Heart sounds

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Image:Gray1216.png Image:Gray1218.png The heart sounds are the noises (sound) generated by the beating heart and the resultant flow of blood through it. This is also called a heartbeat. 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.

1 Normal heart sounds
- 1.1 first heart tone, or S1, "lub"
- 1.2 second heart tone, or S2 (components A2 and P2), "dub"
2 Abnormal sounds
3 Surface anatomy
4 Recording heart sounds
5 See also
6 External links

[edit] Normal heart sounds

[edit] first heart tone, or S1, "lub"

The first heart tone, or S₁, is caused by the sudden block of reverse blood flow due to 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, incoming venous blood flow suddenly reverses back toward the atria, catching and closing the inlet valves and preventing regurgitation of blood from the ventricles back into the atria. The S₁ sound results from reverberation within the blood associated with the sudden block of flow reversal.

[edit] second heart tone, or S2 (components A2 and P2), "dub"

The second heart tone, or S₂, is caused by the sudden block of reversing blood flow due to closure of the aortic valve and pulmonic valve at the end of ventricular systole, i.e beginning of ventricular diastole. As the left ventricle empties, its pressure falls below the pressure in the aorta, aortic blood flow quickly reverses back toward the left ventricle and is stopped by aortic (outlet) valve closure. Similarly, as the pressure in the right ventricle falls below the pressure in the pulmonary artery, the pulmonic (outlet) valve closes. The S₂ sound results from reverberation within the blood associated with the sudden block of flow reversal.

During inspiration, negative intrathoracic pressure causes increased blood return into the right side of the heart, yet some slowing of emptying from the left side. 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 relative to the A₂ component. 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 a "splitting" of the second heart tone in younger people, during inspiration and in the "pulmonic area", i.e. the 2nd ICS (intercostal space) at the left edge of the sternum. During expiration, the interval between the two components normally shortens and the S2 sounds becomes merged.

[edit] Abnormal sounds

Heart murmurs are produced as a result of turbulent flow of blood, turbulence sufficient to produce audible noise. They usually are heard as a whooshing sound. The term murmur only refers to a sound believed to originating within blood flow though or near the heart; rapid blood velocity is necessary to produce a murmur. Though unreliable, soft murmurs are less likely to reflect a serious, if any, health problem; loud murmurs essentially always reflect a problem. Yet most heart problems do not produce any murmur.

Regurgitation through the mitral valve is by far the most commonly heard murmur, sometimes fairly loud to a practiced ear, even though the volume of blood flow may be quite small. Yet, though often obvious, probably about 20% of cases of mitral regurgitation, though obvious using echocardiography, do not produce an audible murmur.

Stenosis of the aortic valve typically produces an systolic ejection murmur. This is more common in older adults or in those individuals having a two, not a three leaflet aortic valve.

Regurgitation through the aortic valve, if marked, is sometimes audible to a practiced ear with a high quality, especially amplified stethoscope.

Regurgitation through the tricuspid or pulmonic valves essentially never produces audible murmurs.

Other audible murmurs are associated with abnormal openings between the left ventricle and right heart or from the aortic or pulmonary arteries back into a lower pressure heart chamber.

As noted, several different cardiac conditions can cause heart murmurs. However, the murmurs produced often change in complex ways with the severity of the cardiac disease. An astute physician can sometimes diagnose cardiac conditions with some accuracy based largely on the murmur, related physical examination and experience with the relative frequency of different heart conditions. However, with the advent of better quality and wider availability of echocardiography and other techniques, heart status can be recognized and quantified much more accurately than formerly possible with only a stethoscope, examination and experience.

Clicks: 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.

Rubs: 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.

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.

[edit] Surface anatomy

The opening and closing of the valves is usually much less loud than the sound of the blood rushing through the valve and "colliding" with the subsequent barrier. Because of this, auscultation to determine function of a valve is usually not performed at the position of the valve, but at the position where the blood will collide after the valve is opened.

Pulmonic valve (to pulmonary trunk): second intercostal space (left)
Aortic valve (to aorta): second intercostal space (right)
Mitral valve (to left ventricle): fifth intercostal space (left)
Tricuspid valve (to right ventricle): fourth intercostal space (left)

[edit] 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.