Normal heart sound: listen to the heart with a stethoscope

2021-05-17 04:21 PM

Locations for listening to heart sounds are not directly over the valve area themselves. The area of ​​the aorta is ascending along the aorta, and the area of ​​the pulmonary artery is ascending along the pulmonary artery.

When listening to a normal heart sound with a stethoscope, it is heard with descriptive sounds like ''lub, dub, lub, dub''. The “lub” sound is associated with the closing of the atrioventricular (AV) valves at the onset of systole, and the “dub” sound is associated with the closure of the semilunar valves (aortic and pulmonary valves). at the end of systole. The “lub” sound is called the first heart sound, and the “dub” sound is the second heart sound because the normal pumping cycle of the heart is assumed to begin when the atrioventricular valve closes at the onset. ventricular cycle.

The first heart sound is related to the closure of the atrioventricular valve

The earliest explanation for the cause of the heart sounds is that the reciprocal "banging" of the leaflets begins to vibrate. However, the closure of the leaflets indicates a small part of the cause, a lot of the sound, caused by blood flow between the effect of "bumping" the cushioning leaflets against each other and blocking blood flow. Instead, the cause of the vibration is that the valves stretch immediately after closing, along with vibrations adjacent to the heart wall and major blood vessels in the heart. That is, in making the first heart sound, the contraction of the ventricles first causes blood to back up against the AV valves, forcing them to close and protrude toward the atria until the junctions suddenly stop and swell. . The good elastic condition of the ligaments and valves then causes increased blood flow to return once more into each corresponding ventricle. The blood mechanism causes the blood and ventricular walls, as well as the valves to stretch, leads to fibrillation and causes turbulence in the blood, and increases resistance to ventricular fullness. For example, a fourth heart sound is often heard in elderly patients with left ventricular hypertrophy.

These vibrations pass through adjacent tissues to reach the chest wall, where they can be heard using a stethoscope.

The second heart sound is associated with the closure of the aortic and pulmonary valves

The result of the second heart sound is the abrupt closure of the semilunar valves (eg, aortic and pulmonary valves) at the end of the systole. When the semilunar valves close, they move the ventricles backward and elastically jerk the blood back into the artery, which causes a brief echo of the blood going back and forth between the artery walls and the valve. semicircle. This vibration occurs in the artery wall then is transmitted mainly along the artery. When the vibrations of the pulses and ventricles are exposed to a "bump sound", such as the chest wall, they produce an audible sound.

Time and intensity of first and second heart sounds

The duration of each heart sound is about a little over 0.1 s, with the first heart sound being about 0.14s and the second about 0.11s. The reason the second tone is shorter in duration than the first is that the semilunar valves are taller than the atrioventricular valves, so they vibrate for a shorter period of time than the atrioventricular (AV) valves.

The frequency range that can be heard in the first and second heart sounds, yes, starts at the lowest frequency that the ear can detect, at about 40 cycles/s, and goes up over 50 cycles/s. S. When special electronics are used to record sound at frequencies and sound below the audible range, start low down to 3 to 4 cycles/s and peak at about 20 cycles/s. For this reason, most heart sounds can be recorded by an electronic heart recorder even though they cannot be heard with a regular stethoscope.

The normal second heart sound has a higher frequency than the first heart sound for two reasons: (1) The pitch of the semilunar valve in comparison to the lower level of the AV valve pitch, and (2) The coefficient Elasticity is greater than the tension of the artery that provides the main.

The difference in frequency of vibrations in heart sounds and heart murmurs in relation to the audible threshold.

The difference in frequency of vibrations in heart sounds and heart murmurs in relation to the audible threshold.

The audible range is between 40 and 50 cycles per second.

Vibration in the chambers of the heart, in comparison with less lax, less elastic chambers of the ventricles, provides the vibration system for the first heart sound. Clinicians use these differences to distinguish the distinctive properties of two corresponding sounds.

The third heart sound occurs at the beginning of the middle third of the diastole

A weak, rumbling third heart sound is occasionally heard in the early middle third of diastole. A plausible but unproven explanation for this sound is that the oscillation of blood back and forth between the walls of the ventricles is initiated by the ejection of blood from the atria. This is similar to water flowing from a faucet into a paper bag, the ingress water bouncing back and forth between the walls to cause vibrations in the walls. The reason the third heart sound does not occur until the middle third of diastole is thought to be that during the first part of diastole, the ventricles are not filled enough to produce the small amount of elastic tension required for echo. The frequency of this sound is usually so low that the ear cannot hear it, but it can often be recorded with a machine. The third heart sound may appear normal in children, adolescents, and young adults but usually indicates systolic heart failure in older adults.

Atrial contraction sound (fourth heart sound)

It is sometimes possible to record atrial heart sounds on a machine, but it is almost never heard with a stethoscope because it is weak and the frequency is very low - usually 20 cycles/second or less. This sound occurs when the atria contract, and is probably due to blood flowing into the ventricles, creating vibrations similar to a third heart sound. The fourth heart sound typically results from the contraction of the atria to fill the ventricles due to decreased ventricular wall dilation and increased resistance to ventricular filling. For example, a fourth heart sound is often heard in older patients with left ventricular hypertrophy.

The area above the thorax to hear normal heart sounds

Listen to the sounds of the heart, usually with the help of a stethoscope, called a stethoscope. The figure shows the areas of the chest wall where the heart valve sounds are most distinct. Although sounds from the valves can be heard in these areas, cardiologists rule out sounds from the various valves by an exclusion process. That is, move the stethoscope from one zone to another, notice the loudness of the sound in different positions, and gradually pick out the sound composition from each valve.

Areas of the chest where the heart sounds are heard best

Image. Areas of the chest where the heart sounds are heard best

The different locations for listening to heart sounds are not directly over the valve area themselves. The area of ​​the aorta is ascending along the aorta by sound conduction up the aorta, and the area of ​​the pulmonary artery is ascending along the pulmonary artery. The tricuspid valve area extends over the right ventricle, and the mitral valve area over the area of ​​the apex of the left ventricle, which is the part of the heart that is closest to the chest wall. The heart is rotated so that the rest of the ventricles are on the deeper side.

Mind bar chart

A small acoustic device specially designed to detect low-frequency sounds is placed on the chest, the heart sounds can be amplified and recorded by a high-speed recorder.

Cardiac recordings of normal and abnormal hearts.

Image. Cardiac recordings of normal and abnormal hearts.

The recording is called the heart sound chart, and the heart sounds appear as waves, as shown in the diagram. Recording A is an example of a normal heart sound, showing first, second, and third heart sound vibrations and even very weak atrial sounds. Of particular note that the third heart sound and the atrial contraction both have a low rumble, the third heart sound can be recorded in about one-third to one-third of the population, and the atrial sound is probably in about one-third of the population. a quarter of everyone.

Related articles: