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Chapter: Medical Electronics : Electro-Physiology and Bio-Potential Recording

PCG (Phono Cardiogram)

The graphical record of heart sound is known as Phono Cardiogram. Here Cardio means the heart.



The graphical record of heart sound is known as Phono Cardiogram. Here Cardio means the heart. The device which is used to measure heart sound is known as phonocardiograph. Auscultation: The technique of listening sound produced by organs and vessels of the body is known as auscultation.


In PCG, different types of heart sounds are measured. These heart sounds are due to the vibrations set up in the blood inside the heart by the sudden closure of valves. In abnormal heart additional sounds are heard between the normal heart sound. These additional sounds are known as murmurs.Murmers is generally caused by improper opening of the valves or by regurgitation.




It is divided into four types


ü Valve closure sound

ü Ventricular filling sound

ü Valve opening sound


ü Extra cardiac sound


Valve closure sound

This sound occurs at the beginning of systole and at the beginning of diastole.


Ventricular filling sound

This sound is occurred at the time of filling of the ventricles.


Valve opening sound

This sound occurs at the time of opening of atrio- ventricular valves and semi lunar




Extra cardiac sound

This sound occur in mid systole or late systole or early diastole


Systole: The contraction of the heart muscle. The systolic pressure is 120mm of Hg. Diastole: The relaxation of the heart muscle. The diastolic pressure is 80 mm of Hg.





Microphone is used to convert heart sound into the electrical signals. Certain positions are recommended to pick up the heart sound by using microphone. The electrical signal picked up by the microphone is amplified by the amplifier block. The amplified output is given to filter block.

Here high pass filter is used. Its cut of frequency is 1 kHz. Here ECG electrode system and ECG amplifiers are usedfor reference for PCG. So ECG and PCG outputs are connected to FM tape recorder and output display unit.






1.     Air coupled microphone- Movement of chest is transferred through the air cushion. It provides low mechanical impedance to the chest.


2.     Contact microphone – it is directly coupled to the chest wall and provides high impedance, high sensitivity, and low noise. Its light weight is also one of the advantageous factor.

The first heart sound is developed during the opening of aortic valve and during the closing of mitral valve


PCG waveform


Frequency of first heart sound consists of 30 to 45 Hz. Second heart sound is usually higher in pitch than the first. Its frequency range is 50Hz to 70 Hz. Third heart sound is extremely weak vibrate sound is extremely weak vibration. Its frequency is below 600 Hz.


Aortic stenos are murmur occurred when the blood is ejected from the left ventricle through aortic valve due to resistance to ejection, the pressure in the left ventricle increased. So turbulent blood flow occur.This turbulent blood impinging the aortic valve. So intense vibration is produced. It produces loud murmur.


Mitral regurgitation murmur- In this murmur, blood flows in backward direction through the mitral valve during systole.


Aortic regurgitation murmur During diastole, sound is heard. In diastole blood flows in the backward direction from aorta to left ventricles when valves are damaged, then this sound is heard.


Mitral stenosis murmur This murmur is produced when blood is passed from left atrium to left ventricle. This sound is very weak.

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