Phonocardiography

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A pediatrician listening to the heart

The phonocardiography (PCG) or Fonokardiografie is the recording of acoustic phenomena of the heart with microphone and heart sound amplifier. It is usually created in combination with an EKG .

There are two ways to use sound writing:

  1. subjective: stethoscope or microphone - filter - loudspeaker
  2. objective: A microphone is also used, which finally feeds the audio signal through a filter to the recorder, which graphically displays the audio signal.

Phonography makes it possible, for example, to obtain information on the assessment of heart sounds and thus to improve the diagnosis of heart valve defects (such as mitral valve insufficiency ).

Subjective method

In the subjective method, what is heard by the doctor is diagnosed directly. No records remain. This method is still used because the human ear can detect small changes and timbres very well. However, it is not able to recognize various parameters that are immediately graphically visible (for example very low tones).

Objective method

With the objective method , the audio signal is recorded and graphically displayed as a curve. The curve can then be compared with a “model curve” for a healthy heart, or with various other curves for pathological phenomena.

A distinction principally by the frequency between:

  • Heart sounds (15–150 Hz )
  • Heart murmur (up to 800 Hz)

The volume of both signals goes up to approx. 30 Phon , depending on the derivation method.

Since the chest or the human tissue acts like a low pass (higher frequencies are perceived as weakened), a filter is used to compensate for the low pass effect.

There are two different measurement methods:

  • Indirect coupling. A closed cap is placed on the chest, creating an air cushion between the membrane and the chest, which transmits the vibrations of the chest to the membrane. In order to prevent external noises, the dome should be closed off from the outside as well as possible.
  • A stamp is used that detects and transmits the vibrations of the skin. External noises are less important here.

Web links

Individual evidence

  1. ^ Klaus Holldack, Klaus Gahl: Auscultation and percussion. Inspection and palpation. Thieme, Stuttgart 1955; 10th, revised edition ibid 1986, ISBN 3-13-352410-0 , pp. 160, 197 and more often.