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Biomedical Instrumentation Lab Lab Experiments

Study of Phono Cardiogram for measurement of Heart sounds


The basic aim of phonocardiograph is to pick up the different heart sounds, filter out the heart sounds and to display or record them.


A Phonocardiogram or PCG is a plot of high fidelity recording of the sounds and murmurs made by the heart with the help of the machine called phonocardiograph, or "Recording of the sounds made by the heart during a cardiac cycle". The sounds are thought to result from vibrations created by closure of the heart valves. There are at least two: the first when the atrioventricular valves close at the beginning of systole and the second when the aortic valve closes at the end of systole. It allows the detection of sub audible sounds and murmurs, and makes a permanent record of these events. In contrast, the ordinary stethoscope cannot detect such sounds or murmurs, and provides no record of their occurrence. The ability to quantitate the sounds made by the heart provides information not readily available from more sophisticated tests, and provides vital information about the effects of certain cardiac drugs upon the heart. It is also an effective method for tracking the progress of the patient's disease.

Heart sounds are classified into four groups on the basis of their mechanism of origin, they are

  1. Valve closure sound
  2. Ventricular filling sound
  3. Valve opening sounds and
  4. Extra cardiac sounds

Heart Sound


Block Diagram

block diagram

These sounds occur at the beginning of systole (first heart sound) and the beginning of diastole (second heart sound). The first heart sound is due to the closure of mitral and tricuspid valves associated with myocardial contraction. And the second heart sounds is due to the closure of the aortic and pulmonary valves. The first heart sounds are low frequency vibrations occur approximately 0.05s after the onset of the QRS complex of the ECG, the first heart sounds last for (0.1 to 0.12s) and the frequency ranges 30-50Hz.The second heart sound is due to the vibrations set up by the closure of semilunar valves. These sounds start approximately ( 0.03 to 0.05)s after the end of T wave of the ECG, this lasts for (0.08 to 0.14)s and have a frequency up to 250Hz.

Ventricular filling sounds: These sounds occur either at the period of rapid filling of the ventricles (third heart sound) or during the terminal phase of ventricular filling. These sounds are inaudible. Third heart sound starts at (0.12 to 0.18) s after the onset of the second heart last approximately (0.04 to 0.08) s. The frequency is about 10 to 100 Hz.

Valve opening sounds: These sounds occur at the time of opening of the atria ventricular valves and semi lunar valves. The fourth heart sound starts approximately (0.12 to 0.18) s after the onset of the P wave. The sound last for (0.03 to 0.06)s. And the frequency is 10 to 50 Hz.

Extra cardiac sounds: These sounds occur in late systole or early diastole and are believed to be caused by thickened pericardium which limits ventricular distensibility. Murmurs are sounds related to non-laminar flow of blood in the heart and the great vessels. They are distinguished from the basic heart sounds such that they have noisy character having long duration and with high frequency components up to 1000 Hz.


Thus, In this study, by using a Phonocardiograph, different heart sounds have been identified and analyzed.