Download Phonocardiography

Phonocardiography
Engr. Hinesh Kumar (Lecturer)
1
Definition
 Phonocardiography is the recording of heart sounds.
 The
heart. like any mechanical pump, produces
characteristic sounds as it beats. These are the sounds the
physician hears with a stethoscope.
 Certain heart murmurs produce sounds in the 1000-Hz
range, and some frequency components exist down to 4
or 5 Hz.
2
Heart Sounds Generation
 The first heart sound is generated at the end of atrial
contraction, just at the onset of ventricular contraction.
 This sound is generally attributed to movement of blood
into the ventricles, the atrioventricular (AV) valves
closing, and the abrupt cessation of blood flow in the atria.
 The second heart sound corresponds to the closing
of the aortic and pulmonary valves.
3
Cont…
 Third heart sound corresponds to the cessation of
ventricular filling.
 Fourth heart sound
is
correlated to the atrial
contraction.
 This last sound has a very low amplitude and a lowfrequency component.
4
Cont…
 The phonocardiograph transducer is a contact or air-
coupled acoustical microphone held against the patient's
chest (shown in fig).
 Various types of microphones are used, but most are the
piezoelectric crystal or dynamic type of construction.
5
Cont…
 The crystal microphone generally costs less and is more rugged

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than the dynamic type.
Also, the crystal microphone produces a larger output signal for a
given level of stimulus
The dynamic microphone uses a moving coil coupled to the
acoustical diaphragm.
The dynamic microphone is used when it is desirable to have a
signal frequency response similar to that of the medical
stethoscope.
An air-coupled microphone with a 2-s time constant is often used
in apex phonocardiography.