Heart sound refers to the vibration caused by myocardial contraction, the closing of heart valves and the impact of blood on ventricular wall and aorta.
Second, the formation of heart sounds.
Each cardiac cycle can produce four heart sounds, and generally the first and second heart sounds can be heard.
The first heart sound appears in systole, marking the beginning of ventricular contraction. You can hear it most clearly at the apex of the heart (the inner side of the left clavicle midline between the fifth ribs of the anterior chest wall). Its pitch is high and low (40~60 Hz), its duration is long (0. 1~0. 12 seconds), and its sound is loud. It produces:
1. is the vibration of ventricular wall caused by the rapid impact of blood flow on atrioventricular valve during ventricular contraction;
2. It is the vibration caused by the closure of the atrioventricular valve and the tension between the valve leaflet and the chordae tendineae.
3. It is the vibration caused by blood shooting from the ventricle and hitting the aortic wall and pulmonary artery wall.
The stronger the ventricular contractility, the greater the first heart sound. The first heart sound is formed by various mechanical vibrations during ventricular contraction, from the closure of atrioventricular valve to the closure of semilunar valve. Among them, myocardial contraction, valve opening and closing, pressure and decompression of blood flow on blood vessel wall all cause mechanical vibration, thus participating in the formation of heart sounds. However, the vibration produced by various activities is different, and the valve closing effect is the most obvious, so the main component of the first heart sound is atrioventricular valve closure.
The second heart sound appears in diastole, which marks the beginning of ventricular diastole. It is divided into two components: aortic sound and pulmonary artery sound, which are heard most clearly in the auscultation area of aorta and pulmonary artery (between the second ribs of the left and right sternum). It is caused by the rapid closure of aortic and pulmonary valves and the impact of blood flow, which makes the roots of aortic and pulmonary walls and the inner wall of ventricle vibrate. Its sound is high (60~ 100 Hz), short duration (0.08 seconds) and weak loudness. Its intensity can reflect the levels of aortic pressure and pulmonary artery pressure. When arterial pressure rises, the second heart sound becomes excited. .
The third heart sound occurs after the second heart sound, with short duration (0.04~0.05 seconds) and low pitch. It is produced in the early stage of ventricular diastole. With the opening of atrioventricular valve, the blood of atrium and pulmonary vein quickly flows into the ventricle (before atrial contraction), causing the vibration of ventricular wall and chordae tendineae. Most children and about half of young people can hear it, which does not necessarily mean that it is abnormal.
The fourth heart sound occurs in the low-frequency vibration before the first heart sound and lasts for about 0.04 seconds. It is the vibration caused by atrial contraction and rapid blood flow filling the ventricle, also known as atrial sound. Most healthy adults can record the lower fourth heart sound on the phonocardiogram, which is difficult to find in general auscultation. It is a low-frequency vibration, and its formation may be related to atrial contraction and early rapid filling. It is normal for children to hear the third and fourth heart sounds, but most adults are pathological.
When the heart valve is diseased, it will cause abnormal vibration and blood flow changes, resulting in abnormal heart sounds and satisfactory murmurs.
Clinically, according to the cycle and nature of heart murmur, it can help diagnose some cardiovascular diseases.
Third, the characteristics of heart sounds.
First heart sound: low pitch and long duration, about 0. 10~0. 12 seconds. Appears in ventricular contraction, which is a sign that the ventricle begins to contract. It is mainly formed by atrioventricular valve closure and accompanying ventricular wall vibration.
Second heart sound: high pitch and short duration, about 0.08~0. 10 second. Appears in ventricular diastolic phase, which is a sign that the ventricle begins to relax. It is mainly formed by the closure of arterial valves.
Third and fourth heart sounds: The third heart sound appears 0. 1~0.2 seconds after the second heart sound, with a low frequency. Its production is related to the rapid flow of blood into the ventricle, which makes the ventricle and valve vibrate. Usually, only children can hear it because it is easy to spread to the body surface. The fourth heart sound is caused by atrial contraction, also called atrial sound.