What Causes The Heart Sounds?

Heart Sounds

The sounds produced or generated by the beating heart during each cardiac cycle, particularly when the heart valves snap shut, are heart sounds. The sounds specifically indicate the turbulence which is generated during the snapping shut of the valves. In cardiac auscultation, examiners can use a stethoscope to hear these distinct and unique sounds, which render information indicating the state of the heart. It can also be detected with the help of a phonocardiograph.

These sounds are generated by the flowing of blood in and out of the chambers of the heart through the valves as and when it closes and opens. Auscultation is utilized in the detection of abnormal or unusual sounds of the heart and decides the course of action further.

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Functioning Of The Heart

The muscular structure, the human heart, has four chambers that pump and receive blood throughout the body. The left atrium picks up the oxygenated blood from the lungs, pumping it into the left ventricle, which in turn pumps the oxygen-rich blood all through the body via a mesh of arteries.

On the other hand, the atrium picks up the deoxygenated blood from the body via veins, pumping it into the right ventricle. The right ventricle pumps blood to the lungs to get oxygenated. The contraction of the left ventricle during pumping out of the blood generates systolic blood pressure in arteries. A mesh of nerve tissues runs through the heart, sending electrical signals to the muscles of the heart, initiating the contraction of the heart.

The valves of the heart make sure that the blood flow is unidirectional by closing and opening during the pumping of the blood. The valves of the heart –

  • Aortic valves between the aorta and left ventricle
  • Pulmonic valves between the pulmonary artery and right ventricle
  • Mitral valves separate the ventricle and left atrium
  • Tricuspid valves separate the right ventricle and right atrium

Creation of Heart Sounds – What Creates Heart Sounds?

The flow of blood generates vibrations in the valves and chambers of the heart, producing audible sounds which are audible through a stethoscope. A low-resistance, smooth blood flow is referred to as a laminar flow. When there is a rough flow offering a high-resistance, referred to as turbulent flow. The vibrations increase through the blood flow turbulence depending on the blood vessel’s diameter and the blood’s –

  • Density
  • Viscosity
  • Velocity

A few functions of the heart which generate heart sounds are –

  • Blood flow through the valve opening
  • Rubbing of cardiac surfaces
  • Closing and opening of the valves of the heart
  • Blood flow into the ventricles of the heart

Types Of Heart Sounds

Heartbeat is constituted by two phases which make up a cardiac cycle. These two phases are –

  • Contraction of ventricles to pump out blood – systole
  • Relaxation of ventricles filling with blood – diastole

There are 4 types of heart sounds –

  • S1 – “lub” caused by the closing of the AV valves
  • S2 – “dub” caused by the closing of semilunar valves
  • S3 – linked with flow of blood into the ventricles
  • S4 – linked with atrial contraction

Generally, the heart makes two sounds – “lub” and “dub”. The third and fourth sounds are audible in individuals, however, they could show abnormalities in the functioning of the heart. While the S1 and S2 are high-pitched, S3 and S4 are low-pitched sounds.

Attributes First sound Second sound Third sound Fourth sound
Cause Generated by the vibration given by the sudden closing of AV valves (Mitral and Tricuspid) at the beginning of ventricular systole at the phase of Isovolumic Contraction Vibration linked with the closing of Semilunar

Valves (Aortic and Pulmonary valves)

Vibration established in the cardiac wall by the inrush of the blood at the time of Rapid Passive Filling

Phase (0.11 sec) of the Ventricular Diastole

Due to the vibration established during Atrial Systole
Traits Soft, long, and Low Pitched. Loud, short, and High Pitched Low-pitched sound, weak and rumbling in nature. Heard with the rapid rush of blood from the atrium into the ventricle as it starts relaxing (heard occasionally) The low-intensity sound audible just before S1 in the cardiac cycle, weak and rumbling
Frequency 25-45 Hz (30-80 cps) 50 Hz (150-200 cps) Below 40 cps 20 cps
Duration 0.14 seconds 0.11 seconds 0.04 seconds Occurs immediately before S1, while the atria of the heart are contracting vigorously
Site of auscultation Audible by over the Mitral and Tricuspid sites Audible by over the Aortic and Pulmonary Areas
Significance
  • Indicates ventricular systole
  • Depicts condition of the myocardium
  • Shows compliance of atrioventricular valves
  • Depicts end of systole and start of diastole
  • Depicts compliance of semilunar valves
  • Shows beginning of ventricular filling
  • It is a cardiac failure when the third sounds as “lub dub ta”
  • Depicts end of ventricular filling occurring just before first heart sound

Heart Murmurs

Heart murmurs are ectopic or abnormal heart sounds. These occur when there are some valvular or other abnormalities that cause turbulence in the flow of blood, either because of the high velocity of ejection or their regurgitation.

Types of Murmurs

Murmurs are of the following types –

  • Aortic stenosis
  • Mitral stenosis
  • Aortic regurgitation
  • Mitral regurgitation

Stenosis –

It is the abnormal narrowing in the blood vessels that is due to the narrowed blood vessels. It is linked with abnormal heart sounds. The main reason is atherosclerosis because of which there is a drop in the stroke volume, resulting in a decrease in the cardiac output. This causes blood to be ejected at high velocities as a result of a decrease in the blood vessel’s diameter.

Regurgitation –

Regurgitation is the flow of the blood in the opposite direction to the normal due to the backward blood flow between chambers or into the heart. It takes place as a result of abnormalities in the valves of the heart.

This was a brief on the causes of heart sounds. Explore related topics on NEET at BYJU’S.

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