Heart sounds

Encyclopedia : H : HE : HEA : Heart sounds

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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.

Normal heart sounds

first heart tone, or S1, \"lub\"

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.

second heart tone, or S2 (A2 and P2), \"dub\"

The second heart tone, or S₂, is caused by the closure of the aortic valve and pulmonic valve 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.

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.

Abnormal sounds

Heart murmurs are produced as a result of turbulent flow of blood, turbulence sufficient to produce audible noise.

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 mitral valve prolapse may have a mid-systolic click along with a murmur.

• Aortic and pulmonary stenosis may cause an ejection click immediately after S₁.

• 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.

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.

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. (See Heart murmur#Interventions that change murmur sounds.)

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.

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.

See also

• Physical examination
• Precordial examination
• Anatomy
• * Heart
• * Heart valve
• ** Aortic valve
• ** Pulmonic valve
• ** Mitral valve
• ** Tricuspid valve
• Pathophysiology
• * Mitral stenosis
• * Mitral regurgitation
• * Aortic stenosis
• * Aortic insufficiency
• * Pulmonic stenosis
• * Pulmonic insufficiency
• * Tricuspid stenosis
• * Tricuspid insufficiency

External links

• [Diagram at umich.edu, with associated sounds]
• [Thinklabs Electronic Stethoscope]
• [Flash tutorials]
• [Overview at dundee.ac.uk]
• [Overview at washington.edu]

 

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