PCG: Advantages and Disadvantages of Phonocardiography

This page covers the advantages and disadvantages of PCG (Phonocardiogram or Phonocardiography). It mentions the benefits or advantages of Phonocardiography and the 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, the PCG waveform recording system block diagram, and the 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 the heart.

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 the closing of mitral/tricuspid valves. It is represented by a frequency of 30 to 100 Hz with a duration of 50 to 100 ms.
• 2nd heart sound: It indicates the closing of aortic/pulmonary valves. It is represented by a frequency of 30 to 100 Hz with a 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.

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 heartbeats and their movements. Hence, it provides details of cardiac conditions.
• The method used in phonocardiography is passive. Hence, it is safe and can be used for a long duration of time.
• It is inherently a cheaper method.
• It can be used to monitor a 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 the 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 a risk of infection to the patients undergoing surgery due to the sterile field.
• Patients are frequently disturbed due to testing.
• Background noise is picked up if an airtight seal between the 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.