Advantages of PCG Phonocardiogram | Disadvantages of Phonocardiography

This page covers advantages and disadvantages of PCG (Phonocardiogram or Phonocardiography). It mentions benefits or advantages of Phonocardiography and drawbacks or disadvantages of Phonocardiography.

Introduction: Bio-medical instruments are used along with bio-sensors to measure health related parameters of patients. There are three commonly used bio-signals viz. ECG, PPG and PCG. ECG measures heart related parameters using electrical activities. PPG measures blood volume changes in the vessel going from heart to fingertips or toes. PCG records sounds and murmurs of the heart. Let us understand PCG signal basics, PCG waveform recording system block diagram and types of microphones used in PCG.

What is PCG ?

PCG is the short form of Phonocardiogram. There are different terms associated with PCG as described below.
Phonocardiography : It is the study of different heart sounds.
Phonocardiograph : It is the instrument which picks up different heart sounds.
Phonocardiogram : It is the graphic record of heart sounds as shown below.

There are two categories viz. heart sound and murmurs. Heart sound refers to transient characteristics with short duration which occurs due to opening/closing of heart valves. Murmurs refer to noisy characteristics with long duration which occurs due to turbulent blood flow in heart.

PCG signal
Figure-1 : PCG Signal

Different types of stethoscopes are used by doctors to check the heart sounds of patients which are early monaural stethoscope, modern binaural stethoscope, modern electronic stethoscope etc. Stethoscope transmits sound from chest to listener via air filled hollow tubes.

There are three parameters associated with PCG signal viz. amplitude, frequency and quality. Following are the characteristics of a PCG signal and shown in the figure-1.
1st heart sound : It indicates closing of mitral/tricuspid valves. It is represented by frequency of 30 to 100 Hz with duration of 50 to 100 ms.
2nd heart sound : It indicates closing of aortic/pulmonary valves. It is represented by frequency of 30 to 100 Hz with duration of 25 to 50 ms.
3rd heart sound : Blood rapid movement into relaxed ventricular chambers. It is represented by frequency of 10 to 100 Hz with duration of 0.04 to 0.08 sec.
4th heart sound : Atrial contraction. It is represented by 10 to 50 Hz with duration 0.03 to 0.06 sec.

PCG recording system
Figure-2 : PCG Recording System

The block diagram depicts components used in a common PCG recording system. As shown microphone (air coupled or contact type), filter and amplifier are used in such system. Different types of microphones are attached to chest to read its movement as per requirements. Filter is used to pass lower signal frequencies. The amplifier is used to amplify the PCG signal for display purpose.

Benefits or advantages of Phonocardiography (PCG)

Following are the benefits or advantages of Phonocardiography (PCG) :
➨It offers real time traces of heart beats and its movements. Hence it provides details of cardiac conditions.
➨The method used in phonocardiography is passive. Hence it is safe and can be used for long duration of time.
➨It is inherently cheaper method.
➨It can be used to monitor large number of people at home itself.
➨The technique is simple and non-invasive and houses low cost opto-electronic elements.
➨Electronic stethoscopes used in PCG can distinguish between low and high frequency PCG signals. This helps to pick up subtle changes in breath sounds as well as helps in hearing murmurs of heart.

Drawbacks or disadvantages of Phonocardiography (PCG)

Following are the drawbacks or disadvantages of Phonocardiography (PCG):
➨Existing microphones used in phonocardiography are bulky and obstructive.
➨There will be risk of infection to the patients undergoing surgery due to sterile field.
➨Patients are frequently disturbed due to testing.
➨Background noise is picked up if airtight seal between stethoscope and skin is not present. Hence physiologic sound transmission is impaired.
➨Stethoscopes used are not capable of generating constructive interference of physiologic sound waves.

Refer ECG sensor vs PPG sensor >>, PPG sensor >> and ECG sensor >> which describes comparison between ECG sensor and PPG sensor with respect to working principles, merits and demerits.

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