Heart sounds

Introduction to heart sound

• With each heart-beat, the detectable heart sounds are produced.
• These sounds represent the auscultatory events of the cardiac cycle.
• Heart sounds can be amplified and recorded by placing an electronically amplified microphone on the chest.
• The recording of such sounds is called a phonocardiogram.
• There are four heart sounds associated with the cardiac cycle.
• Among them only the first and second heart sounds (traditionally referred to as lubb and dupp, respectively) can be heard easily with a stethoscope.

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First heart sound

• It is more complex, lower in pitch and lasts longer than the second sound.
• It occurs as a result of the ventricles contracting which forces blood against auriculo-ventricular valves.
• This causes them to bulge backward towards the atria until the chordae tendinae abruptly stop the bulging.
• The elastic nature of the valves then causes the blood to bounce forward into each ventricle.
• This causes the blood, ventricular walls and valves to vibrate.
• It is these vibrations that produce the first heart sound.

Second heart sound

• It is high in pitch.
• It results from the sudden closing of the semilunar valves.
• This allows them to bulge backward towards the ventricles until their elastic stretch recoils the blood back into the arteries.
• This recoil produces vibrations that reverberate back and froth between the heart walls, arteries and valves.
• When the vibrations contact the chest wall, they create what can be heard as the second heart sound.
• The second heart sound is heard best over the second inter-costals space, where the aorta is closest to the surface.
• Immediately after the second sound there is a short interval of silence.

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Third heart sound

• It is a low-pitched sound which is heard occasionally.
• It is caused by the vibration of the ventricular walls after the atrio-ventricular valves open and the blood pushes into the ventricle.
• This sound is heard best in the tricuspid area.

Fourth heart sound

• It is usually not heard with an unamplified stethoscope in normal heart.
• It is caused by the blood rushing into the ventricles.
• Heart sounds are important tools in diagnosing valvular abnormalities.
• Any unusual sound is called murmur.

References: 

i) https://en.wikipedia.org/wiki/Heart_sounds

ii) https://emedicine.medscape.com/article/1894036-overview

Heart sounds