Phonocardiography

Phonocardiography

 

a diagnostic method of graphic registration of heart sounds and murmurs.

Phonocardiography supplements auscultation (listening). It is used to evaluate objectively the intensity, duration, nature, and origin of sounds and murmurs and to record the third and fourth sounds, which cannot be heard by auscultation. Polycardiography, the simultaneous registering of a phonocardiogram, electrocardiogram, and sphygmogram, is used to record the central pulse in order to determine the duration of the phases of the cardiac cycle, that is, in order to obtain indirect information on myocardial contractility.

A phonocardiograph, the instrument used for phonocardiography, consists of a microphone, an amplifier, a set of frequency filters, and a recording device. The microphone is applied to various points on the chest over the heart region. After amplification and filtration, the electrical oscillations enter separate registration channels to permit the selective recording of low, medium, and high frequencies. The recording is done in a soundproof room while the patient holds his breath at exhalation or, if necessary, at the point of deepest inhalation; the patient must be in a reclining position and must have rested for five minutes.

Figure 1. Phonocardiogram of a healthy person: (I) first sound, (II) second sound

The straight line on the phonocardiogram reflects the systolic and diastolic pauses. A normal first sound (Figure 1) consists of three groups of oscillations. The initial group, which is of low frequency, is produced by the contraction of the ventricular muscles. The central group is of greater amplitude and is produced by the closure of the mitral and tricuspid valves. The final group, which is of low amplitude, is produced by the opening of the aortic and pulmonary valves and the vibrations of the walls of large blood vessels. The second sound consists of two groups of oscillations. The first group, which is of greater amplitude, is produced by closure of the aortic valves; the second group is produced by closure of the pulmonary valves. The normal third sound is caused by muscle vibrations during rapid filling of the ventricles; the normal fourth sound, which is less common, is produced by the contractions of the atria. The normal third and fourth sounds are found chiefly in children and athletes.

Changes shown by the phonocardiograph help diagnose various disorders, including heart diseases. In addition to weakening, intensification, or split of the first or second sounds, such changes include the appearance of pathological third and fourth sounds or of systolic and diastolic murmurs.

REFERENCES

Fitileva, L. M. Klinicheskaia fonokardiografiia, 2nd ed. Moscow, 1968. (Contains bibliography.)
Kel’man, I. M. Elektrokardiografiia i fonokardiografiia, 2nd ed. Moscow, 1974.