1 in 18 people, and 14.4 million people in the United States. There is an approximate chance of 5.30% of having heart murmur or similar heart diseases.

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Other abnormal sounds

With the advent of newer, non-invasive imaging techniques, the origin of other, so-called adventitial sounds or "clicks" has been appreciated. These are short, high-pitched sounds.

  • The atrioventricular valves of patients with mitral stenosis may open with an opening snap on the beginning of diastole.
  • Patients with pericarditis, an inflammation of the sac surrounding the heart (pericardium), may have an audible pericardial friction rub. This is a characteristic scratching, creaking, high-pitched sound emanating from the rubbing of both layers of inflammated pericardium. It is the loudest in systole, but can often be heard also at the beginning and at the end of diastole. It is very dependent on body position and breathing, and changes from hour to hour.
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Changes in heart sounds

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Altered heart sounds due to cardiac conditions

Many cardiac conditions can cause heart murmurs. However, the murmurs produced often change with the severity of the cardiac disease. Often, the astute physician can diagnose a cardiac condition solely on the murmur and related physical examination. Template:Main

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Altered heart sounds due to interventions

There are a number of interventions that can be performed that alter the intensity and characteristics of abnormal heart sounds. These interventions can be performed to differentiate the different heart sounds and obtain a diagnosis of the cardiac anomaly that causes the heart sound.

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  • RESPIRATION
  • ABRUPT STANDING
  • SQUATTING
  • VALSALVA MANEUVER
  • HAND GRIP
  • POST ECTOPIC POTENTIATION
  • AMYL NITRITE
  • METHOXAMINE
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Respiratory changes

Inhalation pressure also causes an increase in the venous blood return to the right side of the heart. Therefore, right-sided murmurs generally increase in intensity with inspiration. The increased volume of blood entering the right sided chambers of the heart restricts the amount of blood entering the left sided chambers of the heart. This causes left-sided murmurs to generally decrease in intensity during inspiration.

With expiration, the opposite hemodynamic changes occur. This means that left sided murmurs Similar to inhalation increased blood flow to the right side of the heart can be facilitated by having the patient lie supine and raising their legs up to a 45 degree angle.

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Recording heart sounds

With the advent of electronic stethoscopes, it is now possible to conveniently record heart sounds. One electronic stethoscope manufactured by Thinklabs provides a port to output stethoscope sounds to an external recording device, such as a laptop or MP3 recorder. The same connection can then be used to listen to the recordings through the stethoscope headphones, allowing for faithful reproduction of low-frequency murmurs and other heart sounds.

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See also

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External links

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